Provisional Application No. 60/325,332, filed September 27,2001, which is incorporated in its entirety as a part hereof.

Field of the Invention This invention relates to a dual-source, single-chamber method and apparatus for epitaxial sputter deposition of epilayers and high quality films.

Background of the Invention One of the problems encountered in using a sputtering process for the formation of a thick epitaxial film (i. e. , thickness over one micrometer) is the difficulty of keeping ultra high vacuum conditions in the presence of a sputter gas for a long time.

Ultra high vacuum conditions are characterized by a low level of the partial pressure of any contaminating gasses present in the deposition chamber.

In U. S. Patent 3,811, 794, a vacuum sublimation pump is described for use in the removal of contaminant gases from a chamber. To create pumping conditions, it is proposed to continuously form a titanium film that would absorb any contaminant gases.

It is proposed to heat a titanium filament above its sublimation temperature in order to create the titanium film, but the film is deposited on the walls of the chamber.

It has now been found that it is advantageous to remove contaminant gases from a film deposition chamber by providing a pump to remove contaminant gases within the chamber in which deposition occurs.

Brief Summary of the Invention One embodiment of this invention is an apparatus for film deposition containing (a) a target for sputtering an epitaxial film, (b) a target for sputtering a pumping getter, and (c) a cryogenic shroud interposed between the epitaxial film target and the pumping getter target.

Various other embodiments of this invention are (a) an apparatus for creating a vacuum in a sputter deposition chamber containing a cylindrical, cryogenic pumping getter disposed within the sputter deposition chamber; (b) an apparatus for film deposition containing, within a single sputtering chamber, (i) a target for sputtering an epitaxial film, and (ii) a target for sputtering a pumping getter; (c) an apparatus for film deposition containing, within a single sputtering chamber, (i) a target, for sputtering, an epitaxial film, that generates contaminants, and (ii) a shroud disposed about the epitaxial film target to reduce the concentration of contaminants within the chamber; and (d) an apparatus for film deposition containing (i) a target for sputtering an epitaxial film, (ii) a target for sputtering a pumping getter, and (iii) a pumping getter interposed between the epitaxial film target and the pumping getter target.

The pumping getter may be cylindrical.

Various other embodiments of this invention are a method of depositing a film by the use of the apparatus of this invention, such as (a) a method of depositing a film by sputtering, in a single sputtering

chamber, (i) an epitaxial film material onto a substrate, and (ii) a pumping getter material onto a pumping getter; (b) a method of reducing contamination in a sputtering chamber by sputtering pumping getter material onto a cryogenic pumping getter disposed within the sputter deposition chamber; or (c) a method of reducing contamination in a sputtering chamber by sputtering pumping getter material onto a pumping getter disposed between a target containing the pumping getter material and a target containing material for sputtering an epitaxial film.

Brief Description of the Drawings Fig. 1 is a cross sectional view of a film deposition device.

Detailed Description of the Invention This invention provides an improved approach for growing high quality thick epilayers using sputtering. This method is particularly useful in the situation in which the sputtering process time is so long that the pumping speed of an ultra high vacuum pump could change while sputtering is on-going.

Instead of using a sublimation process, or a roughing pump (which reduces pressure to about 10-3 Torr), or a thermal molecular pump (which reduces pressure to about 10-7 to about 10-9 Torr), a sputtering process is used in this invention. This approach of this invention typically reduces pressure to about 10-11 to about 10-12 Torr. Specifically, a film of a reactive material (a pumping getter) is formed using a sputtering process.

The gas used to sputter the getter may be the same as the gas also used to sputter a desired product such as an epitaxial film. A typical example of such gas is argon.

In this invention, a sputtering process for growing an epitaxial film and a separate sputtering process for creating a film for a pumping getter are provided in the same sputtering chamber. A sputtering chamber is therefore proved herein that includes two sputtering sources. As shown in Fig. 1, the first sputtering source 2 is for the sputtering of an epitaxial film. The second sputtering source 4 is for the sputtering of reactive materials, such as titanium chromium or titanium-molybdenum, to create a getter.

The first sputtering source and substrate 6 are surrounded by a cryogenic shroud 8, such as a shroud cooled by liquid nitrogen or helium. The second sputtering source is mounted outside of the cryogenic shroud. During the deposition of epitaxial film material, the reactive material, functioning as a pumping getter, effectively absorbs contaminant gases such as H2, N2, CO, CO2, water vapor and the like. As a result of the significantly lower levels of these reactive, contaminant gases being present during film deposition according to the invention, the purity and overall quality of epitaxial films deposited is substantially higher (relative to otherwise similar films produced by other or prior art processes). The pumping speed of the getter film, which may be sputtered simultaneously with the epitaxial film, is substantially constant.

The cryogenic shroud is typically a stainless steel cylinder, filled with a coolant such as liquid nitrogen, that is open on the ends. Contaminant gases may flow out of the open ends. Shields protect the open ends and prevent penetration of the sputtered getter material from entering the space enclosed by the interior of the cylindrically-shaped shroud. The ionized sputtering gas that is utilized to sputter an epitaxial film within the shroud creates a high gas pressure on the inside compared with the outside. This

condition also helps prevent the sputtered getter material from penetrating inside the shroud and contaminating the epitaxial film.

The sputtering chamber of this device includes two sputtering sources. The first sputtering source is for the sputtering of an epitaxial film. The second sputtering source is for the sputtering of reactive materials such as titanium to create getters.

This is the getter pump. The sputtering source for the getter material deposition might be a typical RF (radio frequency) diode sputtering source, or AC, such as at about 13.56 MHz. The getter target thickness must be large enough to provide continuous and simultaneous sputtering of the getter material during the sputtering of the epitaxial film.

The first sputtering source and the substrate are surrounded by a cryogenic shroud, such as a liquid nitrogen shroud. The second sputtering source is mounted outside of the cryogenic shroud. The sputtering of said getter occurs on the outside surface of the cryogenic shroud. During the process of depositing an epitaxial film, the getter effectively absorbs reactive, contaminant gases such as H2, N2, CO, C02, and water vapor that affect the quality of the growing epilayer. A set of shields prevents penetration of the getter material atoms inside the cryogenic shroud, and helps keep the growing epitaxial film free of getter material contamination. The ionized sputtering gas that is utilized to sputter an epitaxial film within the shroud creates a high gas pressure on the inside compared with the outside. This condition also helps prevent the sputtered getter material from penetrating inside the shroud and contaminating the epitaxial film.

In this invention, the first sputtering source 2 and the second sputtering source 4 are preferably, but not necessarily, oriented at approximately ninety degrees with respect to each other, as shown in Figure 1. This arrangement may be desirable inasmuch as the getter material typically deposits on the outside of the shroud, the epitaxial film material deposits on the substrate, the substrate is typically placed to be essentially perpendicular to the walls of the shroud.

In operation, this invention involves an apparatus for film deposition containing (a) a target for sputtering an epitaxial film, (b) a target for sputtering a pumping getter, and (c) a cryogenic shroud interposed between the epitaxial film target and the pumping getter target. In such an apparatus, the cryogenic shroud may be a pumping getter, or the pumping getter may be sputter deposited on the cryogenic shroud. The cryogenic shroud may be a metallic, cylindrically shaped vessel, and may be cooled by liquid nitrogen. The pumping getter target may be a ring, band, coil or collar disposed about the cryogenic shroud, and the material of the pumping getter target may be titanium. The epitaxial film target and the pumping getter target may be located in a single sputtering chamber, and the epitaxial film may have a thickness of greater than one micrometer.

In other embodiments, the invention provides (a) an apparatus for creating a vacuum in a sputter deposition chamber containing a cylindrical, cryogenic pumping getter disposed within the sputter deposition chamber; (b) an apparatus for film deposition containing, within a single sputtering chamber, (i) a target for sputtering an epitaxial film, and (ii) a target for sputtering a pumping getter; (c) an apparatus for film deposition containing, within a

single sputtering chamber, (i) a target, for sputtering an'epitaxial film, that generates contaminants, and (ii) a shroud disposed about the epitaxial film target to reduce the concentration of contaminants within the chamber; or (d) an apparatus for film deposition containing (i) a target for sputtering an epitaxial film, (ii) a target for sputtering a pumping getter, and (iii) a pumping getter interposed between the epitaxial film target and the pumping getter target.

The pumping getter may be cylindrical.

The invention also provides a method of depositing a film by the use of the apparatus of this invention, such as (a) a method of depositing a film by sputtering, in a single sputtering chamber, (i) an epitaxial film material onto a substrate, and (ii) a pumping getter material onto a pumping getter; (b) a method of reducing contamination in a sputtering chamber by sputtering pumping getter material onto a cryogenic pumping getter disposed within the sputter deposition chamber; or (c) a method of reducing contamination in a sputtering chamber by sputtering pumping getter material onto a pumping getter disposed between a target containing the pumping getter material and a target containing material for sputtering an epitaxial film.

In these methods, the epitaxial film and pumping getter may be sputtered simultaneously, and the deposition may occur for at least one hour.