JPH03252131A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide the upper corner of a trench with curvature and form the trench, and to form the diameter of the trench in 0.8mum or less by forming the trench to a composite film using a reflow film and an upper layer, making the reflow film reflow, covering the side face of a lower layer film and forming the trench while employing the composite film as a mask. CONSTITUTION:A process in which two layers or more of a composite film 15 using a reflow film 14 as an upper layer is shaped onto a semiconductor substrate 1, a process in which a trench 17 is formed to the composite film 15, a process in which said reflow film 14 is made to reflow through heat treatment and the side faces of lower layer films 12, 13 are covered, and a process in which a trench 19 is shaped to the semiconductor substrate 11 while employing said composite film 15 as a mask are provided. The oxide film 12, the silicon nitride film 13 and the boron or phosphorus-containing oxide film 14 are formed onto the silicon substrate 11, and a trench 17 is formed to the composite film 15 while using a photo-resist 16 as a mask. The photo-resist 16 is removed, the boron or phosphorus-containing oxide film 14 is made to reflow through heat treatment, the lower layer films 12, 13 are covered, and a trench 18 having curvature is shaped. The trench 19 is formed while employing the trench 18 made to reflow as a mask.

Description

DETAILED DESCRIPTION OF THE INVENTION [Structure of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for forming a trench.

(Prior Art) A trench used in a semiconductor device is used for DRAM (Dy
nastic Random Access Mea+
It is used for increasing the capacitive electrode surface of 3D ory) and for element isolation of various devices.

A trench forming method in a conventional semiconductor device manufacturing method will be described below with reference to the drawings.

FIGS. 2(a) to 2(c) are cross-sectional views illustrating a conventional trench forming method.

First, as shown in FIG. 2(a), about 1000 oxide films 22 are grown on a silicon substrate 21 by thermal oxidation.
A silicon nitride film 23 of about 1,500 layers is deposited on the oxide film 22 by a low pressure CVD method, and an undoped oxide film 24 of about 6,000 layers is deposited on the silicon nitride film 23 by a normal pressure CVD method to form a composite. A film 25 is formed.

Next, in order to form a desired trench, as shown in FIG. Film 25 is anisotropically etched to form grooves 27 to form trenches in silicon substrate 21.

Next, as shown in FIG. 2(C), the photoresist 26
After removing the etching using an oxygen plasma ashing method and a sulfuric acid-hydrogen peroxide mixture, a trench 28 is formed in the silicon substrate 21 using the composite film 25 as a mask using a reactive ion etching technique.

As described above, when a trench is formed using the conventional trench forming method, the shape of the trench is vertical as shown in FIG. 2(e) and the enlarged view of FIG. The shape will be . For this reason, the electric field concentrates at the acute upper corner 35, causing an increase in leakage current and significantly deteriorating the electrical characteristics of the capacitor.

Furthermore, as IC chips are currently becoming more highly integrated, trenches with a trench diameter of 0.8 μm or less are becoming necessary. However, in the conventional trench forming method, the trench diameter is determined using current photolithography technology.
It is difficult to form a trench diameter of 8 μm or less.

(Problems to be Solved by the Invention) As described above, in the trench forming method in the conventional semiconductor device manufacturing method, the upper corner of the trench has an acute angle shape, and the electric field is concentrated at the upper corner, resulting in a leakage current. This caused a significant increase in the electrical characteristics of the capacitor.

Furthermore, with the current photolithography technology that determines the trench diameter, it has not been possible to form a trench diameter of 0.8 μm or less.

The present invention provides a method for manufacturing a semiconductor device, the purpose of which is to form a trench by giving a curvature to the upper corner of the trench, and further to form a trench with a diameter of 0.8 μm or less. be.

[Configuration of the Invention (Means for Solving the Problem) In order to achieve the above object, the present invention includes a step of forming a composite film of two or more layers with a reflow film as an upper layer on a semiconductor substrate; A semiconductor substrate comprising the steps of: forming a groove in the film; reflowing the reflow film through heat treatment to cover the side surfaces of the underlying film; and forming a groove in the semiconductor substrate using the composite film as a mask. This is the manufacturing method.

(Function) In the trench forming method of the present invention, a composite film of two or more layers including a reflow film as an upper layer is formed on a semiconductor substrate, a groove is formed in the composite film, and the reflow film is reflowed by heat treatment. A trench is formed in the semiconductor substrate by covering the side surfaces of the lower layer film and using the resulting composite film as a mask.

In a trench forming method using reactive ion etching technology, the shape of the composite film serving as a mask is reflected in the shape of the trench. In the present invention, a reflow film is used as the upper layer film of the composite film that serves as a mask, and after the reflow film is reflowed, the composite film that serves as a mask for the trench has a curvature, so the upper corner of the trench is can have curvature. By allowing the upper corner of the trench to have a curvature, electric field concentration can be alleviated. Invention curve 4
1, it is possible to reduce the leakage current and significantly improve the electrical characteristics as a capacitor compared to the conventional technology.

In addition, since the sides of the groove of the composite film that serves as a mask are covered with a reflow film, the groove becomes narrower by that much, so the trench diameter is reduced to 0.8
A trench of μm or less can be formed.

(Example) Examples will be described with reference to the drawings.

First, as shown in FIG. 1(a), an oxide film 12 of about 1,000 layers is grown on a silicon substrate 11 by a thermal oxidation method, and a silicon nitride film of about 1,500 layers is grown on the oxide film 12 by a low-pressure CVD method. A film 13 is deposited on the silicon nitride film 13 by normal pressure CV.
Approximately 6,000 people used phosphorus-boron-containing film (reflow film) 1 using D method.
4 is deposited to form a composite film 15 of the oxide film 12, silicon nitride film 13, and phosphorus-boron containing film 14.

Next, as shown in FIG. 1(b), the phosphorus-boron containing film 1
A photoresist 16 is applied on top of the photoresist 16 in the area to be etched to form the desired trench.
6 is removed using photolithography technology. After removal, the composite film 15 is anisotropically etched using a reactive ion etching technique to form grooves 17.

Next, as shown in FIG. 1C, after removing the photoresist 16 using an oxygen plasma ashing method and a sulfuric acid-perhydrogen mixture, heat treatment is performed to reflow the phosphorus-boron-containing oxide film 14. , a groove 18 with curvature is formed by covering the lower layer film (oxide film 12 and silicon nitride film 13).

Finally, as shown in FIG. 2(d), using the grooves 18 formed in the reflowed composite film 15 as a mask, the composite film 15 is
and silicon substrate 11 are anisotropically etched using reactive ion etching technology to form trenches 19.

When a trench is formed using the trench forming method as described above, the reflowed composite film serves as a mask for the trench, as shown in FIG. 1C.

Since the shape of the trench is reflected in the shape of the composite film serving as a mask, the upper corner of the trench can have a curvature. Therefore, electric field concentration at the upper corner of the trench could be alleviated, and leakage current could be reduced. Therefore, it was possible to significantly improve the electrical characteristics as a capacitor.

In addition, since the sides of the groove of the composite film that serves as a mask are covered with a reflow film, the groove becomes narrower by that amount, so the trench diameter is 0.8μ.
m or more trenches can be formed.

In this embodiment, a case has been described in which a phosphorus-boron-containing oxide film deposited by atmospheric pressure CVD is used as a reflow film when forming a trench.

A similar effect can be obtained using an oxide film containing at least one impurity such as arsenic.

[Effects of the Invention] As described above in detail, according to the trench forming method for a semiconductor device of the present invention, a reflow film is used as the upper layer film of the composite film that serves as a mask for forming the trench. A trench with curvature can be formed at the upper corner of the trench, which can alleviate the electric field concentration at the upper corner of the trench.
Leakage current can be reduced. Moreover, a trench with a trench diameter of 0.8 μm or less could be formed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1(a) to 1(d) are cross-sectional views showing the manufacturing process of a semiconductor device of the present invention. FIGS. 2(a) to 2(c) are cross-sectional views showing the manufacturing process of a conventional semiconductor device. FIG. 3 is a sectional view showing problems in the prior art. FIG. 4 is a diagram comparing the electrical characteristics of the prior art and the embodiment of the present invention. 11.21.31... Silicon substrate 12.22
．． 32...Oxide film 13.23.33...Silicon nitride film 14
... Phosphorous boron containing film 15.25 ...
...Composite film 6, 26 7, 27 9, 28 4, 34 ...Photoresist ... Groove ... Reflow groove ... Trench ......Undoped oxide film...Trench top corner...Electrical characteristics of the present invention...Electrical characteristics of conventional technologyヲ１→ Saishin Hammer

Claims (2)

[Claims] (1) A step of forming a composite film of two or more layers including a reflow film on a semiconductor substrate as an upper layer, a step of forming a groove in the composite film, and a step of reflowing the reflow film by heat treatment to form a side surface of the lower layer film. A method of manufacturing a semiconductor device, comprising: a step of covering the semiconductor substrate; and a step of forming a groove in a semiconductor substrate using the composite film as a mask. (2) The method of manufacturing a semiconductor device according to claim 1, wherein the reflow film is a silicon oxide film containing at least one type of impurity such as phosphorus, boron, arsenic, or germanium.