Category Archives: LED Packaging and Testing

The recent restructuring by major global lighting companies will allow LED makers to raise capital for investments in 2015. According to “Top Lighting and LEDs Trends for 2015,” a new white paper issued by the IHS, last year’s restructuring could lead to improved margins for leading companies, along with the potential for lower product prices for consumers.

“For the big three lighting suppliers, the road was bumpy: all of them recorded falling revenue in the first three quarters of 2014,” said William Rhodes, research manager of lighting and LEDs at IHS Technology. “Industry watchers are now looking to see if these giants of the lighting industry can turn the tide in 2015.”

Following are 10 predictions for the lighting and LED industry for 2015, from the IHS technology research team:

1. China—the LED dragon—will continue to grow. The coming year could be pivotal for the global LED industry, given the growing market share of Chinese LED companies throughout the value chain. “In order to compete with international companies and maintain their growth, Chinese vendors must overcome negative perceptions of product quality that continue to plague them, even while they maintain their low pricing,” Rhodes said.

2. The sky is the limit for cloud-based smart lighting. The market for cloud-based smart lighting is unlikely to gain market share in 2015, because public knowledge of companies offering solutions remains limited; however, increased marketing of cloud-based smart lighting could gain mindshare in 2015, positioning the market for future growth.

3. Changing fortunes for lighting companies expected in 2015. The reorganization of the top three lighting manufacturers could turn them into pure-play lighting companies focused on dynamic markets, which would offer greater growth potential. The restructuring will also allow LED makers to raise capital for further investment, and will also let them reduce the hierarchal burden associated with being part of a large conglomerate. “Changes in the corporate structure, could lead to improved margins for the companies, and possibly lower-priced products for consumers,” Rhodes said.

4. Li-Fi, a brighter way to communicate. Visual light communication (LI-Fi) is a new and emerging technology, but implementations of pilot projects, along with greater media interest, is forecast for 2015. “It will be interesting to see how many commercial projects are announced this year, and on what scale,” Rhodes said.

5. Is lighting poised for a quantum leap? As quantum-dot LEDs (QD-LEDs) still have some challenges to overcome, the market will not likely to see vast quantities of commercially available products by 2015 or 2016; however, in the medium to longer term, QD-LEDs could kill off the OLED display market and cause deep disruption to the lighting industry as a whole.”QD-LEDs still have some challenges to overcome, but we might see a very small amount of commercially available products by the end of 2015,” Rhodes said.

6. OLED luminaires, and where to purchase them. Mass-market adoption of OLED lighting is not projected to occur in 2015, but retailers will likely start to offer a premium range of OLED luminaires, which undoubtedly will help create more interest in the overall OLED market in the coming year.

7. LED filament bulbs: incandescent beauty with an LED twist. LED filament lamps, which combine the benefits of LED lamps with the familiar design of incandescent bulbs beloved by traditionalists, are now starting to match other LED offerings, in terms of efficiency, price and color-rendering capabilities. “Ultimately it will be up to consumers to decide if filament bulbs will have their time in the limelight in 2015,” Rhodes said.

8. Packaged LED industry is moving downstream and getting smarter. Smart lighting is another way for companies to attempt to add value and improve profit margins. As the LED lighting market moves downstream with modules and light engines, incorporating smart lighting sensors and controls will be a key trend in 2015.

9. Is your streetlight all that it seems? In the coming year, a couple of smart street lighting pilot projects (e.g., incorporating electric vehicle charging or mobile phone masts into the luminaires) are expected to start moving to larger city-wide installations. “with developments in new technology, as well as the ever-expanding phenomenon of the Internet of Things (IoT), the role that street lights play in our world is set change completely,” Rhodes said.

10. Automotive applications driving optoelectronic components market. With LED headlamp penetration increasing, gesture control getting increasing interest, and hybrid and electric vehicles sales continuing to grow; 2015 will be a lucrative year for the optoelectronic components suppliers who focus on the automotive industry.

Organic semiconductors are prized for light emitting diodes (LEDs), field effect transistors (FETs) and photovoltaic cells. As they can be printed from solution, they provide a highly scalable, cost-effective alternative to silicon-based devices. Uneven performances, however, have been a persistent problem. Scientists have known that the performance issues originate in the domain interfaces within organic semiconductor thin films, but have not known the cause. This mystery now appears to have been solved.

Naomi Ginsberg, a faculty chemist with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory and the University of California (UC) Berkeley, led a team that used a unique form of microscopy to study the domain interfaces within an especially high-performing solution-processed organic semiconductor called TIPS-pentacene. She and her team discovered a cluttered jumble of randomly oriented nanocrystallites that become kinetically trapped in the interfaces during solution casting. Like debris on a highway, these nanocrystallites impede the flow of charge-carriers.

“If the interfaces were neat and clean, they wouldn’t have such a large impact on performance, but the presence of the nanocrystallites reduces charge-carrier mobility,” Ginsberg says. “Our nanocrystallite model for the interface, which is consistent with observations, provides critical information that can be used to correlate solution-processing methods to optimal device performances.”

Ginsberg, who holds appointments with Berkeley Lab’s Physical Biosciences Division and its Materials Sciences Division, as well as UC Berkeley’s departments of chemistry and physics, is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Exciton dynamics reveals aggregates with intermolecular order at hidden interfaces in solution-cast organic semiconducting films.” Co-authors are Cathy Wong, Benjamin Cotts and Hao Wu.

Organic semiconductors are based on the ability of carbon to form larger molecules, such as benzene and pentacene, featuring electrical conductivity that falls somewhere between insulators and metals. Through solution-processing, organic materials can usually be fashioned into crystalline films without the expensive high-temperature annealing process required for silicon and other inorganic semiconductors. However, even though it has long been clear that the crystalline domain interfaces within semiconductor organic thin films are critical to their performance in devices, detailed information on the morphology of these interfaces has been missing until now.

“Interface domains in organic semiconductor thin films are smaller than the diffraction limit, hidden from surface probe techniques such as atomic force microscopy, and their nanoscale heterogeneity is not typically resolved using X-ray methods,” Ginsberg says. “Furthermore, the crystalline TIPS-pentacene we studied has virtually zero emission, which means it can’t be studied with photoluminescence microscopy.”

Ginsberg and her group overcame the challenges by using transient absorption (TA) microscopy, a technique in which femtosecond laser pulses excite transient energy states and detectors measure the changes in the absorption spectra. The Berkeley researchers carried out TA microscopy on an optical microscope they constructed themselves that enabled them to generate focal volumes that are a thousand times smaller than is typical for conventional TA microscopes. They also deployed multiple different light polarizations that allowed them to isolate interface signals not seen in either of the adjacent domains.

“Instrumentation, including very good detectors, the painstaking collection of data to ensure good signal-to-noise ratios, and the way we crafted the experiment and analysis were all critical to our success,” Ginsberg says. “Our spatial resolution and light polarization sensitivity were also essential to be able to unequivocally see a signature of the interface that was not swamped by the bulk, which contributes much more to the raw signal by volume.”

The methology developed by Ginsberg and her team to uncover structural motifs at hidden interfaces in organic semiconductor thin films should add a predictive factor to scalable and affordable solution-processing of these materials. This predictive capability should help minimize discontinuities and maximize charge-carrier mobility. Currently, researchers use what is essentially a trial-and-error approach, in which different solution casting conditions are tested to see how well the resulting devices perform.

“Our methodology provides an important intermediary in the feedback loop of device optimization by characterizing the microscopic details of the films that go into the devices, and by inferring how the solution casting could have created the structures at the interfaces,” Ginsberg says. “As a result, we can suggest how to alter the delicate balance of solution casting parameters to make more functional films.”

MagnaChip Semiconductor Corporation, a Korea-based designer and manufacturer of analog and mixed-signal semiconductor products announced today that it has started to offer 0.18um automotive qualified process technology to foundry customers focused on high reliability automotive semiconductor applications.

This 0.18um automotive process technology consists of modular processes which combine 1.8V/3.3V CMOS, 52V LDMOS/EDMOS, fully isolated 32V nLDMOS and embedded MTP/EEPROM. MagnaChip’s proprietary electrical fuse OTP is also included for precision analog trimming. Full combinations of these modular processes serve a wide range of automotive semiconductor SOC products such as, but not limited to, LED lighting, motor drivers, microcontrollers and ASICs.

This process technology is specially designed for reliable operation at high temperatures and is fully AEC compliant conforming to AEC Q100 Grade 0 specification at 150 degrees C. For example, leakage current of 1.8V rated CMOS devices at 150 degrees C is reduced to ¼ of the leakage of 1.8V CMOS of baseline technologies. Endurance of MTP and EEPROM is 100K cycle and 10K cycle at 150 degrees C, respectively. SPICE model and MTP/EEPROM operation is verified up to 175 degrees C. In addition, high density standard cell libraries, SRAM and analog IPs are qualified in this process.

Namkyu Park, Executive Vice President of MagnaChip’s Semiconductor Manufacturing Services Division stated, “This is another example of our continued effort to expand our specialty technology portfolio for the automotive market. We are very proud to play an increasing role in the fast-growing automotive semiconductor foundry market and are committed to continuing to provide differentiated technology solutions for our customers.”

Headquartered in South Korea, MagnaChip Semiconductor is a Korea-based designer and manufacturer of analog and mixed-signal semiconductor products, mainly for high volume consumer applications.

Scientists at UCL, in collaboration with groups at the University of Bath and the Daresbury Laboratory, have uncovered the mystery of why blue light-emitting diodes (LEDs) are so difficult to make, by revealing the complex properties of their main component – gallium nitride – using sophisticated computer simulations.

Blue LEDs were first commercialised two decades ago and have been instrumental in the development of new forms of energy saving lighting, earning their inventors the 2014 Nobel Prize in Physics. Light emitting diodes are made of two layers of semiconducting materials (insulating materials which can be made conduct electricity in special circumstances). One has mobile negative charges, or electrons, available for conduction, and the other positive charges, or holes. When a voltage is applied, an electron and a hole can meet at the junction between the two, and a photon (light particle) is emitted.

The desired properties of a semiconductor layer are achieved by growing a crystalline film of a particular material and adding small quantities of an ‘impurity’ element, which has more or fewer electrons taking part in the chemical bonding (a process known as ‘doping’). Depending on the number of electrons, these impurities donate an extra positive or negative mobile charge to the material.

The key ingredient for blue LEDs is gallium nitride, a robust material with a large energy separation, or ‘gap’, between electrons and holes – this gap is crucial in tuning the energy of the emitted photons to produce blue light. But while doping to donate mobile negative charges in the substance proved to be easy, donating positive charges failed completely. The breakthrough, which won the Nobel Prize, required doping it with surprisingly large amounts of magnesium.

“While blue LEDs have now been manufactured for over a decade,” says John Buckeridge (UCL Chemistry), lead author of the study, “there has always been a gap in our understanding of how they actually work, and this is where our study comes in. Naïvely, based on what is seen in other common semiconductors such as silicon, you would expect each magnesium atom added to the crystal to donate one hole. But in fact, to donate a single mobile hole in gallium nitride, at least a hundred atoms of magnesium have to be added. It’s technically extremely difficult to manufacture gallium nitride crystals with so much magnesium in them, not to mention that it’s been frustrating for scientists not to understand what the problem was.”

The team’s study, published today in the journal Physical Review Letters, unveils the root of the problem by examining the unusual behaviour of doped gallium nitride at the atomic level using highly sophisticated computer simulations.

“To make an accurate simulation of a defect in a semiconductor such as an impurity, we need the accuracy you get from a quantum mechanical model,” explains David Scanlon (UCL Chemistry), a co-author of the paper. “Such models have been widely applied to the study of perfect crystals, where a small group of atoms form a repeating pattern. Introducing a defect that breaks the pattern presents a conundrum, which required the UK’s largest supercomputer to solve. Indeed, calculations on very large numbers of atoms were therefore necessary but would be prohibitively expensive to treat the system on a purely quantum-mechanical level.”

The team’s solution was to apply an approach pioneered in another piece of Nobel Prize winning research: hybrid quantum and molecular modelling, the subject of 2013’s Nobel Prize in Chemistry. In these models, different parts of a complex chemical system are simulated with different levels of theory.

“The simulation tells us that when you add a magnesium atom, it replaces a gallium atom but does not donate the positive charge to the material, instead keeping it to itself,” says Richard Catlow (UCL Chemistry), one of the study’s co-authors. “In fact, to provide enough energy to release the charge will require heating the material beyond its melting point. Even if it were released, it would knock an atom of nitrogen out of the crystal, and get trapped anyway in the resulting vacancy. Our simulation shows that the behaviour of the semiconductor is much more complex than previously imagined, and finally explains why we need so much magnesium to make blue LEDs successfully.”

The simulations crucially fit a complete set of previously unexplained experimental results involving the behaviour of gallium nitride. Aron Walsh (Bath Chemistry) says “We are now looking forward to the investigations into heavily defective GaN, and alternative doping strategies to improve the efficiency of solid-state lighting”.

The explosive expansion of the Internet of things (IoT) is driving rapid demand growth for microelectromechanical systems (MEMS) devices in areas including asset-tracking systems, smart grids and building automation.

Worldwide market revenue for MEMS directly used in industrial IoT equipment will rise to $120 million in 2018, up from $16 million in 2013, according to IHS Technology (NYSE: IHS). Additional MEMS also will be used to support the deployment of the IoT, such as devices employed in data centers. This indirect market for industrial IoT MEMS will increase to $214 million in 2018, up from $43 million in 2013.

The figure below presents the IHS forecast of global MEMS revenue from direct and indirect IoT uses.

Global market shipments for industrial IoT equipment are expected to expand to 7.3 billion units in 2025, up from 1.8 billion in 2013. The industrial IoT market is a diverse area, comprising equipment such as nodes, controllers and infrastructure, and used in markets ranging from building automation to commercial transport, smart cards, industrial automation, lighting and health. Such gear employs a range of MEMS device types including accelerometers, pressure sensors, timing components and microphones.

“The Internet of things is sometimes called the machine-to-machine (M2M) revolution, and one important class of machines—MEMS—will play an essential role in expansion of the boom of the industrial IoT segment in the coming years,” said Jeremie Bouchaud, director and senior principal analyst for MEMS and sensors at IHS. “MEMS sensors allow equipment to gather and digitize real-world data that then can be shared on the Internet. The IoT represents a major new growth opportunity for the MEMS market.”

More information on the topic can be found in the report entitled “Internet of Things begins to impact High-Value MEMS” from the MEMS & Sensors service of IHS.

Industrial IoT applications for MEMS

Building automation will generate the largest volumes for MEMS and other types of sensors in the industrial IoT market.

Asset tracking is the second-largest opportunity for sensors in industrial IoT. This segment will drive demand for large volumes of MEMS accelerometers and pressure sensors.

The smart grid also will require various types of MEMS, including inclinometers to monitor high-voltage power lines as well as accelerometers and flow sensors in smart meters.

Other major segments of the industrial IoT market include smart cities, smart factories, seismic monitoring, and drones and robotics.

MEMS types

Accelerometers and pressure sensors account for most of the MEMS shipments for direct industrial IoT applications in areas including building automation, agriculture and medical. MEMS timing devices in smart meters and microphones used in smart homes and smart cities will be next in terms of volume.

Indirect benefits

To support the deluge of data that IoT will generate, major investments will be required in the backbone infrastructure of the Internet, including data centers. This, in turn, will drive the indirect demand for MEMS used in such infrastructure.

Data centers will spur demand for optical MEMS, especially optical cross connects and wavelength selective switches. Big data operations also will require large quantities of integrated circuits (ICs) for memory. The testing of memory ICs makes use of MEMS wafer probe cards.

IoT Market

The demand for LED chipsets, primarily for the LED lighting market, is forecast to increase substantially through 2018. According to DisplaySearch, now part of IHS (NYSE: IHS), measured in standard units (500 x 500 micron chip size), demand for LED chipsets are expected to increase 293 percent from 35.8 million in 2013 to 1.4 billion in 2018.

“This forecast growth in the LED market is due in large part to increasing demand from the LED lighting segment,” said Steven Sher, analyst for DisplaySearch. “As average selling prices continue to fall, shipments of all LED lighting products will remain on the rise.”

In 2014 the LED market became more integrated from chip to channel, as competing companies merged and supply-chain companies acquired LED industry players. “The LED chip industry is expected to fare better than the LED package industry, as demand for lighting continues to increase through 2018,” Sher said.

While previously strong, the chipset demand from LCD TV backlights has slowed, due to a combination of sluggish growth in LED-backlit LCD TV sales, as well as improved efficiency in the number of chips used per backlight. For those reasons, growth in the global demand for chipsets used for display backlighting flattened after 2012, with a slow decrease forecast after 2014.

DisplaySearch_LED_Chip_Demand_in_Backlights_and_Lighting_141218

The case is made for delivering liquid precursors from a central delivery system to the epi/dep tool as a vapor of precisely-controlled composition. 

By EGBERT WOELK, Ph.D., Dow Electronic Materials, North Andover, MA, USA and ROGER LOO, Ph.D., imec, Leuven, Belgium 

The epi and deposition processes for silicon-based semiconductor devices have used gaseous and liquid precursors. Gaseous precursors are compounds whose vapor pressure at room temperature is higher than 1500 torr (2000 mbar), which is sufficient to drive a mass flow controller (MFC). Using only one MFC, gaseous precursors can conveniently be metered to the process. Silane and dichlorosilane (DCS) have been used with that method. The industry has also used Trichloro silane (TCS) that boils at around 33°C and can be directly metered to a low pressure epi process using an appropriate MFC. For the epi of SiGe, germane, which is a gas, has been used.

Tetraethylorthosilicate (TEOS) has long been used for the deposition of SiO2 and has mostly been delivered using direct liquid injection (DLI). DLI meters the flow of the liquid precursor to a flash evaporator and provides good control, but flash evaporation requires high temperatures and care must be taken that the precursor compound does not break up prematurely. This can be a challenge for precursors that work at lower deposition temperatures.

More recently, trisilane (Si3H8) has been used for low temperature Si epi and deposition. The delivery of trisilane to the process uses the carrier-gas-assisted delivery method. In the most common implementation, it employs an on-board evaporation ampoule dedicated to one reactor. The same setup has been used for III-V compound semiconductor and LED epi with good success. Driven by cost pressure, however, the LED epi industry is moving from dedicated onboard ampoules to a central delivery system for high-volume precursors like trimethylgallium (TMGa). One part of the cost reduction simply comes from the economies of scale. Another aspect comes from the elimination of excessive hardware, such as thermal baths and pressure controllers, and their maintenance. Most importantly, a substantial part of the cost reduction comes from yield increases due to improved process control. The same central delivery system can be used for trisilane and other liquid CVD precursors for silicon-based CVD for similar cost reduction.

Carrier-gas-assisted precursor delivery

Liquid compounds with an RT vapor pressure between 1 and 400 mbar require carrier-gas-assisted delivery. Many liquid compounds within that vapor pressure range are excellent precursors for CVD and epi processes. For such compounds, the difference between the vapor pressure and the process pressure is too small to drive an MFC for straight metering. Adding a carrier gas increases the pressure to between approximately 760 and 1500 torr (1000 and 2000 mbar). The selection of a good delivery pressure depends primarily on the desired concentration.

The carrier-gas-assisted delivery method has long been used for trimethylgallium (TMGa) and trimethylaluminium (TMAl) for the growth of GaAs and GaN. For the growth of GaAlN and GaInN for LEDs, the composition ratio of the two group III precursors is extremely critical for the performance of the final product. Therefore, the precision of the evaporation and the metering has always been a concern.

FIGURE 1a shows the setup for a straight gas delivery and FIGURE 1b shows the setup for a carrier-gas-assisted delivery. The design shown in Figure 1b requires no modification of the epi/dep tool in order to accept a normally liquid precursor. From an epi/ dep tool perspective, the design shown in Figure 1b behaves just like the straight gas delivery of Figure 1a. As such, it allows the use of the gas mixture from one delivery system at several points of use, i.e. the output of the delivery system can be subdivided. In Figure 1b the precursor vapor is made on demand. While the output (mol flux of precursor per time) is theoretically unlimited, there are practical limits that restrict the output to approximately 20 standard liters per minute (slm). The main limitation is the dynamic range of the metering valve: the best units have a dynamic range of 1 in 104, which means that they can reliably control a flow between 0.002 and 20 slm. This is important for the mol flux precision at smaller flows, i.e. when only one or two tools draw precursor.

FIGURE 1a. High vapor pressure precursor, straight vapor delivery. S: pressure sensor, V: metering valve. S and V are normally integrated into a pressure regulator. MFC meters neat vapor.

FIGURE 1a. High vapor pressure precursor, straight vapor delivery. S: pressure sensor, V: metering valve. S and V are normally integrated into a pressure regulator. MFC meters neat vapor.

FIGURE 1b. Low vapor pressure precursor, carrier gas assisted delivery in Dow's VAPORSTATIONTM Central Delivery System. S: pressure sensor, V: metering valve. MFC meters diluted precursor vapor. Pressure and temperature control guarantee high precision concentration.

FIGURE 1b. Low vapor pressure precursor, carrier gas assisted delivery in Dow’s VAPORSTATIONTM Central Delivery System. S: pressure sensor, V: metering valve. MFC meters diluted precursor vapor. Pressure and temperature control guarantee high precision concentration.

On-board ampoules and central delivery system

There are several designs of carrier-gas-assisted delivery sources. The traditional design meters carrier gas into the ampoule rather than the mixture into the process chamber. Such a delivery system is dedicated to one reactor because the mass flow is metered upstream of the evaporation vessel and the associated MFC is controlled by the epi/dep tool. The ampoule serves two functions: (1) as the transport vessel and (2) as an evaporation device. For cost reasons, the ampoule should be of simple design. This means that trade-offs for the evaporation performance have to be made. The trade-offs result in line-to-line delivery rate variations and a noticeable change of delivery rate over the life of the ampoule. For some products, such changes require run-to-run recipe adjustments. In some cases the on-board ampoule is connected to a central dispense unit that transfers liquid precursor into the on-board ampoule. The result is a complex system that is still subject to delivery rate shifts requiring recipe adjustments.

A new central delivery system design is shown in Figure 1b. The task-optimized evaporator is fitted with temperature, pressure and level sensors that hold the precursor output variation at less than +/-0.4% by use of special stability algorithms. The evaporator is a permanently-installed part of the central delivery system. It is fed from a supply canister and features two precision thermometers inside the precursor liquid and gas distribution baffles and strainers for entrained droplets. Once calibrated, the system delivers a precisely known rate to a number of epi/dep reactors in the fab.

FIGURE 2 shows the output concentration of two calibrated central delivery units under various loads [1]. The curve that is alternately dotted and solid represents the signal of the binary gas sensor, which was alternately connected to one or the other unit. The other curves represent the output of the two units in standard liters per minute. The results show that proper calibration of the temperature and pressure sensors results in error of the delivery of less than +/- 0.4%. This precision cannot be achieved with ordinary on-board ampoules.

FIGURE 2. Output and concentration of two calibrated VAPORSTATIONTM Central Delivery Systems. Concentration remains within +/- 0.4% of set point regardless of load.

FIGURE 2. Output and concentration of two calibrated VAPORSTATIONTM Central Delivery Systems. Concentration remains within +/- 0.4% of set point regardless of load.

Recently, the application of the VAPORSTATION Central Delivery system has been expanded to deliver SnCl4 to a new process for the deposition of GeSn. It was fitted to a gas delivery line that was available on a mainstream silicon epi tool.

GeSn epi using a SnCl4 as new precursor

There has been increasing interest in GeSn and SiGeSn as alternative Group IV semiconductor material for electrical and optical device applications. The continuing expansion of traditional silicon with Sn and Ge offers additional design options for band gap and stress engineering. Over the past years, stress engineering using Ge made a major contribution to the improvement in Si-CMOS device performance. More recently the use of GeSn as a stressor for Ge-CMOS and relaxed GeSn as a virtual substrate, which is used to create tensile strain in a Ge epitaxial film, have been considered. The creation of tensile strain in an epitaxial Ge film is expected to result in germanium with a direct band gap [5] for photonic devices. Epitaxial Ge1-xSnx itself has also been considered as a promising candidate material for lasers and photodetectors. It has been predicted that, for sufficiently high Sn content, relaxed Ge1-xSnx turns into a direct band gap semiconductor [6,7]. Recent work of imec and its partners describe the active functionality based on the heterogeneous integration of strained GeSn/Ge on a Si platform providing photo-detection in the mid-infrared [8].

Due to the poor solubility of Sn in the Ge matrix of less than 1%, the epitaxial growth of (Si)GeSn is very challenging. Low solubility demands out-of- equilibrium growth conditions and, from epitaxial growth point of view, extremely low growth temperatures. Until recently, GeSn was grown by molecular beam epitaxy — a technique that is not suited for mass production. More recently, deuterated stannane, SnD4 has been used as Sn precursor for a CVD process, but the practical application is questionable due to the instability of SnD4.

To eliminate the problems posed by SnD4, imec chose to investigate stannic chloride SnCl4 , a stable, benign, abundant and commercially-available liquid Sn compound. Currently though, most of the CVD reactors for SiGeSn epi are not designed to use liquid precursor sources. In order to facilitate the use of liquid CVD precursors at imec, Dow Electronic Materials provided an R&D version of the central delivery system. It features the output stability and other benefits described above. The use of one of these units enabled imec to use SnCl4 and develop a groundbreaking new CVD process using digermane (Ge2H6) and SnCl4 to grow GeSn epitaxial films in a production-compatible CVD reactor. The films are metastable GeSn alloys with up to 13% substitutional Sn [10,11].

FIGURE 3 shows a typical cross section transmission electron microscope (TEM) picture with associated (224) x-ray diffraction reciprocal space mapping (XRD RSM) of a fully strained GeSn layer, grown on top of a relaxed Ge virtual substrate. The deposition temperature for the GeSn growth was kept low (320°C) in order to allow Sn incorporation in Ge lattice without Sn precipitation or agglomeration.

FIGURE 3. (a) Cross-section TEM of a 40 nm fully strained defect free GeSn layer on 1 lm Ge/Si buffer substrate with 8% Sn grown with AP- CVD using combination of Ge2H6 and SnCl4. (b) RHEED diagram of the Ge0.92Sn0.08 surface after deoxidation in UHV at 420°C. The pattern exhibits a strong (2x1) surface reconstruction along the [110]Ge direction. (c) (224) XRD-RSM of the 40 nm Ge0.92Sn0.08/Ge bilayer showing that GeSn is fully strained on Ge.

FIGURE 3. (a) Cross-section TEM of a 40 nm fully strained defect free GeSn layer on 1 lm Ge/Si buffer substrate with 8% Sn grown with AP- CVD using combination of Ge2H6 and SnCl4. (b) RHEED diagram of the Ge0.92Sn0.08 surface after deoxidation in UHV at 420°C. The pattern exhibits a strong (2×1) surface reconstruction along the [110]Ge direction. (c) (224) XRD-RSM of the 40 nm Ge0.92Sn0.08/Ge bilayer showing that GeSn is fully strained on Ge.

The TEM picture in Fig. 3(a) exhibits a defect-free and high crystalline quality for the 40-nm-thick GeSn layer. Furthermore, the surface quality of the as-grown Ge0.92Sn0.08/Ge/Si heterostructure was investigated by reflection high-energy electron diffraction (RHEED) analysis after ex-situ transfer to a MBE system. An annealing in ultra-high vacuum up to 420°C resulted in an oxide-free GeSn surface showing a strong (2×1) surface reconstruction as seen on RHEED pattern along the [110] azimuth (Fig. 3(b)). Finally, the XRDRSM around the (2 2 4) Bragg reflections (Fig. 3(c)) demonstrates that the grown GeSn layer is fully strained on Ge/Si (001) substrate.

Conclusion

The use of an improved delivery system for liquid CVD precursors allowed the
use of stannic chloride for the growth of GeSn. The new process developed by imec produces metastable GeSn with concentrations of substitutional tin of 13%.
TM Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

References

1. Control of vapor feed from liquid precursors to the OMVPE process, E. Woelk, R. DiCarlo, Journal of Crystal Growth, Available online 29 October 2013, In Press, Corrected Proof.
2. p and n-type germanium layers grown using iso-butyl germane in a III-V metal-organic vapor phase epitaxy reactor, R. Jakomin, G. Beaudoin, N. Gogneau, B. Lamare, L. Largeau, O. Mauguin, I. Sagnes, Thin Solid Films, 519, (2011), 4186–4191.
3. Crystalline Properties and Strain Relaxation Mechanism of CVD Grown GeSn, F. Gencarelli, B. Vincent, J. Demeule- meester, A. Vantomme, A. Moussa, A. Franquet, A. Kumar, H. Bender, J. Meersschaut, W. Vandervorst, R. Loo, M. Caymax, K. Temst, M. Heyns, ECS Trans. 50, (2013), 875-883.
4. Antimony surfactant for epitaxial growth of SiGe buffer layers at high deposition temperatures. Storck, P.; Vorder- westner, M.; Kondratyev, A.; Talalaev, R.; Amamchyan, A.; Woelk, E. Thin Solid Films vol. 518 issue 6 January 1, 2010. p. S23-S29.
5. M. V. Fischetti and S. E. Laux, Journal of Applied Physics 80, 2234 (1996).
6. D. W. Jenkins and J. D. Dow, Physical Review B, 36, 7994 (1987).
7. M. R. Bauer, J. Tolle, C. Bungay, A. V. G. Chizmeshya, D. J. Smith, J. Menéndez and J. Kouvetakis, Solid State Communication 127, 355 (2003).
8. A. Gassenq, F. Gencarelli, J. Van Campenhout, Y. Shimura, R. Loo, G. Narcy, B. Vincent, and G. Roelkens, OPTICS EXPRESS 20 (25) , 27297 (2012).
9. R. F. Spohn and C. B. Richenburg, ECS Transactions 50 (9), 921 (2012).
10. B. Vincent, F. Gencarelli, H. Bender, C. Merckling, B. Douhard, D. H. Petersen, O. Hansen, H. H. Henrichsen, J. Meersschaut, W. Vandervorst, M. Heyns, R. Loo, and M. Caymax, Appl. Phys. Lett., 99, 152103 (2011).
11. F. Gencarelli, B. Vincent, J. Demeulemeester, A. Vantomme, A. Moussa, A. Franquet, A. Kumar, H. Bender, J. Meerss- chaut, W. Vandervorst, R. Loo, M. Caymax, K. Temst, and M. Heyns ECS Journal of Solid State Science and Technology 2 (4), 134 (2013).
12. S. Gupta, B. Vincent, B. Yang, D. Lin, F. Gencarelli, J. Lin, R. Chen, O. Richard, H. Bender, B. Magyari-Koepe, M. Caymax, J. Dekoster, Y.; Nishi, and K. Saraswat, K. Extended Abstracts of the 2013 International Electronic Device Meeting (IEDM) (2012) p. 375.

EGBERT WOELK, PH.D., is director of marketing at Dow Electronic Materials, North Andover, MA. ROGER LOO, PH.D., is a principal scientist at imec, Leuven, Belgium.

By DAVE HEMKER, Senior Vice President and Chief Technology Officer, Lam Research Corp.

Given the current buzz around the Internet of Things (IoT), it is easy to lose sight of the challenges
– both economic and technical. On the economic side is the need to cost-effectively manufacture up to a trillion sensors used to gather data, while on the technical side, the challenge involves building out the infrastructure. This includes enabling the transmission, storage, and analysis of volumes of data far exceeding anything we see today. These divergent needs will drive the semiconductor equipment industry to provide very different types of manufacturing solutions to support the IoT.

In order to fulfill the promise of the IoT, sensor technology will need to become nearly ubiquitous in our businesses, homes, electronic products, cars, and even our clothing. Per-unit costs for sensors will need to be kept very low to ensure the technology is economically viable. To support this need, trailing-edge semiconductor manufacturing capabilities provide a viable option since fully depreciated wafer processing equipment can produce chips cost efficiently. For semiconductor equipment suppliers, this translates into additional sales of refurbished and productivity-focused equipment and upgrades that improve yield, throughput, and running costs. In addition to being produced inexpensively, sensors intended for use in the IoT will need to meet several criteria. First, they need to operate on very low amounts of power. In fact, some may even be self-powered via MEMS (microelectromechanical systems)-based oscillators or the collection of environmental radio frequency energy, also known as energy harvesting/scavenging. Second, they will involve specialized functions, for example, the ability to monitor pH or humidity. Third, to enable the transmission of data collected to the supporting infrastructure, good wireless communications capabilities will be important. Finally, sensors will need to be small, easily integrated into other structures – such as a pane of glass, and available in new form factors – like flexible substrates for clothing. Together, these new requirements will drive innovation in chip technology across the semiconductor industry’s ecosystem.

The infrastructure needed to support the IoT, in contrast, will require semiconductor performance to continue its historical advancement of doubling every 18-24 months. Here, the challenges are a result of the need for vast amounts of networking, storage in the Cloud, and big data analysis. Additionally, many uses for the IoT will involve risks far greater than those that exist in today’s internet. With potential medical and transportation applications, for example, the results of data analysis performed in real time can literally be a matter of life or death. Likewise, managing the security and privacy of the data being generated will be paramount. The real-world nature of things also adds an enormous level of complexity in terms of predictive analysis.

Implementing these capabilities and infrastructure on the scale imagined in the IoT will require far more powerful memory and logic devices than are currently available. This need will drive the continued extension of Moore’s Law and demand for advanced semiconductor manufacturing capability, such as atomic-scale wafer processing. Controlling manufacturing process variability will also become increasingly important to ensure that every device in the new, interconnected world operates as expected.

With development of the IoT, semiconductor equipment companies can look forward to opportunities beyond communications and computing, though the timing of its emergence is uncertain. For wafer processing equipment suppliers in particular, new markets for leading-edge systems used in the IoT infrastructure and productivity-focused upgrades for sensor manufacturing are expected to develop.

The use of a semi-aqueous organic film stripper and residue remover that does not contain N-Methyl-2 pyrrolidone (NMP) is compared with current NMP-based chemistry.

By NIK MUSTAPHA and DR. GLENN WESTWOOD, Avantor Performance Materials, Inc. MARKUS TAN, JOACHIM NG, and YANG MING CHIEH, Philips Lumileds Singapore

Philips Lumileds collaborated with Avantor Performance Materials, a global manufacturer of high-performance chemistries, to evaluate one of Avantor’s post-etch residue remover and photoresist stripper products as a replacement for a current chemistry. Avantor’s J.T. Baker ALEGTM-368 organic film stripper and residue remover is an engineered blend of organic solvents and semi-aqueous compo-nents suitable for bulk photoresist removal and post-etch/ash residue and sidewall polymer removal. Designed to provide broad process latitude in terms of processing times and temperatures, ALEGTM-368 organic film stripper and residue remover is completely water soluble, requires no intermediate solvent rinse, and contains no hydroxylamine (HA), NMP, or fluoride elements.

The authors worked together to assess whether a change to Philips Lumileds’ process of record (POR), using this product, could be accomplished without impacting yield or device quality, and with the desired cost savings.

NMP replacement challenges

Pending changes in environmental, health, and safety regulations in key manufacturing locations around the world may prohibit the use of NMP-based post-etch residue and photoresist removal products in LED manufacturing. The shift can already be observed in Europe and in some parts of Asia and the United States, where companies are moving toward NMP-free manufacturing environments. In today’s competitive environment, it is vital for companies to find alternative chemistries that are not only effective and emphasize good performance, but also provide better cost of ownership. Philips Lumileds is taking a significant step to be part of this change.

Initial verification tests of NMP-free product

As part of the process verification, several wafers were used to check etch rate on critical substrates such as III/V Nitride, Al, Ag, and Au. These wafers were also used to verify the effectiveness of the ALEGTM-368 product to remove photoresist. Data were then compared with the current POR (TABLE 1).

TABLE 1. Comparable etch rate data (A/min) shown by baseline and ALEGTM-368 product on critical substrates.

TABLE 1. Comparable etch rate data (A/min) shown by baseline and ALEGTM-368 product on critical substrates.

It was important to confirm the effectiveness of the ALEGTM-368 product in stripping capability of negative photoresist. A wafer with 5μm thickness was used as an experiment. The wafer was dipped in the ALEGTM-368 product at 75°C followed by a water rinse step. To ensure uniformity of chemical performance, five locations were inspected by a scanning electron microscope (SEM) before and after treatment with the NMP-free product (FIGURE 1). Post-treatment images after dipping the wafer in the ALEGTM-368 product indicated that no resist remained on top of the metal surface (FIGURE 2). This supports the effectiveness of the ALEGTM-368 product; it is capable of stripping photoresist completely, without visible damage to the metal surface.

FIGURE 1. Cross-sectioning images showing resist on top of III/V metal surface before ALEGTM-368 process step.

FIGURE 1. Cross-sectioning images showing resist on top of III/V metal surface before ALEGTM-368 process step.

FIGURE 2. Cross-sectioning images showed no resist on top of III/V metal surface after processing in ALEGTM-368.

FIGURE 2. Cross-sectioning images showed no resist on top of III/V metal surface after processing in ALEGTM-368.

Resist stripping and residue remover verification test on pattern wafers

Further tests were conducted on pattern wafers comparing POR and the ALEGTM-368 product at 75 °C, for 30 minutes. Wafers were then cleaved and subjected to SEM inspection.

LEDs Fig 3a LEDs Fig 3b

 

FIGURE 3. Post-treatment for POR material. No photoresist remained under high-magnification confocal microscope inspection. POR material showed good stripping capability on patterned wafers.

LEDs Fig 4a LEDs Fig 4b

 

FIGURE 4. Post-treatment using the ALEGTM-368 product. No resist remained under high-magnification confocal microscope inspection. POR material showed good stripping capability on patterned wafers. 

 

High-magnification images were obtained to verify cleaning performance and stripping capability of the ALEGTM-368 product and POR wafers. For top-view inspection, a high-magnification confocal microscope was used to verify complete removal of photoresist. Results are shown in FIGURES 3 and 4. Both the POR and the ALEGTM-368 product showed equal performance in terms of cleaning polymer residues and stripping photo resist on patterned wafers (FIGURES 5 and 6). The next critical step was to verify electrical performance for both the POR and the ALEGTM-368 product.

LEDs Fig 5a LEDs Fig 5b

 

FIGURE 5. SEM images showing post-treatment for POR. 

LEDs Fig 6a LEDs Fig 6b

 

FIGURE 6. SEM images showing post-treatment for the ALEGTM-368 product. 

Electrical performance for engineering lots

Wafers were sampled from several production lots before being split into two groups, one group using the baseline and the other using the ALEGTM-368 product. Both groups were processed in an automated tool following the recommended process condition at an operating temperature of 75°C and a processing time of 30 minutes. To achieve wafer uniformity, the tool was equipped with a mega-sonic function and recirculation to ensure effective cleaning of post-etch residues and stripping of negative photoresist.

After chemical treatment, the wafers were given an intermediate rinse using an IPA solvent to remove any remaining traces of the ALEGTM-368 product from the surface of the wafer. Without this step, chemical left on the surface of the wafer could cause corrosion, water marks, or other device defects. Wafers were then subjected to a QDR (quick dump rinse) to remove all remaining solvent on the wafers. This step normally takes five to ten minutes, with noticeable CO2 bubbling to serve as extra protection from corrosion of exposed metal. Finally, all wafers were subjected to a nitrogen dry for five minutes, a vital process since any remaining moisture could cause severe corrosion and impact electrical performance and final yield.

Once all process steps were performed, both groups were subjected to electrical tests to ensure the chips on the wafers were functioning well and within specifications. Results, as indicated in FIGURE 7, showed no significant differences in term of electrical performance for both the baseline and the ALEGTM-368 product. All wafers met specification and were subject to final yield probe.

FIGURE 7. Electrical performance comparing ALEGTM-380 and ALEGTM-368 products for real production wafers.

FIGURE 7. Electrical performance comparing ALEGTM-380 and ALEGTM-368 products for real production wafers.

Comparable Performance in Final Yield

The same production wafers which were processed using the ALEGTM-368 product at 75 °C were then subjected to final yield analysis and compared to current POR. There was slight improvement in the standard deviation for the ALEGTM-368 product when compared to baseline chemistry. Overall, both products showed comparable final yield at 98 percent (FIGURE 8).

FIGURE 8. Yield distribution for ALEGTM-380 and ALEGTM-368 products on real production wafers.

FIGURE 8. Yield distribution for ALEGTM-380 and ALEGTM-368 products on real production wafers.

Reduced Cost of Ownership

It is undeniable that operating cost is a major consideration in LED manufacturing. Prior to adopting the current POR chemistry, Philips Lumileds tried both HA-based and NMP-based chemistries. Using the HA-based chemistry, a pre-treatment process was needed to soften the photoresist prior to stripping, followed by a solvent intermediate rinse. A strip process with the ALEGTM-368 product eliminated this step and resulted in significant cost savings and increased throughput due to process simplification (TABLE 2).

TABLE 2. Higher throughput and better cost of ownership due to a reduction in process steps.

TABLE 2. Higher throughput and better cost of ownership due to a reduction in process steps.

Summary

The NMP-free ALEGTM-368 product was comparable to POR when tested in various steps of the LED manufacturing process, including: substrate compatibility on critical layers, electrical performance on actual device, and final yield. In terms of process simplification, use of the ALEGTM-368 product also showed similar technical benefits as POR, in which a significant reduction of the number of steps and chemicals used in the process leads to improved cost of ownership.

This collaboration demonstrates how a manufacturer can translate its commitment to environmental, health, and safety improvements and reduction of cost of ownership into the commercialization of a new cleaning process which can bolster its competitive position in the global LED manufacturing industry.

NIK MUSTAPHA is a Principal Applications Engineer, AvantorTM Performance Materials, Inc. MARKUS TAN is Chief Process Engineer, JOACHIM NG is Senior Manager-Process Engineering, and YANG MING CHIEH is a Process Engineer at Philips Lumileds Singapore. DR. GLENN WESTWOOD, Senior Research Scientist, AvantorTM Performance Materials, Inc.

Daintree Networks has been named by CIO Review Magazine as one of the ’50 Most Promising Internet of Things (IoT) Companies 2014.’ The list features the best vendors and consultants providing technologies and services related to IoT. In the same issue, Daintree Networks CEO Danny Yu was featured as the ‘Entrepreneur of the Month,’ which highlights his career path and leadership of Daintree Networks to becoming a prominent player in the Enterprise-IoT market and top provider of wireless mesh networking solutions for smart buildings.

A distinguished panel comprised of CEOs, CIOs, CTOs, and analysts including the CIO Review editorial board determined the list of top companies at the forefront of tackling challenges in the Internet of Things market in the U.S. “We are happy to showcase Daintree Networks as a top IoT company due to the success of its ControlScope solution in advancing the IoT landscape for commercial entities,” said Harvi Sachar, publisher and founder, CIO Review. “Daintree’s dedication to true open standards-based solutions continues to break down adoption barriers and provides significant cost advantages to its customers. We’re excited to have them on our top IoT companies list, and to feature Daintree’s leadership, CEO Danny Yu, as the ‘Entrepreneur of the Month.'”

“We are honored to be recognized by CIO Review Magazine as one of the top ’50 Most Promising IoT Companies for 2014,'” said Danny Yu, Daintree Networks CEO. “This distinction reinforces the success of our Enterprise Internet of Things,(E-IoT) approach, which leverages our true open standards-based solutions to provide cost-effective wireless mesh networking for smart buildings. In addition, as ‘Entrepreneur of the Month,’ I appreciate the recognition, but the credit goes to the dedicated, forward-thinking employees of the company who are driving our explosive growth.”