JPH02312283A - Formation of insulating film on polycrystalline silicon film - Google Patents

Abstract

PURPOSE:To improve a capacitance between a floating gate and a control gate in stability and reliability by a method wherein a polycrystalline silicon oxide film is formed, and then the silicon oxide film is turned into an N<+>-type through the ion implantation of N<+>-type impurity. CONSTITUTION:A silicon oxide film 2 is formed using a P-type silicon substrate 1, and a polycrystalline silicon film 3 is formed. Then, a polycrystalline silicon oxide film 4 is formed, and the polycrystalline silicon film 3 is turned into an N<+>-type by the implantation of phosphorus through the polycrystalline silicon oxide film 4. Therefore, the polycrystalline silicon oxide film 4 is formed uniform in thickness in a wafer, and in a non-volatile memory provided with a floating gate formed of a polycrystalline silicon film, an oxide film on the floating gate becomes stable in thickness. By this setup, a capacitance between a floating gate and a control gate can be improved in stability and reliability.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of forming an insulating film on a polycrystalline silicon ridge, and particularly to a method of forming an insulating film with excellent film thickness uniformity. [Summary of the Invention] This invention provides a method for forming an insulating film on a polycrystalline silicon film by ion-implanting N° type impurities after forming an insulating film on a polycrystalline silicon film in a step of forming an insulating film on an N° type packed crystalline silicon film. By making the silicon layer N-type, excellent film thickness uniformity of the insulating film is provided. [Prior Art] Fig. 2+a) to (cl) are cross-sectional views showing the order of steps for forming a thermal oxide film on a general polycrystalline silicon. is formed, and a polycrystalline silicon film 13 is formed. (
FIG. 2(a)) Thereafter, the polycrystalline silicon layer 13 is made into an N-type by a phosphorus diffusion method. (FIG. 2(b)) Next, a polycrystalline silicon thermal oxide film 14 is formed. (FIG. 2(C)) [Problems to be Solved by the Invention] A thermally oxidized film on a polycrystalline silicon film made into an N° type by a phosphorus diffusion method has the following problems. The oxidation rate of the N-type polycrystalline silicon film is much higher than that of crystalline silicon. Therefore, the oxidation rate of the N-type polycrystalline silicon film is much higher than that of crystalline silicon. Variations in the phosphorus concentration of the polycrystalline silicon layer result in non-uniform oxide film thickness within the wafer. The oxide film thickness uniformity within the wafer surface by the conventional method of forming a polycrystalline silicon oxide film is shown in Figure 3 by the chain line. The axis represents the number of times a polycrystalline silicon oxide film is formed. However, the uniformity of the oxide film thickness within the wafer surface is the result of measurement at five points: top, middle, bottom, left, and right, excluding one area around the wafer. (Means for solving the problem) In order to solve the above problem, instead of forming a polycrystalline silicon film and converting it into N-type by phosphorus diffusion immediately after forming a polycrystalline silicon oxide film, The polycrystalline silicon oxide film is made into an N-type by ion implantation of type impurities. In a nonvolatile memory with a floating gate made of polycrystalline silicon, the thickness of the oxide film on the floating gate is stable, so the capacitance between the floating gate and the control gate is also stable, resulting in a highly desirable nonvolatile memory. [Example] The present invention will be described below based on an example.
1~(C1 is a cross-sectional view showing the order of steps for forming a polycrystalline silicon insulating film of the present invention. Using a 6-inch P-type silicon substrate 1, a silicon oxide film 2
11,000 polycrystalline silicon films 3 are formed (FIG. 1(a)). After this, polycrystalline silicon thermal oxidation 1124 is formed (FIG. 1+bl), and then phosphorus ion implantation is performed through the polycrystalline silicon oxide film 4 to convert the polycrystalline silicon film 3 into an N-type. (Figure 1 (C)
)). The uniformity of the oxide film thickness within the wafer surface according to the method of forming a polycrystalline silicon oxide film of the present invention is shown by a solid line in FIG. Third
As is clear from the figure, the film thickness uniformity of the polycrystalline silicon oxide film of the present invention is much better than that of the conventional polycrystalline silicon oxide film.

【Effect of the invention】

The polycrystalline silicon oxide film of the present invention has a uniform oxide thickness within the wafer. In a nonvolatile memory that has a floating gate made of polycrystalline silicon, the thickness of the oxide film on the floating gate is stable, so the capacitance between the floating gate and the control gate is also stable, making it possible to provide a highly reliable nonvolatile memory. .

[Brief explanation of the drawing]

Figure 1 fat~ (C1 is a sectional view showing the order of forming steps for a polycrystalline silicon oxide film of the present invention, Figure 2 fal~ (C1 is a sectional view showing the order of steps for forming a conventional polycrystalline silicon oxide film,
FIG. 3 is a characteristic diagram showing the film thickness uniformity of a conventional polycrystalline silicon oxide film and a polycrystalline silicon oxide film of the present invention. ■...P-type silicon substrate 2...Silicon oxide film 3...Polycrystalline silicon film 4...Polycrystalline silicon oxide film Applicant Seiko Electronics Co., Ltd. Agent Patent attorney Keisuke Hayashi-ichi ~l P-type silicon group 4 anti-m--1 Shape and process of polycrystalline silicon oxide film 'RAM surface diagram not shown 1 Figure 11 Drinking surface old figure 2

Claims (1)

[Claims] A polycrystalline silicon film comprising the steps of forming a polycrystalline silicon film, forming a thermal oxide film on the polycrystalline silicon film, and ion-implanting N^+ type impurities through the thermal oxide film. How to form the upper insulating film.