JPH0344032A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To process the side surface of a polycrystalline silicon electrode in the form of a normal taper, by forming a first polycrystalline silicon film on a semiconductor substrate via an insulating film, selectively etching at the same time a doped polycrystalline silicon film which is formed continuously, and forming a pattern. CONSTITUTION:A thermal oxidation film 2 is formed on a semiconductor substrate 1. A polycrystalline silicon film 3a is formed by low pressure CVD method, and a polycrystalline silicon film 3b is formed while PH3 gas is continuously introduced. The polycrystalline silicon films 3a, 3b of two-layer structure formed in the preceding process are selectively etched by dry etching method, thereby forming a pattern. Isotropic etching is performed under the condition that difference in etching rate is generated by phosphorus concentration in the polycrystalline silicon film, and thus the side face shape is turned into a normal taper. Thereby excellent step coverage of an interlayer insulating film and a conducting film formed in the subsequent process can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a semiconductor device using a polycrystalline silicon layer as an electrode.

2. Description of the Related Art A conventional semiconductor device having polycrystalline silicon as an electrode will be described below. FIGS. 2(a) to 2(C) show an example of a manufacturing process diagram of a conventional semiconductor device. In FIG. 2, 1 is a semiconductor substrate, 2 is an oxide film, 3 is a polycrystalline silicon film, 4 is an oxide film, and 5 is a conductive film. The manufacturing process of the semiconductor device configured as described above will be described below. First, as shown in FIG. 2(a), a thermal oxide film 2 is formed on a semiconductor substrate 1. After forming this polycrystalline silicon film 2, impurities such as phosphorus are doped to lower the resistance value of the polycrystalline silicon film 2, as shown in FIG. 2(b). Next, as shown in FIG. 2(C), after a step of selectively etching the polycrystalline silicon film 2 to form a desired pattern, an oxide film 4 is formed by the CVD method, and then a conductive film 5 is formed. form. The conductive film 5 is patterned and used as wiring.

Problems to be Solved by the Invention However, in the above-mentioned conventional manufacturing process, the polycrystalline silicon film is selectively etched to form a pattern, and the sides of the polycrystalline silicon electrode become steeply shaped. The step coverage of the oxide film 4 and the conductive film 5 formed in the process deteriorates.

Therefore, problems such as leakage in the same layer of the conductive film 5 processed with wiring and poor reliability occur.

The present invention solves the above-mentioned conventional problems, and aims to improve the side surface shape of a patterned polycrystalline silicon electrode and provide good step coverage for interlayer insulating films and conductive films formed in subsequent steps. With the goal.

Means for Solving the Problems In order to achieve many of the objects, the method for manufacturing a semiconductor device of the present invention includes forming a first polycrystalline silicon film on a semiconductor substrate via an insulating film, and then continuously applying a doping gas. After passing through the step of forming a second polycrystalline silicon film while introducing the first. The method includes a step of selectively etching the second polycrystalline silicon layer to form a pattern.

According to the present invention, when selectively etching a polycrystalline silicon layer, the etching rate of the doped second polycrystalline silicon film is faster than that of the undoped first polycrystalline silicon film. By choosing the conditions, the polycrystalline silicon electrode dimensions are smaller at the top than at the bottom. Therefore, the side surface shape of the polycrystalline silicon electrode becomes a forward taper, and it is possible to achieve good step coverage of an interlayer insulating film and a conductive film formed in a later process.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIGS. 1(a) and 1(b) are process diagrams showing a method for manufacturing a semiconductor device in an embodiment of the present invention. In FIG. 1, 1 is a semiconductor substrate, 2 is an oxide film, 3a is an undoped polycrystalline silicon film, 3b is a phosphorus-doped polycrystalline silicon film, 4 is an oxide film, and 5 is a conductive film.

The manufacturing process of the semiconductor device configured as described above will be explained below.

As shown in FIG. 1(a), first, a thermal oxide film 2 is formed on a semiconductor substrate 1. As shown in FIG. Next, a polycrystalline silicon film 3a is formed by low pressure CVD, and a polycrystalline silicon film 4 is formed while continuously introducing PH3 gas.

By introducing PH3 gas, the growth rate of the film decreases, but by adjusting the temperature distribution and pressure inside the furnace, the cutting speed can be reduced.
It is possible to obtain a film thickness distribution.

Next, as shown in FIG. 1(b), the two-layered polycrystalline silicon films 3a and 3b formed in the previous step are selectively etched by dry etching to form a pattern. There are two types of etching conditions: a method in which patterning is completed by anisotropic etching and then isotropic etching is performed, or a method in which etching is performed from the beginning under conditions intermediate between anisotropic and isotropic. In both methods, the isotropic etching conditions are such that the etching rate varies depending on the phosphorus concentration in the polycrystalline silicon film, so that the side shape of the polycrystalline silicon electrode is forward tapered (i.e., the side surface of the electrode is tapered). The cross-sectional shape is trapezoidal), and it is possible to achieve good step coverage of an interlayer insulating film and a conductive film formed in a later process.

Effects of the Invention As described above, according to the present invention, a first polycrystalline silicon film is formed on a semiconductor substrate via an insulating film, and a doped polycrystalline silicon film that is continuously formed is simultaneously selected. By selectively etching and forming patterns,
By processing the side surface shape of the polycrystalline silicon electrode into a forward tapered shape, a semiconductor device with excellent quality can be realized.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are process diagrams showing the manufacturing method of the present invention, and FIGS. 2(a) to (C) are process diagrams showing the manufacturing method according to the conventional method. 1... Semiconductor substrate, 2, 4... Oxide film, 3... Polycrystalline silicon film, 5... Conductive film.

Claims (1)

[Claims] forming a first polycrystalline silicon film on a semiconductor substrate via an insulating film, and further forming a second polycrystalline silicon film while continuously introducing a doping gas;
, a step of selectively etching a second polycrystalline silicon layer to form a pattern; and a step of heat-treating the first and second polycrystalline silicon layers in an N_2 atmosphere. Production method.