Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-06-25
2002-01-01
Anderson, Bruce (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200, C250S492300, C250S42300F, C250S424000, C313S359100, C313S363100, C315S111210, C315S111610
Reexamination Certificate
active
06335535
ABSTRACT:
DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for implanting hydrogen ions to a predetermined depth of the overall body of a semiconducting substrate, such as silicon (Si), an insulating substrate made of SiC, glass, or plastic, or a metal substrate. This invention further relates to an implanting apparatus.
2. Background of the Invention
Purposes for implanting hydrogen ions into a substrate fall into two categories. One of these types is directed to forming a weak porous layer (a void layer) in the substrate by implanting hydrogen ions to shear the substrate. The other type is directed to improving the physical properties of a required object. These various purposes for performing of implantation of hydrogen will now be described in greater detail.
1. Implantation of Hydrogen Ions for the Purpose of Manufacturing SOI Substrate
A Silicon On Insulator (SOI) substrate is a substrate having single crystal Si on an insulating layer thereof. A portion of the SOI substrate has a thick insulating substrate on which Si is placed (a Si/insulating substrate). For example, a structure is known in which a thin Si film is formed on sapphire. However, hetero growth on different crystal suffers from frequent crystal defects. No cleavage can be used and, thus, the cost cannot be reduced. Therefore, a major portion of SOI substrates have a triple-layer structure, the overall body of which is made of Si, and in which a thin insulating layer and single crystal Si exist (Si/insulating layer/Si substrate). The insulating layer is made Of SiO
2
. That is, the triple-layer structure is Si/SiO
2
/Si substrate.
The Si wafer is a low-cost wafer and those having a high quality can easily be obtained. Since the SOI substrate has a structure in which Si is formed on Si, the lattice constant is the same and the number of defects is small. Since cleavage exists, separation of the device can easily be performed. To manufacture the foregoing substrate, an inner porous layer is formed by implanting hydrogen ions. Then, another Si wafer is bonded to perform shearing at the porous layer, and then the surface is polished so that the SOI is manufactured. The foregoing method will be described in greater detail below.
2. Implantation of Hydrogen Ions to Manufacture Single Crystal Si/Glass Substrate
A substrate for a liquid crystal device incorporates a multiplicity of thin-film transistors manufactured on amorphous silicon (a-Si) on a glass plate. Although the foregoing structure is a main portion of the foregoing substrate, the mobility of carriers of a-Si is too low to realize a high speed operation. At present, substrates for liquid crystal devices having the highest performance incorporate a thin polycrystal silicon film (p-Si) formed on a glass substrate. Since mobility of electrons is superior to that of a-Si, high speed operation is realized. The foregoing structure has been suggested in, for example, Technical Report of Sharp Corporation “Low-Temperature Polysilicon TFT-LCD”, Vol. 69, pp. 64 (1997), written by Takashi Itoga, Masataka Ito and Hiroshi Takato.
However, a satisfactory result has not been realized from the foregoing technique. The polycrystal has a multiplicity of grain boundaries, causing scattering of electrons to occur frequently. As compared with single crystal Si, the mobility of electrons is unsatisfactory. Since a multiplicity of grain boundary levels exist in the grain boundary of the polysilicon, electrons are scattered. Therefore, an attempt has been made to decrease the grain boundary levels by implanting hydrogen ions. For example, a suggestion has been made in Japanese Patent Laid-Open No. 8-97432 entitled “Method of Manufacturing Thin-Film Semiconductor Apparatus” filed by Nobuaki Suzuji. According to the foregoing disclosure, when annealing is performed by implanting hydrogen ions, hydrogen terminates Si in the grain boundaries. Thus, the levels can be decreased and the mobility is, therefore, raised.
The polycrystal thin Si film, however, has another problem as well as the low mobility. Since electric currents easily flow along the grain boundary of the polycrystal Si, a great leak current flows between the source and the drain. Therefore, a complicated LDD structure is required. As a result, the SOG (System On Glass) has no possibility of realization. The SOI is used such that hydrogen is implanted into Si to form a porous layer so as to be bonded to a glass plate. Then, a Si substrate is sheared from the porous layer to bond the single crystal thin Si film to the glass substrate. Since the substrate is made of glass in place of Si, a void cutting method can be employed which is similar to the method for manufacturing SOI. Therefore, a method may also be employed in which hydrogen is implanted into a Si wafer to form a weak layer so as to be bonded to a glass plate. Then, the Si layer is thinly separated so that the single crystal Si/oxide/glass layer structure is manufactured.
3. Modification of Solar Cell
At present, solar cells using silicon for electric power mainly use monocrystalline silicon, polycrystalline silicon, amorphous silicon or the like. The amorphous silicon is cheap but its photoelectric conversion efficiency is low (about 8%). On the other hand, the photoelectric conversion efficiency of the monocrystalline and polycrystalline silicon can be 15 to 20%. Accordingly, the latter is mainly used.
The monocrystalline or polycrystalline silicon solar cell is cut similarly to a semiconductor substrate. Accordingly, the thickness of the monocrystalline or polycrystalline silicon solar cell should be 500 &mgr;m to 600 &mgr;m per one sheet. Most of the sheet is wasteful. In order to obtain the photoelectric conversion efficiency of 15 to 20%, it is sufficient that the thickness is several &mgr;m to 20 &mgr;m. Therefore, the void cut method by hydrogen ion implantation is used. The following two methods are generally used for this purpose:
(1) Hydrogen atoms are implanted to the depth of several &mgr;m by the acceleration energy of several hundred KeV to several MeV to perform the void cut.
(2) Hydrogen atoms are implanted to the depth of several tens nm to several &mgr;m to perform the void cut. The insufficient film thickness is made up by expitaxial growing before or after the void cut.
4. Implanting Hydrogen Ions into SiC
A method has been suggested with which a similar void cutting method is employed to manufacture a thin SiC film. The SiC is a semiconductor capable of resisting high temperature and permitted to be used for another purpose. A suggestion has been made about a method of manufacturing a thin SiC film by employing a method similar to that for manufacturing the SOI by forming a porous layer into which hydrogen ions have been implanted and by performing delamination. See “Thin-Film Delamination by Implanting H
+
and Application of Thin-film delamination to SiC”, previous thesis for associated lectures of 45-th relative association, 29
a
-K-2, pp. 803 (1998). However, a substrate having satisfactory qualities has not been manufactured yet. While a variety of attempts have been made, no device has been realized.
As known, the Si-On-Insulator substrate (a so-called SOI substrate) incorporating a single crystal Si semiconductor layer formed on an insulating material has a variety of advantages, for example, high density integration and capability of manufacturing a high-speed device as compared with a usual bulk Si substrate. Therefore, much research and development has been carried out in a multiplicity of facilities. The foregoing advantages have been disclosed in, for example, Special Issue: “Single-crystal silicon on non-single-crystal insulators”; edited by G. W. Cullen, Journal of Crystal Growth, vol. 63, No. 3, pp. 429-590 (1983), which notes that two methods may be available to manufacture the SOI substrate. One is a method (SIMOX) for forming an oxide silicon layer by directly implanting oxygen ions. Another method is a bonding manufacturing method called the void cutting method or a smart cut
Hayashi Tsukasa
Kuwahara Hajime
Miyake Koji
Anderson Bruce
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nissin Electric Co., LTD
Wells Nikita
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