JP3694083B2 - Ruthenium film etching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ruthenium film etching method, and more particularly to a ruthenium film etching method applicable to the manufacture of a semiconductor device using a ruthenium film that requires fine processing.
[0002]
[Prior art]
The background of the present invention will be described by taking as an example a semiconductor device using a multi-element oxide film having a high dielectric constant (hereinafter referred to as a multi-element oxide high dielectric constant film) as a dielectric of a thin film capacitor element.
In the semiconductor device, platinum, which is one of refractory metal-containing films, is used as the electrode material of the thin film capacitor, and a semiconductor device having a fine structure such as a dynamic random access memory device (hereinafter abbreviated as DRAM). In some cases, it is necessary to finely process the platinum electrode on at least one side of the capacitor. For this reason, the platinum film is etched by dry etching using reactive gas plasma. In this etching, a photoresist is usually used as an etching mask. However, since the vapor pressure of the reaction product of platinum etching is low, it is necessary to use the effect of sputtering by ions. The reaction product is redeposited on the side surface perpendicular to the etching surface, such as the side wall of the photoresist pattern, which is an etching mask, to form a film that is difficult to remove (hereinafter referred to as a side wall adhesion film). This sidewall adhesion film must be removed in the manufacturing process of the semiconductor device. However, it is difficult to completely remove the sidewall adhesion film at present, and therefore, a new electrode material that can be etched without causing this sidewall adhesion film. Adoption is desired.
[0003]
Therefore, ruthenium or ruthenium dioxide is currently being studied as a new electrode material that does not cause this sidewall adhesion film. As a method for etching ruthenium or ruthenium dioxide, etching using a mixed gas plasma in which oxygen is the main gas and chlorine, CF ₃ CFH ₂ , or CF ₄ is added thereto has been reported. In this case, since oxygen is used as an etching gas, it is impossible to use a photoresist that is normally used as an etching mask, and a silicon oxide film is used as an etching mask. Among these etching methods, etching with a mixed gas plasma in which chlorine is added to oxygen has the highest etching rate, and is the best etching method in this respect.
[0004]
[Problems to be solved by the invention]
However, when ruthenium is etched by this mixed gas plasma of oxygen and chlorine, as shown in FIG. 6, the following three problems occur. FIG. 6 is a microscopic (SEM) photograph showing the shape of a pattern in the course of etching of a ruthenium film etched by a conventional method. FIG. 6A is an SEM photograph of the etched surface, showing an etched surface and a tapered surface ( (B) shows an SEM photograph of the etched cross section and shows that the etched side surface has a tapered shape. The etching conditions of this conventional method are as follows.
Total gas flow rate of oxygen and chlorine: 100 sccm
Chlorine gas concentration: 7.5%
Discharge pressure: 30 mTorr
RF power: 250 W
Magnetic field strength: 200 Gauss
The first problem is that the ruthenium etching shape becomes a taper shape that protrudes from the skirt portion of the mask pattern of the silicon oxide film, so that the dimension of the ruthenium pattern after etching is the same dimension as the dimension of the etching mask. In the case of a fine pattern that is not finished, the problem is that it is connected to an adjacent pattern. Therefore, it was impossible to form a fine pattern having a pattern extraction dimension (a dimension of a gap between patterns) of 0.3 μm or less (when the film thickness of the ruthenium film was 2000 mm).
The second problem is that the tapered surface of the ruthenium taper shape does not become a smooth surface but a rough surface with a wavy shape. This causes a problem of causing current leakage.
The third problem is that an uneven surface is formed on the ruthenium etching surface in the middle of etching, and when the etching is just finished, a partial ruthenium etching residue reflecting the unevenness is generated, so that ruthenium is removed to remove this residue. This etching needs to be continued (overetching).
[0005]
As described above, in the dry etching of the ruthenium film by the mixed gas plasma of oxygen and chlorine, the above problems occur. And measures to solve the problem are desired. An object of the present invention is to solve the above problems and provide a ruthenium film etching method capable of forming a fine pattern.
[0006]
First, consideration will be given to the cause of the problem in the etching of the ruthenium film.
In ruthenium film etching using a mixed gas plasma of oxygen and chlorine, the main etching reaction product is ruthenium tetroxide having a relatively high vapor pressure, but at the same time etching ruthenium oxides such as ruthenium dioxide with a low oxidation degree. It is generated in a surface or gas plasma. Since these low-oxidation ruthenium oxides have a low vapor pressure, they are once detached from the etching surface by the impact of ions incident from the plasma, but the ruthenium etching surface and the silicon oxide film pattern that is the etching mask It adheres again to the side surface of the film and becomes an obstacle to the progress of etching. In addition, during etching of ruthenium, the silicon oxide film component, which is an etching mask, is also released into the gas plasma by the impact of ions incident from the plasma, and this silicon oxide film component also has a low vapor pressure. It reattaches to the surface and the side surface portion of the silicon oxide film pattern, which is an etching mask, and becomes an obstacle to the progress of etching. These problems in the etching of ruthenium by the above-mentioned mixed gas plasma of oxygen and chlorine are caused by the inhibition of the progress of the etching due to the redeposition of ruthenium oxide having a low degree of oxidation and components of the silicon oxide film.
Therefore, in order to solve the above problem, it is necessary to prevent or reduce the re-deposition of the components of the ruthenium oxide and silicon oxide film having a low degree of oxidation. The method will be described below.
[0007]
[Means for Solving the Problems]
According to a first method of etching a ruthenium film of the present invention, in the method of etching with plasma using a mixed gas containing chlorine and oxygen as a reactive gas, the supply amount of the mixed gas is increased, and the mixed gas flow rate is increased. By increasing the gas, the replacement of the gas is accelerated, the residence time of the gas in the etching chamber (the time required for the replacement of the residence time gas) becomes 45 msec or less, and the amount of oxygen atoms as etching species There is something to increase .
[0008]
In the second method of etching a ruthenium film according to the present invention, an area adjustment dummy pattern is provided so that the area to be etched is 40% or less of the entire area of the sample surface to be etched.
[0009]
A third method of etching a ruthenium film according to the present invention is a method of etching a ruthenium film with a mixed gas plasma containing chlorine and oxygen using a silicon oxide film as an etching mask. At least one compound gas is added at a concentration of 1% to 10% of the total gas flow rate .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Embodiments and effects of a ruthenium film etching method according to the present invention, a method for preventing or reducing the re-deposition of components of low-oxidation ruthenium oxide and silicon oxide film, which can obtain a good etching shape, and effects thereof will be described below. .
First, an example of an etching apparatus used in the present invention is shown in the block diagram of FIG. In the etching chamber 1, a reaction gas inlet 2, an exhaust port 3 connected to a vacuum pump for exhausting the reaction gas from the etching chamber 1, a cathode electrode 4 for applying RF power to discharge, and An anode 5 that is electrically grounded is provided. In addition, an electromagnetic coil 6 that can apply a magnetic field to the discharge region is provided outside the etching processing chamber 1 in order to enhance the discharge. First, the sample 7 to be etched is placed on the cathode electrode 4, and the etching chamber 1 is evacuated from the exhaust port 3 to a vacuum. Etching gas is introduced from the gas inlet 2 while continuing this exhaust, and the etching chamber 1 is maintained at a predetermined pressure. Therefore, RF power and a magnetic field are applied to the cathode electrode 4 from the electromagnetic coil 6 and discharge is started in the etching processing chamber 1 to etch the sample 7. The etching apparatus is not limited to the above, and other types of etching apparatuses may be used.
[0011]
Next, an example of an etching sample used in the present invention will be shown together with a preparation method based on the cross-sectional views shown in the order of steps in FIG. A surface of the silicon substrate 8 is oxidized to form a silicon oxide film 9, and a ruthenium film 10 is formed by a sputter deposition method. A thin silicon oxide film 11 serving as an etching mask for the ruthenium film 10 is formed thereon by a CVD method, and an organic photoresist film 12 is further formed thereon by a spin coating method, and the photoresist film 12 is etched by etching. The pattern to be formed is transferred and a photoresist film 12 pattern is formed (FIG. 2A). Next, the thin silicon oxide film 11 is etched using the photoresist film 12 pattern as a mask by dry etching using a fluorine-containing gas, and then the photoresist film 12 pattern is removed, thereby forming an etching mask for the ruthenium film 10. A thin silicon oxide film 11 pattern is formed to obtain an etching sample.
[0012]
As described above, in order to improve the etching shape, it is necessary to prevent or reduce redeposition of ruthenium oxide having a low degree of oxidation. The reason for the generation of ruthenium oxide with a low degree of oxidation is that the etching species supplied from the gas plasma during etching (considered to be mainly oxygen atoms) is insufficient, and as a method to compensate for this shortage, The following two methods can be considered. The first method is a method of increasing the supply amount of the mixed gas of oxygen and chlorine, thereby increasing the amount of etching species supplied.
In the first embodiment, the relationship between the supply amount of the mixed gas of oxygen and chlorine and the etching shape is grasped, and the gas supply amount for obtaining a good etching shape is set.
The graph of FIG. 3 shows the change in the taper angle of the etching side surface of the ruthenium film when etching is performed by changing the total flow rate of the mixed gas obtained by adding chlorine to oxygen as the etching gas. The etching conditions at this time are as follows.
Chlorine gas concentration: 7.5%
Discharge pressure: 30 mTorr
RF power: 250 W
Magnetic field strength: 200 Gauss
Etching chamber volume: 7000 cc
From FIG. 3, it can be seen that by increasing the flow rate of the mixed gas of oxygen and chlorine, the taper angle of the etching side surface of ruthenium increases, and the shape of the etching side surface approaches vertical. Although not shown, the roughness of the etching surface (surface) and the tapered surface also decreases as the gas flow rate increases. The effect of improving the etching shape by increasing the gas flow rate becomes significant when the gas flow rate is 400 sccm or more (the gas residence time is 41 msec or less), becomes almost saturated when the gas flow rate is 600 sccm (the gas residence time is 28 msec), and increases even further. There was no ridiculous improvement effect. Therefore, it is desirable to set the gas flow rate to 400 sccm or more under this experimental condition, and the best result is obtained at 600 sccm or more. When the gas flow rate was 400 sccm, the taper angle was about 69 degrees, and the adjacent ruthenium film was not connected even when the pattern extraction dimension was 0.15 μm (when the ruthenium film thickness was 2000 mm). Further, at 600 sccm, the taper angle was about 72 degrees, and the adjacent ruthenium film was not connected even when the pattern extraction dimension was 0.13 μm. A much finer pattern than before can be formed.
As described above, it is possible to satisfactorily etch the ruthenium film without causing the taper shape of the etching shape, the roughness of the taper surface, and the roughness of the etching surface, which are problems in the conventional etching method, and fine processing is required. Application to a semiconductor device manufacturing process becomes possible.
The effect of improving the etching of the ruthenium film by increasing the gas flow rate is observed even at other gas pressures. The improvement effect by increasing the gas flow rate is closely related to the residence time of the gas in the gas plasma (corresponding to the discharge region), and the gas exchange is accelerated by increasing the gas flow rate, and the supply amount of ruthenium etching species increases. Moreover, the discharge of ruthenium oxide from the gas plasma to the outside of the etching chamber 1 increases, and the amount of redeposition decreases. Therefore, in other gas pressure conditions, it is not necessary to match the gas flow rate to the above conditions, it is only necessary to match the residence time of the gas, and it is desirable that the residence time of the gas is approximately 45 msec or less, which is approximately the same as the above conditions, Similar effects can be obtained. Furthermore, by making it 30 msec or less, the best etching shape improvement effect can be obtained.
[0013]
Embodiment 2. FIG.
Preventing or reducing the re-deposition of low-oxidation ruthenium oxide to improve the etching shape as described above, that is, lack of etching species supplied from gas plasma during etching, which is the cause of the generation of low-oxidation ruthenium oxide. A second way to compensate is to reduce the amount of ruthenium etched. Specifically, an area adjustment dummy pattern is provided to limit the area of the ruthenium film to be etched, thereby reducing the amount of etching species consumed by etching, resulting in a gas plasma. This is a method for increasing the amount of etching species supplied. This method also reduces the amount of low-oxidation ruthenium oxide released into the gas plasma, thereby reducing the amount of redeposition.
In the second embodiment, the relationship between the area of the ruthenium film to be etched and the etching shape is grasped, and the area to be etched from which a good etching shape is obtained is set.
The graph of FIG. 4 shows changes in the taper angle of the etching shape (side surface) of the ruthenium film when etching is performed while changing the area of the ruthenium film on the sample surface to be etched. The horizontal axis of the graph indicates the ratio of the area to be etched by (area to be etched) / (surface area of the sample). The etching conditions at this time are as follows.
Total gas flow rate of oxygen and chlorine: 300 sccm
Chlorine gas concentration: 7.5%
Discharge pressure: 30 mTorr
RF power: 250 W
Magnetic field strength: 200 Gauss
Etching sample wafer diameter: 6 inch
By reducing the etching area, the taper angle of the etching side surface of the ruthenium film increases and the etching shape approaches vertical. Although not shown, the roughness of the etching surface and (side surface) taper surface also decreases as the etching area decreases. The effect of improving the etching shape by reducing the area to be etched becomes significant when the etching area ratio is 40% or less, that is, the area to be etched is 40% or less of the sample surface area. When the etching area ratio is 40%, the taper angle is about 77 degrees, and even when the pattern extraction size is 0.1 μm (when the ruthenium film thickness is 2000 mm), the adjacent ruthenium film is not connected, which is much more than conventional. A fine pattern could be formed.
The effect of improving ruthenium etching due to this reduction in the etching area ratio is also observed in samples of other sizes, but this improvement depends on the balance between the surface area of the sample and the volume of the plasma that is the source of the etching species there. Therefore, even if the sample size changes, the etching area ratio dependency of the improvement effect does not change and shows the same tendency as in FIG. Therefore, in the etching of the ruthenium film, the etching shape can be improved by setting the etching area ratio to 40% or less regardless of the size of the etching sample.
[0014]
A specific method for reducing the area to be etched will be described below by taking a DRAM, which is a semiconductor device to which the etching method of the present invention is applied, as an example.
The etching method of the present invention is applied to a capacitor lower electrode forming process in a DRAM manufacturing process, and the area occupied by the lower electrode in this process is usually 40% or less with respect to the area of one chip of the DRAM. It is. Therefore, the area to be etched is usually about 60% or more. Therefore, in order to reduce the area to be etched to 40% or less to which this embodiment is applied, it is necessary to devise a special arrangement for the pattern arrangement. In the case of this DRAM, a pattern (dummy pattern) that is not particularly used is arranged on the part to be etched other than the ruthenium pattern to be the capacitor electrode, for example, on the peripheral circuit part so as not to contact the electrode pattern of the capacitor. A method of reducing the area to be etched is taken.
[0015]
Embodiment 3 FIG.
Further, as described above, in order to improve the etching shape, it is necessary to prevent or reduce the redeposition of the components of the silicon oxide film. For re-deposition of silicon oxide film components, the high vapor pressure of silicon fluoride is used, and a small amount of fluorine gas or fluorine compound gas is added to the etching gas to release the silicon oxide film components. Can be changed to a component having a high vapor pressure, thereby preventing reattachment.
In the third embodiment, changes in the etching shape due to the addition of fluorine or a fluorine compound gas are examined. The third embodiment will be specifically described with reference to an example in which CF ₄ gas is used as the fluorine compound gas.
In the microscopic (SEM) photograph of FIG. 5, in etching of a ruthenium film with a mixed gas of oxygen and chlorine, changes in the roughness of the etched surface and tapered surface of the ruthenium film when a small amount of the halogen compound gas CF ₄ gas is added. Indicates. FIG. 5A shows the case where CF ₄ gas is not added, and FIG. 5B shows the case where CF ₄ gas is added. The etching conditions at this time are as follows.
Total gas flow rate of oxygen and chlorine: 100 sccm
Chlorine gas concentration: 7.5%
Discharge pressure: 30 mTorr
RF power: 250 W
Magnetic field strength: 200 Gauss
Addition amount of added CF ₄ : 1 sccm
Compared with the case where CF ₄ is not added (FIG. 5A), the etching surface of the ruthenium film and the taper-shaped surface are roughened by adding a very small amount of CF ₄ of about 1% of the total gas flow rate. Has decreased (FIG. 5B). Further, the taper shape is also improved, and a fine pattern can be formed.
By increasing the amount of CF ₄ gas added, the roughness of the etched surface and the tapered surface is further reduced, but at the same time, the etching rate of the silicon oxide film as an etching mask is increased, and the etching selectivity (etching of the ruthenium film) is increased. (Rate / etching rate of silicon oxide film) is reduced, and excessive addition of CF ₄ is not appropriate, it is desirable to keep it to 10% or less of the total gas flow rate, and more preferably 2-3%.
[0016]
In the third embodiment, the case of CF ₄ gas has been described as an example. However, other fluorine compound gas, CF ₄ , CHF ₃ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ , NF ₃ , The same effect can be obtained by adding SF ₆ or fluorine gas F ₂ and a gas containing one or more of these in the above range.
[0017]
【The invention's effect】
As described above, in the method for etching a ruthenium film according to the present invention, etching is performed with plasma using a mixed gas containing chlorine and oxygen as a reactive gas. By increasing the flow rate, the replacement of the gas is accelerated, and the total flow rate of the mixed gas of oxygen and chlorine is adjusted so that the gas residence time in the etching chamber is 45 msec or less . By increasing the amount, the taper shape of the etching shape, which is a problem in the conventional etching method, the roughness of the taper surface, and the generation of ruthenium oxide that causes the roughness of the etching surface are reduced, and ruthenium oxide Re-adhesion can be reduced, so that etching taper surfaces and surface irregularities can be reduced, and etching Since the taper shape of the groove can be made close to vertical, favorable etching can be performed and a fine pattern can be formed.
[0018]
Further, in the method of etching a ruthenium film with a mixed gas plasma containing chlorine and oxygen, a dummy pattern for adjusting the area is provided so that the area to be etched is adjusted to 40% or less of the entire area of the sample surface to be etched. As a result, the amount of ruthenium oxide released into the gas plasma can be reduced and the amount of redeposition can be reduced. As in the above case, the ruthenium film can be satisfactorily etched and a fine pattern can be formed.
[0019]
Furthermore, in the method of etching a ruthenium film with a mixed gas plasma containing chlorine and oxygen using a silicon oxide film as an etching mask , at least one of fluorine gas and fluorine compound gas is mixed into the mixed gas with a total gas flow rate. By adding at a concentration of 1% or more and 10% or less, it is possible to change the component of the silicon oxide film, which has caused the problem in the conventional etching method, to a component having a high vapor pressure, and to reduce reattachment. The ruthenium film can be satisfactorily etched and a fine pattern can be formed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an etching apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing a sample for etching according to the present invention.
FIG. 3 is a graph showing the relationship between the flow rate of the mixed gas of oxygen and chlorine and the taper angle of the etching side surface of the ruthenium film according to the first embodiment of the present invention.
FIG. 4 is a graph showing a relationship between an area ratio to be etched with respect to a sample according to a second embodiment of the present invention and a taper angle of an etching side surface of a ruthenium film.
FIG. 5 is a microscope (SEM) photograph showing an etching shape of a ruthenium film according to a third embodiment of the present invention together with a conventional example.
FIG. 6 is a microscope (SEM) photograph showing an etching shape of a ruthenium film by a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Etching process chamber, 2 Reaction gas inlet, 3 Gas exhaust, 4 Cathode electrode, 5 Anode electrode, 6 Electromagnetic coil, 7 Etching sample, 8 Silicon substrate, 9, 11 Silicon oxide film, 10 Ruthenium film, 12 Photoresist film.

Claims (3)

In the method of etching a ruthenium film with a mixed gas plasma containing chlorine and oxygen, the supply amount of the mixed gas is increased, and the mixed gas flow rate is increased, thereby speeding up the replacement of the gas, and A ruthenium film etching method, wherein the total flow rate of the mixed gas is adjusted so that the gas residence time is 45 msec or less, and the amount of oxygen atoms as etching species is increased . In the method of etching a ruthenium film by a mixed gas plasma containing chlorine and oxygen, an area adjustment dummy pattern is provided so that the area to be etched is adjusted to be 40% or less of the entire surface of the sample to be etched. A ruthenium film etching method characterized by this. In the method of etching a ruthenium film with a mixed gas plasma containing chlorine and oxygen using a silicon oxide film as an etching mask, at least one of fluorine gas and fluorine compound gas is added to the mixed gas as 1% of the total gas flow rate. A ruthenium film etching method comprising adding at a concentration of 10% or less.

Images