JP3463644B2 - Dry etching method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of selectively dry-etching a material to be processed made of silicon (including polysilicon and amorphous silicon), and particularly when dry etching the material to be processed using a resist layer as a mask. As a pre-treatment, the residual water droplets on the material to be treated are heat treated to form a watermark (dry stain), and then the watermark and the naturally-occurring silicon oxide film are removed by dry etching to prevent the generation of silicon residues due to the watermark. It was done.

[0002]

2. Description of the Related Art Conventionally, as a method of dry etching a polysilicon layer using a resist layer as a mask, FIG.
What is shown to 14 is proposed.

In the process shown in FIG. 12, a polysilicon layer 3 is formed on the surface of a silicon substrate 1 with a silicon oxide film 2 interposed therebetween, and then a silicon oxide film 4 is formed on the surface of the polysilicon layer 3. Then, resist layers 5a and 5b are formed on the silicon oxide film 4 according to a desired gate pattern by a well-known photolithography process.

Next, in the process of FIG. 13, the resist layer 5
The silicon oxide film 4 is patterned by wet etching using a and 5b as a mask and HF (hydrofluoric acid) as an etchant, and the silicon oxide films 4a and 4b are left on the surface of the polysilicon layer 3.
Then, the surface of the polysilicon layer 3 is rinsed with pure water and dried. The drying process at this time is performed using a spin dryer. The spin drying device has a mechanism in which air is introduced into a drying chamber containing a substrate through a filter and exhausted, and the substrate is rotated at a high speed to shake off water droplets.

Next, in the process of FIG. 14, the resist layer 5
The polysilicon layer 3 is patterned by dry etching using a, 5b and the silicon oxide films 4a, 4b as masks to leave the gate electrode layers 3a, 3b on the silicon oxide film (gate insulating film) 2. After that, the resist layers 5a, 5
Remove b.

[0006]

According to the above-mentioned conventional technique, the water drops 6a, 6b and the watermark 7 remain on the surface of the polysilicon layer 3 in the drying process of FIG. O ₂ (oxygen) is supplied to the water droplets 6 a and 6 b from the atmosphere and silicon is melted from the polysilicon layer 3, so that the water droplets 6 a and 6 b eventually change into watermarks mainly composed of silicon oxide. .

In the dry etching process of FIG. 14, the unintentionally generated watermark as described above acts as a mask, so that the polysilicon residues 3x, 3 are formed.
y and 3z are generated. Such polysilicon residue is
Since it has conductivity, it causes an electrical short circuit with respect to the electrodes and wiring, and increases variations in the electrical characteristics of the semiconductor device. As a result, the production yield is lowered.

An object of the present invention is to provide a novel dry etching method capable of preventing the generation of silicon residues due to watermarks.

[0009]

A first dry etching method according to the present invention comprises a step of forming a coating film on a surface of a material to be treated made of silicon, and a predetermined pattern on the coating film. The step of forming a resist layer, and the coating film is selectively removed by wet etching treatment using the resist layer as a mask to leave the coating film in a pattern corresponding to the resist layer and the material to be treated. A step of exposing the surface of the exposed portion corresponding to the removed portion of the coating film, a step of performing a cleaning and drying treatment on the exposed portion of the processed material after the wet etching treatment, and a step of performing the cleaning and drying treatment. A step of heat-treating the water droplets remaining on the exposed portion of the material to be water-marked, and a first dry etching treatment using the resist layer as a mask after the heat-treatment The step of removing the watermark and the naturally-occurring silicon oxide film in the exposed part of the material to be processed, and the resist layer and the remaining part of the coating film as a mask after the first dry etching process And a step of selectively removing the material to be treated by a second dry etching treatment.

According to the first dry etching method, after the coating film is patterned by the wet etching process using the resist layer as a mask, the exposed portion of the material to be processed is washed and dried, whereby the material to be processed is Water drops remain on the exposed part. The remaining water droplets are converted into watermarks by heat treatment. The first dry etching process using the resist layer as a mask removes the watermark and the naturally-occurring silicon oxide film in the exposed portion of the material to be processed.
After that, the material to be processed is patterned by the second dry etching process using the resist layer as a mask. Therefore, in the second dry etching process, generation of silicon residue due to the watermark can be prevented.

A second dry etching method according to the present invention comprises a step of forming a resist layer on a surface of a material to be processed made of silicon according to a predetermined pattern, and exposing the material to be processed after forming the resist layer. Part to be subjected to a cleaning and drying process, and after the cleaning and drying process, a heat treatment for water-marking the water droplets remaining on the exposed part of the material to be treated, and a resist layer after the heat treatment. A step of removing the watermark and the naturally-occurring silicon oxide film in the exposed portion of the material to be processed by a first dry etching process using a mask, and using the resist layer as a mask after the first dry etching process And a step of selectively removing the material to be treated by a second dry etching treatment.

According to the second dry etching method, when a resist layer is formed on the surface of the material to be processed and then the exposed portion of the material to be processed is washed and dried, water drops are formed on the exposed portion of the material to be processed. To remain. The remaining water droplets are converted into watermarks by heat treatment. The first dry etching process using the resist layer as a mask removes the watermark and the naturally-occurring silicon oxide film in the exposed portion of the material to be processed. After that, the material to be processed is patterned by the second dry etching process using the resist layer as a mask. Therefore, in the second dry etching process, generation of silicon residue due to the watermark can be prevented.

[0013]

1 to 6 show a dry etching method according to a first embodiment of the present invention.
Steps (1) to (6) corresponding to steps # 6 to # 6 will be sequentially described.

(1) After the gate insulating film 12 made of silicon oxide is formed on the surface of the semiconductor substrate 10 made of, for example, silicon by the thermal oxidation method or the like, the polysilicon layer 14 is formed on the insulating film 12 by the CVD method or the like. To do. The polysilicon layer 14 is doped with a conductivity type determining impurity such as phosphorus during or after the deposition to reduce the resistance of the polysilicon layer 14 to such an extent that it can be used as a gate electrode layer.

Next, the polysilicon layer 1 is formed by a thermal oxidation method or the like.
An interlayer insulating film 16 made of silicon oxide on the surface of 4
To form. Then, resist layers 18a and 18b are formed on the insulating film 16 by photolithography according to a desired gate pattern.

(2) The portions 16a, 16b of the insulating film 16 are selectively removed by wet etching using the resist layers 18a, 18b as masks and HF as an etchant.
The surface of the polysilicon layer 14 is exposed corresponding to the removed portion of the insulating film 16 while being left in a pattern corresponding to a and 18b. Then, the surface of the polysilicon layer 14 is sequentially subjected to a pure water rinse treatment and a drying treatment. The drying process at this time can be performed using the above-mentioned spin drying device. As a result of the drying process, the water drops 20a and 20b remain on the exposed portion of the polysilicon layer 14, and at the same time, the watermark 22 is also formed.

(3) By subjecting the substrate of FIG. 2 to a heat treatment for the purpose of completely evaporating and drying water, the water droplets 20a, 20a
0b is changed to the watermarks 22a and 22b. As an example, the heat treatment is performed one by one using a heater plate type heating device. That is, the substrate is inserted into the heating chamber, the substrate is set at a position of about 2 mm on the heater plate, and the N ₂ (nitrogen) gas is introduced into the heating chamber and exhausted to perform heat treatment at 120 ° C. for 60 seconds. The heat treatment temperature can be set to about 90 ° C. to 150 ° C., considering that water vapor is smoothly evaporated and that the resist layers 18a and 18b are not altered or deformed. However, since there are many types of resist and the heat resistance temperature is different,
It is not limited to such a range. The heat treatment time is not limited to 60 seconds and can be appropriately selected within the range where the purpose of drying can be achieved.

(4) Water marks 22, 22a, and 22a on the exposed portion of the polysilicon layer 14 by the first dry etching process using the resist layers 18a and 18b as masks.
22b and the naturally occurring silicon oxide film are removed. In the first dry etching treatment, perfluorocarbon (PFC) gas such as CF ₄ , C ₂ F ₆ and C ₄ F ₈ is used as an etching gas, and hydrofluorocarbon such as CHF ₃ and CH ₂ F ₂ is used as a selection ratio adjusting gas. (HFC) gas may be used, and a gas such as Ar or He may be used as a dilution gas.

As an example, dry etching is performed for about 10 seconds using a mixed gas of CHF ₃ / CF ₄ or a mixed gas of CHF ₃ / O ₂ / He to obtain an etching amount of 20 to 80 (corresponding to a thermal oxide film). Preferably 50-6
0) nm etching can be performed. At this time, the selection ratio of silicon oxide / polysilicon is 6
It can be set to 10 (preferably 8). If the selection ratio is high, a large amount of polymer is generated on the surface of the polysilicon layer 14, and the polysilicon layer 14 is processed in the process of FIG.
It hinders dry etching. If the selection ratio is low, the remaining amount of the polysilicon layer 14 may be too small to obtain a desired shape when the polysilicon layer 14 is etched in the step of FIG.

Assuming that the selection ratio is 8, the etching amount of 20 to 80 nm is 2.5 to about the etching amount of the polysilicon layer 14.
This corresponds to 10 nm. The thickness of the naturally-occurring silicon oxide film is usually about 2 to 3 nm, and therefore 20 to 80
It can be removed sufficiently with an etching amount of nm. In the dry etching process of FIG. 4, it is desirable to take care to minimize the film loss of the resist layers 18a and 18b and the polysilicon layer 14.

(5) By selectively removing the polysilicon layer 14 by the second dry etching process using the resist layers 18a and 18b and the insulating films 16a and 16b as masks, the portions 14a and 14b of the polysilicon layer 14 are removed. The gate electrode layer is left on the gate insulating film 12.
Since the watermark is removed in the process of FIG. 4, it is possible to prevent the generation of polysilicon residue due to the watermark in the process of FIG.

(6) The resist layers 18a and 18b are removed by ashing or the like. When an EEPROM (electrically erasable / programmable read only memory) is manufactured, the gate electrode layers 14a, 14a are formed by a thermal oxidation method or the like.
After forming a silicon oxide film on the exposed side of 4b and selectively oxidizing the substrate surface portion not covered by the gate electrode layers 14a and 14b, a second polysilicon layer overlapping the interlayer insulating films 16a and 16b is formed. However, since the subsequent processes are not directly related to the present invention, detailed description thereof will be omitted. In addition, this kind of EEPRO
M is already known as disclosed in Japanese Patent No. 2512181.

In order to confirm the effect of the present invention, the method of FIGS. 1 to 6 is applied to the first wafer (substrate) and the second wafer is used.
A method (corresponding to the conventional method) in which the steps of FIGS. 3 and 4 are omitted from the method of FIGS. Then, the number of defects was inspected on the first and second wafers using a pattern defect inspection apparatus. As a result, the number of defects in the second wafer was 804, whereas the number of defects in the first wafer was 204. Therefore, the number of defects in the first wafer was reduced to about 1/4 of that in the second wafer. Since the defects due to the watermark occupying the entire number of the conventional defects are 60 to 80%, it can be said that the defects based on the watermarks are almost completely eliminated by the present invention.

7 to 11 show a dry etching method according to the second embodiment of the present invention. In the step of FIG. 7, the semiconductor substrate 10 having the polysilicon layer 14 formed on the surface with the gate insulating film 12 interposed therebetween is prepared in the same manner as described with reference to FIG. Then, resist layers 30a and 30b are formed on the polysilicon layer 14 by photolithography according to a desired gate pattern. After this,
Similarly to the above, the surface of the polysilicon layer 14 is sequentially rinsed with pure water and dried. As a result, the water droplets 32a and 32b and the watermark 34 remain on the exposed portion of the polysilicon layer 14.

In the process of FIG. 8, the water drops 32a and 32b are changed into the watermarks 34a and 34b by performing heat treatment in the same manner as described in FIG.

In the step of FIG. 9, the polysilicon layer 1 is subjected to a first dry etching process using the resist layers 30a and 30b as a mask in the same manner as described with reference to FIG.
In the exposed portion of No. 4, the watermarks 34, 34a, 34
b and the naturally occurring silicon oxide film are removed.

In the process of FIG. 10, the resist layers 30a, 3 are formed.
By selectively removing the polysilicon layer 14 by the second dry etching process using 0b as a mask, the portions 14a and 14b of the polysilicon layer 14 are left on the gate insulating film 12 as gate electrode layers. Since the watermark is removed in the step of FIG. 9, it is possible to prevent the polysilicon residue from being generated due to the watermark in the step of FIG. After that, in the process of FIG.
The resist layers 30a and 30b are removed by ashing treatment or the like.

The present invention is not limited to the above-described embodiment, but can be implemented in various modified forms. For example, the following changes are possible.

(1) The material to be processed is not limited to polysilicon (polycrystalline silicon), but single crystal silicon or amorphous silicon may be used.

(2) The coating film formed on the material to be processed is not limited to an insulating film such as silicon oxide, but Ti,
A conductive film such as a refractory metal such as W or Mo or a silicide thereof may be used.

(3) The cleaning process is not limited to a water cleaning process such as rinsing with pure water, and a wet cleaning process involving water droplets can be used.

(4) In the drying process, not only the spin dryer but also known drying means such as IPA (isopropyl alcohol) vapor dryer and Marangoni dryer can be used.

[0033]

As described above, according to the present invention, the generation of silicon residue due to the watermark is prevented, so that the occurrence of an electrical short circuit with respect to the electrode or the wiring can be prevented, or the semiconductor device can be prevented. Variations in electrical characteristics can be reduced, and the effect of improving the manufacturing yield of semiconductor devices and the like can be obtained.

[Brief description of drawings]

FIG. 1 is a substrate cross-sectional view showing a resist layer forming step in a dry etching method according to a first embodiment of the present invention.

FIG. 2 is a substrate cross-sectional view showing a silicon oxide film wet etching step and a rinse / dry step that follow the step of FIG.

FIG. 3 is a substrate cross-sectional view showing a heat treatment step following the step of FIG.

FIG. 4 is a substrate cross-sectional view showing a dry etching step of the silicon oxide film, which is subsequent to the step of FIG.

5 is a substrate cross-sectional view showing a dry etching step of a polysilicon layer, which is subsequent to the step of FIG.

FIG. 6 is a substrate cross-sectional view showing a resist layer removing step that follows the step of FIG.

FIG. 7 is a substrate cross-sectional view showing a resist layer forming step and a rinsing / drying step in a dry etching method according to a second embodiment of the present invention.

8 is a substrate cross-sectional view showing a heat treatment step following the step of FIG.

FIG. 9 is a substrate cross-sectional view showing a dry etching step of the silicon oxide film, which is subsequent to the step of FIG.

FIG. 10 is a substrate cross-sectional view showing a dry etching step of the polysilicon layer, which is subsequent to the step of FIG.

FIG. 11 is a substrate cross-sectional view showing a resist layer removing step following the step of FIG.

FIG. 12 is a substrate cross-sectional view showing a resist layer forming step in a conventional dry etching method.

FIG. 13 is a substrate cross-sectional view showing a wet etching step and a rinse / dry step of the silicon oxide film, which are subsequent to the step of FIG.

FIG. 14 is a substrate cross-sectional view showing a dry etching step of the polysilicon layer, which is subsequent to the step of FIG.

[Explanation of symbols]

10: semiconductor substrate, 12: gate insulating film, 14: polysilicon layer, 14a, 14b: gate electrode layer, 16, 16
a, 16b: interlayer insulating film, 18a, 18b, 30a, 3
0b: resist layer, 22, 22a, 22b, 34, 34
a, 34b: Watermark.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/28 H01L 21/306 H01L 21/3205 H01L 21/3213

Claims (2)

(57) [Claims] 1. A step of forming a coating film on the surface of a material to be treated made of silicon, a step of forming a resist layer on the coating film according to a predetermined pattern, and a wet process using the resist layer as a mask. The coating film is selectively removed by an etching process to leave the coating film in a pattern corresponding to the resist layer and expose the surface of the material to be treated corresponding to the removed portion of the coating film. And a step of performing a cleaning and drying process on the exposed part of the material to be processed after the wet etching process, and a water droplet remaining on the exposed part of the material to be processed is watermarked after the cleaning and drying process. Heat treatment, and after the heat treatment, the first dry etching treatment using the resist layer as a mask is performed to expose the watermark and the natural mark on the exposed portion of the material to be treated. A step of removing a raw silicon oxide film; and a second dry etching process using the resist layer and the remaining portion of the coating film as a mask after the first dry etching process to select the processing target material. Dry etching method including the step of removing selectively. 2. A step of forming a resist layer on a surface of a material to be processed made of silicon in accordance with a predetermined pattern, and a step of performing a cleaning and drying treatment on an exposed portion of the material to be processed after forming the resist layer. After the cleaning and drying processes, a step of performing a heat treatment for converting the water droplets remaining on the exposed portion of the processed material into a watermark, and a step of performing a first dry etching process using the resist layer as a mask after the heat treatment. A step of removing the watermark and the naturally-occurring silicon oxide film in the exposed portion of the material to be processed; and a second dry etching processing using the resist layer as a mask after the first dry etching processing. And a step of selectively removing the material.