Category Archives: Packaging

BY PAUL VAN DER HEIDE, director of materials and components analysis, imec, Leuven, Belgium

To keep up with Moore’s Law, the semiconductor industry continues to push the envelope in developing new device architectures containing novel materials. This in turn pushes the need for new solid-state analytical capabilities, whether for materials characterization or inline metrology. Aside from basic R&D, these capabilities are established at critical points of the semiconductor device manufacturing line, to measure, for example, the thickness and composition of a thin film, dopant profiles of transistor’s source/drain regions, the nature of defects on a wafer’s surface, etc. This approach is used to reduce “time to data”. We cannot wait until the end of the manufacturing line to know if a device will be functional or not. Every process step costs money and a fully functional device can take months to fabricate. Recent advances in instrumentation and computational power have opened the door to many new, exciting analytical possibilities.

One example that comes to mind concerns the development of coherent sources. So far, coherent photon sources have been used for probing the atomic and electronic structure of materials, but only within large, dedicated synchrotron radiation facilities. Through recent developments, table top coherent photon sources have been introduced that could soon see demand in the semiconductor lab/fab environment.

The increased computational power now at our finger tips is also allowing us to make the most of these and other sources through imaging techniques such as ptychography. Ptychog- raphy allows for the complex patterns resulting from coherent electron or photon interaction with a sample to be processed into recognizable images to a resolution close to the sources wavelength without the requirement of lenses (lenses tend to introduce aberrations). Potential application areas extend from non-destructive imaging of surface and subsurface structures, to probing chemical reactions at sub femto-second timescales.

Detector developments are also benefiting many analytical techniques presently used. As an example, transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) can now image, with atomic resolution, heavy as well as light elements. Combining this with increased computational power, allows for further devel- opment of imaging approaches such as tomography, holography, ptychography, differential phase contrast imaging, etc. All of which allow TEM/STEM to not only look at atoms in e.g. 2D materials such as MoS2 in far greater detail, but also opens the possibility to map electric fields and magnetic domains to unprecedented resolution.

The semiconductor industry is evolving at a very rapid pace. Since the beginning of the 21st century, we have seen numerous disruptive technologies emerge; technologies that need to serve is an increasingly fragmented applications space. It’s no longer solely about ‘the central processing unit (CPU)’. Other applications ranging from the internet of things, autonomous vehicles, wearable human-electronics interface, etc., are being pursued, each coming with unique requirements and analytical needs.

Looking ten to fifteen years ahead, we will witness a different landscape. Although I’m sure that existing techniques such as TEM/STEM will still be heavily used – probably more so than we realize now (we are already seeing TEM/STEM being extended into the fab). We will also see developments that will push the boundaries of what is possible. This would range from the increased use of hybrid metrology (combining results from multiple different analytical techniques and process steps) to the development of new innovative approaches.

To illustrate the latter, I take the example of secondary ion mass spectrometry (SIMS). With SIMS, an energetic ion beam is directed at the solid sample of interest, causing atoms in the near surface region to leave this surface. A small percentage of them are ionized, and pass through a mass spectrometer which separates the ions from one another according to their mass to charge ratio. When this is done in the dynamic-SIMS mode, a depth profile of the sample’s composition can be derived. Today, with this technique, we can’t focus the incoming energetic ion beam into a confined volume, i.e. onto a spot that approaches the size of a transistor. But at imec, novel concepts were intro- duced, resulting in what are called 1.5D SIMS and self-focusing SIMS (SF-SIMS). These approaches are based on the detection of constituents within repeatable array structures, giving averaged and statistically significant information. This way, the spatial resolution limit of SIMS was overcome.

And there are exciting developments occurring here at imec in other analytical fields such as atom probe tomography (APT), photoelectron spectroscopy (PES), Raman spectroscopy, Rutherford back scattering (RBS), scanning probe microscopy (SPM), etc. One important milestone has been the development of Fast Fourier Transform-SSRM (FFT-SSRM) at imec. This allows one to measure carrier distributions in FinFETs to unparalleled sensitivity.

Yet, probably the biggest challenge materials characterization and inline metrology face over the next ten to fifteen years will be how to keep costs down. Today, we make use of highly specialized techniques developed on mutually exclusive and costly platforms. But why not make use of micro-electro-mechanical systems (MEMS) that could simultaneously perform analysis in a highly parallel fashion, and perhaps even in situ? One can imagine scenarios in which an army of such units could scan an entire wafer in the fraction of the time it takes now, or alternatively, the incorporation of such units into wafer test structure regions.

BY PETE SINGER

There’s an old proverb that the shoemaker’s children always go barefoot, indicating how some professionals don’t apply their skills for themselves. Until lately, that has seemed the case with the semiconductor manufacturing industry which has been good at collecting massive amounts of data, but no so good at analyzing that data and using it to improve efficiency, boost yield and reduce costs. In short, the industry could be making better use of the technology it has developed.

That’s now changing, thanks to a worldwide focus on Industry 4.0–more commonly known as “smart manufacturing” in the U.S. – which represents a new approach to automation and data exchange in manufacturing technologies. It includes cyber-physical systems, the Internet of things, cloud computing, cognitive computing and the use of artificial intelligence/deep learning.

At SEMICON West this year, these trends will be showcased in a new Smart Manufacturing Pavilion where you’ll be able to see – and experience – data-sharing breakthroughs that are creating smarter manufacturing processes, increasing yields and profits, and spurring innovation across the industry. Each machine along the Pavilion’s multi-step line is displayed, virtually or with actual equipment on the floor – from design and materials through front-end patterning, to packaging and test to final board and system assembly.

In preparation for the show, I had the opportunity to talk to Mike Plisinski, CEO of Rudolph Technologies, the sponsor of the Smart Pavilion about smart manufacturing. He said in the past “the industry got very good at collecting a lot of data. We sensors on all kinds of tools and equipment and we’d track it with the idea of being able to do predictive maintenance or predictive analytics. That I think had minimal success,” he said.

What’s different now? “With the industry consolidating and the supply chains and products getting more complex that’s created the need to go beyond what existed. What was inhibiting that in the past was really the ability to align this huge volume of data,” he said. The next evolution is driven by the need to improve the processes. “As we’ve gone down into sub-20 nanometer, the interactions between the process steps are more complex, there’s more interaction, so understanding that interaction requires aligning digital threads and data streams.” If a process chamber changed temperature by 0.1°C, for example, what impact did it have on lithography process by x, y, z CD control. That’s the level of detail that’s required.

“That has been a significant challenge and that’s one of the areas that we’ve focused on over the last four, five years — to provide that kind of data alignment across the systems,” Plisinski said.

Every company is different, of course, and some have been managing this more effectively than others, but the cobbler’s children are finally getting new shoes.

By Pete Singer

Increasingly complicated 3D structures such finFETs and 3D NAND require very high aspect ratio etches. This, in turn, calls for higher gas flow rates to improve selectivity and profile control. Higher gas flow rates also mean higher etch rates, which help throughput, and  higher rates of removal for etch byproducts.

“Gas flow rates are now approaching the limit of the turbopump,” said Dawn Stephenson, Business Development Manager – Chamber Solutions at Edwards Vacuum. “No longer is it only the process pressure that’s defining the size of the turbopump, it’s now also about how much gas you can put through the turbopump.”

Turbopumps operate by spinning rotors at very high rates of speed (Figure 1). These rotors propel gases and process byproducts down and out of the pump. The rotors are magnetically levitated (maglev) to reduce friction and increase rotor speed.

Figure 1. Spinning rotors propel gases and process byproducts out of the pump.

The challenge starts with processes that have high gas flow rates, over a thousand sccm, and lower chamber pressures, below 100 mTorr.  Such processes include chamber clean steps where high flows of oxygen-containing gases are used to remove and flush the process byproducts from inside the chamber, through Silicon via (TSV) in which SF6is widely used at high gas flowrates for deep silicon reactive ion etch (RIE) and more recently, gaseous chemical oxide removal (COR) which typically uses HF and NH3to remove oxide hard masks.

However, the challenge is intensified with the more general trend to higher aspect ratio etch across all technologies.

Stephenson said the maximum amount of gas you can put through a maglev turbo is determined by two things: the motor power and the rotor temperature. Both of these are affected adversely by the molecular weight of the gas. “The heavier the molecule, the lower the limit. For motor power, if the gas flow rate is increased, the load on the rotor is increased, and then you need more power. Eventually you reach a gas flow at which you exceed the amount of power you have to keep the rotor spinning and it will slow down,” she said.

The rotor temperature is an even bigger limiting factor. “As gas flow rates increase, the number of molecules hitting the rotor are increased. The amount of energy transferred into the rotors is also increased which elevates the temperature of the rotor. Because the rotor is suspended in a vacuum and because it’s levitated, it’s not very easy to remove that heat from the rotor because its primary thermal transfer is through radiation,” she explained.

Pumping heavier gases, particularly ones that have poor thermal conductivity, cause the rotor temperature to rise, leading to what is known as “rotor creep.”Rotor creep is material growth due to high temperature and centrifugal force (stress).  Rotor creep deformation over time narrows clearances between rotor and stator and can eventually lead to contact and catastrophic failure (Figure 2).

Figure 2. Edwards pumps have the highest benchmark for rotor creep life temperature in the industry, due to the use of a premium aluminum alloy as the base material for its mag-lev rotors, combined with a low stress design.

Where it gets even worse are in applications where the turbopump is externally heated to reduce byproduct deposition inside the pump. Such a heated pump will have a higher baseline rotor temperature and significantly lower allowable gas flowrates than an unheated one. This becomes a challenge particularly for the heated turbopumps on semiconductor etch and flat panel display processes using typical reactant gases such as HBr and SF6.  “Those are very heavy gases with low thermal conductivity and the maximum limit of the turbopump is actually quite low,” Stephenson said.

The good news is that Edwards has been diligently working to overcome these challenges. “What we have done to maximize the amount of gas you can put into our turbopumps is to  ensure our rotors can withstand the highest possible temperature design limit for a 10 year creep lifetime.   We use a premium alloy for the base rotor material and then beyond that we have done a lot of work with our proprietary modeling techniques to design a very low stress rotor because the creep is due to two factors: the temperature and the centrifugal stress. Because of those two things combined, we’re able to achieve the highest benchmark for rotor creep life temperature in the industry,” she said.

Furthermore, the company has worked on thermal optimization of the turbopump platform. “That means putting in thermal isolation where needed to try to help keep the rotor and motor cool. At the same time, we also need to keep the gas path hot to stop byproducts from depositing. We have also released a high emissivity rotor coating that helps keep the rotor cool,” Stephenson said. A corrosion resistant, black ceramic rotor coating is used to maximize heat radiation, which helps keep the rotor cool and gives more headroom on gas flowrate before the creep life temperature is reached.

Edwards has also developed a unique real-time rotor temperature sensor: Direct, dynamic rotor temperature reporting eliminates over-conservative estimated max gas flow limits and allows pump operation at real maximum gas flow in real duty cycle while maintaining safety and lifetime reliability.

In summary, enabling higher flows at lower process pressures is becoming a critical capability for advanced Etch applications, and Edwards have addressed this need with several innovations, including optimized rotor design to minimize creep, high emissivity coating, and real time temperature monitoring.

The development of a new class of materials with superior functionalities is essential to enable emerging process schemes for wafer- or panel-level FO packaging.

BY KIM YESS, Director of Technology Development, Wafer-Level Packaging Business Unit Brewer Science, Rolla, MO

Fan-out (FO) packaging is one of the most talked- about advanced packaging solutions for heterogeneous integration. Although it has been available for nearly a decade for the chips used in mobile devices, its popularity has spiked in the past two years, thanks to Apple’s adoption of TSMC’s integrated fan-out package-on-package (InFO PoP) for its A10 and A11 processors, and the Apple Watch. As a result, FO has quickly progressed to the mainstream, with outsourced semiconductor and test service providers (OSATs), foundries and integrated device manufacturers (IDMs) vying for market share.

What’s driving FO innovation?

According to Yole Développement, smartphone appli- cation processors are the main beneficiaries of high- density fan-out (HDFO)’s excellent performance and thin profile. As a result, as shown in FIGURE 1, the HDFO market was worth $500 million in 2017 and was predicted to exceed $1 billion if other players, namely Qualcomm, Samsung and Huawei switch to HDFO [1].

Jan Vardaman, TechSearch International, said Apple selected InFO PoP for its A10 processor because of power noise reduction and signal integrity improvement, in addition to being thin enough to enable a low-profile PoP solution as small as 15 x 15 mm.

In addition to HDFO, the market is growing for conventional FO, driven by new applications such as audio CODECs, power management ICs, radar modules and RF[2].

The automotive electronics market—particularly advanced driver assistance systems (ADAS) and autonomous vehicles—is also being explored as a viable application for FO because of the flexibility and fast time to market it provides, as well as the ability to adapt to new sensor system protocols.

Exploring new processes

In this race to provide the most reliable, highest-density solution, many manufacturing approaches have emerged. FO is not only becoming more versatile, it is also reaching high enough densities to offer a cost-effective alternative to 2.5D interposers. As the demand for FO increases, packaging processes are being explored in both the wafer and panel formats. This is driving a need for new and better-performing materials that address more stringent specifications to meet, for example, finer line and space requirements, as well as the improved elongation needed for advanced high-density FO.

Thanks to recent innovations in packaging materials, three new process approaches have been developed to bridge these gaps. One approach involves new carrier- assist release-layer materials for creation of the redistribution layer (RDL)-first/chip-last buildup processes. Another important development is an alternative to lithography dielectric patterning that uses laser-ablated dielectric materials. Lastly, an alternative to the molding process in the chip-first approach that uses a laminated die stencil and gap-fill materials is under development.

Carrier-assist release layer for chip-last FO

Low-density FO is built using a chip-first approach, which involves first placing the chips on a substrate wafer followed by over-mold to create a reconstituted wafer, with subsequent RDL and solder-ball placement. On the other hand, HDFO processes like TSMC’s InFO technology use a chip-last approach. Also known as RDL-first, this approach (with target features of ≤2 μm l/s) begins with a layer-by-layer buildup of the RDL on a carrier wafer, followed by die placement and over-mold.

Currently, manufacturers turn to permanent bonding, followed by backgrinding to remove the carrier wafer. This is because conventional temporary bond/debond materials cannot withstand the downstream RDL processes that subject the build-up layers to high temperatures and vacuum conditions, as well as harsh chemical environments. However, backgrinding is a destructive process, creating debris that can cause damage to the device itself.

The new approach uses neither a temporary nor a permanent bonding process. Instead, it utilizes a release layer on the carrier substrate to allow separation of the FO wafer from the carrier at the end of the process flow.

The challenge with this new method is designing a material that withstands high- temperature process steps as well as strong mechanical stresses without delaminating or distorting the reconstituted wafer. Additionally, the material must be adaptable to the new FO panel-level processes (FOPLP) along with existing round wafers, as the industry innovates in that direction.

Manufacturers are investigating the use of copper foil lamination, as an alternative to physical vapor deposition of the seed layer. The copper laminating process requires a material that is flexible enough to sufficiently laminate layers on top of the substrate, and that can be cured using UV radiation or heat to yield a structurally stable base that meets the thermomechanical and chemical resis- tance requirements of the build-up process.

Additionally, it must be releasable by ultraviolet(UV) laser ablation or other UV exposure. To meet these needs, a new class of so-called “triangle” polymeric materials has been conceived that have advantages over standard-application release layers because they are multi functional. Specifically, these “triangle” materials can be laminated, cured and debonded, adding flexibility to the carrier-assisted process (FIGURE 2).

Dielectric RDL patterning

Traditional RDL patterning uses a complicated, 24-step photolithography process that employs photosensitive dielectric materials and masks to create trace patterns, followed by Cu plating to route the signal from the chip out of the package to the solder balls. This process, developed with round wafers in mind, uses spin-coated dielectrics. Unfortunately, these lithography processes are too costly to utilize in innovative package designs that must meet the stringent requirements for most markets [3].

As the industry moves to HDFO and begins to investigate panel-level processes to reduce cost and improve yield, alternative patterning approaches are being developed that can achieve resolutions down to 5 μm with an ultimate goal of 2 μm l/s. Laser ablation is one alter- native to photolithography for creating finer-featured RDL patterns while achieving all these goals.

The combination of a high-power excimer laser source, large-field laser mask and precision projection optics enables the accurate replication and placement of fine resolution circuit patterns without the need for any wet processing. In addition, with excimer laser patterning technology, the industry gains a much wider choice of dielectric materials (photopatternable and non-photopatternable) to help achieve further reductions in manufacturing costs as well as enhancements in chip or package performance [4].

By using excimer laser ablation, many process steps and costly materials can be eliminated from the manufacturing flow, including resist coating, baking, developing and resist stripping and etching using harsh chemicals [5].

FIGURE 3 demonstrates the considerable cost savings of laser ablation over photolithography. Activity-based cost modeling was used to carry out the cost comparison between the two processes. With activity-based cost modeling, a process flow is divided into a series of activities, and the total cost of each activity is calculated. The cost of each activity is determined by analyzing the following attributes: time, amount of labor and cost of material required (consumable and permanent), tooling cost, all capital costs, and yield loss associated with the activity.

Laser-ablated patterning is a room-temperature process that works by using a dielectric material to build up RDL fixtures, and excimer and solid-state lasers to ablate the material and direct-write a pattern. Laser ablation allows for depth and side-wall angle control, making it possible to create feature sizes <5 μm. It also reduces chemical waste streams. Additionally, fewer steps, fast removal rates and high throughput lead to a lower-cost solution in comparison with traditional photolithography (Fig. 3).

Photosensitive dielectric materials often fall short of meeting the required mechanical and thermal properties, and therefore need a variety of process “work-arounds” that add to the cost of ownership. Alter- natively, non-photopatternable dielectric materials can be designed using a vast selection of chemical platforms, which improves the possibility of meeting the thermal and mechanical property requirements.

As with all new approaches, laser ablation is not without some challenges. Post-laser-ablation cleaning and debris removal, along with surface roughness as a result of the ablation step, need to be addressed. Additionally, the laser system needs to achieve a high ablation rate for high throughput. While the process costs of laser ablation are lower than photolithography, there is still a significant equipment capacity investment required to add laser tools to the manufacturing line. This may delay overcoming the most critical challenge: convincing the industry to embrace laser ablation patterning over conventional approaches.

Development of the dielectric material is ongoing to further push the resolution of laser-ablated materials. In addition to spin and spray coating, other deposition methods being investigated include slot-die coating, ink-jet printing, Vermeer coating, spray coating and laminate film.

Laminated polymeric die-stencil fill concept

Chip-first is the standard approach for conventional FO packages, including embedded wafer level ball grid arrays (eWLBs), redistributed chip packages (RCPs), M-Series and others. It calls for placing die into the mold compound before the RDL processing steps. One of the challenges of this approach that impacts final yield is the die shift that can occur during the RDL processes. Additionally, in multi-die FOWLP configurations that combine disparate technologies to essen- tially form a system-in-package (SiP), the dies may be of different sizes and heights. Additionally, the mismatch in coefficient of thermal expansion (CTE) between all of the materials involved leads to severe warpage of the reconstituted wafer.

A new carrier-based approach developed to combat this problem replaces the over-mold structure around the dies with a laminated die stencil (FIGURE 4). A release layer is first applied to a carrier, followed by a curable adhesive backing layer. Next, the die stencil film is laminated to the curable adhesive backing layer. The dies are then placed in the stencil openings and attached to the adhesive backing layer during thermal curing. The gaps between the dies and stencil are then filled with a flexible yet curable polymeric material, yielding a stable reconstituted substrate. This is followed by construction of the RDLs while still supported on the carrier. Finally, the reconsti- tuted substrate is released from the carrier.

The stencil can be fabricated as a sheet from a variety of high-temperature-stable thermoplastics including, for example, carbon-fiber-filled polyetheretherketone (PEEK), which has an in-plane CTE of <10 ppm/K.

The pre-formed cavities can be configured for different die sizes and types to fabricate SiP components. The curable adhesive backing layer is comparatively soft and tacky before it is cured. This property allows the die-stencil film to be laminated to the structure at low temperatures.

This process not only addresses the die shift issue that plagues the chip-first approach, it also enables varying levels of die thickness. When placed in the stencil, the polymeric material allows the dies to sink and adjusts itself within the stencil. Once the dies are set, the material is cured, which locks them in place. Additionally, the process offers high-temperature stability, better CTE matching for warpage control, and high throughput.

Summary and conclusion

Fan-out packaging is on track to be a game-changing advanced packaging technology that will enable heterogeneous integration architectures. Applications have already expanded beyond smartphones, with HDFO targeting emerging applications.

Substrate handling and RDL strategies will be increasingly important, if not critical, for both conventional and HDFO technologies. To this end, the development of a new class of materials with superior functionalities is essential to enable emerging process schemes for wafer- or panel-level FO packaging.

The gamut of application needs for wafer support includes simple thinning processes during the backside processing of ultrathin, 300-mm silicon wafers, as well as reconstituted substrates for RDL fabrication. In addition to new materials, novel manufacturing approaches are also needed to further optimize the FO process flow.

KIM YESS is Director of Technology Development, Wafer-Level Packaging Business Unit Brewer Science, Rolla, MO

Acknowledgements

The author would like to thank Amy Lujan, SavanSys, for her contribution to this article regarding activity- based cost modeling.

References

1. Yole Developpement, “Fan-out Packaging Confirms its Success Story,” 3D InCites, September 14, 2017.
2. P. Garrou, “ITLE 356 SEMI Taiwan Part 1: Fan-out Packaging Players, Applications, and Market Growth,” Solid State Technology, October 2017.
3. H.Hichri,M.Arendt,andM.Gingerella,“Novel Process of RDL Formation for Advanced Packaging by Excimer Laser Ablation,” 2016 IEEE 66th Electronic Components and Technology Conference (ECTC), Las Vegas, NV, 2016, pp. 1733-1739. doi: 10.1109/ECTC.2016.225
4. H. Hichri, Ibid.
5. R. Zoberbier, M. Souter, “Laser Ablation, Emerging Patterning Technology for Advanced Packaging,” SUSS MicroTec Lithography GmbH, January 2010

Optimized stepping, based on parallel analysis of die placement errors and prediction of overlay errors, can increase lithography throughput by more than an order of magnitude and deliver commensurate reductions in cost of ownership. The productivity benefits of optimized stepping are demonstrated using a test reticle with known die placement errors.

KEITH BEST, Director of Lithography Applications Engineering, Rudolph Technologies, Inc., Wilmington, Mass.

Fan out wafer and panel level packaging (FOWLP/ FOPLP) processes place individual known good die on reconstituted wafer (round) or panel (rectangular) substrates, providing more space between die than the original wafer. The additional space is used to expand (fanout) the die’s I/O connections in order to create a pad array large enough to accommodate solder balls that will connect the die to the end-use substrate.The processes used to create these redistribution layers (RDL) are similar to wafer fabrication processes, using patterns defined by photolithography, with feature sizes typically ranging from a few micrometers to tens of micrometers. The placement and reconstitution molding processes introduce significant die placement errors that must be corrected in the photolithography process to ensure accurate overlay registration among the multiple vias and distribution layers that are built up to form the RDL. The errors can be measured on the lithography tool, but this significantly impacts throughput as the measurement process for each die may take as much or more time than the exposure itself.

Current best-practice methods employ an external metrology system to measure the displacement of each die. This metrology data is converted into a stepper correction file that is sent to the lithography stepper tool, eliminating the need to measure displacement on the stepper and more than doubling stepper throughput. An important enhancement to this method, optimized stepping, varies the number of die per exposure based on a predictive yield analysis of the displacement measurements, potentially multiplying throughput 20X or more. Results obtained using a test reticle that includes intentionally displaced die pads, vias, and RDL features typical of an FOWLP/FOPLP process confirm the validity of the approach.

Introduction

Die placements on reconstituted wafer or panel substrates include translational and rotational placement errors. The pick and place process itself introduces initial error. Additional error is created in the mold process and by instability of the mold compound through repeated processing cycles. As a result, the position of the die must be measured before each exposure in the lithog- raphy system to ensure sufficient registration with the underlying layer.

Displacement errors can be measured in the lithography tool, but the measurements are slow, typically taking as much time as the exposure. Moving the measurement to a separate system and feeding corrections to the stepper can double throughput.

Optimized stepping adds predictive yield analysis to the external measurement and correction procedures and increases the number of die included in the exposure field up to a user-specified yield threshold. FIGURE 1 illustrates the exposure/measurement loop. The measurement and analysis are repeated after each layer is exposed, calculating a new set of corrections. In addition to corrections, the software engine analyzes the displacement errors to predict yield (based on a user desig- nated limit for acceptable registration error) for multiple die exposure fields of varying sizes. The method requires tight integration of the stepper and measurement system with the controlling software.

With RDL features currently reaching sizes as small as 2μm, die placement measurements and pattern overlay registration requirements are also continuing to tighten. The speed of the measurement/correction/prediction calculation for each wafer/panel is also an important consideration. It must be faster than the exposure time to avoid becoming the throughput limiting step. Note that this requirement refers to the total exposure for multiple die per field which can be much less than the time needed to expose each die individually. The metrology system used in this work (Firefly system, Rudolph Technologies) can meet these challenges and measure placement errors for >5,000 die on a 510mm x 515mm panel in less than 10 minutes.

The stepper must be able to accept externally generated corrections for translation, rotation, and magnification.

It must also have a large exposure field and the ability to automatically select different images from the reticle (masking blades), changing the size of the field for each exposure. The stepper used in this work was the JetStep system from Rudolph Technologies.

The third critical piece of the optimized stepping loop is the software engine (Discover software, Rudolph Technol- ogies) which calculates displacement corrections and predicts yield for various multi-die exposure configura- tions. It also enables statistical process control (SPC) and controls genealogy.

Balancing yield and throughput

Optimized stepping uses a reticle that includes multiple exposure fields each comprising die arrays of different sizes. In FIGURE 2 the arrays range from a single die to an 8 X 8 array of 64 die. On a wafer containing random displacement errors, the smallest overlay error will be achieved by aligning the exposure pattern for each die individually. However, this accuracy comes at a high cost of reduced throughput. Optimized stepping analyzes the measured displacement errors and calculates the number of die that will meet a designated overlay error limit for various field sizes. It then selects the combination of fields that maximizes throughput. In operation, the stepper automatically selects the correct reticle image and adjusts the field size to expose the selected array.

The yield prediction algorithm (FIGURE 3) uses a recursive splitting procedure that initially predicts yield for the largest available field. If the prediction does not meet user-defined yield requirements, it splits the field and re-evaluates the prediction, repeating this cycle for decreasing field sizes until all exposures yield satisfactory results. The user designates an aggressiveness factor (larger values mean more aggressive splits) and specifies yield requirements in an exposure shot pyramid that determines the number of failures allowed for each available field size.

Results

Optimized stepping was evaluated using a test reticle with multiple field sizes containing die that included pads, vias and RDL structures typical of FOWLP/FOPLP. The patterns included predefined offsets in some of the structures for feed forward measurement testing. Application of the corrections calculated from the die placement error measurements yielded overlay errors of < +/-3μm (FIGURE 4).

Productivity vs. yield

FIGURE 5 illustrates the potential benefits of optimized stepping applied to a panel process. In the example the panel contains approximately 4,500 die. A conventional serial process, with placement errors measured on the stepper, takes a little over six hours, including three hours for measurement and three hours for exposure. Making the measurements outside the stepper in parallel with the exposure halves the cycle time per panel to three hours, and the exposure time becomes the throughput limiting step. The third case is optimized for productivity, using larger field sizes and more relaxed yield requirements. It reduces cycle time to less than 10 minutes. The final case balances throughput against more stringent yield require- ments and results slightly higher cycle times that are still nearly an order of magnitude shorter than the conventional serial process of the first case.

Conclusion

Optimized stepping can increase lithography throughput by more than an order of magnitude and deliver commensurate reductions in cost of ownership. The method also provides a means to balance productivity (throughput) against yield, adding an extra dimension of flexibility for optimizing profitability. Optimized stepping requires a stepper that can use externally calculated corrections and automatically change field size and reticle position. The metrology system must have sufficient accuracy and speed (faster than the accelerated exposure time). The control software must be able to predict yields based on measured displacement errors and control the stepper. Using a test reticle with known displacement errors, we have verified the accuracy of the metrology system and correction procedures and demonstrated the productivity benefits of optimized stepping.

KEITH BEST is Director of Lithography Applications Engineering, Rudolph Technologies, Inc., Wilmington, Mass.

Market shares of semiconductor equipment manufacturers shifted significantly in Q1 2018 as Applied Materials, the top supplier dropped, according to the report “Global Semiconductor Equipment: Markets, Market Shares, Market Forecasts,” recently published by The Information Network, a New Tripoli-based market research company.

The chart below shows shares for the first quarter (Q1) of calendar year 2017 and 2018. Market shares are for equipment only, excluding service and spare parts, and have been converted for revenues of foreign companies to U.S. dollars on a quarterly exchange rate.

Applied Materials lost significant market share YoY, from 18.4% of the $13.1 billion Q1 2017 market to 17.7% of the $17.0 billion Q1 2018 market. This drop follows a 1.8 share-point loss by Applied Materials for CY 2017 compared to 2016. The company competes with Lam Research and TEL in the deposition and etch market, and both gained share at the expense of Applied Materials.

At the other end of the spectrum, smaller semiconductor companies making up the “other” category lost 2.4 share points as a whole.

Much of the equipment revenue growth was attributed to strong growth in the DRAM and NAND sectors, as equipment was installed in memory manufacturers Intel, Micron Technology, Samsung Electronics, SK Hynix, Toshiba, and Western Digital. The memory sector, which grew grown 61.5% in 2017, is forecast to add another 28.5% in 2018 according to industry consortium WSTS (World Semiconductor Trade Statistics).

TEL recorded growth of 120.3% YoY in Korea, much of it on NAND and DRAM sales to Samsung Electronics and SK Hynix, and 69.5% YoY in Japan, much of it on NAND sales to Toshiba at its Fab 6 in Kitakami, Japan. Lam Research gained 42.2% and 70.5% YoY, respectively, in Korea and Japan.

Following the strong growth in the semiconductor equipment market, The Information Network projects another 11.5% growth in 2018 for semiconductor equipment.

Today at its Imec Technology Forum USA in San Francisco, imec, the research and innovation hub in nano-electronics and digital technology, announced that it has demonstrated ultra-low power, high-bandwidth optical transceivers through hybrid integration of Silicon Photonics and FinFET CMOS technologies. With a dynamic power consumption of only 230fJ/bit and a footprint of just 0.025mm2, the 40Gb/s non-return-to-zero optical transceivers mark an important milestone in realizing ultra-dense, multi-Tb/s optical I/O solutions for next-generation high-performance computing applications.

The exponentially growing demand for I/O bandwidth in datacenter switches and high-performance computing nodes is driving the need for tight co-integration of optical interconnects with advanced CMOS logic, covering a wide range of interconnect distances (1m-500m+). In the presented work, a differential FinFET driver was co-designed with a Silicon Photonics ring modulator, and achieved 40Gb/s NRZ optical modulation at 154fJ/bit dynamic power consumption. The receiver included a FinFET trans-impedance amplifier (TIA) optimized for operation with a Ge waveguide photodiode, enabling 40Gb/s NRZ photodetection with an estimated sensitivity of -10dBm at 75fJ/bit power consumption. High-quality data transmission and reception was also demonstrated in a loop-back experiment at 1330nm wavelength over standard single mode fiber (SMF) with 2dB link margin. Finally, a 4x40Gb/s, 0.1mm2wavelength-division multiplexing (WDM) transmitter with integrated thermal control was demonstrated, enabling bandwidth scaling beyond 100Gb/s per fiber.

“The demonstrated hybrid FinFET-Silicon Photonics platform integrates high-performance 14nm FinFET CMOS circuits with imec’s 300mm Silicon Photonics technology through dense, low-capacitance Cu micro-bumps. Careful co-design in this combined platform has enabled us to demonstrate 40Gb/s NRZ optical transceivers with extremely low power consumption and high bandwidth density,” says Joris Van Campenhout, director of the Optical I/O R&D program at imec. “Through design optimizations, we expect to further improve the single-channel data rates to 56Gb/s NRZ. Combined with wavelength-division multiplexing, these transceivers provide a scaling path to ultra-compact, multi-Tb/s optical interconnects, which are essential for next-generation high-performance systems.”

This work has been carried out as part of imec’s industrial affiliation R&D program on Optical I/O and was presented at the 2018 Symposia on VLSI Technology and Circuits (June 2018) in a “late news” paper. Imec’s 200mm and 300mm Silicon Photonics technologies are available for evaluation by companies and academia through imec’s prototyping service and the iSiPP50G multi-project wafer (MPW) service.

Smart technologies take center stage tomorrow as SEMICON West, the flagship U.S. event for connecting the electronics manufacturing supply chain, opens for three days of insights into leading technologies and applications that will power future industry expansion. Building on this year’s record-breaking industry growth, SEMICON West – July 10-12, 2018, at the Moscone Center in San Francisco – spotlights how cognitive learning technologies and other disruptors will transform industries and lives.

Themed BEYOND SMART and presented by SEMI, SEMICON West 2018 features top technologists and industry leaders highlighting the significance of artificial intelligence (AI) and the latest technologies and trends in smart transportation, smart manufacturing, smart medtech, smart data, big data, blockchain and the Internet of Things (IoT).

Seven keynotes and more than 250 subject matter experts will offer insights into critical opportunities and issues across the global microelectronics supply chain. The event also features new Smart Pavilions to showcase interactive technologies for immersive, virtual experiences.

Smart transportation and smart manufacturing pavilions: Applying AI to accelerate capabilities

Automotive leads all new applications in semiconductor growth and is a major demand driver for technologies inrelated segments such as MEMS and sensors. The SEMICON West Smart Transportation and Smart Manufacturing pavilions showcase AI breakthroughs that are enabling more intelligent transportation performance and manufacturing processes, increasing yields and profits, and spurring innovation across the industry.

Smart workforce pavilion: Connecting next-generation talent with the microelectronics industry

SEMICON West also tackles the vital industry issue of how to attract new talent with the skills to deliver future innovations. Reliant on a highly skilled workforce, the industry today faces thousands of job openings, fierce competition for workers and the need to strengthen its talent pipeline. Educational and engaging, the Smart Workforce Pavilion connects the microelectronics industry with college students and entry-level professionals.

In the Workforce Pavilion “Meet the Experts” Theater, recruiters from top companies are available for on-the-spot interviews, while career coaches offer mentoring, tips on cover letter and resume writing, job-search guidance, and more. SEMI will also host High Tech U (HTU) in conjunction with the SEMICON West Smart Workforce Pavilion. The highly interactive program supported by Advantest, Edwards, KLA-Tencor and TEL exposes high school students to STEM education pathways and useful insights about careers in the industry.

Releasing its Mid-Year Forecast at the annual SEMICON West exposition, SEMI, the global industry association representing the electronics manufacturing supply chain, today reported that worldwide sales of new semiconductor manufacturing equipment are projected to increase 10.8 percent to $62.7 billion in 2018, exceeding the historic high of $56.6 billion set last year. Another record-breaking year for the equipment market is expected in 2019, with 7.7 percent forecast growth to $67.6 billion.

The SEMI Mid-Year Forecast predicts wafer processing equipment will rise 11.7 percent in 2018 to $50.8 billion. The other front-end segment, consisting of fab facilities equipment, wafer manufacturing, and mask/reticle equipment, is expected to jump 12.3 percent to $2.8 billion this year. The assembly and packaging equipment segment is projected to grow 8.0 percent to $4.2 billion in 2018, while semiconductor test equipment is forecast to increase 3.5 percent to $4.9 billion this year.

In 2018, South Korea will remain the largest equipment market for the second year in a row. China will rise in the rankings to claim the second spot for the first time, dislodging Taiwan, which will fall to the third position. All regions tracked except Taiwan will experience growth. China will lead in growth with 43.5 percent, followed by Rest of World (primarily Southeast Asia) at 19.3 percent, Japan at 32.1 percent, Europe at 11.6 percent, North America at 3.8 percent and South Korea at 0.1 percent.

SEMI forecasts that, in 2019, equipment sales in China will surge 46.6 percent to $17.3 billion. In 2019, China, South Korea, and Taiwan are forecast to remain the top three markets, with China rising to the top. South Korea is forecast to become the second largest market at $16.3 billion, while Taiwan is expected to reach $12.3 billion in equipment sales.

The following results are in terms of market size in billions of U.S. dollars:

The Equipment Market Data Subscription (EMDS) from SEMI provides comprehensive market data for the global semiconductor equipment market. A subscription includes three reports: the monthly SEMI Billings Report, which offers an early perspective of the trends in the equipment market; the monthly Worldwide Semiconductor Equipment Market Statistics (SEMS), a detailed report of semiconductor equipment bookings and billings for seven regions and over 22 market segments; and the SEMI Mid-year Forecast, which provides an outlook for the semiconductor equipment market. For more information or to subscribe, please contact SEMI customer service at 1.877.746.7788 (toll free in the U.S.). For more information online, visit: http://info.semi.org/semi-equipment-market-data-subscription

By integrating the design of antenna and electronics, researchers have boosted the energy and spectrum efficiency for a new class of millimeter wave transmitters, allowing improved modulation and reduced generation of waste heat. The result could be longer talk time and higher data rates in millimeter wave wireless communication devices for future 5G applications.

The new co-design technique allows simultaneous optimization of the millimeter wave antennas and electronics. The hybrid devices use conventional materials and integrated circuit (IC) technology, meaning no changes would be required to manufacture and package them. The co-design scheme allows fabrication of multiple transmitters and receivers on the same IC chip or the same package, potentially enabling multiple-input-multiple-output (MIMO) systems as well as boosting data rates and link diversity.

Researchers from the Georgia Institute of Technology presented their proof-of-concept antenna-based outphasing transmitter on June 11 at the 2018 Radio Frequency Integrated Circuits Symposium (RFIC) in Philadelphia. Their other antenna-electronics co-design work was published at the 2017 and 2018 IEEE International Solid-State Circuits Conference (ISSCC) and multiple peer-reviewed IEEE journals. The Intel Corporation and U.S. Army Research Office sponsored the research.

Georgia Tech researchers are shown with electronics equipment and antenna setup used to measure far-field radiated output signal from millimeter wave transmitters. Shown are Graduate Research Assistant Huy Thong Nguyen, Graduate Research Assistant Sensen Li, and Assistant Professor Hua Wang. (Credit: Allison Carter, Georgia Tech)

“In this proof-of-example, our electronics and antenna were designed so that they can work together to achieve a unique on-antenna outphasing active load modulation capability that significantly enhances the efficiency of the entire transmitter,” said Hua Wang, an assistant professor in Georgia Tech’s School of Electrical and Computer Engineering. “This system could replace many types of transmitters in wireless mobile devices, base stations and infrastructure links in data centers.”

Key to the new design is maintaining a high-energy efficiency regardless whether the device is operating at its peak or average output power. The efficiency of most conventional transmitters is high only at the peak power but drops substantially at low power levels, resulting in low efficiency when amplifying complex spectrally efficient modulations. Moreover, conventional transmitters often add the outputs from multiple electronics using lossy power combiner circuits, exacerbating the efficiency degradation.

“We are combining the output power though a dual-feed loop antenna, and by doing so with our innovation in the antenna and electronics, we can substantially improve the energy efficiency,” said Wang, who is the Demetrius T. Paris Professor in the School of Electrical and Computer Engineering.  “The innovation in this particular design is to merge the antenna and electronics to achieve the so-called outphasing operation that dynamically modulates and optimizes the output voltages and currents of power transistors, so that the millimeter wave transmitter maintains a high energy efficiency both at the peak and average power.”

Beyond energy efficiency, the co-design also facilitates spectrum efficiency by allowing more complex modulation protocols. That will enable transmission of a higher data rate within the fixed spectrum allocation that poses a significant challenge for 5G systems.

“Within the same channel bandwidth, the proposed transmitter can transmit six to ten times higher data rate,” Wang said. “Integrating the antenna gives us more degrees of freedom to explore design innovation, something that could not be done before.”

Sensen Li, a Georgia Tech graduate research assistant who received the Best Student Paper Award at the 2018 RFIC symposium, said the innovation resulted from bringing together two disciplines that have traditionally worked separately.

“We are merging the technologies of electronics and antennas, bringing these two disciplines together to break through limits,” he said. “These improvements could not be achieved by working on them independently. By taking advantage of this new co-design concept, we can further improve the performance of future wireless transmitters.”

The new designs have been implemented in 45-nanometer CMOS SOI IC devices and flip-chip packaged on high-frequency laminate boards, where testing has confirmed a minimum two-fold increase in energy efficiency, Wang said.

The antenna electronics co-design is enabled by exploring the unique nature of multi-feed antennas.

“An antenna structure with multiple feeds allows us to use multiple electronics to drive the antenna concurrently. Different from conventional single-feed antennas, multi-feed antennas can serve not only as radiating elements, but they can also function as signal processing units that interface among multiple electronic circuits,” Wang explained. “This opens a completely new design paradigm to have different electronic circuits driving the antenna collectively with different but optimized signal conditions, achieving unprecedented energy efficiency, spectral efficiency and reconfigurability.”

The cross-disciplinary co-design could also facilitate fabrication and operation of multiple transmitters and receivers on the same chip, allowing hundreds or even thousands of elements to work together as a whole system. “In massive MIMO systems, we need to have a lot of transmitters and receivers, so energy efficiency will become even more important,” Wang noted.

Having large numbers of elements working together becomes more practical at millimeter wave frequencies because the wavelength reduction means elements can be placed closer together to achieve compact systems, he pointed out. These factors could pave the way for new types of beamforming that are essential in future millimeter wave 5G systems.

Power demands could drive adoption of the technology for battery-powered devices, but Wang says the technology could also be useful for grid-powered systems such as base stations or wireless connections to replace cables in large data centers. In those applications, expanding data rates and reducing cooling needs could make the new devices attractive.

“Higher energy efficiency also means less energy will be converted to heat that must be removed to satisfy the thermal management,” he said. “In large data centers, even a small reduction in thermal load per device can add up. We hope to simplify the thermal requirements of these electronic devices.”

In addition to those already mentioned, the research team included Taiyun Chi, Huy Thong Nguyen and Tzu-Yuan Huang, all from Georgia Tech.