Etching a substrate: processes – Gas phase etching of substrate – Etching a multiple layered substrate where the etching...
Reexamination Certificate
1999-12-13
2001-12-18
Dang, Thi (Department: 1763)
Etching a substrate: processes
Gas phase etching of substrate
Etching a multiple layered substrate where the etching...
C427S248100, C427S255120, C427S398100, C427S534000
Reexamination Certificate
active
06331260
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to thin film deposition, and, in particular, relates to an apparatus and method of making stand-alone thin films.
Most of the single crystal semiconductor wafers produced to date, including silicon and gallium arsenide, have been manufactured by crystal growth techniques that rely on melting of the material. In the Czochralski technique, for example, the purified semiconductor material is first melted in a suitable vessel. Next, a seed crystal is dipped down into the melt and slowly withdrawn. If everything is done right, a long cylinder, called a boule, of the single crystal material is obtained. The boule is sliced up into many thin wafers which are then polished to get the wafers into a usable form for device manufacturing.
An alternative method of growing thin crystalline wafers of a material is to grow the layers by chemical vapor deposition (CVD) onto a single crystal substrate of a different, but readily available material. The process is called heteroepitaxy. Heteroepitaxy takes advantage of the fact that certain single crystal wafers, for example, silicon, are commercially available in large diameters. However, this technique has one major problem that is related to the high temperature (500-1200° C.) required for the CVD process. When the thin film-substrate is cooled down to room temperature after the growth is complete, the difference in the thermal expansion coefficients of the two different materials causes the film-substrate to bow and crack. U.S. Pat. No. 4,368,098, disclosed the deposition of material by the CVD process and is incorporated by reference.
One method of trying to prevent this bowing and cracking has been to grow a buffer layer between the film and the substrate. The paper by R. M. Lum, et al., Appl. Phys. Lett., 51, 36(1987), describes a method for growing gallium arsenide on silicon. It relies on growing a thin semi-amorphous gallium arsenide layer at low temperatures (425° C.) followed by a thicker gallium arsenide layer grown at standard CVD temperatures (about 700° C.). This method is shown to improve the crystalline quality. However, this technique is not totally successful in removing all of the stress induced by the thermal expansion differences.
A second method described by S. Sakai, Appl. Phys. Lett., 51, 1069(1987) involves pre-stressing the substrate in the opposite direction of the thermal expansion difference induced stress. This is accomplished by placing a substrate on a graphite holder with a screw-like push rod pushing against the back of the substrate (See FIG. 2 of the above) until the substrate is bowed. The holder and substrate are then placed in the CVD hot zone, heated up to growth temperature and the film is then grown on the substrate. The holder and substrate are then cooled to room temperature and the substrate is removed. The technique has two main drawbacks. First, it would be difficult to design a reactor injection system that would grow uniformly thick films across the whole wafer. Second, the technique will only work with substrates that are not brittle and break when stressed
SUMMARY OF THE INVENTION
This invention, referred to as Vapor Deposition (VD) of Stand-alone Films, is a process and apparatus for producing single crystal, polycrystal or amorphous stand-alone films. The process has two steps: First, thin layers of the desired materials are deposited by VD onto a hot foreign single crystal substrate wafer held by a substrate holder. The second step is to chemically etch away the substrate while still being held by the substrate holder while the film-substrate is still hot. The etch is stopped as soon as all of the foreign substrate is consumed. This leaves just the thin film which is then cooled down to room temperature.
The substrate holder of the present invention has therein a pocket for the substrate. The bottom surface of this space has a plurality of channels for carrying an etching gas which is input by a central channel in the substrate holder.
The thin films can be deposited by any of the various VD methods. The standard CVD process relies on thermal decomposition of the reactants on the substrate to produce the thin film material. However, other types of variations of VD could be used in this invention as long as the process also involves heating the substrate during deposition. The heating during deposition is key because it is the cooling of the film-substrate from the deposition temperature that causes the materials to become stressed (due to the difference in the thermal expansion coefficients). For example, plasma assisted CVD and D.C. or RF sputtering are commonly used to produce crystalline and/or polycrystalline thin films. Other VD processes such as Molecular Beam Epitaxy (MBE) could in principle, be used. The only limitation on the VD method that is used is that the process system hardware must be able to handle the hot etching gases and byproducts without corrosion induced problems. Thus, MBE could be used to vapor deposit the films but because it is an ultra-high vacuum system, it would cause more problems than it is worth. The typical CVD system hardware on the other hand is made to handle corrosive materials. Therefore, the preferred implementation that is described in the following paragraphs will be a CVD system that has a cooled reactant injector system such as in U.S. Pat. No. 5,129,360.
This invention is a process for growing free standing thin (<0.025″) crystalline or amorphous large diameter (2″-10″) wafers without the bowing and/or cracking. Silicon and gallium arsenide wafers used in the semiconductor industry are examples of commercially available substrates that would be usable by this invention.
Therefore, one object of the present invention is to provide a process for producing a stand-alone thin film.
Another object of the present invention is to provide a substrate holder for use in a VD apparatus having therein an actively cooled effusion device.
Another object of the present invention is to provide a process for the deposition of a thin film on a substrate and the removal of that substrate to leave the thin film.
Another object of the present invention is to provide a process for producing stand-alone thin films without any stress defects therein.
Another object of the present invention is to provide a process for the removal of a deposited thin film from a substrate at or about the deposition temperature.
These objects and many other objects and advantages of the present invention will be readily apparent to one skilled in the pertinent art from the following detailed description of a preferred embodiment of the invention and the related drawings.
REFERENCES:
patent: 5270077 (1993-12-01), Kenemeyer et al.
patent: 5270294 (1993-12-01), Wu et al.
patent: 5314652 (1994-05-01), Simpson et al.
Ahern Brian S.
Weyburne David W.
Collier Stanton E.
Dang Thi
The United States of America as represented by the Secretary of
LandOfFree
VD process and apparatus for producing stand-alone thin films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with VD process and apparatus for producing stand-alone thin films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and VD process and apparatus for producing stand-alone thin films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2588514