JP2779659B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an improvement in a method of manufacturing an SOI (silicon-on-insulator) substrate, in which one of two silicon wafers bonded together via an insulating film is damaged or contaminated. The purpose of the present invention is to provide a method for manufacturing a bonded long-thin SOI substrate by thinning the film to a uniform thickness without performing a process, and manufacturing a first silicon wafer and a second silicon wafer via an insulating film. Adhering, removing the first silicon wafer or the second silicon wafer from a partial area to form a groove, forming a silicon nitride film on the side wall of the groove, and forming the silicon nitride film on the side wall. Forming a silicon dioxide layer in the formed trench, removing the silicon nitride film, and using the silicon dioxide layer as a stopper to form the first silicon wafer; The wafer or the second silicon wafer is selectively polished to reduce its thickness.

[Industrial applications]

The present invention relates to an improvement in a method for manufacturing a SOI (silicon-on-insulator) substrate.

[Conventional technology]

The SOI substrate is characterized in that isolation between elements is easier than in a bulk substrate, and that the characteristics of the formed element are excellent. Above all, a bonded SOI substrate that can take advantage of bulk crystallinity has attracted attention because of its excellent performance.

As shown in FIG. 2A, the bonded SOI substrate oxidizes the surfaces of the first silicon wafer 1 and the second silicon wafer 2 to form an insulating film 3, and then, as shown in FIG. As shown in the figure, the two are overlapped with the insulating film 3 interposed therebetween and bonded by performing a heat treatment, as shown in FIG.
The thickness of one silicon wafer, for example, the first silicon wafer 1 is reduced, and an element is formed on the silicon layer having the reduced thickness.

On the other hand, as the thickness of the silicon layer on which the element is formed is smaller, the performance of the LSI formed on the element is improved.
In recent years, attention has been paid to an ultrathin SOI substrate in which the thickness of a silicon layer on which an element is formed is 1 μm or less. in this case,
In-plane variation of the thickness of the silicon layer on which the element is formed
Since it is necessary to suppress the variation in the thickness of the supporting substrate, it is impossible to reduce the thickness of the silicon wafer using a grinding technique or a polishing technique based on the back surface.

A conventional technique for thinning one of the bonded silicon wafers will be described below. As shown in FIG. 3 (a), a first silicon wafer 1 and a second silicon wafer 2 are bonded together via an insulating film 3, and one of the silicon wafers, for example, the first silicon wafer 1 is bonded. Grinding is performed to a thickness not less than a thickness required for forming an element. Next, as shown in FIG. 1B, the first silicon wafer 1 and the insulating film 3 are patterned to form a groove 6. Next, a silicon dioxide layer 9 is formed in the groove 6 by thermal oxidation using the mask of silicon nitride or the like used in the previous step (patterning step) as it is, as shown in FIG. I do. When selective polishing is performed using a polishing agent whose polishing rate for silicon dioxide is extremely smaller than the polishing rate for silicon, the upper surface of the silicon dioxide layer 9 formed at the bottom of the groove 6 functions as a stopper. As shown in (d), the surface of the first silicon wafer 1 is uniformly thinned so as to coincide with the upper surface of the silicon dioxide layer 9 formed at the bottom of the groove 6.

[Problems to be Solved by the Invention] By the way, when selectively polishing one of the two bonded silicon wafers, for example, the first silicon wafer 1, of the silicon dioxide layer 9 formed in the groove 6, The silicon dioxide layer formed on the side wall of the groove 6 is peeled off from the first silicon wafer 1, and the stripped silicon dioxide pieces are mixed into the abrasive to polish the surface of the first silicon wafer 1. Damage. In addition, the stripped silicon dioxide pieces adhere to the surface of the first silicon wafer 1 to be polished, and remain without being removed even after cleaning. As a result, the manufacturing yield when devices are formed on this SOI substrate is significantly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate this drawback. One of the two silicon wafers bonded together with an insulating film is thinned to a uniform thickness without damaging or contaminating the surface. It is an object of the present invention to provide a method for manufacturing an ultra-thin bonded SOI substrate with good yield.

[Means for solving the problem]

The above object is achieved by the first silicon wafer (1) and the second silicon wafer (1).
Is bonded through an insulating film (3), and the first silicon wafer (1) or the second silicon wafer (2) is removed from a partial area to form a groove ( 6), a silicon nitride film (7) is formed on the side wall of the groove (6), and the silicon nitride film (7) is formed in the groove (6) formed on the side wall. 8), removing the silicon nitride film (7), and using the silicon dioxide layer (8) as a stopper, the first silicon wafer (1) or the second silicon wafer (2) And a method of manufacturing a semiconductor device having a step of selectively polishing to reduce the thickness.

[Action]

In the method for manufacturing a bonded SOI substrate according to the present invention, a groove 6 is formed in the first silicon wafer 1 or the second silicon wafer 2, and a silicon nitride film 7 is formed on a side wall of the groove 6. The silicon dioxide layer 8 is formed only in the bottom of the groove 6, and is not formed on the side wall of the groove 6. Moreover, in the method for manufacturing a bonded SOI substrate according to the present invention, after removing the silicon nitride film 7 formed on the side wall of the groove 6, the first silicon wafer 1 or the second silicon wafer 2 is polished. Therefore, when the first silicon wafer 1 or the second silicon wafer 2 is polished, the side wall of the groove does not exist. Therefore, when the first silicon wafer 1 or the second silicon wafer 2 is selectively polished by using the silicon dioxide layer 8 as a stopper, the silicon dioxide layer which has been formed as the side wall of the groove in the prior art is used in the present invention. Therefore, it is not possible to peel off the silicon wafer, and therefore, it is possible that the silicon dioxide particles present in the prior art but not present in the present invention may damage or contaminate the silicon wafer surface. The silicon wafer is a silicon dioxide layer 8
The film is uniformly thinned to the same height as the surface.

〔Example〕

Hereinafter, a method for manufacturing a bonded SOI substrate according to an embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 1 (a), the surfaces of the first silicon wafer 1 and the second silicon wafer 2 are oxidized to form an insulating film 3, and the two are overlapped with the insulating film 3 therebetween.
Heat to a temperature of ° C. and bond, one silicon wafer,
For example, the first silicon wafer 1 is ground to reduce its thickness to about 2 μm.

Referring to FIG. 1 (b), a silicon nitride layer 4 is formed on the first silicon wafer 1 using a CVD method, a resist layer 5 is formed thereon, and patterned using a photolithography method. The resist layer 5 is removed from the groove formation region, the silicon nitride layer 4 is dry-etched using carbon tetrafluoride gas using the remaining resist layer 5 as a mask, and then the first layer is formed using carbon tetrachloride or the like. The silicon wafer 1 is dry-etched to form a groove 6 reaching the insulating film 3.

As shown in FIG. 1 (c), the silicon nitride film 7 is heated to 1,050 ° C. and supplied with ammonia gas to perform thermal nitridation.

Referring to FIG. 1D, the insulating film 3 exposed in the groove 6 is removed by etching using hydrofluoric acid to expose the second silicon wafer 2.

As shown in FIG. 1E, the second silicon wafer 2 exposed in the groove 6 is thermally oxidized by heating to about 1,100 ° C. to form a silicon dioxide layer 8 at the bottom of the groove 6. The silicon dioxide layer 8
Is formed such that the surface thereof is higher than the surface where the insulating film 3 is in contact with the first silicon wafer 1 by about 0.5 μm as an example.

Referring to FIG. 1F, the silicon nitride layer 4 formed on the first silicon wafer 1 and the silicon nitride film 7 formed on the side wall of the groove 6 are removed using hot phosphoric acid, and ethylenediamine and colloidal are removed. When the first silicon wafer 1 is selectively polished using a selective polishing method using a mixed solution with silica as an abrasive, the silicon dioxide layer 8 functions as a stopper, and the first silicon wafer 1 Surface and insulating film 3
Is uniformly thinned to a thickness of about 0.5 μm corresponding to the difference in height from the surface in contact with the first silicon wafer 1. The ratio of the polishing rate of the above abrasive to silicon and silicon dioxide was 500: 1, and the silicon dioxide layer 8
Functions well as a stopper.

〔The invention's effect〕

As described above, in the method of manufacturing a semiconductor device according to the present invention, after the silicon nitride film is formed on the side wall of the groove formed in the first silicon wafer or the second silicon wafer, selective polishing is performed in the groove. Is formed only on the bottom of the groove, not on the side wall of the groove. Moreover, in the method for manufacturing a bonded SOI substrate according to the present invention, after removing the silicon nitride film formed on the side walls of the groove, the first silicon wafer or the second silicon wafer is polished. Therefore, when polishing the first silicon wafer or the second silicon wafer, there is no sidewall of the groove. Therefore, in the process of selectively polishing the first silicon wafer 1 or the second silicon wafer 2 using the silicon dioxide layer as a stopper, the silicon dioxide layer which has been formed as the side wall of the groove in the prior art is replaced by the present invention. In this case, it cannot be exfoliated, and therefore, by the silicon dioxide strips that were present in the prior art but not in the present invention,
The surface of the silicon wafer (thinned silicon wafer) will not be damaged or contaminated, and the silicon wafer will be uniformly thinned to the same height as the surface of the silicon dioxide layer 8. The manufacturing yield of the bonded ultrathin SOI substrate can be improved.

[Brief description of the drawings]

1 (a) to 1 (f) are manufacturing process diagrams of an SOI substrate according to one embodiment of the present invention. FIG. 2 is an explanatory diagram of a bonded SOI substrate. FIG. 3 is a manufacturing process diagram of an SOI substrate according to the prior art. DESCRIPTION OF SYMBOLS 1 ... First silicon wafer, 2 ... Second silicon wafer, 3 ... Insulating film, 4 ... Silicon nitride layer, 5 ... Resist layer, 6 ... Groove, 7 ... Silicon nitride film, 8 , 9 ... silicon dioxide layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/76-21/765 H01L 21/304 H01L 27/12

Claims (1)

(57) [Claims] 1. A first silicon wafer (1) and a second silicon wafer (2) are bonded via an insulating film (3), and said first silicon wafer (1) or said second silicon The wafer (2) is removed from a part of the area to form a groove (6).
Forming a silicon nitride film (7) on the side wall of the groove (6); and forming a silicon dioxide layer (8) in the groove (6) having the silicon nitride film (7) formed on the side wall. Forming, removing the silicon nitride film (7), and selectively polishing the first silicon wafer (1) or the second silicon wafer (2) using the silicon dioxide layer (8) as a stopper. A method for manufacturing a semiconductor device, comprising a step of reducing the thickness.