JPS6053457B2 - Photomask manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photomask for exposure in photolithography technology which is widely used in fields such as the semiconductor industry.

It is particularly useful for pattern contact exposure methods in photolithography technology.

Conventionally, photomasks for exposure have generally been made by coating a glass substrate with an emulsion containing silver particles or a thin film of chromium, chromium oxide, iron oxide, silicon, etc. in a desired pattern as a light shielding part. It is used.

When contact exposure is performed using such an exposure photomask, the following problems occur.

When a photoresist film is formed on a desired substrate and a photomask for exposure is placed in close contact with it, there are problems such as the photoresist film adhering to the photomask and peeling, or the photomask and the substrate to be processed being stuck together and being unable to be separated. It is. These directly reduce the yield of the product. In general, adhesion is a phenomenon that is controlled by the strength of the interaction between different objects, so in order to weaken the adhesion, it is sufficient to weaken the interaction at the interface between the objects.

The strength of the interaction is evaluated by the surface free energy of the substances that make up the interface and the stabilization free energy at the interface. Conventionally, attempts have been made to lower the surface free energy of a photomask to weaken its adhesion to a photoresist.

Typical methods include a method of forming an organic film on the surface of the photomask, and a method of bonding an alkoxy group of alcohol or a silane derivative such as hexamethyldisilazane to the hydroxyl group on the surface of the photomask. It is known that photomasks manufactured by these methods are significantly less likely to destroy the photoresist due to adhesion to the photoresist. As such a known example,
For example, JP-A-2227@, JP-A-49-1054
6 Wani, JP-A-50-120975, JP-A-51-13
There are issues such as No. 926. However, the above method has the following drawbacks.

1 In the method of forming an organic film on the photomask surface, the organic film peels off from the photomask during repeated mask alignment because the adhesion between the organic film and chromium, etc. that form the mask pattern of the photomask is weak. However, it is unsuitable for mass production. 2. In the method of bonding reactive organic substances with hydroxyl groups on the photomask surface, the reactivity of the hydroxyl groups on the glass of the photomask and the hydroxyl groups on chromium and other substances forming the light-shielding parts is different; It is difficult to bond attachment groups uniformly to the surface.

Moreover, hydroxyl groups present on substances other than glass generally have poor reactivity, and it is not possible to sufficiently lower the energy of the surface. The present invention compensates for the drawbacks of the prior art described above and provides a new technique for manufacturing a photomask that is difficult to adhere to a photoresist. It is desirable that a photomask that is difficult to adhere to a photoresist satisfies the following requirements.

That is, 1. Having uniform surface free energy over the entire surface in contact with the photoresist. 2. The surface free energy must be as low as possible, and no new interactions will be induced upon contact with the photoresist.

3.The effect can be sustained sufficiently.

4.No deterioration in characteristics as an exposure mask.

In order to achieve such an object, the present invention takes the following steps.

A transparent dielectric film is deposited by sputtering on the surface of the photomask where the pattern is formed. FIG. 1 shows a cross-sectional view of a photomask. 1 is a photomask substrate, 2
3 is a thin film forming the light shielding portion t, and 3 is a transparent dielectric film formed by sputtering.

Next, a surface treatment is performed so that the surface free energy of the surface of this dielectric film is lower than the surface free energy of the substrate to be processed. More specifically, in a photomask manufacturing method in which a transparent dielectric film made of an oxide is formed by sputtering on a surface of a predetermined photomask substrate on which a mask pattern is formed, the transparent dielectric The thickness of the body film is set to 10 to 30 nWi, and then surface treatment is performed to make the surface free energy of the transparent dielectric film surface lower than the surface free energy of the surface in contact with the photoresist of the processing substrate.

As a sputtering target for forming a transparent dielectric film, fused silica, Corning No. 0080:
Soda Lime, Company 7740: Pyrex, Company 70
59, 7913: It is preferable to use Vycor, phosphorus glass, alumina, or the like.

Silicon oxide is particularly useful because the dielectric film is transparent to visible light or ultraviolet light, has strong adhesion to the photomask, and is useful for making surface treatments effective on the surface of the dielectric film. It is. The sputtering method may be performed by following a well-known method, but it is important to include a small amount of oxygen (02) in the atmosphere. The atmospheric gas for sputtering is preferably a rare gas, such as argon (Ar).
), krypton (Kr), etc. are used extensively, and the pressure is 5×10-1 Pa ~
About 5×10) Pa is introduced. In this case, 02 gas is A
A suitable proportion is 0.1 to 10% relative to r gas. The reason for adding oxygen gas is to prevent oxygen loss when the dielectric target material is deposited into a film. The thickness of the transparent dielectric film is preferably 10 to 30 nTr1.

The reason for this is that when the film thickness is increased, the surface of the transparent dielectric film causes irregular reflections, and depending on the film thickness, interference effects occur. The following methods are available as surface treatment methods for making the surface free energy of the surface of the dielectric film lower than the surface free energy of the substrate to be processed.

(1) A method in which a sample substrate is exposed to silane derivative vapor. As a silane derivative, hexamethyldisilazane (
(CH3)3SiNHSi(CH3)3, )trimethylchlorosilane ((CH3)3SiC), dimethyldichlorosilane ((C)2SiC12), methyltrichlorosilane ((CH3)SiCl3), etc., R, SiNH
SiR, and RnSiCl4-. Here, R represents an alkyl group CnH2n+1. There is a compound represented by the general formula: Appropriate atmosphere temperature is 20 to 200°C, and processing time is approximately 3 to 3 times. (2) A method of exposing a sample substrate to a plasma atmosphere containing vapor or gas of a predetermined organic substance.

As specific examples, the use of primary, secondary, and tertiary alcohols, fluorinated alcohols, freon, etc. shows remarkable effects. (
3) A method of applying reflux treatment with alcohol.

Alcohols that have a particularly remarkable effect on the purpose of the present invention include primary alcohols having 4 or more carbon atoms, and secondary alcohols having 3 or more carbon atoms.
Examples include alcohols containing a fluorine atom in the side chain, such as 1.1●1●3●3●3-hexafluoro-2-propanol. (4) Furthermore, the objective can also be achieved by forming a transparent dielectric film on the sample substrate by sputtering and then treating it with an organic compound containing fluorine.

Examples of organic compounds containing fluorine include coating agents such as product numbers FC72l and FC7O6 manufactured by Sumitomo Taisho Co., Ltd., and product numbers FCl34. There are 7 tons of FCl surfactant. The manufacturing method of the present invention has the following features and can manufacture an exposure photomask that satisfies required characteristics.

(1) The transparent dielectric film is formed by sputtering.

Therefore, since the photomask is heated to only about 15 C) at most during film formation, it is also applicable to low melting point glasses such as soda lime glass, which are generally used as photomask substrates. (2) The thickness of the transparent dielectric film is 1
By setting the thickness to 0nTT1 to 30nm, absorption and interference of exposure light do not pose any practical problems.

Therefore, even if the surface treatment is performed later, the characteristics as a mask will not deteriorate. (3) There are no materials or atmospheric gases used in the manufacturing process that pose any danger or toxicity to the human body.
It's safe enough.

Example 1 An ordinary chrome mask having a chromium thin film provided as a light blocking portion on a glass substrate is prepared.

This was washed with organic solvent and water. This board is connected to RF (
Ra-DiO Frequency) is attached to the substrate holder of a sputtering device. As is commonly done, the substrate holder is cooled by passing cooling water to prevent the temperature of the substrate from rising. Fused quartz was used as a dielectric target for sputtering. A water-cooled metal electrode is bonded to the back surface of this target, and high frequency waves can be supplied through this electrode. After mounting the board, use a vacuum evacuation system (auxiliary evacuation using a diffusion pump and a rotary pump, or an evacuation system consisting of a turbo molecular and a rotary pump, etc.) to 5×10−
Exhaust to 10rr' or less. Next, the sputtering gas is introduced into the sputtering chamber through the leak valve, and the degree of vacuum is increased to 6×10
-1Pa ~ 3×10) One point in the Pa range, for example 9×10
-1Pa is fixed. The component of the sputtering atmosphere gas was a mixed gas of argon (Ar) and oxygen (02). At this time, the ratio of 02 gas to Ar is 0.1 to 10% in terms of pressure. In this example, it was set to 1%. High frequency power is supplied from a high frequency power source through the metal electrode. The high frequency power density at this time is 1 to 3W1c1i. Pre-sputtering is performed in this state. In this case, either apply a shutter on the mask substrate or move the substrate away from directly below the target in a position where a transparent dielectric film will not be directly deposited.After preliminary sputtering is completed, open the shutter or move the substrate directly below the target. The film was set and deposited to a film thickness of 20r1m. The appropriate distance between the target and the substrate holder during sputter deposition is 40 m to 6 i. The surface of the deposited SiO2 film was treated with silane derivative HMDS (hexamethyldisilazane ((CHG)3SiNHSi(C
H3) 3)) Exposure to steam at 150'C for 10 minutes.

Through this treatment, a trimethylsilyl group ((CH3)3Si-) is chemically bonded to the surface of the SiO2 film. Therefore, the surface energy of the photomask became 24 mJId. The adhesive strength between the photoresist and the processed substrate is usually 707
nJId. The surface free energy 24 of the aforementioned mask
TrI. Since JIa is sufficiently smaller than the adhesion strength of 70 mJIa between the photoresist and the substrate to be processed, it is considered that the adhesion strength between the photomask and the photoresist is reduced. As a result of performing mask alignment using the photomask manufactured by the above method, no defects in the photoresist due to adhesion between the photomask and the photoresist were found over the entire surface of the 3-inch wafer.

Furthermore, even when 10 consecutive wafers were subjected to mask alignment, the effect could be maintained. Up to now, we have explained examples using fused silica as a target, but it is also possible to use Corning Corporation numbers such as 0080: soda lime, 7740: Pyrex, 7059: semiconductor substrate glass, 7913: Vycor, phosphorus glass, alumina, etc. Deposited sputtered films and the like were similarly effective.

In this case, the above 0080 glass, 7740 glass, 70
When glass such as 59 glass is used as a target,
It is more effective to increase the 02 partial pressure of the sputtering gas than in the case of fused silica. For example, a more preferable range is 0.1% to 10%. The present invention is equally applicable to photoresist materials other than Ml35OJ shown in the examples.

In other words, as a negative type photoresist, KTFR
．． ．． KODAK747 (manufactured by Kodak), HUNT
-HR2OO (manufactured by Hantto), 0MR (manufactured by Tokyo Ohka),
As a positive type photoresist, the above AZl35OJ
In addition, AZ such as 1350, 1350H1303, 111
Series (manufactured by Shitsuplay), WAYCOAT295.39
5 (manufactured by Hunt), 0FPR (manufactured by Tokyo Ohka), G, AF
'102, 105 (manufactured by GAF), KODAK8O9 (
A similar effect was observed for Kodatsuku Co., Ltd.). Example 2 A photomask is prepared in which a chromium oxide thin film is provided as a light blocking portion on a glass substrate.

This is attached to the substrate holder of the RF sputtering apparatus as described in Example 1. Soda lime glass (Corning Corporation number: 0080) was used as the dielectric target. A mixed gas of argon and oxygen is introduced so that the degree of vacuum in the sputtering chamber is approximately 0-1 Pa. Monooxygen is 5%
And so. In this way, a film with a thickness of 15
A 11TrL soda lime glass film is formed by sputtering. Next, a photomask on which a transparent dielectric film was formed as described above was placed in the reaction vessel of the high-frequency plasma device; .5r
0rr was introduced.

Next, an input of 25 W was applied to the high frequency electrode to form a plasma containing 2,2,2-trifluoroethanol in the reaction vessel. By holding one powder in this state, the surface free energy of the photomask is 9.6erg.
It became 1ci. In this example, 2,2,2-trifluoroethanol was used as the surface treatment.

Other organic vapors include trimethylchlorosilane which is a silane compound, butanol which is a primary alcohol, isopropanol which is a secondary alcohol, tert-butanol which is a tertiary alcohol, octafluorop AI gun which is a freon, etc. The same effect could be obtained using . Example 3 A photomask in which a chromium thin film was provided as a light shielding part on a glass substrate was prepared.

Using fused silica as a dielectric target, a transparent dielectric film having a thickness of 20r1TrL is formed in the same manner as in the example. As a method of reducing the energy consumption of the photomask surface, we used surface treatment using alcohol reflux treatment. A photomask was placed in a conventional reflux device, and a mixed solution of n-octanol and n-tetradecane was added in an amount sufficient to fully immerse the photomask in the solution.

The mixture was then gradually heated to reflux at -23 rc. By keeping the temperature at 1% in this state, n-octoxy groups (n-C8Hl, O-) are chemically bonded to the photomask surface, and the surface free energy of the photomask is 15erg.
It became 'd. Although surface treatment with other alcohols can be carried out in exactly the same manner, the following alcohols are particularly effective for the purpose of the present invention. Examples of primary alcohols having 4 or more carbon atoms include butanol, pentanol, hexanol, decanol, and tetradecanol; examples of secondary alcohols having 3 or more carbon atoms include isopropanol, Sec-
Examples of tertiary alcohols include butanol, hexiganol-3, octano-3, decanol-3, Te
Examples include rt-butanol, 2-methylhexanol-2, and 3-methyldecanol-3. Example 4 Another method for surface treatment of a photomask to obtain the same effect as shown in Example 1 is to use an organic compound containing fluorine atoms.

For example, there is a method of using a coating agent such as FC72l or FC7O6 manufactured by Sumitomo Taisho Co., Ltd., or a surfactant solution such as FCl76 manufactured by Sumitomo Taisho Co., Ltd. All of these materials are organic compounds containing fluorine atoms. Here, the case where FC72l is used will be explained as an example.

After organic cleaning of the chrome mask as in Example 1, SiO
Two films are formed by a 20nWL1 sputtering method. Next, add 1 ml of FC72l to a solution diluted with Freon π at room temperature.
Soaked for minutes. Next, use an infrared heating device to heat the temperature to 100°C for 1
I did some baking. Through this treatment, the surface free energy of the mask surface became 9.5erg1c11. As a method for reducing the energy on the photomask surface, it is also effective to combine the methods shown in Examples 1 to 4 above.

For example, there is a method in which a photomask surface is treated by the method shown in Example 1 and then a film is formed with a coating agent. In this case, the free energy of the photomask surface is determined by the final surface treatment. Table 1 lists combinations of surface treatments that are particularly effective for the purposes of the present invention.

As explained above, according to the present invention, the surface free energy of a photomask can be reduced to 9.5 to 15ergIcI1.

The materials normally used to manufacture semiconductor devices (processed substrates during photoetching) are single crystal Sil, polycrystalline Si, etc. ．． SiO2, PSG (phosphorus glass), Si3N
, , A1-Si alloy, MO, etc. All of these materials have large surface free energy. Therefore, as shown in the examples, if the photomask surface is made to have a low energy level (preferably about 3(t)Rglcrl or less) by surface treatment, adhesion between the photomask and the photoresist can be completely prevented.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the photomask of the present invention. 1...Photomask substrate, 2...Thin film forming a light shielding part, 3...Transparent dielectric film.

Claims (1)

[Claims] 1. A photomask manufacturing method in which a transparent dielectric film made of an oxide is formed by sputtering on the surface of a predetermined photomask substrate on which a mask pattern is formed,
Oxygen is contained in the sputtering atmosphere, the thickness of the transparent dielectric film to be formed is set to 10 to 30 nm, and the surface free energy of the surface of the transparent dielectric film is then lowered than the surface free energy of the surface in contact with the photoresist of the processed substrate. A method for producing a phosmask characterized by surface treatment.