JP3166350B2 - Method for manufacturing semiconductor device - 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 for increasing an ashing speed of a barrel type plasma ashing apparatus used in a semiconductor wafer processing step.

[0002]

2. Description of the Related Art Fine processing in a semiconductor wafer processing step is performed by etching a base insulating film, a semiconductor film, and a metal film via a photoresist film on which a pattern is formed by exposure and development. After the completion of the etching, it is necessary to remove the photoresist film used as the mask from the wafer surface.

A plasma ashing apparatus is an apparatus for ashing and removing a photoresist film using oxygen gas plasma (hereinafter abbreviated as ashing).
(B) shows an example of a barrel type plasma ashing apparatus. That is, the pressure inside the quartz reaction vessel 1 is reduced by the vacuum pump 2, and when the inside of the reaction vessel 1 reaches a desired degree of vacuum,
The valve 3 is opened and oxygen gas O ₂ is introduced into the reaction vessel 1 from the processing gas introduction pipe 5 while maintaining a constant flow rate under the monitoring of the flow meter 4.

As shown in FIG. 7, the reaction vessel 1 has a double-tube cylindrical structure in which an aluminum tunnel 6 is housed, and a quartz boat 7 disposed in the tunnel 6 A plurality of silicon wafers 8 having a photoresist film attached thereto are arranged.

When the degree of vacuum in the reaction vessel 1 becomes constant, high-frequency power of 13.56 MHz is applied to the electrode 10 by the RF oscillator 9 to cause a discharge and generate oxygen gas plasma in the reaction vessel 1. Let it. The auto-tuning circuit 11 is provided for automatically adjusting discharge to optimal conditions in order to always stabilize the plasma state that changes during ashing.

The ashing action of the photoresist film by the oxygen gas plasma is performed by lowering the molecular weight of the polymer resin by a chemical reaction between the atomic oxygen O generated in the O ₂ plasma and the polymer resin, and reducing CO by the oxidation of the low molecular weight resin. ₂ and H ₂ O. The photoresist film attached to the silicon wafer 8 simply reacts with oxygen radicals by the following reaction when the photoresist film is simply denoted by C _x H _y. As a result, CO ₂ and H ₂ O are emitted from the exhaust pipe 12.

O ₂ → O * (oxygen radical) C _x H _y + O * → CO ₂ ↑ + H ₂ O プ ラ ズ マ The plasma process is cleaner than the wet process, and the yield of integrated circuits having fine processing patterns is particularly high. Although it has the advantage of contributing to the improvement of reliability, it is necessary not only to remove the photoresist film but also to make the etching a dry process with the progress of miniaturization. The photoresist film is subjected to plasma irradiation of an etching gas when used as an etching mask, and is further exposed to an ion beam when impurities are introduced by ion implantation. Ashing of the photoresist film by gas plasma has become an indispensable manufacturing technique in the miniaturization process because the photoresist film that has been irradiated is transformed into a state in which it cannot be sufficiently removed by a chemical agent.

The ashing rate of a photoresist film by oxygen gas plasma is not limited to plasma conditions such as gas pressure, high frequency applied power, gas composition, and temperature, but also gas flow rate, degree of vacuum, number of processed wafers, arrangement of wafers, surface area of wafers, and the like. Also depends on the sample conditions.

The ashing speed increases linearly with the applied high frequency power, but there is a gas pressure which shows a maximum value with respect to the gas pressure. The value of the gas pressure depends on the applied high frequency power or the discharge of the plasma apparatus. It changes depending on the form and shape. The ashing action is performed in an O ₂ gas plasma, and it has been reported that the ashing speed is further increased by adding a small amount of CF ₄ to the O ₂ gas plasma.

In the plasma ashing of a photoresist film, the so-called "loading effect" depends on the total exposed surface area of the sample, as in the case of plasma etching.
Is shown. This is because the concentration of the oxygen radical, which is a reactive species, is low, and it is derived from the model that the ashing speed decreases in inverse proportion to the entire exposed area of the sample.

FIG. 8 shows the relationship between the number of wafers processed by oxygen gas plasma and the ashing speed. Specifically, as shown in FIG.
FIG. 10 is a graph showing the measured ashing time (minutes) and the decrease in the photoresist film thickness (× 10 ³ Å) when the number of wafers is sequentially increased to 10, 30, 50, and 60 sheets. In general, it has been confirmed that the relationship between the number of processed wafers and the resist ashing speed tends to increase the time required for ashing as the number of wafers increases. Since the ashing speed increases exponentially with respect to temperature, the amount of ashing increases linearly with time if care is taken to keep the sample temperature constant during ashing.

As described above, when ashing is performed in a state in which a large number of samples are arranged in a boat and inserted into a double-cylindrical plasma apparatus, the ashing speed increases with time due to a rise in temperature during the ashing, and the amount of ashing increases. Is known to increase at an accelerated rate with respect to time.

However, the purpose of ashing is to sufficiently remove the photoresist film by incineration and generally does not require precise control such as plasma etching.
In a standard integrated circuit manufacturing process, ashing is performed on a large number of samples at the same time using a normal cylindrical plasma device.

Further, as described above, the photoresist film is also used as a mask at the time of ion implantation, and it is necessary to evaluate the ashing speed when receiving the ion irradiation. In particular, if the sample temperature becomes extremely high due to the increase in the current density and the acceleration voltage during ion implantation, the subsequent ashing operation may become difficult.

As described above, the ashing speed of the photoresist film depends on the type of the resist, the sample temperature, the “loading effe
ct "such changes in various factors, yet when subjected to prolonged O ₂ plasma gas than necessary sample, since there is a possibility that phenomena such as the oxidation proceeds irradiation damage caused or wafer surface occurs, ashing At present, proper management technology for speed is required.

[0016]

However, in such a conventional barrel type plasma ashing method, there is a problem that the ashing speed of the photoresist film is limited and is likely to become a bottleneck in improving the working efficiency. . In particular, when the ashing method is applied to a semiconductor device having a multilayer structure, a plurality of photolithography steps such as opening a window for impurity diffusion, opening a contact hole in an interlayer insulating film, and forming a metal pattern for an electrode, etc. Since the photoresist ashing step must be performed, the ratio of the time required for the ashing to the entire process becomes extremely high, which adversely affects the work efficiency.

Further, in recent semiconductor devices, there is a strong demand for higher frequencies and higher functions, and accordingly, the finer exposure patterns and higher integration have been promoted. Therefore, the photoresist remaining on the wafer has a fine structure portion. Is increasing. In such a highly miniaturized photolithography process, when ashing a photoresist in which a fine pattern is drawn, a residue of ashed and carbonized photoresist may remain in the minute portion, and no residue remains. Ashing requires a long time. Further, when ashing a photoresist attached to a wafer having a pattern cut by etching, there is a problem that the time required for the ashing varies depending on the presence or absence of a fine pattern and its shape.

Accordingly, the present invention solves the problems of the conventional method of manufacturing a semiconductor device, increases the ashing speed of a photoresist film deposited on a silicon wafer, and provides a finely patterned photoresist. It is an object of the present invention to provide a method for manufacturing a semiconductor device in which a photoresist film is not left on a wafer even when applied to a film.

[0019]

According to the present invention, in order to achieve the above object, a semiconductor wafer having a photoresist film attached thereto and a container filled with an organic substance are inserted and arranged in a closed type reaction container. After depressurizing the inside, oxygen gas is introduced while maintaining a constant flow rate, high-frequency power is applied to the electrodes provided in the reaction vessel, and oxygen gas plasma is generated by discharge, and the oxygen gas plasma adheres to the semiconductor wafer. Provided is a method of manufacturing a semiconductor device in which a removed photoresist film is removed. A photoresist used in a semiconductor wafer processing step is used as the organic material filled in the container.

Further, a metal corrugated plate is placed in a container, and a photoresist is attached to the front and back surfaces of the corrugated plate, so that the surface area of the photoresist that reacts with oxygen radicals is increased. Further, the pressure of oxygen gas was 0.8 Torr or more, and the flow rate was about 5 cm ³ / min or more.

[0021]

According to the method of manufacturing a semiconductor device, the high molecular weight resin is reduced to a low molecular weight by the chemical reaction between the atomic oxygen generated in the oxygen gas plasma and the organic substance, and the CO ₂ and H ₂ are reduced to the low molecular weight resin by the oxidation. The photoresist film adhering to the silicon wafer reacts with oxygen radicals and is removed as CO ₂ and H ₂ O by the decomposition and vaporization of O.

In particular, according to the present invention, the ashing speed increases and the ashing speed decreases as the number of processed wafers increases. This is typically a reactive species
Because of the low concentration of certain oxygen radicals, the ashing rate decreases in inverse proportion to the total exposed area of the sample . Follow
Therefore , the ashing speed is limited by the surface area of the resist to be ashed .
A corrugated sheet and a resin attached to the front and back surfaces of the corrugated sheet
Photoresist that reacts with oxygen radicals
The surface area becomes extremely large, resulting in oxygen radicals
It is considered that the concentration was high.

[0023]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a semiconductor device manufacturing method according to an embodiment of the present invention;

In the schematic diagram of the apparatus shown in FIG. 1, reference numeral 1 denotes a sealed reaction vessel made of quartz, and the pressure in the reaction vessel 1 is reduced by a vacuum pump 2. Reference numeral 5 denotes an oxygen gas introduction pipe, and a valve 3 and a flow meter 4 are provided in the middle of the introduction pipe 5.

The reaction vessel 1 has a double-tube cylindrical structure in which an aluminum tunnel 6 is housed, as in the conventional example. A plurality of silicon wafers 8 are juxtaposed. In this embodiment, the silicon wafer 8 has a size of 4 inches in diameter, and a positive resist is adhered to one side with a thickness of 1.2 μm. 9 is an RF oscillator, 10 is an electrode, 11 is an auto-tuning circuit, and 12 is an exhaust pipe.

The diameter of the quartz reaction vessel 1 was 30 cm and the depth was 50 cm. The pressure of the oxygen gas in the reaction vessel 1 was 0.8 Torr or more, and the flow rate was about 5 cm ³ / min or more. This is a pressure at which plasma can be generated stably.

As a characteristic method of this embodiment, a quartz container 13 filled with an organic substance such as a resin is inserted and placed in the tunnel 6 housed in the reaction container 1.
In this embodiment, a photoresist used in a semiconductor wafer processing step is used as an example of an organic substance such as a resin.

FIGS. 2, 3 and 4 show the details of the above-mentioned container 13 and the filled organic substance.
3 is provided with an aluminum corrugated plate 14.
The photoresist 15 as an organic substance is attached to the front and back surfaces of the substrate 4. The reason for using the corrugated plate 14 is to increase the surface area of the photoresist 15 that reacts with oxygen radicals as described later.

The operation of this embodiment will be described below. First, the silicon wafer 8 and the container 13 filled with the organic substance are placed in the reactor 1 in the state shown in the figure, and then the vacuum pump 2 is started. Then, when the inside of the reaction vessel 1 reaches a desired degree of vacuum, the valve 3 is opened and oxygen gas O ₂ is introduced into the reaction vessel 1 from the introduction pipe 5 while maintaining a constant flow rate under the monitoring of the flow meter 4. .

Next, by applying a predetermined high frequency power to the electrode 10 by the RF oscillator 9, oxygen gas plasma is generated in the reaction vessel 1 by discharge. The output of the RF oscillator 9 is 50, which is the maximum output of the RF oscillator 9 used.
0 W. The auto-tuning circuit 11 automatically adjusts the discharge to the optimum condition and operates to always stabilize the plasma state that changes during ashing.

When the photoresist 13 poured into the container 13 is put into the reaction container 1 as it is, the vacuum pump 2
When the pressure is reduced by the pressure, the photoresist 15 may be boiled and overflow out of the container 13. Therefore, the photoresist 15 poured is discarded and the photoresist 1 adhered to the container 13 and the corrugated plate 14 is removed.
5 was sufficiently dried before ashing and then used.

Then, the molecular resin of the high molecular resin is made low molecular by a chemical reaction between the atomic oxygen O generated in the oxygen gas plasma and the high molecular resin, and the low molecular resin is decomposed and vaporized into CO ₂ and H ₂ O by oxidation of the low molecular resin. photoresist film C _x H _y deposited on the silicon wafer 8 by the action reacts with oxygen radicals CO
₂ , and H ₂ O, which are diffused from the exhaust pipe 12 via the vacuum pump 2. The effect of the container 13 is maintained until the total ashing time becomes about 20 hours when the resist is not supplied.

The experimental results show that the oxygen gas pressure is 0.8 T
orr, and the flow rate per unit time and unit volume is 5
With cm ^{3/30 2} × 50 or more, the sample wafer 20 Like the maximum load of the boat being used, the ashing time required to completely remove the resist is about 30 minutes, the oxygen gas consumption The amount was about 150 cc, the ashing time for 10 sample wafers was about 45 minutes, and the oxygen gas consumption was about 225 cc.

FIG. 5 shows a silicon wafer 8 in this embodiment.
Is a graph in which the relationship between the number of sheets and the ashing speed is plotted. Curve (1) shows the case where a container 13 filled with an organic substance such as resin is inserted into the reaction vessel 1, and curve (2) shows the case where the same vessel 3 is inserted. The case is not shown. More specifically, the ashing time for 20 sample wafers is reduced from about 30 minutes required before placing the container 13 containing the resist to about 15 minutes, and the oxygen gas consumption is also reduced from about 150 cc. It was reduced to about 75cc by half.

In addition, even when ashing is performed only on a wafer where no residue remains on the fine pattern portion on the silicon wafer 8 and the residue remains, it is possible to completely remove the resist in a short time.

Therefore, according to the present embodiment, the length of the ashing time according to the number of wafers shown in FIG. 8 is reversed. As the number of processed wafers increases, the ashing speed increases and the ashing time decreases. Turned out to be.

This can be considered as follows.
That is, since the concentration of the oxygen radical, which is a reactive species, is generally low, the ashing speed decreases in inverse proportion to the entire exposed area of the sample. Accordingly, although the ashing speed is limited by the surface area of the resist to be ashed, in this embodiment, the reaction with oxygen radicals is caused by the corrugated plate 14 placed in the container 3 and the photoresist 15 attached to the front and back surfaces of the corrugated plate 14. It is considered that the surface area of the photoresist 15 becomes extremely large, and as a result, the concentration of oxygen radicals becomes high.

Therefore, in the manufacture of various semiconductor devices, the ashing method according to the present invention is applied to remove the photosensitive positive resist applied to the surface of the semiconductor wafer, whereby the reaction is accelerated as compared with the conventional method. Thus, the ashing speed can be greatly improved.

[0039]

As described above in detail, according to the method of manufacturing a semiconductor device according to the present invention, the surface area of a photoresist which reacts with oxygen radicals by an organic substance contained in a container becomes extremely large, and the concentration of oxygen radicals increases. As a result, the photoresist film deposited on the silicon wafer can be reacted with oxygen radicals to remove the photoresist film based on vaporization.

According to the present invention, as the number of processed wafers increases, the ashing speed increases and the ashing time can be shortened. In particular, the ashing method is applied to a semiconductor device having a multilayer structure. In this case, the photoresist ashing operation time, which is performed each time a plurality of photolithography steps are performed, is reduced, so that the ratio of the time required for the ashing to the entire process can be reduced and the operation efficiency can be increased.

Furthermore, due to recent demands for higher frequency and higher functionality in semiconductor devices, even if photoresist patterns remaining on the wafer are increased due to the progress of miniaturization and high integration of the exposure pattern, even if the fine portions are increased in the photoresist remaining on the wafer, The residue of the ashed and carbonized photoresist is prevented from remaining, and there is no variation in the ashing time due to the presence or absence and the shape of the fine pattern, and the effect of uniforming the process can be obtained.

[Brief description of the drawings]

FIG. 1A is a schematic diagram showing one embodiment of a method for manufacturing a semiconductor device according to the present invention. FIG.
Sectional schematic drawing which follows the bb line of (A).

FIG. 2 is a cross-sectional view illustrating an example of filling a container with a photoresist adopted in the present embodiment.

FIG. 3 is a plan view of FIG. 2;

FIG. 4 is a partially enlarged view of FIG. 2;

FIG. 5 is a graph plotting the relationship between the number of wafers and the ashing speed when the present invention is applied.

FIG. 6A is a schematic view showing one example of a conventional method for manufacturing a semiconductor device. FIG. 6B is a schematic sectional view taken along line BB of FIG. 6A.

FIG. 7 is a perspective view showing a main part of FIG. 6 partially cut away.

FIG. 8 is a graph plotting the relationship between the number of wafers and the ashing speed in the related art.

[Description of Signs] 1 ... (quartz) reaction vessel 2 ... vacuum pump 3 ... valve 4 ... flow meter 5 ... (oxygen gas) inlet tube 6 ... tunnel 7 ... (quartz) boat 8 ... silicon wafer 9 ... RF Oscillator 10 ... Electrode 11 ... Auto tuning circuit 12 ... Exhaust pipe 13 ... Container 14 ... Corrugated plate 15 ... Photoresist

Claims (4)

(57) [Claims] 1. A semiconductor wafer having a photoresist film attached thereto and a container filled with an organic substance are inserted and arranged in a closed reaction vessel, and after reducing the pressure in the reaction vessel, oxygen gas is maintained at a constant flow rate. A high-frequency power is applied to an electrode provided in a reaction vessel to generate oxygen gas plasma by discharge, and the oxygen gas plasma removes a photoresist film attached to the semiconductor wafer. Device manufacturing method. 2. The method of manufacturing a semiconductor device according to claim 1, wherein a photoresist used in a semiconductor wafer processing step is used as the organic substance filled in the container. 3. The method according to claim 1, wherein a metal corrugated plate is placed in the container, and a photoresist is attached to the front and back surfaces of the corrugated plate to increase the surface area of the photoresist reacting with oxygen radicals. Of manufacturing a semiconductor device. 4. The method according to claim 1, wherein the pressure of the oxygen gas is 0.8 Torr or more and the flow rate is about 5 cm ³ / min or more.