JP2000223478A - Method of opening connection hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of opening a minute connection hole, in accordance with a desired pattern, without producing a bowing shape. SOLUTION: In this method, the gas where He gas is mixed in the gas, having fluorocarbon for its main components in the range of flow ratio of He gas to all etching gas being not less than 60% volume % or over and 90 volume % or under, is used as etching gas when opening a connection hole 58 piercing a silicon oxide film 54, by etching a silicon oxide film 54 by plasma etching method. When opening a connection hole high in aspect ratio, the flow ratio of He gas to all etching gas is put in the range of 70 volume % or over and 85 volume % or under. As fluorocarbon, at least either CH2F2 or C4F8 can be used. The gas having fluorocarbon for its main components includes CO gas and O2 gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of opening a connection hole, and more particularly to a method of opening a connection hole having a straight hole wall without showing a bowing shape.

[0002]

2. Description of the Related Art In a process of manufacturing a semiconductor device, particularly in a process of forming a wiring, a lower wiring or a diffusion region of a substrate and an upper wiring formed thereon via an interlayer insulating film (silicon oxide film). Must be electrically connected. Usually, in such a case, a contact hole is formed to penetrate the silicon oxide film, expose a lower wiring or a diffusion region of the substrate, and then fill the contact hole with a conductor to form a contact. By forming an upper wiring so as to connect to the contact, the lower wiring or the diffusion region of the substrate and the upper wiring are connected via the contact.

Here, a conventional method of forming a contact hole when forming a contact will be described with reference to FIG. FIGS. 4A to 4C are cross-sectional views of the substrate in each step when a contact hole is opened according to a conventional method. In the conventional opening method, first, FIG.
As shown in FIG. 1A, a silicon oxide film 14 is formed on a silicon substrate 12. Next, a photoresist film is applied on the silicon oxide film 14 and patterned, and FIG.
As shown in FIG.
Is formed with the mask 16 for etching. Next, a fluorocarbon-based gas reactive with the silicon oxide film, for example, CF ₄ , CHF ₃ , CH ₂ F ₂ ,
The silicon oxide film 14 is etched by a plasma etching method using an etching gas containing C ₄ F ₈ as one of the main components, and a contact hole 18 is opened as shown in FIG.

[0004]

By the way, with the increase in the degree of integration and miniaturization of the semiconductor device, the hole diameter is 0.25 μm.
It is required to form the following fine contacts and, therefore, contacts having a necessarily high aspect ratio. In order to form a fine contact, it is necessary to open a contact hole having a fine and straight hole wall and a high aspect ratio.

However, the above-described conventional contact hole opening method has the following two problems. First,
When the oxide film is plasma-etched to open the contact hole, there is a problem that the hole shape bows as shown by the broken line in FIG. If the contact hole has a bowing shape, the coverage of the buried metal deteriorates in the step of burying the contact hole following the opening of the contact hole. As a result, it is difficult to satisfactorily fill the contact hole (form a plug), causing defects such as voids and sheaths, and further, a disconnection phenomenon may occur due to voids in the contact.
That is, it is difficult to form a contact with high electrical connection reliability.

Second, when an attempt is made to open a contact hole having a large aspect ratio, first, as shown in FIG. 6A, the opening of the etching mask is etched to change its shape. As shown in FIG. 6B, there is a problem that the shape near the opening above the contact hole changes from a predetermined shape due to a change in the shape of the resist serving as an etching mask, and the size of the opening increases. On the other hand, with the miniaturization of semiconductor devices, it is necessary to open a contact hole having a large aspect ratio, and when the size near the opening of the contact hole becomes large, it becomes necessary to increase the pitch of the contact hole. An obstacle to integration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming fine connection holes in a desired pattern without generating a bowing shape.

[0008]

Means for Solving the Problems To prevent the occurrence of a bowing shape
Stop solution The present inventor has examined the cause of bowing shape as the first problem, it was found the following. The bowing shape often occurs mainly when an attempt is made to open a contact hole having a hole diameter of 0.25 μm or less and an aspect ratio of 5 or more. It is for the following reasons.
When plasma etching of the silicon oxide film is performed, a deposition film of a reaction product is formed very close to the opening of the contact hole. Then, Ar ions ionized in the plasma on the substrate sputter the deposited film formed very close to the hole opening, and the components of the sputtered deposited film are as shown by the solid line in FIG. Redeposits on the lower hole side wall. The redeposited deposited film becomes a thick film and hinders the progress of the etching of the lateral oxide film.On the other hand, in a region below the redeposited deposited film, the deposited film is thin, so that the lateral oxide film becomes thin. Etching proceeds. As a result, as shown by a broken line in FIG. 5, a contact hole having a bowing shape is opened.

The inventor of the present invention has noticed that if the thickness of the deposited film is constant over the entire height of the contact hole wall, the deposited film does not have a bowing shape, and a gas for promoting the improvement of the coverage of the deposited film is used as an etching gas. Thought about doing it. Then, as a result of performing an etching experiment using a surface wave plasma etching apparatus while variously changing the composition of the etching gas, C ₄ F containing He gas in a predetermined range was obtained.
_8. It has been found that a contact hole without a bowing shape can be opened by etching an oxide film using a mixed gas of CO, He and O ₂ .

Here, the configuration of the surface acoustic wave plasma etching apparatus used in the experiment will be described with reference to FIG. As shown in FIG. 7, the surface wave plasma etching apparatus 30
It comprises a plasma chamber 32 for generating plasma 31 and a microwave waveguide system for guiding microwaves to the plasma chamber 32. Plasma chamber 32
Is made of quartz, which separates a chamber region from a microwave waveguide system, with a wafer stage 34 on which a wafer is mounted on the upper surface and an exhaust port 36 connected to a vacuum suction device (not shown) below. Is provided on the upper part. A wafer stage 34 constituting a cathode, and a plasma chamber 32
An RF power supply 38 is connected to the wafer stage 34 in order to apply an RF voltage of 400 kHz between the wafer stage 34 and an annular anode 35 provided above the wafer stage 34. An etching gas is introduced into the plasma chamber 32 via a gas inlet 40.

The microwave waveguide system has a frequency of 2.45 GHz.
a waveguide 42 for guiding microwaves from a microwave source (not shown) of z, a Teflon (registered trademark) dielectric waveguide 44 connected to the waveguide 42, a rectangular microwave dispersion plate 46, It is composed of

The above-described surface wave plasma etching apparatus 30
An etching experiment was performed using a mixed gas of C ₄ F ₈ , CO, He, and O ₂ as an etching gas and etching a BPSG film and a photoresist film under the following conditions. Pressure: 20 mTorr Microwave output: 1100 W RF bias output: 800 W Constant flow rates of C ₄ F ₈ gas, CO gas and O ₂ gas were set at 15 sccm, 30 sccm, and 5 sccm, respectively, and the flow rate of He gas was changed from 0 sccm to 500 sccm. Then, a contact hole was opened, and the shape of the contact hole was observed with an SEM (scanning electron microscope). FIG.
(A), FIG. 8 (b) and FIG. 8 (c) respectively show He
It is a copy of the SEM photograph of the contact hole when the gas flow rate is 0 sccm, 80 sccm, and 400 sccm.

FIG. 8 shows that the flow rate of He gas is 0 sc
When the flow rate of He gas is 80 sccm and 400 sccm, a contact hole having a good shape without a bowing shape can be opened. When the flow rate of the He gas is 500 sccm, a bowing shape occurs in the contact hole. Therefore, by using a mixed gas in which the flow rate of He gas is in a range of 80 sccm to 400 sccm, and in terms of a flow rate ratio, in a range of 60% by volume to 90% by volume, a straight contact hole without a bowing shape is opened. Can be.

In the above experiment, the etching rate was measured, and the results shown in FIG. 9 were obtained. In FIG. 9, the horizontal axis represents the flow rate of He gas (sccm), and the vertical axis represents the etching rate (Å / min). FIG. 9 shows that the etching rate for the BPSG film is high when the flow rate of the He gas is in the range of 80 sccm to 400 sccm, that is, when the flow rate of the He gas is in the range of 61% to 89% of the total flow rate of the etching gas.

Opening of Contact Hole with Predetermined Shape and Dimensions The present inventor investigated the second problem that a shape change occurs when a contact hole with a higher aspect ratio is opened, and found the following. If the hole diameter is constant, a large aspect ratio of the contact hole means that the thickness of the silicon oxide film (interlayer insulating film) that opens the contact hole is large. Specifically, the second problem often occurs when the contact hole diameter is 0.25 μm, the aspect ratio is 8 or more, and thus the thickness of the interlayer insulating film is 2 μm or more. Therefore, when a contact hole having a high aspect ratio is opened, the thick interlayer insulating film is etched, so that the etching time is lengthened and the etching mask made of the photoresist film is also etched more. When the etching amount of the mask increases, the pattern shape of the mask is damaged, and the dimension of the pattern changes. Therefore, a contact hole having a desired processing size cannot be opened.

In order to open a contact hole having a high aspect ratio, it is necessary to etch only an oxide film without etching a mask.
In other words, it is necessary to use an etching gas having a high selectivity between the photoresist film and the silicon oxide film. Although increasing the thickness of the etching mask is one solution, as long as the etching mask is formed by patterning using a photolithography method, the resolution at the time of exposure is restricted, and the current thickness is limited. Specifically, it is difficult to increase the thickness of the photoresist film to 2 μm or more.

Therefore, as shown in FIG. 10 obtained by rearranging FIG. 9 obtained in the above experiment, the flow rate of He gas is 120 sccm.
When the flow rate of He gas ranges from 71% to 86% of the total flow rate of the etching gas, the selectivity of the BPSG film to the photoresist film increases. If the silicon oxide film is etched using an etching gas containing He gas at a flow ratio in this range, the photoresist film is etched with a high selectivity, and the oxide film is etched before the pattern is damaged. Can be opened. Therefore, the opening diameter of the opening of the contact hole does not increase as in the related art.

Based on the above findings, in order to achieve the above object, a method for forming a connection hole according to the present invention comprises etching a silicon oxide film by a plasma etching method,
When opening the connection hole penetrating the silicon oxide film, He gas was mixed with a gas containing fluorocarbon as one of the main components in a flow rate ratio of He gas to all etching gases of 60% by volume or more and 90% by volume or less. It is characterized in that a gas is used as an etching gas.

In the method of the present invention, the silicon oxide film is Si
O ₂ CVD film, BPSG film, PSG film, means a BSG film, or the like. The connection hole refers to a hole for forming a contact which penetrates the silicon oxide film and connects the lower diffusion region or the wiring to the upper wiring, regardless of the name and structure of the contact hole, via hole, through hole and the like. Absent.

In a preferred embodiment of the method of the present invention, the flow ratio of He gas to the total etching gas is in the range of 70% by volume to 85% by volume. When the flow ratio of the He gas is in this range, the selectivity between the silicon oxide film and the photoresist film is increased, and damage due to etching of the pattern of the photoresist film is prevented. No connection holes can be opened.
Therefore, in this embodiment, even if the aspect ratio of the connection hole is large, in particular, the aspect ratio of the connection hole is 8 or more, it is possible to open the connection hole having an accurate hole diameter which is not enlarged at the opening.

The fluorocarbon used in the method of the present invention comprises:
As long as it is a compound of F and C, it can be used without any restriction on its molecular structure. However, from the viewpoint of increasing the etching rate, it is preferably at least one of CH ₂ F ₂ and C ₄ F ₈ . The flow ratio of the fluorocarbon is preferably 1% by volume.
Not less than 20% by volume. The gas containing fluorocarbon as one of the main components used in the method of the present invention includes CO gas and O ₂ gas. By mixing the CO gas, the selectivity between the photoresist film and the silicon oxide film can be increased. Preferably, the flow ratio of the CO gas is set to 6% by volume or more and 40% by volume or less. Further, by mixing the O ₂ gas, the amount of the deposited film generated in the connection hole can be reduced. Preferably, the flow ratio of the O ₂ gas is set to 1% by volume or more and 5% by volume or less.

Although the method of the present invention can be applied to the opening of a connection hole regardless of the size of the hole diameter, it is most suitable for the opening of a connection hole having a small diameter, for example, a connection hole having a hole diameter of 0.25 μm or less.

[0023]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Embodiment 1 This embodiment is an example of an embodiment of a method for opening a connection hole according to the present invention, and FIGS. 1A to 1C show a method for opening a contact hole according to the method of this embodiment. FIG. 9 is a cross-sectional view of the substrate in each process. In the present embodiment, first, as shown in FIG.
A 5 μm silicon oxide film 54, for example, a BPSG film is
Formed by Method D. Next, as shown in FIG. 1B, a photoresist film for KrF line exposure is
The film is formed by Å. Exposing the photoresist film to KrF rays,
By patterning by developing, a mask 56 having a pattern 55 having a hole diameter of 0.20 μm is formed.

Next, the surface wave plasma etching apparatus 3
By using a mixed gas of C ₄ F ₈ , CO, He and O ₂ as an etching gas, the silicon oxide film 54 was etched using a mask 56 under the following conditions to open a contact hole 58. Pressure: 20 mTorr Microwave output: 1100W RF bias output: 800 W gas flow _{rates: C 4 F 8 / 15sccm,} CO / 30sccm He / 90sccm, O 2 / 5sccm

In the present embodiment, as shown in FIG.
Although the pattern 55 of No. 6 was slightly scraped and damaged at the upper edge 56a of the opening, a contact hole 58 having a hole diameter of 0.20 μm and a substantially straight hole side wall which did not show a bowing shape was able to be opened.

[0026] As a comparative example Comparative Example Embodiment 1, except that with Ar gas in place of He gas, the same gas flow rate as in the first embodiment, the silicon oxide film 54 in etching conditions and etching contact A hole 58 was opened. The obtained contact hole 58 has a bowing shape as shown in FIG. 2, and has a hole diameter D _O of 0.25 μm at the widest part, which is remarkably different from the straight contact hole 18 obtained in the first embodiment. A control was shown.

Embodiment 2 This embodiment is another example of the embodiment of the method for opening a connection hole according to the present invention. FIG. 3 is a sectional view of a contact hole opened according to the method of the present embodiment. In the present embodiment, the thickness of the silicon oxide film 54 formed on the silicon substrate 52 is 2.0 μm, which is larger than the thickness of 1.5 μm of the first embodiment, and is the same as that of the first embodiment. To form a photoresist film, pattern it,
A mask 56 having a pattern having a hole diameter of 0.20 μm is formed.

Next, the contact hole 58 was opened by etching the silicon oxide film in the same manner as in Embodiment 1 except that the flow ratio of the He gas was set to 75% by volume. As shown in FIG. 3, although the upper edge 56a of the opening of the mask 56 is slightly cut and damaged, the opened contact hole 58 does not show a bowing shape and substantially includes the opening of the contact hole 58. A contact hole 58 having a straight hole side wall and a hole diameter of 0.20 μm could be opened.

[0029]

According to the present invention, when a silicon oxide film is etched by a plasma etching method and a connection hole penetrating the silicon oxide film is opened, a flow ratio of the gas containing fluorocarbon as a main component is 60 vol. % To 90% by volume
By using a gas mixed with He gas in the following range as an etching gas, the hole diameter is particularly 0.25 μm.
The following contact holes can be opened in a favorable shape that does not exhibit a bowing shape. Further, the flow ratio of He gas to the total etching gas is set to 70% by volume or more and 85% or more.
By setting the volume% or less, it is possible to open a contact hole having a high aspect ratio of not less than 8 in a predetermined shape and a predetermined size.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views of a substrate in each step when a contact hole is opened according to the method of the first embodiment.

FIG. 2 is a sectional view of a contact hole obtained in a comparative example.

FIG. 3 is a sectional view of a contact hole opened according to the method of Embodiment 2;

FIGS. 4 (a) to 4 (c) are cross-sectional views of a substrate in each step when a contact hole is opened according to a conventional method.

FIG. 5 is a cross-sectional view of a contact hole showing a bowing shape.

FIG. 6A is a cross-sectional view showing a state where a mask is etched, and FIG. 6B is a cross-sectional view of a contact hole whose diameter is enlarged at an upper edge of an opening.

FIG. 7 is a schematic diagram illustrating a configuration of a surface wave plasma etching apparatus.

FIGS. 8A to 8C are simulated cross-sectional photographs taken by SEM of contact holes opened in an experiment, respectively.

FIG. 9 is a graph showing the relationship between the flow rate of He gas and the etching rate.

FIG. 10 is a graph showing a relationship between a He gas flow rate and a BPSG / PR selection ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Silicon substrate 14 Silicon oxide film 16 Mask 18 Contact hole 30 Surface wave plasma etching apparatus 31 Plasma 32 Plasma chamber 34 Wafer stage 36 Exhaust port 37 Quartz partition 38 RF power supply 40 Gas introduction port 42 Waveguide 44 Teflon dielectric conductor Waveguide 46 Microwave dispersion plate 52 Silicon substrate 54 Silicon oxide film 56 Mask 58 Contact hole

Continued on the front page F-term (reference) 4M104 DD08 DD16 DD19 DD66 DD67 DD71 EE14 EE15 HH14 5F004 BA20 BB13 BB14 CA06 DA00 DA15 DA22 DA26 DB03 EB01 5F033 QQ09 QQ12 QQ15 QQ19 QQ28 QQ35 QQ37 RR04 RR13 SSWWRR

Claims (7)

[Claims] When a silicon oxide film is etched by a plasma etching method and a connection hole penetrating the silicon oxide film is opened, a flow rate ratio of He gas to all etching gases is in a range of 60% by volume to 90% by volume. A method of opening a connection hole, wherein a gas obtained by mixing He gas with a gas containing fluorocarbon as one of the main components is used as an etching gas. 2. The method according to claim 1, wherein the flow ratio of He gas to the total etching gas is in the range of 70% by volume to 85% by volume. 3. Fluorocarbon as CH ₂ F ₂ and C
Opening process of the contact hole according to claim 1 or 2, characterized by using at least one of ₄ F _8. 4. The method for opening a connection hole according to claim 1, wherein the gas containing fluorocarbon as one of the main components includes a CO gas and an O ₂ gas. 5. The method for opening a connection hole according to claim 1, wherein the connection hole having a hole diameter of 0.25 μm or less is opened. 6. The method according to claim 1, wherein the silicon oxide film formed on the underlayer is etched to open a connection hole and expose the underlayer. How to open the connection hole. 7. The method according to claim 2, wherein an aspect ratio of the connection hole is 5 or more.