JPH02240963A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to form an Si island in a smooth tapered shape without a steep step by a constitution wherein the Si island whose side wall has a tapered shape and which comprises an SOI(Silicon On Insulator) structure by sacrificial oxidation. CONSTITUTION:A silicon semiconductor layer 13 is formed on an insulator substrate 11. A mask pattern which has an opening part selectively on the silicon semiconductor layer 13 is used, and the silicon semiconductor layer 13 is selectively oxidized. A selective oxide film 15 whose end part intrudes into the lower part of the periphery of the opening part in a tapered shape is formed. Then, the selective oxide film 15 is selectively etched, and a silicon semiconductor island whose side wall has a tapered shape is formed. In this way, the side wall of the Si island having an SOI structure can be formed in the smooth tapered shape. Thus, a transistor having a mesa type structure without breakdown at steps, etching remnant and deterioration in gate breakdown strength can be obtained. Leakage from a part between a source and a drain due to radiation damage can be suppressed.

Description

[Detailed Description of the Invention] [(Already Required)] To solve the problem of a method for forming Si islands in SO■, where when the side walls of the Si islands have an acute angle, they cause step breakage in the electrodes and a decrease in the withstand voltage of the insulating film. [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and in particular to a method for manufacturing a semiconductor device, in which the sidewalls of 5olO3t islands are tapered by sacrificial oxidation.
The present invention relates to a method for forming Si islands using a method of forming Si islands (con-on-in-layer). In radiation-resistant devices, thick isolation films are subject to significant radiation damage and cause source-drain leakage. SOt has the advantage that it can be formed into a mesa structure and does not require the use of a thick isolation film between elements. Therefore, radiation damage can be reduced and leakage between the source and drain can be prevented.

[Conventional technology]

FIG. 4 shows a typical conventional method for forming Si islands in 301. As shown in FIG. 4(a), Si is deposited on the surface of the Si substrate 1.
After forming the insulation 11!2 of O□ or sapphire, a Si layer 3 is formed on the entire surface. Then, selective etching is carried out using a resist mask or the like using an ordinary photolithography method to form Si islands 3' as shown in FIG. 4(b).

[Problem to be solved by the invention]

Since the side wall of the Si island formed as described above has a steep cape, when a gate oxide film 4 and a gate 5 are subsequently formed thereon, for example, as shown in FIG. 4(C), the step becomes steep. Therefore, when the gate 5 is etched, a gate etching residue 6 is generated, which may cause a short circuit in the circuit.

Further, as shown in FIG. 4(d), when forming the lower layer wiring 7 on the Si island 3 and then forming the glabellar insulating film 8 and the upper layer wiring 8, if the step of the Si island is sharp, the glabellar insulating film 8 will be coverage 9
(Therefore, there is a possibility that the upper layer wiring 8 may be broken 10).

Therefore, an object of the present invention is to provide a method for forming Si islands into a smooth tapered shape without sharp steps.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a step of forming a silicon semiconductor layer on an insulating substrate, and selecting the silicon semiconductor layer using a mask pattern having selective openings on the silicon semiconductor layer. oxidizing to form a selective oxide film whose end portion tapers into the lower part of the periphery of the opening, and selectively etching the selective oxide film to form a silicon semiconductor island having a tapered sidewall. Provided is a method for manufacturing a semiconductor device characterized by comprising the steps of:

[For production]

According to the sacrificial oxidation method of the present invention, Si islands with very smooth sidewall shapes are formed. Since the shape of the selective oxide film is formed symmetrically with respect to the active Si surface, the above problem does not occur under normal selective oxidation conditions, so even when etched with this film, there are no problems such as step cuts or etching residuals. . In addition, by controlling the thickness of Si3N4, it is possible to obtain Si islands with a continuous curved shape.
Even if the gate oxide is formed at low temperature, local thinning is no longer caused (Dah-Bin Kao et al., (I
international Electron Devi
ce Meeting 1985 * 388),
Deterioration of gate oxide film breakdown voltage can be prevented.

(Example) Si substrate 11. Si is placed on a Sol substrate whose surface is oxidized 12.
A St layer 13 for forming an island is formed to a thickness of 5000 mm. Furthermore, the surface of the 33 layer 13 is oxidized to a thickness of 100
After forming the initial oxide film (not shown), Si3N, film 1
4 to a thickness of 1000. Then, the Si, N, film 14 and the initial 5iO1 film thereunder are patterned to serve as a mask for selective oxidation. Setting the ratio of the thickness of the 5iJa film 14 to the initial oxide film to be 10 or more is convenient for obtaining a selective oxide film with sidewalls having smooth curves.

[FIG. 1(a)] Next, the 5iJi 13 is selectively oxidized using the 5iJa film 14 as a mask. The resulting selective oxide film 15 enters the lower part of the <<5isNa film 14 in a tapered shape, as shown in FIG. 1(b), and is vertically symmetrical.

The 5isNa film 14 is removed, and the selective oxide film 15 is further removed selectively with respect to Si using a conventional method. The Si island 13' obtained in this way is complementary to the shape of the selective oxidation 1115, and has a tapered shape with a smooth slope. [1st
FIG. 2(C)] FIG. 2(a) shows a case where a wiring layer is formed on the Si island thus obtained. Further, FIG. 2(b) shows a case where a wiring layer is formed on the selective oxide film formed as shown in FIG. 1(b), but in this case, there is no problem such as disconnection in the wiring layer. It is known. On the other hand, as mentioned above, since the Si island in FIG. 2(a) and the selective oxide film in FIG. 2(b) have substantially symmetrical shapes, there is also a disconnection in the wiring layer on the Si island in FIG. 2(a). There are no other problems.

FIG. 3 shows an example in which the Si&13' fabricated in FIG. 1 is used as a substrate, and a gate oxide film 16 with a thickness of 200 mm and a gate electrode 17 made of aluminum with a thickness of 14 mm are formed thereon.

Since the step in such a gate electrode 17 is gentle,
There is no disconnection as described above, and even when the gate electrode 17 is patterned, no etching residue is generated as shown in FIG.

The taper etching method for SiN has been known for a long time, but in taper etching, the taper end is sharply cut, although it has an obtuse angle, so when a gate oxide film and a gate electrode are formed on top of it, the sharp corner will cause damage. There is a problem that the withstand voltage decreases.

Conventionally, although Sol is suitable for radiation-resistant elements, as explained earlier, there were problems with the conventional method of forming Si islands, so a thick inter-element isolation film formed on the surface of the Si substrate was used. At that time, impurities that would increase the impurity concentration of the Si substrate were placed under the element isolation film to counter radiation damage.

However, increasing the impurity concentration infinitely leads to a decrease in the junction breakdown voltage between the substrate and the drain, so there is a practical restriction. However, according to the method of the present invention,
It becomes possible to manufacture a Sol structure without step cuts, etching residues, and deterioration of gate breakdown voltage, and it can be put to practical use in radiation-resistant elements.

〔Effect of the invention〕

According to the present invention, it is possible to form the side wall of the Si island of the 501 structure into a smooth tapered shape, and as a result, it is possible to form a transistor or star with a mesa structure without step breakage or deterioration of etching residual gate withstand voltage. leakage between the source and drain due to radiation damage can be suppressed.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining the steps of the embodiment, and FIG. 4 is a diagram for explaining the conventional method. 11...Si substrate, 12-...Si0g insulating film, 13...5iJi, 13'...Si
Island, 14...Si, N, film, 15...Selective oxide film, 16...Gate oxide film, 17...Gate electrode. (a) (a) (b) (b) Figure 2 13'' Example 1 Figure 63

Claims (1)

[Claims] 1. Forming a silicon semiconductor layer on an insulating substrate, selectively oxidizing the silicon semiconductor layer using a mask pattern having selective openings on the silicon semiconductor layer,
A step of forming a selective oxide film whose end portion tapers into the lower part of the periphery of the opening, and a step of selectively etching the selective oxide film to form a silicon semiconductor island having a tapered side wall. A method of manufacturing a semiconductor device, comprising: