JP3277414B2 - 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, and more particularly to anisotropic etching of a laminate of an antireflection film containing oxygen and a silicon material layer. The technology to be realized.

[0002]

2. Description of the Related Art As the degree of integration of semiconductor devices increases, the minimum processing size thereof is rapidly reduced.
For example, 16MD currently being transferred to mass production lines
The minimum processing size of the RAM is about 0.5 μm, but it is 0.35 μm or less in the next generation 64 MDRAM, and the next generation 2
In a 56MDRAM, it is expected to be reduced to 0.25 μm or less.

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 a near-ultraviolet light source, or 0.35 μm
In the 0.25μm (deep submicron) class,
A far ultraviolet light source such as KrF excimer laser light (wavelength 248 nm) is used. In particular, in the photolithography technology for forming a fine mask having a line width of 0.4 μm or less,
In order to prevent a decrease in contrast and resolution due to halation and standing wave effects, an antireflection film for weakening light reflected from the underlying material layer is almost indispensable.

As a constituent material of the anti-reflection film, amorphous silicon, TiN, TiON and the like 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, a process in which the reflectance of the W (tungsten) -polycide film is suppressed by the SiON film to perform fine gate processing is a typical process.

[0005]

After the patterning of the resist mask is completed by the photolithography, the antireflection film is naturally etched in the next etching step. Here, during the etching, particularly at the time of over-etching,
It has become clear that oxygen released from N may deteriorate the anisotropic shape of the base material layer. This problem will be described with reference to FIG.

FIG. 2A shows a state of the wafer before the start of etching.
via iO _x film 12 W- polycide film 15 and the Si
An ON antireflection film 16 is sequentially laminated, and a resist mask 17 patterned in a predetermined shape is formed thereon. Here, the W-polycide film 15
From the lower side in this order, the polysilicon layer 13 containing impurities and WSi _x (tungsten silicide) layer 14 which are sequentially stacked.

The W-polycide film 15 is formed of Cl ₂ / O ₂
When etching is performed using a mixed gas, etching proceeds by generating SiCl _x , WCLO _x , CO _x , NO _{x, and the} like as etching reaction products. On the other hand, on the side wall surface of the pattern, a carbon-based polymer derived from decomposition products supplied by forward sputtering of the resist mask is deposited, and the side wall protective film 18 is formed. If the etching temperature is sufficiently low, SiCl _x having a relatively low vapor pressure among the etching reaction products will also be a component of the sidewall protective film 18. As a result, at the end of the just etching, as shown in FIG. 2B, a gate electrode 15a having an anisotropic shape is formed. In the drawings, each of the material layers after the etching is shown by adding the suffix a to the original code.

However, if overetching is further performed, the shoulder of the SiON antireflection film 16a may be exposed as the edge of the resist mask 17 recedes, as shown in FIG. 2 (c). SiON has an elemental composition ratio of approximately Si: O: N = 2: 1: 1, and S
Si-rich compared to iO ₂ . Therefore, the resistance to Cl-based plasma is weak, and active O ^* is easily released when the exposed shoulder is sputtered. Then this O
^{The *} removes the sidewall protection film 18 in the form of CO _x , thereby reducing the sidewall protection effect. In addition, since the W-polycide film 15 to be etched is also reduced during over-etching, the radicals are relatively excessive.

As a result, as shown in FIG.
The undercut gate electrode 15b is formed. Here, each material layer in which an undercut has occurred is shown by adding a suffix b to the original code. Undercut is W
In liable WSi _x layer 14b is etched in the form of ClO _x, the most significant occurrence. As described above, when the anisotropic shape of the gate electrode is degraded, serious problems such as the wiring resistance deviating from the design value and the difficulty in forming the side wall for achieving the LDD structure arise.

The deterioration of the anisotropic shape at the time of over-etching is a phenomenon that can occur not only in the above-described SiON antireflection film but also when an antireflection film capable of easily releasing oxygen is used. Therefore, an object of the present invention is to provide a dry etching method for a silicon-based material layer that can maintain anisotropy during overetching even when an antireflection film containing oxygen is used.

[0011]

Means for Solving the Problems The present inventor has conducted intensive studies in order to achieve the above-mentioned object, and has found that the anisotropy reduction at the time of overetching is reduced, (i) the sidewall protection effect is enhanced, or (ii) The present invention has been proposed based on the idea of avoiding the side wall protection effect as much as possible, based on one of the following ideas.

That is, according to the dry etching method of the present invention, when etching a silicon-based material layer whose surface is covered with an antireflection film containing oxygen, the antireflection film is first etched, and then the fluorine-based chemical species is etched. Etching the silicon-based material layer using an etching gas capable of generating a halogen-based species and an oxygen-based species other than the above, while promoting the deposition of a reaction product containing the halogen-based species and silicon. It is.

The most typical halogen-based species other than fluorine-based species are chlorine-based and bromine-based species, and iodine-based species may be used in some cases. These halogen-based species and oxygen-based species may be supplied from the same compound or from different compounds.

Alternatively, the above-mentioned etching of the silicon-based material layer is brought to a just-etched state, and then the over-etching is performed by reducing the generation ratio of the oxygen-based chemical species to the halogen-based chemical species in comparison with the just-etching step. May be. Here, the generation ratio may be zero.

Here, as a constituent material of the oxygen-containing antireflection film, SiON is particularly suitable from the viewpoint of supporting future excimer laser lithography.
SiON can be etched using an etching gas that can generate at least carbon-based species and fluorine-based species. As the etching gas in this case, a fluorocarbon-based compound or a hydrofluorocarbon-based gas generally used for etching SiO ₂ can be appropriately selected or used in combination.

When the silicon-based material layer is a refractory metal polycide film, a typical practical process can be realized. The most typical material for the high melting point metal in this case is tungsten.

At least at the time of etching the silicon-based material layer, the substrate holding the silicon-based material layer may be cooled. The process in this case is a so-called low-temperature etching process, and the substrate is generally cooled to 0 ° C. or lower. However, in dry etching, unless a cooling means is particularly employed, the substrate temperature may be 100 to 200 due to heat of chemical reaction or radiation heat from plasma.
Since the temperature usually rises to about ° C, it can be considered that low-temperature etching in a broad sense is also used to cool it and maintain it near room temperature.

[0018]

In the present invention, since the etching gas used for etching the silicon-based material layer can generate halogen-based species other than fluorine and oxygen-based species, Si is converted to halogen such as chloride and bromide. Of course, the refractory metal can be removed in the form of an oxyhalide. Therefore, W-
Even in the etching of a laminated film system composed of two types of material layers having different etching characteristics such as a polycide film, it is possible to achieve an anisotropic shape with a single gas system without switching the gas composition in the middle. it can.

Further, since this etching is carried out while accelerating the deposition of a reaction product between the halogen-based chemical species and silicon, even when the oxygen-based active species are released from the antireflection film at the time of over-etching, the side wall protective film is formed. Even if a part of the carbon-based polymer is removed, the sidewall protective substance is always replenished, and there is no fear that the anisotropy is reduced. The reaction product is mainly SiCl _x when using a chlorine-based species, and mainly SiBr _x when using a bromine-based species. At this time, if the substrate is cooled, the reactivity of the radicals is suppressed, and the vapor pressure of these reaction products is reduced to promote the deposition, whereby the anisotropic etching can be advantageously promoted.

When the antireflection film is made of SiON, Si atoms are extracted in the form of SiF _x by using an etching gas capable of generating at least a carbon-based chemical species and a fluorine-based chemical species for etching. O atoms, each N atom CO _x, by being pulled out in the form of NO _x, etching progresses rapidly.

Alternatively, by increasing the generation ratio of the oxygen-based chemical species to the halogen-based chemical species during over-etching compared to the just-etching step, the increase in the oxygen-based chemical species present in the etching reaction system can be reduced. It can also be suppressed. This is based on the above-mentioned (i) idea of suppressing the deterioration of the side wall protection effect as much as possible, whereas the above-mentioned (i) idea of promoting the deposition of the reaction product enhances the side wall protection effect. . Since the oxygen-based species do not contribute to the acceleration of the etching after the refractory metal silicide layer disappears, the generation ratio of the oxygen-based species was reduced during overetching where this layer was scarcely present (or set to zero). ) Does not adversely affect the etching characteristics.

[0022]

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

Embodiment 1 In this embodiment, a wafer is cooled at a low temperature and a SiC film is formed by etching a laminated system of a W-polycide film and a SiON anti-reflection film using a Cl ₂ / O ₂ mixed gas.
This is an example in which the deposition of l _x is promoted and the anisotropic shape of the gate electrode is maintained. This process will be described with reference to FIG.

FIG. 1A shows the structure of a wafer used as an etching sample in this embodiment. That is, S
A W-polycide film 5 and an SiON anti-reflection film 6 are sequentially laminated on an i-substrate 1 via a gate SiO _x film 2 having a thickness of about 10 nm, and a resist mask 7 patterned in a predetermined shape is further formed thereon. Is formed. Here, the W- polycide film 5, order from the lower layer side, in which impurities and WSi _x layer 4 having a thickness of about 100nm of polysilicon layer 3 and a thickness of about 100nm containing are sequentially laminated. 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 made of a negative type three-component chemically amplified resist material (manufactured by Shipley Co .; trade name: SAL-60).
It is formed to a thickness of about 1 μm and a pattern width of about 0.25 μm using 1) and a KrF excimer laser stepper.

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 0.4 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 200 W (800 kHz)
z) Wafer mounting electrode temperature: −50 ° C. In this etching step, as shown in FIG. 1B, the SiON antireflection film 6a was etched. This etching proceeds based on the ion assist mechanism of CF _x ⁺ , but since the O content of SiON is relatively small,
The carbon-based polymer derived from the fluorocarbon-based gas is easily deposited. Therefore, the etching rate was about one third of the etching rate of SiO _{2 under} the same conditions.

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 75 SCCM O ₂ flow rate 5 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: −20 ° C. In this etching step, as shown in FIG. 1C, the W-polycide film 5 is made of WCLO _x , SiCl _x , C
Was removed in the form of O _x or the like.

The above-mentioned wafer cooling temperature is the same as that of a conventional W-type wafer using an amorphous silicon film as an anti-reflection film.
Approximately 20 ° C. lower than the conditions for processing the polycide gate electrode. As a result, not only the carbon-based polymer derived from the decomposition product of the resist mask, but also a portion of the reaction product SiCl _x having a reduced vapor pressure at such a low temperature efficiently deposits on the pattern side wall surface and has a sufficient thickness. Was formed. As a result, the gate electrode 5a having an anisotropic shape
Was formed. In the drawings, each of the material layers after the etching is shown by adding the suffix a to the original code.

Further, about 50% over-etching was performed under the same conditions. In this process, as shown in FIG. 1D, the resist mask 7 receded, and ions in the plasma were incident on the exposed shoulder of the SiON antireflection film 6a to release O ^* . This O ^* consumed the carbon-based polymer in the sidewall protective film 8. In addition, the amount of Cl ^{* in} the vicinity of the pattern at this time increases as the number of objects to be etched decreases. However, a sufficient amount of SiCl
_Since the supply of _x was continued, no decrease in the side wall protection effect was observed. Therefore, a favorable anisotropic shape of the gate electrode 5a could be maintained even during overetching.

Embodiment 2 In this embodiment, in the same W-polycide gate electrode processing, the etching gas at the time of over-etching is made of a single composition of Cl ₂ , thereby minimizing a decrease in the side wall protection effect. This is an example. In this embodiment, FIG.
Using the same wafer as shown in FIG.
The antireflection film 6 was etched under the same conditions as in Example 1.

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 just etched under the following conditions. Cl ₂ flow rate 75 SCCM O ₂ flow rate 5 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. This just etching is performed by using the underlying gate SiO _x film 2
Was terminated when exposure began.

Next, over-etching was performed by changing the etching conditions as follows as an example. Cl ₂ flow rate 80 SCCM O ₂ flow rate 0 SCCM Gas pressure 0.4 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 10 W (2 MHz) Wafer mounting electrode temperature 0 ° C. In this over-etching step, the concentration of oxygen-based chemical species near the pattern increases due to the exposure of the shoulder of the SiON antireflection film 6a. This increase is offset by omitting O ₂ from the gas composition. As a result, the weakening of the carbon-based polymer on the pattern side wall surface can be suppressed, and the anisotropic shape of the gate electrode 5a can be maintained.

In this embodiment, since the etching of the W-polycide film 5 is performed in two steps, anisotropic etching is realized even at a wafer temperature higher than that in the first embodiment. Since this condition is equivalent to the usual W-polycide gate electrode processing, the time required for cooling the wafer can be reduced, and the throughput can be improved.

Although the present invention has been described based on two embodiments, the present invention is not limited to these embodiments. For example, in the above-described embodiment, Cl ₂ is exemplified as a compound for supplying a chlorine-based chemical species.
1, BCl ₃ or the like may be used. Alternatively, Cl ₂ O,
The chlorine-based chemical species and the oxygen-based chemical species may be simultaneously supplied from the same compound by using chlorine oxide such as ClO ₂ .

Alternatively, a bromine-based chemical species may be supplied instead of the chlorine-based chemical species, and SiBr _x may be used as a reaction product as a component of the sidewall protective film. SiBr _x is S
Since the vapor pressure is lower than that of iCl _x , it is effective for strengthening the side wall protective film. Etching using a bromine-based chemical species also has the advantage of maintaining high selectivity to the gate SiO _x film. However, depending on the type of the high melting point metal contained in the silicon-based material layer, there is a possibility that a metal bromide having a low vapor pressure may be generated. Therefore, the use of the bromine-based chemical species is limited to such a low possibility.

In addition, it goes without saying that the details of the configuration of the sample wafer, the etching apparatus to be used, the etching conditions, and the like can be appropriately changed.

[0036]

As is apparent from the above description, according to the present invention, even if the antireflection film containing oxygen is partially exposed due to the retreat of the resist mask during overetching, This makes it possible to prevent the sidewall protective film from being weakened by the released oxygen-based active species, and to perform favorable anisotropic processing.

In particular, the present invention uses WN using SiON which is promising as an antireflection film for excimer laser lithography.
It can be typically applied to the next generation gate processing processes, such as the case of performing polycide processing, and its industrial utility value is remarkably high.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a W-polycide gate electrode processing process to which the present invention is applied in the order of steps, (a) showing a state of a wafer before starting etching,
(B) is a state where the SiON antireflection film is etched,
(C) shows a state where the gate electrode is anisotropically etched while the side wall protective film is formed, and (d) shows a state at the time of overetching.

FIG. 2 is a schematic cross-sectional view for explaining a problem of a conventional W-polycide gate electrode processing process;
(A) is the state of the wafer before the start of etching, (b) is the state of S
The state in which the iON anti-reflection film and the W-polycide film are etched, the state in which the sidewall protective film is lost during overetching, and the state in which the anisotropic shape of the gate electrode is deteriorated are shown in FIG.

[Explanation of symbols]

1 ... Si substrate 2 ... gate SiO _x film 3 ... polysilicon layer 4 ... WSi _x layer 5 ... W- polycide film 5a ... gate electrode 6 ... SiON antireflection film 7: resist mask 8: sidewall protective film

Claims (4)

(57) [Claims] 1. A dry etching method for etching a silicon-based material layer whose surface is coated with an oxygen-containing antireflection film, comprising: a step of etching the antireflection film; Then
In both cases, the substrate holding the silicon-based material layer is cooled.
The silicon-based material while using an etching gas capable of generating a halogen-based species other than a fluorine-based species and an oxygen-based species to promote the deposition of a reaction product between the halogen-based species and silicon; A step of etching a layer. 2. A dry etching method for etching a silicon-based material layer having a surface coated with an oxygen-containing antireflection film, comprising: a step of etching the antireflection film; Then
In both cases, the substrate holding the silicon-based material layer is cooled.
The silicon-based material while using an etching gas capable of generating a halogen-based species other than a fluorine-based species and an oxygen-based species to promote the deposition of a reaction product between the halogen-based species and silicon; A just etching step of substantially etching the layer by the thickness of the layer, and the silicon gas using an etching gas capable of making a generation ratio of the oxygen-based species to the halogen-based species smaller than that in the just etching step. An over-etching step of etching a remaining portion of the base material layer. 3. The antireflection film containing oxygen is made of SiO.
3. The dry etching method according to claim 1, wherein the anti-reflection film is made of N and is etched using an etching gas capable of generating at least a carbon-based chemical species and a fluorine-based chemical species. . 4. The dry etching method according to claim 1, wherein the silicon-based material layer is a refractory metal polycide film.