JP3570098B2 - Dry etching method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dry etching method, and more particularly, to a dry etching method for forming a wiring pattern from an Al-based material layer formed on a SiO ₂ interlayer insulating film.
[0002]
[Prior art]
As the degree of integration of semiconductor devices such as LSIs advances and the design rules thereof are miniaturized from sub-half micron to quarter micron, the wiring pattern width is also reduced. Conventionally, as a wiring material of a semiconductor device, Al or an Al-Si alloy obtained by adding 1 to 2% of Si to Al, and an Al-Cu alloy obtained by adding 0.5 to 1% of Cu as a measure against stress migration are used. Many system materials are used. In dry etching of the Al-based material layer, a chlorine-based gas is used, and a mixed gas of BCl ₃ / Cl ₂ disclosed in Japanese Patent Publication No. 59-22374 is a typical example. A chemical species that contributes as a main etching species in the dry etching of the Al-based material layer is a chlorine radical, which causes a spontaneous and extremely rapid etching reaction to proceed. However, since etching proceeds isotropically with chlorine radicals alone, the ion assist reaction usually proceeds under conditions where the incident ion energy is increased to some extent, and the decomposition products of the resist mask sputtered by the incident ions are formed on the side walls. High anisotropy is achieved by using it as a protective film. BCl ₃ is a compound added to reduce a natural oxide film on the surface of the Al-based material layer, and also plays an important role of supplying BCl _x ⁺ as incident ions.
[0003]
By the way, in a process of sputtering a resist mask using a somewhat large incident ion energy in order to secure the high anisotropy as described above, a decrease in resist selectivity inevitably becomes a problem. The selectivity is only about 2. Such low selectivity causes a dimensional conversion difference from a resist mask in the processing of a fine wiring pattern, or causes a deterioration of an anisotropic shape. On the other hand, under the design rules of highly miniaturized semiconductor devices, it is required to reduce the thickness of a resist coating film from the viewpoint of improving the resolution in photolithography. Therefore, it is becoming difficult to achieve both high resolution based on a thin resist coating and high-precision etching through a resist mask formed from the thin resist coating.
[0004]
In order to cope with such a problem, conventionally, means for depositing a reaction product on the surface of a resist mask have been proposed. For example, in the Proceedings of the 33rd Integrated Circuit Symposium (1987), P114 reports a process using SiCl ₄ as an etching gas. This is to improve the etching resistance of the resist mask by coating the surface of the resist mask with Si. Also, Proceedings of the 11th Symposium on Dry Process , P45, II-2 (1989) has been reported process using BBr _3. This is intended to further enhance the etching resistance of the resist mask by coating the surface of the resist mask with CBr _x having a low vapor pressure. For protection mechanisms, such as a resist mask according to this CBr _x is, Monthly Semiconductor World, December 1990, are described in detail in P103~107 (press journal published by), a value of about 5 is reported as a resist selection ratio ing.
However, in order to obtain high resist selectivity, such as the numerical value of selectivity of approximately 5, must be a large accumulated amount of Si and CBr _x, possibly deteriorating the particle level is large.
[0005]
Another problem specific to the etching of the Al-based material layer is after-corrosion due to residual chlorine. Particularly in recent years, disadvantageous conditions have been prepared from the viewpoint of preventing after-corrosion, such as addition of Cu to an Al-based material layer, or lamination of an Al-based material layer with a different material layer such as a barrier metal or an antireflection film. A more thorough countermeasure than ever has been desired. As countermeasures against after-corrosion, plasma cleaning using a fluorocarbon-based gas such as CF ₄ or CHF ₃ , removal of a resist mask and a side wall protective film by oxygen plasma ashing, combination of plasma cleaning with CH ₃ gas and substrate washing are known. I have. All of these are intended to remove residual chlorine, either by replacing chlorine or bromine with fluorine to increase the vapor pressure of the reaction product, or by removing a resist mask or sidewall protective film containing a large amount of residual chlorine to the atmosphere. It is removed by ashing before opening, a chlorine compound is converted into an inert compound such as ammonium chloride, or at the same time, a coating of AlF ₃ or Al ₂ O ₃ having high corrosion resistance is made of an Al-based material. By forming on the surface of the layer, after-corrosion is suppressed. However, the fact is that even if the above-mentioned countermeasures are taken, they do not provide a decisive effect. In view of such circumstances, it has been eager to establish after-corrosion-free dry etching of an Al-based material layer having a high resist selectivity by a clean process that does not cause an increase in particles.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to improve a high resist selectivity and after-corrosion resistance, to provide a clean etching process that does not cause an increase in particles, and to achieve a high integration, high performance, and a high design that are designed based on fine design rules. An object of the present invention is to provide a dry etching method that can meet any requirements of reliability.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the dry etching method according to the first aspect of the present invention, the Al-based material layer formed on the substrate is formed by combining one of H ₂ O and H ₂ O ₂ with a chlorine-based compound. An etching step of performing etching while forming an oxychloride of Al as a sidewall protective film with the etching gas having the etching gas.
[0008]
In the dry etching method of the invention of claim 2, an Al-based material layer formed on the substrate, an etching gas having as of one of H ₂ O or H ₂ O ₂ and chlorine-based compounds, sidewall protection The film is characterized by comprising an etching step of etching while forming an oxychloride of Al, and a plasma treatment step of heating the substrate after the etching step and using a gas containing a fluorine-based compound.
[0009]
In the dry etching method according to the third aspect of the present invention, the substrate on which the Al-based material layer is formed is controlled to a room temperature or less,
An etching step of etching the Al-based material layer with an etching gas containing either H ₂ O or H ₂ O ₂ and a sulfur-based compound that generates free sulfur in plasma under discharge dissociation conditions; It is characterized by having.
[0010]
In the dry etching method according to the fourth aspect of the present invention, the substrate on which the Al-based material layer is formed is controlled to a room temperature or lower,
The Al-based material layer, and either one of the one H 2 _O or H ₂ O _2, and an etching step of etching with an etching gas having a sulfur-based compounds which form free sulfur in a plasma discharge dissociation conditions ,
A plasma treatment step of heating the substrate after the etching step and using a gas containing a fluorine-based compound.
[0011]
In a preferred embodiment of the plasma processing step according to claims 2 and 4, the plasma density is 1 × 10 ¹¹ cm ⁻³ or more and 1 × 10 ¹⁴ cm ⁻³ or less.
[0012]
The operation of the above means will be described below.
The method according to claim 1, further comprising the step of etching with an etching gas containing one of H ₂ O and H ₂ O ₂ and a chlorine-based compound, wherein the wiring material layer made of Al or the like is oxychlorinated. The etching proceeds with the substance as a main reaction product. Oxychlorides, such as Al and Ti, which are generally used as wiring material layers, have a lower vapor pressure than pure chloride, and although reaction products are volatilized and removed at the bottom of the pattern subjected to vertical irradiation of ions, The oxides and oxychlorides of these metals are not volatilized in the side wall portions which are not subjected to the vertical irradiation, and anisotropic processing is performed by forming a side wall protective film. At the time of over-etching, in which the object to be etched is removed and the etchant becomes excessive, H atoms dissociated from H ₂ O or H ₂ O ₂ trap chlorine radicals, prevent progress of side etching, and cause anisotropic processing patterns. It is possible to maintain the natural shape.
[0013]
Therefore, since the etching form of the Al-based material layer has many elements of the ion-assisted reaction from the conventional radical reaction-based one, the side wall protection of the carbon-based polymer which is a decomposition product of the resist as in the related art is performed. It is not necessary to deposit a thick film, and anisotropic processing of a fine pattern can be performed even under etching conditions in which incident ion energy is reduced, so that selectivity to a resist mask can be improved. Then, an etching mask that can sufficiently withstand practical use can be formed even from a thin photoresist coating film, and it is possible to prevent the occurrence of a difference in processing dimension conversion, and not to sacrifice high resolution in photolithography.
[0014]
In addition, since the amount of carbon-based polymer deposition required to achieve high anisotropy and high selectivity can be reduced, particle contamination can be reduced, and after etching in a form incorporated into the carbon-based polymer. Therefore, the residual chlorine existing on the side wall of the wiring pattern is also reduced, so that the after-corrosion resistance is also improved. Furthermore, since the reduction of the incident ion energy also contributes to the improvement of the underlayer selectivity, the sputtering of the interlayer insulating film underlying the Al-based material layer during over-etching is reduced, and is taken in by the reattachment to the wiring pattern side wall. The residual chlorine existing in the form of reduced amount is also reduced, and after-corrosion can be effectively suppressed.
[0015]
After the etching step of the Al-based material layer according to Claims 2 and 4, the method further includes a step of heating the substrate and performing a plasma processing step using a gas containing a fluorine-based compound, so that the after-corrosion countermeasures are more thoroughly implemented. The chlorine remaining in the vicinity of the wiring pattern after etching is replaced with fluorine, and the vapor pressure of the wiring pattern side wall protective material that binds or occludes the residual chlorine is increased by plasma radiant heat, direct heating of the substrate, etc. Easier to do. Therefore, even if moisture in the air is adsorbed on the substrate after etching, a local battery using residual chlorine as an electrolyte is less likely to be formed, and after-corrosion of the Al-based material layer can be almost completely suppressed. Further, by setting the plasma density in the plasma processing step to 1 × 10 ¹¹ cm ⁻³ or more and 1 × 10 ¹⁴ cm ⁻³ or less, it is possible to set process conditions in which incident ion energy is suppressed without impairing the processing speed. Become.
[0016]
Liberating substrate Al based material layer is formed of claims 3 to control the room temperature or below, the Al-based material layer and one of those of H _{2 O} or H ₂ O _2, the plasma discharge dissociation conditions The one having a step of etching with an etching gas having a sulfur-based compound that generates sulfur is one that further reduces pollution and improves after-corrosion resistance, and includes metal oxychloride, which is an etching reaction product, In addition to the carbon-based polymer, sulfur can be used for the sidewall protective film of the wiring pattern. Since sulfur is deposited on a substrate controlled at room temperature or lower, the incident ion energy required for anisotropic processing can be further reduced, and selectivity can be improved and damage can be reduced. In addition, since the amount of carbon-based polymer deposited can be further reduced, particle contamination and after-corrosion can be more effectively reduced. Further, sulfur deposited on the substrate is easily sublimated when the substrate is heated to about 90 ° C. or higher, and thus does not become a source of particle contamination.
[0017]
【Example】
Hereinafter, the order of steps of a specific example of the present invention will be described with reference to the schematic sectional view of FIG.
FIG. 3A shows a state in which a resist mask is formed on an Al-based material layer, and FIG. 3B shows a state in which a wiring pattern having an anisotropic shape is formed and a sidewall protective film is formed. FIG. 3C shows a state in which the sidewall protective film has been removed, and FIG. 4D shows a state in which the resist mask has been removed by ashing.
[0018]
Example 1
In this embodiment, an Al-based material layer in which an Al layer containing a barrier metal, 1% Si and 0.5% Cu, and an antireflection film are sequentially laminated is mixed with Cl ₂ / BCl ₃ / H ₂ O. This is an example of dry etching using a gas. This will be described with reference to FIGS. 1 (a), 1 (b) and 1 (d).
[0019]
As shown in FIG. 1A, a barrier metal 4 having a Ti layer 2 having a thickness of about 0.03 μm and a TiN layer 3 having a thickness of about 0.07 μm on an SiO ₂ interlayer insulating film 1, and 1% Si and An Al-based material layer 7 is formed in which an Al layer 5 containing 0.5% Cu and having a thickness of about 0.4 μm and a TiON antireflection film 6 having a thickness of about 0.1 μm are sequentially laminated. Further, a wafer as a substrate having a resist mask 8 formed on the Al-based material layer 7 by a photolithography process was prepared. Then, the wafer was set in an RF bias applying type magnetic field microwave plasma etching apparatus, and the Al-based material layer 7 was dry-etched under the following conditions.
[0020]
Gas flow rate Cl ₂ / BCl ₃ / H ₂ O = 80/40/30 sccm
Pressure 2Pa
Microwave power 900W (2.45GHz)
RF bias 40W (2MHz)
Wafer temperature Normal temperature The etching rate of the Al-based material layer 7 was approximately 1 μm / min, and the selectivity with respect to the resist was approximately 4. Since H ₂ O is a liquid source, it was supplied to the etching chamber in a state of being vaporized by means such as heating evaporation or He gas bubbling.
[0021]
In the etching process under the above conditions, the radical reaction mainly using chlorine radicals dissociated and generated from Cl ₂ and BCl ₃ by ECR discharge is assisted by ions such as Cl _x ⁺ , BCl _x ⁺ , and O ^+. , The Al-based material layer 7 is mainly removed as a product such as AlCl _x , AlOCl _x , TiCl _x , and TiOCl _x . At the same time, a carbon-based polymer is generated from the decomposition product of the resist mask 8, and the amount of the carbon-based polymer is not as large as that of the conventional process. By forming the side wall protective film 9 as shown in (b), it contributes to anisotropic processing. Thus, the wiring pattern 7a having a favorable anisotropic shape could be formed.
[0022]
Further, since the incident ion energy required for anisotropic processing is reduced and the etching process can be performed with a smaller RF bias power than before, the SiO ₂ interlayer insulating film 1 is sputtered and the side wall of the wiring pattern 7a is formed. No phenomenon of reattachment was observed. Therefore, the amount of chlorine remaining on the side wall of the wiring pattern 7a after the etching was greatly reduced, and as a result, the occurrence of after-corrosion was suppressed. After the etching was completed, the wafer was subjected to O ₂ plasma ashing in a plasma ashing apparatus under ordinary conditions. As a result, as shown in FIG. 1D, the resist mask 8 and the side wall protective film 9 were removed by burning. Since the amount of the carbon-based polymer generated in the process of the present example was small, the particle level was low even in the wafer obtained after performing the processing a considerable number of times.
[0023]
Example 2
This embodiment is an example in which the Al-based material layer 7 is dry-etched while cooling the wafer at a low temperature using an S ₂ Cl ₂ / H ₂ O mixed gas. This will be described with reference to FIGS. 1 (a), 1 (b) and 1 (d).
[0024]
As in the first embodiment, as shown in FIG. 1A, a barrier metal 4 having a Ti layer 2 having a thickness of about 0.03 μm and a TiN layer 3 having a thickness of about 0.07 μm on an SiO ₂ interlayer insulating film 1. An Al-based layer in which an Al layer 5 containing 1% Si and 0.5% Cu and having a thickness of about 0.4 μm, and a TiON antireflection film 6 having a thickness of about 0.1 μm are sequentially laminated. A wafer was prepared, on which the material layer 7 was formed, and on which the resist mask 8 was formed on the Al-based material layer 7 by a photolithography process. Then, the wafer was set in an RF bias applying type magnetic field microwave plasma etching apparatus, and the Al-based material layer 7 was dry-etched under the following conditions.
[0025]
Gas flow rate S ₂ Cl ₂ / H ₂ O = 90/20 sccm
Pressure 2Pa
Microwave power 900W (2.45GHz)
RF bias 20W (13.56MHz)
Wafer temperature 0 ℃
The cooling of the wafer was performed by supplying and circulating an ethanol-based refrigerant from a chiller provided outside the apparatus to a cooling pipe embedded in the wafer mounting electrode. Since H ₂ O is a liquid source, it was supplied to the etching chamber in a state of being vaporized by means such as heating evaporation or He gas bubbling.
[0026]
In the etching process under the above conditions, sulfur generated by dissociation from S ₂ Cl ₂ as well as oxychloride and carbon-based polymer of Al and Ti also contribute as a component of the sidewall protective film 9. Therefore, the wiring pattern 7a having a good anisotropic shape as shown in FIG. 1B was able to be formed even under the condition where the RF bias power was further reduced from the case shown in the first embodiment. The etching rate of the Al-based material layer 7 in this embodiment was 900 nm / min, which was lower than that in the case of Embodiment 1 due to the cooling of the wafer and the increase of the deposits, but the resist selectivity was improved to approximately 6. . As a result, almost no decrease in the thickness of the resist mask 8 and no retreat of the edge were observed. In addition, the amount of carbon-based polymer generated can be further reduced by an amount that can be expected to deposit sulfur, and the underlayer selectivity is improved by further lowering the bias, and the sputter re-deposition of the SiO ₂ interlayer insulating film 1 is suppressed. As a result, the after-corrosion resistance has been greatly improved. After the etching was completed, the wafer was subjected to O ₂ plasma ashing in a plasma ashing apparatus under ordinary conditions. As a result, as shown in FIG. 1D, the resist mask 8 and the side wall protective film 9 were promptly removed. The sidewall protective film 9 contains a carbon-based polymer and sulfur. The sulfur is removed by sublimation by plasma radiation heat or reaction heat, and is also removed by a combustion reaction by oxygen radicals, leaving any particle contamination on the wafer. I never did.
[0027]
Example 3
In the present embodiment, after the Al-based material layer 7 is dry-etched while cooling the wafer at a low temperature by using a mixed gas of S ₂ Cl ₂ / H ₂ O _2, a reaction product attached to the side wall of the wiring pattern 7 a is removed. This is an example in which the residual chlorine is replaced with fluorine by a plasma post-treatment using a CF ₄ / O ₂ mixed gas. This will be described with reference to FIGS. 1 (a), (b), (c) and (d).
[0028]
As in the first embodiment, as shown in FIG. 1A, a barrier metal 4 having a Ti layer 2 having a thickness of about 0.03 μm and a TiN layer 3 having a thickness of about 0.07 μm on an SiO ₂ interlayer insulating film 1. An Al-based layer in which an Al layer 5 containing 1% Si and 0.5% Cu and having a thickness of about 0.4 μm, and a TiON antireflection film 6 having a thickness of about 0.1 μm are sequentially laminated. A wafer was prepared, on which the material layer 7 was formed, and on which the resist mask 8 was formed on the Al-based material layer 7 by a photolithography process. Then, the wafer was set in an RF bias application type magnetic field microwave plasma etching apparatus, and the Al-based material layer 7 was dry-etched under the following conditions.
[0029]
Gas flow rate S ₂ Cl ₂ / H ₂ O ₂ = 90/20 sccm
Pressure 2Pa
Microwave power 900W (2.45GHz)
RF bias 15W (2MHz)
Wafer temperature 0 ℃
The cooling of the wafer was performed by supplying and circulating an ethanol-based refrigerant from a chiller provided outside the apparatus to a cooling pipe embedded in the wafer mounting electrode. Since H ₂ O ₂ is a liquid source, it was supplied to the etching chamber in a state of being vaporized by means such as heating evaporation or He gas bubbling.
[0030]
Subsequently, the wafer was transferred to a post-processing chamber, and plasma post-processing was performed under the following conditions.
[0031]
Gas flow rate CF ₄ / O ₂ = 100/50 sccm
Pressure 10Pa
Microwave power 900W (2.45GHz)
RF bias 0W (2MHz)
Wafer temperature 100 ℃
[0032]
By this plasma post-treatment, the side wall protective film 9 was promptly removed as shown in FIG. The mechanism of this removal is, for carbon-based polymers, combustion by oxygen radicals, increase in vapor pressure by fluorine substitution, and the like, and for sulfur-based compounds, sublimation by wafer heating, combustion by oxygen radicals, and the like. Incidentally, chlorine remaining after being occluded or bonded to the resist mask 8 by the plasma post-treatment was also replaced by fluorine.
[0033]
Subsequently, the wafer was subjected to O ₂ plasma ashing in a plasma ashing apparatus under ordinary conditions. As a result, as shown in FIG. 1D, a wiring pattern 7a having a good anisotropic shape without an ashing residue could be formed. Then, even after the wafer on which the wiring pattern 7a was formed was opened to the atmosphere for 72 hours, no occurrence of after-corrosion was observed.
[0034]
As described above, specific examples of the present invention have been described in Examples 1, 2 and 3, but the present invention is not limited thereto, and the gist of the invention, such as the film type and structure of an object to be etched, an etching apparatus, and etching conditions, is described. It can be appropriately selected without departing from the scope.
For example, in addition to the ECR plasma etching apparatus used in this embodiment, a high-density plasma etching apparatus such as an ICP, a TCP, a helicon wave plasma etching apparatus, or various etching apparatuses such as a parallel plate RIE apparatus may be used. Application is also possible. Further, as a gas used for the plasma post-treatment, a NF ₃ / O ₂ mixed gas, an SF ₆ / O ₂ mixed gas, or the like can be used in addition to the CF ₄ / O ₂ mixed gas. Further, a rare gas such as Ar or He which can be expected to have a sputtering effect, a dilution effect, a cooling effect and the like may be appropriately added to the etching gas used in the present invention.
[0035]
【The invention's effect】
According to the present invention, since the etching form is changed from a conventional radical reaction to an ion assist reaction, it is necessary to deposit a carbon-based polymer, which is a decomposition product of a resist, thickly as a sidewall protective film as in the related art. Therefore, anisotropic processing of a fine wiring pattern can be performed even under etching conditions in which incident ion energy is reduced, and selectivity to a resist mask and a base can be improved. In addition, the amount of carbon-based polymer deposited necessary to achieve high anisotropy and high selectivity can be reduced, so that particle contamination can be reduced as compared with the prior art. Further, the amount of chlorine remaining on the side wall of the wiring pattern after the etching is reduced by being incorporated into the carbon-based polymer and the reattachment to the underlayer, so that the after-corrosion resistance is greatly improved. Therefore, it is possible to provide a dry etching method which is designed based on a fine design rule and can respond to any demands of high integration, high performance and high reliability.
[Brief description of the drawings]
FIGS. 1A and 1B are schematic cross-sectional views showing a process of the present invention in the order of steps, in which FIG. 1A shows a state in which a resist mask is formed on an Al-based material layer, and FIG. (C) shows a state in which the sidewall protective film has been removed by post-processing, and (d) shows a state in which the resist mask has been removed by ashing.
[Explanation of symbols]
1 ... SiO ₂ interlayer insulating film, 2 ... Ti layer, 3 ... TiN layer, 4 ... barrier metal, 5 ... Al-Si-Cu layer, 6 ... TiON antireflection film, 7 ... Al based material layer, 7a ... wiring pattern, 8. Resist mask

Claims (5)

Al-based material layer formed on the substrate,
An etching step of performing etching while forming an Al oxychloride as a sidewall protective film with an etching gas containing either H ₂ O or H ₂ O ₂ and a chlorine-based compound. Dry etching method. Al-based material layer formed on the substrate,
An etching step of performing etching while forming an oxychloride of Al as a sidewall protective film with an etching gas containing one of H ₂ O or H ₂ O ₂ and a chlorine-based compound;
After the etching step,
A plasma processing step of heating the substrate and using a gas containing a fluorine-based compound. Controlling the substrate on which the Al-based material layer is formed to a room temperature or lower,
The Al-based material layer,
An etching step of etching with an etching gas containing either H ₂ O or H ₂ O ₂ and a sulfur-based compound that generates free sulfur in plasma under discharge dissociation conditions. Dry etching method. Controlling the substrate on which the Al-based material layer is formed to a room temperature or lower,
The Al-based material layer,
An etching step of etching with an etching gas containing either H ₂ O or H ₂ O ₂ and a sulfur-based compound that generates free sulfur in plasma under discharge dissociation conditions;
After the etching step,
A plasma processing step of heating the substrate and using a gas containing a fluorine-based compound. The dry etching method according to claim 2, wherein a plasma density in the plasma processing step is 1 × 10 ¹¹ cm ⁻³ or more and 1 × 10 ¹⁴ cm ⁻³ or less.

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