KR0176714B1 - Dry etching method - Google Patents

Abstract

The present invention relates to a method capable of etching a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer with high anisotropy, low pollution, high selectivity, and high speed without using a flan gas.

According to the method of the present invention, an anisotropic process can be realized while protecting the sidewall mainly by the reaction product of the resist material and Br by etching the polyside film using an etching gas formed by adding at least HBr to the fluorine-based gas.

By using fluorine-based gas or HBr alone to overetch the uniform process on the wafer surface, high speed and improved substrate selectivity can be realized.

The over etching process proceeds with oxygen plasma treatment to oxidize the reaction product to enhance the sidewall protection effect and to improve the anisotropy.

Finally, the change in the emission spectrum intensity during the etching is monitored to determine the etch termination point of the high melting point metal silicide layer to enable accurate setting of the etching conditions.

Description

Dry etching method

1a and 1b is a cross-sectional view showing the dry etching method according to an embodiment of the present invention in the order of processes,

1A is a process chart for forming a photoresist pattern.

1B is an etching process diagram of a polyside film.

2 is a cross-sectional view showing the state of the substrate at the time when the etching of the tungsten silicide layer is finished in the etching process of the polyside film.

Fig. 3 is a light emission spectrum diagram when the tungsten silicide layer and the polycrystalline silicon layer are etched by SF ₆ / HBr system as an example of the position of the etching end point with respect to the high melting point metal silicide layer according to the present invention.

FIG. 4 is a diagram showing a spectral difference in the emission spectrum shown in FIG.

5 is a diagram showing a temporary change in the emission intensity at 519 nm in the emission spectrum shown in FIG.

6A and 6B are cross-sectional views illustrating a state in which etching residues are generated during dry etching of a polyside film.

6A is a cross-sectional view showing a state of a substrate before etching starts.

6B is a cross-sectional view showing a state of the substrate after etching.

7 is a cross-sectional view showing a state in which an undercut is generated in a DOPOS pattern in a conventional dry etching process for a polyside film.

* Explanation of symbols for main parts of the drawings

1 semiconductor substrate 2 gate oxide film

3: polycrystalline silicon (DOPOS) layer 4: tungsten silicide layer

5: polyside film 6: photoresist layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method, and more particularly, to a method for etching a polyside film used for a gate electrode or the like with high anisotropy and high plate selectivity without using a plonium gas.

Conventionally, polysilicon has been widely used as the gate wiring material of LSI. However, as the demand for higher speed of devices increases, high melting point metal silicide having a resistance lower than about one order of polysilicon has been used. When the gate wiring layer is formed by using a high melting point metal silicide, the so-called polyside film is formed by laminating a high melting point metal silicide layer on the gate insulating film through a polycrystalline silicon (DOPOS) layer into which impurities are introduced. Adoption is mainstream. This is to dispose a polysilicon layer that has been successful in the conventional process at the interface with the gate insulating film most likely to affect device characteristics and reliability, and to reduce the resistance in the high melting point metal silicide layer thereon.

However, such polyside film has to realize anisotropy with respect to two different kinds of materials, thus bringing new problems to the dry etching technique. That is, in the etching of the polyside film, the lower DOPDS layer is etched faster than the upper high melting point metal silicide layer due to the difference in vapor pressure of the generated halogen compound or the reaction layer at the interface between the DOPOS layer and the high melting point metal silicide layer. For this reason, deformation, such as undercut or cut, tends to occur in the pattern.

For example, as illustrated in FIG. 6A, the polyside film 15 including the DOPOS layer 12 and the high melting point metal silicide layer 14 is formed on the silicon substrate 11 through, for example, the insulating film 12 of silicon oxide. When the polyside film 15 is etched with the resist pattern 16 as a mask when deposited on the substrate, an abnormal shape is frequently caused as shown by way of example in FIG. That is, since the undercut 17 is formed below the high melting point metal silicide pattern 14a formed in the anisotropic shape under the resist pattern 16, the generated DOPOS pattern 13d becomes narrower than the desired pattern width.

The abnormalities of these shapes cause an offset region in which impurities are not introduced during ion implantation for forming the source-drain region, or a decrease in dimensional accuracy in forming sidewalls for realizing the LDD structure. In particular, it is not allowed in submicron devices.

To realize anisotropic etching, (1) increase ion energy, (2) add deposition gas to the etching gas system to perform sidewall protection, (3) perform sidewall protection by reaction products of the etching target and etching gas, and the like. This is considered, but there are many challenges to be solved, respectively. That is, there is a problem that the retreat of the resist or increase of damage to ①, the generation of particle contamination to ②, and the sidewall protection effect to ③ are changed depending on the etching area, so that a uniform pattern cannot be obtained. If all of these are not solved, practical anisotropic etching cannot be performed.

Conventionally, the most widely used etching gas for polyside films is, for example, Flon 113 (C ₂ Cl ₃ F ₃ ) as reported in Semiconductor World (published by Press Journal), pages 126 to 130, October 1989. It is mainly composed of plonic gas represented by. In order to have a fluorine atom and a chlorine atom in a molecule | numerator, this gas advances an etching reaction effectively by both a radical mode and an ionic mode, and also enables highly anisotropic etching while performing sidewall protection by depositing a carbon-type polymer. .

However, it is pointed out that plonic gas causes the destruction of the earth's ozone layer, and it is expected to be difficult to use in the future. Therefore, in the field of dry etching, it is urgent to find a substitute for the plonite gas and to establish an effective use method thereof.

It is also important to establish high selectivity for the etch base in the polyside film etching field.

For example, in order to employ a polyside film in the formation of the gate wiring, the etching base often becomes a silicon oxide layer for providing a gate insulating film, which acts as an etching finish. In recent years, since the thickness of the gate insulating film has been reduced, overetching is performed during the etching process to remove the etching residues for the reasons described below, so that a process of presenting good etching base selectivity is required.

The reason for overetching is explained next with reference to FIGS. 6A and 6B. For example, when etching the substrate shown in FIG. 6A, most of the polyside film 15 is etched to form the etching residue 13b when the high melting point metal silicide pattern 14a and the DOPOS pattern 13a are formed. (13c) may be produced, and the extent of such etching residues varies depending on the variation of etching conditions or the planar nonuniformity of the etching target. Although not shown, when the polyside film is formed in one step or multiple steps, the etching residue tends to be formed in that step or multiple steps. This etching residue should be removed by over etching, but high selectivity is required because the thickness of the insulating film 12 which is the etching base is considerably thin.

In view of the demand for miniaturization of the above devices, the discovery of replacement products for the flan gas, and the improvement of the etching base selectivity, HBr has recently been attracting attention as an etching gas. For example, Digest of Papers, 1989, Digest of papers, 1989, 2nd Microprocess Conference, page 190, performs reactive ion etching using HBr on n + type DOPOS layers to achieve good anisotropic shapes. An example is reported. Br has a large atomic radius and does not easily penetrate the etched material into the crystal lattice or the grain boundary. Therefore, it is difficult to cause spontaneous etching reaction, but it can cause the etching reaction in the case of ionic shock and achieve anisotropy. An advantageous etching type can be provided. Therefore, various attempts have been made to perform good anisotropic etching by using Br-based etching species and by setting the bias power appropriately to secure a high selectivity with the gate oxide film serving as the etching base.

However, although the dry etching by the HBr has some improvement in the anisotropic etching of the DOPOS layer, it has become apparent that the following problems arise when applied to the etching of the silicide film. That is, since the high melting point metal silicide layer is sputtered and removed, the bromide of the high melting point metal contaminates the inside of the etching chamber, and since the Br species radicals, which are inherently less reactive, are used as the etching species, etching using conventional plonium gas is performed. Compared to this, the etching rate is drastically lowered.

Accordingly, the main object of the present invention is to realize the etching of the polyside film with high speed, high selectivity, high anisotropy, and low pollution without using a plonic gas, and determine the interface between the high melting point metal silicide layer and the polycrystalline silicon layer. It is to provide an etching method that allows.

The present invention has been proposed to achieve the above object.

That is, the dry etching method according to the first aspect of the present invention is a dry etching method of a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer, wherein the polyside film is an etching gas formed by adding at least HBr to a fluorine-based gas. It is characterized by etching using.

The dry etching method according to the second aspect of the present invention is characterized by comprising a first process of etching as in the first aspect, and a second process of overetching using HBr.

The dry etching method according to the third aspect of the present invention is characterized in that a fluorine-based gas is used instead of HBr during the second process of the second aspect.

The dry etching method according to the fourth aspect of the present invention comprises the first step as described above, the second step of performing oxygen plasma treatment, and the third step of overetching. It is.

The dry etching method according to the fifth aspect of the present invention provides a dry etching method of a polyside film as in the first aspect, wherein the end point of etching of the high melting point metal silicide layer is determined by monitoring the change in emission spectrum intensity. It is.

In the first aspect of the present invention, an etching gas obtained by adding at least HBr to a fluorine-based gas is used. According to such a gas system, etching can be performed at an effective rate by fluorine radicals generated by discharge, and high anisotropy can be expected from the sidewall protection effect mainly caused by the reaction product between the resist material layer and Br.

In the second aspect, after the completion of etching of the polyside film by the gas system, overetching is performed using HBr alone. Accordingly, high selectivity to the gate oxide film is maintained, and both the polyside film and the polysilicon layer can be completely removed from all wafer surfaces without lowering the etching speed of the overall process.

In the third feature, unlike the second feature, overetching is performed by using a fluorine-based gas. As a result, the overetching speed is sufficiently increased.

In the fourth aspect, overetching is performed by an oxygen plasma treatment of the substrate, whereby the reactive component of the sidewall protective film layer formed in advance is oxidized immediately so that not only the anisotropic shape can be improved but also the sidewall protection effect can be increased. do.

In the fifth aspect, the interface between the high melting point metal silicide layer and the polycrystalline silicon in etching the polyside film is determined by detecting a decrease in the emission spectrum intensity around the interface which is believed to be due to the reduction in the consumption of etching species. This makes it possible to more thoroughly control the etching conditions.

According to the dry etching method of the present invention, when etching a polyside film formed by stacking a high melting point metal silicide layer and a polycrystalline silicon layer, an etching reaction utilizing the advantages of fluorine-based gas and HBr can be advanced.

For example, if the fluorine-based gas is used alone, since the reaction product of the polysilicon layer and the fluorine radical is rapidly removed at the time when the cross section of the polysilicon layer is exposed, the etching rate of this layer is high melting point. It is relatively faster than the etching rate of the metal silicide layer, and in many cases, an undercut is caused to the polysilicon layer.

In addition, when HBr is used alone, the Br-based radical generated is a chemical species that is difficult to spontaneously react with any of the high melting point metal silicide layer or the polycrystalline silicon layer, and the reaction product between the resist material and Br Because of the deposition, the etching rate is drastically lowered. In addition, when the high melting point metal silicide layer is etched, bromide of the high melting point metal is generated, which causes particle contamination, and does not provide a practical process.

However, as with the first aspect of the present invention, with the etching gas in which at least these fluorine-based gases and HBr are mixed in an appropriate ratio, the aforementioned drawbacks are complementarily covered. That is, firstly by the highly reactive fluorine-based gas Etching speed of practical level is secured. Further, Br having a large mass effectively sputters the resist material to form a reaction, and as a result of this deposition on the sidewall portion of the polyside pattern together with SiBr _x , the occurrence of undercut in the polysilicon layer is prevented. In addition, H contained in HBr contributes to decomposition of the resist material, or has an effect of capturing excess fluorine radicals in the system and removing them in the form of fluoric acid. In addition, since no deposition gas is used in the etching system, there is no fear that particles are generated in the gas phase and the inside of the etching chamber may be stigmatized. Thus, according to the first aspect of the present invention, anisotropic etching is realized at high speed and under clean conditions.

In the second aspect of the present invention, the above-described process is substantially finished by etching the polyside film as the first etching step and then overetched by HBr alone as the second etching step. The polyside film can be completely removed while maintaining the high selectivity. Since most of the etching has already been completed in the first etching step, the overall etching rate is not significantly reduced. In addition, since HBr is used alone, selectivity with respect to the gate insulating film generally made of silicon oxide or the like is also improved. The reason is that silicon oxide is not substantially etched by HBr in theory, ignoring the ion sputtering effect, as predicted from the relative magnitude of the interatomic bonding energy of Si-O Si-Br. In addition, since the high melting point metal silicide layer does not exist at the stage where the second etching process is performed, even if HBr is used alone, there is no fear of causing particle contamination by the high melting point bromide.

In the third aspect of the present invention, overetching is carried out using substantially only a fluorine-based gas to remove the polyside film at high speed without significantly lowering the selectivity of the etching base. In the third aspect of the present invention, as predicted from the relative magnitude of the interatomic bonding energy of Si-F Si-Br, the selectivity to silicon oxide in the third aspect is determined by the second characteristic. Somewhat inferior to selection. However, the etching speed is high, because the over etching is mainly performed by fluorine radicals. The anisotropic shape is naturally maintained because the sidewall protective film is already formed on the pattern side wall through the prior etching process.

According to a fourth aspect of the present invention, an oxygen plasma treatment is performed before overetching, and by this step, active SiBr _x attached to the sidewall of the pattern as an etching reaction product is easily oxidized, thereby providing a satisfactory anisotropy treatment. There is.

In the fifth aspect of the present invention, attention is paid to the fact that the intensity of the emission spectrum decreases during dry etching of the polyside film by using an etching gas containing fluorine-based gas and HBr. It is used to determine the interface between the metal silicide layer and the polycrystalline silicon layer. In general, the emission intensity of a halide of tungsten, which is a typical high melting point metal, is extremely low, but it is extremely difficult to determine the etch termination point of this layer depending on the specific emission of the reaction product from the high melting point metal silicide layer. However, in the fifth aspect of the present application, the interface can be determined by monitoring the decrease in the emission intensity in a specific wavelength range which is thought to be due to the change in the amount of etching species consumption. In this way, the etching conditions can be more thoroughly adjusted. For example, since the polycrystalline silicon layer has a higher reactivity to fluorine radicals than the high melting point metal silicide layer, the polycrystalline silicon layer may be positioned at the above-described interface, thereby increasing the HBr content in the etching gas, thereby realizing a more effective anisotropic process. On the other hand, depending on the type of film forming apparatus used, since the high melting point metal silicide layer frequently undergoes minute variations in composition, it is necessary to optimize the fluorine-based gas to HBr mixing ratio. However, since the optimal mixing ratio is not necessarily required for etching the polysilicon layer, it is convenient to use the interface as a means for setting the time for changing the composition of the etching gas.

Next, a preferred embodiment of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to this embodiment.

Example 1

This Embodiment 1 is an example in which the first feature of the present invention is applied to etching a polyside film serving as a gate electrode. This etching step will be described with reference to FIGS. 1A and 1B.

First, as shown in FIG. 1A, a DOPOS layer corresponding to a lower layer of, for example, a gate oxide film 2 made of silicon oxide and a polyside film 5 is formed on a semiconductor substrate 1 made of single crystal silicon or the like. 3) After sequentially stacking the tungsten silicide layer 4 corresponding to the upper layer of the polyside film 5, the photoresist layer 6 is used as a mask for etching the polyside film 5 on the surface of the tungsten silicide layer. ) Was selectively formed.

Next, the gas shown in FIG. 1A is set in a traveling flat plate type RIE (reactive ion etching) apparatus, and the SF ₆ flow rate (flow rate) 20SCCM, the HBr flow rate 10SCCM, and the gas pressure 1.0 Pa (= 7.5m Torr) And etching under the condition of RF power 300W. Under these conditions, an etching reaction mainly comprising a radical reaction proceeds rapidly, and as shown in FIG. 1B, at least a sidewall protective film (not shown) is formed in the sidewall portion of the polyside film 5. Accompanying with this, a gate electrode having a pattern width of 0.35 탆 was formed with good anisotropy. According to this condition, since the ion incident energy is relatively low at about 250V, the occurrence of damage is suppressed. Here, the sidewall protective film is mainly composed of a carbon-based polymer produced by sputtering the photoresist layer 6 by Br, and it is considered that SiBrx and the like are mixed therein. Since the etching gas does not contain the deposition gas, very little particles are generated in the gas phase layer and contamination by the high melting point metal bromide does not occur, so that a very clean process can be performed.

In the above example, SF ₆ is used as the fluorine-based gas, but in addition, NF ₃ , ClF ₃ , F ₂ , HF, and the like may be used. The mixing ratio of HBr to these fluorine-based gases is preferably about 1 to 50 mol%. If less than the above range, the sidewall protection effect is insufficient, and if more than the above range, the etching rate may be lowered.

In addition, N ₂ or O ₂ may be appropriately added to the etching gas, and reaction products of these gases and Si may be added to the components of the side wall protective film to enhance the side wall protection effect. Moreover, you may mix suitably rare gases, such as argon and helium, in anticipation of a sputter effect, a dilution effect, and a cooling effect.

Incidentally, in the above example, tungsten silicide was used as the high melting point metal silicide constituting the upper layer of the polyside film 5, but the type of the high melting point metal silicide is not limited thereto, and other high melting points such as molybdenum, titanium, and tantalum are used. It may contain a metal.

Example 2

According to a second aspect of the present invention, the second embodiment is an example in which overetching with HBr is performed following the etching performed in the first embodiment.

That is, according to the conditions in Example 1, as the first etching step, the polyside film 5 is etched in the finished state of the etching step shown in FIG. 1b, the supply of SF ₆ is stopped, and then the HBr flow rate is reduced. A 2nd etching (over etching) process was performed at 30SCCM. In the second etching step, the selectivity to the gate oxide film 2 is further higher than that of the first etching step, so that only the remaining DOPOS layer is effectively removed without damaging the underlying. Thus, uniform etching is achieved throughout the wafer. In addition, particle contamination did not occur in the second etching step. The second etching was completed in a short time, and the total etching time was not extended.

Example 3

The third embodiment is an example in which over etching by SF ₆ is continuously performed on etching by SF ₆ / HBr system according to the third aspect of the present invention.

The substrate to be etched is as shown in FIG. 1A. The substrate was placed in a microwave plasma etching apparatus having a magnetic field and subjected to polyside film under the conditions of SF ₆ flow rate 20SCCM, HBr flow rate 30SCCM, gas pressure 0.67Pa (= 5mTorr), microwave power 850W and RF bias power 100W (13.56MHz). (5) was etched to the same depth as the film thickness. Under this condition, the etching rate of the DOPOS layer was 7700 dl / min.

Next, the supply of HBr was terminated and the over-etching was performed by adjusting the SF ₆ flow rate to 50 SCCM. As a result, etching was performed at a rate of 15200 kW / min, which was about twice the etching rate, thereby reducing the overetching time and obtaining improved results.

If SF ₆ is used alone, the etching base selectivity may be lowered, but this problem can be solved by terminating or reducing the influence of RF bias power during overetching. The reason is that when the RF bias power, i.e., the ion incidence energy is lowered, the etching rate of silicon oxide is lowered, while the etching rate of silicon materials such as DOPOS does not change very much. The silicon material may be etched by fluorine radicals, and at this time, the silicon bias is not as dependent on the RF bias power as the etching of the silicon oxide by ion assist. This makes it possible to overetch while reducing the etching of the gate oxide film 2. If etching is performed by SF ₆ alone from the beginning, undercut is generated. On the other hand, if the HBr / SF ₆ mixed system is used for overetching as an expectation, the etching rate does not increase, which is not practical.

Example 4

This embodiment 4 is an example in which an oxide plasma treatment is inserted between etching and over etching of the polyside film 5 according to the fourth aspect of the present invention.

First, as the first step, anisotropic etching was performed by the SF ₆ / HBr etching gas system until the preceding etching step described in Example 3 was completed. The etching up to this time may use the same conditions as in Example 3.

Next, microwave discharge was performed for 5 seconds by oxygen plasma treatment under the conditions of an oxygen gas flow rate of 50 SCCM, a microwave power of 850 W, and an RF bias power of 0 W. As a result, a thin oxide film was formed on the sidewalls. It is known to perform sidewall protection by oxidizing the sidewall, but in the process of Example 3, since the reaction product SiBrx attached to the sidewall of the etched pattern is very unstable, it is chemically active and easily oxidized, thus It is thought that side wall protection can be performed efficiently.

Next, in the third step, overetching was performed using HBr. The over-etching conditions were HBr gas flow rate 50SCCM, microwave power 510W, and RF bias power 0W. Here, as shown in FIG. 1B, a satisfactory anisotropic pattern of polyside film 5 was formed.

On the other hand, SF ₆ may be used instead of HBr for overetching.

Example 5

This example 5 is an example of monitoring the change in intensity of the emission spectrum during etching in accordance with the fifth aspect of the present invention.

In this embodiment, the tungsten silicide layer 4 is produced in accordance with the change in the emission spectrum intensity that appears between 450 nm and 650 nm using a mixed etching gas mainly comprising at least HBr added to a gas that can easily generate fluorine radicals. It was configured to determine the end point of the etching of.

First, the substrate shown in FIG. 1A was etched under the same conditions as the first half of the etching shown in Example 3. FIG.

3 shows light emission spectra in the case of etching of the tungsten silicide layer 4 and the DOPOS layer 3. In this figure, the vertical axis and the horizontal axis respectively show the intensities of intensities in arbitrary units and the wavelength in nm, and the spectra I and the spectra II respectively show emission spectra during the etching of the tungsten silicide layer 4 and the DOPOS layer 3. Indicates.

4 shows the spectral difference, that is, the difference between the emission spectrum I at the time of etching the tungsten silicide layer 4 and the emission spectrum II at the time of etching the DOPOS layer 3. In the figure, the upper portion of the center line is the region where the luminescence intensity is increased during the etching of the tungsten silicide layer 4, and the lower portion is the region where the luminescence intensity during the etching of the DOPOS layer 3 is increased.

As can be understood from this figure, the emission intensity during the etching of the DOPOS layer 3 is generally lower than that of the tungsten silicide layer 4 over a wide wavelength range of 450 nm to 650 nm.

The chemical species of the luminescent material is not known in detail, but since the luminescence intensity during the etching of the polysilicon layer progressing at a faster etching rate is low, the emission at the above wavelength is not due to the etching reaction product, but due to the etching. It can be inferred that the decrease in the emission intensity is due to the increased consumption of etching species.

According to one embodiment, the temporal change in the emission intensity at the wavelength of 519 nm is shown enlarged in FIG. Here, the vertical axis and the horizontal axis represent the sensitivity and the etching time in arbitrary units, respectively. The etching of the tungsten silicide layer 4 ends approximately 30 seconds after the start of etching. At this point the state of the substrate is as shown in the example of FIG. When attempting to etch the tungsten silicide layer 4 and the DOPOS layer 3 by adjusting the optimum etching conditions, respectively, such an interfacial crystal is effective in adjusting the optimum etching conditions for etching such a layer.

In addition, although the light emitting line used for end point determination is set to 519 nm in FIG. 5, other wavelengths, 505 nm or 539 nm or the like, which can confirm the difference in the light emission intensity may be used.

Claims (5)

A dry etching method of a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer, wherein the polyside film is etched using an etching gas formed by adding at least HBr to a fluorine-based gas. A dry etching method of a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer, comprising: a first process of etching the polyside film using an etching gas formed by adding at least HBr to a fluorine-based gas, and using HBr A dry etching method comprising the second step of over etching. A dry etching method of a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer, the first step of etching the polyside film using an etching gas formed by adding at least HBr to a fluorine-based gas, and using a fluorine-based gas. Dry etching method comprising a second step of over-etching. A dry etching method of a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer, the first step of etching the polyside film using an etching gas formed by adding at least HBr to a fluorine-based gas, and oxygen plasma treatment. And a second step of overetching and a third step of overetching. In the dry etching method of a polyside film composed of a high melting point metal silicide layer and a polycrystalline silicon layer, the polyside film is etched using an etching gas formed by mixing at least HBr with a fluorine-based gas, and the emission spectrum intensity change is monitored. A dry etching method for determining the end point of etching of the melting point metal silicide layer.

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