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Arsine Purification via Distillation

IP.com Disclosure Number: IPCOM000030613D
Publication Date: 2004-Aug-19
Document File: 7 page(s) / 73K

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Arsine Purification via Distillation

Background

Arsine is used in the manufacture of III-V compound semiconductors.  Key products include gallium arsenide and aluminum gallium arsenide epitaxial layers in compound semiconductors.  These layers are grown by MOVPE (Metal Organic Vapor Phase Epitaxy) or MOCVD (Metal Organic Chemical Vapor Decomposition) processes.  In these processes, gaseous arsine (a group V chemical) is reacted with a group III metal organic compound to produce the corresponding epitaxial layer at temperatures of 600-800 C.  Typically, significant excess of arsine is used; usually 20-200 times by weight.  Due to the excess arsine usage, MOCVD process is very sensitive to trace level of contaminants in arsine. 

In the epitaxial layers, typical levels of background contaminants considered acceptable are <5x1014 atoms/cm3.  At these values, the concentration of the contaminant is < 10 ppb in the epitaxial layer.  These values are extremely low and pose a significant problem for the suppliers of arsine.  In general, arsine sold today is able to meet these requirements.  However, there are instances where higher background in the epitaxial layers is noted and attributed to arsine.

We have determined that key contaminants in arsine may include H2S,

COS

, H2O, GeH4, and SiH4.  If these impurities are present above a certain threshold, then quality problems occur in arsine usage.  Unfortunately, the exact magnitudes of these threshold values remain unclear.  The threshold values appear to be below current analytical specifications and detection limits in most cases. 

The trace impurities are formed during the manufacture of arsine and most originate from zinc arsenide that is used to produce arsine.  The magnitude of the impurities varies in zinc arsenide and that in turn results in variations in their quantities in arsine.  It is imperative that robust purification methods be employed to remove these impurities to levels well below the threshold value such that arsine users do not see their impact on their devices.

This paper pertains to development of robust purification methods for arsine where process sensitivity to varying quantities of trace impurities in the feed is eliminated.  We propose to remove the key contaminants via multistage distillation with reflux, or a combination of multistage distillation with reflux and aqueous caustic treatment.

Theoretical Work

Theoretical calculations were carried out to determine the effectiveness of distillation process to remove the key impurities.  Three case studies are shown in Table1.  GeH4, SiH4 are more volatile than arsine, H2S and

COS

have comparable volatility while H2O is much heavier than arsine.

Table 1

Theoretical Calculations on the Effectiveness of Distillation

Species

Distillation Cases:  Separation Factors in the Final Product

 

Case 1:  Simple Flash; 50% vapor rejected;

Heavies è Final Product

Case 2: Single cut Distillation; 5 Stages; Reflux Ratio 2;...