JPH02125427A - Forming method for contact hole - Google Patents

Abstract

PURPOSE:To simply form a fine contact hole having a satisfactory step coverage by forming a hole corresponding to a contact hole pattern, forming a resist skirt with taper in the inward direction of the hole, then isotropically etching an insulating film, and further anisotropically etching the resist skirt under the conditions of gradually rearward etching. CONSTITUTION:A hole 14A corresponding to a contact hole pattern is formed at a resist layer 14, and a resist skirt 14a tapered in the inward direction of the hole 14A is formed. Then, with the layer 14 as a mask an insulating film 12 is isotropically etched to form a recess 12A having larger maximum opening size W1 than the minimum opening size corresponding to the hole 14A. Then, a contact hole 12B gradually decreasing the opening size in a depthwise direction in a range smaller than the maximum opening size W1 of the recess 12A is so formed by anisotropically etching under the conditions of gradually etching rearward the skirt 14a as to arrive at the surface of semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a contact hole forming method used in manufacturing semiconductor devices and the like.

[Summary of the Invention] The present invention involves dividing the etching process into two steps, an isotropic etching process and a subsequent anisotropic etching process, when forming a contact hole in an insulating film by etching using a resist layer as a mask. In the anisotropic etching process, the contact hole is formed so that the opening size gradually decreases in the depth direction by using regressive etching of the tapered resist bottom in the resist hole, thereby making the contact hole finer and forming a step. This made it possible to improve coverage.

[Prior Art] Conventionally, as a method for forming contact holes in LSI etc.,
A device as shown in FIG. 8 is known.

In FIG. 8, an insulating film 2 made of silicon oxide or the like is formed on the surface of a semiconductor substrate l. insulation! ! After forming a resist layer 3 on top of 2.

Holes 3A are formed in the resist layer 3 by exposing and developing according to a desired contact hole pattern. Then, heat treatment is applied to the resist layer 3 having the holes 3A to soften the resist, so that the resist skirt portions 3a within the holes 3A are tapered and further spread inward. Thereafter, a contact hole 2A is formed by subjecting the insulating film 2 to an anisotropic etching process using the resist layer 3 as a mask. In this case, the resist hem 3a recedes (etches backward) due to etching, so
The inner wall surface 2a of the contact hole 2A is inclined outward (
The opening size gradually decreases in the depth direction).

[Problems to be Solved by the Invention] According to the above-mentioned prior art, the inner wall surface 2a of the contact hole 2A has an inclined shape, so that when a wiring metal such as Au is deposited over the contact hole 2A, a step is formed. Although step coverage can be improved to some extent, it is not necessarily sufficient.

Furthermore, when forming the tapered resist skirt 3a by utilizing the softening of the resist, it is difficult to control the minimum opening size W of the hole 3A with good reproducibility, especially when forming a small-sized contact hole. Then, the opening size W may become zero, and a situation may arise in which the contact hole 2A cannot have a desired slope. Therefore, the above-mentioned conventional techniques have the problem of being unsuitable for forming fine contact holes.

An object of the present invention is to easily form fine contact holes with good step coverage.

[Means for Solving the Problems] The contact hole forming method according to the present invention includes forming a resist layer on an insulating film covering a conductor, and then subjecting this resist layer to exposure and development according to a desired contact hole pattern. to form a hole corresponding to the contact hole pattern and form a resist foot tapered inwardly of the wire hole, and then perform an isotropic etching process on the insulating film using the resist layer as a mask. A recess with a maximum opening size larger than the minimum opening size is formed corresponding to the hole, and the insulating film is anisotropically etched using the resist layer as a mask under conditions such that the resist foot is gradually etched backwards. The present invention is characterized in that a contact hole whose opening size gradually decreases in the depth direction within a range smaller than the maximum opening size of the recess is formed so as to reach the conductor from the recess by performing a chemical etching process.

[Function] According to the contact hole forming method of the present invention, the tapered resist bottom portion is formed not by resist softening treatment but by exposure and development treatment, so that it is possible to form fine contact holes.

In addition, after forming the recesses by isotropic etching,
By using an anisotropic etching process that involves regressive etching of the bottom of the resist, a contact hole whose opening size gradually decreases in the depth direction within a range smaller than the maximum opening size of the recess is formed. It has a roundness corresponding to the curvature of the inner wall of the recess, and the profile exhibits an inclination at a depth deeper than the recess, resulting in an improvement in step coverage compared to a conventional simple inclined surface.

[Example] Figures 1 to 3 show a contact hole forming method according to an example of the present invention, and the steps (
1) to (3) will be explained in order.

(1) Semiconductor substrate such as silicon! A resist layer 14 is deposited on an insulating film 12 of silicon oxide or the like covering the surface of the resist layer 12 by a known method. Then, by exposing and developing the resist layer 14 according to a desired contact hole pattern, holes 1 corresponding to the contact hole pattern are formed.
4A, and a resist hem 14a tapered inward of the hole 14A.

(2) Next, using the resist layer 14 as a mask, the insulating film 12 is
By performing an isotropic etching process on the hole υ 14A, a recess 12A having a maximum opening size W1 larger than its minimum opening size Wo is formed corresponding to the hole υ 14A. In this case, either wet etching or dry etching may be used as the isotropic etching process, but the etching conditions are such that the resist hem 14a is not etched backwards.Usually, the inside of the recess 12A is selected. The wall surface 12a is formed in a curved shape.

(3) Next, by performing an anisotropic etching process on the insulating film 12 using the resist layer 14 as a mask under such conditions that the resist foot 14a is gradually etched backward, the maximum opening size W1 of the recess 12A is reduced. A contact hole 12B whose opening size gradually decreases in the depth direction within a small range is formed in the recess 12.
It is formed so as to reach the semiconductor surface from A. As the etching progresses, the resist bottom portion 14a recedes, so that the inner wall surface 12b of the contact hole 12B is formed to be inclined outward.

If the minimum opening size of the contact hole 12B is W2,
w2''=Wo. Furthermore, if the minimum opening size of the hole 14A at the end of etching is W3, this has the relationship W2<W3<W with respect to Wt and W2.

In this case, if an etching device with a low power density such as a Burr 7-inch type RIE (reactive ion etching) device is used, the resist bottom portion 14a is less likely to recede. To do this, the power must be increased, which increases the ion bombardment.

This lowers the selectivity with respect to the underlying semiconductor.

On the other hand, in single-wafer high-density plasma etching equipment that uses polymer deposition to obtain anisotropy,
The resist foot portion 14a can be retreated without reducing the selectivity with respect to the underlying semiconductor. Therefore, in carrying out this invention.

Preferably, a single-wafer high-density plasma etching apparatus is used.

In the anisotropic etching process shown in FIG.
The etching conditions were controlled so that the profile of B showed a linear slope.
It is also possible to obtain a profile as shown in FIG.

FIG. 4 shows that the power (high frequency power) density is increased stepwise as etching progresses as shown in FIG.
This figure shows a cross section of the contact hole when etching is finished at time o, and the profile of the contact hole 12B shows a polygonal slope.

FIG. 5 shows the cross section of the contact hole when the power density is continuously increased as the etching progresses as shown in FIG. It shows a curved slope.

[Effects of the Invention] As described above, according to the present invention, it is possible to form fine contact holes with good step coverage.
This has the effect of realizing highly reliable electrodes and wiring in semiconductor devices such as SI.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of a substrate showing a contact hole forming method according to an embodiment of the present invention, and FIGS. 4 and 5 are
6 and 7 are cross-sectional views of the substrate showing other different embodiments of the anisotropic etching process, respectively. The figure is a cross-sectional view of a substrate showing an example of a conventional contact hole forming method. 10... Semiconductor substrate, 12... Insulating film, 12A.
...Concave portion, 12B...Contact hole, 12a, 1
2b...Inner wall surface, 14...Resist layer, 14a...
...Resist hem.

Claims (1)

[Claims] 1. (a) depositing a resist layer on the insulating film covering the conductor; and (b) exposing and developing the resist layer according to a desired contact hole pattern. (c) isotropically etching the insulating film using the resist layer as a mask; (d) forming a recess corresponding to the hole and having a maximum opening size larger than the minimum opening size by etching the resist under conditions such that the resist skirt is gradually and regressively etched; A contact hole whose opening size gradually decreases in the depth direction within a range smaller than the maximum opening size of the recess is formed so as to reach the conductor from the recess by performing anisotropic etching on the insulating film using the layer as a mask. A contact hole forming method including a process. 2. The contact hole forming method according to claim 1, wherein in the anisotropic etching process, the etching conditions are changed stepwise so that the profile of the contact hole exhibits a polygonal slope. 3. Contact hole formation according to claim 1, characterized in that in the anisotropic etching process, the etching conditions are continuously changed so that the profile of the contact hole exhibits a smooth curved slope. Law.