Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-06-28
2004-05-18
Pham, Long (Department: 2814)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S149000
Reexamination Certificate
active
06737307
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method for microelectronics fabrication and the microelectronic structure formed and more particularly, relates to a method for forming amorphous silicon films on a single crystal silicon substrate and the semiconductor structure formed.
BACKGROUND OF THE INVENTION
In semiconductor fabrication technology, thin films of silicon that does not have a single crystal structure are frequently used in forming microelectronic devices. These non-single crystal silicon includes amorphous silicon and polycrystalline silicon. For instance, amorphous silicon is widely used in the formation of TFT (thin film transistor) devices and for CMOS gates when a dual gate process is used. Polysilicon films have numerous applications in forming microelectronic devices including gate conductors in MOSFETs when the films are heavily doped, as a dopant source for contacts of shallow junctions in bipolar transistors, and as a conducting layer for interconnections. The amorphous and polysilicon thin films can be formed by a variety of chemical vapor deposition techniques, i.e. LPCVD (low pressure chemical vapor deposition), PECVD (plasma enhanced chemical vapor deposition) and RTCVD (room temperature chemical vapor deposition). The amorphous silicon films can also be formed by a physical vapor deposition technique. The chemical vapor deposition technique is carried out typically by the decomposition process of a silicon-containing gas, such as silane (SiH
4
) or disilane (Si
2
H
6
) with or without a diluting gas of argon. For a LPCVD process, the typical deposition temperature runs between 500° C. and 700° C. at a typical chamber pressure from 100 mTorr and 500 Torr. The structure of the silicon film deposited, i.e. of either amorphous or polycrystalline, depends mainly on the deposition temperature. For instance, amorphous silicon films are normally deposited at a deposition temperature below 575° C. A transition between the amorphous structure and the polycrystalline structure occurs between the temperature of 575° C. and 600° C. such that polycrystalline silicon is normally deposited at a temperature higher than 580° C. The amorphous silicon structure which has no detectable crystallinity can be converted to polycrystalline structures upon further heat treatment above 600° C. The grain size increases upon heat treatment at even higher temperatures.
When an amorphous silicon film is directly deposited on top of a single crystal silicon substrate, problems of surface imperfection is frequently observed. The surface imperfection appears in the form of unevenness due to irregularly formed protrusions, or islands on the top surface of the amorphous silicon film layer. The obtaining of a smoothly deposited surface of the amorphous silicon film on top of a single crystal silicon substrate is therefore impossible. This leads to difficulties in using amorphous silicon films in various microelectronic applications incorporating the MEMS (micro-electro-mechanical-system) technique such as the fabrication of a cantilever beam for a micro-relay, or in the fabrication of a suspended mirror in a digital mirror display, or in a glass-to-glass bonding application, or in the solar cell application. In the above discussed microelectronic applications that incorporate the MEMS technique, an amorphous silicon film that has a smooth top surface and a minimum defect density on the top surface must be obtained.
For instance, in the application of the cantilever beam for the micro-relay and the suspended mirror in the digital mirror display, a key element for the MEMS process is the capability of growing a relatively thick amorphous silicon film that has a smooth top surface. The amorphous silicon film is frequently used as a sacrificial layer, i.e. to be later removed, in these applications. While currently the amorphous silicon film may be grown by LPCVD, PECVD or PVD, various processing difficulties exist that prevent the successful implementation of these deposition techniques. For instance, in order to form an amorphous silicon film that has low surface defect density by the LPCVD method, the deposition temperature must be around 550° C. which is not compatible with the CMOS process. On the other hand, when the amorphous silicon film is deposited by the PVD technique, the film produced has poor adhesion and thus greatly limits its deposition thickness.
It is therefore an object of the present invention to provide a method for forming amorphous silicon films on single crystal silicon substrates that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for forming amorphous silicon films that have low defect density and a smooth top surface on a single crystal silicon substrate.
It is a further object of the present invention to provide a method for forming amorphous silicon films-on single crystal silicon substrates that are compatible with a front-end CMOS process.
It is another further object of the present invention to provide a method for forming amorphous silicon films on single crystal silicon substrates that does not require an annealing process after the deposition.
It is still another object of the present invention to provide a method for forming amorphous silicon films on single crystal silicon substrates that can be integrated with a MEMS process.
It is yet another object of the present invention to provide a semiconductor structure of an amorphous silicon film deposited on a single crystal silicon substrate with a smooth top surface on the amorphous silicon film.
It is still another further object of the present invention to provide a semiconductor structure on a single crystal silicon substrate that includes a single crystal silicon substrate, a buffer layer on top of the substrate, and an amorphous silicon film deposited on top of the buffer layer.
It is yet another further object of the present invention to provide a semiconductor structure that is built on a single crystal silicon substrate including a buffer layer of silicon oxide, silicon nitride, silicon carbide or metal in-between an amorphous silicon film and a single crystal silicon substrate.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for forming amorphous silicon films that have low defect density on a single crystal silicon substrate and structures formed are provided.
In a preferred embodiment, a method for forming amorphous silicon films with low defect density on single crystal silicon can be carried out by the operating steps of providing a single crystal silicon substrate; depositing a buffer layer in a material capable of surviving a process temperature of 500° C. on top of the single crystal silicon substrate, the buffer layer has a thickness of at least 500 Å; and depositing an amorphous silicon film on a top surface of the buffer layer.
The method for forming amorphous silicon films with low defect density on single crystal silicon may further include the step of selecting the material for the buffer layer from the group consisting of silicon oxide, silicon nitride, silicon carbide and metals, or the step of depositing the buffer layer to a thickness between about 500 Å and about 1500 Å, or the step of depositing the buffer layer by a technique selected from the group consisting of chemical vapor deposition, plasma enhanced chemical vapor deposition and physical vapor deposition. The method may further include the step of depositing the amorphous silicon film by a technique selected from the group consisting of plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, room temperature chemical vapor deposition and physical vapor deposition, or the step of depositing the amorphous silicon film to a thickness between about 1 &mgr;m and about 10 &mgr;m, or the step of depositing the amorphous silicon film in a deposition chamber fabricated of stainless steel.
The method for forming amorphous silicon films with low
Kuo Nai-Hao
Lee Yuh-Wen
Liu Wen-Jiun
Tsai Po-Hao
Industrial Technology Research Institute
Tung & Associates
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