JP2722768B2 - Etching method of multilayer resist layer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for etching a multilayer resist layer performed in the field of manufacturing semiconductor devices and the like, and more particularly to achieving an anisotropic shape and after-corrosion caused by a base material. The present invention relates to a method that can prevent the occurrence of a problem.

[Summary of the Invention]

The first invention of the present invention is a so-called three-layer resist using a lower resist layer, an intermediate film, and an upper resist layer.
In the process, at least O ₂ using the upper resist layer and the intermediate film patterned in a predetermined shape as a mask.
When etching the lower resist layer with an etching gas containing a gas and a Cl ₂ gas, the substrate was heated to −80 to 0 ° C.
Thus, the anisotropic shape can be achieved even when the amount of Cl ₂ gas added is relatively small.

According to a second aspect of the present invention, when etching a multilayer resist layer formed on a base material layer made of an Al-based material, etching of the lower resist layer includes etching containing at least O ₂ gas and Cl ₂ gas.・ After performing while forming the side wall protective film with the gas, by performing plasma treatment with the F-based gas, the residual Cl in the side wall protective film is replaced with F to prevent the occurrence of after-corrosion. is there.

Further, the third invention of the present invention provides a method for etching a lower resist layer according to the second invention, wherein the substrate is cooled to −80 to 0 ° C., so that the amount of Cl ₂ gas added is relatively small. Another object of the present invention is to make it possible to achieve an anisotropic shape and to easily remove residual Cl to prevent the occurrence of after-corrosion.

[Conventional technology]

As the design rules of semiconductor devices have become extremely finer at the submicron level and even at the quarter micron level, the demands for various processing techniques have become even more severe.

Photolithography technology is no exception, and the use of a multilayer resist method is becoming essential as the exposure wavelength becomes shorter in the deep ultraviolet region, which is the wavelength region of excimer laser light, in order to obtain high resolution. The multilayer resist method is a method using a combination of at least two types of resist layers, a lower resist layer thick enough to absorb a surface step of a substrate and a thin upper resist layer thin enough to achieve high resolution. A well-known method consists of a thick lower resist layer on a base material layer, an extremely thin intermediate film made of SOG (spin-on-glass), and a thin upper resist layer patterned by photolithography. There is a so-called three-layer resist process that uses multiple resist layers. In this process, first, the upper resist layer is patterned into a predetermined shape, and using this as a mask, the intermediate film and the underlying resist layer thereunder are developed. This development is generally performed by dry etching using O ₂ gas or the like.

Incidentally, it is actually extremely difficult to perform anisotropic processing of a multilayer resist layer at high speed and with good controllability. This is because if high-speed performance is prioritized, the reaction mainly depends on the radical mode, so the anisotropy decreases.If priority is given to anisotropy, the reaction mainly depends on the ion mode. This is because there is an essential problem that speeding up becomes difficult because of the necessity.

For this reason, various studies have conventionally been made to achieve both anisotropy and high speed.

A so-called low-temperature etching method in which etching is performed while cooling the wafer temperature at the time of etching to 0 ° C. or lower is also one of the techniques to be noted. In this technique, the radical reaction on the side wall is frozen by lowering the wafer temperature at the time of etching, and anisotropic processing is performed with low ion energy. For example, 35th Spring Meeting of the Japan Society of Applied Physics Spring Meeting, page 496, lecture number 28a-G-4
(1988), the wafer temperature was set to -100 ° C with liquid nitrogen.
Oxygen plasma of the multilayer resist layer
There has been reported an example in which an anisotropic shape is achieved by performing etching without significantly lowering the etching rate.

On the other hand, an attempt has been made to perform anisotropic processing using a sidewall protective film. For example, the present inventor has previously described Japanese Patent Application No. 1-64.
No. 086, the etching of the multilayer resist layer
By adding a Cl-based gas to an O ₂ gas generally used as a gas, anisotropic processing is performed while depositing CCl _x , which is a reaction product of the Cl-based gas and a lower resist layer, as a sidewall protective film. Propose technology to do.

[Problems to be solved by the invention]

As described above, various techniques for etching a multilayer resist layer at high speed and with high anisotropy have been proposed, but there are still many problems to be solved.

For example, in the above-mentioned technology for lowering the wafer temperature to about -100 ° C with liquid nitrogen, it is necessary to maintain the wafer temperature at the time of etching at -100 ° C. However, there are problems such as an increase in the size of the apparatus and an increase in cost. further,
Since the vapor pressure of the reaction product is extremely low in such a low temperature range, there is a concern that the reaction product may be thickly deposited on the pattern side wall to increase the pattern width. Therefore, even if low-temperature etching is performed, it is a practically desirable process to raise the operating temperature range to a higher temperature.

On the other hand, in the method using a mixed gas system of O ₂ gas and Cl-based gas previously proposed by the present inventor, in order to perform anisotropic processing at room temperature, the amount of added Cl-based gas is about 60% of the total. ~ 80%
It is necessary to set relatively high. However, the use of a large amount of Cl-based gas may cause problems such as generation of particle contamination due to an increase in deposits, reduction in reproducibility, and reduction in etching rate, and further improvement is desired. .

Further, when an etching mask for the Al-based material layer is to be formed by a multilayer resist layer, if the Cl-based gas is contained in an etching gas for etching the multilayer resist layer as described above, After-corrosion may occur when the Al-based material layer is exposed. In the after-corrosion in this case, residual Cl in the side wall protective film combines with Al to generate a chlorine compound such as AlCl _{3 having} strong deliquescent, which absorbs moisture to form electrolytic droplets, which is a hydrogen-generating type. This may be due to the formation of a local battery.

Therefore, the present invention provides an O ₂ gas and Cl
Even if the lower resist layer is etched with an etching gas containing a base gas, a method that does not cause the occurrence of particle contamination, a decrease in reproducibility, a decrease in the etching rate, the occurrence of after-corrosion, and an increase in equipment size The purpose is to provide.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to achieve the above object, and found that O ₂
Using an etching gas obtained by adding Cl ₂ gas to the gas,
Also, it has been found that if low-temperature etching is performed, good anisotropy is achieved even with a relatively small amount of Cl ₂ gas added, the etching rate is not reduced, and etching can be performed in a higher temperature range than before. .

Further, when the etching of the multilayer resist layer on the Al-based material layer is performed using the above-described etching gas, after-etching is effectively performed by performing a plasma treatment using an F-based gas after the etching. Found to be prevented.

Furthermore, if low-temperature etching of the multilayer resist layer on the Al-based material layer is performed using the above-described etching gas,
The formation amount of the side wall protective film can be reduced,
It has been found that the effect of preventing corrosion can be further enhanced.

The present invention has been completed based on the above findings.

That is, the method for etching a multilayer resist layer according to the first invention of the present invention comprises the steps of patterning a multilayer resist layer formed by laminating a lower resist layer, an intermediate layer, and an upper resist layer on a base material layer in this order. Performing a step of patterning the upper resist layer into a desired shape to form an upper resist pattern; and
Forming an intermediate film pattern by patterning the intermediate layer using the pattern as a mask;
The upper layer resist by etching gas containing at least O ₂ gas and 10-20% of Cl ₂ gas with cold state,
Etching the lower resist layer using the pattern and the intermediate film pattern as a mask.

The method for etching a multilayer resist layer according to the second invention of the present invention is a multilayer resist formed by laminating a lower resist layer, an intermediate film, and an upper resist layer in this order on a base material layer mainly composed of Al. In the method of etching a multilayer resist layer for patterning a layer, a step of patterning the upper resist layer into a desired shape to form an upper resist pattern, and patterning the intermediate layer using the upper resist pattern as a mask A step of forming an intermediate film pattern;
At least in a state cooled to ° C. O ₂ gas and 10-20% of Cl ₂
A step of etching the lower resist layer using the upper resist pattern and the intermediate film pattern as a mask with an etching gas containing a gas, and a step of performing a plasma treatment with an F-based gas. is there.

[Action]

In the present invention, the lower resist layer of the layers constituting the multilayer resist layer is etched using an etching gas containing at least an O ₂ gas and a Cl ₂ gas. According to such a mixed gas system, a process in which a polymer having a composition of CCl _x is deposited on the pattern side wall by reacting the Cl ₂ gas with the organic resist material, and a process in which the O ₂ gas etches the polymer is removed. Happens in conflict. Therefore, even under relatively high gas pressure and low DC bias conditions where a reaction in the radical mode normally proceeds to cause undercut under the mask, anisotropic processing using the sidewall protective film can be performed. It is possible, and the etching rate can be much higher than that of the reaction in the normal ion mode.

The above is the etching mechanism common to the two inventions of the present invention. In the first invention, the substrate is cooled to −80 to 0 ° C. during etching. Thereby, first, the etching reaction of the resist due to oxygen radicals is appropriately suppressed, which is advantageous in achieving an anisotropic shape. In addition, at low temperatures, the vapor pressure of the reaction product CCl _x is much lower than normal temperature, and the side wall protective film is easily formed.Therefore, the content of Cl ₂ gas is greatly reduced as compared with the conventional mixed gas system. The same effect can be obtained, and the occurrence of particle contamination and a decrease in etching rate can be prevented.
However, in the case of the present invention, the above-described cooling down to −100 ° C. is unnecessary, and a general-purpose organic solvent or the like is used as a refrigerant for −80 to −80 ° C.
Cooling at 0 ° C. is sufficient. Therefore, excessive deposition of the reaction product is suppressed, and there is no danger of an increase in the pattern width, and a relatively simple cooling device such as a chiller can be used, which is advantageous in terms of equipment and cost. Become.

In the second invention, when the above-described etching gas having such excellent characteristics is applied to the etching of a multilayer resist layer formed on an Al-based base material layer, a plasma treatment with an F-based gas is performed after the etching is completed. . That is,
In order to prevent after-corrosion, a technique that is generally performed as a post-processing of etching of Al wiring layer etc.
In other words, the present invention is also applied to post-processing of etching of the multilayer resist layer. As a result, only the merit of adding Cl ₂ gas to the etching gas can be obtained.

Further, in the second invention, the above-mentioned etching is
It is carried out while cooling to 80 to 0 ° C. In this case, the content of Cl ₂ gas in the etching gas can be greatly reduced as in the case of the first invention, so that the deposition of the side wall protective film is reduced and the influence of residual Cl is reduced accordingly. Therefore, the plasma treatment with the F-based gas becomes easy, and
The effect of preventing after-corrosion on the base material layer is further enhanced.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 In this embodiment, an application example of the first invention of the present invention will be described with reference to FIGS. 1 (A) to 1 (D).

First, as shown in FIG. 1A, a wafer was prepared in which a lower resist layer (2), an intermediate film (3), and an upper resist layer (4) were sequentially laminated on a base material layer (1). . Here, the lower resist layer (2) is a novolak-based positive photoresist (manufactured by Tokyo Ohka Kogyo Co., Ltd .; trade name: OFPR80)
0) is applied to a thickness of about 1 μm, the intermediate film (3) is an SOG (trade name: OCD Type2 manufactured by Tokyo Ohka Kogyo Co., Ltd.) applied to a thickness of about 0.15 μm, and The resist layer (4) is formed by applying a novolak-based positive type photoresist (trade name: TSMR-V3, manufactured by Tokyo Ohkasha Co., Ltd.) to a thickness of about 0.8 μm.

Next, the upper resist layer (4) is patterned through selective exposure with g-line (436 nm) and development with an alkali developing solution (NMD-3, manufactured by Tokyo Ohka Co., Ltd.), as shown in FIG. 1 (B). Then, an upper resist pattern (4a) was formed.

Next, using a magnetron RIE (reactive ion etching) apparatus, for example, C ₃ F ₈ flow rate 50 SCCM, gas pressure 1
The intermediate film (3) is patterned using the upper vapor resist pattern (4a) as a mask under the conditions of 5 mTorr and a high frequency bias power of 1500 W to form an intermediate film pattern (3a) as shown in FIG. 1 (C). Formed.

Next, ECR (Electron Cyclotron Resonance) plasma
The above-mentioned wafer was set on the wafer setting electrode of the etching apparatus, and the wafer setting electrode was cooled to a predetermined temperature. In this state, O ₂ gas flow rate 40 SCCM, Cl ₂ gas flow rate 10 SCCM, gas pressure 1
0mTorr, microwave power 850W, high frequency bias power
Under the condition of 200 W, the lower resist layer (2) was etched using the upper resist pattern (4a) and the intermediate film pattern (3a) as masks.

Here, if anisotropic processing is achieved by the contribution of a sidewall protective film (not shown), a lower resist pattern (2a) having vertical walls is formed as shown in FIG. The multilayer resist pattern (5) is completed. However, the upper resist pattern (4
The reason a) is not shown is that the lower resist layer (2) is removed at the same time as the etching. However, in low-temperature etching, the wafer temperature at which anisotropic processing can be achieved differs depending on the combination of the type of etching gas and the material to be processed. Therefore, the undercut ratio (%) at each temperature was measured while changing the wafer temperature.

As shown in FIG. 3, the undercut ratio is defined as the amount of retreat of the lower resist pattern (2b) measured from the end of the intermediate film pattern (3a) serving as a mask as 1, and the lower resist pattern (2). When the height of 2b) is h, (l /
h) Value defined by x100.

Regarding the wafer temperature, the temperature of the ethanol supplied as a coolant from the chiller to the wafer installation electrode should be changed in the experiment in the temperature range higher than normal temperature by setting the normal heater temperature, and in the experiment in the temperature range lower than normal temperature. Was controlled by. However, during the etching, the wafer temperature rises above the initially set temperature. For example, a chiller using ethanol as a coolant can cool to about -100 ° C, but when the initial set temperature is -80 ° C, the wafer temperature during etching rises to around -60 ° C. Therefore, the following wafer temperatures described in this specification all refer to the wafer temperature during etching.

For comparison, etching using only O ₂ gas was performed in the same manner, and the undercut ratio (%) was measured. The conditions in this case were an O ₂ gas flow rate of 50 SCCM, a gas pressure of 10 mTorr, a microwave power of 850 W, and a high frequency bias power of 200 W.

The results are shown in FIG. In the figure, the ordinate represents the undercut ratio (%), the abscissa represents the wafer temperature (° C.), the plot of white circles (○) represents the experimental results with a mixed gas of O ₂ gas and Cl ₂ gas, The plots correspond to the results of comparative experiments using O ₂ gas alone. From these results, the undercut ratio increases with increasing wafer temperature in any gas system. However, when etching is performed using a mixed gas of O ₂ gas and Cl ₂ gas, the O ₂ gas It is clear that the undercut ratio can be reduced in a high temperature range as compared with the case of using only one. O not fully suppress the undercut be cooled to -60 ° C. in ₂ gas alone, the mixed gas system of the O ₂ gas and Cl ₂ gas can be suppressed almost completely undercut at about -24 ° C. As a result, the state shown in FIG. 1 (C) was achieved. This shows the extremely high practicality of the present invention from the viewpoint of equipment and cost. further,
In the prior art, the Cl ₂ gas addition amount of 60 to 80% was required to almost completely suppress the undercut at room temperature, but in the present invention, the Cl ₂ gas addition amount can be significantly increased by using simple cooling together. (In the example described above, the Cl ₂ gas addition amount is 20%), the same effect can be obtained, and the effectiveness of the present invention is also demonstrated from this viewpoint.

Note that the present invention is not limited to the present embodiment,
Changes can be made as appropriate without departing from the spirit of the present invention.

For example, the O ₂ gas amount is 45 SCCM and the Cl ₂ gas flow rate is 5 SCCM
In the case of the Cl ₂ gas addition amount of 10%, undercut was almost completely suppressed at a wafer temperature of about −60 ° C.

In a chiller using a chlorofluorocarbon-based refrigerant (for example, manufactured by Sumitomo 3M Co., Ltd., Fluorinert, etc.), -70 is used.
Since cooling down to about ° C. is possible, this may be used depending on the type of etching gas or material to be processed.
In this case, assuming that the initial set temperature is -20 to 30C, the wafer temperature during etching is approximately 0C.

Further, the material of the intermediate film (3) is not limited to the above-mentioned SOG, but may be silicon oxide or plasma C deposited by CVD or the like.
Silicon nitride, polycrystalline silicon, or the like deposited by VD or the like may be used.

Further, an inert gas or the like may be added as a diluting gas to the mixed gas system as needed.

Embodiment 2 In this embodiment, an application example of the second invention of the present invention will be described. The description with reference to the drawings is omitted.

First, a multilayer resist layer consisting of a lower resist layer, an intermediate film, and an upper resist layer is formed on an Al (1% Si-containing) wiring layer in the same manner as in Example 1, and the upper resist layer is patterned by photolithography. Then, an upper resist pattern was formed. Next, the intermediate film was patterned using the upper resist pattern as a mask to form an intermediate film pattern.

Next, using an ECR type plasma etching apparatus, a wafer temperature of −60 ° C., an O ₂ gas flow rate of 45 SCCM, a Cl ₂ gas flow rate of 5 SCCM,
The lower resist layer was etched using the upper resist pattern and the intermediate film pattern as masks under the conditions of a gas pressure of 10 mTorr, a microwave power of 850 W, and a high frequency bias power of 200 W. At this time, by concurrently using the cooling of the wafer, the anisotropic processing was achieved by the contribution of the sidewall protective film even with a small amount of Cl ₂ gas added.

Subsequently, the wafer was transferred to a parallel plate type plasma etching apparatus via a vacuum transfer means, and the NF ₃ gas flow rate was 50 SCCM,
Plasma treatment was performed under the conditions of a gas pressure of 10 mTorr and an AC bias voltage of -120 V. By this process, residual Cl in the sidewall protective film
Was replaced with F and the intermediate film pattern was removed. At this time, the wafer transferred to the parallel plate type plasma etching apparatus via the vacuum transfer means is in a state of being cooled at a low temperature, and there is a possibility that dew condensation may occur if the temperature is naturally returned to room temperature. went. As a result, the residual Cl was extremely easily replaced with F due to the fact that the deposition amount of the side wall protective film was originally small, the effect of heating, and the like. Even when the wafer was left in the air, no after-corrosion was observed in the Al wiring layer.

〔The invention's effect〕

As is clear from the above description, when the present invention is applied, good anisotropic processing of a multilayer resist layer can be performed with good reproducibility without causing particle contamination and lowering the etching rate in a three-layer resist process. It is possible to do well. Further, when the underlying material layer of the multilayer resist layer is an Al-based material, after-corrosion can be effectively prevented. Furthermore, the cooling performed in the first invention and the second invention of the present invention does not require any large and complicated equipment, and is advantageous in cost. Therefore, the present invention is particularly effective for manufacturing a semiconductor device having a fine design rule and high performance.

[Brief description of the drawings]

1 (A) to 1 (D) are schematic sectional views showing an embodiment of the first invention of the present invention in the order of steps, and FIG. 1 (A) shows a lower layer on a base material layer. Resist layer,
The state in which the intermediate film and the upper resist layer are formed, the first
FIG. 1B shows a patterning step of an upper resist layer by photolithography, FIG. 1C shows a patterning step of an intermediate film, and FIG. 1D shows an etching step of a lower resist layer. FIG. 2 is a characteristic diagram showing the wafer temperature dependence of the undercut ratio in etching using a mixed gas system of O ₂ gas and Cl ₂ gas, as compared with that of an O ₂ gas alone system. FIG. 3 is a schematic cross-sectional view showing a state where an undercut has occurred in the etching of the lower resist layer. DESCRIPTION OF SYMBOLS 1 ... Base material layer 2 ... Lower resist layer 2a, 2b ... Lower resist pattern 3 ... Intermediate film 3a ... Intermediate film pattern 4 ... Upper resist layer 4a ... Upper resist pattern 5 ... Multilayer resist ·pattern

Claims (2)

(57) [Claims] A lower resist layer, an intermediate layer,
And a multilayer resist layer etching method for patterning a multilayer resist layer formed by laminating an upper resist layer in this order, a step of forming an upper resist pattern by patterning the upper resist layer into a desired shape. Forming an intermediate film pattern by patterning the intermediate layer using the upper resist pattern as a mask, and at least O ₂ gas while the substrate is cooled to −80 to 0 ° C.
Etching the lower resist layer with the upper resist pattern and the intermediate film pattern as a mask using an etching gas containing 10 to 20% Cl ₂ gas. . 2. A multi-layer resist layer etching method for patterning a multi-layer resist layer formed by laminating a lower resist layer, an intermediate film, and an upper resist layer on a base material layer mainly composed of Al in this order. Patterning the upper resist layer into a desired shape to form an upper resist pattern; forming an intermediate film pattern by patterning the intermediate layer using the upper resist pattern as a mask; With at least O ₂ gas while cooling to 80 ~ 0 ° C
A step of etching the lower resist layer using the upper resist pattern and the intermediate film pattern as a mask with an etching gas containing 10 to 20% Cl ₂ gas; and performing a plasma treatment with an F-based gas. A method for etching a multi-layer resist layer, comprising: