Process Gas Purification

Pall’s process gas purification systems remove impurities that pose a major threat to the vitality of the PV Silicon/CIGS wafer. Molecular impurities, also known as gaseous or volatile impurities, have recently become of greater concern as sources of defects and can be effectively removed with Pall’s expert purification solutions. These filters work to expel impurities including moisture, oxygen, carbon dioxide, carbon monoxide, hydrocarbons and metal carbonyls. Pall purification systems utilize a reactive bed of material in order to expel impurities from the gas stream in areas where traditional particle filtering is ineffective. High purity materials are used which provide background level contaminant removal without contributing metals or other harmful contaminants to the process stream.

CIGS Based Thin FIlms

Common process feedstock gases used in PECVD and CVD tools consist of silane, hydrogen,

germane, and ammonia. The post-deposition etching is performed with the use of corrosive gases such as hydrogen chloride (HCl) and hydrogen bromide (HBr). Moisture contamination in the process line can cause a reaction with the silane gas, forming silicon dioxide nuclei. If the nuclei condenses, siloxanes are formed which can cluster and form particles. This reaction can take place upstream or downstream of a particle filter. The installation of a Gaskleen® purifier assembly with Pall's AresKleen™ SIP material will remove the moisture and siloxanes, which will significantly reduce the particle formation. HCl and HBr are highly corrosive gases that can form a strong acid in the presence of moisture that will corrode most metals including 316L stainless steel. Hence, the removal of moisture in both gases is essential in preventing any corrosive effects to both the gas line and associated equipment such as regulators, valves & MFCs. The reduction of moisture will be greatly enhanced by using a Pall purifier with AresKleen HCLP or HBRP purification media.

SIlicon Based Thin FIlms

Typical argon impurity levels found in physical vapor deposition (PVD) / sputtering tools are: moisture (0.5 ppm), oxygen (2 ppm), and total hydrocarbons (0.4 ppm). The following contaminants, emanating from the process gases and gas delivery system components, are often present in the vacuum chambers: H2O, O2, CO, CO2, H2, N2, methane and non-methane hydrocarbons. These contaminants are often adsorbed to the chamber walls under atmospheric conditions, but tend to desorb at the operating pressures typically used during sputter deposition (<200mT).

The elevated temperatures required for thermal processing can exacerbate the release of gases from chamber walls and increase molecular impurities. For Argon purification Pall recommends the Gaskleen gas purifier assemblies that combine AresKleen media with Ultramet-L™ stainless steel filter media. APIMS test data show AresKleen INP medium has a strong affinity for oxygen and carbon containing molecular species in argon, effectively removing these impurities to sub 100 ppt levels.

The trace contaminating gases can cause defects in the thin film layers in addition to increasing chamber pump unplanned down time. Oxygen contamination can lead to uncontrolled oxidation of metal layers and metal targets within the sputter or PVD tools. Trace water vapor can contribute both hydrogen and oxygen molecules to process chambers and metal layers. Carbon contamination might result in the formation of thin polymer films on process chambers and metal surface layers.

Virtually all gaseous contaminants found in gas delivery systems and process gases can lead to defects and longer process times, ultimately resulting in manufacturing yield losses and lower tool throughput. These factors can negatively impact overall tool cost-of-ownership (COO) and lead to unforeseen costs but can be mitigated using Pall's advanced purifier technologies. The control and reduction of trace oxygen and hydrocarbon species can be achieved using Pall purifiers with AresKleen™ INP medium.

Benefits:

• Enhanced process stability
• Increased area/process efficiency
• Reduction in Silicon/CIGS defects
• Drop in retrofits to existing particle filters
• Custom media tailored to purify a variety of gases
• Low Cost-of-Ownership (COO)

Pall’s Process Gas Purification systems and materials provide effective removal of impurities in areas where particle filtration is ineffective. Contact a Pall expert help you optimize your process gas purification systems to maximize your sites performance by reducing defects and increasing yields.