JP3008451B2 - Etching method of silicon-based material to be etched - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for etching a silicon-based material to be etched. In particular, the present invention relates to an etching method for etching a portion to be etched having a silicon layer and a refractory metal silicide layer on a substrate. INDUSTRIAL APPLICABILITY The present invention can be used as an etching method for etching a so-called polycide structure or the like, for example, when manufacturing a semiconductor device or the like.

[Summary of the Invention]

The present invention provides a method of etching a silicon-based material to be etched, which etches a portion to be etched having a silicon layer formed on a substrate and a high melting point metal silicide layer, wherein hydrogen bromide and a gas capable of generating fluorine radicals are used. By etching the silicon substrate and the refractory metal silicide layer under the same conditions by performing etching while cooling at least the portion to be etched of the substrate to 0 ° C. or less using the contained etching gas. It is.

[Background of the Invention]

A structure in which a silicon layer and a refractory metal silicide layer are formed on a substrate is used, for example, in the field of semiconductor devices, for example, to form a gate wiring structure.

Refractory metal silicide has been widely used as a gate wiring material for semiconductor devices such as conventional LSIs.
It is advantageous because the resistance value is smaller than silicon, and
By interposing a silicon (especially polysilicon) layer between the refractory metal silicide and the base, reliability at an interface (for example, an interface with SiO ₂ as a gate insulating film) can be maintained.

The above structure is generally called polycide in the sense that silicide is usually laminated on polysilicon.

When such a polycide structure is continuously etched and patterned, two different materials must be etched with good anisotropy. For this reason, conventionally, for example, Freon 113 (C ₂ Cl
₃ F ₃₎ an etching gas mainly containing a so-called CFCs or freons called fluorocarbon gas as typified have been used.

However, these fluorocarbon gases have environmental problems such as destruction of the ozone layer, and it is desirable to avoid using them. In addition, there is a high possibility that the device cannot be used due to the so-called CFC regulations.

For this reason, it is desired to develop an etching gas system which can be used as an alternative etching gas, and which can realize good anisotropy for both the silicon layer and the refractory metal silicide layer, and achieve good etching. ing.

Against such a background, the present inventors have previously developed HBr / SF ₆
An etching technique using a gas system containing hydrogen bromide and a gas capable of generating fluorine radicals, such as a mixed gas system, has been proposed (Japanese Patent Application No. 2-10489 filed on January 22, 1990).

According to this technique, a polycide film composed of a refractory metal silicide layer and a polysilicon layer can be etched at a high speed and with good selectivity while maintaining high anisotropy.

The technique proposed by the present inventors is advantageous because the polycide structure can be favorably etched without using a fluorocarbon-based gas, but depending on the base of the material to be etched, it is difficult to obtain a selectivity with the base. There was a problem that there was.

For example, when used for the gate wiring structure, SF often underlying a SiO ₂ film for generally forming a gate oxide film, etching of the SiO ₂ film must be suppressed as much as possible, for example, as an etching gas ₆ / When an HBr mixed gas system is used, it may be difficult to obtain a selective ratio with respect to the underlying SiO _2, and it may be difficult to realize good etching. In some cases, undercutting may occur in the silicon layer during overetching.

This problem will be described below with reference to FIG.

For example, as shown in FIG. 2 (a), a material to be etched is DOPOS (doped) which is a silicon layer 3 on a substrate 11 comprising a substrate 1 and an insulating film 2 (SiO ₂ ) which is a gate oxide film. Polysilicon) and WSix which is a high melting point silicide layer 4
In the case of a material in which a portion to be etched 10 which is a polycide film made of (tungsten silicide) is formed, etching is performed using an SF ₆ / HBr etching gas system using the photoresists 51 and 52 as masks as shown in the figure. At the time of the just etch, the silicon etching residue 3b shown in FIG. 2 (b) or the etching residue 3b may occur especially between the resists 51 and 52. This more or less occurs due to fluctuations in etching conditions, in-plane non-uniformity of the material to be etched, and the like. For this reason, it is necessary to remove the remaining etchings 3a and 3b by performing over-etching. However, in this case, for example, the SF
_{If the 6} / HBr gas system is used as it is, the selectivity with SiO ₂ cannot be obtained, and desired favorable etching cannot be achieved.

HBr alone from NMRI, or SF ₆ alone was etched, drawn when to perform over-etching followed, but the selection ratio problem with SiO ₂ is improved, or not sufficient etching rate, or silicon Or undercutting of the layer. For example, if the polycide structure as shown in FIG. 3A is etched and over-etched in this way, as shown in FIG. 3B, an undercut 3a 'having a hollow shape may occur in the silicon pattern 31. And good etching cannot be realized.
(In FIGS. 2 and 3, 31, 311, 312 are etched silicon patterns, and 41, 411, 412 are also high-melting metal silicide patterns. In order to prevent shape deterioration at the time of etching, a technique of using a side wall protection method has been proposed. One is described in JP-A-63-239950.

Further, as described above, the portion to be etched 10 has a laminated structure of two layers of materials having different vapor pressures of reaction products of the refractory metal silicide layer 4 and the silicon layer 3 during dry etching. In this case, when the silicon layer 3 is etched under the condition of etching the refractory metal silicide layer 4, the undercut 3a 'is similarly formed on the side wall.
May occur.

In order to avoid this, that is, to suppress the occurrence of undercut which may occur in the silicon layer at the time of over-etching, and to realize etching of a good shape, the present applicant firstly requires the silicon layer formed on the base to be In a method of etching a silicon-based material to be etched to etch a portion to be etched having a refractory metal silicide layer,
Japanese Patent Application No. 2-47074 proposes a technique in which etching is performed using an etching gas containing hydrogen bromide and a gas capable of generating fluorine radicals, and then over-etching is performed using only a gas capable of generating fluorine radicals. .

On the other hand, when etching is performed up to the silicon layer 3 such as DOPOS using FS ₆ / HBr that does not cause reattachment to the high melting point metal layer 4 such as WSix, the undercut 3a ′ is formed in the silicon layer 31 as described above. In order to prevent this, for example, it is conceivable to use a mode in which the WSix layer is etched using an SF ₆ / HBr mixed gas system, and then the DOPOS layer is etched with HBr alone.

However, in these techniques, when processing an etching target material having a step (for example, an etching target material having a step due to LOCOS), an interface between a high melting point silicide layer / silicon layer (for example, WSix / DOPOS), It is difficult to determine the end point of overetching, and it is not always easy to apply the method to a material to be etched of all shapes.

That is, when the etching conditions for the refractory metal silicide layer and the silicon layer are changed, it is necessary to determine the end point of the etching of the refractory metal silicide layer (for example, the end point of etching between WSix / DOPOS) with high accuracy. There is
This is not always easy. In the above-mentioned patent application, the present applicant has proposed a technique of determining an etching end point by monitoring a change in emission spectrum intensity.
For the material to be etched having a step as described above,
This technique is also difficult to use. That is, if there is a step, as shown in FIG. 4, the thickness in the vertical direction of the portion b in the figure corresponding to the step becomes thick, and the film thickness to be substantially etched becomes another flat portion ( a). Since the emission spectrum intensity is monitored by the entire light emission, the interface at the flat portion a can be accurately detected. However, according to the end point determination, there is a possibility that an etching residue may occur at the portion b, and the uniform etching is performed. Cannot be achieved.
For example, if the WSix layer 4 remains, it is difficult to remove the etching residue in the subsequent steps since the etching rate is low.

[Problems to be solved by the invention]

Under the circumstances described above, development of a process capable of etching a portion to be etched having a silicon layer and a high-melting-point metal silicide layer under the same conditions without changing the etching conditions of both is desired.

In view of the above circumstances, the present invention can etch a silicon layer and a refractory metal silicide layer under the same conditions, and can prevent deterioration of the shape due to the occurrence of undercut or the like at the time of overetching. It is an object to provide an etching method that can achieve etching.

[Means for solving the problem]

In order to achieve the above object, an etching method of the present invention is directed to a method of etching a silicon-based material to be etched, which etches a portion to be etched having a silicon layer formed on a substrate and a refractory metal silicide layer. And an etching gas containing a gas capable of generating fluorine radicals, while etching at least the portion to be etched of the substrate while cooling it to a temperature range of more than −100 ° C. and 0 ° C. or less, and a silicon layer and a high melting point metal. Each layer with the silicide layer is etched under the same etching conditions.

The configuration of the present invention will be described below with reference to FIG. 1 showing an embodiment of the present invention, which will be described in detail later.

That is, the etching method of the present invention is a silicon-based etching method for etching a portion to be etched 10 having a silicon layer 3 and a high-melting metal silicide layer 4 formed on a substrate 1 as exemplified in FIG. In the method of etching a material to be etched, at least a portion to be etched 10 of the substrate 1 is heated to a temperature range of more than −100 ° C. and 0 ° C. or less using an etching gas containing hydrogen bromide and a gas capable of generating a fluorine radical. While etching while cooling, each layer of the silicon layer 3 and the refractory metal silicide layer 4 is etched under the same etching conditions to obtain an etching shape as exemplified in FIG. 1 (b).

[Action]

According to the present invention, when etching the silicon layer / the refractory metal silicide layer, the reaction at the side wall is suppressed due to the effect of lowering the temperature. In addition, a protective film is easily formed by SiBrx, which is a reaction product between the gas and the material to be etched. Therefore, even if a mixed gas system of hydrogen bromide and a gas capable of generating fluorine radicals such as SF ₆ / HBr is used, no undercut is formed in the silicon layer. Therefore, even if the refractory metal silicide layer and the silicon layer are etched under the same conditions, a good shape can be obtained, so that continuous etching can be performed under the same conditions. As a result, good etching can be realized without performing measurement of an etching end point at a difficult interface.

In previous reports example, by using a SF ₆ alone as the etching gas, by performing the following cold cooling -100 ° C., but is obtained by that it is possible to anisotropic processing of the polysilicon layer, in the present invention This is carried out, for example, at −50 ° C. or −70 ° C.
It can be achieved at higher temperatures, on the order of ° C. Further, there is no need to add a deposition gas such as F113, and there is no problem of particles.

Further, by changing the flow rate ratio of HBr,
It is possible to obtain a good shape at each temperature other than the above.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, needless to say, the present invention is not limited to the embodiments described below.

Embodiment 1 In this embodiment, the present invention is applied to a case where a material to be etched having a structure as shown in FIG. 1A is patterned in forming a pattern of a semiconductor device.

The silicon-based material to be etched in this embodiment includes a silicon layer 3 formed on a substrate (a substrate made up of a silicon substrate serving as the substrate 1 and SiO _{2 serving as the} gate oxide film 2 in this example) 11 and a refractory metal. The portion to be etched 10 having the silicide layer 4 is provided. In particular, the refractory metal silicide layer 4 is made of tungsten silicide, and the silicon layer is made of polysilicon, especially DOPOS doped with impurities. Although DOPOS doped with phosphorus P is used here, any material such as silicon doped with B may be used depending on desired conductivity.

In this example, a magnetic field microwave etcher was used as an etching apparatus.

 The etching conditions were as follows.

Substrate cooling temperature Ts: −70 ° C. Microwave power: 250 mA Gas used: SF ₆ / HBr = 40/10 SCCM While maintaining the above conditions, that is, under the same conditions, the refractory metal silicide layer as WSix layer and DOPOS The silicon layer 3 is continuously etched.

As a result, the reaction is suppressed at the side wall, and the reaction product is generated.
By the effect of the side wall protection by SiBrx, a good anisotropic processed shape without undercut as shown in FIG. 1 (b) could be obtained. In the figure, 41 is a refractory metal silicide pattern, and 31 is a silicon pattern.

The present invention can be carried out in various modes other than the above-described specific examples. For example, under the conditions of the above embodiment, in addition to the above SF ₆ as an etching gas, NF ₃ , C
A gas obtained by adding at least HBr to a gas that generates fluorine radicals such as lF ₃ , F ₂ , and HF can be used. The present invention may be carried out in various other aspects.

〔The invention's effect〕

As described above, according to the present invention, when etching a portion to be etched having a silicon layer and a high-melting metal silicide layer formed on a substrate, good etching can be performed without using a problematic gas such as chlorofluorocarbon. In particular, it is possible to suppress the occurrence of undercuts that may occur in the silicon layer during over-etching, to achieve etching with a good shape, and to achieve this effect by adjusting the etching conditions for the silicon layer and the refractory metal silicide layer. Need to frog,
In addition, the present invention can be achieved by continuous etching under the same conditions without having to detect the end point of the etching at the interface necessary for that.

[Brief description of the drawings]

1 (a) and 1 (b) are cross-sectional views showing the steps of Example-1 in each step of a material to be etched. 2 and 3 each show a conventional technique, and FIG. 4 shows a problem. 3 ... silicon layer (DOPOS layer), 4 ... refractory metal silicide layer (WSix layer), 5 ... photoresist, 10 ... etched part, 11 ... base.

Claims (1)

(57) [Claims] 1. A method for etching a silicon-based material to be etched for etching a portion to be etched having a silicon layer and a high-melting metal silicide layer formed on a substrate, comprising: a gas capable of generating hydrogen bromide and fluorine radicals; Using an etching gas containing, at least the portion to be etched of the substrate exceeds −100 ° C. and 0 ° C.
A method for etching a silicon-based material to be etched, wherein etching is performed while cooling to a temperature in the following range, and each of a silicon layer and a refractory metal silicide layer is etched under the same etching conditions.