JP2009251243A - Method of removing pellicle adhesive residue - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To completely remove the residue of a pellicle adhesive made of a silicone resin without damaging a mask pattern of a mask substrate. <P>SOLUTION: After the residue of the pellicle adhesive is treated with an alkali solution, the residue is treated using an acid solution containing sulphuric acid and removed. It is preferred that the alkali solution is an ammonia solution or TMAH solution and the concentration of the alkali solution is not less than 1% by mass. It is further preferred that the concentration of the sulfuric acid solution is not less than 5% by mass and oxygenated water of 30% by mass is added to the sulfuric acid solution at a volume ratio of 1 to 50%. Further, respective treatment temperatures are preferably not lower than 50°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to removing an adhesive residue remaining on a mask substrate when the pellicle is peeled from the mask substrate.

Semiconductor devices have been increasingly integrated and miniaturized recently, and now ArF (λ = 193 nm) exposure is used for the most advanced device fabrication. This ArF exposure is used in combination with a liquid immersion method, a double exposure method, or the like, and is considered to be the main force for manufacturing advanced devices for a while.
If foreign matter such as particles generated in the exposure system reaches the mask pattern, it will cause an abnormality in the projected pattern on the wafer, and as long as the foreign matter stays on the mask, it will cause a serious problem that defective patterns will continue to be produced. In order to protect the photomask, a thin organic film called a pellicle is currently attached via a peripheral frame at a position several mm away from the pattern on the mask (see FIG. 1A).

Usually, the pellicle has a structure stretched in a rectangular frame, and is attached to a quartz glass mask via an adhesive. However, in the production of advanced devices, it is considered that organic substances (outgas) and foreign matters generated from the adhesive are also involved in the yield reduction.
An acrylic resin is generally used as an adhesive for the pellicle, but there is a concern that outgas may be generated from the acrylic resin, which may cause a problem in the manufacture of advanced devices. There are silicone-based resins as chemically stable adhesives, but silicone resins are generally known as stable materials in various chemicals and harsh environments. I can say that.

However, there are situations where the stability of the silicone resin becomes a problem. The pellicle may be replaced at a certain period or frequency. In this case, it is necessary to remove the pellicle frame from the mask substrate. Since the silicone resin has a chemically stable property, a silicone residue may remain on the mask when the frame is peeled off (see FIG. 1C).
Silicone resins are also known to vitrify as they are exposed to ultraviolet rays, and there is an aspect that the vitrification makes it more difficult to remove.
Because it is a chemically stable material, it is difficult to remove it if it remains, and a mask that has a fine pattern is a method that changes the shape of the pattern even though it removes the remaining residue. (Hydrogen fluoride treatment, etc .: melting quartz) cannot be employed.

Also, NaOH and KOH treatment, which is known as a method for removing a silicone resin, can cause small mobile ions such as Na and K to remain in the quartz mask during cleaning or diffuse near the surface during subsequent device processes. In addition, there is a possibility that it may diffuse into the exposure apparatus, making it difficult to adopt.
Conventionally, a peeling method has been proposed in which a temperature difference is provided between the pellicle frame and the photomask when the pellicle frame is attached, the photomask is set to a high temperature, and the pellicle frame is set to a low temperature so that no adhesive residue remains on the photomask side. However, when the adhesive is a silicone resin, it is not effective as a peeling method because it has a property stable to high and low temperatures.

JP 2008-32981 A

  In view of the above circumstances, an object of the present invention is to completely remove a pellicle adhesive residue made of a silicone resin without damaging the mask pattern of the mask substrate.

  The method for removing a pellicle adhesive residue according to the present invention is characterized in that the pellicle adhesive residue is removed by treatment with an acid solution containing sulfuric acid after treatment with an alkaline solution. It is preferable that the alkaline solution is an aqueous ammonia solution or a TMAH solution, and the concentration of the alkaline solution is 1% by mass or more. Further, the concentration of the sulfuric acid solution is preferably 5% by mass or more, and 30% by mass of hydrogen peroxide water is preferably added to the sulfuric acid solution in a volume ratio of 1 to 50%. Each of them is preferably 50 ° C. or higher.

  According to the present invention, it is possible to completely remove the adhesive residue remaining on the mask substrate without worrying about damage or alteration of the mask pattern on the mask substrate.

As a result of diligent research, the present inventor has reached the following knowledge. First, as a method for removing the silicone resin residue, CMOS compatible processing is essential. That is, it is essential to perform treatment with a chemical solution generally used for cleaning a semiconductor wafer and the like without containing alkali, alkaline earth or other metal ions. A method for removing the silicone residue was examined while maintaining this premise. The method is to replace the remaining silicone resin with ammonia compatible with CMOS or TMAH (Tetramethyl).
High temperature alkali treatment with ammonium hydroxide). With this alone, the residue can hardly be removed and there is no significant change in appearance, but this is a method in which the residue is completely removed by high-temperature treatment with an acid such as sulfuric acid.

This mechanism is estimated as follows. A siloxane bond (—Si—O—Si—), which can be said to be a skeleton of the silicone resin, is subjected to an alkali treatment to dissociate this bond (—Si—O—R + HO—Si—: R is a cation). Subsequently, the weakened silicone resin is completely removed by performing high-temperature sulfuric acid treatment. In this case, the effect can be expected even if hydrogen peroxide is added to sulfuric acid. This is a method widely used for removing organic contaminants from semiconductors as sulfuric acid hydrodehydration (also called SPM cleaning or piranha cleaning).
Hereinafter, the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is an explanatory schematic diagram showing that adhesive residue remains due to peeling of the pellicle, (a) is an explanatory schematic diagram showing a mask substrate system on which the pellicle is mounted, (b) is a partially enlarged view thereof, and (c). FIG. 4 is an explanatory schematic view showing that an adhesive residue is generated by peeling the pellicle. FIG. 2 is an explanatory schematic diagram for explaining a method for measuring an adhesive residue. FIG. 3 is a graph showing the state of the residue after treatment in Experimental Example 1.
The pellicle 1 in which the pellicle film 2 is fixed to the pellicle frame 3 is masked by a pellicle adhesive 6 so as to cover a mask pattern (metal pattern) 5 formed on the mask substrate (quartz substrate) 4. 4 (FIG. 1A). When the pellicle 1 is peeled off from the mask substrate 4, a part of the pellicle adhesive 6 remains as an adhesive residue 7 (FIG. 1C).

The adhesive residue 7 remaining on the pellicle frame 3 can be removed by appropriate measures including mechanical measures if necessary, but the adhesive residue 7 remaining on the mask substrate 4 The mask substrate 4 needs to be removed without affecting the mask substrate 4.
The presence / absence / amount of the adhesive residue 7 remaining on the mask substrate 4 can be confirmed by, for example, the measurement method shown in FIG. According to the measurement method shown in FIG. 2, it is confirmed by scanning the contact distance measuring terminal 8 provided with a proximity distance sensor for measuring the contact distance across the pellicle adhesion mark 9.

[Experimental example]
A pellicle frame was attached to the front side of the quartz mask substrate via a silicone resin, and the adhesive surface was irradiated with ultraviolet rays from the back side of the quartz substrate. Thereafter, the frame was peeled off from the quartz substrate, and the following treatment was performed to remove the residue.
Reference: No treatment 1: Treatment at 80 ° C. 30% sulfuric acid treatment for 30 minutes only 2: Treatment with 5 mass% NH ₄ OH treatment for 10 minutes (80 ° C.) + 30% sulfuric acid treatment for 30 minutes (80 ° C.)
Treatment 3: 5% by mass NH ₄ OH treatment 30 minutes (80 ° C.) + 30% sulfuric acid treatment 30 minutes (80 ° C.)
Treatment 4: 5% by mass NH ₄ OH treatment 120 minutes (80 ° C.) + 30% sulfuric acid treatment 30 minutes (80 ° C.)

  After the treatment, the cross-sectional shape of the portion where the residue remained before the treatment was observed with a step gauge. The results are shown in FIG. As a result, the residue was not completely removed only by the sulfuric acid treatment (treatment 1). However, in the ammonia treatment + sulfuric acid treatment, it can be seen that the residue is removed as the ammonia treatment time becomes longer. As a result, substantially no residue was observed in treatments 3 and 4. In addition, in an accompanying experiment of this experiment, it was experimentally found that the ammonia concentration / temperature at which the effect can be confirmed is 1 mass% or more and 50 ° C. or more.

[Experimental example 2]
An experiment similar to Experimental Example 1 was performed using TMAH instead of ammonia. As a result, no residue was observed when the concentration of TMAH was 3 mass%, the temperature was 80 ° C., and the treatment time was 4 hours.
Basically, in the present invention, dilute solution and low-temperature treatment are effective in alkali treatment and sulfuric acid treatment, but in this case, treatment for a very long time is required, which is not practical. As a practical range, the ammonia concentration and temperature were 1% by mass or more and 50 ° C. or more, and TMAH was 0.5% by mass or more and 50 ° C. or more. Further, it is considered empirically appropriate that the concentration / temperature of sulfuric acid is 1% by mass or more and 50 ° C. or more.

It is explanatory explanatory drawing which shows that an adhesive residue remains by peeling of a pellicle, (a) is an explanatory schematic diagram which shows the mask substrate system which attached the pellicle, (b) is the elements on larger scale, (c) is by pellicle peeling It is an explanatory schematic diagram showing that an adhesive residue is generated. It is an explanatory schematic diagram showing an example of a method for measuring an adhesive residue. 6 is a graph showing a state of a residue after treatment according to Experimental Example 1.

Explanation of symbols

1: Pellicle 2: Pellicle film 3: Pellicle frame 4: Mask substrate 5: Mask pattern (metal pattern)
6: Pellicle adhesive 7: Adhesive residue 8: Separation distance measuring terminal 9: Frame mark

Claims (10)

  A method for removing a pellicle adhesive residue, comprising: removing a residue after peeling of a pellicle frame adhered using a silicone resin by treating with an acid solution containing sulfuric acid after treating with an alkaline solution.   2. The method for removing a pellicle adhesive residue according to claim 1, wherein the alkaline solution is an aqueous ammonia solution.   3. The resin removal method for a pellicle adhesive residue according to claim 2, wherein the concentration of the aqueous ammonia solution is 1% by mass or more.   The method for removing a pellicle adhesive residue according to claim 2 or 3, wherein the treatment temperature with the aqueous ammonia solution is 50 ° C or higher.   The method for removing a pellicle adhesive residue according to claim 1, wherein the alkaline solution is a TMAH solution.   The method for removing a pellicle adhesive residue according to claim 5, wherein the concentration of the TMAH solution is 0.5% by mass or more.   The method for removing a pellicle adhesive residue according to claim 5 or 6, wherein a treatment temperature with the TMAH solution is 50 ° C or higher.   The method for removing a pellicle adhesive residue according to any one of claims 1 to 7, wherein the concentration of the sulfuric acid solution is 5% by mass or more.   The method for removing a pellicle adhesive residue according to claim 8, wherein the temperature of the sulfuric acid solution is 50 ° C or higher.   The method for removing a pellicle adhesive residue according to claim 8 or 9, wherein 30% by mass of hydrogen peroxide water is added to the sulfuric acid solution in a volume ratio of 1 to 50%.

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