JPH03248531A - Etching method for silicon material to be etched - Google Patents

Abstract

PURPOSE:To etch a part to be etched with a silicon layer and a high melting point metal silicide layer in a desirable shape by etching with gas containing gas for generating hydrogen bromide and fluorine radical, and then overetching only with gas for generating the radical. CONSTITUTION:After etching is performed with gas containing hydrogen bromide and gas for generating fluorine radical, overetching is performed only with the gas for generating the radical. Accordingly, a part 10 to be etched with a silicon layer 3 and a high melting point metal silicide layer 4 is etched in a desirable shape at a sufficient speed before overetching, and deterioration of the shape due to undercut, etc., at the time of overetching can be prevented. Thus, the etching can be performed.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

Industrial Application Field Overview of the Invention Background of the Invention Problems to be Solved by the Invention Means for Solving Problems Examples of Actions Example-1 Example-2 Example-3 Effects of the Invention [Industrial Applications] Field] Each invention of the present application relates to a method of 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 that includes a silicon layer and a refractory metal silicide layer on a substrate. The present invention
For example, when manufacturing semiconductor devices, it can be used as an etching method for so-called polycide structures.

[Summary of the invention]

Each invention of the present application generates hydrogen bromide and fluorine radicals in an etching method for a silicon-based material to be etched, which etches a notched portion of a workpiece having a silicon layer and a refractory metal silicide layer formed on a substrate. Etching is carried out using an etching gas containing a suitable gas, and each has the following characteristics.

That is, the invention of claim 1 of the present application suppresses the occurrence of undercuts on the side wall during overetching and obtains a good etched shape by overetching only with a gas that can generate fluorine radicals after the above etching. This is how it was done.

The invention of claim 2 of the present application further performs oxygen ashing treatment after the above etching, and then performs over-etching, thereby suppressing the occurrence of undercuts on the side wall during over-etching and obtaining a good etched shape. It is.

The invention according to claim 3 of the present application determines the etching end point of the high melting point metal silicide layer by monitoring the change in the intensity of the emission spectrum, thereby determining the appropriate etching end time, thereby realizing good etching. It is something.

(Background of the Invention) A structure in which a silicon layer and a high melting point metal silicide layer are formed on a substrate is used, for example, in the field of semiconductor devices.
For example, it is used to form a gate wiring structure.

High melting point metal silicide is a polycrystalline material that has been widely used as a gate wiring material for conventional semiconductor devices such as LSI.
It is advantageous because it has a lower resistance value than silicon, and
By interposing a silicon (especially polysilicon) layer between the high melting point metal silicide and the base, reliability at the interface (for example, the interface with 5i02 as a gate insulating film) can be maintained.

The above structure is generally referred to as polycide, meaning that silicide is typically layered on polysilicon.

When patterning such a polycide structure by etching, it is necessary to perform etching with good anisotropy for two different materials.
Etching gases mainly containing fluorinated carbon-based gases called fluorocarbons or freons have been used.

However, these fluorinated carbon-based gases have environmental problems such as destruction of the ozone layer, and it is desirable to avoid their use. There is also a high possibility that it will no longer be usable due to so-called fluorocarbon regulations.

Therefore, it is desired to develop an etching gas system that can replace the above etching gas, and that can achieve good anisotropy for both the silicon layer and the high-melting metal silicide layer, and can achieve etching with a good shape. ing.

Against this background, the present inventors first developed HBr/S
proposed an etching technology using a gas system containing hydrogen bromide and a gas capable of producing fluorine radicals, such as a mixed gas system (patent application ``Dry etching method'' filed on January 22, 1990).

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

[Problem that the invention seeks to solve]

As mentioned above, the technique proposed by the present inventors is advantageous because it can effectively etch polycide structures without using fluorocarbon gas, but depending on the substrate of the material to be etched, there may be a problem with the substrate. The problem remains that it is sometimes difficult to obtain a selectivity ratio.

For example, when used in a gate wiring structure, the base is often a SiO□ film to form a gate oxide film on -S.
This 5in2 film must also serve as an etching stopper film, but for example, when using an SF6/HBr mixed gas system as the etching gas, the underlying S
It is difficult to obtain a selectivity ratio with etching, making it difficult to achieve good etching.In some cases, undercuts may occur in the silicon layer during over-etching.
etc. may occur.

This problem will be explained with reference to FIG. 7 as follows.

For example, as shown in FIG. 7(a), the material to be etched is a substrate 1 and an insulating film 2 (Si) serving as an etching stopper.
On the substrate 11 consisting of DO
In the case of a material in which the etched portion 10 is a polycide film made of PO3 (doped polysilicon) and a high melting point silicide layer 4 -Six (tungsten silicide), a photoresist 51 is used as shown in the figure.
．． When etching is performed using SF, /HBr etching gas system using 52 as a mask, during just etching,
In the silicon etching residue shown by reference numeral 3a in FIG. 7(b), or especially between the resists 51 and 52,
An etching residue 3b may be left. This occurs to a greater or lesser extent due to variations in etching conditions, in-plane non-uniformity of the material to be etched, etc. Therefore, it is necessary to perform over-etching to remove the etched residues 3a and 3b. However, in this case, for example, the above S
If the F6/HBr gas system is used as is, the selectivity to SiO□ cannot be achieved, and the desired good etching cannot be achieved.

If etching is performed with WBr or 5126 alone from the beginning and then over-etching is performed, the problem of selectivity with SiO2 will be improved, but the etching rate may not be sufficient or the silicon layer may be etched. Undercuts may occur. For example, when a polycide structure as shown in FIG. 8(a) is etched and over-notched in this manner, a hollow-shaped underforce/ant 3a' is created in the silicon pattern 31 as shown in FIG. 8(b). This may occur, making it impossible to achieve good etching. (In addition, in Figures 7 and 8, 31
゜311.312 is the silicon pattern after etching,
Similarly, 41°41L412 is a high melting point metal silicide pattern. In addition, in order to prevent shape deterioration during etching, Japanese Unexamined Patent Publication No. 6
3-239950).

Furthermore, as described above, the portion to be etched 10 has a laminated structure of two layers of materials, the high melting point metal silicide layer 4 and the silicon layer 3, each having a different vapor pressure of the reaction product during dry etching. In this case, if the silicon layer 3 is etched under the same conditions as the high melting point metal silicide layer 4, undercuts may occur on the sidewalls (3a).
' may occur. In order to avoid this, it is desirable to perform etching by setting optimum conditions for each layer from the viewpoint of anisotropic processing with high lamination.

However, even if it is desired to change the etching conditions of the high melting point metal silicide layer 4 and the silicon layer 3 from the above point of view or other reasons, in order to realize this, it is necessary to change the etching conditions of the high melting point metal silicide layer 4. It is necessary to be able to determine the end point (for example, determine the etching end point between WSix/DOPO3) with high precision, but this has been extremely difficult with conventional techniques.

The inventions of the present application are intended to solve the above-mentioned problems, and the invention of claim 1.2 suppresses the occurrence of undercuts that may occur in the silicon layer during over-etching, and achieves etching with a good shape. The purpose is to achieve the following. Another object of the invention is to easily and reliably determine the etching end point of a high melting point metal silicide layer, thereby achieving etching with a good shape.

[Means for solving problems]

In order to achieve the above object, each invention of the present application takes the following configuration.

That is, the invention of claim 1 of the present application provides a method for etching a silicon-based material to be etched that includes a silicon layer and a refractory metal silicide layer formed on a substrate. This method is characterized in that etching is performed using an etching gas containing a gas that can generate radicals, and then over-etching is performed using only a gas that can generate fluorine radicals.

The invention of claim 2 of the present application provides a method for etching a silicon-based material to be etched, which etches a portion to be etched that has a silicon layer and a high-melting point metal silicide layer formed on a substrate, using hydrogen bromide and fluorine radicals. The method is characterized in that etching is performed using an etching gas containing a gas that can be generated, further an oxygen ashing process is performed, and then over-etching is performed.

The invention according to claim 3 of the present application provides an etching method for a silicon-based material to be etched, which etches a part to be etched that has a silicon layer formed on a substrate and a refractory metal silicide layer formed thereon. Etching is performed using an etching gas containing hydrogen chloride and a gas capable of generating fluorine radicals, and the etching end point of the high melting point metal silicide layer is determined by monitoring changes in the intensity of the emission spectrum. It is.

[For production]

The invention according to claim 1 of the present application performs etching using an etching gas containing hydrogen bromide and a gas capable of generating fluorine radicals, and then performs overetching using only a gas capable of generating fluorine radicals. The part to be etched, which has a silicon layer and a high-melting point metal silicide layer, can be etched at a sufficient speed and with a good shape before over-etching, and during over-etching, the shape can be improved due to the occurrence of undercuts. Deterioration can be prevented and good etching can be achieved.

The invention of claim 2 of the present application performs etching using an etching gas containing hydrogen bromide and a gas capable of generating fluorine radicals, further performs an oxygen ashing process, and then over-etches the silicon layer. Before over-etching, the part to be etched which has a high melting point metal silicide layer can be etched at a sufficient speed with a good shape, and during over-etching, the sidewall protection effect due to oxidation prevents the occurrence of undercuts, etc. It is possible to achieve good etching of the shape.

The invention according to claim 3 of the present application performs etching using an etching gas containing hydrogen bromide and a gas capable of generating fluorine radicals, and monitors changes in the intensity of the emission spectrum to form a high melting point metal silicide layer. Since it is characterized by determining the etching end point,
By monitoring the spectrum of wavelengths that exhibit specific behavior when the material to be etched changes, it is possible to determine the end point of etching with high precision.

〔Example〕

Embodiments of each invention of the present application will be described below with reference to the drawings. However, it goes without saying that each invention is not limited to the examples shown below.

Example 1 This example embodies the invention of claim 1 of the present application, and in particular, when patterning a semiconductor device,
As shown in FIG. 1, the present invention is applied when patterning is performed using photoresists 51 and 52 in close proximity.

The silicon-based material to be etched in this example is the base 1
1 (in this example, a base body consisting of a silicon substrate, which is the substrate 1, and SiO□, which functions as an etching stopper film 2); 10. In particular, the heavy metal silicide layer 4 consists of tungsten silicide and the silicon layer consists of polysilicon, in particular DOPO3 doped with impurities.

In this example, as a first step, under the following conditions,
Etching was performed until it was just etch.

I y Chia Cucas: SFa/HBr = 20
/ 30SCCM Current: 7250mA RF applied force: 100 mm Pressure: 5 mTorr Next, as a second step, over-etching is performed. As explained using FIG. 7, even if etching is performed under just etching conditions, due to in-plane non-uniformity of the material to be etched and variations in etching conditions, etching may occur as shown in FIG. 7(b). For the remaining 3a, or when the distance between the resists 51 and 52 is narrow like this, see Figure 7 (b).
This is because the etching residue 3b in ) may remain.

The over-etching conditions of this embodiment are such that SF, which is a gas capable of generating fluorine radicals, is used as the etching gas.

That is, the test was carried out under the condition of SF = 505 CCM.

DOPO3 forming the silicon layer 3 in this example is
The etching rate for the gas system is SFb /HBr =
In the case of 20/305 CCM, it is 7,700 people/min, whereas in the case of gas system SFi = 50 SCCM, it is 15,200 people/win in the case of RF bias power = 100-.

Therefore, the overetching time is such that the etching gas is SF
, by using it alone, it can be shortened to about half.

Additionally, the RF bias power during overetching is reduced to zero W.
If the concentration is lowered to 100%, the selectivity to SiO□, which is the underlying stopper film 2, will also increase. This is because while the etching rate of SiO□ decreases, the etching rate of silicon such as DOPO3 does not change much. This is thought to be because silicon is etched by fluorine radicals, so etching of SiO□ by ion assist does not depend on RF bias power. As a result, the base SiO
□It is possible to perform over-etching while reducing layer etching. If SF is etched alone from the beginning, undercuts will occur, while HBr
/SF, if the mixed system is directly used for over-etching, the speed will not increase and it is not practical.

FIG. 1(b) shows an example of a pattern shape obtained by etching. In the figure, 411 and 412 are high melting point metal silicide (WSix) patterns, and 311° and 312 are silicon layer (DOPO3) patterns.

Although the above example is applied to the case where two patterning resists 5L52 are present adjacent to each other, it is of course possible to suitably utilize the case where patterning is performed using a single resist pattern. This embodiment can be used, for example, to form a polycide gate structure.

As mentioned above, in this example, when etching tungsten polycide, first just etching was performed using SF, /HBr-based gas, and then only SFi was used as the etching gas as an over-etching process. The RF bias power in the over-etching process using SFi can be configured to be zero W, thereby shortening the time of the over-etching process after anisotropic etching using SF, /HBr and ensuring the selectivity. This is what made it possible.

Example 2 This example embodies the invention of claim 2 of the present application. The silicon-based material to be etched in this example is shown in FIG.
5in2 which functions as etching stopper film 2
The etched portion 1o includes a silicon layer 3 and a high melting point metal silicide layer 4 formed on a spiky base. In particular, the heavy metal silicide layer 4 is made of tungsten silicide, and the silicon layer is made of polysilicon,
In particular it consists of DOPO3 doped with impurities.

In this embodiment, as a first step, 5F67HB
Anisotropic etching is performed using an etching gas system until just etching is achieved. The etching up to this point is as follows:
The same conditions as in 1 may be used.

Next, as a second step, oxygen ashing treatment is performed under the following conditions. That is: Electrical enclosure gas: 02 = 50SCCM current
: 250mA RF bias power: Discharge for 5 seconds under zero condition. This forms a very thin oxide film on the sidewalls. It is known that the sidewalls are protected by oxidizing the sidewalls, but in this method, the etched patterns 41, 31 (see FIG. 2(b)
It is thought that the reaction product 5iBrx attached to the sidewalls of (see) is very unstable and is therefore chemically active and easily oxidized, so that the oxidation is carried out more efficiently.

After that, over-etching is performed. In this example, the following conditions were used in the overetching process following the oxygen ashing process.

Etching gas: HBr = 50 SCCM Current: 150 mA RF bias electric crab 50 - When hydrogen bromide is used as the etching gas during over-etching, a high selectivity to SiO□ can be obtained, so the oxidized sidewalls are Undercuts can be suppressed.

This makes it possible to perform etching with a high selectivity with respect to the underlying StO□ while maintaining an anisotropic shape.

However, SF or other gas may be used for over-etching.

As mentioned above, in this example, SFb/H, which is a mixed gas system of hydrogen bromide and a gas that can generate fluorine radicals, was used.
After just etching with Br, 02 plasma treatment is performed and sidewall oxidation is performed, followed by overetching. In this example, HBr was used as the etching gas for the overetching process, so the tungsten polycide structure was It has been made possible to carry out the over-etching process so as to obtain etched patterns of good shape without causing undercuts.

The structure after etching is shown in FIG. 2(b).

Example 3 This example embodies the invention of claim 3 of the present application.

The silicon-based material to be etched in this example is as shown in FIG. 3(a), and is the same as the material to be etched in Example 2.

In this example, a gas obtained by adding HBr to a gas that can easily generate at least fluorine radicals was used as the etching gas in the first step, and
The end point of the etching of the WSix layer, which is the high melting point metal silicide layer 4, is determined based on the change in the intensity of the emission line appearing at m.

In this example, as a first step, etching was performed on the etched portion 10 made of the tungsten polycide structure shown in FIG. 3(a) under the following conditions.

Etching gas: SF, /HBr =20/303
CCM Microwave Electric Crab 25On+A RF bias: 100W By etching under the above conditions, etching without contamination (re-deposition) by reaction product oxides can be achieved. During this etching, the emission line at 519 nm was monitored to determine the end point of etching of the WSix layer, which is the high melting point metal silicide layer 4.

As described above, etching is performed on the high melting point metal silicide layer 4 (
WSix layer), and a shape in which the surface of the silicon layer 3 was exposed as shown in FIG. 3(b) was obtained.

The change in emission intensity at 519 nm during etching is shown in the sixth column.
As shown in the figure. This peak was detected with a sensitivity of 67.

This method of determining the end point of etching utilizes the fact that there is a difference in luminous intensity when etching a high melting point metal silicide such as WSix and when etching silicon such as DOPO8.

This will be explained using FIGS. 4 and 5 as follows.

Figure 4 shows the emission spectrum I during WSix etching.
(indicated by a broken line) and the emission spectrum (indicated by a solid line) upon DOPOS etching are shown superimposed, and it can be seen that there is a considerable difference between the two depending on the wavelength.

FIG. 5 shows the difference between the two, and is obtained by subtracting the emission spectrum (I) during DOPOS etching from the emission spectrum I during WSi etching. The line above the horizontal axis indicates a stronger emission line during WSix etching, and the line below the horizontal axis indicates a line where emission is stronger during DOPOS etching.

As can be understood from each figure, the wavelength 519 used in the example
Between 500 and 600nII1 including nn+,
It can be seen that there is a clear difference in the intensity of the emission spectra.

As mentioned above, the etching speed of WSix is DOP
Although the etching rate is higher than that of O3, the generated intensity is greater, but the details of the cause of this difference are unknown. It is presumed that this is probably due to the properties of the high melting point metal (W).

As described above, in this embodiment, in etching a high melting point metal polycide structure, particularly a tungsten polycide structure, a gas obtained by adding HBr to a gas that can easily generate at least F radicals is used in the first step of etching the WSix layer. Since the emission intensity change in the vicinity of 500 to 600 nm was used to determine the etching end point of the core layer, the etching end point of the high melting point metal silicide layer 4 can be determined easily and precisely. Therefore, it is effective when changing the conditions, such as when etching the refractory metal silicide layer 4 and the silicon layer 3 such as DOPO3 under different conditions to perform etching under the optimum conditions for each.

Under the conditions of this example, the above S
In addition to F, it is also possible to use a gas such as NF, CfF, F2°HF, which is obtained by adding at least HBr to a gas that generates fluorine radicals. DOPO3 itself is HB
It is possible to perform sufficient etching with r alone.

Further, although the emission line used for end point determination was set to 519 nm, any wavelength that allows the difference in emission intensity to be confirmed may be used, and other wavelengths such as 505 nm and 539 nm may also be used.

As described above, by employing the present invention, this embodiment can highly accurately determine the end point during etching of the high melting point metal silicide layer 4 (in this embodiment, the WSix layer), and has a good etching structure such as a tungsten polycide structure. Anisotropic processing can be easily achieved.

〔Effect of the invention〕

As described above, according to each invention of the present application, good etching can be achieved when etching a portion to be etched that has a silicon layer and a high melting point metal silicide layer formed on a substrate. The invention according to claim 2 can suppress the occurrence of undercuts that may occur in the silicon layer during over-etching, and achieve etching with a good shape. This can be determined reliably and etching of a good shape can be achieved.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are sectional views showing the steps of Example 1 at each step of the material to be etched. FIGS. 2(a) and 2(b) show the same steps in Example 2. FIGS. 3(a) and 3(b) show the same steps in Example 3. Figures 4 to 6 are diagrams for explaining Example-3, where Figure 4 is an emission spectrum diagram, Figure 5 is a diagram showing differences in emission spectra, and Figure 6 is a change in emission intensity at 519 nm. FIG. FIG. 7 and FIG. 8 are diagrams each showing the prior art. 3...Silicon (DOPO3), 4...High melting point metal silicide (WSix), 5...Photoresist, 1
0... Part to be etched, 11... Substrate.

Claims (1)

[Claims] 1. In an etching method for a silicon-based material to be etched, which etches a part to be etched having a silicon layer and a high melting point metal silicide layer formed on a substrate, hydrogen bromide and fluorine radicals are generated. A method for etching a silicon-based material to be etched, characterized in that etching is performed using an etching gas containing a gas to be etched, and then over-etching is performed using only a gas that can generate fluorine radicals. 2. In an etching method for a silicon-based material to be etched, which etches a part to be etched having a silicon layer and a high-melting point metal silicide layer formed on a substrate, the etching method includes hydrogen bromide and a gas capable of generating fluorine radicals. A method for etching a silicon-based material to be etched, characterized by etching using an etching gas, further performing oxygen ashing treatment, and then over-etching. 3. In an etching method for a silicon-based material to be etched, which etches a part to be etched that has a silicon layer and a high-melting point metal silicide layer formed on a substrate, the etching method includes hydrogen bromide and a gas capable of generating fluorine radicals. Etching is performed using etching gas, and
1. A method for etching a silicon-based material to be etched, characterized in that the etching end point of a high melting point metal silicide layer is determined by monitoring changes in emission spectrum intensity.