JPH0799432B2 - Cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a cleaning method, in particular, a method of immersing in a cleaning liquid such as a photomask, reticle and mask blank used for manufacturing semiconductor ICs, etc. Prevents selective adhesion on the film and improves the cleaning quality of photomasks, reticles, mask blanks, etc., which eliminates dimensional abnormalities and shape defects of patterns transferred onto wafers, and improves the quality of semiconductor ICs. A method for cleaning a sample having a light-shielding film formed on a glass substrate by immersing it in a cleaning solution for cleaning in order to improve the manufacturing yield, and A dummy substrate made of a substance having a high zero charge point and resistance to a cleaning liquid is arranged near the sample for cleaning.

[Industrial application field]

The present invention is a photomask used for manufacturing semiconductor ICs,
The present invention relates to a reticle and a method for cleaning a mask blank by immersing it in a cleaning liquid.

In recent years, with the progress of high integration, a reticle is used to form various patterns in the manufacture of semiconductor ICs, and a method of directly baking a pattern on a silicon wafer or a compound semiconductor wafer by a step-and-repeat method is mainstream. It has become.

Therefore, if a foreign matter having a certain size and a sufficient light-shielding property is attached to the cleaned reticle even at one place, all the wafers having the pattern baked using the reticle will be defective. There is danger. Therefore, when cleaning the reticle, it is necessary to take special care to prevent foreign matter from adhering to it.

[Conventional technology]

FIG. 2 is a schematic configuration diagram of an example of a mask cleaning apparatus conventionally used for cleaning a reticle.

In the figure, 51 is an aqueous solution 52 of, for example, [sulfuric acid (H ₂ SO ₄ ) + hydrogen peroxide (H ₂ O ₂ )] heated to about 80 to 100 ° C.
A chemical cleaning tank using 53, 53 is a rapid water supply / drainage cleaning tank that repeats rapid supply and discharge of pure water 54, 55 is a hot water cleaning tank in which warm pure water 56 heated to, for example, about 50 to 60 ° C. flows, and 57 is a normal temperature An ultrasonic cleaning tank that irradiates ultrasonic waves of about 800 to 1000 KHz while flowing pure water 54, 58 is an intermittent pure water supply port, 59 is an intermittent drainage port, 60 is a warm pure water supply port, 61 is a pure water supply port, Reference numeral 62 is a drain gutter that receives the overflowed pure water, and 63 is an ultrasonic transducer.

Further, FIG. 3 shows an example of a reticle, where 1 is a glass substrate made of transparent quartz or the like, 2 is a film formed by sputtering or the like to a thickness of, for example, about 600 to 700 Å, and a predetermined shape is formed by photolithography. The chrome film pattern 3 which is a light-shielding film patterned in 3 is formed by reactive sputtering on the chrome film in order to prevent reflection and improve wear resistance, and is patterned together with the chrome film.
Indicates a chromium oxide film with a thickness of 400 to 300Å.

In the conventional cleaning method, when cleaning the reticle shown in FIG. 3 using the mask cleaning apparatus shown in FIG. 2, the schematic side cross section of the cleaning jig is shown in FIG. , The reticle 4 is placed on a quartz alignment table 5,
A plurality of sheets are vertically arranged side by side through guide grooves 6 formed in the arranging table 5, and the arranging table 5 is held by a human being or a robot through a quartz handle 7 as shown in the drawing,
The reticle is immersed in the chemical cleaning tank 51, the hot water rapid drainage cleaning tank 54, the warm water cleaning layer 55, and the ultrasonic cleaning tank 57 of the cleaning device (see FIG. 2) for about 5 minutes in order, and after the final ultrasonic cleaning is completed. 4 was placed on the above-mentioned stand 5 and naturally dried.

[Problems to be Solved by the Invention]

However, according to the above-mentioned conventional method, when cleaning or pulling up the reticle, foreign particles (particles) that are usually present at a rate of about 10 particles / ml in pure water are formed on the light-shielding film pattern having a chromium oxide film with a high zero charge point. If the foreign particles are selectively adhered to the pattern edge of the light-shielding pattern, the pattern transferred from the reticle onto the wafer may have abnormal dimensions or defective shape.

This phenomenon is similar not only to the reticle but also to a normal photomask or a mask blank before patterning a light-shielding film. In the photomask, the chip pattern transferred onto the wafer becomes defective, and in the mask blank, the light-shielding occurs. There has been a problem that patterning failure of the film occurs.

Therefore, the present invention prevents foreign particles in pure water from selectively adhering to the light-shielding film to improve the cleaning quality of photomasks, reticles, mask blanks, etc., and thereby the pattern transferred onto the wafer. It is an object of the present invention to improve the manufacturing yield of semiconductor ICs and the like by eliminating dimensional abnormalities and defective shapes.

[Means for Solving the Problems]

The above-mentioned problem is a cleaning method in which a sample having a light-shielding film formed on a glass substrate is immersed in a cleaning liquid for cleaning, and has a higher zero charge point than a substance forming a surface layer of the light-shielding film, Further, it is solved by the cleaning method according to the present invention, in which a dummy substrate made of a substance having resistance to a cleaning liquid is arranged near the sample for cleaning.

[Action]

The zero charge point is the pH value of the solution when the surface concentration difference between the hydrogen ion and the hydroxide ion on the solid surface becomes zero when the solid is immersed in the solution. Therefore, the pH value of the zero charge point is high. The higher the substance, the higher the surface potential when immersed in the solution. The surface of the solid is negatively charged in an aqueous solution having a high pH value and positively charged in an aqueous solution having a low pH value as compared with its zero charge point.

On the other hand, most of the current photomasks, reticles and mask blanks have a light-shielding film made of chromium on a glass substrate made of quartz glass, and on top of that, the surface reflectance of ultraviolet rays is lowered and at the same time chemical resistance and abrasion resistance are also reduced. It has a structure with a chromium oxide film added to improve its properties.

When cleaning the mask, reticle, and mask blank having such a structure, in the pure water cleaning, glass (SiO ₂ ) and chromium oxide are simultaneously present in the pure water. When the zero charge points of both are examined, there is a considerable difference between glass (3.6 pH) and chromium oxide 7.0 (pH). Then, in pure water having a pH value of 7.0, the glass surface is negatively charged, and the potential of the chromium oxide surface is almost zero. On the other hand, foreign particles existing in pure water are mainly negatively charged, and the foreign particles are selectively attached to the chromium oxide film having a large potential difference.

Therefore, in the method of the present invention, a substance such as a metal oxide having a higher zero charge point value than the substance on the light-shielding film, for example, a chromium oxide film, and having resistance to the cleaning liquid, such as aluminum oxide (sapphire). ) Is placed near a mask, reticle, mask blank, etc., and cleaned to remove foreign particles in pure water on the surface of the sapphire substrate that is more positively charged than the surface of the chromium oxide film. The particles are positively sucked and adhered, thereby significantly reducing the amount of foreign particles adhering to the light-shielding film having the chromium oxide film. This improves the manufacturing yield of semiconductor ICs and the like formed by using the mask and reticle, and also improves the yield of the mask and reticle formed by using the mask blanks.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to the drawings with respect to an embodiment.

FIG. 1 is a schematic side cross-sectional view of one embodiment schematically showing a state where hot water washing is performed in the washing apparatus using the method of the present invention. A stand for horizontally supporting and arranging the substrates in parallel, 6 is a guide groove for vertically supporting a plurality of substrates in parallel, 7 is a handle for suspending the stand, and 4 is an insertion support in the guide groove. Reticle, 8 is a dummy substrate made of, for example, aluminum oxide (sapphire) that is inserted and supported in the guide groove, 55 is a hot water washing tank, 56 is hot pure water, and 60 is, for example, 50 to 60 ° C.
Reference numeral 62 denotes a hot pure water supply port, and 62 denotes a drain gutter for receiving the overflowing hot pure water.

As shown in this figure, in the method of the present invention, the dummy substrate 8 made of sapphire or the like and the reticle 4 are alternately mounted in the guide groove 6 of the cleaning arranging table 5 so as to shield the reticle 4 from light. A dummy substrate 8 made of sapphire having a higher equicharge point than the surface layer (chromium oxide film) of the light-shielding film pattern 9 is provided in the vicinity of the film pattern (specifically, for example, a chromium oxide film is deposited on the chromium film pattern) 9. In this state, for example, running water washing with warm pure water 56 is performed for a predetermined time, for example, about 5 minutes. It is appropriate that the distance from the surface of the light-shielding film pattern 9 of the reticle 4 to the dummy substrate 8 is about 1 mm.

As shown in the above examples, in the method of the present invention,
For example, the dummy substrate 8 having a high zero charge point and the reticle 4 are alternately mounted on the arranging table 5, whereby a substance having a high zero charge point is arranged in the vicinity of the light-shielding film 9 of the reticle 4, and the arranging table 5 is placed in this state. The reticle 4 mounted on is immersed in, for example, the chemical cleaning tank 51, the rapid water drainage cleaning tank 53, the warm water cleaning tank 55, and the ultrasonic cleaning tank 57 in the cleaning apparatus shown in FIG. The reticle that has been washed is washed in the dust-free atmosphere while it is still mounted on the arranging table 5 and is naturally dried. As a result of inspecting the surface of the light-shielding film pattern of the reticle washed in this way with a mask surface defect measuring device, the number of foreign particles of 0.2 μmφ or more detected to be attached to the surface is
It is confirmed that the number is about 1 to 2 per square centimeter, and can be reduced to 1/5 to 1/10 as compared with the conventional about 10 pieces.

The dummy substrate is usually made of a metal oxide, but it is desirable that the dummy substrate be crystallized into a transparent glass in order to prevent the cleaning liquid from seeping in.

Further, when the method of the present invention is applied, the type of cleaning liquid contained in the cleaning apparatus and the structure of the cleaning tank are not limited to the types of the above-described embodiments.

Although the method of the present invention has been described for cleaning the reticle in the above embodiments, the method of the present invention is also applicable to cleaning a mask blank having a photomask and a light-shielding film before patterning. Similarly, it is of course possible to greatly reduce the number of adhering foreign particles.

The dummy substrate may be arranged facing the light-shielding film formed on the substrate to be cleaned such as a photomask, a reticle, a mask blank, and so as to be close to the dummy substrate. The arrangement is not limited to the alternating arrangement shown in the embodiment.

〔The invention's effect〕

As described above, according to the method of the present invention, the number of foreign particles adhering to the photomask, reticle, etc. that have been cleaned can be greatly reduced compared to the conventional method, and therefore, transfer onto a wafer using a photomask or reticle. The accuracy of the formed pattern is improved, and the manufacturing yield of semiconductor ICs is improved. Further, the number of foreign particles adhering to the mask blank can be significantly reduced, so that the patterning accuracy of the light-shielding film is improved and a high quality photomask or reticle can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of an embodiment of the method of the present invention, FIG. 2 is a schematic configuration diagram of an example of a mask cleaning apparatus, FIG. 3 is a schematic side sectional view of an example of a reticle, and FIG. 4 is cleaning. It is a schematic side sectional view of a jig. In the figure, 1 is a glass substrate, 2 is a chromium film pattern, 3 is a chromium oxide film, 4 is a reticle, 5 is a stand, 6 is a guide groove, 7 is a handle, 8 is a dummy substrate, 9 is a light shielding film pattern, 51 Is a chemical cleaning tank, 52 is an aqueous solution such as [H ₂ SO ₄ + H ₂ O ₂ ], 53 is a rapid water supply / drainage cleaning tank, 54 is pure water, 55 is hot water cleaning tank, 56 is warm water, 57 is an ultrasonic cleaning tank, Reference numeral 58 is an intermittent pure water supply port, 59 is an intermittent discharge port, 60 is a hot pure water supply port, 61 is a pure water supply port, 62 is a drain gutter, and 63 is an ultrasonic transducer.

Claims (1)

[Claims] 1. A cleaning method in which a sample having a light-shielding film formed on a glass substrate is immersed in a cleaning solution for cleaning, and has a higher zero-charge point than a substance constituting a surface layer of the light-shielding film. ,
In addition, a cleaning method is characterized in that a dummy substrate made of a substance having resistance to a cleaning liquid is arranged in the vicinity of the sample for cleaning.