JPS61276226A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an oxide film having superior insulation characteristics on the surface of the silicon substrate, which has a solid configuration, of a silicon semiconductor element and to improve the reliability of the element by a method wherein a thermal oxidation is performed to the silicon substrate at a specific temperature, an oxide film of a specific thickness is formed and after the oxide film is removed, the desired oxide film is formed. CONSTITUTION:A thermal oxidation is first performed to the surface of a silicon substrate 11 having a solid configuration at 900 deg.C or more, an oxide film 16 of 100Angstrom or less is formed and after this oxide film is removed, the desired oxide film 17 is formed. For example, an oxide film is adhered on the silicon substrate 11, part of the oxide film, which is located on the element forming region, is removed by performing a normal photo etching and masking materials 12 are formed. Then, an anisotropic etching is vertically performed on the silicon substrate 11 by an RIE using the same masking materials 12 as masks and a groove part 13 is formed. After that, the masking materials 12 are removed, a thermal oxidation is performed once at 900 deg.C or more in an oxidizing atmosphere and after the oxide film 16 of 100Angstrom or more and 500Angstrom or less is formed, the oxide film 16 is etched away and coner parts 14 and 15 in the groove part 13 are made round. After that, the gate oxide film 17 and a gate electrode 18 are formed and the grooved capacitor is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor device, and for example, to a method for manufacturing a MOS canister on a silicon substrate having a three-dimensional shape.

[Technical background of the invention and its problems]

When a thermal oxide film is formed on a silicon surface having a three-dimensional shape, a phenomenon is observed in which the oxide film is thinner in concave or convex parts of the silicon surface than in flat parts. The cause of this is due to the depressions or protrusions on the silicon surface.
This is because the oxidation rate decreases in this area due to the concentration of stress that occurs during thermal oxidation. The concentration of stress becomes more pronounced as the radius of curvature of the concave or convex portions becomes smaller, and therefore the possibility of thinning the film increases. Furthermore, in concave or convex parts, the electric field is concentrated due to the three-dimensional shape, so the Fowl in this part is
The er -Nordheim current increases significantly and the insulation properties of the oxide film deteriorate.

This can be explained using the case of a trench-horizontal capacitor in Figure 4 (a).
) to (C) will be briefly explained. First, Figure 4 (
As shown in a), a P-type (100) silicon substrate 21 having a specific resistance of about 5 to 50 [ΩIll'fi-1 is prepared, and a mask material n is formed on the element formation region of this substrate 11. Next, as shown in FIG. 2(b), the silicon substrate 21 is anisotropically etched using the mask material n as a mask, for example, to a depth of 2 (
A groove B of approximately 1.0 μm is formed. Thereafter, as shown in FIG. 2C, a gate oxide film and a gate electrode δ are formed by thermal oxidation in the trench portion A, thereby creating a trench capacitor.

However, this type of conventional method has the following problems. That is, when forming the gate oxide film, the oxidation rate is slower at the convex corners A and the concave corners τ than at the flat areas, so that the gate oxidation [2
4, the film thickness at the corner portion 1617 is thinner than that at the flat portion. Furthermore, since electric field concentration also occurs at the corner portions 16 and 17, the Fowler of the gate oxide film
-The Nordhefm current increases and the insulation properties are significantly degraded compared to the case of a flat capacitor.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing a semiconductor device that can improve the insulating properties of an oxide film when it is formed on a silicon surface having a three-dimensional shape, thereby increasing the reliability of the device.

[Summary of the Invention] The present invention involves thermally oxidizing a silicon surface having a three-dimensional shape at at least 900°C or higher to form an oxide film with a thickness of 100λ or more and 500Å or less, and then removing this oxide film by etching, or Thermal oxidation is performed in an oxidizing atmosphere containing less than 10% of hydrogen chloride to form an oxide film, and this oxide film is then removed by etching to give the silicon surface a rounded shape. This method suppresses the local thinning of the oxide film and the concentration of electric fields.

〔Effect of the invention〕

According to the present invention, the shape of trees on the silicon surface can be rounded. Specifically, FIGS. 2(a) to 3(C) and 3(a) to 3(C) show cases of concave corners and convex corners, respectively. When the concave corner 31 shown in FIG. 2(a) is thermally oxidized, an oxide film 32 is formed as shown in FIG. 2(1)). The concentration of stress that occurs at the corners during oxidation slows down the oxidation rate at the corners.
The interface between the oxide film 32 and silicon is rounded. 'When the oxide film 32 is removed by etching, the silicon surface becomes rounded as shown in FIG. On the other hand, when the silicon surface having the convex corners 41 shown in FIG. 3(a) is thermally oxidized, an oxide film 42 is formed as shown in FIG. 3(b). During oxidation, stress concentration occurs at the corners, but at temperatures above 900°C, the viscous flow of the oxide film has a stress-relieving effect, which prevents the oxidation rate from decreasing.
As shown in the figure, the interface between the oxide film 42 and silicon is rounded. This effect is further enhanced when the oxidizing agent contains hydrogen chloride in an amount of 10% or less. When the 0 oxide film 42 is removed by etching, the silicon surface becomes rounded as shown in FIG.

By rounding the three-dimensional silicon surface as described above, it is possible to prevent local thinning of the oxide film and concentration of electric fields during subsequent oxidation, and the insulation properties of the oxide film are significantly improved. do.

[Embodiments of the invention]

FIGS. 1A to 1C show cross-sectional views of the manufacturing process of a Mizohori capacitor according to an embodiment of the present invention. First, as shown in Figure 1 (→), P type (100
) A silicon substrate (semiconductor substrate) 11 is prepared, an oxide film of about 0.8 μm is deposited on this substrate 11, and the oxide film on the element formation area is removed by performing a normal photolithography process. to form the mask material ratio. Next, as shown in the same figure (b), using the same mask material blade, a silicon substrate 31 t-IE
The groove portion 13 is formed by anisotropic etching of 2 (μm) vertically. Thereafter, the mask material 12 is removed, and the corners 14 and 15 of the groove 13 are rounded using this manufacturing method. That is, as shown in FIG.
After forming oxidation [16] of 0λ or less, this is removed by etching. Alternatively, once the oxide film 16 is formed by thermal oxidation in an oxidizing atmosphere containing 10% or less hydrogen chloride, this is removed by etching. Thereafter, a gate oxide film 17 and a gate electrode 18 are formed by a well-known method as shown in FIG.

Thus, according to this embodiment, the corners of the trench in the trench-horizon capacitor can be rounded, which prevents the gate oxide film from becoming thinner at the corner and from concentrating the electric field at the corner, thereby improving the reliability of the device. can be improved.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various changes without departing from the gist thereof.

FIG. 4 is a cross-sectional view showing a method of rounding the capacitor, and FIGS.

11, 21... silicon substrate (semiconductor substrate), 12
, 22...mask material (silicon oxide film), 13,
23... Groove portion, 16, 32, 42... Oxide film, 14, 26, 41... Convex corner, 15
, 27 , 31 ... concave corner, 17 , 24 ...
Gate oxide film, 18,5...gate electrode.

Agent: Patent attorney: Kensuke Chika (and 1 other person) Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) When oxidizing a silicon surface having a three-dimensional shape, a step of thermally oxidizing the silicon surface at least at 900° C. or higher to form an oxide film with a thickness of 100 Å or more and 500 Å or less, and a step of removing the oxide film; A method of manufacturing a semiconductor device, comprising the step of: thereafter forming a desired oxide film on the silicon surface. (2) When oxidizing a silicon surface having a three-dimensional shape, there is a step of thermally oxidizing the silicon surface in an oxidizing agent atmosphere containing 10% or less hydrogen chloride to form an oxide film, and a step of removing the oxide film. A method for manufacturing a semiconductor device, comprising the steps of: and then forming a desired oxide film on the silicon surface.