JP3344027B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method used in the field of microfabrication such as the manufacture of semiconductor devices. The present invention relates to a method of performing anisotropic etching without causing the etching.

[0002]

2. Description of the Related Art As high integration of semiconductor devices progresses at an accelerated pace, their minimum processing dimensions are rapidly reduced. For example, at present 16
The minimum processing size of the MDRAM is about 0.5 μm, but is 0.35 μm or less (sub-half micron) in the next generation 64 MDRAM, and 0.2 μm in the next generation 256 MDRAM.
It is expected to be reduced to less than 5 μm (quarter micron).

It is no exaggeration to say that the degree of miniaturization depends on the photolithography technique for forming a mask pattern. For the current 0.5 μm class processing, g-line (wavelength 436 nm) and i-line (wavelength 365
nm) or near-ultraviolet light source is used.
In the 35 μm to 0.25 μm (deep submicron) class, KrF excimer laser light (wavelength 248 n
m) etc. is required.

However, since the excimer laser light is light of a single wavelength, a standing wave effect is easily generated due to multiple interference in the resist film. As a result, there arise problems such as a change in the size of the resist pattern above and below the step on the wafer surface, and formation of pleated irregularities on the side wall surface of the resist pattern. Therefore, an antireflection film for reducing the reflected light from the base material layer is essential.

As a constituent material of the antireflection film, amorphous silicon, TiN, TiON, etc. have been used in many cases, but recently, SiON (silicon oxynitride) has been used.
Has good optical properties in the far ultraviolet region, and is expected to be applied to excimer laser lithography. For example, the reflectance of a W (tungsten) -polycide film or an Al (aluminum) -based material
The fine electrode processing suppressed by the N film is a typical process.

[0006]

After the patterning of the resist mask is completed by the photolithography, the antireflection film is naturally etched in the next etching step. During this etching, it has become clear that the oxygen-based active species released from the SiON may cause the shape of the underlying material layer to occur. This problem will be described with reference to FIGS.

FIG. 9 shows the state of the wafer before the start of etching. Here, a W-polycide film 25 and a SiON anti-reflection film 26 are sequentially stacked on a Si substrate 21 via a gate oxide film 22, and a resist mask 27 patterned in a predetermined shape is formed thereon. I have. The W-polycide film 25 is formed of a polysilicon layer 23 containing impurities and a WSi
_x (tungsten silicide) layer 24 is sequentially laminated.

Next, the SiON antireflection film 26 is
Etching is performed using a fluorocarbon-based gas usually used for etching the iO ₂ -based material layer. In this etching process, a carbon-based polymer is deposited from the plasma, but this deposition tends to be excessive in the etching of SiON. This is because the element composition ratio of SiON is approximately Si:
This is because O: N = 2: 1: 1, and the number of O atoms contributing to the removal of the carbon-based polymer is smaller than that of SiO ₂ . As a result, the cross-sectional shape of the etched SiON antireflection film 16a becomes tapered as shown in FIG.
The pattern edge protrudes outside the pattern edge of the resist mask 27.

When the W-polycide film 25 is etched in this state, the SiO.sub.
Ions enter the exposed surface of the N anti-reflection film 26a, and O ^*
Is sputtered out. Therefore, even if an attempt is made to use the carbon-based polymer derived from the resist mask 27 for sidewall protection, the carbon-based polymer is immediately removed in the form of CO _x , and the desired sidewall protection effect cannot be obtained.
As a result, as shown in FIG. 11, consisting of WSi _x layer 24b and the polysilicon layer 23b caused an undercut, a gate electrode 25b having deteriorated anisotropic shape is formed. In particular, when the above etching Cl ₂ / O ₂ mixed gas is used, W from WSi _x layer 24 is easily pulled out in the form of WClO _x, undercut increases the WSi _x layer 24b.

As described above, when the anisotropic shape of the gate electrode is deteriorated, serious problems such as difficulty in forming a side wall for achieving the LDD structure, as well as deviating the wiring resistance from the design value, occur.

The deterioration of the shape is not limited to the above-described SiON anti-reflection film, but also when another anti-reflection film capable of easily releasing oxygen is used. This is a phenomenon that can similarly occur when other material layers are etched. Therefore, an object of the present invention is to provide a method for preventing deterioration of anisotropy due to an antireflection film in etching of a laminated film system in which an antireflection film containing oxygen is stacked.

[0012]

A dry etching method according to the present invention is proposed to achieve the above-mentioned object, and comprises a method of forming a material layer to be etched, the surface of which is coated with an antireflection film containing oxygen. When etching through a resist mask, the first step of dry-etching the antireflection film under anisotropic etching conditions and the reflection of the antireflection film under an isotropic etching condition using a diluted hydrofluoric acid solution treatment. A second step of retreating the pattern edge of the prevention film to at least a vertical projection position of the pattern edge of the resist mask, and a third step of dry-etching the material layer to be etched.

Here, the material layer to be etched is a material layer having a relatively high reflectance which requires an antireflection film in order to improve the resolution of photolithography, and is typically a W-polycide film, This is a wiring material layer such as an Al-based multilayer film. The isotropic etching conditions can be achieved by wet etching using a diluted hydrofluoric acid solution.

The position of the pattern edge after the antireflection film is receded in the second step is determined by taking into account the margin for the oblique incidence component of ions in the plasma, and The position may be slightly inward from the projection position. However, if it is retreated too much inward, the gap between the resist mask and the material layer to be etched becomes large, and radicals may enter from this space to degrade the anisotropic shape of the material layer to be etched. Can be Therefore, in practice, at least the resist mask pattern
It is sufficient to retract the edge to the vertical projection position.

As a constituent material of the oxygen-containing antireflection film, a SiON-based material is particularly preferable from the viewpoint of supporting future excimer laser lithography. This SiON-based material may contain H depending on the gas composition at the time of film formation. SiON may be etched using an etching gas containing a fluorocarbon-based compounds usually widely used for etching the SiO _x based material layer.

The pattern edge of the SiON-based antireflection film generated by the above etching can be retreated by performing a diluted hydrofluoric acid solution treatment. The retreat amount can be determined based on the processing time at this time.

[0017]

According to the present invention, when the etching of the anti-reflection film is completed, the pattern edge of the anti-reflection film is retracted at least to the vertical projection position of the pattern edge of the resist mask. Perpendicular incidence does not occur. Therefore, even when the underlying material layer to be etched is etched, supply of oxygen-based active species from the antireflection film does not occur, the removal of the sidewall protective film is prevented, and the anisotropic shape of the material layer to be etched is reduced. It can be maintained. Further, since the vertical incidence range of ions is accurately defined by the original pattern width of the resist mask, the occurrence of a dimensional conversion difference can be prevented.

In particular, when an antireflection film made of a SiON-based material is etched using an etching gas containing a fluorocarbon-based compound, the etching characteristic of SiON is intermediate between SiO ₂ and Si. The cross-sectional shape is easily tapered. Therefore, the retreat of the pattern edge as described above is extremely effective in eliminating the vertical incidence surface of ions to the antireflection film.

If this retreating treatment is performed by a diluted hydrofluoric acid solution treatment, that is, wet etching, the antireflection film can be immersed in the horizontal direction by an isotropic chemical reaction.
Moreover, the underlying material layer to be etched is not damaged.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Embodiment 1 In this embodiment, in processing a W-polycide gate electrode, a SiON antireflection film on a W-polycide film is c-C
Example of etching using a ₄ F ₈ / CH ₂ F ₂ mixed gas, performing dilute hydrofluoric acid treatment to retreat the pattern edge, and etching a W-polycide film using a Cl ₂ / O ₂ mixed gas It is. This process will be described with reference to FIGS.

FIG. 1 shows the configuration of a wafer used as an etching sample in this embodiment. Here, a W-polycide film 5 and a SiON antireflection film 6 are sequentially laminated on a Si substrate 1 via a gate oxide film 2 having a thickness of about 10 nm, and a resist mask patterned in a predetermined shape is further laminated thereon. 7 are formed. Here, W-
The polycide film 5 includes, in order from the lower layer, a polysilicon layer 3 containing an impurity and having a thickness of about 100 nm and a thickness of about 100 nm.
m and WSi _x layer 4 of which are sequentially stacked. The SiON antireflection film 6 is deposited to a thickness of about 30 nm by a plasma CVD method. Further, the resist mask 7 is formed to a thickness of about 1 μm and a pattern width of about 0.25 μm using a positive type chemically amplified resist material (manufactured by Shipley Co .; trade name: XP8843) and a KrF excimer laser stepper. I have.

This wafer was set in an RF bias applying type magnetic field microwave plasma etching apparatus for processing SiO ₂ , and the SiON antireflection film 6 was etched under the following conditions as an example. c-C ₄ F ₈ flow rate 50 SCCM CHF ₃ flow rate 20 SCCM gas pressure 0.5 Pa microwave power 1000 W (2.45 GH)
z) RF bias power 300 W (800 kHz)
z) Wafer mounting electrode temperature 0 ° C. (using alcohol-based refrigerant) The above conditions are typical etching conditions for the SiO _x -based material layer, and the SiON antireflection film 6 is etched based on the CF _x ⁺ ion assist mechanism. Is done. However, S
Since the O content of iON was small, the deposition of a carbon-based polymer (not shown) became excessive, and the cross-sectional shape of the obtained SiON antireflection film 6a was tapered as shown in FIG.

Next, the above wafer is diluted with a diluted hydrofluoric acid solution (HF:
(H ₂ O = 5: 100) for 30 seconds. As a result, the SiON anti-reflection film 6a is immersed in the horizontal direction, and as shown in FIG. 3, the pattern edge is retreated to the vertical projection position of the pattern edge of the resist mask 7.
An ON antireflection film 6b was obtained.

Next, the wafer is set in another magnetic field microwave plasma etching apparatus for gate processing,
As an example, the W-polycide film 5 was etched under the following conditions. Cl ₂ flow rate 72 SCCM O ₂ flow rate 8 SCCM Gas pressure 0.4 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 40 W (2 MHz) Wafer mounting electrode temperature 0 ° C (using alcohol-based refrigerant)

In this etching step, as shown in FIG. 4, the W-polycide film 5 is made of WClO _x , SiCl _x.
And so on. At this time, the side wall protective film 8 made of a carbon-based polymer is formed due to the sputter product of the resist mask 7, but O ^* is no longer sputtered from the SiON antireflection film 6b shielded by the resist mask 7. Since it is not removed, the sidewall protective film 8 is not removed. Therefore, gate electrode 5a having the same pattern width as resist mask 7 and having a good anisotropic shape
Could be formed. In the drawings, each of the material layers after the etching is shown by adding the suffix a to the original code.

This anisotropic shape could be maintained even after about 50% over-etching was performed.

Embodiment 2 In this embodiment, in the Al-based wiring processing, the SiON anti-reflection film on the Al-based multilayer film is etched using a mixed gas of c-C ₄ F ₈ / CH ₂ F ₂ , and then the diluted fluorine is removed. This is an example in which the pattern edge is retreated by performing an acid treatment, and the Al-1% Si layer and the barrier metal are etched using a BCl ₃ / Cl ₂ mixed gas. This process will be described with reference to FIGS.

First, as shown in FIG. 5, an Al-based multilayer film in which a barrier metal 14, an Al-1% Si layer 15, and a SiON antireflection film 16 are sequentially laminated on an SiO ₂ interlayer insulating film 11 is formed. Further, a resist mask 1 is further formed thereon.
7 was prepared by patterning a wafer. Here, the barrier metal 14 is, for example, a layer in which a Ti layer 12 and a TiON layer 13 are sequentially stacked from the lower layer side.

Next, the SiON antireflection film 16 was etched under the same conditions as in Example 1 to obtain a tapered SiON antireflection film 16a as shown in FIG. Further, a dilute hydrofluoric acid solution treatment was performed under the same conditions as in Example 1, and as shown in FIG.
An N antireflection film 16b was obtained.

Next, the wafer is set in an RF bias applying type magnetic field microwave plasma etching apparatus,
As an example, the Al-1% Si layer 15 and the barrier metal 14 were etched under the following conditions. BCl ₃ flow rate 60 SCCM Cl ₂ flow rate 90 SCCM Gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 50 W (2 MHz) Wafer mounting electrode temperature 30 ° C (water cooling)

The above gas composition is a standard chlorine-based gas composition for Al etching. At this time, a sidewall protective film 18 made of a carbon-based polymer is formed from the resist mask 17, but O ^* is no longer sputtered out of the SiON antireflection film 16b shielded by the resist mask 17, The sidewall protective film 18 is not removed. Therefore, Al-1% having the same pattern width as the resist mask 17 and having a favorable anisotropic shape
The Si layer 15a and the barrier metal 14a could be formed. In the drawings, each of the material layers after the etching is shown by adding the suffix a to the original code.

This anisotropic shape could be maintained even after about 50% over-etching was performed.

Although the present invention has been described based on two embodiments, the present invention is not limited to these embodiments. It goes without saying that details such as the configuration of the sample wafer, the etching apparatus to be used, and the conditions of the dry etching and the wet etching can be appropriately changed.

[0035]

As is apparent from the above description, in the present invention, the etching of the material layer to be etched is performed after the pattern edge of the antireflection film is retreated at least to the vertical projection position of the pattern edge of the resist mask. Accordingly, it is possible to suppress the release of the oxygen-based active species from the antireflection film, and to perform a favorable anisotropic processing without generating a dimensional conversion difference. Since the retreating process is performed by dilute hydrofluoric acid solution treatment, expensive equipment is not required, and the retreating amount is determined in a self-aligned manner, so that an extra lithography step is not required. Therefore, the present invention can be implemented inexpensively using existing equipment.

The present invention is particularly applicable to the next-generation and subsequent fine electrode processing using SiON which is promising as an antireflection film for excimer laser lithography, and its industrial utility value is remarkable. It is big.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a state of a wafer before etching in processing of a W-polycide gate electrode to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view showing a state where the SiON antireflection film of FIG. 1 is etched.

FIG. 3 is a schematic cross-sectional view showing a state in which a dilute hydrofluoric acid solution treatment of the SiON antireflection film of FIG. 2 is performed to retreat a pattern edge thereof.

FIG. 4 is a schematic cross-sectional view showing a state in which a gate electrode is formed by anisotropically etching the W-polycide film of FIG. 3;

FIG. 5 is a schematic cross-sectional view showing a state of a wafer before etching in Al-based wiring processing to which the present invention is applied.

6 is a schematic cross-sectional view showing a state where the SiON antireflection film of FIG. 5 is etched.

FIG. 7 is a schematic cross-sectional view showing a state in which a dilute hydrofluoric acid solution treatment of the SiON anti-reflection film of FIG. 6 is performed to retreat a pattern edge thereof.

FIG. 8 is a schematic cross-sectional view showing a state in which an Al-based wiring pattern is formed by anisotropically etching the Al-1% Si layer and the barrier metal of FIG.

FIG. 9 is a schematic cross-sectional view showing a state of a wafer before etching in conventional W-polycide gate electrode processing.

FIG. 10 is a schematic cross-sectional view showing a state where the SiON antireflection film of FIG. 9 is etched.

11 is a schematic cross-sectional view showing a state in which O ^* is sputtered out of the resist mask of FIG. 10 and the anisotropic shape of the gate electrode is deteriorated.

[Explanation of symbols]

5 ... W-polycide film 6,16 ... SiON antireflection film 6a, 16a ... (tapered) SiON antireflection film 6b, 16b ... (retracted) SiON antireflection film 7, 17: resist mask 8, 18: sidewall protective film 14: barrier metal 15: Al-1% Si layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/027

Claims (3)

(57) [Claims] In a dry etching method for etching, via a resist mask, a material layer having a surface coated with an antireflection film containing oxygen, the antireflection film is dried under an anisotropic etching condition. A first step of etching and a step of retreating a pattern edge of the antireflection film to at least a vertical projection position of the pattern edge of the resist mask by isotropic etching conditions using a diluted hydrofluoric acid solution treatment . And a third step of dry-etching the material layer to be etched. 2. The oxygen-containing antireflection film is made of SiO.
2. The dry etching method according to claim 1, comprising an N-based material. 3. The dry etching method according to claim 2, wherein in the first step, the antireflection film is dry-etched using an etching gas containing a fluorocarbon-based compound.