JP3435897B2 - Plasma 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 plasma etching method used in the field of manufacturing semiconductor devices and the like, and more specifically, it is used for patterning a layer to be etched using a resist mask having an inversely tapered cross section. The present invention relates to a plasma etching method with improved controllability.

[0002]

2. Description of the Related Art As semiconductor device design rules such as LSI are miniaturized from a level of half micron to quarter micron, lithography and plasma capable of faithful patterning to fine design rules in the manufacturing process of semiconductor devices. Etching technology is required.
Among them, in the field of lithography, by adopting a short-wavelength light source such as KrF excimer laser light (248 nm) as an exposure light source of a stepper, g-line (436 nm) or i-line (365 n) by a conventional ultra-high pressure Hg lamp is adopted.
m) is used as a light source, a high resolution can be obtained relatively easily, and it is possible to form a resist mask having a pattern width of about 0.25 μm or less.

In excimer laser lithography,
A three-component negative chemically amplified resist is used, which uses a novolak resin or the like that has little absorption in the wavelength range of excimer laser light as a base resin, and also adds a photoacid generator and an acid crosslinking agent that have little light absorption to the base resin. A negative resist is a type of resist in which an exposed region is insoluble in an alkaline developer due to a crosslinking reaction and remains as a resist mask.

[0004]

This negative type chemically amplified resist is easily affected by the intensity distribution of exposure light, and the closer it is to the surface of the exposure region, the more the crosslinking reaction proceeds and the less soluble it is.
Therefore, after development, the upper pattern width having high exposure light intensity is formed wider than the lower pattern width having low exposure light intensity. It may be shaped. With such a reverse-tapered fine-width resist mask, when the layer to be etched is plasma-etched,
It became clear that the following problems occur. This problem will be described with reference to FIGS.

FIGS. 3A to 3D are schematic sectional views showing problems in patterning a layer to be etched with a resist mask having an inverse taper shape. As a layer to be etched, a refractory metal polycide layer for forming a gate electrode to which the minimum design rule is applied is taken as an example, and this is a C layer.
The case of plasma etching using a mixed gas of l ₂ / O ₂ will be taken as an example.

First, as shown in FIG. 3A, a gate oxide film 2, a polycrystalline silicon layer 3 and a WS are formed on a semiconductor substrate 1.
A refractory metal silicide layer 4 such as i _x is sequentially formed, and a resist mask 5 for patterning the gate electrode is further formed. The resist mask 5 has an inverse taper shape.

The substrate to be etched shown in FIG.
When plasma etching is performed using an l ₂ / O ₂ mixed gas, the upper refractory metal silicide layer 4 forms WO _x Cl _y , which is an oxychloride having a large vapor pressure, as a reaction product, and this WO _x Cl _y is Patterning proceeds in the form of being desorbed by being assisted by ion incidence. However,
On the surface of the layer to be etched in the vicinity of the lower surface of the inclined side wall of the resist mask 5 having the inverse taper shape, there is little or no ion incidence. Therefore, the reaction product desorbed from the layer to be etched is redeposited on the inclined side wall portion which is behind the ion incidence, and the side wall deposition film 7 is formed by the reaction product. This state is shown in FIG.

The side wall deposited film 7 formed by this reaction product may grow while expanding its width. In particular, O ₂ in the mixed gas is grown.
When the mixing ratio of WCl _x is insufficient, WCl _{x with} a low vapor pressure
Is predominant, and this WCl _x also participates in the formation of the side wall deposited film 7 by the reaction product, so that the growth of the side wall deposited film 7 in the width direction by the reaction product is promoted. That is, the pattern width of the resist mask 5 is widened, and a dimensional conversion difference occurs in the refractory metal polycide layer pattern. In addition, CRC Handbook of Chem
istry and Physics 75th. Ed
According to the Ition (1994, CRC Press), the following values are reported for the boiling points of WOCl _4, WCl ₅ and WCl ₆ . WOCl ₄ 227.5 ° C. WCl ₅ 275.6 ° C. WCl ₆ 346.7 ° C. From these boiling point data as well, the WCl _x- based reaction product has a surface to be etched compared to the WO _x Cl _y- based reaction product. Clearly, it is difficult to dissociate. Regarding the mechanism for plasma etching the refractory metal silicide layer with a Cl ₂ / O ₂ mixed gas, for example, 19
Proceedings of 94 Micro Process Conference, p22
8. There is a report on the lecture number pF4.

The sidewall deposition film 7 formed by the reaction product remains as a residue as shown in FIG. 3C even after the resist mask 5 is ashed. The residue of the side wall deposited film 7 due to this reaction product is thicker than the side wall deposited film generated when plasma etching is performed using a resist mask having a rectangular shape or a forward tapered shape. Therefore, it takes a long time for the wet process for removing the residue of the sidewall deposition film 7 due to the reaction product with a dilute hydrofluoric acid solution, and the underlying gate oxide film is also etched by this wet process, so that the gate oxide film Since the damaged portion 2a is generated, the control of the film thickness of the gate oxide film is hindered. This state is shown in FIG.

Another problem is the nonuniformity of the gate electrode width due to the loading effect. This problem will be described with reference to FIGS. 4A shows a plurality of gate electrodes in the memory cell region in which the MOS transistors are densely formed, and FIG. 4B shows plasma etching of the gate electrodes in the peripheral circuit region in which a single MOS transistor is formed. It is a schematic sectional drawing which shows the said state. As shown in FIG. 4A, the gate electrode is L / S.
When it exists as a continuous pattern, the amount of the reaction product per unit area by the plasma etching is small, so that the amount of the side wall deposition film 7 attached by the reaction product is small and the difference in size conversion is small. On the other hand, when the gate electrode exists as an isolated pattern, the opposite is true, and the side wall deposition film 7
Has a large adhesion amount, is thickly deposited, and has a large dimensional conversion difference. Therefore, there arises a problem that the value of the dimensional conversion difference of the gate electrode varies within the same semiconductor chip.

The present invention is a plasma etching method of a fine width using a resist mask having a so-called inverse taper shape as described above, which does not cause a dimensional conversion difference or a loading effect regardless of the kind of the layer to be etched and has a processed shape. It is an object to provide a plasma etching method having excellent controllability.

[0012]

The plasma etching method of the present invention is proposed to solve the above-mentioned problems. That is, in the plasma etching method in which the upper pattern width is formed wider than the lower pattern width to pattern the layer to be etched by using the resist mask having the inclined sidewall portion, the upper pattern width is set to the target pattern width. The width is set wider, and the shoulder portion above the resist mask having the inverse taper shape is made of Ar and O ₂
The target value pattern is obtained by removing the sputtering by the mixed gas of
Part of sputtering product
As it is or by recombining to form a carbon-based polymer, and by redepositing the carbon-based polymer on the inclined sidewall portion, the inclined sidewall portion is shaped into a shape substantially vertical to the layer to be etched, After the substantial pattern width of the resist mask is set to the pattern width of the target value, the layer to be etched is patterned to the pattern width of the target value by using the shaped rectangular resist mask. To do.

The present invention can be preferably used when the resist mask is formed of a chemically amplified resist.

[0014]

The difference in dimensional conversion of the layer to be etched occurs due to the resist mask having an inversely tapered shape and the presence of the inclined side wall. Therefore, in the present invention, prior to the patterning of the layer to be etched, the overhanging portion on the resist mask is removed, and the removed portion is redeposited in the concave portion of the inclined side wall portion where the ion incidence is small, and the inverse taper shape is changed to a substantially rectangular shape or By shaping into a weak forward taper shape, the problems of the dimensional conversion difference and the loading effect described above are solved. In this case, since the material deposited on the inclined side wall portion is a carbon-based polymer which is a sputtering product of the resist mask, the deposition amount is not affected by the pattern density of the resist mask. After the plasma etching, it is possible to remove the ashing at the same time as the resist mask.
Alternatively, since it is only necessary for a very short time, there is no fear that the gate oxide film will be reduced or damaged.

As a technique similar to the present invention, there is a technique disclosed in Japanese Patent Laid-Open No. 5-3181 filed by the present applicant earlier. This is to correct the shape by depositing a reaction product from the plasma of the etching gas on the inclined side wall portion of the reverse taper-shaped resist mask. Therefore, the etching gas species are limited to those capable of depositing reaction products, and there is a concern that the gate oxide film may be reduced if the deposited reaction products cannot be removed by O ₂ plasma ashing. In terms of points, there was still room for improvement. The present invention can provide a plasma etching method that eliminates these concerns.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings referred to in the embodiments, the same reference numerals are given to the same components as those in FIGS. 3 and 4 used in the description of the conventional example.

Example 1 This example is an example in which a refractory metal polycide layer is plasma-etched by an inverse taper-shaped resist mask to form a gate electrode and a wiring extending from the gate electrode. This is shown in FIG. )-(D).

The substrate to be etched shown in FIG. 1 (a) employed in this embodiment is basically the same as that of the conventional example shown in FIG. 3 (a).
Is the same as that shown in. That is, a gate oxide film 2 having a thickness of 10 nm is formed on a semiconductor substrate 1 made of silicon or the like by thermal oxidation, and subsequently, a polycrystalline silicon layer 3 containing impurities and a refractory metal silicide layer 4 made of WSi _x are formed by low pressure CVD.
To a thickness of 70 nm to form a refractory metal polycide layer. The thickness of each material layer is merely exemplary. A negative chemically amplified resist SAL-601 (manufactured by Shipley) is spin-coated on the refractory metal polycide layer to form a resist layer having a thickness of 1 μm, and the resist layer is selectively exposed by a KrF excimer laser stepper to post it. A resist mask 5 was formed through baking and alkali development treatment.

The resist mask 5 has an inverse taper shape peculiar to a negative type chemically amplified resist and has an inclined side wall portion. The pattern width of the resist mask 5 is 0.23 μm at the uppermost width portion and 0.18 μm at the lowermost width portion.
It was m.

The substrate to be etched shown in FIG. 1A is set on the substrate stage of, for example, a substrate bias application type ECR plasma etching apparatus, and the resist mask 5 is first subjected to a sputtering process under the following conditions. Ar 50 sccm O ₂ 5 sccm Gas pressure 0.4 Pa Microwave power 850 W (2.45 GHz) Substrate bias 40 W (2 MHz) Substrate temperature 0 ° C. The upper portion of the resist mask 5 by the sputtering process.
Particularly, the shoulder portion protruding in a taper shape is sputtered, and the resist or its decomposition product is released. Some of these sputtering products are directly or recombined and redeposited on the inclined sidewall portion of the resist mask 5 as a sidewall deposition film 6 made of a carbon-based polymer. As a result, the inclined side wall portion of the resist mask 5 is shaped into a substantially vertical shape or a nearly vertical forward tapered shape with respect to the layer to be etched.
The pattern width of the resist mask 5 after the shaping is set to a target value of 0. 0 as the width of the thickness of the side wall deposited film 6 made of a carbon-based polymer, that is, the substantial pattern width of the resist mask 5.
It was 20 μm. This state is shown in FIG. The substantial shape of the resist mask 5 is round except that the upper shoulder portion is removed by sputtering.
It has a substantially rectangular shape. This round portion does not affect the etching shape of the layer to be etched.

In the present sputtering process, it may be possible that the side wall deposition film 6 is excessively deposited by the carbon-based polymer and the substantial pattern width of the resist mask 5 after shaping becomes larger than the target value. In such a case, a means such as reducing the sputtering amount of the resist mask by controlling the substrate bias or the sputtering time or increasing the mixing ratio of O ₂ gas to reduce the deposition amount of the carbon-based polymer by the combustion reaction can be adopted. Good.

Next, using the resist mask 5 having a shaped shape, the refractory metal polycide layer composed of the refractory metal silicide layer 4 and the polycrystalline silicon layer 3 is anisotropically processed under the following plasma etching conditions. Cl ₂ 75 sccm O ₂ 6 sccm Gas pressure 0.4 Pa Microwave power 850 W (2.45 GHz) Substrate bias 80 W (2 MHz) Substrate temperature 20 ° C. In this etching step, the refractory metal silicide layer 4 made of WSi _x is used. As described above, WO _{x is} used as a reaction product.
Patterning proceeds by a mechanism in which Cl _y is formed and this is assisted by the incident energy of ions such as Cl ⁺ . The reaction product of the polycrystalline silicon layer 3 is mainly SiCl _x .
In any of the layers to be etched, since the shaped resist mask 5 does not have an inclined side wall that is a shadow of ion incidence, excessive deposition of etching reaction products on the side walls of the resist mask does not occur. Therefore, the dimensional conversion difference does not occur in the formed high melting point metal polycide electrode,
Anisotropic processing was performed to a target pattern width of 0.20 μm. This state is shown in FIG.

After the plasma etching is completed, it is possible to easily remove both the resist mask 5 and the side wall deposited film 6 made of carbon-based polymer under normal ashing conditions. Further, when the etching reaction product such as WCl _x is thinly deposited on the side surface of the pattern, it can be removed in a very short time with a dilute hydrofluoric acid solution or the like, so that the gate oxide film 2 is reduced or damaged. Nothing.

According to this embodiment, a resist mask having a fine width and an inverse taper shape is sputtered with Ar to shape the shape, and then the refractory metal polycide layer is plasma-etched. Anisotropic patterning of the gate electrode has become possible.

Embodiment 2 This embodiment is an example in which an Al-based metal wiring is formed by plasma-etching a laminated structure including an Al-based metal layer using a resist mask having an inverse taper shape. This is shown in FIG.
This will be described with reference to (d).

The substrate to be etched shown in FIG. 2A is S
_{On the} inter-layer insulating film 8 of iO ₂ or the like, by sputtering and reactive sputtering, an adhesion layer / barrier metal layer 9 composed of a Ti layer and a TiN layer, an Al-based metal layer 10 composed of an Al-1% Si alloy, and a TiN layer. The antireflection layer 11 and the resist mask 5 are sequentially formed in this order. The thickness of each layer is, for example, 10 n for the Ti layer.
m, TiN layer 40 nm, Al-based metal layer 10 350 n
and the antireflection layer 11 has a thickness of 25 nm. The resist mask 5 was spin-coated with a negative type chemically amplified resist SAL-601 (manufactured by Shipley Co., Ltd.) in the same manner as in Example 1 to form a resist layer having a thickness of 1 μm, which was selectively exposed by a KrF excimer laser stepper. Then, it is formed through post-baking and alkali development.

The resist mask 5 has an inverse taper shape peculiar to a negative type chemically amplified resist and has an inclined side wall portion. The pattern width of the resist mask 5 is 0.23 μm at the uppermost width portion and 0.18 μm at the lowermost width portion.
It was m.

The substrate to be etched shown in FIG. 2A is set on the substrate stage of, for example, a substrate bias application type ECR plasma etching apparatus, and the resist mask 5 is first subjected to a sputtering process under the following conditions. Ar 50 sccm O ₂ 5 sccm Gas pressure 0.4 Pa Microwave power 850 W (2.45 GHz) Substrate bias 40 W (2 MHz) Substrate temperature 0 ° C. The upper portion of the resist mask 5 by the sputtering process.
Particularly, the shoulder portion protruding in a taper shape is sputtered, and the resist or its decomposition product is released. Some of these sputtering products are directly or recombined and redeposited on the inclined sidewall portion of the resist mask 5 as a sidewall deposition film 6 made of a carbon-based polymer. As a result, the inclined side wall portion of the resist mask 5 is shaped into a substantially vertical shape or a nearly vertical forward tapered shape with respect to the layer to be etched.
The pattern width of the resist mask 5 after the shaping is set to a target value of 0. 0 as the width of the thickness of the side wall deposited film 6 made of a carbon-based polymer, that is, the substantial pattern width of the resist mask 5.
It was 20 μm. This state is shown in FIG.

In the present sputtering process, it is conceivable that the side wall deposition film 6 is excessively deposited by the carbon-based polymer and the substantial pattern width of the resist mask 5 after shaping becomes larger than the target value. In such a case, means such as reducing the sputtering amount of the resist mask by controlling the substrate bias, or increasing the mixing ratio of O ₂ gas to reduce the deposition amount of the carbon-based polymer by the combustion reaction may be adopted.

Next, the antireflection layer 11, the Al-based metal layer 10 and the adhesion layer / barrier metal layer 9 are continuously anisotropically processed under the following plasma etching conditions using the resist mask 5 having a shaped shape. BCl ₃ 60 sccm Cl ₂ 90 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) Substrate bias 50 W (2 MHz) Substrate temperature 20 ° C. This etching condition is a general Al-based metal. However, it is also possible to etch a Ti-based material layer such as Ti or TiN. Since the resist mask 5 shaped by the side wall deposited film 6 made of a carbon-based polymer does not have an inclined side wall that is a shadow of ion incidence, a dimensional conversion difference occurs in the formed laminated wiring made of an Al-based metal. However, the target pattern width of 0.20 μm was anisotropically processed. This state is shown in FIG.

After the plasma etching is completed, it is possible to easily remove both the resist mask 5 and the side wall deposited film 6 made of carbon-based polymer by ashing. According to the present embodiment, an inverse tapered resist mask having a fine width is sputtered with Ar to shape the shape, and then a laminated structure including an Al type metal layer is plasma-etched to obtain an Al type metal having no dimensional change. It became possible to pattern the system laminated wiring.

Although the present invention has been described above with reference to two embodiments, the present invention is not limited to these embodiments, and a resist mask having an inverse taper shape is used to form a layer to be etched without a dimensional change. It can be applied to various plasma etching methods for anisotropic processing.

For example, the negative chemically amplified resist is exemplified as the resist material for forming the inversely tapered resist mask, but the positive chemically amplified resist is also likely to have the inversely tapered shape or the overhang shape. The present invention can be preferably applied. Control of the etching shape of the gate electrode by a positive type chemically amplified resist pattern having an eave-shaped overhang portion is disclosed in, for example, Japanese Patent Application Laid-Open No. 6-5565. This is to control the pattern shape by using both dry etching and wet etching. Other multilayer resist masks,
Needless to say, the present invention can be applied to a resist mask which is exposed by g-line and i-line and has an inverse tapered shape.

WSi _x , MoSi as the layer to be etched
Other refractory metal polycide layer using a refractory metal silicide layer, such as _x and TaSi _x, can be suitably applied to a plasma etching of the polycrystalline silicon and a refractory metal layer alone. Further, even when processing the contact hole in the interlayer insulating film, if the resist taper having the inverse taper shape is adopted, plasma etching with excellent shape controllability of the contact hole is possible.

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 is converted 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, as the etching apparatus used for sputtering the resist mask and patterning the layer to be etched, a substrate bias application type ECR plasma etching apparatus was adopted.
Helicon wave plasma etching equipment, ICP (Inductive
ly Coupled Plasma) etching equipment, TCP (Transfor
It goes without saying that various etching devices such as a mer coupled plasma) etching device can be used.

[0037]

As is apparent from the above description, according to the present invention, the inclined side wall portion of the reverse taper-shaped resist mask made of a chemically amplified resist or the like used for plasma etching with a fine design rule is made substantially vertical. Since plasma etching is performed after shaping, patterning without a size conversion difference or a loading effect is possible. Therefore, the gate electrode, wiring, and interlayer connection of a highly integrated semiconductor device can be realized with high reliability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a first embodiment to which the present invention is applied in the order of steps, in which (a) is a refractory metal composed of a polycrystalline silicon layer and a refractory metal silicide layer on a base gate oxide film. A polycide layer is formed and an inverse taper-shaped resist mask is further formed, (b) is a shape in which the inverse-tapered resist mask is shaped, (c) is a state in which the refractory metal polycide layer is plasma-etched,
(D) is a state where the resist mask is removed by ashing.

FIG. 2 is a schematic cross-sectional view for explaining a second embodiment to which the present invention is applied in the order of steps, in which (a) is an adhesion layer / barrier metal layer, an Al-based metal layer, and an Al-based metal layer on the underlying interlayer insulating film. An antireflection layer is formed, and a resist mask having an inverse taper shape is further formed. (B) is a state where the resist mask having an inverse taper shape is shaped. (C) is a laminated structure including an Al-based metal layer formed by plasma. Etched state, (d) is a state where the resist mask is removed by ashing.

FIG. 3 is a schematic cross-sectional view for explaining a problem of a conventional plasma etching method, and FIG. 3A is a refractory metal polycide layer including a polycrystalline silicon layer and a refractory metal silicide layer on an underlying gate oxide film. And a reverse-tapered resist mask is formed, and (b) shows plasma etching using the reverse-tapered resist mask, and a sidewall deposition film of reaction products on the inclined sidewall of the resist mask. Is thickly deposited, (c) is a state in which the resist mask is removed by ashing, and (d) is a state in which the sidewall deposition film formed by the reaction product is removed by a wet process.

FIG. 4 is a schematic cross-sectional view for explaining another problem of the conventional plasma etching method, in which (a) shows a pattern shape of a layer to be etched in a continuous pattern area and (b) shows a pattern shape of an etching target layer in an isolated pattern area.

[Explanation of symbols]

1 Semiconductor substrate 2 Gate oxide film 2a Damaged part of gate oxide film 3 Polycrystalline silicon layer 4 Refractory metal silicide layer 5 Resist mask 6 Sidewall deposited film of carbon-based polymer 7 Side wall deposited film by reaction products 8 Interlayer insulation film 9 Adhesion layer and barrier metal layer 10 Al-based metal layer 11 Antireflection layer

Claims (2)

(57) [Claims] 1. A plasma etching method for patterning a layer to be etched by using a resist mask having a sloped sidewall portion by forming a pattern width of an upper portion wider than a pattern width of a lower portion. The width of the pattern is set wider than the pattern width, and the shoulder portion above the resist mask is mixed with Ar and O ₂ .
The target pattern width is removed by sputtering
While narrowing, part of the sputtering product is
Remains or recombining with the carbon-based polymer, redeposit the carbonaceous polymer on the inclined side wall portions, by shaping the inclined side wall portions in a substantially vertical shape to the etched layer, substantially of the resist mask A plasma etching method, which comprises patterning the layer to be etched to have a pattern width of the target value after setting a target pattern width of the target pattern width. 2. The plasma etching method according to claim 1, wherein the resist mask is formed of a chemically amplified resist.