Gas separation: processes – Solid sorption – Inorganic gas or liquid particle sorbed
Reexamination Certificate
2001-09-17
2002-10-08
Simmons, David A. (Department: 1724)
Gas separation: processes
Solid sorption
Inorganic gas or liquid particle sorbed
C095S900000, C502S415000
Reexamination Certificate
active
06461411
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of gas purification, and to the ultra-purification of bulk or matrix gases that are useful in the microelectronics manufacturing industry. More specifically, the invention relates to methods and materials for selectively removing trace hydride impurities and moisture from matrix hydride gases and inert or non-reactive gases.
BACKGROUND OF THE INVENTION
As semiconductors become smaller and the devices using semiconductors become more sophisticated and therefore more demanding of the semiconductors, the perfectness property of semiconductors becomes an issue of great concern. The manufacture of semiconductors involves the use of reactive gases that are composed of various elements. In addition, manufacturing processes such as metal-organic chemical vapor deposition (MOCVD) and other related manufacturing techniques are used in the manufacture of semiconductors. In these processes the purity of the reactive gases plays a large part in determining the quality of the semiconductor product being manufactured, and in particular the electronic quality of the semiconductor product. Consequently, there is an increasing demand in the microelectronics industry for ultra-pure process gases. Thus, the ultra-purification of gases useful in microelectronics processes has experienced extensive technological effort and advances.
Existing methods of purifying gases used in manufacturing microelectronics devices are generally insufficient for meeting the need for ultra-pure gas. While parts-per-billion (ppb) levels of impurities were tolerable at one time, such levels are now regarded in many processes as too high. This technological effort is nourished by improvements in the analytical techniques that are used to detect impurities in gases. Presently, the ability exists to provide impurity detection limits that are in the ppt levels, for example by using Atmospheric Pressure Ion Mass Spectrometry (APIMS).
Group IIIB metals (e.g., gallium (Ga) and indium (In)) and group VB elements (e.g., phosphorus (P), arsenic (As), and nitrogen (N)) are of special importance in the manufacture of semiconductors in that they are constituents of the so-called Group III/V semiconductors. For example, arsine (AsH
3
), phosphine (PH
3
) and ammonia (NH
3
) are used in the manufacture of Group III/V semiconductors such as gallium arsenide (GaAs), indium phosphide (InP) and gallium nitride (GaN), respectively. Traces of foreign elements in these semiconductor materials are harmful, especially if the foreign elements are Group IVB elements (e.g., Si and Ge) and/or Group VIB elements (e.g., S and Se), which adversely contribute an acceptor effect or a donor effect to the semiconductor material. Unfortunately, trace impurities of Group IVB and VIB elements are very common in so called “pure gases”. For example, phosphine and arsine may include traces of silane (SiH
4
), germane (GeH
4
), hydrogen sulfide (H
2
S) and hydrogen selenide (H
2
Se). In addition, trace quantities of oxygen (O
2
), oxides such as carbon monoxide (CO) and/or carbon dioxide (CO
2
), and oxides derived from phosphine and arsine (e.g., HxP
y
O
z
, and HxAs
y
O
z
, wherein x, y and z are small integer numbers) have also been detected in “pure gases.” Such impurities are also harmful in semiconductor processes.
Impurities in hydride gases used in the production of semiconductor devices, especially hydride-impurities of other elements, may originate from the hydride bulk gas itself, or from materials that are within gas handling and distribution devices such as gas containers, gas cylinders, gas valves and gas regulators, and even from gas lines that interconnect these devices.
U.S. Pat. No. 5,385,689 discloses a method of purifying semiconductor process gases using a scavenging composition that removes water, oxygen and other oxidants and Lewis acids from gas streams such as hydrogen, nitrogen, helium, neon, argon, krypton, and xenon, and Group IVA-VIA hydride gases such as silane (SiH
4
), germane (GeH
4
), ammonia (NH
3
), phosphine (PH
3
), arsine (AsH
3
), hydrogen sulfide (H
2
S), and hydrogen selenide (H
2
Se). The scavenging composition is formed by the deposition of a Group IA metal (Na, K, Rb, Cs, or mixtures or alloys thereof) onto an inert, macroreticulate polymer support, followed by pyrolysis at an elevated temperature.
Japanese Patent Application No. 4124001A2 describes a method of purifying arsine using an activated alumina gel. Nitrogen gas that has been heated to 110-200° C. is used to activate a granular alumina gel. Unpurified arsine is brought into contact with the alumina gel, and the temperature is raised to remove impurities from the arsine. However, JP 4124001A2 specifically states that the alumina should not be heated to temperatures over 200° C., stating that temperatures over 200° C. will turn the alumina gel into a powder, thereby rendering the alumina incapable of purifying gases.
Nippon Sanso Corporation has developed an alumina catalyst called MN Purificator™ (also called NSC NeoBead, NeoBead or NB) which selectively removes silane from arsine (Japanese Patent No. 2-246533; Takuya, et al.,
J. Cryst. Growth,
124: 272-277 (1992)). The mechanism whereby silane is removed from arsine by the MN Purificator™ as the arsine passes through alumina is proposed to be a chemical reaction as shown in Equation 1.
SiH
4
+[Al(OH)]
2
→(AlO)
2
—SiH
2
+2H
2
(1)
Alumina such as the NeoBead material mentioned above is known to remove silane and hydrogen sulfide impurities from inert gas streams such as nitrogen and from the hydride gases arsine and phosphine. However the NeoBead material is ineffective in the elimination of traces of germane impurities from hydride and inert gas streams.
Watanabe, et al. (
Journal of Materials Science: Materials in Electronics,
9:127-132 (1998)) describe the adsorption of B
2
H
6
and H
2
Se on porous &ggr;-alumina (gamma-alumina) and amorphous silica, and discusses the reactivity of hydrides (B
2
H
6
, PH
3
, AsH
3
, and H
2
Se) to alumina and silica in terms of the basicity of adsorbents and the proton affinity of hydrides.
Ikeda, et al. (
Journal of Crystal Growth,
124:272-277 (1992)), describe the reduction of the H
2
O and SiH
4
content of in AsH
3
by treating the inner surface of an aluminum cylinder in order to form a clean and smooth oxide layer, and by developing a catalyst that selectively decomposes the SiH
4
.
A need remains in the art for an effective purifier apparatus and purification method for removing trace impurities from so-called pure gases, specifically the removal of trace hydride impurities from bulk or matrix hydride and non-reactive or inert gases. In particular, there is a need for the selective removal of trace quantities of hydride impurities of Group VB elements such as phosphorus (P) and arsenic (As) and Group IVB elements such as silicon (Si) and germanium (Ge) from hydride gases and non-reactive or inert gases. Such hydride impurities pose environmental and health hazards because of their extreme toxicity, and elimination of these hydrides from bulk and matrix gases is desirable down to the sub-ppm level
SUMMARY OF THE INVENTION
The present invention overcomes the deficiencies of prior art adsorption-based gas purification systems that seek to remove impurities from hydride gases. The invention provides a gas purification system that is especially adapted for, but is not limited to, use in the purification of gases that are thereafter used in the manufacture of semiconductor devices.
Accordingly, this invention provides a method for the selective removal of trace quantities of hydride impurities that may be present in bulk or matrix hydride, inert, and non-reactive gases in parts-per-million (ppm) to parts-per-billion (ppb) levels to provide purified hydride, inert, or non-reactive matrix gases that contain less than about a 1 ppb impurity level of the unwanted hydrides. In particular, this invention provides a method for the selective and effective removal of trace levels
Fraenkel Dan
Watanabe Tadaharu
Hogan & Hartson LLP
Lawrence Frank M.
Matheson Tri-Gas
O'Rourke Sarah S.
Petersen Steven C.
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