Category Archives: Gases



December 11, 2015

A variety of gases are used in semiconductor manufacturing for process reactions in chemical vapor deposition, etching, ion implantation and many other processes. They are also used for such diverse purposes as chamber cleaning and purging. Generally speaking, gases are classified as processes gases for the first set of applications and bulk gases for the second. Bulk gases are hydrogen, helium and nitrogen, for example, which can be produced on-site through air separation plants. Process gases are typically supplied in the familiar gas tanks, or sometimes gas tanker trailers if the volume required is high enough. In some parts of the world, underground piping is used to supply multiple fabs

Aside for the gas type, the most common concern is the purity of the gas. Purity is often discussed in the “number of nines” level of purity. Gases that are 99.999% pure, for example, are “five nines” purity, gases that are 99.9999% pure are “six nines” purity and so on. Alternatively, trance contaminants are measured in parts per million (ppm), parts per billion (ppb) or even parts per trillion (ppt). Higher levels of purity are, of course, more difficult to produce and are therefore more costly. They are also more difficult to measure accurately. An ongoing challenge in the semiconductor industry is that gas users — IC manufacturers — tend to specify the highest level of purity available, but it’s often unknown if that higher level of purity actually provides any kind of benefit to device performance or yield. Indeed, sometimes trace impurities have proved to have some kind of beneficial effect and removing them can actually decrease performance.

Another important aspect — some would say the most important aspect — is safety. Gases can be toxic, carcinogenic, flammable, pyrophoric, corrosive and generally hazardous. A silane leak, for example, could result in a pocket of silane in a corner of the fab, which could explode. Arsine and phosphine, commonly used in ion implantation, are deadly in ppb and ppt, respectively. Fortunately, the semiconductor industry has an excellent safety record and danger to fab personnel is minimal — as long as established safety protocols are closely followed. This include storing gas cylinders in well monitored gas cabinets.

By Pete Singer, Editor-in-Chief

Opportunities for cost savings abound in the “sub-fab” of semiconductor operations where the vacuum pumps and gas abatement systems

Dr. Michael Czerniak, Environmental Solutions Business Development Manager, at Edwards Ltd.

Dr. Michael Czerniak, Environmental Solutions Business Development Manager, at Edwards Ltd.

reside. Typically, these systems are running full tilt, no matter what’s going on in the process tool.

In a case where the cobbler’s children may finally be getting new shoes, work is underway to improve the communication between sub-fab equipment and process tools so that fuel in gas abatements systems can be turned off if there’s nothing to abate, and vacuum pumps can be throttled back or slowed if there’s nothing to pump.

“If you have equipment that is enabled with this capability, you can access these savings by essentially turning down the power or the fuel gas consumption when they’re not actually required for chip processing, said Dr. Michael Czerniak, Environmental Solutions Business Development Manager, at Edwards Ltd.

Czerniak gave a talk at 2:00pm on Tuesday at SEMICON West as part of the Sustainable Manufacturing Forum. The forum, held on Tuesday in Moscone North, Hall E, Room 132 from 10:00am to 5:00pm, allows experts to share the latest information on the environmental and social impacts of advanced technologies that are likely to be introduced into semiconductor manufacturing in the near future.

At SEMICON West in 2014, Czerniak was honored with SEMI’s Merit Award, along with Daniel Chlus (IBM) and Lance Rist (RistTex). The trio, were part of the Energy Saving Equipment Communication Task Force responsible for developing new standards designed to help reduce energy consumption in production equipment, specifically the SEMI E167 standard.

While production equipment and support equipment are all capable of reduced utility consumption, implementation has been slow due to lack of a standard.

SEMI’s E167 solved one piece of the puzzle – enabling the factory host to tell the process too that there are no wafers coming, for example – another standard is needed for the tool to communicate with sub-fab equipment that it, too, can power down. That is where a new standard, SEMI S23 comes in. “Once the tool has decided it doesn’t need pumps and abatement for the next 45 minutes or so — whatever it decides — it can then cascade that message down to the subfab where the energy savings will actually take place,” Czerniak explained.

At SEMICON West, a working group of the SEMI S23 task force is preparing additions to the Related Information section of SEMI S23 to provide for suggested utility-consumption test conditions and report formats for some components and peripheral equipment commonly used in semiconductor manufacturing equipment systems.

The components initially considered are dry vacuum pumps, refrigerated chillers and heat exchangers, although other components such as process power equipment may be considered soon. Also under discussion is the inclusion of Related Information for the application of efficiency rating systems for components and peripheral equipment. The goal of the working group is to produce suggested new Related Information in SEMI S23 for consideration on a future SEMI Standards Ballot.

“We’re working pretty hard as part of a SEMI standards committee – to get standardized signaling for that sort of information – so that all pump and abatement suppliers can get access to signals that allow them to do these energy savings,” Czerniak said.

Czerniak said this will work best in a new facility, once the tools have the ability to communicate directly with the pumps and abatement systems. In a retrofit scenario, it can be a challenge to get those signals. “We’re talking about getting signals derived from loadlock pumps,” he said.

In practice, it may be impossible to actually turn off vacuum pumps completely, particularly those that are pumping byproducts that tend to condense inside the pump. “You generally don’t want to switch them off due to the risk of not being able to restart them. In those cases, what you do is typically reduce the frequency at which you spin them and save maybe 10-15% of the running power. To get them back to full speed and full operating temperature isn’t such a long period of time,” Czerniak said.

On the other hand, with gas abatement systems, particularly those that burn fuel (i.e., natural gas) to destroy the byproducts, it’s possible to shut them to near zero. “In our case, we usually just leave them running on a pilot flame. They come back on line in tens of seconds, and you save about 90% of your fuel gas. There are very significant savings,” Czerniak said. “At the same time, you also save on your CO2 footprint. It gets to be quite an important factor when people do CO2 audits of their manufacturing process so they can put green stickers on their end products.”

This has been the focus of one of the working groups in the European EEM450PR project, which is focused on 450mm tool developed (similar work is underway at the G450C Consortium in Albany).

In his talk on Tuesday, Czerniak described those models that were constructed as part of the EEM450PR project to simulate the impact of green modes, at various levels of wafer inactivity, initially for 300mm, and then extended for a hypothetical 450mm fab. It was also noted that additional savings would be possible in the facility, e.g. reduced process cooling water when the pump and abatement thermal load is reduced. The model was then validated by looking at data from a HVM 300mm fab, simulating the effect of green modes (without actually implementing them), and also live green mode implementation on pumps and abatement at imec’s R&D lab in Europe.

A live demonstration was also conducted in the G450C Albany fab on some installed 450mm toolsets, as part of the complementary and collaborative engagement between the regions on the 450mm topic, in order to validate the assumptions for future 450mm fabs.

SEMI-GAS Systems, a provider of ultra-high purity gas delivery equipment, recently broadened the capabilities of its custom Xturion Blixer gas blender product line. The new options include system auto-purging and a dynamic stream gas analyzer to facilitate the blending of highly corrosive gases into gas mixtures, as needed in semiconductor and microelectronics fabrication processes.

Based on a preset component ratio, Blixer receives regulated process gases from two or more independent gas sources and blends them to the desired composition in the system’s on-board accumulator tank. The system then draws from the accumulator tank and delivers the uniform gas mixture through the process gas outlet to a tool or gas distribution manifold.

To oversee all of these system operations, Blixer utilizes a SEMI-GAS GigaGuard PLC controller with an ergonomically front-mounted 8.0″ color touch screen. In addition, the PLC controller manages the electrical components and pneumatically actuated valves for process gas delivery and fully automated purging sequences.

Mass flow controllers regulate the volumes of component and balance gases to be blended according to the controller’s pre-programed blend recipe. Recipe percentages can be adjusted by the system’s operator through the touchscreen, allowing for on-site process modifications.

To ensure a highly accurate blend composition, the GigaGuard PLC works in conjunction with the system’s dynamic stream gas analyzer by continuously withdrawing a small sample from the accumulator tank. If the analyzer signifies the mixture is outside of the preset tolerance range, the system will automatically adjust the blend percentages to approach the set point value.

Should the system recognize an error, external system lights and audible alarms will commence, signaling operators of warnings and/or shutdown conditions. To provide emergency manual shutdown, an externally mounted UL-approved Emergency Off (EMO) push button is provided. Remote shutdown options are also available with an optional kit that can communicate via an Ethernet network, enabling centralized, facility-wide equipment monitoring and data collection.

Like all SEMI-GAS custom Xturion systems, each unit is user-configurable to accommodate application-specific flows, pressures, mixture percentages, and blending accuracies. Various analyzer configurations are also adjustable to precisely tailor the system’s operational needs for each application.

All Blixers meet SEMI S2 and Uniform Fire Code requirements and are equipped with UL-approved fire sprinklers, a 1/4″ high-impact polycarbonate plastic safety viewing shield, and gas identification labels. The standard enclosure is constructed of powder coated 11 gage cold rolled steel and is 87 inches tall, 40 inches wide and 28 inches deep, including an 8-inch exhaust collar for venting to the facility’s ducting.

Internal panel components are autogenously welded, helium leak tested and certified to the highest purity standards. All valves, regulators, transducers, tubing and fitting bodies are 316L stainless steel to prevent deterioration from the corrosive process gases and resulting mixtures.

SEMI-GAS Systems Gas Blender

Storing gas on a sorbent provides an innovative, yet simple and lasting solution.

BY KARL OLANDER, Ph.D. and ANTHONY AVILA, ATMI, Inc., an Entegris company, Billerica, MA

The period following the introduction of subatmospheric pressure gas storage and delivery was punctuated by continuous technical innovation.

Even as the methodology became the standard for supplying ion implant dopants, it continued to rapidly evolve and improve. This article reflects on the milestones of the last 20 years and considers where this technology goes from here.

From the beginning, the semiconductor industry’s concern over using highly toxic process gases was evident by the large investment being made in dedicated gas rooms, robust ventilation systems, scrubbers, gas containment protocols and toxic gas monitoring. While major advances have been made in the form of automated gas cabinets and valve manifold boxes, gas line components, improved cylinder valves and safety training, the underlying threat of a catastrophic gas release remained.

Risk factors targeted

The underlying risk with compressed gases is twofold: high pressure, which provides the motive force to discharge the contents of a cylinder, and secondly, a relatively large hazardous production material inventory, which can be released during a containment breach. Pressure also is a factor in component failure and gas reactivity, e.g., corrosion. Mitigating these issues would considerably increase safety.

FIGURE 1. The stages of developing a new chemical precursor for use in commercial IC production.

FIGURE 1. The stages of developing a new chemical precursor for use in commercial IC production.

Analysis of the risks suggested an on-demand, point-of-use gas generator would improve safety by both reducing operating pressure and gas inventory[1]. The challenges associated with this approach include complexity of operation and gas purity, especially in a fab or process tool setting. Chemical generation of arsine, while possible, per equation [A], also substituted a highly reactive toxic solid for arsine[2]. Considerable safety and environmental issues accompanied the operation of such a generator. An on-demand, point-of-use electrochemical approach for supplying arsine, per equation [B], would also eliminate the need for high pressure storage if the associated operational issues could be overcome. Numerous attempts at developing a commercial electrochemical generator just never proved successful[3].

[A] KAsH2 + H2O —> AsH3/H2O + KOH
[B] As(s) + 3H2O + 3e(-) —> AsH3(g) + 3OH(-)

Innovation from a simple(r) solution

Pressure swing adsorption processes utilize the selective affinity between gases and solid adsorbents, and are widely used to recover and purify a range of gases. Under optimal conditions, the gas adsorption process releases energy and produces a material that behaves mores like a solid than a gas.

Early work at reversibly adsorbing toxic materials on a highly porous substrate showed promise. In 1988, the Olin Corporation described an arsine storage and delivery system where the gas was [reversibly] adsorbed onto a zeolite, or microporous alumino- silicate, material[4]. A portion of the stored gas could be recovered by heating the storage vessel to develop sufficient arsine pressure to supply a process tool. In 1992, ATMI supplied a prototype system based on the Olin technology to the Naval Research Lab in Washington, D.C.

The breakthrough that lead to the first commercial subatmospheric pressure gas storage and delivery system occurred when ATMI reported the majority of the adsorbed gas could be supplied to the process by subjecting the storage vessel to a strong vacuum. Using vacuum rather than thermal energy simplified the process, providing the means for an on-demand system[5]. Using a sorbent had the effect of turning the gas into something more akin to a “solid.” That characteristic, coupled with the absence of a pressure driver, delivered an inherently safe condition. The vacuum delivery condition also helped define where the technology would find its first application: ion implantation[6].

Safe and efficient gas storage and delivery

In 1993, prototype arsine storage and delivery cylinders based on vacuum delivery were beta tested at AT&T in Allentown, PA[g] [f]. The system was trademarked Safe Delivery Source®, or SDS®. Papers were presented on safe storage and delivery of ion implant dopant gases the following year in Catania, Sicily at the International Ion Implant Technology Conference[7].

The goal to find a safer method to offset the use of compressed gases was realized: (1) gas is stored at low pressure (ca. 650 Torr at 21°C) and (2) the potential for large and rapid gas loss is averted. Leaks, if they occur, whether by accidental valve opening or a containment breach, would be first inward into the cylinder. Once the pressure equalizes, gas loss to the environment would be governed mainly by diffusion as the gas molecules remain associated with the sorbent. The SDS package, while not a gas generator per se, effectively functions like one.

FIGURE 2. Cutaway view of SDS3 carbon pucks within a finished cylinder.

FIGURE 2. Cutaway view of SDS3 carbon pucks within a finished cylinder.

While subatmospheric pressure operation is an artifact of having to “pull the gas” away from the sorbent, it has become synonymous with safe gas delivery. The optimization work which followed focused on reducing pressure drop in the gas delivery system by improving conductance in valves, mass flow controllers and delivery lines. A restrictive flow orifice was no longer required. The new gas sources proved to work best when in close proximity to the tool.

The years after this technology introduction also saw considerable efforts to improve the sorbent; ultra-pure carbon replaced the zeolite-based material used in the first generation SDS (SDS1), roughly doubling the deliverable quantities of gas per cylinder. These granular carbon sorbents in the SDS2 were later replaced by solid, round monolithic carbon “pucks” in SDS3 (FIGURE 2), which necessitated the cylinder be built around the sorbent[8]. This improvement again roughly doubled gas cylinder capacity.

Recognized in international standards

In 2012, the United Nations (U.N.) recognized the uniqueness of adsorbed gases and amended the Model Regulation for the Transport of Dangerous Goods by creating a new “condition of transport” for gases adsorbed on a solid and assigning a total of 17 new identification numbers and shipping names to the Dangerous Good List. Adoption is expected to occur by 2015. A few of the additions are noted here.

Arsine   – UN 2188 – compressed
Arsine, adsorbed – UN 3522 – SDS
Phosphine – UN 2199 – compressed
Phosphine, adsorbed – UN 3525 – SDS

FIGURE 3. The evolution of a SAGS Type 1 gas package.

FIGURE 3. The evolution of a SAGS Type 1 gas package.

In recent years, fire codes have been updated through the definition and classification of subatmospheric Gas Systems, or SAGS, based on the internal [storage] pressure of the gas.9 Systems based on both sub-atmospheric pressure storage and delivery are designated as Type 1 SAGS. It is important to note that the UN definition for adsorbed gases, and the resulting new classifications mentioned above, only applies to Type 1 SAGS, defined as follows: Subatmospheric Gas Storage and Delivery System (Type 1 SAGS). A gas source package that stores and delivers gas at sub-atmospheric pressure and includes a container (e.g., gas cylinder and outlet valve) that stores and delivers gas at a pressure of less than 14.7 psia at NTP.

It is also worth mentioning that sub-atmospheric pressure gas delivery can also be achieved using high pressure cylinders by embedding a pressure reduction and control system. The Type 2 SAGS typically employs a normally closed, internal regulator[s] that a vacuum condition to open. This is not a definition of sub-atmospheric storage and delivery, but of sub-atmospheric delivery only. Subatmospheric Gas Delivery System (Type 2 SAGS). A gas source package that stores compressed gas and delivers gas subatmospherically and includes a container (e.g., gas cylinder and outlet valve) that stores gas at a pressure greater than 14.7 psia at NTP and delivers gas at a pressure of less than 14.7 psia at NTP.

In general, Environmental Safety and Health managers, risk underwriters and authorities having jurisdiction recognize the importance of SAGS and requires recommend their use whenever process conditions allow[10].

Expanding SAGS into new applications

Taking the lessons learned from SDS2/SDS3 in ion implant operations, along with key findings from
other applications like HDP-CVD (the SAGE package) and combined with sorbent purification and carbon nanopore size tuning, SAGS Type 1 packages are poised to offer their safety advantages in new and emerging areas, as well as add even more safety and efficiency benefits. Currently, a new package called Plasma Delivery SourceTM (PDSTM) is available for high flow rate applications, while maintaining all the safety attributes of the SAGS Type 1 package.

Also, in addition to the inherent safety, PDS employs a pneumatic operator (valve) to the cylinder which further minimizes the opportunity for human error. In an emergency, such as a toxic gas alarm, pressure excursion, loss of exhaust, etc., gas flow at the source can be quickly stopped and the cylinder isolated. Cycle/purge operations are made safer as human involvement is minimized. Human-initiated events, like over-torqueing the valve, failing to close the valve or even back-filling a cylinder with purge gas, are prevented.

Arsine 200 559 835
Phosphine 85 198 385

Expanding the use of SAGS beyond the domain of ion implant involves successfully navigating key process factors such as operating pressure, flow rates, proximity to the tool and purity. One approach includes coupling the PDS cylinder and gas cabinet together to yield a plug and play “smart” delivery system. Unlike high pressure systems, which are more concerned with excess flow situations, knowing and controlling pressure allows a SAGS cabinet to operate at a reduced risk. This enables linking cabinet ventilation rates with the system operating pressure. During normal operating conditions, the exhaust rate could be reduced by up to 80 percent because the system is operating sub-atmospherically. Should the operating pressure exceed a preset threshold, the exhaust flow would automatically revert to a higher range or the cylinder valve would close.

The future, therefore, could see these PDS packages extended to another level by incorporating them into smart delivery systems, which will further reduce risk, maximize efficiency, improve cost of ownership and expand the footprint for SAGS into new applications like plasma doping, solar, epitaxy and etch.


During the last 20 years, the semiconductor industry undertook a large effort to develop safer gas delivery technologies to reduce risks associated with dopants used in ion implant. Many technologies were considered, including chemical and electrochemical gas generators, complexing gases with ionic liquids or mechanically controlling cylinder discharge pressure using embedded regulator devices.

In the end, storing gas on a sorbent provided an innovative, yet simple and lasting solution. Gas-sorbent interactions are well understood, reproducible and can be achieved with a minimum of moving parts. Gas release risks, driven by pressure, are all but removed from consideration. And any potential for human error continues to be a target for improvement wherever toxic gases are used.


1. Proc. Natl. Acad. Sci. USA 89 pp 821-826, 1992.
2. Appl. Phys. Lett., 60 1483
3. Electron Transfer Technology, US Patent 59225232
4. Olin Corporation, US Patent US4744221A
5. Advanced Technology Materials, US Patent US5518528 6. Many thanks to Dan McKee and Lee Van Horn for being the first of many early adopters.
7. Proceedings of the Tenth International Conference on Ion Implantation Technology, 1994, pp 523-526.
8. DOT-SP 13220.
9. NFPA 318, Standard for the Protection of Semiconductor Fabrication Facilities 2012 Edition. 10. SAGS in the FAB, SST reference

ATMI is a wholly owned subsidiary of Entegris, Inc. ATMI, Safe Delivery Source, SDS, Plasma Delivery Source and PDS are trademarks of Entegris, Inc. in the U.S., other countries, or both. All other names are trademarks of their respective companies.