JPH024269A - Photoresist removing method - Google Patents

Abstract

PURPOSE:To perfectly decompose and remove a photoresist film on a semiconductor base plate by coating said base plate with the photoresist film, and coating the surface of a photoresist pattern obtained by exposure and development with sulfuric acid, and heating the base plate to a prescribed temperature to accelerate decomposition of the photoresist. CONSTITUTION:The rotated silicon wafer 1 is coated with a prescribed amount of hot concentrated sulfuric acid 9 always kept at high concentration by storing it in an airtightly closed vessel immediately before dehydrating and decomposing the photoresist 3 with the hot concentrated sulfuric acid, and heated with an infrared lamp 7 and a heater 12 to accelerate the dehydration and decomposition reaction of the photoresist 3, and thus it is perfectly decomposed. Then, the sulfuric acid 9 containing decomposed photoresist 3 is washed off by spraying pure water 15 over the whole surface of the wafer 1 while it is rotated, and the water 15 remaining can be removed by rotating the wafer 1 at high speed, thus permitting the residual photoresist 3 on the wafer 1 to be removed to a high cleanliness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing photoresist used in photolithography, which is one of the manufacturing processes of semiconductor devices.

[Conventional technology]

Conventionally, the remaining photoresist was removed by immersing a Si wafer in a solution of heated concentrated sulfuric acid with the addition of hydrogen peroxide as an oxidizing agent, as described in Japanese Patent Publication No. 53-35436. was. In this conventional removal method, hydrogen peroxide is not added to concentrated sulfuric acid to remove the photoresist remaining on the Si wafer, so that the amount of concentrated sulfuric acid is reliably reduced.

In addition, since concentrated sulfuric acid has strong hygroscopicity, even if it is left to stand while being heated, it forms a hydrate (H2So4nH20) and the sulfuric acid concentration decreases.

As the sulfuric acid concentration decreases, the ability to remove photoresist remaining on the Si wafer rapidly deteriorates. Figure 2
Figure 2 shows changes in sulfuric acid concentration, decomposition time of positive type photoresist, and number of foreign substances in sulfuric acid.

As the concentration of sulfuric acid decreases, it may take longer to decompose and remove the photoresist remaining on the Si wafer, or carbon residue in the sulfuric acid may rapidly increase due to insufficient decomposition. become.

In other words, the photosensitizer and base polymer contained in the photoresist can be dehydrated and decomposed when the sulfuric acid concentration is 84.5 wt% or more, at which the sulfuric acid absorbs moisture and completely forms a hydrate of H2SO4.H2O. Concentration is 84.5wt%
This indicates that dehydration and decomposition become difficult when the amount is below. As described above, conventional removal methods do not take into account the deterioration of the photoresist removal ability due to a decrease in the sulfuric acid concentration.

[Problem to be solved by the invention]

The above conventional technology is a method of decomposing and removing the photoresist remaining on the Si wafer through the dehydration and decomposition reaction of concentrated sulfuric acid and the oxidation and decomposition reaction of hydrogen peroxide, which is an oxidizing agent.However, hydrogen peroxide is added to concentrated sulfuric acid. However, the problem was that it was difficult to remove the resist with a high level of cleanliness. The dehydration and decomposition reaction of the photoresist is carried out efficiently, and the photoresist deteriorated by implantation of ions such as As can be removed with high purity.

[Means for solving problem i1] The above purpose is to pour heated concentrated sulfuric acid into a sealed container to prevent it from absorbing moisture in the atmosphere, apply only the necessary amount onto a spun Si wafer, and apply infrared rays. This is achieved by dehydrating and decomposing the remaining photoresist by heating it with a lamp or heater, and then washing off the sulfuric acid containing the decomposed photoresist from the Si wafer with pure water.

[For production]

When hot concentrated sulfuric acid is applied to the positive type photoresist remaining on the Si wafer, carboxylic acid is generated by oxidizing the photosensitizer, and this carboxylic acid makes it easier to dissolve the base polymer, which is used to decompose and remove the photoresist. do. Who are the inventors?

As shown in FIG. 2, it was revealed that the decomposition rate of photoresist slowed down as the concentration of hot sulfuric acid decreased. Additionally, if hot concentrated sulfuric acid is left unused, it absorbs moisture from the atmosphere and the sulfuric acid concentration decreases. The moisture absorption rate of this hot sulfuric acid increases in proportion to the area of contact between the sulfuric acid and the atmosphere (opening area of the container). Therefore, with the method of immersing the Si wafer in hot concentrated sulfuric acid filled in a container, it is difficult to prevent the concentration of sulfuric acid from decreasing.

In the present invention, by storing hot concentrated sulfuric acid in a closed container, sulfuric acid can always be kept at a high concentration. The photoresist on the Si wafer is completely decomposed by heating with a heater to increase the concentration of concentrated sulfuric acid to promote the dehydration and decomposition reaction of the photoresist.After the zero decomposition, pure water is sprayed over the entire surface of the Si wafer while rotating the Si wafer. and wash it away with hot concentrated sulfuric acid containing the decomposed photoresist. Note that the pure water remaining on the Si wafer can be removed from the Si wafer by rotating the Si wafer at high speed.

By the above operations, the remaining photoresist on the Si wafer can be removed with high purity.

〔Example〕

The present invention will be explained in more detail with reference to Examples.

FIG. 1 is an explanatory view showing a cross section of a photoresist removing apparatus which is an embodiment to which the method of the present invention is applied.

By means of a vacuum suction tube 5 provided inside the support base 4.・
,' (Hold the Si wafer 1 horizontally and rotate the support stand 4 while heating the Si wafer 1 to 110° C. with the heater 6 provided on the upper part of the support stand 4. At the same time, open the sealed tank 8.
The concentrated sulfuric acid 9 stored in the tank 8 is heated to about 50°C by the heater 10 installed at the bottom of the tank 8, and then the valve 11 is heated.
was opened, and several mQ of concentrated sulfuric acid 9 was applied to the Si wafer 1 through a nozzle 13 heated to 50° C. by a heater 12.

Close valve 11. After coating, the infrared lamp 7 is turned on to maintain the surface temperature of the Si wafer 1 at 150°C.
The photoresist 3 on the i-wafer 1 is dehydrated and decomposed with 1 sulfuric acid 9. After the treatment, the concentrated sulfuric acid 9 containing the dehydrated and decomposed resist on the Si wafer 1 is washed away by opening the valve 17 with pure water 15 heated by the heater 16 provided at the bottom of the tank 14, and then the support is moved at high speed. After washing with pure water, drain and dry. It depends on the film thickness of the photoresist 3 on the Si wafer 1 and the condition of the photoresist (change in quality due to ion implantation, etc.).

Apply concentrated sulfuric acid to the surface of Si wafer 1 again and wash with pure water.

Repeat the draining and drying process.

Note that the heater temperature used in the embodiment is set at an optimum temperature depending on the film thickness of the photoresist 3, etc.

The pure water 15 for washing away the concentrated sulfuric acid 9 on the Si wafer 1 does not need to be hot water, and a means for improving the cleaning efficiency by applying ultrasonic energy or high pressure to the pure water may be added.

Further, in order to maintain the surface concentration of the Si wafer 1 at a high temperature, a high frequency wave other than the infrared lamp 7 may be used.

〔Effect of the invention〕

Using a photoresist removal apparatus to which the method of the present invention is applied, a comparative evaluation was conducted with the following method of immersion in a sulfuric acid-hydrogen peroxide mixed solution.

The conventional method (method A) of removing photoresist by immersing a Si wafer in a mixed solution of sulfuric acid and hydrogen peroxide involves adding 100 wQ of hydrogen peroxide to 1 liter of sulfuric acid and heating the Si wafer to 120°C. The wafers were immersed and cleaned.In addition, 10 Si wafers were soaked in the same mixture (10 is 6
Each time 50-inch wafers were cleaned, 10 mQ of hydrogen peroxide solution was added and then cleaned. FIG. 3 shows the results of measuring the number of foreign particles reattached to the Si wafer when the photoresist was removed after coating and baking a 1 to 2 μm positive type photoresist on the Si wafer.

In method A (curve a), as the number of Si wafers started increases, the number of foreign particles reattached to the Si wafer also increases. This occurs because the photoresist is not completely decomposed and hydrophobic foreign matter tends to adhere to the Si wafer. By making the Si wafer surface hydrophilic, it is possible to reduce the re-adhesion of foreign matter, but a large-scale effect cannot be expected.

In contrast, in the present invention (curve b), the number of foreign substances adhering to the Si wafer surface can be reduced regardless of the surface condition of the Si wafer or the number of starting lots. The above data shows that the method of the present invention is effective in reducing the number of foreign particles on the Si wafer surface.

Residual (or adsorbed) photoresist on the Si wafer surface when 2 μm of photoresist was coated on the Si wafer and prebaked (90°C) was successively removed using method A and the method of the present invention.
The carbon content was evaluated using an Auger electron analyzer. The evaluation results are shown in Figure 4. When cleaning is performed using Method A, carbon is significantly detected in Si wafers manufactured after the 30th lot. This is considered to be due to deterioration of the decomposition ability over time due to the sulfuric acid concentration decreasing in proportion to the increase in the number of starting lots. On the other hand, in the method according to the present invention, even if 100 lots of Si wafers are started, Si
No carbon was detected in the wafer. The above data shows that the method of the present invention is effective in cleaning the surface of a Si wafer with a high degree of cleaning.

An example will be described in which the method of the present invention is applied to the removal of photoresist into which As ions have been implanted, which was insufficiently removed by Method A. After applying a positive type photoresist to a thickness of 2 μm on a Si wafer and pre-baking it (90°C), As ions were implanted (implantation energy 80KeV, implantation amount 10”, /a#), and then an infrared lamp was injected using the method of the present invention. The decomposition rate (k) of the photoresist was determined when the Si wafer heating temperature was changed by adjusting the light intensity.The measurement results are shown in Figure 5.Increasing the Si wafer heating temperature increases the decomposition rate. Under the conditions of a Si wafer heating temperature of 167° C., it is possible to decompose a 2 μm photoresist in 2 minutes.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a cross section of a photoresist removal apparatus according to an embodiment of the method of the present invention, FIG. Figure 3 is a diagram showing the measurement results of the number of foreign particles reattached to the Si wafer after removing the positive type resist on the Si wafer, and Figure 4 shows the surface of the Si wafer after removing the positive type photoresist on the S1 wafer. FIG. 5 is a diagram showing the results of analysis using an Auger electron analyzer, and FIG. 5 is a diagram showing the results of the decomposition rate of positive type photoresist when the Si wafer heating temperature is changed using the method of the present invention. DESCRIPTION OF SYMBOLS 1... Si wafer, 2... Oxide film, 3... Photoresist, 4... Support stand, 5... Vacuum suction tube, 6, 1
0゜12.16...Heater, 7...Infrared lamp,
8゜14...Tank. 9... Concentrated sulfuric acid. 11°17...Valve. 13°18...Nozzle, 15...Pure water.躬联力 5ε Sea urchin 8 to low I) number (口・・7t) 躬圀石田 連 連 (鑓supply) I (-1 to XIO3)

Claims (1)

[Claims] 1. Apply concentrated sulfuric acid on the photoresist pattern formed by exposing and developing the photoresist film applied on the semiconductor substrate, and heat the semiconductor substrate to a set temperature with a heater to accelerate the decomposition of the photoresist. A photoresist removal method characterized by completely decomposing and removing a photoresist film on a substrate.