Fishing – trapping – and vermin destroying
Patent
1993-10-21
1996-01-02
Hearn, Brian E.
Fishing, trapping, and vermin destroying
437 62, 437974, 148DIG50, 148DIG135, H01L 2176
Patent
active
054808324
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for fabrication of a semiconductor device and particularly to a manufacturing method preferred for isolating elements from each other by forming a deep trench on a silicon substrate.
BACKGROUND ART
Up to now a method for isolating respective elements from each other by means of an insulator has been known as a element isolating method used in a monolithic semiconductor integrated circuit.
In the Japanese patent Application Laid Open No. 59852-1986, for example, a semiconductor device manufacturing method of isolating elements from each other by forming an isolation trench on a bonded SOI (silicon on insulator) substrate is disclosed. This method is the one which makes an SOI substrate by bonding a silicon substrate 42 with another silicon substrate 40 on which surface an insulating film 41 is formed as shown in FIG. 36(A) through an insulating film 41 as shown in FIG. 36(B), forms isolation trenches 43 reaching to the insulating film 41 in the SOI substrate from one main surface of this SOI substrate, then forms an insulating film 44 on the surface of the SOI substrate including inside walls of the isolation trench 43 by thermal oxidation or the like as shown in FIG. 36(C), fills the isolation trenches 43 with polysilicon 45 as shown in FIG. 36(D), removes extra parts of the insulating film 44 and polysilicon 45 which comes out from the isolation trenches 43, and electrically completely isolates respective element areas 46 from the substrate 40 or from each other by means of an insulator as shown FIG. 36(E).
As disclosed on page 66 of a reference paper "Ultra-Fast Silicon Bipolar Technology", for example, a method for forming an isolation trench for isolating respective elements from each other after forming a field oxide film which has a thick portion and a thin portion on the main surface of a silicon substrate is known as a method for forming an isolation trench. The method will be described in the following.
As shown in FIG. 37, the method forms one by one in order a partially trick field oxide film 32, a silicon nitride film 33 and a silicon oxide film to be used as a mask on the main surface of a silicon substrate 31, forms an opening by selectively etching the field oxide film 32, the silicon nitride film 33 and the silicon oxide film 34 in an area where the field oxide film is thin in thickness, then forms an isolation trench 35 by etching the silicon substrate 31 through the opening. And it etches off the silicon oxide film 34 used as a mask, forms an insulating film 36 on an inside wall of the isolation trench 35, then fills polysilicon 37 in the isolation trench 35. Further, it performs etching back of the polysilicon 37 deposited on the silicon nitride film 33 when filling the isolation trench with the polysilicon 37, etches off the silicon nitride film 33, and then forms a silicon oxide film 38 on the top of the polysilicon 37 in the isolation trench (see FIG. 38). In this manner, the method electrically divides completely the silicon substrate 31 into respective element areas by the isolation trench 35 and the insulating film 36.
In a series of manufacturing treatments shown in FIG. 36(A) to 36(E), up to now as described above, an oxide film is generally formed on the surface of an SOI substrate as a mask for forming an isolation trench on the SOI substrate. And the oxide film used as the mask for forming an isolation trench has been removed at once after forming the isolation trench. However as shown in FIG. 36(E), in case of isolating an element area 46 by insulating film 41 from a substrate 40, an insulating film for isolating from the substrate is exposed inside the isolation trench immediately after forming the isolation trench. In this case, since the insulating film 41 inside the SOI substrate for isolating substrate and the oxide film for the mask have about equal etching rate, so that, if attempting to etch off the oxide film as the mask immediately after forming the isolation trench, the insulating film inside the substra
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Komura Atsushi
Miura Shoji
Sakakibara Toshio
Sugisaka Takayuki
Dang Trung
Hearn Brian E.
Nippondenso Co. Ltd.
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