JPH0294520A - Dry etching method - Google Patents

Abstract

PURPOSE:To obtain a dry etching method which generates no side etching in the films except tungsten group films and which has a high etching selection ratio to silicon oxide by using a mixed gas composed of chlorine containing oxygen as an etching gas. CONSTITUTION:A resist pattern R is formed onto an silicon wafer 11, on a surface of which an silicon oxide film 12 and a tungsten silicide 13 are deposited, through a photolithographic method. A cathode 3 is placed onto the silicon wafer 11, evacuation is conducted through a gas exhaust port 10, and chlorine gas containing 5.1% oxygen is introduced from gas supply ports 9 as an etching gas. A high-frequency power supply 5 and a motor 8 are driven, and discharge is promoted while high-density plasma is generated by utilizing magnetron discharge by an orthogonal electromagnetic field shaped on the surface of the wafer by permanent magnets 7, thus conducting etching. The tungsten silicide film 13 after etching is not side-etched and is patterned with extremely excellent etching accuracy at that time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a dry etching method, and particularly to a dry etching method for thin films containing tungsten or tungsten silicide.

(Prior Art) In recent years, semiconductor devices have become faster and more highly integrated, and research into miniaturization and higher density of constituent elements is progressing rapidly.

However, with this miniaturization and higher density, various problems have arisen in the manufacturing process of semiconductor devices.

For example, in the case of wiring, the reduction in design standards has resulted in smaller wiring widths, but the increase in the number of active elements has made wiring more complex, and the number of electrical connections has also increased. The amount of time required for construction is only increasing. Therefore, it is necessary to use a material with low resistivity.

Furthermore, when manufacturing MOSFETs, materials are selected to form gate electrodes in a self-aligned manner with the aim of significantly reducing area and improving performance.

Furthermore, it must be able to withstand subsequent high temperature processes.

Molybdenum Mo, molybdenum Mo,
Examples include high melting point metals such as tungsten W and their silicides.

One of the gate electrode structures using this high melting point metal and its silicide is silicide (silicide) on polycrystalline silicon.
There is a structure called a five-layer polycide gate structure.

This structure is said to be the most practical structure because it allows for low wiring resistance while preserving the silicon gate process.

Among them, two types are tungsten silicide WSi x called tungsten polycide and polycrystalline silicon.
Layered membranes are becoming widely used.

Sulfur hexafluoride (SF6) is used in the dry etching process used in the buttering process of these tungsten materials.
, fluorine gas such as carbon tetrafluoride (CF4), mixed gas of fluorine gas and Bffi (02), chlorine (CI2
), mixed gas of C1 gas and fluorine gas, mixed gas of carbon tetrachloride (CCl2) and oxygen, boron trichloride (B
A mixed gas of Cl2> and chlorine is used.

For example, when tungsten polycide is etched with a fluorine-based gas, lateral etching wraps around the underlying polycrystalline silicon (side etching), resulting in poor pattern accuracy. Furthermore, since fluorine-based gas directly reacts with silicon oxide, when the underlying layer is silicon oxide, there is a problem in that etching selectivity is poor and even silicon oxide is etched.

Furthermore, in order to avoid this side etching, a method using a mixed gas of carbon tetrachloride and oxygen has also been proposed.

In this method, in order to improve the selectivity with respect to the underlying silicon oxide material, it is desirable to perform low temperature etching in which the sample temperature is kept below zero degrees Celsius to suppress the etching rate of the silicon oxide material.

However, when this is done, carbon tetrachloride sometimes liquefies and becomes impossible to etch.

Furthermore, the thickness of the silicon oxide film that is the base of the gate electrode (gate insulating film) has recently become thinner, from 100 to 200 mm, as semiconductor devices become smaller. For this reason,
When using an etching gas with a small ratio (selectivity) between the etching speed of tungsten-based materials and the etching speed of silicon oxide, such as a mixed gas of boron trichloride and chlorine, the etching does not stop at the silicon oxide, but instead diffuses into the underlying silicon oxide layer. It often progresses to layers,! ! There was a problem in that the i-manufacturing yield decreased.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a dry etching method in which the etching selectivity of tungsten-based materials to silicon oxide is high.

Furthermore, when etching eight multilayered films including tungsten-based films such as tungsten polycide, the present invention prevents side etching of films other than tungsten-based films such as polycrystalline silicon, and allows etching to be selectively performed on silicon oxide. It is an object of the present invention to provide a dry etching method with a high etching ratio.

(Structure of the Invention) (Means for Solving the Problems) Therefore, in the present invention, a mixed gas of chlorine gas containing oxygen is used as the etching gas.

Preferably, a mixed gas of chlorine gas containing 2 to 6% enzyme is used as the etching gas.

Furthermore, in the present invention, during dry etching using this mixed gas, the pressure within the vacuum container is set to 5 Pascal or less.

Furthermore, in the present invention, the upper layer is a tungsten silicide film,
When etching the tungsten polycide whose lower layer is a polycrystalline silicon film, as described above, a mixed gas of chlorine gas containing oxygen is used as the etching gas.

(Function) As a result of various experiments, the present inventors tried etching with chlorine gas instead of fluorine, which inevitably causes side etching. However, when etching is attempted using only chlorine gas, the reaction products do not evaporate and remain as deposits on the substrate surface, hindering the progress of etching. Therefore, it was discovered that when oxygen was added thereto, the reaction product evaporated well and the etching progressed without side etching, and this was developed based on this discovery.

For example, consider the etching reaction of tungsten silicide WSix. Ions or neutral active species that fly to the tungsten silicide surface with high energy react with tungsten at that position and WCl is generated, but WCIy evaporates and remains as a deposit on the surface. By adding oxygen here, WCIxOy
is formed. Here, W Cl < O, y is volatile.

In this way, in the present invention, side etching can be suppressed by using a mixed gas of chlorine gas containing oxygen as the etching gas.

In addition, to reduce side etching, it is desirable to perform the etching under low pressure, because chlorine reacts with tungsten in the form of ions or neutral active species, but it is generated by electric discharge and flies with high energy. The neutral active species reacts with tungsten at that position and etching progresses, but when the concentration of chlorine neutral active species increases, the residence time of the neutral active species on the sidewall of the tungsten film increases and the etching progresses in the lateral direction. This is thought to be because it allows the reaction to proceed.

Therefore, in order to reduce side etching, it is desirable to perform etching at a lower pressure.

Furthermore, when the pressure is low, the selectivity of the tungsten film to silicon oxide is improved and side etching of polycrystalline silicon in the polycide structure is reduced. This is because when the pressure is lowered, the concentration of neutral active species decreases, and on silicon oxide or polycrystalline silicon, silicon chlorine oxidation Th5
iCIxO, is attached, which acts as a protective film,
This is thought to be due to a decrease in the etching rate of silicon oxide and polycrystalline silicon.

Furthermore, since the etching rate of a tungsten silicide film and the etching rate of a polycrystalline silicon film are almost the same with a mixed gas containing 2 to 6% oxygen, even when etching tungsten polycide, the etching rate of the polycrystalline silicon film is No side etching occurs in the silicon film.

In addition, since the mixed gas of chlorine gas containing oxygen has a liquefaction temperature or solidification temperature of -70 degrees Celsius or lower, it is possible to perform etching at low temperatures, suppressing the etching of silicon oxide while etching tungsten. It becomes possible to perform etching of based materials. Therefore, the etching selectivity with respect to silicon oxide can be increased.

(Example) Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. M1 is a diagram showing a schematic configuration of a magnetron type reactive ion etching apparatus used in the dry etching method of the embodiment of the present invention.

This etching apparatus includes a vacuum chamber 1, an anode 2 and a cathode 3 disposed within the vacuum chamber to generate plasma.
and a high frequency power source 5 which is connected via a matching box 4 for reducing reflected waves and applies a high frequency to this cathode 3, and ill! on the cathode 3. A permanent magnet 7 that generates a magnetic field parallel to the wafer 6 placed thereon, a motor 8 that rotates the permanent magnet 7, and a gas supply port 9 and a gas discharge port that supply and discharge gas in the vacuum container. 10, which facilitates generation of cathode drop voltage (bias voltage) by applying high frequency and promotes discharge,
Etching is performed by generating high-density plasma using magnetron discharge caused by an orthogonal electromagnetic field formed by the permanent magnet 7 on the surface of the sea urchin convexity.

Next, an etching method using this apparatus will be explained.

First, as shown in FIG. 2(a), a silicon oxide film 1
2, and tungsten silicide (WS i2.7
A resist pattern R is formed on the silicon wafer 11 formed by depositing the resist pattern R using the t-tritho method.

This silicon wafer 11 is placed on the cathode 3 of the device.
! After evacuating through the gas exhaust port 10, t8 gas containing 5.1% oxygen is introduced as an etching gas through the gas supply port 9, the high frequency power source 5 and the motor 8 are driven, and the In addition to promoting lightning, etching is performed by generating high-density plasma using magnetron discharge caused by orthogonal electromagnetic fields formed on the surface of the substrate by the permanent magnets 7.

Here, the engineering frequency power density of the cathode 3 is 0.4 W/d, and the magnetic field strength on the wafer due to the permanent magnet 7 is 100 Gauss.
, the distance between the electrodes is 30 an, and the temperature of the wafer is -
14 degrees, the flow rate of chlorine gas and oxygen gas is 501/ni respectively.
n, 3 ml/min, and pressure 5 Pa.

At this time, tungsten silicide [13
As shown in FIG. 2(b), the patterning is performed with extremely good etching accuracy without side etching. Moreover, the selection ratio is also 8 or more. Selectivity ratio is 8J:J,
The above can also be used for patterning a gate electrode when the gate insulating film has a thickness of about 100A.

Furthermore, FIG. 3 shows the results of measuring the etching selectivity to silicon oxide by changing only the pressure while keeping the other conditions unchanged. As is clear from this figure, the etching selectivity was good when the culmness was 3 Pa to 7 Pa. Here, it can be seen that when the pressure is set to 3 Pa or less, the selection ratio decreases. This is thought to be because the mean free path of the ions becomes longer and the ion energy increases, making it easier to etch silicon oxide and lowering the selectivity. However, at this time, it is possible to increase the selectivity by further lowering the wafer temperature. On the other hand, when the pressure is 7.7 Pa or more, the number of neutral active species that are not accelerated by the electric field increases, and side etching occurs in the tungsten silicide.

Further, FIG. 4 shows the cross-sectional shape after etching when the pressure was set to '5 Pa and only the flow rate of oxygen was changed. When no oxygen is added at all, the resist pattern Rr3 and tungsten silicide 13 are
Deposits such as WC+ adhere to the side walls of the substrate, preventing etching from proceeding. Then, when the oxygen flow rate is increased to about 2%,
The deposits are significantly reduced and etching begins to progress well, but when the oxygen flow rate exceeds 6%, the deposits increase again and the etching progress is hindered. Also, increase the oxygen flow rate to 9.1
% or more, a deposit of WSilo is formed, making it difficult for etching to proceed, and this deposit cannot be removed by normal processing.

As can be seen from the above measurement results, when the flow rate ratio of oxygen to chlorine is about 5.1% and the pressure is 5 Pa or less,
Patterning with a vertical cross-sectional shape is possible without side etching.

Example 2 Further, as a second example, patterning of tungsten polycide as shown in FIG. 5 will be described.

First, as shown in FIG. 5(a), a gate insulating film 22 is formed on the surface of a silicon wafer 21 on which a desired device region is formed.
And a two-layer structure consisting of polycrystalline silicon film 23a and tungsten silicide 23b! After forming the resist pattern 23, a resist L-pattern R is formed and placed on the cathode 3 of the apparatus shown in FIG. 1 in the same manner as in the first embodiment.

Then, perform etching in the same manner. At this time, the high frequency power density of the v@ electrode is 0.4 W/cffl, and the permanent magnet 7 on the wafer ([4 intensity is 100 GaUS
S, the distance between the electrodes is 30ctn, and the wafer temperature is −
14 degrees, the flow rates of chlorine gas and B gas are each 50 Il/
min, 31/+in, and pressure 5 Pa. The cross-sectional shape after etching is shown in FIG. 5(b). Extremely high precision patterning is possible without causing side etching in the polycrystalline silicon film 23a and without etching the underlying silicon oxide.

Furthermore, at this time, the etching rate was measured by changing only the pressure while keeping the other conditions unchanged, and the results are shown in FIG. In FIG. 6, the song Pi1a is a curved line.

Curves C are WSi2-7. The etching rate of n+ type polycrystalline silicon and silicon oxide is shown.

Note that this etching rate is xo for n-medium polycrystalline silicon, 5. Silicon B is indicated by ×5. As is clear from this figure, when the pressure was about 3 Pa to 7 Pa, the etching rate of WSi2.7 and n+ type polycrystalline silicon was sufficiently higher than that of silicon oxide, and the etching selectivity was good. This figure shows that when the pressure is set to 3 Pa or less, the etching rate of silicon oxide increases and the selectivity decreases. This is thought to be because the mean free path of the ions becomes longer and the ion energy increases, making it easier to etch silicon oxide and lowering the selectivity. However, at this time, it is possible to increase the selectivity by further lowering the wafer temperature. On the other hand, 7.
When the pressure is 7 Pa or more, the number of neutral active species that are not accelerated by the electric field increases, and side etching occurs in the tungsten silicide.

Further, FIG. 7 shows the etching speed when the pressure was set to 5 Pa and only the flow rate of the M cable was changed.

Also in FIG. 7, curve a2 curve ab and curve C are on the same sphere as in FIG. 6, respectively, with WSi2.7. The etching rate of n+ type polycrystalline silicon and silicon oxide is shown. If MM is not added at all, deposits such as WC+ will adhere to the side walls of the resist pattern R and the tungsten silicide 13, and etching will not proceed.
If it is north of this point, a WSilOo deposit is formed and etching does not proceed, and this deposit is the normal 51! ! It cannot be removed.

In the examples, a magnetron type reactive ion etching device was used, but even if a parallel flat root type reactive ion etching device or an ECR type anti-nonreactive ion etching device was used, there was no deposit left in the same device and the selectivity was high. It becomes possible to pattern with excellent accuracy and a vertical cross-sectional shape.

(Effects of the Invention) As explained above, according to the dry etching method of the present Komei, since chlorine gas containing oxygen is used as the reactive gas, selective etching can be performed without side etching. Etching with a good ratio becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a magnetron type reactive ion etching apparatus used in the method of the embodiment of the present invention, and FIGS. 2(a) and 2(b) are the dry etching process of the first embodiment of the present invention. Figure 3 is a diagram showing the relationship between pressure and selection ratio, Figure 4 is a diagram showing the relationship between oxygen f, quantity ratio and cross-sectional shape after etching, Figure 5 (a) and Figure 5 (b
) is a diagram showing the dry etching process of the second embodiment of the present invention, FIG. 6 is a diagram showing the relationship between pressure and etching rate in the same process, and FIG. 7 is a diagram showing the relationship between oxygen concentration and etching rate. FIG. 1... Vacuum container, 2... Anode, 3... Anode, 4...
...Matching box, 5...High frequency power supply, 6...
・Wafer, 7...Permanent magnet, 8...Motor, 9...
- Gas supply port, 10... Gas discharge port, 11... Silicon wafer, 12... Silicon oxide film, 13... Tungsten silicide<WSi2.7), 21... Silicon wafer. 22... Gate insulating film, 23a... Multi-crystalline silicon film, 23b... Tungsten silicide, 23...
Two-layer surface film formation, R...resist pattern. Fig. 2 (G) Fig. (b) Fig. 5 (a) Fig. 5 (b) Repulsion (Po) Fig. 3 Fig. 4 Pressure (Pal Fig.

Claims (5)

[Claims] (1) A dry etching method characterized by introducing an etching gas into a vacuum container and using chlorine gas containing oxygen as the etching gas when etching a thin film including a tungsten film or a tungsten silicide film. . (2) The dry etching method according to claim 1, wherein the chlorine gas contains 2 to 6% oxygen. (3) The dry etching method according to claim (1), wherein the pressure within the vacuum container is 5 Pascal or less. (4) The dry etching method according to claim 1, wherein the thin film has a multilayer structure including a tungsten silicide film as an upper layer and a polycrystalline silicon film as a lower layer. (5) The dry etching method according to claim 4, wherein the thin film has a base layer made of a silicon oxide layer.