JPH02294031A - Formation of trench - Google Patents

Abstract

PURPOSE:To improve the dielectric strength of an insulating film by performing isotropic and anisotropic etching when a silicon substrate is etched and forming large angular bevels at the upper edge of a trench. CONSTITUTION:When anisotropic etching is successively performed to the surface of a silicon substrate 1 while the degree of vacuum is lowered to a prescribed value after an oxide film 2 which acts as a mask is formed on the surface of the substrate 1 and isotropic etching is performed to the surface of the substrate 1 under a prescribed condition by reactive ion etching, a trench 3 with angular bevels at its upper edge is formed. Since the upper edge of the trench 3 is largely beveled in the course of the isotropic etching process, concentration of electric fields can be relieved. Therefore, the dielectric strength of an insulating film 5 can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a trench for a trench capacitor in a semiconductor memory device, and particularly to a method for forming a trench for a trench capacitor in a semiconductor dynamic random access memory. It is. (Prior Art) In recent years, the density of semiconductor memory devices has been increasing, and in particular, the density and integration of dynamic random access memories (hereinafter referred to as DRAMs) have been remarkable. The development of DRAM is largely due to the development of high-density formation technology for memory cells, which occupy more than half of the chip size. One of the technologies for increasing density is the trench capacitor structure. A method of forming a trench capacitor used in a conventional DRAM will be explained with reference to FIG.

FIGS. 2(a) to 2(C) are enlarged cross-sectional views of essential parts showing the process of forming a conventional trench capacitor. Figure 2 (a
), first, a III oxide 2 serving as a mask is formed on the surface of a silicon substrate 1, and then a trench 3 is formed by etching. Next, after removing the oxide film 2 that served as a mask, the trench 3
In order to round off the upper edge, when it is placed in a heating furnace and subjected to fake oxidation treatment, an oxide film 4 is formed over the entire surface as shown in FIG. 2(b).

Next, after removing the oxide film 4, an insulating film 5 and a T-shaped electrode 6 are formed on the inner wall surface of the trench 3 and the edge surface along the inner wall surface of the trench 3, and the trench capacitor shown in FIG. 2(c) is formed. (Improved reliability of trench capacitors,
Se++iconductor World, 198
7. 8 Shinozaki, Watanabe). (Problem to be Solved by the Invention) However, in the above formation method, the roundness of the upper edge of the trench 3 formed by the fake oxidation treatment is small, so the voltage resistance of the insulating film 5 is reduced due to electric field concentration at the edge. The problem was that it was inferior.

The present invention solves the above-mentioned problems and provides a method for forming a trench that allows a trench capacitor with excellent voltage resistance to be obtained.

(Means for Solving the Problems) In order to solve the above problems, the present invention performs isotropic etching and anisotropic etching when etching a silicon substrate.

(Function) Due to the above-mentioned horizontal formation, the upper edge of the trench is largely chamfered in the isotropic etching process, which alleviates the concentration of electric field and greatly improves the voltage resistance of the insulating film.

(Example) An embodiment of the present invention will be explained with reference to FIG.

FIGS. 1(a) to 1(c) are enlarged cross-sectional views of essential parts showing the order of steps for forming a trench capacitor according to the present invention.

In FIG. 1(a), first, an oxide film 2 serving as a mask is formed on the surface of a silicon substrate 1, and then reactive ion etching (hereinafter referred to as RIE) is used to perform etching at 300 nm.
W, 70mTorr, SF. /CCIl. =1
After isotropic etching is performed under the conditions of 30/10 3CCH, the vacuum level is lowered to 15 mTorr and anisotropic etching is performed to form a trench 3 with a chamfered upper edge. .

Next, after removing the oxide film 2 that served as the mask, an insulating film 5 is formed on the inner wall surface of the trench 3 and the edge surface along this.
and form the electrode 6.

As described above, according to this embodiment, the chamfered corners formed at the upper edges of the trenches 3 have obtuse angles, which alleviates the concentration of the electric field, and therefore greatly improves the voltage resistance of the insulating film. In this embodiment, the conventionally used fake oxidation process is omitted, but if the fake oxidation process is performed before forming the insulating film 5, a capacitor with a more stable high voltage resistance can be obtained.
Furthermore, it goes without saying that the present invention can be applied not only to trench capacitors but also to trench gates.

(Effects of the Invention) As described above, according to the present invention, a large corner chamfer is formed on the upper edge of the trench, so that the voltage resistance of the insulating film can be greatly improved.

[Brief explanation of drawings]

FIGS. 1(a) to (C) are enlarged cross-sectional views of essential parts showing the order of forming steps for a trench capacitor of the present invention, and FIGS. 2(a) to (C) show steps for forming a conventional trench capacitor. FIG. 3 is an enlarged cross-sectional view of main parts. 1... Silicon substrate, 2, 4... Oxide film, 3
... trench, 5 ... insulating film, 6 ...
·electrode. Patent applicant Matsushita Electronics Co., Ltd.

Claims (3)

[Claims] (1) A method for forming a trench by etching for forming a trench capacitor or the like on the surface of a silicon substrate, which method is characterized in that the trench is formed by isotropic etching and anisotropic etching. (2) The trench forming method according to claim (1), characterized in that wet etching and dry etching are combined. (3) Claim (1) characterized in that two or more of the conditions for dry etching, such as applied power, pressure, type of reaction gas, and gas flow rate, are used in combination. Trench formation method described.