Tag Archives: letter-wafer-tech

At the SPIE Advanced Lithography conference in San Jose, Calif., Applied Materials, Inc., today announced the industry’s first in-line 3D CD SEM metrology tool for solving the challenges of measuring the high aspect ratio and complex features of 3D NAND and FinFET devices. The new Applied VeritySEM 5i system offers state-of-the-art high-resolution imaging and backscattered electron (BSE) technology that enable exceptional CD control in-line. Using the VeritySEM 5i system can speed up chipmakers’ process development and production ramp, and improve device performance and yield in high-volume production.

“Complex 3D structures require new measurement dimensions, increasing the demands placed on metrology technologies,” said Itai Rosenfeld, corporate vice president and general manager of Applied’s Process Diagnostics and Control group. “Continuing to rely on traditional CD SEM techniques to measure 3D devices is virtually impossible. Offering imaging innovations based on Applied’s expertise in advanced e-beam technology and image processing for fast, accurate on-device CD SEM metrology, allows our customers to see, measure and control their 3D device during R&D, ramp and volume production. Multiple customers using the tool are already benefiting from better yields with these new 3D devices. This system should continue to set the benchmark for the industry as chipmakers require new precision materials engineering capabilities to transition to 3D architectures and scale beyond the 10nm node.”

Innovations in metrology precision are needed to improve device performance, reduce variability and boost yields of increasingly intricate high-performance, high-density 3D devices. An advanced high-resolution SEM column, tilted beam and BSE imaging give the VeritySEM 5i system its unique 3D metrology capability to measure and monitor the most vital and challenging FinFET and 3D NAND structures in-line. Specifically, BSE imaging for via-in-trench bottom CD enables chipmakers to ensure connectivity between underlying and overlaying metal layers. For controlling FinFET sidewall, as well as gate and fin height, where the smallest variation impacts device performance and yield, the VeritySEM 5i tool’s tilt-beam provides exact, repeatable in-line measurements. High-resolution BSE imaging enables continued vertical scaling through enhanced sensitivity for measuring the asymmetrical sidewall and bottom CDs of 3D NAND devices with very high aspect ratios reaching up to 60:1 and beyond.

Applied Materials, Inc. (Nasdaq:AMAT) is the global leader in precision materials engineering solutions for the semiconductor, flat panel display and solar photovoltaic industries. Our technologies help make innovations like smartphones, flat screen TVs and solar panels more affordable and accessible to consumers and businesses around the world. Learn more at www.appliedmaterials.com.

Cymer, an ASML company, a developer of lithography light sources used by chipmakers to pattern advanced semiconductor chips, today announced the shipment of its first XLR 700ix light source. Enabling higher scanner throughput and process stability for 14nm chip manufacturing and beyond, the XLR 700ix provides improvements in bandwidth, wavelength and energy stability to reduce process variability and increase yield through improvements in wafer critical dimension (CD) uniformity; software enhancements to increase light source predictability and availability; and reduction in helium and power consumption to decrease operating costs.

Cymer also introduced DynaPulse as a product upgrade option for OnPulse customers. DynaPulse enables chipmakers to extend their capital investment and achieve the same performance improvements standard in the XLR 700ix to their ArF immersion installed base. Essentially eliminating bandwidth as a source of variation to improve on-wafer critical dimension (CD) uniformity, the XLR 700ix and DynaPulse utilize the same patented technology to tightly control bandwidth specifications (300+5fm) and achieve stable on-wafer performance.

“Customers have recognized the new performance, process stability and sustainability improvements of the XLR 700ix to enable higher system efficiency for leading-edge manufacturing applications, and are eager to realize the same benefits within their installed base,” said Ed Brown, Chief Executive Officer of Cymer Light Source. “DynaPulse now makes it easier for chipmakers to achieve a high level of performance and productivity across their entire ArF immersion light source fleet.”

From enhanced service to product upgrade options, such as SmartPulse and DynaPulse, OnPulse customers experience reduced cost of operation, enhanced productivity and predictable costs that scale directly with wafer production. For example, the SmartPulse data capture and analysis tool enables chipmakers to better monitor key light source parameters in real-time, with field-to-field resolution, prevent excursions and make adjustments to achieve a high level of performance, and ultimately increase wafer output per tool. SmartPulse enables chipmakers to better monitor and keep light sources within tighter bandwidth control achieved with DynaPulse.

As the newest additions to the family, XLR 700ix and DynaPulse demonstrate Cymer’s continued investment in research and development to support DUV technology extensions for 14nm chip manufacturing and beyond.

Graphene, a single-atom-thick lattice of carbon atoms, is often touted as a replacement for silicon in electronic devices due to its extremely high conductivity and unbeatable thinness. But graphene is not the only two-dimensional material that could play such a role.

University of Pennsylvania researchers have made an advance in manufacturing one such material, molybdenum disulphide. By growing flakes of the material around “seeds” of molybdenum oxide, they have made it easier to control the size, thickness and location of the material.

Unlike graphene, molybdenum disulfide has an energy band gap, meaning its conductivity can be turned on and off. Such a trait is critical for semiconductor devices used in computing. Another difference is that molybdenum disulphide emits light, meaning it could be used in applications like LEDs, self-reporting sensors and optoelectronics.

The study was led by A. T. Charlie Johnson, professor in the Department of Physics & Astronomy in Penn’s School of Arts & Sciences, and includes members of his lab, Gang Hee Han, Nicholas Kybert, Carl Naylor and Jinglei Ping. Also contributing to the study was Ritesh Agarwal, professor of materials science and engineering in Penn’s School of Engineering and Applied Science; members of his lab, Bumsu Lee and Joohee Park; and Jisoo Kang, a master’s student in Penn’s nanotechnology program. They collaborated with researchers from South Korea’s Sungkyunkwan University, Si Young Lee and Young Hee Lee.

Their study was published in the journal Nature Communications.

“Everything we do with regular electronics we’d like to be able to do with two-dimensional materials,” Johnson said. “Graphene has one set of properties that make it very attractive for electronics, but it lacks this critical property, being able to turn on and off. Molybdenum disulphide gives you that.”

Graphene’s ultra-high conductivity means that it can move electrons more quickly than any known material, but that is not the only quality that matters for electronics. For the transistors that form the basis for modern computing technology, being able to stop the flow of electrons is also critical.

“Molybdenum disulphide is not as conductive as graphene,” Naylor said, “but it has a very high on/off ratio. We need 1’s and 0’s to do computation; graphene can only give us 1’s and .5’s.”

Other research groups have been able to make small flakes of molybdenum disulphide the same way graphene was first made, by exfoliating it, or peeling off atomically thin layers from the bulk material. More recently, other researchers have adopted another technique from graphene manufacture, chemical vapor deposition, where the molybdenum and sulfur are heated into gasses and left to settle and crystalize on a substrate.

The problem with these methods is that the resulting flakes form in a scattershot way.

“Between hunting down the flakes,” said Kybert, “and making sure they’re the right size and thickness, it would take days to make a single measurement of their properties”

The Penn team’s advance was in developing a way to control where the flakes form in the chemical vapor deposition method, by “seeding” the substrate with a precursor.

“We start by placing down a small amount of molybdenum oxide in the locations we want,” Naylor said, “then we flow in sulfur gas. Under the right conditions, those seeds react with sulfur and flakes of molybdenum disulphide being to grow.”

“There’s finesse involved in optimizing the growth conditions,” Johnson said, “but we’re exerting more control, moving the material in the direction of being able to make complicated systems. Because we grow it where we want it, we can make devices more easily. We have all of the other parts of the transistors in a separate layer that we snap down on top of the flakes, making dozens and potentially even hundreds, of devices at once. Then we were able to observe that we made transistors that turned on and off like they were supposed to and devices that emit light like they are supposed to.”

Being able to match up the location of the molybdenum disulphide flakes with corresponding electronics allowed the researchers to skip a step they must take when making graphene-based devices. There, graphene is grown in large sheets and then cut down to size, a process that adds to the risk of damaging contamination.

Future work on these molybdenum disulphide devices will complement the research team’s research on graphene-based biosensors; rather than outputting the detection of some molecule to a computer, molybdenum disulfide-based sensors could directly report a binding event through a change in the light they emit.

This research also represents first steps that can be applied toward fabricating a new family of two-dimensional materials.

“We can replace the molybdenum with tungsten and the sulfur with selenium,” Naylor said, “and just go down the periodic table from there. We can imagine growing all of these different materials in the places we choose and taking advantages of all of their different properties.”

Today, KLA- Tencor Corporation introduced two advanced metrology systems that support the development and production of 16nm and below IC devices: Archer 500LCM and SpectraFilm LD10. The Archer 500LCM overlay metrology system provides accurate overlay error feedback through all stages of the yield ramp, helping chipmakers resolve overlay issues associated with innovative patterning techniques, such as multi-patterning and spacer pitch splitting. Through reliable, precise measurement of film thickness and stress, the SpectraFilm LD10 films metrology system enables qualification and monitoring of the films and film stacks used in fabrication of FinFETs, 3D NAND and other leading-edge devices. The new systems are key products in KLA-Tencor’s unique 5D patterning control solution, which drives optimal patterning results through the characterization and monitoring of fab-wide processes.

“As the industry leader in non-destructive optical metrology, we have closely collaborated with our customers to understand their challenges in optimizing pattern overlay, critical dimensions and films quality,” stated Ahmad Khan, group vice president of KLA-Tencor’s Parametric Solutions Group. “Across foundry, logic and memory, our customers require production-capable metrology systems that produce the data necessary to decipher complex process issues. Full-featured metrology systems, such as our new Archer 500LCM and SpectraFilm LD10 platforms, implement multiple innovations that facilitate measurement flexibility across a broad range of applications, helping our customers drive current-node yield and investigate next-node technologies.”

With both imaging and unique laser-based scatterometry measurement technologies, the Archer 500LCM overlay metrology system offers a wide range of measurement options and supports a diverse range of overlay measurement target designs, such as in-die, small pitch and multi-layer targets. This flexibility enables cost-effective generation of accurate overlay error data that can be used for scanner corrections or for identification of inline excursions, helping engineers determine when to re-work wafers or adjust processes to meet strict patterning requirements. Multiple Archer 500LCM systems are in use at foundry, logic and memory manufacturers worldwide where they provide an independent assessment of overlay performance for advanced development and high volume production.

The SpectraFilm LD10 introduces a laser-driven plasma light source, producing reliable, high-precision film measurements for a broad range of film layers, including the thin, multilayer film stacks used in forming complex device structures such as FinFETs. Characterization of the thick, multilayer film stacks found in 3D NAND flash devices is enabled with a new infrared-based subsystem. With a significant increase in throughput compared to the previous-generation Aleris® platform, the SpectraFilm LD10 maintains high productivity while qualifying and monitoring the increased number of film layers associated with multi-patterning and other leading-edge fabrication techniques. Multiple SpectraFilm LD10 orders have been placed for use in advanced IC development and production.

The Archer 500LCM and SpectraFilm LD10 systems join the SpectraShape 9000 critical dimension and device profile metrology platform, K-T Analyzer advanced data analysis system and many other process control systems in supporting KLA-Tencor’s comprehensive 5D patterning control solution. To maintain the high performance and productivity demanded by leading-edge IC manufacturing, the Archer 500LCM and SpectraFilm LD10 systems are backed by KLA-Tencor’s global, comprehensive service network.

A new spin on spintronics


February 17, 2015

A team of researchers from the University of Michigan and Western Michigan University is exploring new materials that could yield higher computational speeds and lower power consumption, even in harsh environments.

Most modern electronic circuitry relies on controlling electronic charge within a circuit, but this control can easily be disrupted in the presence of radiation, interrupting information processing. Electronics that use spin-based logic, or spintronics, may offer an alternative that is robust even in radiation-filled environments.

Making a radiation-resistant spintronic device requires a material relevant for spintronic applications that can maintain its spin-dependence after it has been irradiated. In a paper published in the journal Applied Physics Letters, from AIP Publishing, the Michigan research team presents their results using bulk Si-doped n-GaAs exposed to proton radiation.

How Does Spintronics Work?

Modern electronic devices use charges to transmit and store information, primarily based upon how many electrons are in one place or another. When a lot of them are at a given terminal, you can call that ‘on.’ If you have very few of them at the same terminal, you can call that ‘off,’ just like a light switch. This allows for binary logic depending on whether the terminal is ‘on’ or ‘off.’ Spintronics, at its simplest, uses the ‘on/off’ idea, but instead of counting the electrons, their spin is measured.

“You can think of the spin of an electron as a tiny bar magnet with an arrow painted on it. If the arrow points up, we call that ‘spin-up.’ If it points down, we call that ‘spin-down.’ By using light, electric, or magnetic fields, we can manipulate, and measure, the spin direction,” said researcher Brennan Pursley, who is the first author of the new study.

While spintronics holds promise for faster and more efficient computation, researchers also want to know whether it would be useful in harsh environments. Currently, radioactivity is a major problem for electronic circuitry because it can scramble information and in the long term degrade electronic properties. For the short term effects, spintronics should be superior: radioactivity can change the quantity of charge in a circuit, but should not affect spin-polarized carriers.

Studying spintronic materials required that the research team combine two well established fields: the study of spin dynamics and the study of radiation damage. Both tool sets are quite robust and have been around for decades but combining the two required sifting through the wealth of radiation damage research. “That was the most difficult aspect,” explains Pursley. “It was an entirely new field for us with a variety of established techniques and terminology to learn. The key was to tackle it like any new project: ask a lot of questions, find a few good books or papers, and follow the citations.”

Technically, what the Michigan team did was to measure the spin properties of n-GaAs as a function of radiation fluence using time-resolved Kerr rotation and photoluminescence spectroscopy. Results show that the spin lifetime and g-factor of bulk n-GaAs is largely unaffected by proton irradiation making it a candidate for further study for radiation-resistant spintronic devices. The team plans to study other spintronic materials and prototype devices after irradiation since the hybrid field of irradiated spintronics is wide open with plenty of questions to tackle.

Long term, knowledge of radiation effects on spintronic devices will aid in their engineering. A practical implementation would be processing on a communications satellite where without the protection of Earth’s atmosphere, electronics can be damaged by harsh solar radiation. The theoretically achievable computation speeds and low power consumption could be combined with compact designs and relatively light shielding. This could make communications systems faster, longer-lived and cheaper to implement.

Gigaphoton Inc., a lithography light source manufacturer, announced today that it has successfully achieved continuous operation of 140W EUV light source at 50 percent duty cycle on its prototype laser-produced plasma (LPP) light sources for EUV lithography scanners. It is widely believed that 140W is the output power required by EUV light sources for mass production applications.

This achievement was a result of further advancements in key technologies developed by Gigaphoton, such as Droplet Generators capable of producing tin (Sn) droplets smaller than 20 μm in diameter, the single-wavelength, solid-state pre-pulse laser and main pulse CO2 laser, and the debris mitigation technology using high-output superconducting magnets and Sn etching. The achievement of 140W continuous operation output at 50 percent duty cycle symbolizes that the industry is close to its final stages in realizing mass production-capable EUV scanners. Gigaphoton remains committed to further continuing its R&D efforts and aims to achieve 250W output by the end of 2015.

“The achievement of continuous operation, 140W output at 50 percent duty cycle, with our EUV light source proves we are very close to achieving high power, low cost, and stable LPP light sources required by our customers,” said Hitoshi Tomaru, President and CEO of Gigaphoton. “I believe that Gigaphoton’s expertise and efforts to develop the LPP light source will accelerate the development of EUV scanners for high-volume manufacturing. This achievement also serves to further encourage the industry to introduce EUV scanners as the next-generation lithography tools.”

Further details related to this press release will be presented at the SPIE Advanced Lithography Symposium held at the San Jose Convention Center from February 23 through 26, 2015.

This milestone was achieved as part of a program subsidized by New Energy and Industrial Technology Development Organization (NEDO).

Scientists from Ghent University and imec announce today that they demonstrated interaction between light and sound in a nanoscale area. Their findings elucidate the physics of light-matter coupling at these scales – and pave the way for enhanced signal processing on mass-producible silicon photonic chips.

In the last decade, the field of silicon photonics has gained increasing attention as a key driver of lab-on-a-chip biosensors and of faster-than-electronics communication between computer chips. The technology builds on tiny structures known as silicon photonic wires, which are roughly a hundred times narrower than a typical human hair. These nanowires carry optical signals from one point to another at the speed of light. They are fabricated with the same technological toolset as electronic circuitry.

Fundamentally, the wires work only because light moves slower in the silicon core than in the surrounding air and glass. Thus, the light is trapped inside the wire by the phenomenon of total internal reflection. Simply confining light is one thing, but manipulating it is another. The issue is that one light beam cannot easily change the properties of another. This is where light-matter interaction comes into the picture: it allows some photons to control other photons.

Publishing in Nature Photonics, researchers from the Photonics Research Group of Ghent University and imec report on a peculiar type of light-matter interaction. They managed to confine not only light but also sound to the silicon nanowires. The sound oscillates ten billion times per second: far more rapid than human ears can hear. They realized that the sound cannot be trapped in the wire by total internal reflection. Unlike light, sound moves faster in the silicon core than in the surrounding air and glass. Thus, the scientists sculpted the environment of the core to make sure any vibrational wave trying to escape it would actually bounce back. Doing so, they confined both light and sound to the same nanoscale waveguide core – a world’s first observation.

Design features that contributed most to the improved performance include increased rotational speed, integrated rotor sleeves, and increased purge injection temperature.

BY MIKE BOGER, Edwards Vacuum, Tokyo, Japan

The use of high-k dielectric films deposited through atomic layer deposition, primarily in batch furnaces, has intensified, particularly in the manufacture of memory devices and high-k metal gates (HKMG) in logic devices. ALD uses a sequential purge and injection of the precursor gases to generate slow, but accurate growth of the films one atomic layer at a time. One of the precusors is typically a metal organic compound from a liquid source, commonly zirconium or hafnium-containing materials, followed by ozone to create the high-k film.

Wafers are usually processed in a furnace with batch sizes of 200 or more wafers. Reliability of the vacuum system is imperative to prevent contamination and consequent scrapping of the wafers. Unexpected failures can cause significant loss of work in process and process downtime. For example, if the vacuum pump seizes suddenly due to internal contamination by process by-products, the pressure in the pipe between the vacuum and furnaces rises, and there is a risk that powder deposited in the pipe will flow back into the furnace. This powder can not only contaminate wafers in the furnace, but also force a time-consuming clean-up that may remove the furnace from operation for a day or more.

The challenge

The mean-time-between-service (MTBS) for a vacuum pump used in semiconductor manufacturing varies greatly depending on the particular process it supports and the design of the pump. For the ALD processes considered here most failures caused process by-products can be grouped into four categories.

  • Corrosion – Attack on the metal components of the pump results in the opening of clearances leading to loss of base vacuum. Depending on the location of corrosion, the oxidation of the metal may actually generate powder that can cause seizure of rotating elements.
  • Plating – The deposition of metal compounds on the surface of internal components fouls internal mechanism clearances, causing the pump to seize.
  • Powder ingestion – Powder that enters the pump can jam rotating elements, leading to seizure.
  • Condensation – Compounds in the pumped gas stream transition from a gaseous to a solid phase within the pump, depositing on internal surfaces and eventually leading to loss of clearance and seizure.

Monitoring of pump operating conditions, such as input power, current, and running temperature, can provide an indication of the health of the pump. Events that lead to failure are generally gradual in nature. Advance notice periods can be measured in days. However, failures of vacuum pumps on high-k ALD processes often happen suddenly with little to no indication of distress prior to seizure.

A typical example of a vacuum pump used on a high-k ALD process is shown in FIGURE 1. This pump was used in a full production environment and consisted of a 1,800 m3h-1 mechanical booster mounted above a 160 m3h-1 dry pump. In this case, the pump exhibited a strong spike in running power, approximately 20 times normal, and was immediately removed for inspection. Significant deposition is evident in the booster (Fig. 1 left) and also in the last stage of the dry pump (Fig. 1 right). Evidence of the loss of clearance that caused the spike in input power is observed as a shiny area on the rotor lobe. In operation this pump was exposed to TEMAH (hafnium-containing liquid precursor), TMA (aluminum-containing liquid precursor), and ozone for producing HfO2 and TMA Al2O3. It was exchanged after 1,200 hours of use.

ALD 1-A ALD 1-B

 

FIGURE 1. A picture of a disassembled pump after 1,200 hours of use on a high-k ALD process showing the deposition in the booster (left) and loss of clearance in the last stage of the dry pump (right). 

FIGURE 2 provides another example of a pump that was removed due to detection of a spike in input current. In this case, the booster, second stage, and final stage of the pump are shown. Although the process was nominally the same (deposition of HfO2 and Al2O3), the deposition pattern is different. In this case, the booster and early stages of the dry pump show signs of a thin coating of a material that exhibits a green iridescent sheen. The final stage of the pump has a brown powder accumulation, but of a lighter color than that shown in Fig. 1.

FIGURE 2. Pictures of a disassembled pump that was removed for inspection after only 457 hours due to a large current spike detected during operation. In order, the pictures show the booster, second stage of the dry pump, and the final stage of the dry pump.

FIGURE 2. Pictures of a disassembled pump that was removed for inspection after only 457 hours due to a large current spike detected during operation. In order, the pictures show the booster, second stage of the dry pump, and the final stage of the dry pump.

In both of the examples shown in Figs. 1 and 2, the service interval of the pump was short and below the user’s expectations. In these cases, which are representative of all the pumps used on this process, the user was forced to exchange pumps frequently to minimize the risk of wafer loss. Other customers had similar experiences. TABLE 1 lists the films deposited and the preventative maintenance service intervals implemented by four customers. Analysis of serviced pumps suggested that processes depositing zirconium oxide were more challenging for the pump.

Screen Shot 2015-02-10 at 5.30.54 PM

Analysis

To better understand the reliability improvement challenge, a sample of the deposited material from a failed pump was analyzed. The results of the analysis, shown in FIGURE 3, revealed deposits rich in carbon and metal oxides, consistent with metal-organic precursors. The rate of oxide deposition appeared to be higher than that which would occur through pure ALD mechanisms, suggesting some chemical vapor deposition (CVD) or decomposition of the gases being pumped.

FIGURE 3. Analysis of the deposition within a failed pump showing hafnium, oxygen, and carbon components.

FIGURE 3. Analysis of the deposition within a failed pump showing hafnium, oxygen, and carbon components.

A survey of literature [1], [2], [3], [4] revealed that the typical reactants used in high-k ALD can react at high pressure and at low temperature without the need for external energetic activation. This suggests that even if there were no CVD or decomposition of gases within the pump, ALD-like films can still be deposited on the internal surfaces of the pump.

A simulation of the vapor pressure of TEMAH (one of the precursors used) within the pump was conducted, assuming a mass flow rate of 0.2 mg min−1 for TEMAH. The simulation results were compared to the measured vapor pressure of TEMAH to determine if there was any risk of TEMAH condensing within the vacuum pump. The results, shown in FIGURE 4, suggest that there are sufficient safety margins in the actual conditions. The TEMAH will stay in vapor form while it travels through the pump, even if the actual flow varied by an order of magnitude from that assumed. Moreover, the pump temperature could be reduced substantially without risk of condensing TEMAH within the pump.

FIGURE 4. Vapor pressure of TEMAH (0.2 mg/min with 14 slm of nitrogen) and simulated vapor pressure of TEMAH in the dry pump, inlet to outlet.

FIGURE 4. Vapor pressure of TEMAH (0.2 mg/min with 14 slm of nitrogen) and simulated vapor pressure of TEMAH in the dry pump, inlet to outlet.

A number of pumps were inspected, a large majority of which were pumps exchanged prior to seizure. Unfortunately, although powder was evident in the final stages of all pumps, not all pumps had powders of the same color. Moreover, as seen in the middle photograph of Fig. 2, some pumps and boosters were relatively clean exhibiting just a green sheen of deposition.

None of the observations, other than powder in the final stage of the dry pump, were consistently repeatable, suggesting that factors upstream of the pump were also contributing to short service intervals. Powder loading varied between pumps and within the pumps, although the heaviest deposition was always located in the final stages of the dry pump. It is normal for the most deposition to occur near the exhaust of the pump because of the generally increased temperature of the exhaust gas and the increase in vapor pressure of the materials being pumped.

A diagram of the dry pump stages from inlet to outlet is shown in FIGURE 5, where the sleeves are also shown. Consistently, the final stage shaft sleeve, which is located between the 4th and 5th stage of the pump, was the weakest link in the design. Deposition would collect on the sleeve’s surface. Resulting friction between the sleeve and the stator would cause the components to heat, expand, and finally seize the pump.

FIGURE 5. Schematic of the dry pump mechanism showing inlet (1st stage) to outlet (5th stage). Rotor sleeves are shown in green.

FIGURE 5. Schematic of the dry pump mechanism showing inlet (1st stage) to outlet (5th stage). Rotor sleeves are shown in green.

FIGURE 6 shows the sleeves from between three stages of a pump exchanged for service. Another example is shown in the right side picture of Fig. 1. The sleeves are steel with a PTFE coating, giving them a green color. Evidence of the deposition is clear in the shaft sleeves on the right side of the picture.

FIGURE 6. Picture of sleeves in an exchanged pump showing deposition on the outer surfaces.

FIGURE 6. Picture of sleeves in an exchanged pump showing deposition on the outer surfaces.

Extending pump service intervals

Inconsistencies in powder deposition that suggested variations in upstream conditions were ultimately traced to condensation in the gas lines to the process chamber. The amount of condensed liquid and the length of the flow step in the ALD cycle affected the amount of deposition. When the user took care to avoid condensation, a much more consistent pattern of deposition was observed within the pump.

For any particular dry pump, the two most convenient elements that can be adjusted are the nitrogen purge and the temperature of the pump. Adding purge, or changing the location of the purge, can affect the partial pressure of the gases being pumped. Purge can also affect the temperature of the gas being pumped. In this case the purge flow was already 76 slm and further increase could have affected the downstream gas abatement device.

Experiments to extend the MTBS focused on the pump running temperature. Temperature changes within the pump can dramatically affect the propensity of the pumped gases to condense on the internal surfaces of the pump as well as the rate of reactions of any gases being pumped. However, varying the pump temperature from 140°C to nearly 180°C made any appreciable change to the service interval.

Finally, two pumps with designs that differed significantly from the original pump were evaluated. Additionally, new pump A provided significantly greater capacity at higher inlet pressures than new pump B, at the expense of greater power consumption. The results are shown in TABLE 2.

Screen Shot 2015-02-10 at 5.32.47 PM

New Pump A was initially installed with a temperature set point of 130°C. It was removed after six months for inspection prior to failure. New Pump B was tested with a temperature set point of 110°C. It was removed after six months prior to failure. A comparison of the internal condition of the Original Pump and New Pump B is shown in FIGURE 7.

FIGURE 7. Pictures comparing the third stage of the original pump and New Pump B showing the different deposition patterns.

FIGURE 7. Pictures comparing the third stage of the original pump and New Pump B showing the different deposition patterns.

Four differences in the new pump design are believed to have contributed to improved reliability:

  • 180% increase in rotational speed (180%) resulting in less residence time of the pumped gases.
  • Reduced operating temperature. Although many semiconductor processes benefit from a hot pump, this ALD process does not.
  • No rotor sleeves. The rotor sleeve in the new pumps was integrated with the rotor element itself. This not only removed the necessity for a coating, but appeared to strengthen the mechanism.
  • Heated purge. The purge in the new pumps is warmed to within 95% of the stator temperature to prevent cooling effects and reduce the chance of spontaneous condensation of gases.

Subsequent experience with a large number of pumps and customers has confirmed the advantages provided by the new pump design. New pump B is the recommended pump for this application with fixed service intervals varying between 4 and 6 months depending on the specific characteristics of the process supported.

Conclusions

Deposition of high-k materials using ALD is a widely used technique for today’s transistor and memory structures. At early introduction of the process in high volume manufacturing, pump reliability became a key concern. Careful analysis and cooperation with customers resulted in extending the service interval of the pumps from one to up to six months, an achievement that significantly reduced operating expenses and production losses due to wafer contamination and equipment downtime caused by unexpected pump failures. Analysis of the pump condition and test results showed that, more than temperature or purge, a different pump design provided the greatest improvement in service intervals. Design features that contributed most to the improved performance include increased rotational speed, integrated rotor sleeves, and increased purge injection temperature.

References

1. J. M. et al., “Impact of Hf-precursor choice on scaling and performance of high-k gate dielectrics hf-based high-k materials,” ECSTrans., p. 59, 2007.
2. X. L. et al., “Ald of hafnium oxide thin films from tetrakis (ethylmethylamino) hafnium and ozone,” J. of ECS, vol. 152, 2005.
3. H. Furuya, “Formation of metal oxide film,” Sep 2008, patent application: US20080226820 A1.
4. Y. S. et al., “Atomic layer deposition of hafnium oxide and hafnium silicate thin films using liquid precursors and ozone,” J. Vac. Sci. Tech. A, vol. 22, 2004.

A novel approach to growing nanowires promises a new means of control over their light-emitting and electronic properties. In a recent issue of Nano Letters, scientists from the U.S. Department of Energy’s Lawrence Berkeley National Lab (Berkeley Lab) demonstrated a new growth technique that uses specially engineered catalysts. These catalysts, which are precursors to growing the nanowires, have given scientists more options than ever in turning the color of light-emitting nanowires.

The new approach could potentially be applied to a variety of materials and be used for making next-generation devices such as solar cells, light emitting diodes, high power electronics and more, says Shaul Aloni, staff scientist at Berkeley Lab’s Molecular Foundry, a DOE user facility, and lead author on the study.

Since the early 2000s, scientists have made steady progress in cultivating nanowires. Initially, early nanowire samples resembled “tangled noodles or wildfire-ravaged forests,” according to the researchers. More recently, scientists have found various conditions lead to the growth of more orderly nanowire arrays.

For instance, certain substrates on which the nanowires grow create conditions so that the nanowire growth orientation is dictated by the substrate’s underlying crystal structure. Unfortunately, this and other approaches haven’t been foolproof and some nanowires still go rogue.

Moreover, there is no simple way to grow different types of nanowires in the same environment and on the same substrate. This would be useful if you wanted to selectively grow nanowires with different electronic or optical properties in the same batch, for example.

“At the Molecular Foundry we are aiming to develop new strategies and add new tools to the bag of tricks used for nanomaterials synthesis,” says Aloni. “For years we were searching for cleverer ways to grow nanostructures with different optical properties in identical growth conditions. Engineering the catalyst brings us closer to achieving this goal.”

The researchers focused on nanowires made of gallium nitride. In its bulk (non-nanoscale) form, gallium nitride emits light in the blue or ultraviolet range. If indium atoms are added to it, the range can be extended to include red, essentially making it a broad-spectrum tunable light source in the visible range.

The problem is that adding indium atoms puts the crystal structure of gallium nitride under stress, which leads to poorly performing devices. Gallium nitride nanowires, however, don’t experience the same sort of crystal strain, so scientists hope to use them as tunable, broad-spectrum light sources.

To achieve their control, the team focused on the catalysis which guide the nanowire growth. Normally, researchers use catalysts made of a single metal. The Berkeley team decided to use metallic mixtures of gold and nickel, called alloys, as catalysts instead.

In the study, the researchers found that the gallium-nitride nanowire growth orientation strongly depended on the relative concentration of nickel and gold within the catalyst. By altering the concentrations in the alloy, the researchers could precisely manipulate, even on the same substrate in the same batch, the orientation of the nanowires.

“No one had used bi-metalic catalysts to control growth direction before,” says Tevye Kuykendall, scientist at Berkeley Lab’s Molecular Foundry. Kuykendall says the mechanism driving the new growth process is not fully understood, but it involves the different tendencies of gold and nickel to align with various crystallographic surfaces at point where nanowires start to grow.

The researchers also showed that depending on the growth direction chosen, different optical properties were observed thanks to the crystal surfaces exposed at the surface of the nanowire. “One of the things that make nanostructures interesting, is that the surface plays a larger role in defining the material’s properties,” says Aloni. This leads to changes in optical properties not seen in larger-bulk materials, making them more useful.

Aloni says the team will next focus more on the chemistry of the different nanowire surfaces to further tailor the nanowire’s optical properties.

Researchers at The University of Texas at Austin’s Cockrell School of Engineering have created the first transistors made of silicene, the world’s thinnest silicon material. Their research holds the promise of building dramatically faster, smaller and more efficient computer chips.

Made of a one-atom-thick layer of silicon atoms, silicene has outstanding electrical properties but has until now proved difficult to produce and work with.

Deji Akinwande, an assistant professor in the Cockrell School’s Department of Electrical and Computer Engineering, and his team, including lead researcher Li Tao, solved one of the major challenges surrounding silicene by demonstrating that it can be made into transistors —semiconductor devices used to amplify and switch electronic signals and electrical power.

The first-of-their-kind devices developed by Akinwande and his teamrely on the thinnest of any semiconductor material, a long-standing dream of the chip industry, and could pave the way for future generations of faster, energy-efficient computer chips. Their work was published this week in the journal Nature Nanotechnology.

Until a few years ago, human-made silicene was a purely theoretical material. Looking at carbon-based graphene, another atom-thick material with promise for chip development, researchers speculated that silicon atoms could be structured in a broadly similar way.

Akinwande, who also works on graphene transistors, sees value in silicene’s relationship to silicon, which chipmakers already know how to work with.

“Apart from introducing a new player in the playground of 2-D materials, silicene, with its close chemical affinity to silicon, suggests an opportunity in the road map of the semiconductor industry,” Akinwande said. “The major breakthrough here is the efficient low-temperature manufacturing and fabrication of silicene devices for the first time.”

Despite its promise for commercial adaptation, silicene has proved extremely difficult to create and work with because of its complexity and instability when exposed to air.

To work around these issues, Akinwande teamed with Alessandro Molle at the Institute for Microelectronics and Microsystems in Agrate Brianza, Italy, to develop a new method for fabricating the silicene that reduces its exposure to air. To start, the researchers let a hot vapor of silicon atoms condense onto a crystalline block of silver in a vacuum chamber. They then formed a silicene sheet on a thin layer of silver and added a nanometer-thick layer of alumina on top. Because of these protective layers, the team could safely peel it of its base and transfer it silver-side-up to an oxidized-silicon substrate. They were then able to gently scrape some of the silver to leave behind two islands of metal as electrodes, with a strip of silicene between them.

In the near-term, Akinwande will continue to investigate new structures and methods for creating silicene, which may lead to low-energy, high-speed digital computer chips.