Category Archives: Atomic Layer Deposition


Chemical Vapor Deposition

December 11, 2015

Chemical vapor deposition (CVD) is used to produce high-purity thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile byproducts are also produced, which are removed by gas flow through the reaction chamber.

Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, filaments, carbon nanotubes, SiO2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and various high-k dielectrics. The CVD process is also used to produce synthetic diamonds.

Applications include shallow-trench isolation, pre-metal dielectric, inter-metal dielectric, and passivation. CVD processes are also important in strain engineering that uses compressive or tensile stress films to enhance transistor performance through improved conductivity.

Additional Reading

Taking 2D materials from lab to fab, and to technology

New materials require new approaches

Deposition equipment market witnesses a year of significant change

Atomic Layer Deposition

December 11, 2015

There are four main segments in the thin-layer deposition equipment market – atomic layer deposition (ALD), chemical vapor deposition (CVD), epitaxy, and physical vapor deposition (PVD), also known as sputtering. Although CVD equipment represents the largest equipment type, ALD represents the fastest growing equipment category.

ALD is a technique capable of depositing a variety of thin film materials from the vapor phase. As device requirements push toward smaller and more spatially demanding structures, ALD has demonstrated potential advantages over alternative deposition methods, such CVD and PVD due to its conformality and control over materials thickness and composition. These desirable characteristics originate from the cyclic, self-saturating nature of ALD processes [1].

‪Layers are formed during reaction cycles by alternately pulsing precursors and reactants and purging with inert gas in between each pulse. Each atomic layer formed by this sequential process is a result of saturated surface-controlled reactions. For example, a metal precursor pulse of trimethylaluminum (Al(CH3)3) followed by an oxygen reactant pulse (H2O vapor) results in the formation of a layer of aluminum oxide, a metal oxide compound that can be used as a high-k dielectric.

Building devices atom by atom enables very precise control over the process. Because the ALD process is self-limiting, it results in films with a precise thickness and conformality, even over varied surface topographies. It can be applied to produce different oxides, nitrides or other compounds. ALD provides excellent surface control and can produce thin, uniform and pinhole-free films over large areas by single or tailored multiple layer deposition. Nanolaminates or stacked layers of different materials can also be produced, in a straightforward manner, in the ALD reactor. ​

According to new report by Global Industry Analysts, Inc., the global market for thin layer deposition equipment in semiconductor applications is projected to reach US$13.6 billion by 2020, driven by expanding electronics industry and parallel growth in demand for semiconductor solutions.

In terms of R&D, metal ALD has been challenging because of lack of suitable chemistry and nucleation problems. The development of processes for platinum group metals was a success but need for good industrial processes for many other metals still exists. Metal sulfides are old ALD materials and in industrial use in electroluminescent display production but ALD of selenides and tellurides has been much less studied. The need of chalcogenides in phase change materials and development of alkyl silyl precursors for selenium and tellurium has improved the situation. There is still a need to develop new ALD processes for microelectronics, low-k materials, 2D materials and oxides for transparent TFTs, according to Markku Leskelä, University of Helsinki, Finland.

In addition to applications in microelectronics there are many emerging areas where ALD has been introduced. One important area is energy technology materials. ALD films are used in silicon solar cells as passivation layers and they are extensively studied in many other areas such as dye sensitized solar cells, lithium ion batteries, supercapacitors and fuel cells. Indicative for these and many other applications is the use of known – mostly oxide –processes for protection. Li ion batteries make an exception and new materials and processes have been developed for lithium compounds. Research is also underway to adapt ALD processes to high-throughput roll-to-roll production for printed/flexible electronics.

Key players in the ALD deposition arena include Applied Materials Inc., ASM International N.V., Jusung Engineering Co. Ltd., Lam Research Corporation, Oxford Instruments, Picosun, Tokyo Electron Limited, ULVAC Technologies Inc., Ultratech/Cambridge Nanotech and Veeco Instruments Inc., among others.

The American Vacuum Society hosts an annual conference on Atomic Layer Deposition dedicated to the science and technology of atomic layer controlled deposition of thin films.



Suggested additional reading

Atomic layer deposition goes mainstream in 22nm logic technologies

Successful industrialization of high-density 3D integrated silicon capacitors for ultra-miniaturized electronic components

Particle Atomic Layer Deposition

JVST A – Most Read Atomic Layer Deposition Articles Published in 2014

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.



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


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.


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.


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.

April 28, 2011 — ASM International N.V. (NASDAQ: ASMI and Euronext Amsterdam: ASM) received multiple system orders for its plasma enhanced atomic layer deposition (PEALD) reactor from a leading memory customer in Asia. Second, the company qualified a new PEALD oxide application with a memory manufacturer for the 2X nm node.

“Our innovative PEALD technology is seeing strong market validation with high-volume business from multiple top tier memory customers,” said Tominori Yoshida, general manager of ASM’s Plasma Products business unit. “Our increasing range of production-ready PEALD applications position us to support memory manufacturers now and as they move towards the challenging 1X nm node.”

The PEALD systems were ordered by a leading memory customer for high-volume manufacturing and will be installed in multiple facilities in Asia. The reactors will be used to deposit dielectrics for advanced lithography double patterning applications at the 3X nm technology node and below. This order represents the second major manufacturer to adopt ASM’s PEALD system for use in double patterning in high volume manufacturing.

ASM also qualified a new oxide application for an advanced PEALD SiO layer that targets manufacturing at the 2X nm node and below. The new application is expected to enter volume production later this year with a different Asia-based manufacturer.

ASM’s PEALD reactors are optimized to deposit dielectrics including SiO, SiN and SiCN. The process delivers conformal thin films at low temperatures, for double patterning lithography technologies where thin dielectrics are deposited over temperature-sensitive photoresists for critical dimension control and pitch reduction.

Each of the systems ordered includes multiple PEALD reactors implemented on ASM’s XP platform. The XP is a production-proven standard platform that can be configured with plasma enhanced chemical vapor deposition (PECVD), thermal ALD or PEALD reactors.

Also see: Below 22nm, spacers get unconventional: Interview with ASM

ASM International N.V. and its subsidiaries design and manufacture equipment and materials used to produce semiconductor devices, wafer processing (Front-end segment) as well as assembly and packaging (Back-end segment). ASM International’s common stock trades on NASDAQ (symbol ASMI) and the Euronext Amsterdam Stock Exchange (symbol ASM). For more information, visit ASMI’s website at

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Executive Overview

Atomic layer deposition (ALD) will be used in multiple areas of the 22nm logic process flow despite initial concerns about the technology’s viability for high-volume manufacturing. Each application space creates a unique need for manufacturing equipment configuration and technology variations – from single-wafer ALD systems for extremely tight process control, batch ALD systems for low COO operation, to mini-batch systems for a meld of COO and process control for multi-layer applications. Selection of the appropriate manufacturing toolset is as critical to eventual technology adoption as the process itself, and final implementation will require the correct toolsets to ensure that the ALD films can be deposited in a cost efficient manner.

M. Verghese, ASM, Phoenix, AZ USA;  J. W. Maes, ASM, Leuven, Belgium; N. Kobayashi, ASM, Tokyo, Japan

Since its invention in the 1970s, atomic layer deposition (ALD) has been used in a variety of applications ranging from electroluminescence display manufacturing to industrial coatings [1]. Over the last decade, the semiconductor industry has slowly been adopting ALD reactors for critical layers where the benefits of ALD enable scaling and improved performance. With the upcoming transition to 22nm, process flows are being adapted to allow ever more ALD layers. As a variant of chemical vapor deposition (CVD), ALD techniques capitalize on surface saturation reactions to deposit extremely smooth, dense, and highly conformal films through a process that is relatively insensitive to fluctuations in process temperature and reactant flux. The ALD process relies on sequential introduction of the reactants into the reaction space, separated by inert gas purges, such that repetition of the ALD cycles results in a monolayer by monolayer growth of the deposited film. Thickness of the film can then be precisely controlled by adjusting the number of ALD cycles.

Process considerations for single-wafer tools

DRAM manufacturers were the first to use ALD to ensure conformal deposition of high-k dielectrics in high aspect ratio capacitor structures. Aggressive scaling of device dimensions and the subsequent requirement of low thermal budgets to control dopant diffusion continue to push the entire semiconductor industry to displace conventional CVD, plasma enhanced CVD (PECVD), and sputtering techniques with novel ALD processes in critical areas such as transistor gate stack formation and spacer defined double patterning. The low throughputs that are typically associated with ALD techniques have been a barrier to its adoption in mainstream production flows. However, these concerns are being addressed by intelligent equipment design to optimize the ALD process and hardware for individual application spaces. At the 22nm node, the logic industry will use ALD in several key process steps – both in front end transistor formation and in back end metallization and interconnect. Each application has highly specific requirements and calls for different hardware configurations for the optimal production solution.

Single-wafer ALD chambers are ideal when the application demands extremely thin films with precise thickness and uniformity control. Single-wafer systems can also most easily handle difficult precursor chemistries such as low vapor pressure, decomposition prone liquids and solids since ALD cycle times are typically short (in the order of a few seconds) and the source delivery systems can be placed in close proximity to the reaction chamber. Purge efficiency can be optimized relatively easily in single-wafer systems and as a result, these chambers are ideal for pure ALD deposition.

Figure 1. Need for complete ALD high-k/metal gate solution in 22nm logic transistors.

Single-wafer ALD systems also have high precursor utilization efficiencies and hence, are a good fit for processes that use expensive precursor materials. For example, high-k dielectrics and metal gates for transistor gate oxide and electrodes require deposition of films as thin as 10Å while maintaining within wafer uniformities of <1%, 1σ. Hafnium-based high-k gate oxides typically use hafnium chloride, a solid precursor, for its excellent electrical performance when compared to metal organic chemistries [2]. Single-wafer systems tend to be the best choice for gate oxide deposition as they are very capable of delivering this highly condensable precursor. Furthermore, replacement gate devices require multiple, conformal metal films <50Å thick to ensure that space remains for a gate contact fill (Fig. 1). Single-wafer plasma-enhanced ALD (PEALD) is also used for the deposition of silicon oxide, silicon nitride, and silicon carbon nitride gate spacers. PEALD enables low-temperature deposition (<400°C), excellent conformality, and lower wet etch rates than films deposited by plasma enhanced CVD (PECVD). Film stress can also be varied from compressive to tensile by varying plasma processing conditions [3]. Techniques such as PVD and CVD are unable to attain the step coverage, thickness control, and cross-wafer uniformities required for such an application; single-wafer ALD has been gradually replacing these techniques in high performance logic gate structures since the 45nm node [4]. By the 22nm node, all primary gate stack materials will be deposited by ALD processes. The advent of three-dimensional architectures such as FinFETs, and the film conformality requirements that come therewith, will ensure that ALD will be the deposition technique of choice for the next several generations of advanced logic gate stack structures.

Batch tools for thicker films/high-aspect ratios

When film thicknesses are less than one hundred angstroms thick, ALD process times are typically no longer than a few minutes. Single-wafer tools then give acceptable throughput performance and short turn-around times. However, for some applications, the process times are inevitably longer. This can occur when thicker layers are required or when films have to be deposited in high-aspect ratio structures. Substrates with high-aspect ratio structures have a larger surface area than planar wafers and usually require a higher precursor dose and subsequently need longer pulses and purge times to enable effective gas transport into and out of the structures. Also, some ALD chemistries can have lower growth rates than others and some processes may require relatively long pulses to ensure complete surface reactions to achieve the desired film quality.

The throughput and cost-of-ownership (COO) performance of batch ALD approaches with ~100 wafer loads in one reactor can be substantially better than that of single-wafer systems. Pulse and purge times have to be longer in batch reactors because the volume of the reactor is larger and the gas transport depends more on diffusion (rather than forced convection) than in single-wafer systems. However, the total increase in cycle time is smaller than a factor of 100, more on the order of 10-50. Process optimization in a batch system is more complex than in a single-wafer system but for ALD chemistries that result in self-limiting ALD surface reactions, relatively good uniformities and step coverage can still be achieved. The precursor flow and total dose that is delivered to the batch reactor is typically much larger than in single-wafer applications, especially when high aspect ratio device structures are involved. However, techniques such as direct liquid injection (DLI) can be used to mitigate precursor dose delivery issues as long as the vapor pressure of the precursor is sufficiently high. Low vapor pressure precursors (which also can be solid powders) are more troublesome in batch equipment due to risk of condensation and decomposition associated with the high residence time in the reactors.

ALD titanium nitride using titanium chloride and ammonia meet all the criteria required to make batch processing an attractive option. Titanium nitride films are used in several applications in logic devices: electrodes for replacement gates, electrodes for embedded DRAM devices, barrier films in tungsten contacts, and through- silicon-via (TSV) structures. Required film thicknesses are in the range of 20−150Å.

Figure 2. Step coverage of batch pulsed CVD TiN film in 32:1 trenches.

The process can be run in two modes: a strict ALD mode where completely separated titanium chloride and ammonia pulses are used (resulting in a growth rate of ~0.3Å/cycle), but also in a second mode in which one of the two pulses is actually a CVD pulse. In the pulsed CVD mode, a higher (3-5x) growth rate can be achieved. Batch reactors are able to run ALD-like processes such as pulsed CVD, with good results. The resulting film resistivity is a function of deposition temperature. In the ALD mode, one can use about 100°C lower deposition temperature to achieve the same resistivity as films deposited by the pulsed CVD mode [5]. Figure 2 shows an example of the deposition of a thicker layer of titanium nitride in a high aspect ratio structure. A highly conformal film is achieved, with step coverage of better than 95%, using the ALD-like pulsed CVD process mode in a batch reactor. Batch reactors can run at a throughput of greater than 30wph per reactor for 10nm films. These results demonstrate that batch-type ALD reactors are an attractive tool choice for some of the new ALD applications in future logic devices.

Mini-batch or multi-wafer ALD systems

When deposition of thicker films using complex precursors is required at reasonable throughputs and with short turn around times, a mini-batch or multi-single-wafer ALD system is the most appropriate. Mini-batch and multi-single-wafer ALD reactors meld the flexibility of single-wafer systems with the productivity of batch reactors. Typically, a mini-batch reactor processes four to five wafers together in one reactor and a multi-single-wafer system processes four to five wafers in individual reactors packaged in one module. These types of reactors can result in improved COO when compared to single-wafer systems as they occupy less floor space and rely on fewer, shared sub-systems. For example, gas panels, RF systems, and pumps can be combined for use on a mini-batch system whereas single-wafer tools would require multiple individual sub-systems. In addition, creative design of mini-batch systems can allow the use of direct plasma to enable plasma-enhanced ALD processes.

Spacer-defined double-patterning (SDDP) will likely be introduced to manufacture highly scaled lines and spacers for 22nm logic devices. In this technology, a conformal, ALD silicon oxide (SiO2) film is deposited directly on photoresist at extremely low temperatures. This is followed by an anisotropic etch-back process that results in the formation of SiO2 spacers that act as hard masks with smaller pitches. For this application, a mini-batch (multi-single-wafer) system is useful – ensuring high throughput in a system that can utilize direct plasma to enable deposition at near room temperatures. PEALD SiO2 using a mini-batch system results in conformal deposition at low-temperatures (<100°C) with within-wafer and wafer-to-wafer uniformity < 1%, three sigma. Throughputs can be achieved at >45wph per reactor at 20nm film thickness with high equipment utilization due to in situ remote plasma cleaning capability.

One cycle of PEALD SiO2 consists of 3 steps: chemisorption of an aminosilane precursor on the substrate, purging the precursor by inert gas flow, and plasma-assisted surface reaction of chemisorbed precursor with reactant gas. The RF-based plasma pulse is <400ms in length. Growth per cycle (GPC) of PEALD SiO2 increases with decreasing deposition temperature [6]. This GPC temperature dependence indicates the ALD reaction is limited by the desorption rate of the physisorbed precursor, which increases with increasing deposition temperature. Because this is an ALD process, film thickness is proportional to cycle number and thickness can be precisely controlled. These PEALD films have been confirmed to not cause plasma damage to the underlying substrate/films as the RF power during the deposition process is much smaller (<50W) than that of conventional PECVD.

Figure 3. PEALD SiO2 deposition on resist at 50ºC.

As shown in Fig. 3a, 300Å of a conformal SiO2 film can be deposited directly on resist at 50°C without any damage. Furthermore, in situ treatments can be used to widen the space between lines and/or reform the resist shape. Figure 3b shows an example of in situ treatment before SiO2 deposition. In this case, the resist is slimmed isotropically by ~65Å. Within wafer uniformity of the treatment process is typically <2%, 3σ. This is a good example showing the process flexibility gained by using a mini-batch system, while sustaining the high throughputs required for manufacturing.


Overcoming the initial barriers to adoption has required the creation of several toolset configurations to address the unique issues in specific applications. Single-wafer, batch and mini-batch ALD solutions are available, each with thermal and plasma enhanced capabilities, and selection of the appropriate manufacturing toolset is as critical to eventual technology adoption as the process itself. In very cost sensitive markets such as memories, cost-of-ownership (COO) will be a main driver for equipment selection. In foundry or other logic applications, equipment choice is more a mix between COO, turn-around time and process performance considerations and choices of equipment type have to be made with careful regard to the specific application.


1. C. Goodman, et al., “Atomic Layer Epitaxy,” Jour. of Appl. Physics, R65-R81, 1986.

2. D. Triyoso, et al., “Physical and Electrical Characteristics of Atomic-Layer-Deposited Hafnium Oxide Formed Using Hafnium Tetrachloride and Tetrakis(ethylmethylaminohafnium),” Jour. of Appl. Physics, Vol. 97, 124107, 2005.

3. H. P. W. Hey et. al., “Ion Bombardment: A Determining Factor in Plasma CVD,” Solid State Technology, pp. 139-144, April, 1990.

4 . L. Niinistö, et. al., “Advanced Electronic and Optoelectronic Materials by Atomic Layer Deposition: An Overview with Special Emphasis on Recent Progress in Processing of High-k Dielectrics and Other Oxide Materials,” Physica Status Solidi (a), 201, p. 1443–1452, 2004

5. E. Granneman, et al., Batch ALD: Characteristics, Comparison with Single-wafer ALD, and Examples, Surface and Coatings Technology, Vol. 201, p. 8899 – 8907, 2007.

6 . A. Kobayashi, et al., Temperature Dependence of GPC with PEALD-SiO,” Proc. 10th Inter. Conf. on Atomic Layer Deposition, p. 31, 2010.


Mohith Verghese earned a BS in chemical engineering from the U. of Texas at Austin and a MS in chemical engineering from the U. of Arizona. He is technical product manager of ALD technologies at ASM America, Phoenix, AZ, USA; ph: +1-602-470-2736, email:  [email protected]

Jan Willem Maes received his PhD in applied physics from Delft U. of Technology and works at ASM Belgium on ALD and EPI process application development projects.

Nobuyoshi Kobayashi earned a BS, a MS, and a PhD in solid state physics from the U. of Tokyo. He is director of PECVD and PEALD technologies at ASM Japan, Tama in Tokyo.

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