JP2720404B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an etching method for etching a film of polycrystalline silicon, silicide, a high melting point metal, silicon nitride, or the like with a bromine-based gas. Forming a silicon oxide film on the surface layer by extracting carbon from the surface layer of the patterned resist film containing silicon at least on the surface layer, and oxidizing silicon to obtain a silicon oxide film for the purpose of obtaining the ratio; And etching the film to be etched using a bromine-containing etching gas such as HBr using the resist film having the layer formed on the surface as a mask.

[Industrial applications]

The present invention relates to an etching method, and more particularly, to an etching method for etching a film of polycrystalline silicon, single crystal silicon, silicide, a high melting point metal, silicon nitride, or the like with a bromine-based gas.

As the integration and speed of semiconductor devices increase, it becomes necessary to form patterns with high precision.

For example, in the case where a gate electrode of a transistor is formed by patterning a conductive material film, the width of the gate electrode is precisely controlled by performing anisotropic etching having a high selectivity with respect to a base. It is necessary to perform etching so that characteristics are not deteriorated.

In particular, when etching a polycrystalline silicon film formed in a stepped region, the polycrystalline silicon tends to remain in the stepped portion, and to completely remove the polycrystalline silicon, it is much longer than in a plane. Since over-etching is required for a long time, etching with a high selectivity is required to protect the base. For example, the selectivity may be 10 degrees for 256K DRAM, but 20 or more for 4M DRAM and 60 for 64M DRAM.
As described above, desirably, a selection ratio of 100 or more is required.

Further, also regarding the cross-sectional shape of the patterned film, there is no dimensional shift with respect to the mask pattern width, and the etching method in which the cross-sectional shape is vertical, and the side wall is forward tapered, and the taper angle is highly controllable. Etching is required.

[Conventional technology]

When patterning polycrystalline silicon film, nitride film, etc., RIE (Reactive Io) with high anisotropy and high selectivity
n Etching) method, ECR (Electron Cyclotron Resonance)
The etching method such as the etching method is applied.

By the way, when patterning is performed by these etching methods, it is necessary to perform etching without undercut even if overetching is performed.
As shown in the figure, when etching the film 61 exposed from the mask 60, a carbon-containing substance is mixed into an etching gas, and a film 63 containing carbon is attached to the side wall of the film 61 to prevent undercut of the side wall. The method, as shown in FIG.
The film 70 exposed from the mask 71 by cooling the substrate
Or lowering the reaction probability of the side wall 72, or a method of preventing undercutting depositing a reaction product 72 in its side wall, the bromine-containing compounds such as bromine (Br ₂₎ or hydrogen bromide (HBr) There is a method of etching using a gas.

However, according to the first method, the polymer containing carbon is deposited not only on the side wall of the film 61 but also on the inner wall of an etching chamber (not shown), which is separated and becomes a source of particles to lower the yield. There is a disadvantage that carbon causes an increase in the etching rate of the underlying oxide film 62 and a decrease in the selectivity.

According to the second method, when, for example, sulfur hexafluoride is used as the fluorine-based gas, a high selectivity can be obtained. However, in order to increase the anisotropy, the temperature of the film is set to −100 ° C.
Since it is necessary to cool below, there is a disadvantage that the mechanism of the etching apparatus is complicated and expensive. Further, with a chlorine-based gas such as Cl ₂ , the wafer must be cooled to 0 ° C. or less, and the selectivity is not sufficient.

[Problems to be solved by the invention]

On the other hand, according to the third method, the carbon is not contained in the etching gas, and the carbon is not cooled to a special low temperature.
Since a degree of selectivity can be obtained, the underlying oxide film is not removed during overetching.

However, when carbon is mixed in, the Si—O bond of the underlying oxide film is replaced by a C—O bond to cause cleavage or
The electron distribution changes due to the presence of Si and the Si—O bond is weakened, so that etching proceeds even with a bromine-based gas, and the selectivity decreases to about 10 to 30. Therefore, when over-etching is required, there is a disadvantage that it is difficult to form a highly accurate pattern using an organic resist mask.

Of course, if carbon is not mixed in, the silicon oxide film is not etched because the Si—O bond is not cleaved only by bromine atoms. Therefore, if a silicon oxide film or a nitride film is used as a mask instead of a resist, a high selectivity can be obtained, but in this case, it is necessary to pattern the silicon oxide film or the nitride film using the resist, There are problems that the etching process becomes complicated and that it takes time to form a silicon dioxide film or a nitride film by a vapor phase growth method.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an etching method capable of obtaining a high selectivity even when a carbon-containing resist is used as a mask.

[Means for solving the problem]

The above-described problem is a step of forming a resist film that is patterned and contains silicon at least in the surface layer, extracting carbon from the surface layer of the resist film, and oxidizing silicon contained in the surface layer to form a surface layer of the resist film. Forming a silicon oxide film on the substrate, and etching the film to be etched using a bromine-containing etching gas using the resist film having the silicon oxide layer formed on the surface as a mask. Solved by the method.

[Action]

According to the present invention, a patterned resist film containing silicon is used as a mask.

As a method of containing silicon in the resist film, a resist film is formed by a silicon-containing resist material and is patterned, or a resist film is formed by a commonly used resist material, and after patterning the resist film, Some can silylate the surface layer.

Then, before etching the film to be etched using the resist film as a mask, the carbon contained in the resist film surface layer is extracted and the resist film surface is oxidized,
The silicon oxide film 6 is formed on the surface layer.

In this state, even if the film to be etched is etched, no carbon atoms are emitted from the surface of the resist film, so the etching rate of the silicon oxide layer on the surface of the resist film and the silicon oxide layer underlying the film to be etched is reduced. Will be.

Therefore, when etching the film to be etched, an etching rate and a selectivity derived from the etching gas containing bromine can be obtained, and the selectivity of the film to be etched to the oxide film can be made 30 or more.

〔Example〕

(A) Embodiment 1 FIG. 1 is a process drawing showing a cross section of an embodiment of the present invention, wherein reference numeral 1 denotes a semiconductor substrate made of silicon,
On top of this, a 1,000 mm thick silicon oxide film (SiO ₂ film) 2 formed by a thermal oxidation method or a vapor phase growth method, and a 3,000 mm thick polycrystalline silicon film formed by a vapor phase growth method or the like. The films 3 are formed in order (FIG. 1A).

Hereinafter, the step of patterning the polycrystalline silicon film 3 will be described in detail.

First, a positive resist film 4 made of a silicon-containing resist material containing about 5 to 75% of silicon and oxygen is deposited on the polycrystalline silicon film 3 by spin coating.
After coating and forming to a thickness of 000 mm (FIG. 1 (b)), an area where no pattern is to be formed is irradiated with ultraviolet light.
The resist film 4 was developed with a solvent to form a window 5 in the photosensitive portion (FIG. 1 (c)). Here, as the silicon-containing resist material, a material comprising polyphenylsilsesquioxane, an alkali-soluble silicon resin having an acetylated hydrogen group, and a diazonaphthoquinone compound was used.

Next, when the resist film 4 is heated at a temperature of 300 ° C. for about 60 minutes in an oxygen atmosphere, carbon contained in the silicon-containing resist material is combined with oxygen on the surface of the resist film 4 to form carbon dioxide (CO 2). ₂ ) or carbon monoxide (CO), which is removed from the resist film 4 and evaporated, while silicon in the resist film 4 is combined with oxygen to form silicon dioxide (Si).
O ₂ ), an SiO ₂ layer 6 with extremely low carbon content was formed on the surface of the resist film 4 (FIG. 1 (d)).

Subsequently, the polycrystalline silicon film 3 was etched by using an etching apparatus described below using an etching gas containing hydrogen bromide.

FIG. 2 is a structural view showing a reactive ion etching (RIE) apparatus for etching the polycrystalline silicon film 3 with the substrate 1 inserted therein. In the figure, reference numeral 10 is provided in an etching chamber 11. An electrostatic chuck 12 is attached to the upper surface of a lower electrode 10a for applying a high frequency voltage, and the other electrode 10b facing the electrostatic chuck 12 is a pair of electrodes.
Are electrically grounded, and the etching chamber 11 is provided with a gas supply port 13 and an exhaust port 14, so that an etching gas is supplied between the pair of electrodes 10 and the chamber 11
It is configured to reduce the pressure inside.

2, reference numeral 15 denotes an electrode plate attached to the electrostatic chuck 12, 16 denotes a DC power supply for applying a voltage to the electrode plate 15,
Reference numeral 17 denotes a high-frequency power supply connected to the electrode 10a.

Although not shown, the lower electrode 10a is water-cooled, and the wafer temperature during etching can be controlled by changing the cooling water temperature. The wafer temperature during the etching was measured by a fluorescent optical fiber thermometer (not shown).

Although not shown, the inner wall of the etching chamber 11 exposed to plasma and the surface of the upper electrode 10b were covered with a carbon-free material such as quartz glass. Further, an etching rate may be obtained in real time during etching by a laser interferometer (not shown).

The substrate 1 is fixed on the electrostatic chuck 2 of this apparatus, and while supplying hydrogen bromide (HBr) gas into the chamber 11 at a flow rate of 200 SCCM, the pressure in the chamber 11 is reduced to 0.1 Torr and 1.11 W Power was applied to the electrode 10a at a size of / cm ² , and etching was performed for about 30 seconds to remove the thin SiO ₂ film 7 formed on the surface of the polycrystalline silicon film 3 as shown in FIG. . The HBr used here had a purity of 99.99% and a carbon content of 30 ppm in terms of CO ₂ conversion by volume.

Thereafter, the flow rate of the HBr gas was changed to 50 SCCM, the high frequency power density was changed to 0.66 W / cm ^2, and the polycrystalline silicon film 3 in the region exposed from the window 5 of the resist film 4 was etched (first).
Figure (f). At this time, the resist was formed on the surface of the resist film 4.
Since the SiO ₂ layer 6 hardly contains carbon, SiO ₂
When the layer 6 was exposed to the plasma, little carbon was knocked out.

As a result, the etching rate of SiO ₂ does not increase,
A decrease in the selectivity of the polycrystalline silicon film 3 to the SiO ₂ film 2 was suppressed, and the removal of the SiO ₂ film 2 during over-etching was prevented.

Note that the etching rate of the patterned polycrystalline silicon film 3 was determined by a laser interferometer.

The selection ratio of the polysilicon film 3 to the SiO ₂ film 2, after completing the etching of the polycrystalline silicon film 3, an SiO ₂ film 2 thereunder for 1 minute over-etching continues, the SiO ₂ film 2 The etching rate was determined from the amount of decrease in the film thickness, and the etching rate of the polycrystalline silicon film 3 determined by the laser interferometer was divided by the etching rate of the SiO ₂ film 2.

As a result, when the temperature of the substrate 1 is 90 ° C., the etching rate and the selectivity in the above embodiment are 300 nm / min and the selectivity is 300. Observation of the cross section with a scanning electron microscope confirmed that the cross section was vertical.

Further, when the substrate temperature is 20 ° C., as shown in FIG. 3, the cross section of the polycrystalline silicon film 3 has a taper angle θ = 70.
°, the etching rate in this case was 200 nm / min, and the selectivity was 40. Here, the reason for the tapered shape is that a reaction product is formed on the side wall portion of the polycrystalline silicon film 3 during etching due to the low temperature.
It has been confirmed by analysis of deposits on the side wall that SiBr _x adheres to prevent the progress of etching.

In addition, when the substrate temperature is 50 to 150 ° C., patterning of a vertical cross-sectional shape without a dimensional shift is possible,
If the temperature is lower than 50 ° C., the taper angle θ becomes larger as the temperature decreases.

(B) Embodiment 2 As shown in FIG. 4 (a), a positive type novolak-based resist film 22 is formed on the polycrystalline silicon film 21 as a flattening layer.
It was formed to a thickness of 1.5 μm and baked.

Then, a negative type siloxane resist film 23 as a silicon-containing resist was applied thereon to a thickness of 3000.degree., Exposed to an electron beam, then removed by a solvent and patterned (FIG. 4 (b)).

Next, the siloxane resist film 23 was used as a mask, and the novolak-based resist film 22 was etched by an RIE method using oxygen gas at an oxygen gas flow rate of 100 SCCM and a pressure of 0.02 Torr. While the carbon on the surface of the film 23 is combined with oxygen and removed as carbon dioxide (CO ₂ ) or carbon monoxide (CO), the silicon in the siloxane resist film 23 is combined with oxygen to form SiO _2. Therefore, an SiO ₂ layer 24 was formed on the surface (FIG. 4 (c)).

Thereafter, using the siloxane resist film 23 and the novolak resist film 22 as a mask, the polycrystalline silicon film 21 is patterned with HBr in the same manner as in the first embodiment (FIG. 4 (d)). Similarly, when the temperature of the substrate 1 is 90 ° C., the etching rate is 300 nm / min, the selectivity is 300, and when the cross section of the etched polycrystalline silicon film 3 is observed with a scanning electron microscope, the cross section is The shape was confirmed to be vertical.

Further, when the substrate temperature is 20 ° C., as shown in FIG. 3, the cross section of the polycrystalline silicon film 3 has a taper angle θ = 70.
°, the etching rate in this case was 200 nm / min, and the selectivity was 40.

By the way, when etching the polycrystalline silicon film 21,
Although the side wall of the novolak-based resist film 22 is exposed,
Since the ions in the HBr plasma collide almost perpendicularly to the substrate surface, the amount of carbon struck from the side walls of the novolak resist film 22 is extremely small, and the etching ratio is reduced.
It did not drop below 30.

Reference numeral 25 in FIG. 4 denotes an SiO ₂ film formed between the silicon substrate 20 and the polycrystalline silicon film.

(C) Embodiment 3 In Embodiments 1 and 2 described above, the SiO ₂ layer was formed on the surface of the resist film by using a silicon-containing resist material, but a commonly used organic resist material was used. Then, a resist film is patterned to form a resist film. Thereafter, the surface of the resist film can be silylated to contain silicon, and the surface can be oxidized to form an SiO ₂ layer.

 An embodiment in that case will be described below.

First, as shown in FIG. 5, SiO of the root substrate 30 surface ₂
A polycrystalline silicon film 32 is formed on the film 31, and a positive type organic resist material is applied thereon to form a resist film 33 (FIG. 5 (a)), which is exposed and developed. (FIG. 5 (b)).

Thereafter, the substrate 30 was placed in a heating furnace (not shown), and the inside of the heating furnace was heated to 4 Torr while supplying hexamethyldisilazane (HMDS) at a flow rate of 50 SCCM, and the substrate 30 was heated at a temperature of 130 ° C. for about 3 hours. The surface of the resist film 33 was silylated to take in 5-10% of silicon. (FIG. 5 (c)).

Thereafter, oxygen gas was subjected to plasma processing at a flow rate of 100 SCCM, 0.1 Torr, and high-frequency power density of 0.6 W / cm ^{2. As} shown in FIG. 5 (d), the surface of the silylated resist film 33 was subjected to oxygen plasma. Carbon is combined with oxygen to generate and remove carbon dioxide (CO ₂ ) or carbon monoxide (CO), and oxygen is combined with silicon on the surface to form SiO ₂
Layer 34 was formed.

In this case, the SiO ₂ layer 34 on the silylated resist film 33
Since the formation speed is higher than that on the polycrystalline silicon, the SiO ₂ film 35 formed on the surface of the polycrystalline silicon film 32 is extremely thin, and this film is formed by HBr with different etching conditions as in the first embodiment. Easily removed.

Further continuing, it was etched polycrystalline silicon film 32 by HBr, because never carbon is released from the surface of the resist film 33, the underlying polycrystalline silicon film 32 SiO ₂
The film 31 was not etched, and no decrease in the selectivity with respect to the SiO ₂ film 31 was observed (FIG. 5E).

Etching rate, selectivity, etching rate is 30
0 min / min, the selectivity was about 30 to 300. At a substrate temperature of about 50 to 150 ° C., a vertical etching without dimensional shift could be performed. At a temperature of 50 ° C. or lower, a forward tapered shape having a larger taper angle θ as the temperature decreased was formed.

(D) Example 4 In Example 3, HMDS was used as the silylating substance, but dichlorodimethylsilane could be used as the silylating substance. At this time, the resist film 33 is exposed in a 190 Torr dichlorodimethylsilane atmosphere,
When the resist film 33 was heated at a temperature of about 1 hour for about 1 hour, its surface was silylated.
After heating at a temperature of about 15 minutes for about 15 minutes, a SiO ₂ layer was formed on the surface. The following HBr etching was performed in Example 1.
The same processing as described above was performed.

As a result, when the temperature of the substrate 1 is 90 ° C., the etching rate is 300 nm / min, the selectivity is 300. When the cross section of the etched polycrystalline silicon film 3 is observed with a scanning electron microscope, It was confirmed that the cross-sectional shape was vertical.

Further, when the substrate temperature is 20 ° C., as shown in FIG. 3, the cross section of the polycrystalline silicon film 3 has a taper angle θ = 70.
°, the etching rate in this case was 200 nm / min, and the selectivity was 40.

(E) Example 5 In the above Examples 1 to 4, the resist film 33 was formed of an organic photoresist, but PMMA (polymethyl methacrylate) could also be used.

At this time, PMMA is applied on the polycrystalline silicon film 32 by about 1.0 μm.
m, and after patterning this by electron beam exposure, place this resist film in a chloroalkylsilane atmosphere and irradiate the surface with DUV light of 250 nm or less using a mercury lamp. The surface was silylated and baked at 160 ° C. for 10 minutes to form a SiO ₂ layer on the surface. The subsequent etching with HBr is the same as in the first embodiment.

As a result, when the temperature of the substrate 1 is 90 ° C., the etching rate is 300 nm / min, the selectivity is 300. When the cross section of the etched polycrystalline silicon film 3 is observed with a scanning electron microscope, It was confirmed that the cross-sectional shape was vertical.

Further, when the substrate temperature is 20 ° C., as shown in FIG. 3, the cross section of the polycrystalline silicon film 3 has a taper angle θ = 70.
The etching rate in this case was 200 nm / min, and the selectivity was 40.

(F) Other Examples As a means for forming a resist film containing silicon on at least a surface layer on polycrystalline silicon and forming an SiO ₂ layer on the surface thereof, as shown in the above-mentioned embodiment, In addition to a method of performing heat treatment in an oxygen atmosphere, a method of performing plasma treatment on the resist film surface by an RIE method using oxygen, or the like, a method in which the resist surface is damaged by an RIE method using an inert gas such as argon, There is also a method in which the surface is oxidized by exposing the resist to an atmosphere.

(Comparative example)

The sample of FIG. 1 (c) for comparison was replaced with the following (d) SiO ₂
The etching process shown in FIGS. 3E and 3F was performed without performing the layer forming process. The etching conditions are the same as in the first embodiment. As a result, the etching shape and the etching rate of polycrystalline silicon were exactly the same as those in Example 1, but the etching rate of the silicon oxide film was large, and the selectivity was 15 at a wafer temperature of 90 ° C. and 10 at a wafer temperature of 20 ° C. It was smaller than in Example 1.

〔The invention's effect〕

As described above, according to the present invention, while containing silicon, carbon is extracted from the surface layer of the patterned resist film, and the surface of the resist film is oxidized to form a silicon oxide film on the surface layer. Since carbon atoms do not escape from the surface of the resist film during subsequent etching with a bromine-based gas, the increase in the etching rate of the silicon oxide layer on the surface of the resist film and the silicon oxide layer underlying the film to be etched is suppressed. can do. As a result, even with a simple resist mask process that does not use a silicon oxide film or a nitride film as a mask, an etching rate derived from an etching gas containing bromine such as HBr and a high selectivity can be obtained, and etching without damage to the base can be performed. .

In addition, during dry etching using hydrogen bromide, high-purity hydrogen bromide gas containing only 40 ppm or less of carbon is used, and the inner wall of the etching chamber is made of a material that does not contain carbon, such as quartz glass or alumina. By covering, vertical and forward taper etching can be performed with a high selectivity, and the generation of particles due to the carbon polymer can be suppressed, so that a semiconductor device can be manufactured with a clean and high yield.

Here, polycrystalline silicon was used as a material to be etched. When etching a high melting point metal nitride film such as a nitride film, single crystal silicon, or the like, the silicon-containing resist is similarly oxidized, but a high selectivity can be obtained by silylating and oxidizing the resist.

In addition, dry etching using hydrogen bromide
The same applies to other types of dry etching devices such as a microwave plasma etching device, an ECR plasma etching device, and a magnetron RIE device in addition to the E device. Hydrogen bromide gas has a higher vapor pressure and less corrosiveness than other bromine-based gases such as bromine, so there is no need to worry about corrosive or clogging of mass flow and gas piping.
It is as easy to handle as chlorine. Toxicity is 3ppm
It is safer than 0.1 ppm of bromine and 1 ppm of chlorine.

[Brief description of the drawings]

1 (a) to 1 (g) are process drawings showing a cross section of an embodiment of the present invention, FIG. 2 is a schematic diagram showing an example of an etching apparatus used in the present invention, and FIG. FIG. 4 is a cross-sectional view showing another example of the polycrystalline silicon film patterned according to the first embodiment of the present invention. FIGS. 4 (a) to 4 (d) are process diagrams showing a cross section of the second embodiment of the present invention. FIGS. 5 (a) to 5 (e) are process diagrams showing a third embodiment of the present invention in cross section, and FIGS. 6 (a) and 6 (b) are processes showing a first conventional example in cross section. FIGS. 7 (a) and 7 (b) are process drawings showing a second conventional example in cross section. (Explanation of reference numerals) 1, 30 ... substrate, ₂ , 31 ... SiO ₂ film, 3, 32 ... polycrystalline silicon film, 4 ... silicon-containing resist film, 33 ... resist film, 5 ... window, 6, 34: SiO ₂ layer, 7: SiO
₂ film, 20 substrate, 21 polycrystalline silicon film, 22 novolak resist film, 23 siloxane resist film,
24: SiO ₂ layer, 25: SiO ₂ film.

Claims (4)

(57) [Claims] An etching method using a bromine-containing etching gas with a resist film having a silicon oxide layer as a surface layer as a mask. 2. A step of exposing, developing and patterning a silicon-containing resist film formed above a film to be etched, extracting carbon in a surface layer of the patterned silicon-containing resist film, and oxidizing silicon in the surface layer. Forming a silicon oxide layer by etching, and using the silicon-containing resist film provided with the silicon oxide layer as a mask and etching the film to be etched using a bromine-containing etching gas. 2. The etching method according to claim 1, wherein: 3. A step of exposing, developing and patterning a resist film formed on the film to be etched, a step of silylating a surface layer of the patterned resist film, and a step of silylating the surface layer of the resist film. A step of forming a silicon oxide layer by extracting carbon and oxidizing silicon; and a step of etching the film to be etched using a bromine-containing etching gas using the resist film having the silicon oxide layer as a surface layer as a mask. 2. The etching method according to claim 1, comprising: 4. The etching method according to claim 1, wherein the film to be etched is etched by exposing the film to be exposed to a plasma of a reaction gas containing hydrogen bromide gas.