JPH08274077A - Plasma etching - Google Patents

Abstract

PURPOSE: To plasma-etch a refractory metal polycide layer with an etching gas containing at least chlorine oxide compound gas, so as to achieve high levels of properties, such as, selectivity, anisotropy and antipollution property, while maintaining a practical etching rate. CONSTITUTION: A gate insulating film 2 is formed on a semiconductor substrate 1, and a refractory metal polycide layer 5 is formed thereon. In addition, a resist mask 6 patterned in a predetermined shape is formed on the refractory metal polycide layer, thus forming a substrate to be etched. The substrate is set on a substrate stage of a biased ECR plasma etching system, and the refractory metal polycide layer 5 is continuously etched using the resist pattern 6 as a mask. In this case, plasma etching is performed with an etching gas containing at least a chlorine oxide compound gas, for example, a gas selected from the group consisting of Cl2 O, ClO2 , and Cl2 O7 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching method, and more specifically, when etching a refractory metal polycide layer to form a refractory metal polycide gate electrode / wiring, anisotropy, selectivity, The present invention relates to a novel plasma etching method for a refractory metal polycide layer that can meet various requirements such as etching rate and cleanliness.

[0002]

2. Description of the Related Art Polycrystalline silicon has been widely used as a gate electrode / wiring material for semiconductor devices such as LSIs. In recent years, the design rule of this semiconductor device has been miniaturized from a half micron level to a quarter micron level, and as the demand for high-speed devices such as highly integrated memory devices has increased, it is about an order of magnitude lower than that of polycrystalline silicon. Refractory metal silicides having a resistance value are being used. When forming a gate electrode using refractory metal silicide, first consider the interface characteristics with the gate insulating film, which easily affects the device characteristics and reliability, and first consider the impurities that have been proven in the past on the gate insulating film. A polycrystal silicon (DOPOS) layer is formed, and a refractory metal silicide layer is stacked on top of this. Such a laminated structure is collectively called polycide. Tungsten silicide as a refractory metal silicide (WSi _x) is common, referred to in particular tungsten polycide polycide having the WSi _x (W polycide).

By the way, the polycide layer brings new difficulties to the plasma etching process because it is necessary to continuously perform anisotropic etching on two types of material layers having different etching characteristics. That is, the lower polycrystalline silicon layer has a higher etching rate due to the difference in vapor pressure of the halide, which is an etching reaction product, and the interface between the polycrystalline silicon layer and the refractory metal silicide layer Undercuts and side etches are likely to occur in the formed pattern due to the formation of a new reaction layer. These shape abnormalities cause a shift in the channel region width, an offset region where impurities are not implanted at the time of ion implantation for forming source / drain regions, and a decrease in dimensional accuracy at the time of sidewall formation for realizing an LDD structure. Let
In addition, there is also an increase in wiring resistance due to a decrease in wiring cross-sectional area, both of which are unacceptable problems for deep submicron rule devices.

Conventionally, a gas that has been widely used as an etching gas for polycide is, for example, Monthly Semiconductor World magazine (published by Press Journal), October 1989.
It is a chlorofluorocarbon (CFC) gas represented by Freon 113 (C ₂ Cl ₃ F ₃ ) as reported on pages 126 to 130 of the monthly issue. This is because the F atom and the Cl atom coexist in the molecule, so that the reaction in the radical mode and the reaction in the ion assist mode both proceed, and further, the carbon-based polymer is deposited to form the side wall protective film, so that a high-speed difference occurs. Isotropic etching is possible.

However, as is well known, it has been pointed out that CFC gas contributes to the destruction of the ozone layer of the earth, and in the field of dry etching as well, from the viewpoint of environmental protection, an etching gas and a substitute for CFC gas can be used. There is an urgent need to establish the technology for its use, that is, the dechlorofluorocarbon process.

A demand for miniaturization of such design rules,
Also, from the viewpoint of CFC removal, there has been an attempt to utilize a Br compound as a main etching species in recent years. For example, J.Vac.
Sci.Technol. , A8 (3) , May / Jun 1990, p1696 and Digest
of Papers 1989 2nd MicroProcess Conference, p19
0, or in JP-A-2-89310, HBr
N ⁺ -type polycrystalline silicon gate electrode etching using Br ₂ and Br ₂ has been reported. Br has a large ionic radius,
It does not easily enter the crystal lattice or crystal grain boundaries of the silicon-based material layer. Therefore, there is little concern that the silicon-based material layer is isotropically etched uncontrollably like fluorine radicals (F ^* ), and anisotropic etching can be advanced by the ion assist mechanism. Further, as is clear from the fact that the interatomic bond energy of Si—O bond is much larger than that between Si—Br, a high selection ratio with the gate insulating film made of SiO ₂ can be achieved. Furthermore, since the surface of the resist mask can be coated with a CBr _x polymer having a low vapor pressure, the Br-based etching gas is also advantageous in that the selectivity with respect to the resist can be improved.

[0007] Further, as another measure for removing CFCs, CFC1
In place of No. 13, etching of the W polycide layer with Cl ₂ / CH ₂ F ₂ mixed gas system is described in, for example, Proceedings of 52nd Annual Meeting of the Society of Applied Physics (1991 Autumn Meeting).
8. There is a report in Lecture No. 9a-ZF-6. By optimizing the mixing ratio of this gas system, anisotropic etching can be performed by using the carbon-based polymer derived from CH ₂ F ₂ for the side wall protection film.

Further, it has been proposed to attempt to achieve this by cooling the substrate to be etched at a low temperature, rather than achieving high anisotropy in the side wall protective film formed by depositing a polymer product. This process, which is so-called low temperature etching, is a method of controlling the temperature of the substrate to be etched to 0 ° C. or lower, thereby freezing or suppressing the radical reaction in the lower portion of the resist pattern to prevent a shape abnormality such as undercut. For example, in the 35th Joint Lecture on Applied Physics (Spring Annual Meeting 1988) Proceedings p495, Lecture No. 28a-G-2, the wafer was cooled to -130 ° C. and silicon was used using SF ₆ gas. An example in which a substrate is etched by a trench and an n ⁺ -type polycrystalline silicon layer is etched is reported.

[0009]

As described above, although a process in which de-CFC is taken into consideration has been conventionally proposed, each of the above-mentioned dry etching methods still has a problem to be solved. First, B including HBr
When the process using the r-based gas is applied to the etching of the W polycide layer, a large amount of WBr _x is sputtered during the etching of the upper layer WSi _x , which adheres to the wall of the etching chamber due to its low vapor pressure and deteriorates the particle level. Let In addition, B, which is basically less reactive,
Since the r-type chemical species is used as the etchant, there is a problem that the etching rate is lowered.

On the other hand, etching with a Cl ₂ / CH ₂ F ₂ mixed gas system has a problem that the carbon-based polymer tends to be excessively deposited. That is, CH ₂ F ₂ is C ₄ F ₈ ,
Compared with gas such as C ₂ Cl ₂ F ₄ (CFC114) or CCl ₄ , there are many reaction products, and therefore, the etching rate by incident ions is low. For example, 1988 Dry Process Symposium Abstracts p74, II-8 There is a report. Therefore, the use of CH ₂ F ₂ gas is highly likely to leave problems such as particle contamination and etching rate.

In contrast to the above two methods, low temperature etching is considered to be one of the effective means for the de-CFC process. However, if the achievement of high anisotropy is to rely only on freezing or suppression of radical reaction, it is necessary to control the temperature at a cryogenic level that requires cooling by liquid nitrogen. For this reason, problems such as maintenance of the cooling device and reliability of the vacuum seal portion occur on the device side. In addition, it takes a long time to cool the substrate to be etched and the subsequent temperature rising process, and the decrease in throughput cannot be overlooked.

An object of the present invention is to secure a practical etching rate and to achieve various levels of difficult-to-stand characteristics such as a resist mask selectivity, a base material layer selectivity, high anisotropy and low contamination. To provide a plasma etching method for a refractory metal polycide layer, which can be performed in a realistic temperature range.

Another object of the present invention is to prevent undercut and side etching of the polycide gate electrode, shift the channel region width, and offset that impurities are not implanted at the time of ion implantation for forming source / drain regions. There are no problems such as generation of a region, reduction of dimensional accuracy when forming a sidewall for realizing an LDD structure, and increase of wiring resistance due to reduction of wiring cross-sectional area.
A plasma etching method capable of forming a semiconductor device having good controllability.

[0014]

The plasma etching method of the present invention is also proposed in order to solve the above-mentioned problems, and a high melting point metal polycide layer formed on a substrate is
It is characterized in that plasma etching is performed by using an etching gas containing at least a chlorine oxide-based compound gas.

Further, the plasma etching method of the present invention is
A first plasma etching step of plasma-etching the refractory metal polycide layer formed on the substrate with a mixed gas containing at least a chlorine oxide-based compound gas and an F-based gas; And a second plasma etching step of plasma-etching the lower polycrystalline silicon layer with an etching gas containing a Br-based gas. The F-based gas here means SF ₆ , NF ₃ , C
It may be a general-purpose gas containing a fluorine atom such as F ₄ or XeF ₂ .

Furthermore, in the plasma etching method of the present invention, the refractory metal polycide layer formed on the substrate is
Plasma etching is performed while controlling the substrate to be etched to room temperature or below by an etching gas containing at least a chlorine oxide-based compound gas and an S-based compound gas that can generate free sulfur in plasma under discharge ionization conditions. . As an S-based compound gas that can generate free sulfur in plasma under discharge ionization conditions, an S / S ratio having an X / S ratio of less than 6 is used.
X-based gas (X represents a halogen element or hydrogen), for example _{S 2 F 2, SF 2,} SF 4, S 2 F fluoride other than SF _6, such as _{10 Iougasu, S 2 Cl 2, S 3} Cl 2, SCl
Sulfur chloride gas such as ₂ , S ₂ Br ₂ , S ₃ Br ₂ , SB
Sulfur bromide gas such as r ₂ and H ₂ S can be exemplified. SF ₆ gas, which is well known as a sulfur fluoride compound, has an F / S ratio of 6 and does not release free sulfur into plasma under discharge ionization conditions.
Exclude this. In addition, the term below room temperature referred to here is
It means the temperature of a clean room in a normal semiconductor manufacturing process, and it is usually about 25 ° C. or lower, and low-temperature cooling at a level of −several tens of ° C. is not required.

Examples of the chlorine oxide compound gas employed in the present invention include Cl ₂ O, ClO ₂ and Cl ₂ O ₇ , and at least one of them may be used alone or in combination.

[0018]

The essence of the present invention employs a chlorine oxide type compound gas as an etching gas, and in the etching of a refractory metal silicide layer, a refractory metal oxychloride having a relatively large vapor pressure is used as a reaction product. The point is that the etching reaction proceeds while it is generated.

Generally, the refractory metal oxychloride has a vapor pressure intermediate between that of the refractory metal chloride and that of the refractory metal fluoride. Therefore, etching of refractory metals with chlorine oxide-based compound gas has a higher etching rate than that with Cl-based gas, and the oxychloride-based compound gas is ion-assisted only at the bottom of the pattern where ions are vertically incident. The reaction product is volatilized or removed by sublimation. On the other hand, at the side wall of the pattern where the vertical incidence of ions does not occur in principle, the reaction product is not removed and it functions as a side wall protective film, protecting the side surface of the pattern from isotropic radical reaction due to excessive radicals. Then
Prevent side etching. Therefore, unlike the case of the conventional plasma etching using the F-based gas, it is not necessary to deposit the polymer-based sidewall protection film thickly, and highly anisotropic processing is achieved. Further, unlike the case of using a Br-based gas gas, there is no fear of causing a significant decrease in the etching rate or generation of etching residues. The boiling points of W compounds, which are typical refractory metals, are shown below. WF ₆ 17.5 ° C WOCl ₄ 227.5 ° C WCl ₅ 275.6 ° C WBr ₅ 333 ° C

Next, in the lower polycrystalline silicon layer, while the etching reaction proceeds while forming SiCl _x as a reaction product, SiO _x is formed on the side surface of the pattern, which serves as a side wall protective film. However, anisotropic etching is achieved.

Further, at the time of over-etching, the film loss of the underlying oxide film such as the gate oxide film is reduced as compared with the case of using the F-based gas, and high selective ratio etching is possible. Therefore, also in the patterning of polycrystalline silicon, a high selection ratio with respect to the underlying material layer can be obtained without cooling the substrate to be etched at an extremely low temperature, and it is possible to perform patterning in one step together with the refractory metal silicide layer, thereby improving throughput. Contribute to improvement.

As an example, a technique of using a mixed gas of Cl ₂ and O ₂ as an etching gas for patterning a refractory metal layer such as W is disclosed in JP-A-6-108272. It is in principle possible to pattern the refractory metal polycide layer with this mixed gas, but it is necessary to study the optimization of the mixing ratio and the process when the composition of the mixed gas deviates. There are problems of unstable products and complication of etching gas introduction system valves and mass flow meters.

The etching mechanism of the refractory metal polycide layer using the chlorine oxide type compound gas is as described above.
In the present invention, in order to achieve a higher etching rate, a higher anisotropy and a higher selection ratio, a method of plasma etching in two steps is proposed. That is, in the first plasma etching step for patterning the refractory metal silicide layer, F ^* is added to the etching reaction system by using a mixed gas of a chlorine oxide-based compound gas and an F-based gas, so that the vapor pressure is large. Generate WF ₆ . Thereby, the improvement of the etching rate is achieved. On the other hand, the side surface of the patterned refractory metal silicide layer is protected by a refractory metal oxychloride or WCl _x or WO _x , and the mechanism of ensuring anisotropy is the same as in the case of chlorine oxide compound gas alone gas. Is.

Subsequently, in the etching of the lower polycrystalline silicon layer, the etching gas containing Br-based gas is used for patterning to perform anisotropic etching while ensuring a high selection ratio with respect to the underlying gate oxide film. Is achieved.

The third point of the present invention is to add a sulfur-based compound capable of releasing free sulfur (S) in plasma under discharge ionization conditions to a chlorine oxide-based compound gas, and to add sulfur onto the substrate to be etched. Is to etch while depositing. In this case, in addition to WClO ₄ which is an etching reaction product, sulfur deposition can also be used as a sidewall protective film. Further, the low temperature cooling effect of appropriately cooling the substrate to be etched promotes the deposition of the decomposition products of the resist mask and the decomposition products of the resist mask containing halogen. All of these deposits adhere to the patterning side surface where no ions are incident and suppress the radical reaction, so that highly anisotropic processing without side etching is possible. In addition, since the sidewall protection film is strengthened, it is possible to reduce the incident ion energy required for anisotropic processing, and it is possible to improve the selection ratio and reduce damage to the underlying material layer such as the gate oxide film. More thorough.

In addition to sulfur compounds capable of releasing free sulfur (S) into plasma under discharge ionization conditions, N
If an N-based gas such as ₂ is added, it is possible to proceed with etching while depositing a sulfur nitride-based compound such as (SN) _n (polythiazyl) on the substrate to be etched. The deposited film of polythiazyl exerts a stronger sidewall protection effect than sulfur. The N-containing gas, it is possible to use N ₂ H ₂ and its derivatives and NF ₃ or the like in addition to the N _2.

The side wall protective film made of sulfur or polythiazil can be removed by sublimation by heating the substrate to be etched after the etching is completed, and no contamination or particle contamination is left on the substrate to be etched. The sublimation temperature is about 90 ° C. for sulfur and about 150 ° C. for polythiazyl in a reduced pressure atmosphere. Sulfur or polythiazil may be removed by ashing at the same time as the resist mask during resist ashing.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

Example 1 In this example, the present invention is applied to a gate electrode / wiring process,
The W polycide layer is made of Cl ₂ O (mp = −20 ° C., bp =
This is an example of etching using a gas (3.8 ° C.). This process will be described with reference to FIG.

First, as shown in FIG. 1A, for example, 8
SiO is formed on the semiconductor substrate 1 made of silicon or the like having an inch diameter.
_{After the} gate insulating film 2 made of 2 is formed to a thickness of 10 nm, a refractory metal polycide layer 5 is formed on the gate insulating film 2, and a resist mask 6 patterned to have a predetermined shape is further formed on the high melting point metal polycide layer 5 to form a substrate to be etched. The refractory metal polycide layer 5 is formed by sequentially depositing and laminating a 100-nm-thick polycrystalline silicon layer 3 doped with an n-type impurity and a 100-nm-thick refractory metal silicide layer 4 made of WSi _x . The resist mask 6 is, for example, a negative type 3
A chemical amplification type photoresist (trade name: SAL-601 manufactured by Shipley Co., Ltd.) of a component type was applied and exposed to KrF excimer laser to form a pattern width of 0.35 μm.

Next, this substrate to be etched is set on a substrate stage of, for example, a substrate bias application type ECR plasma etching apparatus, and the refractory metal polycide layer 5 is continuously etched using the resist pattern 6 as a mask. The etching conditions at this time are as follows, for example. Cl ₂ O flow rate 25 sccm Gas pressure 0.67 Pa Microwave power 850 W (2.45 GHz) RF bias power 150 W (13.56 MH)
z) Substrate temperature at room temperature

In this etching step, the radical reaction mainly containing Cl ^*, which is generated by dissociation from Cl ₂ O by ECR discharge, proceeds by a mechanism assisted by ions of Cl ⁺ , O ^+, etc. The refractory metal silicide layer 4 exposed from the mask 6 is removed by etching in the form of oxychloride such as WOCl ₄ or SiCl _x , and the polycrystalline silicon layer 3 is changed to SiCl _x . At the same time, WCl _x , WO _x or SiO _x having a low vapor pressure adheres and deposits on the side surfaces of the resist mask 6 and the refractory metal polycide layer 5 where patterning proceeds, and the side walls are formed as shown in FIG. The protective film 7 is formed. Although the side wall protective film 7 has a small amount of deposition, it exhibits high etching resistance and contributes to anisotropic processing. The side wall protective film 7 also contains a small amount of decomposition products obtained by sputtering the resist mask 6 and decomposition products containing halogen.

As a result of this etching, the resist mask 6
A pattern of the refractory metal polycide 5 having a good anisotropic shape was formed immediately below. Further, since the etching reaction system does not contain a fluorine-based chemical species, a high selection ratio can be obtained even with respect to the underlying gate insulating film 2, and damage or film reduction of the gate insulating film 2 can be prevented.

After the etching is completed, the substrate to be etched is conveyed to the plasma ashing apparatus attached to the above etching apparatus, and the resist mask 6 and the side wall protective film 7 are removed by O ₂ plasma ashing. Finally, the ashing residue may be removed by performing spray type spin cleaning with pure water. Megasonic cleaning and brush scrubbing are also effective for removing ashing residues. As a result,
As shown in FIG. 1C, a gate electrode / wiring consisting of a refractory metal polycide 5 pattern having a good shape with a width of 0.35 μm was obtained.

According to the present embodiment, the one-step etching using the chlorine oxide-based compound gas alone gas does not cause side etching, and polyside gate processing with a high gate insulating film selection ratio and a high resist mask selection ratio is achieved. .

Example 2 In this example, the same refractory metal polycide layer was etched in two steps, and in the first etching step, ClO ₂ was used first.
After etching the upper layer side WSi _x with the / SF ₆ mixed gas, in the second etching step, the lower layer side polycrystalline silicon layer is etched by switching to HBr gas. This process will be described with reference to FIG. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals.

The substrate to be etched of this embodiment is shown in FIG.
Shown in Since this is the same as FIG. 1A, the description is omitted. This substrate to be etched is a substrate bias application type EC
The refractory metal silicide layer 4 made of WSi _x is etched under the following conditions by setting the R plasma etching apparatus. ClO ₂ flow rate 25 sccm SF ₆ flow rate 25 sccm Gas pressure 0.67 Pa Microwave power 850 W (2.45 GHz) RF bias power 150 W (13.56 MH)
z) Etching substrate temperature at room temperature

In this etching step, a radical reaction using a large amount of F ^* and Cl ^*, which are dissociated and produced from SF ₆ by ECR discharge, as main etchants causes SF _x ⁺ and Cl ^+.
Etching progresses at a high speed by a mechanism assisted by ions such as. WSi _x exposed from the resist mask 6 is
WF _x , WOF _x , SiF _x, WOCl _x, etc. are formed and selectively removed. The formation mechanism of the side wall protective film 7 is
This is similar to the mechanism described above in Example 1, and the WC
The main component is l _x , WO _x, and decomposition products of the resist mask, and etching proceeds anisotropically.
This first etching step was completed when the polycrystalline silicon layer 3 was exposed as shown in FIG. 1B, but the high melting point metal silicide layer was formed on the polycrystalline silicon layer 3 exposed from the resist mask 6. In some cases, the remaining portions 4a of 4 are scattered.

Next, the remaining portion 4a of the refractory metal silicide layer and the polycrystalline silicon layer 3 are etched under the following etching conditions as an example. HBr flow rate 50 sccm Gas pressure 0.67 Pa Microwave power 850 W (2.45 GHz) RF bias power 150 W (13.56 MH)
z) Substrate temperature to be etched Normal temperature In this etching step, the radical reaction mainly consisting of Br ^* proceeds in a form of assisting the ion incidence without the F ^* and Cl ^* participating in the reaction. The components of the side wall protective film 7 include decomposition products of the resist mask 6 and bromine.

As a result, as shown in FIG. 2C, the polycide gate electrode is formed with a good anisotropic shape without causing side etching. Further, a high selection ratio was secured for the underlying gate insulating film 2 and no damage was given. After that, normal O ₂ plasma ashing was performed to remove the resist mask 6 and the side wall protective film 7, and the polycide gate electrode shown in FIG. 2D was completed.

According to this embodiment, it is possible to improve the throughput by shortening the etching time and process the gate electrode satisfying all the characteristics of high anisotropy, high selectivity, low damage and low particles. In the second etching step, a small amount of O ₂ may be added to Br-based gas.

Example 3 In this example, S ₂ Cl ₂ was adopted as an S-based compound gas capable of producing free sulfur in plasma under discharge ionization conditions, and a Cl ₂ O / S ₂ Cl ₂ mixed gas was used. In this example, the W polycide layer is etched in one step. This process will be described again with reference to FIG.

The substrate to be etched used in this example is the same as that used in Example 1 and shown in FIG. This substrate to be etched is, for example, a substrate bias application type ECR.
It is set on the substrate stage of the plasma etching apparatus, and the refractory metal polycide layer 5 is etched using the resist pattern 6 as a mask. The substrate stage of the etching apparatus used in this embodiment incorporates a mechanism for controlling the substrate to be etched below room temperature by circulating, for example, an ethanol coolant. The etching conditions at this time are
For example: Cl ₂ O flow rate 25 sccm S ₂ Cl ₂ flow rate 25 sccm Gas pressure 0.67 Pa Microwave power 850 W (2.45 GHz) RF bias power 100 W (13.56 MH)
z) Substrate temperature 0 ° C. Since the foot point of S ₂ Cl ₂ is 135.6 ° C.,
The container is heated by a heater or the like to be vaporized and introduced into the etching chamber. At this time, the introduction pipe system was heated by a ribbon heater or the like to prevent dew condensation due to condensation of S ₂ Cl ₂ inside the pipe.

In this etching step, a radical reaction using Cl ^*, which is dissociated and produced from Cl ₂ O and S ₂ Cl ₂ by ECR discharge, as a main etching species, causes Cl ⁺ and SCl.
_The reaction proceeds by a mechanism assisted by ions such as _x ⁺ , O ^+, etc., and the refractory metal silicide layer 4 exposed from the resist mask 6 is in the form of oxychloride such as WOCl ₄ or SiCl _x. The crystalline silicon layer 3 is SiC
It becomes l _{x and is} selectively removed. At the same time, on the resist mask 6 and the side surface of the refractory metal polycide layer 5 where patterning proceeds, simultaneously with WCl _x , WO _x or SiO _x having a low vapor pressure, sulfur dissociated from S ₂ Cl ₂ is deposited and deposited. As shown in FIG. 1B, the side wall protective film 7 is formed. Although the side wall protective film 7 has a small amount of deposition, it exhibits high etching resistance and contributes to anisotropic processing. The side wall protective film 7 also contains a small amount of decomposition products obtained by sputtering the resist mask 6 and decomposition products containing halogen.

In this embodiment, the substrate to be etched is set at 0 ° C.
Since it is cooled to a relatively low temperature, the radical reaction on the side surface of the pattern is suppressed, and the contribution of the above-mentioned strong side wall protective film is excellent regardless of the condition that the incident ion energy is reduced. Anisotropic processing is possible. Naturally, the damage and loss of the gate oxide film, which is the base material layer, is further reduced. Further, since the amount of sulfur deposition is utilized, the deposition of carbon-based polymer, which is a decomposition product of the resist mask, can be reduced, and particle contamination in the substrate and the chamber can be reduced.

As a result, a pattern of the refractory metal polycide 5 having a good anisotropic shape was formed immediately below the resist mask 6. After the etching is completed, the substrate to be etched is transferred to the plasma ashing device attached to the above-mentioned etching device, and the resist mask 6 and the side wall protective film 7 are removed by O ₂ plasma ashing. Finally, the ashing residue may be removed by performing spray type spin cleaning with pure water. Megasonic cleaning and brush scrubbing are also effective for removing ashing residues. As a result, as shown in FIG. 1C, a gate electrode / wiring consisting of a refractory metal polycide 5 pattern having a good shape with a width of 0.35 μm was obtained.

According to the present embodiment, the side etching is eliminated by the one-step etching with the mixed gas of the chlorine oxide-based compound gas and the S-based compound gas which can generate free sulfur in the plasma under the discharge ionization condition. As compared with the first embodiment, the polycide gate processing having a higher selection ratio to the gate insulating film 2 and a higher selection ratio to the resist mask 6 is achieved.

Although the present invention has been described with reference to three embodiments, the present invention is not limited to these embodiments.

For example, as the chlorine oxide compound gas, Cl
_{Although 2} O and ClO ₂ are used, Cl ₂ O ₇ may be used as described above in the section of means for solving the problem.

As the fluorine-based gas, S exemplified in the examples is used.
In addition to F ₆ , general-purpose F-based compounds having F atoms such as NF ₃ , ClF ₃ and XeF ₂ can be used.

In addition, if a rare gas such as He or Ar is used as the additive gas, various effects such as sputtering, cooling, dilution and discharge stability can be expected.

In particular, if N ₂ is introduced as an additive gas,
Sulfur nitride compounds such as polythiazyl (SN) _n inorganic polymers that react with S atoms released from sulfur compounds or fluorinated sulfur compounds that can release free sulfur into plasma under discharge dissociation conditions Can be used as a sidewall protection film. This etching method also has a high selection ratio,
It is an excellent method for achieving high anisotropy and low damage.

The refractory metal silicide layer is made of the above-mentioned WSi.
Besides MoSi _x of _x, TaSi _x, it may be a TiSi _x and various silicide layer.

Polycrystalline silicon is usually used as the lower layer of the refractory metal polycide layer. However, as disclosed in Japanese Patent Application Laid-Open No. 63-163 filed by the applicant of the present invention, amorphous silicon is used. May be used. The etching characteristics of amorphous silicon are almost the same as those of polycrystalline silicon. This amorphous silicon also has a polycide structure because it changes into polycrystalline silicon by the activation heat treatment process of the implanted impurities at the stage of finally functioning as the gate electrode / wiring of the MOSFET.

Further, the substrate bias applying type ECR plasma etching device was adopted as the etching device to be used, but a parallel plate type RIE device, a helicon wave plasma etching device, an ICP (Inductively Coupled Plasm) device was used.
a) Etching equipment, TCP (Transformer Coupled Plas)
Of course, it is possible to use various etching devices such as ma) etching devices.

[0056]

As is apparent from the above description, the present invention employs a chlorine oxide-based compound gas in the etching of a high-melting-point metal polycide layer such as W polycide. The oxyfluoride can be used as a reaction product. The oxyfluoride of the refractory metal is removed by the ion assist reaction only on the vertical incident surface of the ions, and the etching reaction proceeds at a practical etching rate. Further, on the side surface of the pattern, it becomes possible to use a reaction product having a low vapor pressure such as refractory metal oxyfluoride or refractory metal oxide or chloride as a side wall protective film. For this reason, the side surface of the pattern is protected from the side attack of radicals, side etching is prevented, and the incident ion energy required for anisotropic etching can be reduced. This allows
The selection ratio with respect to the underlying gate insulating film is improved, damage to the gate insulating film can be reduced, and the problem of redeposition due to underlying sputtering can be solved. Of course, the selection ratio with respect to the resist mask is also improved, which is advantageous in reducing the dimensional conversion difference due to the receding of the resist pattern.

In the first etching step for patterning the refractory metal silicide layer by plasma etching in two stages, a mixed gas of a chlorine oxide-based compound gas and an F-based gas and a second etching for patterning the polycrystalline silicon layer are used. If a Br-based gas is used in the process, the etching rate of the refractory metal silicide layer is improved, the throughput of the entire process is improved, and the anisotropy and selectivity are further improved.

Further, if a chlorine oxide-based compound gas and an S-based compound gas capable of producing free sulfur in plasma under discharge ionization conditions are used together, the deposition of sulfur or polythiazil can be utilized, and the side wall protective film can be more effective. It will be strong.
For this reason, it is possible to reduce the substrate bias and the deposition of the carbon-based polymer, so that it is possible to reduce the particle contamination on the substrate and in the etching chamber while securing the above effect.

Since no CFC gas is used,
The dechlorofluorocarbon process becomes possible, which can contribute to a cleaner environment.

[Brief description of drawings]

1A and 1B are schematic cross-sectional views for explaining Embodiments 1 and 2 to which the present invention is applied, in the order of steps, in which FIG. The melting point metal polycide layer is formed and a resist mask is further formed. (B) The refractory metal polycide layer is etched to form a refractory metal polycide pattern. (C) is the resist mask and sidewall protection. The film is removed and the refractory metal polycide pattern is completed.

2A and 2B are schematic cross-sectional views for explaining a third embodiment to which the present invention is applied in the order of steps, in which FIG. 2A is a high-level view of a polycrystalline silicon layer and a refractory metal silicide layer formed on a base gate insulating film. A state where a melting point metal polycide layer is formed and a resist mask is further formed, (b) is a state where the high melting point metal silicide layer is etched to expose the polycrystalline silicon layer, and (c) is a state where the polycrystalline silicon layer is etched. Then, the refractory metal polycide pattern is formed, and (d) shows the refractory metal polycide pattern completed by removing the resist mask and the sidewall protection film.

[Explanation of symbols]

 1 semiconductor substrate 2 gate insulating film 3 polycrystalline silicon layer 4 refractory metal silicide layer 4a residual part of refractory metal silicide layer 5 refractory metal polycide layer 6 resist mask 7 sidewall protection film

Claims (4)

[Claims] 1. A plasma etching method for a refractory metal polycide layer, which is formed by laminating a polycrystalline silicon layer and a refractory metal silicide layer on a substrate in this order, wherein a plasma is formed by an etching gas containing at least a chlorine oxide-based compound gas. A plasma etching method for a refractory metal polycide layer, which comprises etching. 2. A plasma etching method for a refractory metal polycide layer in which a polycrystalline silicon layer and a refractory metal silicide layer are laminated in this order on a substrate, and at least chlorine oxide-based compound gas and F-based gas are used. A first plasma etching step of plasma etching the refractory metal silicide layer with a mixed gas containing the gas; and a second plasma etching step of plasma etching the polycrystalline silicon layer with an etching gas containing at least a Br-based gas. A method of plasma etching a refractory metal polycide layer, comprising: 3. A plasma etching method for a refractory metal polycide layer in which a polycrystalline silicon layer and a refractory metal silicide layer are stacked in this order on a substrate, wherein at least chlorine oxide compound gas and discharge ionization conditions are used. Plasma etching method for a refractory metal polycide layer, characterized in that the substrate to be etched is plasma-etched while being controlled to room temperature or below by an etching gas containing an S-based compound gas capable of generating free sulfur in plasma. . 4. The chlorine oxide-based compound gas is Cl ₂ O or C.
3. At least one selected from the group consisting of 10 ₂ and Cl ₂ O _7.
Or the plasma etching method according to any one of 3 above.