JPH11162941A - Dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method that does not depend on the crystal structure of titanium silicide and controls shapes in a highly anisotropic manner that prevents undercuts and side etch in worm holes. SOLUTION: A titanium silicide layer 5 formed on a silicon substrate 1 is dry etched in this method. A hard mask 8 is formed on the titanium silicide layer. Then, the titanium silicide layer 5 is etched using plasma of a mixed gas that is obtained by adding a methane gas and boron trichloride to chlorine or hydrogen bromide so that the sidewall of the etched layer is protected by methane. As a result, high anisotropic etching is secured regardless of the crystal structure of titanium silicide. Addition of the boron trichloride minimizes the difference of etch rates of titanium silicide and silicon nodule and prevents occurrence of etching residue.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a dry etching method for performing an etching process on a semiconductor substrate by using a plasma etching apparatus. The dry etching method in the case.

[0002]

2. Description of the Related Art Since titanium silicide, which is a metal silicide, is a low-resistance material, application to a gate electrode and a bit line is being studied in the development of an ultra-fine DRAM device intended for high-speed operation. An etching process for forming a gate electrode and a bit line requires anisotropic etching without undercut in order to improve device performance. In particular, since the gate electrode greatly affects device performance, a highly anisotropic etched shape is required.

As an etching method using titanium silicide as a material for a gate electrode, for example, as described in Japanese Patent Application No. 6-29257, hydrogen bromide (HBr) and chlorine (Cl ₂ ) are used. It has been proposed to perform etching by a magnetron RIE apparatus using a mixed gas of 1 to 1 and a mixing ratio of 1: 1 to 1: 9 and a pressure of 30 mTorr or less.

In this method, a resist mask is not used by optimizing a gas mixture ratio, a pressure and a magnetic field, that is, a silicon nitride film or a silicon oxide film (hereinafter, referred to as a hard mask) is used as an etching mask material. This is used to control the etching shape. It is known that when an etching process is performed using a hard mask, the effect of protecting the sidewall of the etching layer is generally low. In the above-described etching method, Si-Br, which is a reaction product of bromine and silicon, has a pressure as low as possible (10 mTorr or less) and has a low saturated vapor pressure.
The film is formed as a side wall protective film on the side wall of the etching layer (titanium silicide), thereby realizing high anisotropy during etching.

[0005] On the other hand, titanium silicide is formed by a sputtering method, and its crystal structure is amorphous or amorphous depending on the substrate temperature during film formation or the heat treatment temperature after film formation.
It can be classified into three forms of the crystal structure of C49 and C54. That is, an amorphous structure,
In the heat treatment at 0 ° C. or more and 800 ° C. or less, the crystal structure of C49,
The heat treatment at 850 ° C. or higher has a C54 crystal structure. This heat treatment is performed to suppress the variation in the resistance value of the thinned titanium silicide.

[0006]

However, in the above-mentioned method of etching titanium silicide disclosed in Japanese Patent Application Laid-Open No. 6-29257, no mention is made of the crystal structure of titanium silicide. Further, the present inventor has found that when the crystal structure of titanium silicide is different, when etching is performed with a mixed gas of hydrogen bromide and chlorine, the etching reactivity is significantly different even when applying the etching conditions in which the mixing ratio is optimized. I found that.

That is, as shown in FIG. 3A, a silicon thermal oxide film 2, a polysilicon film 3, a titanium nitride film 4, and a titanium silicide film 5 are sequentially formed on a silicon substrate 1 to form a titanium silicide film. When patterning the laminated film by etching with the hard mask 8 formed on the 5 to form the gate wiring, etching was performed for each case where the crystal structure of the titanium silicide film 5 was different.

When the titanium silicide film 5 is a titanium silicide 16 having an amorphous structure, an undercut due to etching hardly occurs, and its cross-sectional shape is shown in FIG.
As shown in FIG. On the other hand, the titanium silicide film 5
Is titanium silicide 1 having a crystal structure of C49 or C54
In the case of 7, 18, the undercut 10 is generated by the etching process, and the cross-sectional shape is as shown in FIG. The cause of the undercut 19 is that titanium silicide 17, 1 having a C49 or C54 crystal structure is formed.
8 has high etching reactivity with chlorine, Si-Br
This is considered to be due to the difficulty in optimizing the mixing ratio of hydrogen bromide (HBr) because the effect of the film on protecting the side wall of the titanium silicide film 5 is small. In addition, even when etching is performed using only hydrogen bromide, a worm-like side etch 20 easily occurs on the side wall of the titanium silicide film 5 (see FIG. 3C).

The above phenomenon suggests that the Si-Br film is not perfect as a sidewall protective film depending on the type of crystal structure (phase) of the titanium silicide film. In particular, it has been found that when the substrate temperature at the time of etching is 20 ° C. or higher, the worm-like side etch 20 becomes remarkable. In addition, in a film of titanium silicide having a crystal structure of C49 or C54, a lump of silicon called silicon nodule is generated. In particular, when silicon having a solid solubility or higher exists in the titanium silicide layer, silicon nodules are easily generated. The silicon nodule 21 is shown in FIG.
As shown in (d), it becomes the main cause of the etching residue 23. This is because the silicon nodule 21 has a lower etching rate than titanium silicide, and
The reason for this is that it generates residuals. In particular, when a gas having a high mixing ratio of chlorine is used, the etching rate difference between the two becomes remarkable, resulting in severe etching residue.

The present invention has been made in view of the above circumstances, and in a method of dry-etching titanium silicide, a highly anisotropic method that does not depend on the crystal structure of titanium silicide and does not cause undercuts or worm-like side etching. An object of the present invention is to provide a dry etching method having a characteristic shape controllability.

[0011]

According to the present invention, there is provided a dry etching method for a titanium silicide layer formed on a substrate, comprising: forming a mask pattern for etching on the titanium silicide layer; ,
It is characterized in that the titanium silicide layer is etched by gas plasma using a mixed gas obtained by adding methane gas to chlorine or hydrogen bromide.

The etching may be performed by gas plasma using a mixed gas obtained by adding boron trichloride to a mixed gas system obtained by adding methane gas to chlorine or hydrogen bromide.
Therefore, as the mixed gas used for etching the titanium silicide layer, chlorine / methane gas, hydrogen bromide / methane gas, chlorine / methane gas / boron trichloride, hydrogen bromide / methane gas / boron trichloride can be applied.

Further, instead of the titanium silicide layer, the titanium silicide layer and the titanium nitride layer of the laminated film (titanium polycide) formed by sequentially laminating a polysilicon layer, a titanium nitride layer, and a titanium silicide layer are etched. Also applicable to cases.

According to the present invention, in a gas plasma of a mixed gas obtained by adding methane gas to chlorine or hydrogen bromide, methane gas dissociates due to collision with electrons in the plasma. As a result, a side wall protective film mainly made of carbon is formed on the side wall of titanium silicide which is an etching layer. The sidewall protective film mainly composed of carbon atoms does not chemically react with titanium silicide, and the sidewall protective film formed by strong bonding between carbon atoms is
It has sufficient etching resistance. As a result, even if the crystal structure of titanium silicide is different, undercut or worm-like side etch due to chlorine or hydrogen bromide is suppressed.

When a mixed gas obtained by adding methane gas to chlorine or hydrogen bromide and further adding borane trichloride is used, there is an effect of minimizing a difference in etch rate between titanium silicide and silicon nodule. As a result, the etching of the titanium silicide and the silicon nodule proceeds at a nearly constant speed, so that the silicon nodule does not function as a micromask. Therefore, it is possible to significantly suppress the etching residue.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the dry etching method of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a dry etching apparatus used in the method of the present invention.
Metal container 11 of 57 mm and height of 125 mm and caliber 3
It is surrounded by a quartz top plate 12 having a thickness of 57 mm and a thickness of 20 mm. During the etching, the pressure in the vacuum chamber 11 is kept at 10 mTorr or less.

An RF antenna 13 having a spiral planar shape is provided on the upper surface of the quartz top plate 12, and a high frequency voltage of 13.56 MHz is applied to the RF antenna 13. Plasma used for etching in the vacuum vessel 11 is as follows:
It is generated by an inductively coupled discharge. Inductively coupled discharge
It is excited by an induced electric field generated from the RF antenna 13.

A stage-like bias electrode 14 is provided below the vacuum vessel 11, and a semiconductor substrate 15 to be etched is placed on the bias electrode 14.
A high frequency voltage of 13.56 MHz is applied to the bias electrode 14. The bias electrode 14 has a role of controlling energy when ions in the plasma enter the semiconductor substrate 15.

Next, a first embodiment of the dry etching method of the present invention will be described with reference to FIG. The dry etching method of the present invention uses a mixed gas (a mixed gas obtained by adding methane gas to chlorine or hydrogen bromide, or a mixed gas thereof) used for etching titanium silicide or titanium polycide formed on a silicon substrate. Furthermore, the mixed gas to which chlorinated chlorinated is added has a feature. According to the gas plasma of the mixed gas, highly anisotropic etching without undercut or the like can be realized regardless of the crystal structure of titanium silicide. .

First, the silicon substrate 1 is thermally oxidized to form a silicon thermal oxide film 2 with a thickness of 7 nm. Next, a polysilicon film 3 is formed on the silicon thermal oxide film 2 to a thickness of 100 nm. The polysilicon film 3 is activated by doping phosphorus. Next, after a titanium nitride film 4 is formed to a thickness of 10 nm by using a sputtering method, a titanium silicide film 5 is successively formed by using a sputtering method.
A film is formed to a thickness of 00 nm. The composition ratio of titanium silicide was a ratio of titanium: silicon of 1: 2.4.

Next, a rapid thermal array (RT)
Using the method A), the titanium silicide film 5 is subjected to a heat treatment at 850 ° C. for 10 seconds in a nitrogen atmosphere. As a result, the titanium silicide film 5 changes from an amorphous state to a C54 crystal structure. Next, CVD as an etching mask
After the oxide film 6 is formed to a thickness of 180 nm by the CVD method, a photosensitive resist is applied, and is exposed and developed by a KrF excimer laser lithography apparatus.
A resist mask pattern 7 having a um line width is formed (see FIG. 2A).

Next, the CVD oxide film 6 is dry-etched with a mixed gas of CF ₄ , CHF ₃ and Ar to form a hard mask 8. After the unnecessary resist mask pattern is removed (see FIG. 2B), the titanium silicide film 5 and the titanium nitride film 4 having the crystal structure of C54, and then the polysilicon film 3 are continuously dry-etched.

The etching conditions at that time are as follows. For the etching of the titanium silicide film 5 and the titanium nitride film 4, a mixed gas obtained by adding boron trichloride to a mixed gas of methane diluted to 4% with chlorine and Ar is used. Chlorine gas flow rate is 50sccm, Ar diluted methane is 100s
It was changed from ccm to 200 sccm. Pressure is 2mTorr
, And the RF power of the plasma source was 250 W and the RF power on the bias side was 150 W. Note that the temperature of the silicon substrate 1 was fixed at 20 ° C. At this time, the etching rate of the titanium silicide film 5 is 300 nm / min.
Is obtained.

In the subsequent etching of the polysilicon film 3, the hydrogen bromide is set to 150 sccm, the pressure is set to 8 mTorr, the RF power of the plasma source is set to 200 W, and the R on the bias side is set.
The F power was set to 50W. At this time, the etch rate of the polysilicon film 3 is 100 nm / min. Since hydrogen bromide is used as a gas for etching the polysilicon film 3, etching can be performed while maintaining high selectivity with the silicon thermal oxide film (gate oxide film) 2 as a base. As a gas for etching the polysilicon film 3,
Chlorine may be used instead of hydrogen bromide, or a mixed gas of hydrogen bromide or chlorine and oxygen may be used. After the etching, acid stripping is performed to remove unnecessary sidewall deposits.

The end point monitoring of the etching of the titanium silicide film 5 uses an emission wavelength of 405 nm. Since the emission intensity decreases during the just-etching of the titanium silicide film 5, the timing for switching to the etching condition of the polysilicon film 3 can be easily determined.

According to the above etching conditions, a methane gas is added to the mixed gas for etching the titanium silicide film 5, so that a sidewall protective film having sufficient etching resistance is formed on the side surface of the titanium silicide film 5. as a result,
The etching of the titanium silicide film 5 and the titanium nitride film 4 can secure high anisotropy controlled perpendicular to the hard mask, and as shown in FIG. Thus, a titanium polycide gate wiring 9 having a highly anisotropic etching shape with a line width of 0.2 μm was obtained. Moreover, since boron trichloride was added to the mixed gas, silicon nodules in the titanium silicide film 5 could be removed, and generation of etching residues could be completely suppressed.

Next, a second embodiment of the dry etching method will be described. The steps up to the step of forming the hard mask 8 and stripping the unnecessary resist are the same as those in the method of the first embodiment, and a description thereof will be omitted. A mixed gas for etching the titanium silicide film 5 and the titanium nitride film 4 and a gas (mixed gas) for etching the polysilicon film 3 are different from those of the first embodiment. That is, the etching of the titanium silicide film 5 and the titanium nitride film 4 uses a mixed gas of chlorine and methane diluted to 4% with Ar. The gas flow rate of chlorine was 50 sccm, and the methane diluted with Ar was 100 sccm to 200 sccm. The pressure was fixed at 2 mTorr, and R
F power 250 W, bias side RF power 200
W. The temperature of the silicon substrate 1 was set to 60 ° C. At this time, the etching rate of the titanium silicide film 5 is 350 nm / 5 min.

In the subsequent etching of the polysilicon film 3, 150 sccm of hydrogen bromide, 2 sccm of oxygen, pressure of 8 mTorr, and RF power of the plasma source are set to 200.
W and the RF power on the bias side were 50 W. At this time, the etching rate of the polysilicon film 3 is 130 nm / min.
Is obtained.

Note that the same method as in the first embodiment is used for monitoring the end point of the etching. By setting the substrate temperature to a high temperature and increasing the bias power, the etching residue caused by the silicon nodules can be suppressed, and by adding methane to the mixed gas, a sufficient sidewall protective film is formed, resulting in undercuts and worm-like Thus, a titanium polycide gate wiring 9 having a highly anisotropically etched shape having a line width of 0.2 μm without side etching was obtained (FIG. 2C).

Next, a third embodiment of the dry etching method will be described. In this embodiment, when etching the titanium silicide film 5 and the titanium nitride film 4, hydrogen bromide is used instead of chlorine gas. That is, a mixed gas of hydrogen bromide and methane diluted to 4% with Ar is used. The gas flow rate of hydrogen bromide was 50 sccm, and the methane diluted with Ar was 50 sccm to 100 sccm. Pressure is 2mT
orr, and the plasma source RF power is 250
W and the RF power on the bias side were 150 W. In addition,
The temperature of the silicon substrate 1 was 20 to 80 ° C. At this time, the etching rate of the titanium silicide film 5 is 150 nm /
min is obtained.

In the subsequent etching of the polysilicon film 3, 150 sccm of hydrogen bromide, 2 sccm of oxygen, a pressure of 8 mTorr, and an RF power of a plasma source of 200
W and the RF power on the bias side were 50 W. At this time, the etching rate of the polysilicon film 3 is 130 nm / min.
Is obtained. Note that the same method as in the first embodiment is used for monitoring the end point of the etching.

According to this embodiment, when etching the titanium silicide film 5 and the titanium nitride film 4, hydrogen bromide having lower etching reactivity than chlorine is used, so that the etching rate is reduced. However, since the difference in etch rate between titanium silicide and silicon nodule is also reduced, an etching residue hardly occurs. In addition, as a result of formation of a sufficient side wall protective film by addition of methane,
When the substrate temperature was in the range of 20 ° C. to 80 ° C., a titanium polycide gate 9 having a highly anisotropically etched shape having a line width of 0.2 μm without undercut or worm-like side etch was obtained (FIG. 2C). ).

In the above embodiments, the etching of titanium silicide having the crystal structure of C54 has been described.
It was confirmed that a titanium polycide gate wiring 9 having a highly anisotropic etching shape having a line width of 0.2 μm and having no undercut or worm-like side etch as compared with C54 was obtained. Therefore, in the dry etching method of titanium silicide or titanium polycide, by performing etching with gas plasma using a mixed gas of methane and chlorine or hydrogen bromide, highly anisotropic regardless of the crystal structure (phase) of titanium silicide. Thus, it is possible to control the etching shape.

[0034]

According to the present invention, in the dry etching method for titanium silicide or titanium polycide, the crystal structure of titanium silicide is etched by performing gas plasma with a mixed gas of methane and chlorine or hydrogen bromide. By improving the side wall protection effect regardless of (phase), undercut and side etching can be suppressed, and highly anisotropic etching can be performed, so that fine titanium silicide or titanium polycide wiring can be obtained. As a result, it becomes possible to manufacture ultra-fine high-speed electronic devices of submicron or less.

Further, by adding boron trichloride to a mixed gas in which methane is added to chlorine or hydrogen bromide, silicon nodules which cause etching residues can be removed by etching.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view of a dry etching apparatus used in a dry etching method of the present invention.

FIGS. 2 (a) to 2 (c) are cross-sectional explanatory views showing cross sections of a semiconductor substrate in respective steps of a dry etching method of the present invention.

3 (a) to 3 (d) show cross sections when a gate wiring is formed on a substrate by dry etching.
(A) is a cross-sectional explanatory view by anisotropic etching, (b) is a cross-sectional explanatory view when an undercut occurs, (c) is a cross-sectional explanatory view when a side etch occurs, and (d) is an etching residue. FIG. 7 is an explanatory cross-sectional view of a case in which such a case occurs.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 silicon thermal oxide film 3 polysilicon film 4 titanium nitride film 5 titanium silicide film 6 CVD oxide film 7 resist mask pattern 8 hard mask 9 titanium polycide gate wiring

Claims (8)

[Claims] 1. A method for dry etching titanium silicide, comprising: forming a titanium silicide layer on a substrate; forming a mask pattern for etching on the titanium silicide layer; and a mixed gas of chlorine and methane gas. Etching the titanium silicide layer with gas plasma according to claim 1. 2. The dry etching method according to claim 1, wherein the mixed gas used in the etching step is:
A dry etching method using hydrogen bromide and methane gas instead of chlorine and methane gas. 3. The dry etching method according to claim 1, wherein the mixed gas used in the etching step is:
A dry etching method in which hydrogen bromide, methane gas and boron trichloride are used instead of chlorine and methane gas. 4. The dry etching method according to claim 1, wherein the mixed gas used in the etching step is:
A dry etching method in which chlorine, methane gas and boron trichloride are used instead of chlorine and methane gas. 5. A method for dry-etching titanium silicide, comprising: forming a laminated film on a substrate by sequentially laminating a polysilicon layer, a titanium nitride layer, and a titanium silicide layer; Forming a mask pattern for etching; a first etching step of etching the titanium silicide layer and the titanium nitride layer with a gas plasma of a mixed gas of chlorine and methane gas; A second etching step of etching the polysilicon layer with at least one gas of hydrogen or a gas system in which oxygen is added to a combination of the above gases. 6. The dry etching method according to claim 5, wherein the mixed gas used in the first etching step is hydrogen bromide and methane gas instead of chlorine and methane gas. 7. The dry etching method according to claim 5, wherein the mixed gas used in the first etching step is hydrogen bromide, methane gas, and boron trichloride instead of chlorine and methane gas. 8. The dry etching method according to claim 5, wherein the mixed gas used in the first etching step is chlorine, methane gas, and boron trichloride instead of chlorine and methane gas.