Other Applications for UltraPure Steam
ALD
Ultrapure water vapor is a necessary part of the reaction chemistry needed to form ALD films. RASIRC Steamers deliver very low concentration at high cycle times and low cost.
RTP
300 mm RTP requires the safe, accurate delivery of high volumes of ultrapure steam. RASIRC can meet this challenge with an economical solution.
Lithography
Immersion lithography places a layer of pure water between the projection lens and the wafer. Any contaminant within the water can lead to change in refractive index and a project defect on the wafer. Micro-bubbles in the water can also lead to project defects on the wafer.
RASIRC Steamers deliver ultrapure water at point of use that is ionically pure, particle free, and free of micro-bubbles, providing a competitive advantage to the lithography tool manufacturer.
Flat Panels
As the substrate size increases, the chemical and water bath usage increases dramatically. Steam cleaning provides a very cost effective method for applying and removing chemistry from the wafer surfaces. The use of steam as a replacement for water can reduce chemical requirements by 1000 fold. In addition, steam can be used to form isolation layers between films and annealing of films to reduce defects and improve cell efficiencies.
VCSELS
Two factors are critical to yield when manufacturing the oxide aperture in VCSELs:
- Oxide growth rate
- Film quality
Oxide growth rate is limited by temperature and water vapor pressure while film quality is limited by contaminants.
Users of the RASIRC Steamer demonstrated increased growth rate and uniformity by elimination of the oxygen carrier gas.
The RASIRC Steamer steam purification system provides an alternative to bubblers and vaporizers by increasing the partial pressure of water and improving water vapor purity.
| Purification Performance Results (ppb) |
| |
DI Water Source |
Pre-Purified Steam |
Purified Steam |
| Total Metals |
19.8 |
0.15 |
0.009 |
| Total Organic Carbon |
1200 |
380 |
22 |
| Total Silica |
28 |
4.3 |
0.7 |
| Urea |
2200 |
48 |
2.6 |
| Ammonium |
1.468 |
1.117 |
0.116 |
Diffusion Furnaces
RASIRC provides an inherently safe and ultrapure process for delivery of steam for the oxidation process in diffusion furnaces. This process replaces alternate techniques that are either unsafe due to the explosive combustion of oxygen and hydrogen to generate pure water, or of limited purity and throughput due to the bubbling of nitrogen through water.
Wafer Cleaning
The history of semiconductor capital equipment follows a natural progression from wet to dry processes. As the market for dry processes matures, new markets will evolve. The biggest and most likely to follow is the wet cleaning tools from dip and dunk to dry/vapor cleaning.
One issue holding back this space has been the development of an effective vapor cleaning solution. The ability to deliver high flows of ultrapure water vapor is an enabling technology for this next technology advancement. The move from wet to dry could enable a single chamber to be added to existing cluster tools, eliminating the need for a wet bench process.
Water for Injection
Water for injection (WFI) is water that is converted to steam in multi-step stills and then condensed under aseptic conditions. RASIRC eliminates pyrogen carryover by purifying the steam with a non-porous material. The purification segment of the technology is disposable to minimize cross contamination and simplify GMP and validation processes.
Alternate technologies require large stainless steel stills. WFI made in metal stills will pick up metal ion contamination, including iron, chrome, nickel, and other toxic metals with unknown effects on the end use of the water. The scalability of the RASIRC Steamer enables ultrapure steam that is particle and metal free to be delivered locally in quantities from ml/hour up to liters/hour.
Wave Guides
Steam is used for generating thick oxide films used managing optical signals. Applications that can benefit from this include optical components, instruments, lasers, fiber optics, electro-optical instrumentation, and electronics.
Growing thick oxide is a time consuming process that can take from days to weeks to complete. RASIRC pure steam reduces operating costs and reduces the time to grow oxides by providing a 100% water vapor environment.
RASIRC reduces costs, improves quality, and dramatically improves safety associated with these applications. Unlike the established pyrolytic process that generates water vapor by combustion of oxygen and hydrogen, RASIRC proprietary technology starts with de-ionized water, so it operates at lower temperatures, and can help eliminate hydrogen from a process and facility.
AMC
Steam is frequently used as the water vapor source to adjust cleanroom humidity. Urea easily passes through most RO/DI water systems. This urea is both injected with the steam and converted to ammonia in the steam generator. This generates high levels of both ammonia and Urea in the cleanroom air, leading to haze on photolithography optics, and T-topping of Photoresist.
Instead of removing the sources of ammonia upstream, most fabs are spending money downstream with chemical filters to address the symptom instead the of the cause.
RASIRC Steamers use a non-porous hydrophilic membrane that selectively allows water vapor and steam to pass through it. The chart below shows some typical results. Significant reduction can be seen in all contaminants, even with difficult contaminants such as Urea and ammonia.
| Purification Performance Results (ppb) |
| |
DI Water Source |
Pre-Purified Steam |
Purified Steam |
| Total Metals |
19.8 |
0.15 |
0.009 |
| Total Organic Carbon |
1200 |
380 |
22 |
| Total Silica |
28 |
4.3 |
0.7 |
| Urea |
2200 |
48 |
2.6 |
| Ammonium |
1.468 |
1.117 |
0.116 |
Sterilization
Clean steam is commonly used to sterilize devices and materials used in medical and pharmaceutical applications. RASIRC ensures that this remains a pure process, without introducing pyrogens or other entrained metals and materials.
Drug Discovery
Water for drug discovery is advancing to high throughput, low volume sampling. RASIRC delivers ultrapure water that is pyrogen and metal free, which could enable results otherwise obscured by alternate delivery systems.
Nanotechnology
For repeatable and reliable carbon nanotube (CNT) fabrication, tools are needed to control whether CNT are single- or multi-wall, straight or bent, long or short, and clean or dirty. Water vapor addition to the process is turning out to be the main 'control knob' for all of these processes. Precise delivery of water vapor will determine what the CNT looks like, what its yield is, and how contamination free the structure is. Water vapor is both the gas pedal and the steering wheel for CNT fabrication.
The process of growing CNT on catalysts leads to self-poisoning of the catalyst and cessation of the process. Through the addition of small amounts of water vapor, the catalyst can be kept free of molecular contamination. This enables longer carbon fibers to be grown under the same general process conditions.
Adding more water first leads to breaks in the CNT, which enable more tube opens. Further addition ceases the process. Metallic species are the sites for bends and branches of CNT. Addition of water vapor can react with metallic species to volatize and remove them, which stops branching and bending. Water vapor changes the CNT from multi-walled to single wall and ensures the single wall tubes are clean and free of amorphous carbon debris.
RASIRC technology is the first and only system to generate ultra pure water vapor that can deliver precise amounts of water vapor that is purified for both ionic contaminants and dissolved gases. Needing only filtered house de-ionized (DI) water and power, the RainMaker® Humidification System (RHS) adds controlled amounts of water vapor to any carrier gas. It can humidify inert gases, as well as oxygen, hydrogen, or corrosive gases. The system is capable of delivering into both atmosphere as well as vacuum process pressures.
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