JP4766836B2 - Photomask substrate cleaning method - Google Patents

Description

The present invention is a photomask substrate, it relates to a spin type cleaning method for cleaning processing while rotating.

  In the manufacturing process of semiconductors and the like, organic substances, dust such as metal, and foreign matters attached to a substrate used for manufacturing semiconductors such as silicon wafers and photomasks are the largest cause of a decrease in manufacturing yield. Therefore, the cleaning process for removing dust, foreign matters, etc. is one of the most important processes in the manufacturing process of semiconductors, etc., and conventionally, there are various methods such as immersion cleaning, spin cleaning, scrub cleaning, brush cleaning, etc. The cleaning method is performed. Among these cleaning methods, immersion cleaning (see, for example, Patent Document 1), which is a method that does not directly damage the substrate without bringing a brush or the like into direct contact with the surface of the substrate used in semiconductor manufacturing, and spin. Type cleaning (see, for example, Patent Document 2) is the most commonly performed method.

Immersion cleaning, which is one of the conventional semiconductor substrate cleaning methods, will be described based on the configuration diagram of a conventional immersion cleaning apparatus shown in FIG. The cleaning treatment is usually performed by a cleaning solution 61 using a high-temperature solution of a mixed solution of sulfuric acid and hydrogen peroxide (referred to as sulfuric acid / hydrogen peroxide) or a mixed solution of aqueous ammonia and hydrogen peroxide (referred to as ammonia / hydrogen peroxide). This is performed by immersing the substrate 63 to be cleaned in the cleaning tank 62 filled with the above. Foreign matter such as dust on the surface of the immersed substrate 63 is dissolved in the cleaning liquid 61 and removed. The cleaning liquid 61 is constantly circulated by a pump 64 and is filtered by a filter 65 so as to maintain a certain degree of cleanliness.
However, it is difficult to completely remove the contaminants brought into the cleaning treatment tank 62 by the substrate 63 to be cleaned only with the circulation filtration, and the immersion cleaning method has a principle of re-contamination after cleaning the substrate 63 in principle. Have.

In order to improve the above-mentioned problem of substrate recontamination, a spin-type cleaning method is performed. For example, FIG. 7 shows a cross-sectional view of a conventional spin cleaning apparatus. In the spin cleaning apparatus shown in FIG. 7, the substrate 71 to be cleaned is held in a horizontal state on a substrate holding jig 73 installed on a rotation shaft 72 of the apparatus. The substrate 71 rotates about the center of the substrate, and the cleaning liquid 75 blown out from the nozzle 74 is discharged onto the rotating substrate 71, dissolves the foreign matter on the substrate 71, and is discharged out of the substrate 71 by centrifugal force. In this case, since the cleaning liquid 75 is basically disposable, there is no problem of recontamination of the substrate 71. In the above, the cleaning liquid 75 is discharged onto the substrate 71 at room temperature or heated. Further, during the cleaning of the substrate surface, the back surface side of the substrate 71 is cleaned with ultrapure water 76 at room temperature as necessary.
JP-A-5-343379 JP 2002-198345 A

  The conventional immersion cleaning described above has an advantage of high cleaning ability because it can be processed for a long time with a strong cleaning solution at a high temperature and a high concentration. However, on the other hand, the contamination brought about by the substrate to be cleaned accumulates in the cleaning treatment tank, and the problem of reattachment occurs that contaminates the clean substrate. In addition, a large amount of cleaning liquid is required to fill the cleaning tank and the circulation system of the cleaning liquid with the cleaning liquid. Therefore, a certain amount of high-temperature cleaning liquid is used for several days. For this reason, deterioration of the cleaning liquid becomes a problem.

  In the conventional spin cleaning, it is necessary to keep supplying the cleaning liquid to the substrate surface during the cleaning process. For this reason, when the cleaning liquid is made disposable, it is practically impossible to perform the treatment for a long time with the high temperature cleaning liquid. In order to solve this problem, there is a method of collecting and reusing the cleaning liquid, but even in this case, when the cleaning liquid is recovered, foreign substances such as dust that dissolves in the cleaning liquid or floats in the cleaning liquid are completely removed. Separation from the cleaning liquid may be structurally difficult, and the advantages of the spin cleaning are lost, resulting in the deterioration of the cleaning liquid similar to the immersion cleaning and the problem of redeposition due to contamination of the cleaning liquid.

  The present invention is for solving the above-mentioned problems, and has a high cleaning ability with a small amount of cleaning liquid when cleaning a substrate used for manufacturing a semiconductor such as a silicon wafer or a photomask. It is an object of the present invention to provide a cleaning method and a spin type cleaning apparatus with very little reattachment to a substrate.

The method for cleaning a semiconductor substrate of the present invention, washing a photomask substrate in the same spin table, in the cleaning method of a photomask substrate using the cleaning apparatus of spinning to drying at normal temperature on a surface of the substrate to low-speed rotation A small amount of the cleaning liquid is dropped from the nozzle on the top of the substrate to the center position of the substrate to spread it evenly on the surface of the substrate and prevent the cleaning liquid from splashing from the top of the substrate so that the cleaning liquid is accumulated on the surface of the substrate. And a jig that rotates at a low speed while the cleaning liquid is accumulated on the substrate surface, supplies high-temperature ultrapure water to the back surface of the substrate, has a flat lower surface, and can maintain the lower surface at a high temperature. In the vicinity of the cleaning liquid on the substrate, and the substrate and the cleaning liquid are heated to a high temperature and held for a certain period of time to clean the substrate surface, and after the cleaning process for a certain period of time, Supplying ultrapure water from the upper plate, wash away the cleaning solution cleaning solution is disposable, and a third step of removing, from the first step to the third step is repeated by switching the washing liquid It is what I did.
In the method for cleaning a semiconductor substrate according to the present invention, the cleaning liquid used for switching is sulfuric acid / hydrogen peroxide and ammonia / hydrogen peroxide.

The spin cleaning apparatus according to the present invention holds a substrate used for semiconductor manufacturing, and has a nozzle for supplying ultrapure water from below the substrate and a nozzle for supplying a cleaning liquid from above the substrate, The spin cleaning apparatus for cleaning and drying the substrate has a mechanism for heating the substrate from above.
In the spin cleaning apparatus according to the present invention , the mechanism for heating the substrate from above is a jig having a flat lower surface and capable of holding the lower surface at a high temperature.

According to the cleaning method of the present invention, unlike the conventional spin cleaning method, it is not necessary to continuously supply a high temperature cleaning liquid during the substrate cleaning process, and it is possible to continue supplying the heat source as a high temperature supplied from the back surface. Only ultrapure water is required. Therefore, long-time processing is possible without consuming a large amount of cleaning liquid. In addition, since the cleaning liquid is not used in a circulating manner, a new liquid is disposed for each substrate, so that the cleaning liquid is not deteriorated. Furthermore, since the cleaning liquid is not heated in advance before the cleaning process and is maintained in an inactive state at room temperature, the deterioration of the cleaning liquid over time can be minimized. As described above, it is possible to realize a cleaning method that has an extremely high cleaning ability that is higher than that of the immersion type cleaning method and that has very little foreign matter reattachment, which is an advantage of the spin type cleaning method.
The configuration of the cleaning apparatus of the present invention eliminates the need for a temperature control and circulation apparatus for the cleaning liquid, reduces the introduction cost and maintenance of the apparatus, and reduces the cost of the substrate cleaning process.

The substrate to be cleaned in the present invention is not limited to a substrate used for a semiconductor such as a silicon semiconductor substrate, a compound semiconductor substrate, a photomask blank substrate, or a photomask substrate, but a liquid crystal display substrate, an electronic component mounting substrate, or the like is also used. be able to.
The best mode for carrying out the present invention will be described below with reference to the drawings.

(First embodiment)
1 to 4 are schematic cross-sectional views showing processing steps of the substrate cleaning method according to the present invention. 1 to 4, the same reference numerals are used to indicate the same parts.
FIG. 1 is a cross-sectional view showing a state before the cleaning process. A substrate 12 to be cleaned is placed on the spin cleaning apparatus 11. The substrate 12 is held in a horizontal state so as not to move during rotation by a substrate holding jig 14 such as a stopper provided on the spin table 13. The substrate holding jig 14 is provided with a space so that the center of the substrate 12 is the center of the rotation axis, the substrate is held horizontally, and the back surface of the substrate can be cleaned with ultrapure water. Subsequently, while rotating the substrate 12 at a low speed, room-temperature ultrapure water 16 is supplied from the back surface nozzle 15 provided on the spin rotation shaft to the back surface of the substrate. The reason why ultrapure water 16 is supplied to the back surface of the substrate is that a part of the cleaning liquid may go around from the front surface side to the back surface, and a trace due to the dirty cleaning solution may remain on the back surface. This is because it is a source of contamination in the next process, and therefore it is preferable to perform the backside cleaning of the substrate.
The rotational speed of the low-speed rotation is preferably set to about several rpm to several tens rpm in accordance with the next dropping of the cleaning liquid.
Although not shown, it is usually preferable to install the spin cleaning apparatus 11 in a cleaning chamber.

Next, as shown in FIG. 2, the cleaning liquid dropping step, while the spin table 13 is rotated at a low speed, a room-temperature cleaning liquid 21 is dropped on the surface of the substrate 12 so as to rise on the surface of the substrate 12. Spread evenly on the surface. The rotation speed of the low-speed rotation is several rpm to several tens of rpm in order to spread the cleaning liquid uniformly on the substrate and prevent the cleaning liquid from splashing from the substrate when the cleaning droplet is dropped, and to keep the cleaning liquid on the substrate. However, it is preferable.
As the cleaning solution 21 used in the present invention, a chemical solution such as sulfuric acid / hydrogen peroxide or ammonia / water that is usually used for substrate cleaning is used. As the sulfuric acid perwater, for example, a cleaning solution containing about 0.1 to 0.25 of 30% hydrogen peroxide water with respect to 96% sulfuric acid 1 by volume is used. A cleaning solution containing 1% 30% hydrogen peroxide and 5 to 10 pure water with respect to 28% aqueous ammonia solution 1 is used.
The amount of the cleaning liquid 21 to be dripped only needs to spread uniformly over the entire surface of the substrate, and depends on the size and shape of the substrate to be cleaned, the surface tension of the cleaning liquid, and the like. For example, a 6-inch square photomask substrate If so, it can be spread evenly over the entire surface with several tens of ml.
When the cleaning liquid 21 is dripped, the ultrapure water 16 at room temperature is continuously supplied to the back surface side of the substrate 12 to keep the back surface of the substrate 12 clean. In the present invention, this process is the first process.

  Next, as shown in FIG. 3, the substrate is rotated at a low speed with the cleaning liquid on the surface of the substrate, while high-temperature ultrapure water 31 is supplied to the back surface of the substrate, and the substrate 12 and the substrate are placed on the substrate 12 and the substrate. The accumulated cleaning liquid 32 is held for a certain time while being heated. At this stage, the cleaning liquid 32 such as sulfuric acid / hydrogen peroxide accumulated on the substrate surface is in a high temperature active state, and the high temperature cleaning liquid 32 efficiently dissolves contaminants such as organic substances, metals, and foreign matters adhering to the substrate 12. To do. As the temperature of the high-temperature ultrapure water 31, the higher the temperature, the higher the effect of heating the substrate 12 and the cleaning liquid 32 on the substrate, and a temperature range of about 60 ° C. to 95 ° C. is more effective, and 80 ° C. -90 degreeC is more preferable. The temperature of the heated cleaning liquid 32 is preferably about 40 ° C to 90 ° C. The time for holding the high temperature cleaning liquid 32 on the substrate 12 for a certain period of time is determined in consideration of the temperature of the cleaning liquid 32, the degree of contamination of the substrate 12, the cleaning effect, production efficiency, and the like, and must be strictly controlled. However, for example, when sulfuric acid / hydrogen peroxide at 80 ° C. is used, a time range of about 3 to 10 minutes can be applied. In the present invention, this step is the second step.

Next, as shown in FIG. 4, the rinsing process after the cleaning process, after the cleaning process for a certain time, while the substrate 12 is rotated at a low speed, the room-temperature ultrapure water 41 is supplied onto the surface of the substrate 12. Is thoroughly rinsed with ultrapure water 41, and a cleaning solution such as sulfuric acid / hydrogen peroxide containing contaminants is washed out of the substrate 12 from the substrate surface. The number of rotations at low speed is preferably about several tens of rpm. In the present invention, this step is the third step.
Next, for example, the substrate 12 is dried by spin drying by high-speed rotation, and the substrate cleaning process is completed.
By using the cleaning method with high cleaning ability of the present invention, a substrate used for a high-quality semiconductor without reattachment of foreign matters can be obtained, and since the cleaning liquid is kept at room temperature, the deterioration of the liquid over time can be achieved. Few.

In this onset Ming, after the rinsing step shown in FIG. 4, by switching the washing liquid, repeat from the first step of the up third step.
For example, if the first cleaning solution is sulfuric acid / hydrogen peroxide, the second cleaning solution can be used by switching to another cleaning solution such as ammonia water, and after a series of cleaning processes, the substrate is dried to complete the substrate cleaning process. Applicable.
In this case, the substrate surface cleaning nozzle may be used by switching the cleaning liquid with a single nozzle, or two or more nozzles may be provided and switched for each cleaning liquid.
By switching and using different cleaning liquids, it becomes possible to remove dirt that is difficult to clean with only one type of cleaning liquid, and a higher cleaning effect can be obtained.

In the second step of the present invention, as shown in FIG. 5, using a spin cleaning apparatus 51 of the present invention also comprises a heating mechanism on the surface side of the substrate 12, the washing liquid was piled on the base plate 12 32 It also heated from the top.
The heating mechanism on the substrate surface side can be performed by a heating method using a radiant heat source such as an infrared lamp, or a heating method using close contact with a high temperature plate or the like.
The latter heating method will be further described with reference to FIG.

FIG. 5 shows a spin cleaning apparatus 51 according to the present invention , in addition to heating the substrate 12 and the cleaning liquid 32 on the substrate 12 from the back surface side of the substrate 12 by the high-temperature ultrapure water 31, heating from the front surface side of the substrate 12. This shows the state of performing. After depositing the cleaning liquid on the substrate surface, a plate 52 having a chemical lowering surface such as quartz and having a flat lower surface and a mechanism 53 for heating the surface is brought close to the surface of the substrate 12, for example, at a position about 2 mm away. ,Deploy.
When the plate 52 is installed on the upper part of the substrate, the cleaning liquid spreads in the gap between the upper plate 52 and the surface of the substrate 12, becomes the high-temperature cleaning liquid 32 by the heating from the back side of the substrate and the heat of the plate 52. The effect is increased.
The plate 52 can be maintained at a high temperature of 40 ° C. or higher by making the inside of the plate 52 have a structure in which temperature-controlled water having a high temperature of about 80 ° C. flows to form the heating mechanism 53.
In this embodiment, as compared with the case of heating only from the back surface of the substrate, the substrate surface is also heated and a higher cleaning effect is obtained.

( Reference Example 1 )
A 6-inch square photomask substrate to be cleaned is placed on a spin-type cleaning device, and the substrate is rotated at a low speed of 30 rpm. About 50 ml of sulfuric acid / hydrogen peroxide at room temperature (96% sulfuric acid: 30% hydrogen peroxide solution = 5: 1) was dropped from the nozzle as a cleaning solution so that the surface was evenly spread over the substrate surface. .
As it is, the cleaning liquid is rotated at a low speed of 10 rpm on the surface of the substrate, while ultrapure water at 80 ° C. is supplied to the back surface of the substrate and held for 10 minutes while heating the substrate and the cleaning liquid.
At this stage, the sulfuric acid / hydrogen peroxide accumulated on the surface became active and dissolved contaminants on the substrate such as organic matter, metal and foreign matter.
Next, ultrapure water at room temperature was supplied from the top of the substrate, and sulfuric acid / hydrogen peroxide containing contaminants was washed out to the outside of the substrate by rotating at a low speed of 50 rpm.
After sufficiently rinsing and removing sulfuric acid from the substrate surface, the substrate was dried by high-speed spin drying to complete the cleaning process, and the substrate was taken out from the cleaning apparatus.
By the cleaning method of this reference example, a high-quality photomask substrate without reattachment of foreign matters was obtained.

Example 1
In this embodiment, the cleaning liquid is switched.
In the same process as in Example 1, a 6-inch square photomask substrate was washed with sulfuric acid / hydrogen peroxide (96% sulfuric acid: 30% hydrogen peroxide solution = 5: 1 by volume), and rinsed with ultrapure water. After that, the substrate was cleaned using ammonia overwater (28% aqueous ammonia solution: 30% hydrogen peroxide solution: pure water = 1: 1: 5 by volume) as the second cleaning solution.
In the case of this example, foreign matter that could not be removed by washing with sulfuric acid / hydrogen peroxide alone was also washed away with ammonia / hydrogen peroxide, and a high-quality photomask substrate was obtained.

(Reference Example 1)
The silicon wafer substrate having a diameter of 8 inches to be cleaned, is placed on a spin type cleaning device according to the present onset bright, by low-speed rotating the substrate at 25 rpm, while supplying ultrapure water at room temperature from the back nozzle on the back surface of the substrate About 60 ml amount of sulfuric acid / hydrogen peroxide at room temperature was dropped from a nozzle provided on the top of the substrate so as to swell on the surface of the substrate, and spread uniformly on the surface of the substrate.
Next, the substrate is rotated at a low speed of 10 rpm while the cleaning liquid is piled up on the surface of the substrate, ultrapure water of 80 ° C. is supplied to the back surface of the substrate, and the substrate is heated from the lower side, while having a flat lower surface, A quartz plate with a structure in which high-temperature water at a high temperature of about 80 ° C. flows is placed close to the substrate surface, at a position of about 2 mm from the cleaning solution on the substrate, and the substrate and the cleaning solution are placed from above. Was also heated and held for 10 minutes.
At this stage, the sulfuric acid / hydrogen peroxide accumulated on the surface became active and dissolved contaminants on the substrate such as organic matter, metal and foreign matter.
Next, the plate was removed, ultrapure water was supplied from the upper part of the substrate, and sulfuric acid / hydrogen peroxide containing contaminants was washed out to the outside of the substrate by rotating at a low speed of 50 rpm.
After sufficiently rinsing with ultrapure water to remove sulfuric acid from the substrate surface, the substrate was dried by high-speed spin drying, the cleaning process was completed, and the substrate was taken out of the cleaning apparatus.
In the cleaning method of this example using the spin cleaning apparatus according to the present invention, a high-quality silicon wafer substrate without reattachment of foreign matters was obtained.

Sectional drawing which shows before the cleaning process of the cleaning method of the present invention Sectional drawing which shows the washing | cleaning droplet lowering process of the washing | cleaning method of this invention Sectional drawing which shows the washing process process of the washing | cleaning method of this invention Sectional drawing which shows the rinse process after the washing process of the washing | cleaning method of this invention Sectional drawing which shows another form of the washing | cleaning process of the washing | cleaning method of this invention, and the spin type cleaning apparatus of this invention Configuration of conventional immersion cleaning equipment Cross-sectional view of a conventional spin cleaning device

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Spin type cleaning apparatus 12 Substrate 13 Spin table 14 Substrate holding jig 15 Back surface nozzle 16 Room temperature ultrapure water 17 Nozzle 21 Room temperature cleaning liquid 31 High temperature ultrapure water 32 High temperature cleaning liquid placed on substrate 41 Room temperature ultra high temperature Pure water 51 Spin cleaning device 52 Plate 53 Heating mechanism 61 Cleaning liquid 62 Cleaning treatment tank 63 Substrate to be cleaned 64 Pump 65 Filter 66 Heater 71 Substrate to be cleaned 72 Rotating shaft 73 Substrate holding jig 74 Nozzle 75 Cleaning liquid 76 Ultrapure water at room temperature

Claims (2)

In a photomask substrate cleaning method using a spin-type cleaning apparatus that cleans and dries a photomask substrate on the same spin table , a normal temperature cleaning solution is applied to the surface of the substrate rotating at a low speed from a nozzle on the top of the substrate. A first step of dropping a small amount on the substrate, spreading it uniformly on the substrate surface, preventing the cleaning liquid from splashing from the substrate, and depositing the cleaning liquid on the substrate surface; and depositing the cleaning liquid on the substrate surface. While rotating at a low speed in the state, supplying high-temperature ultrapure water to the back surface of the substrate, and having a flat lower surface, a jig capable of holding the lower surface at a high temperature is brought close to the cleaning liquid on the substrate, A second step of cleaning the substrate surface by heating the substrate and the cleaning liquid for a predetermined time while heating to a high temperature; and after the cleaning process for a predetermined time, supplying ultrapure water from above the substrate; Wash the disposable wash away washing liquid, a third and a step, from the first step to the third step, the method of cleaning the photomask substrate and repeating to switch the cleaning liquid to be removed . 2. The method for cleaning a photomask substrate according to claim 1, wherein the cleaning liquid used for switching is sulfuric acid / hydrogen peroxide and ammonia / hydrogen peroxide.

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