JPH02292823A - Etching process - Google Patents

Abstract

PURPOSE:To enable the high selection ratio to be shown even if a resist film containing carbon is used as a mask by a method wherein an objective film is etched with the etching gas containing bromide by use of a mask of a resist film having a surface silicon oxide layer. CONSTITUTION:An objective film 3 is etched with an etching gas containing bromide by use of a mask of a resist film 4 having a surface silicon oxide layer 6. For example, the positive type resist film 4 comprising silicon containing resist material is formed on the polycrystalline silicon film 3 and then exposed and developed for patterning process. Next, when the resist film 4 is heated at the temperature of 300 deg.C in oxygen atmosphere for around 60 minutes, the carbon contained in the silicon containing resist material is combined with oxygen producing CO2 or CO to be removed from the surface of the resist film 4. On the other hand, the silicon contained in the resist film 4 is combined with oxygen to form the SiO2 layer 6 on the surface of the resist film 4. Lastly, the polycrystalline film 3 is etched by reactive ion-etching process using the etching gas containing hydrogen bromide.

Description

[Detailed Description of the Invention] [Summary] Regarding the etching method of etching films such as polycrystalline silicon, silicide, high melting point metal, silicon nitride, etc. using bromine-based gas, when using an organic resist as a mask, high For the purpose of obtaining a selective ratio, carbon is extracted from the surface layer of a patterned resist film containing silicon at least in the surface layer, and
A step of oxidizing silicon to form a silicon oxide film on its surface layer, and using the resist film with the silicon oxide layer formed on its surface as a mask, etching the film to be etched using a bromine-containing etching gas such as HBr. It consists of a process.

[Industrial application field]

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, high melting point metal, silicon nitride, or the like using a bromine-based gas.

As semiconductor devices become more highly integrated and operate at higher speeds, it becomes necessary to form patterns with high precision.

For example, when patterning a conductive material film to create a gate electrode for a transistor, the width of the gate electrode is precisely controlled by applying anisotropic etching with a high selectivity to the underlying layer. It is necessary to perform etching so that the characteristics do not deteriorate.

In particular, when etching a polycrystalline silicon film formed in a region with a step, polycrystalline silicon tends to remain in the step, and in order to completely remove it, it is necessary to take a much longer etching process than when etching on a flat surface. Since time-consuming overetching is required, etching with a high selectivity is required to protect the underlying layer. For example, 256KD RAM
In this case, the selectivity ratio may be 10 degrees, but it is 20 or more for a 4-gate DRAM, 60 or more for a 64-gate DRAM, and preferably 100 degrees.
The above selection ratio is required.

Furthermore, regarding the cross-sectional shape of the patterned film,
There is a need for an etching method in which there is no dimensional shift with respect to the mask pattern width and in which the cross-sectional shape is perpendicular, and an etching method in which the side walls are tapered and the taper angle is highly controllable.

[Prior Art] When patterning polycrystalline silicon films, nitride films, etc., RIE (React
ive Ton Etching) method, E C R (
Electron Cyclotron Resonan
Etching methods such as the ce) method are applied.

By the way, when patterning is performed using these etching methods, it is necessary to perform etching without undercutting even if over-etching is performed.
As shown in the figure, when etching the film 61 exposed from the mask 60, a carbon-containing substance is mixed into the etching gas, and a carbon-containing film 63 is attached to the side wall of the film 61 to prevent undercutting of the side wall. Method: (1) As shown in FIG. 7, the reaction probability of the side wall 72 of the film 70 exposed from the mask 71 is reduced by cooling the substrate, or the reaction product 72 is deposited on the side wall to form an undercut. How to prevent bromine (Brz) and hydrogen bromide (HB)
There is an etching method using a bromine-containing gas such as r). However, according to the first method, the carbon-containing polymer is It! The carbon deposits not only on the side walls of J61 but also on the inner walls of the etching chamber (not shown), which peels off and becomes a source of particles, lowering the yield, and carbon increases the etching rate of the underlying oxide film 62, reducing the selectivity. It has the disadvantage that it causes a decrease in

According to the second method, if sulfur hexafluoride, for example, is used as the fluorine-based gas, a high selectivity can be obtained, but in order to increase the anisotropy, the temperature of the membrane must be lowered to -100°C. Since it is necessary to cool the etching apparatus below, there is a drawback that the mechanism of the etching apparatus becomes complicated and expensive. Further, when using a chlorine-based gas such as 2, the wafer must be cooled to below 0°C, and the selectivity is not sufficient.

[Problems to be Solved by the Invention] On the other hand, according to the third method, vertical or tapered etching can be performed for 30 to 30 minutes without incorporating carbon into the etching gas and without cooling to a special low temperature. 20
Since a selectivity of about 0 is obtained, the underlying oxide film is not removed during over-etching.

However, when carbon is mixed in, the St-0 bonds in the underlying oxide film are replaced by C-O bonds and are cleaved, or C-
Due to the presence of , the electron distribution changes and the St10 bond becomes weaker, so that even with bromine gas, etching progresses and the selectivity decreases to about 10 to 30. Therefore, when over-etching is required, it becomes difficult to form a highly accurate pattern using an organic resist mask.

Of course, unless carbon is mixed in, Si-○ bonds will not be cleaved by bromine atoms alone, so the silicon oxide film will not be etched. Therefore, a high selectivity can be obtained by using a silicon oxide film or nitride film as a mask instead of a resist, but in this case, it is necessary to pattern the silicon oxide film or nitride film using a resist. In addition to complicating the etching process, there are also problems in that it takes time to form a silicon dioxide film or a nitride film using a vapor phase growth method.

The present invention has been made in view of these problems, and an object of the present invention is to provide an etching method that can obtain a high selectivity even when a resist containing carbon is used as a mask.

(Means for Solving the Problems) The above-mentioned problems include 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 removing carbon contained in the surface layer. A step of oxidizing silicon to form a silicon oxide film on the surface layer of the resist film, and using the resist film with the silicon oxide layer formed on the surface as a mask, etching the film to be etched using a bromine-containing etching gas. The problem is solved by an etching method characterized by comprising steps.

[For production]

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

As a method for containing silicon in a resist film, a resist film is formed using a silicon-containing resist material and patterned, or a resist film is formed using a resist material used in 1-II and this is patterned. Some later silylate the surface layer.

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

In this state, even if the film to be etched is etched, carbon atoms will not come out 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. I will let you do it. Therefore, when etching/etching a film to be etched/etched, it is possible to obtain the etching rate and selectivity derived from the etching gas containing bromine, and to increase the selectivity of the film to be etched to the oxide film to 3Q or higher. be able to.

(Example) (a) Practical example 1 FIG. 1 is a process diagram showing an example of the present invention in cross section, and the reference numeral l in the figure is a semiconductor substrate made of silicon, on which are A silicon oxide film (SiOz film) 2 with a film thickness of 1.000 mm formed by a thermal oxidation method, a vapor phase growth method, etc.
A polycrystalline silicon film 3 having a thickness of 3,000 wafers is formed by vapor phase growth or the like (FIG. 1(a)).
．． The details of the step of patterning the polycrystalline silicon film 3 will be explained below.

First, a positive resist ll1i! is made of a silicon-containing resist material containing about 5 to 75% silicon and oxygen.
4, polycrystalline by spin coating method? Recon membrane 3
After forming a resist film 4 on the top of the film to a thickness of 3,000 mm (Fig. 1 (b)), the area where no pattern is to be formed is irradiated with ultraviolet light, and then the resist film 4 is developed with a solvent and exposed to heat. A window 5 was formed in the light part (FIG. 1(C)). Here, the silicon-containing resist material used was one made of an alkali-soluble silicone resin having hydrogen groups obtained by acetylating polyphenylsilsesquioxane, and a diazonaphthoquinone compound.

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 combines with oxygen on the surface of the resist film 4, and carbon dioxide ( Co■) or carbon monoxide (CO
) while evaporating and being removed from the resist film 4,
Since the silicon in the resist 11!4 combines with oxygen to form silicon dioxide (Sing), the surface of the resist film 4 has a very low carbon content of Sin. Layer 6 was formed (Fig. 1(d)). Subsequently, the polycrystalline silicon film 3 was etched using an etching apparatus described below using an etching gas containing hydrogen bromide.

FIG. 2 is a configuration diagram showing a reactive ion etching (RIE) apparatus for etching the polycrystalline silicon film 3 into which the substrate 1 is inserted, and the reference numeral 10 in the figure is located inside the etching chamber 11. A pair of W. An electrostatic chuck l is attached to the upper surface of the lower electrode 10a to which a high frequency voltage is applied.
2 is attached, and the other electrode 10b facing the electrostatic chuck 12 is electrically grounded. Furthermore, the etching chamber 11 is provided with a gas supply port 13 and an exhaust port 14 to supply a pair of etching gases. It is configured to supply air between the electrodes 10 of the chamber 1 and to reduce the pressure inside the chamber 1.

In FIG. 2, reference numeral 15 indicates an electrode plate attached to the electrostatic chunk 12, 16 a DC power supply for applying voltage to the electrode plate 15, and 17 a high frequency power supply connected to the electrode 10a.

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

Although not shown, the inner wall of the etching chamber 11 and the surface of the upper electrode fIilob, which are exposed to plasma, were covered with a carbon-free material such as quartz glass. Furthermore, the etching rate may be determined in real time during etching using a laser interferometer (not shown).

The substrate 1 was fixed on the electrostatic chuck 2 of this device, and hydrogen bromide (HBr) gas was introduced into the chamber 1 at a flow rate of 2003 CCH.
1, while reducing the pressure inside the chamber 11 to 0. I.T.
At the same time, the pressure is reduced to 1.11 W/cJ and a power of 1.11 W/cJ is applied to the electrode 10a, and as shown in FIG.
Etching was performed for about 30 seconds to remove film 7.

The IIBr used here had a purity of 99.99%, and the carbon content was aoppmO in terms of volume ratio in terms of CO2.

After this, the flow rate of IBr gas was changed to 50SCCM, the high frequency power density was changed to 0.66W/cffl, and the window of the resist 1114 was changed to 50SCCM. Polycrystalline silicon film 3 in the area exposed from
was etched (Fig. 1(f)). At this time, since the Si02156 formed on the surface of the resist film 4 contained almost no carbon, almost no carbon was knocked out even when the SiO2 layer 6 was exposed to plasma.

As a result, the etching rate of SiOz does not increase, and SiO■It! This suppresses the decrease in the selectivity of the polycrystalline silicon film 3 to the polycrystalline silicon film 3 to
It was possible to prevent the iO2 film 2 from being removed.

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

Furthermore, the selection ratio of the polycrystalline silicon film 3 to the SiOz film 2 is determined by
Continue to over-etch the underlying Sing film 2 for 1 minute, determine the etching rate from the amount of decrease in the film thickness of the SiO2 film 2, and use the etching rate of the polycrystalline silicon film 3 determined by the laser interferometer as described above. (2) Calculated by dividing by the etching rate of film 2.

As a result, when the temperature of the substrate 1 is 90°C, the etching rate and selectivity of the above example are 300 nm/min and the selectivity is 300. When the cross section of No. 3 was observed using a scanning electron microscope, it was confirmed that the cross section was vertical.

Further, when the substrate temperature is 20°C, the cross section of the polycrystalline silicon film 3 has a taper angle θ=
The etching rate was 200 nm/min and the selection ratio was 40. Note that the reason for the tapered shape is that SiBrX, which is a reaction product, adheres to the side wall of the polycrystalline silicon film 3 during etching due to the low temperature, which hinders the progress of etching. This has been confirmed by analysis of kimonos.

Note that when the substrate temperature is 50 to 150°C, patterning with a vertical cross-sectional shape without dimensional shift is possible, and below 50'C, the tapered shape becomes larger as the taper angle θ increases as the temperature decreases.

? b) Example 2 As shown in FIG. 4(a), a positive novolac resist film 22 is formed as a flattening layer on a polycrystalline silicon film 21.
was formed to a thickness of 1.5 μm and baked.

Then, a negative siloxane resist film 23 as a silicon-containing resist is applied to a thickness of 3000 mm on top of this.
After exposing this to an electron beam, it was removed with a solvent and patterned (Fig. 4(b)). Next, using the siloxane resist film 23 as a mask, the novolac resist film 22 was etched by RIE using oxygen gas at an oxygen gas flow rate of 10Q SCCM and a pressure of 0.02 Torr. Carbon on the surface of the siloxane resist film 23 combines with oxygen to form carbon dioxide (Cow) or carbon monoxide (Co).
On the other hand, the silicon in the siloxane resist M23 combines with oxygen to form SiO■, so that Si? (2) A layer 24 was formed (FIG. 4(C)).

After this, using the siloxane resist film 23 and the novolak resist film 22 as masks, the polycrystalline silicon film 21 is patterned with +lBr 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 30°C.
0 nm/llin, selectivity 300, and etched polycrystalline silicon II! ! When the cross-section of No. 3 was observed using a scanning electron microscope, it was confirmed that the cross-sectional shape was vertical. Further, when the substrate temperature is 20°C, the cross section of the polycrystalline silicon film 3 has a Taber angle θ-
The etching rate was 20Or+m/m!n and the selection ratio was 40.

By the way, when etching the polycrystalline silicon film 21,
Although the sidewalls of the novolac resist film 22 are exposed, the ions in the HBr plasma collide with the substrate surface almost perpendicularly, so the amount of carbon ejected from the sidewalls of the novolac resist film 22 is extremely large. The etching ratio was not lowered to 30 or less.

Note that reference numeral 25 in FIG. 4 indicates a Sing film formed between the silicon substrate 20 and the polycrystalline silicon film.

? c) Example 3 In Example 1.2 described above, a silicon-containing resist material was used to form a SiO layer on the surface of the resist film, but a commonly used organic resist material was used. It is also possible to form a pattern on a resist film, then silylate the surface of this resist film to contain silicon, and oxidize the surface to form a SiO2 layer.

An example in this case will be described below.

First, as shown in FIG.
A polycrystalline silicon film 32 is formed on the ing film 31, and a positive type organic resist material is applied thereon to form the resist film 3.
3 was formed (Fig. 5 (a)), and was patterned by exposure and development. Figure 5(b)).

After this, the substrate 30 was placed in a heating furnace (not shown), and the inside of the heating furnace was set to 4 Torr while hexamethyldisilazane (HMDS) was supplied at a flow rate of 50 SCCH, and the substrate 30 was heated at a temperature of 130° C. for about 3 hours. When heated, the surface of the resist film 33 became silylated and incorporated 5 to 10% silicon. (Figure 5(c)). After this, oxygen gas was supplied at a flow rate of 100 SCCM, 0. When plasma processing was performed at I Torr and high frequency power density of 0.6 W/cti, as shown in FIG. Co■) or carbon monoxide (CO) was generated and removed, and oxygen was combined with the silicon on the surface to form the Sing layer 34. In this case, SiO■ on the silylated resist film 33
Since the formation speed of the layer 34 is faster than that on the polycrystalline silicon, the SiOl formed on the surface of the polycrystalline silicon M32
i! 35 is extremely thin, and this film was formed by using HBr with different etching conditions as in Example 1. simply removed.

When the polycrystalline silicon film 32 was subsequently etched with HBr, carbon was not released from the surface of the resist film 33, so the SiO2 film 31 underlying the polycrystalline silicon film 32 was not etched, and the SiO2 film was etched. 31
No decrease in the selectivity ratio was observed for (Fig. 5(e)
).

Etching rate, selection ratio is 30
0 min/win, and the selection ratio was about 30 to 300.

Further, at a substrate temperature of about 50 to 150° C., vertical etching with no dimensional shift was possible, and at below 50° C., a forward tapered shape with a larger taper angle θ was formed as the temperature decreased.

(d) Example 4 In this Example 3, HMDS was used as the silylation substance, but dichlorodimethylsilane could also be used as the silylation substance. At this time, the resist film 33 was exposed to a dichlorodimethylsilane atmosphere of 190 Torr and heated at a temperature of about 110°C for about 1 hour.
The surface became silylated, and when this resist film 33 was further exposed to the atmosphere and heated at a temperature of 150° C. for about 15 minutes, a SiO layer was formed on the surface. H below
Etching with Br was performed in the same manner as in Example 1.

The results show that when the temperature of the substrate 1 is 90°C, the etching rate is 300 nm/sin and the selectivity is 300. Furthermore, when the cross section of the etched polycrystalline silicon film 3 is observed with a scanning electron microscope, It is f! that the cross-sectional shape is vertical! It has been certified.

Further, when the substrate temperature is 20°C, the cross section of the polycrystalline silicon film 3 has a Taber angle of θ-7 as shown in FIG.
The etching rate was 200 rv/min and the selection ratio was 40.

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

At this time, approximately 1 % of PMMA is applied on the polycrystalline silicon film 32.
．． After coating the resist film to a thickness of approximately 0 μm and patterning it by electron beam exposure, the resist film was placed in a chloroalkylsilane atmosphere, and its surface was irradiated with DUV light of 250 nm or less using a mercury lamp. The surface was silylated and baked for 160° CIO to form a Sing layer on the surface. The rest of the etching with HBr is the same as in Example 1.

The results show that when the temperature of the substrate 1 is 90°C, the etching rate is 300 nm/min and the selectivity is 300, and 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.

Furthermore, when the substrate temperature is 20°C, the cross section of the polycrystalline silicon film 3 has a taper angle of θ-
The etching rate was 200 nm/min and the selection ratio was 40.

(f) Other Examples As a means of forming a resist film containing silicon in at least the surface layer on polycrystalline silicon and forming a Si02 layer on the surface, it is possible to Methods of heat treatment in an atmosphere and RI using oxygen
In addition to a method in which the surface of the resist film is plasma-treated using the E method, etc., there is a method in which the surface of the resist is damaged by the RIE method using a secondary active gas such as argon, and then the surface is oxidized by exposing the resist to an oxygen atmosphere. There is also.

[Comparative example]

The sample in Figure 1 (c) for comparison was replaced with the following (d) Sho
The etching process shown in Figures (e) and (f) was performed without performing the T-layer formation process. The etching conditions are the same as in Example 1. As a result, the etching shape and etching rate of polycrystalline silicon were exactly the same as 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 15 at a wafer temperature of 20°C. 1
0, which is smaller than that of Example 1.

〔Effect of the invention〕

As described above, according to the present invention, containing silicon,
In addition, 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, so that carbon atoms are removed from the resist film during subsequent etching with bromine gas. Since it does not come out from the surface of the resist film, it is possible to suppress an 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.
As a result, even with a simple resist mask process that does not use a silicon oxide film or nitride film as a mask, it is possible to obtain a high etching rate and selectivity derived from an etching gas containing bromine such as HBr, and to perform etching without damaging the underlying layer. .

In addition, during dry etching using hydrogen bromide, highly pure hydrogen bromide gas containing less than 40 ppm of carbon is used, and the inner walls of the etching chamber are made of carbon-free materials such as quartz glass and alumina. By covering the surface with the carbon polymer, vertical and forward Taber etching can be performed with a high selection ratio, and the generation of particles due to carbon polymer can be suppressed, making it possible to manufacture semiconductor devices cleanly and with a high yield.

Here, polycrystalline silicon was used as the material to be etched, but other silicides such as tungsten silicide, molybdenum silicide, titanium silicide,
When etching high melting point metals such as tungsten and molybdenum, high melting point metal nitride films such as tungsten nitride film and titanium nitride film, and single crystal silicon, the silicon-containing resist is oxidized in the same way, but the resist is oxidized. A high selectivity can be obtained by chemical treatment and oxidation.

In addition, dry etching using hydrogen bromide is
In addition to the E device, other types of dry etching devices such as a μ-wave plasma etching device, an ECR plasma etching device, a magnetron RrE device, etc. may be used. In addition, hydrogen bromide gas has a higher vapor pressure and is less corrosive than other bromine-based gases such as bromine, so there is no need to worry about corrosion or clogging of mass flow or gas piping, and it can be used with chlorine. It is about the same level of ease of handling. The permissible toxicity level is 3 ppm, 0.1 ppm for bromine and 1 ppm for chlorine.
It is safer compared to

[Brief explanation of the drawing]

FIGS. 1(a) to (g) are process diagrams showing an embodiment of the present invention in cross section; FIG. 2 is a schematic diagram showing an example of an etching apparatus used in the present invention; FIG. A cross-sectional view showing another example of a polycrystalline silicon film patterned according to the first embodiment of the invention, and FIGS. 4(a) to 4(d) are process diagrams showing a second embodiment of the invention in cross-section. , FIGS. 5(a) to (e) are process diagrams showing the third embodiment of the present invention in cross section, FIGS. 6(a) and (b) are process diagrams, and FIGS. 7(a) and ( b) This is a process diagram. Is the first conventional example shown in cross section?Is the second conventional example shown in cross section? Explanation of symbols) 1, 30...Substrate, 2, 31...SiO■ film, 3, 32...Polycrystalline silicon film, 4...Silicon-containing resist film, 33...Resist film, 5 ...Window, 6, 34...SiO2N, 7...Sift film, 20...Substrate, 21...Polycrystalline silicon film, 22...Novolak resist film, 23...Siloxane resist film, 24...SiO* layer, 25...SiO* film. FIG. 1 is a process diagram showing an embodiment of the present invention in cross section. (Part 1) A schematic diagram showing an example of an enoching device used in the present invention. FIG. 2 is a process diagram showing an embodiment of the present invention in WT plane. 1 Figure (Part 2) Figure 3 (a) (b) Process diagram showing the first conventional example in cross section Figure 16 (b) Process diagram showing the second conventional example in cross section Figure 7 Figure 4 (d ) Process diagram s5 diagram showing the example of Jli (b) in cross section

Claims (4)

[Claims] (1) An etching method comprising the steps of etching a film to be etched using a bromine-containing etching gas using a resist film having a silicon oxide layer as a surface layer as a mask. (2) A step of exposing and developing a silicon-containing resist film formed above the film to be etched to pattern it; extracting carbon from the surface layer of the patterned silicon-containing resist film and oxidizing the silicon in the surface layer; a step of forming a silicon layer, using the silicon-containing resist film with the silicon oxide layer on the surface as a mask;
2. The etching method according to claim 1, further comprising the step of etching the film to be etched using a bromine-containing etching gas. (3) A step of exposing and developing a resist film formed on the film to be etched to pattern it, a step of silylating the surface layer of the patterned resist film, and a step of removing carbon contained in the surface layer of the silylated layer. A step of extracting the silicon and oxidizing the silicon to form a silicon oxide layer; and a step of etching the film to be etched using a bromine-containing etching gas using the resist film with the silicon oxide layer formed on the surface as a mask. 2. The etching method according to claim 1, further comprising: (4) The etching method according to claim 1, wherein the film to be etched is exposed to plasma of a reactive gas containing hydrogen bromide gas.