JP3973103B2 - Manufacturing method of mask blanks - Google Patents

Description

  The present invention relates to a method for manufacturing a mask blank with a resist film, in which a resist is uniformly coated on a main surface of a mask blank substrate to form a resist film.

  Conventionally, when a resist film is formed on a mask blank having a square substrate and a thin film formed on the substrate, a uniform film is formed without forming a thick resist film at the four corners of the substrate. In addition, a resist spin coating method using a spin coater that spins the substrate to coat the resist is generally used. As a typical example of this spin coating method, there is a resist coating apparatus and a resist spin coating method disclosed in Patent Document 1.

The resist coating apparatus and the resist spin coating method will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing the structure of a resist coating apparatus.
As shown in FIG. 1, the resist coating apparatus is dropped by a chuck 2 for installing and fixing the substrate 1, a nozzle 4 for dropping the resist 3, and a motor 5 for rotating the chuck 2. And a cup 7 for preventing the resist 6 from being scattered around during rotation.

Then, in the resist spin coating method using this resist coating apparatus, a resist 3 is dropped from a nozzle 4 onto the thin film surface of a rectangular substrate 1 having a predetermined size fixed to a chuck 2, and the substrate 1 is moved to a motor 5. Rotate by. Then, the resist 3 dropped by the centrifugal force generated on the substrate 1 rotated by the motor 5 is applied onto the substrate 1 as a resist film having a desired film thickness.
At this time, a predetermined rotation speed (may be described as a main rotation speed in this specification) corresponding to a desired film thickness and a predetermined rotation time (in this specification, a main rotation time) may be described. ) And the product of the predetermined number of rotations and the predetermined rotation time as appropriate, and rotating the substrate to make the resist film thickness uniform, and the uniforming step Subsequently, the substrate is rotated at a rotational speed lower than the set rotational speed of the homogenizing step (in some cases, described as a dry rotational speed in this specification), and the substrate is obtained by the homogenizing step. And a drying step of drying the homogenized resist while substantially maintaining the uniformity of the resist film thickness.

Japanese Patent Publication No. 4-29215

In recent years, due to the demand for improving the CD variation accuracy accompanying the miniaturization of the pattern transferred to the semiconductor substrate or the like by the mask manufactured from the mask blank described above, the request for in-plane uniformity of the resist film thickness formed on the mask blank is required. It is getting stricter year by year. Recently, in-plane uniformity of the resist film thickness (the difference between the maximum value and the minimum value of the resist film thickness within one substrate) is required to be 50 mm or less.
In order to meet this requirement, the rotation conditions of the resist coating method described above are set such that, for example, the set rotation speed R of the substrate in the homogenization step is 100 to 6000 rpm, the predetermined rotation time T is the rotation speed of the substrate is the set rotation speed. 20 seconds or less after reaching R, the product of the set rotation speed R and the rotation time T is set to 24000 rpm · second or less, and the rotation of the drying process following the homogenization process is appropriately selected to be 130 rpm or less, The in-plane uniformity of the resist film thickness is set to 50 mm or less.

On the other hand, when manufacturing a mask from mask blanks, a mask manufacturing method using an electron beam (EB) is adopted, and from the background of resist development for that purpose, resists formed on high-precision mask blanks for LSIs are currently polymer type resists. The solution is mainstream.
This polymer resist solution generally has a high viscosity of more than 5 cp and is difficult to dry in the drying step in the above-described resist coating step. Therefore, it is necessary to set the rotation time in the drying step to be relatively long. However, in the above resist coating method, in order to dry the resist film while maintaining the in-plane uniformity of the thickness of the resist film coated on the substrate, the rotation is continued at a low rotational speed for a relatively long time. Rotation must be continued until no substantial change in film thickness is exhibited after completion of the rotation. As a result, this drying step becomes a rate-limiting step of the resist coating step, and there is a problem that productivity is poor.

In recent years, in the mask manufacturing technique using an electron beam, as a measure for improving the resolution of the mask pattern, the acceleration voltage of the electron beam at the time of resist drawing (exposure) is going to shift from the current 10-20 keV to 50 keV or more. Yes. Therefore, a chemically amplified resist having high sensitivity with respect to a high acceleration voltage of 50 keV or more and having higher resolution has attracted attention.
However, this chemically amplified resist is weak against chemical contaminants such as amine compounds, for example, and causes deterioration of the resist function (deterioration of pattern shape due to sensitivity fluctuation, reduction of resolution, etc.). The degree of deterioration of the resist function is generally considered to depend on the integration of the concentration of chemical contaminants to which the resist film is exposed and the exposure time.
Therefore, in the formed resist film, the shorter the exposure time to the atmosphere, the more stable the resist function (preventing resist function deterioration) is ensured. Furthermore, the longer the exposure time, the greater the risk that the resist function will be impaired. In some cases, there is a problem that a significant dimensional difference (sensitivity fluctuation) with respect to a set dimension, a pattern resolution failure difference, or the like occurs.
Further, as a common problem of the above-described polymer type resist and chemically amplified resist, the resist film formed on the main surface of the substrate by the above-described resist coating method has a film thickness and a film thickness by the above-described drying process. It is dried to such an extent that the internal uniformity hardly changes. However, the resist film that wraps around the side surface of the substrate is generally 3 to 10 times thicker than the resist film formed on the main surface, so it is completely dried. It is not carried out and remains in the so-called dry state. In this state, an unnecessary film removing device that dissolves and removes the resist film formed at an unnecessary portion of the peripheral portion of the substrate where the next step of the resist coating step is performed, a heating device that heats the resist film, and a transfer device If the side surface of the substrate is conveyed by the gripping means, the resist adheres to the gripping means. When the resist adheres to the gripping means, there is a problem that it causes dust generation and adheres to the resist film surface of the mask blank, resulting in a defect.

The present invention has been made in view of the above-mentioned problems, and the first problem is even when a resist that requires a long drying time in spin coating, such as a polymer resist solution, is used. Another object of the present invention is to provide a mask blank manufacturing method capable of improving productivity and preventing defects on the resist film surface.
The second problem is the production of mask blanks that have good resist function stability and can prevent defects on the resist film surface even when chemically amplified resists with poor environmental resistance are used. Is to provide a method.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1) After dropping a resist solution on the main surface of a mask blank substrate having a predetermined size, the substrate is rotated at a predetermined main rotation speed and a predetermined main rotation time. The substrate is rotated at a predetermined drying rotation speed and a predetermined drying rotation time after the homogenization step, and a homogenization step of forming a resist having a uniform film thickness on the main surface of the substrate. And a drying step of drying the resist having a uniform film thickness, and a method of manufacturing a mask blank having a uniform film thickness on the main surface of the substrate by the homogenization step. On the main surface of the substrate, the substrate is rotated at a first drying rotational speed lower than the main rotational speed until the resist in the form of a film has almost no change in film thickness and in-plane uniformity of the film thickness. After drying the resist formed in The mask blank manufacturing method is characterized in that the substrate is rotated at a second drying speed higher than the first drying speed to dry the resist formed on the side surface of the substrate.

(Configuration 2) The mask blank manufacturing method according to Configuration 1, wherein the first drying rotation speed is 50 to 450 rpm, and the second drying rotation speed is 700 rpm or more.

(Configuration 3) The mask blank manufacturing method according to Configuration 1 or 2, wherein the resist is a polymer resist.

(Structure 4) The resist coating method according to Structure 1 or 2, wherein the resist is a chemically amplified resist.

(Structure 5) After a resist film is formed on the main surface of the mask blank substrate, a solvent is supplied to the resist film formed at an unnecessary portion in the peripheral portion of the substrate to dissolve and remove the resist film. An unnecessary film removing step. The method of manufacturing a mask blank according to any one of Configurations 1 to 4, further comprising: an unnecessary film removing step.

(Structure 6) In the unnecessary film removing step, a main surface of the substrate is covered with a cover member, and a solvent is supplied to a solvent supply path formed in the cover member while rotating the substrate and the cover member together. The method for producing a mask blank according to Configuration 5, wherein unnecessary portions of the resist film formed in unnecessary portions are dissolved and removed.
(Structure 7) The mask blank manufacturing method according to Structure 5 or 6, wherein the resist film is heat-treated after the unnecessary film removing step.

  As described in the configuration (1), the drying process is a resist that has a uniform film thickness on the main surface of the substrate by the homogenization process. The substrate is rotated at a first drying rotation speed lower than the main rotation speed until the resist is formed on the main surface of the substrate to dry, and then at a second drying rotation speed higher than the first drying rotation speed. By rotating the substrate and forcibly drying the resist formed on the side surface of the substrate, the resist formed on the side surface of the substrate can be completely dried. In addition, dust generation can be prevented, so that no foreign matter adheres to the resist film surface and becomes a defect. In addition, since the time of the drying process in the spin coating process can be shortened, productivity can be improved and the time in an incompletely dry state that is easily affected by the environment can be shortened. Deterioration (sensitivity fluctuation, pattern shape deterioration, resolution reduction, etc.) can be suppressed.

  In order to ensure the in-plane uniformity of the resist film thickness, the first drying rotation time at the first drying rotation speed in the drying process is applied to the resist uniformly coated on the main surface of the substrate by the homogenization process. It is preferable that the resist film thickness and the in-plane uniformity of the resist film thickness be changed for a time that hardly changes. Here, the resist film thickness and the in-plane uniformity of the resist film thickness hardly change that the in-plane uniformity of the resist film thickness and the resist film thickness other than thermal factors (for example, heat treatment performed after the spin coating process). A state where sex does not change.

As in the configuration (2), the specific rotation speeds of the first drying rotation speed and the second drying rotation speed in the drying step are preferably 50 to 450 rpm and 700 rpm or more, respectively.
If the first drying speed is less than 50 rpm or exceeds 450 rpm, the coating conditions (main rotation speed, main rotation time) that optimize the in-plane uniformity of the resist film thickness are extremely limited conditions. In addition, the in-plane uniformity of the resist film thickness is also deteriorated, which is not preferable. Further, when the second drying rotational speed is less than 700 rpm, the effect of improving productivity and the stability of resist function is reduced, and the resist formed on the side surface of the substrate is less preferable because the drying effect by rotating the substrate is reduced. .

  As in the configuration (3), when a polymer resist is used, it is difficult to dry. Therefore, by applying the present invention, productivity can be improved by about 25 to 45%.

As in the configuration (4), when a chemically amplified resist is used as the resist,
By applying the present invention, it is possible to shorten the time in an incompletely dry state that is easily affected by the environment, and therefore it is possible to suppress and further prevent deterioration of resist function (decrease in sensitivity stability). . Accordingly, when a resist pattern is formed by patterning a resist, a dimensional error with respect to a design dimension can be reduced. Moreover, when the cross-sectional shape of a resist pattern is favorable and especially the line width of a resist pattern is small, resist patterns do not connect on the surface.

After the resist film is formed on the main surface of the mask blank substrate as in the configuration (5), a solvent is supplied to the resist film formed at an unnecessary portion in the peripheral portion of the substrate to form the resist film. By dissolving and removing, dust generation due to peeling of the resist film at the peripheral edge of the substrate can be prevented, and surface defects of the mask blank can be prevented.
Covering the main surface of the substrate with the cover member, and rotating the substrate and the cover member together as shown in the configuration (6), covering the main surface of the substrate with the cover member, By supplying a solvent to the solvent supply path formed on the substrate, supplying the solvent to unnecessary portions, and dissolving and removing unnecessary portions of the resist film, resist film residues at unnecessary portions can be prevented. Therefore, it is preferable. Since the resist film residue causes dust generation, the surface defect of the mask blank can be surely prevented by preventing the resist film residue.
As in the configuration (7), after the unnecessary film removing step, the resist film is heat-treated, that is, the unnecessary film removing step is performed before the resist film is heat-treated, so that the unnecessary portion is dissolved and removed. It is preferable because there is no film residue and it can be easily removed.
The present invention is particularly effective for mask blanks that are mask masters for LSIs and VLSIs that require a fine resist pattern among mask blanks.

According to the present invention, firstly, even in the case of a resist that requires a long drying time in spin coating such as a polymer type resist, the mask blanks that improve productivity and prevent defects on the resist film surface. We were able to provide a manufacturing method.
Second, the present invention provides a mask blank manufacturing method that has good resist function stability and is capable of preventing defects on the resist film surface even with a chemically amplified resist having poor environmental resistance. I was able to.

The spin coating method according to the present invention will be described again with reference to FIG.
In the spin coating method according to the present invention, for example, a spin coater shown in FIG. 1 is used to coat and form a resist on a rectangular substrate.
The spin-coating device has a chuck 2 for mounting and fixing the substrate 1, a nozzle 4 for dropping the resist 3, a motor 5 for rotating the chuck, and the dropped resist 6 during rotation. And a cup 7 for preventing scattering to the periphery. In addition, you may provide the exhaust means for generating an airflow toward the board | substrate from the cup upper direction.

Since the substrate to be coated by the spin coating method of the present invention is a substrate having a quadrangular shape, it is difficult to form a uniform resist film on the substrate without passing through at least the following two steps. .
The first step is a homogenization step in which a resist solution is dropped on the substrate, the substrate is rotated at a predetermined main rotation speed and a predetermined main rotation time, and the resist film thickness is mainly uniformed. The second step is a drying step in which the substrate is rotated at a predetermined drying rotation speed and a predetermined drying rotation time after the homogenization step, and mainly the uniformized resist is dried.

In the conventional resist coating method, the above-mentioned main rotation speed R1, main rotation time T1, drying rotation speed R2, and drying rotation time are set according to the resist type so that the in-plane uniformity of the resist film thickness is 50 mm or less. T2 was selected as appropriate. In particular,
Main rotation speed R1: 750 to 2000 rpm
Main rotation time T1: 1 to 30 sec
Drying speed R2: 50 to 450 rpm
Drying rotation time T2: It was set within the range of 10 sec or more. Here, the drying rotation time T2 refers to the time required for the resist film to be completely dried.
When the above-described exhaust means is provided in the spin coater, the resist solution is dropped and the exhaust means is operated until the rotation stops after the substrate starts rotating so that an airflow is applied to the substrate from above the cup. Alternatively, the exhaust means may be started after the homogenization step is finished and the drying step is started, and is operated until the rotation is stopped, so that the airflow is applied to the substrate from above the cup. The wind speed of the airflow is appropriately selected according to the size of the spin coater, the type of resist, and the like, but it is preferable that the wind speed is 1 m / sec or more.

  The feature of the present invention lies in the drying process, and the resist uniformly applied on the substrate by the homogenization process has a resist film thickness and a resist film thickness surface other than thermal factors (for example, subsequent (dry) rotation). The resist formed on the main surface of the substrate is dried by rotating at the above-described drying speed R2 (= first drying speed) until the internal uniformity does not substantially change, and then the first drying speed The substrate is rotated at a second drying rotation number higher than the number, the resist formed on the side surface of the substrate is forcibly dried, and is rotated until the resist formed on the substrate is completely dried. As described above, the second drying rotation speed is appropriately selected within a range of 700 rpm or more according to the resist type.

  Here, the first drying rotation time is appropriately selected according to the type of resist. In the case of a resist having a low viscosity, the first drying rotation time may be a relatively short time of 10 to 60 seconds. In the case of a resist having a high viscosity, the first drying rotation time is a relatively long time of 30 to 200 sec. If it is not rotated at the drying speed, the in-plane uniformity of the resist film thickness is deteriorated, which is not preferable.

Further, the upper limit of the second drying rotation speed is limited by the performance of the spin coater.
For example, the second drying rotational speed may be appropriately selected from the viewpoint of safety, such as preventing the substrate from being removed during the rotation. From the viewpoint of safety, the second drying rotation speed is preferably 3000 rpm or less. Note that, as described above, the rotation speeds of the first drying rotation speed and the second drying rotation speed are appropriately selected according to the type of resist.

The relationship between the rotation time and the rotation speed in the conventional resist coating method and the resist coating method according to the present invention will be described with reference to the drawings.
FIG. 2 is a graph showing the relationship between the rotation time and the number of rotations in the conventional resist coating method and the resist coating method according to the present invention.
In FIG. 2, the horizontal axis is time, and the vertical axis is the rotation speed. The relationship between the rotation time and the rotation speed in the resist coating method according to the present invention is indicated by a solid line, and the relationship between the rotation time and the rotation speed according to the conventional technique is indicated by a dashed line.

  As shown in FIG. 2, in the resist coating method of the present invention, after the homogenization step of rotating the main rotation time T1 at the main rotation speed R1, the substrate is rotated at the first drying rotation time t21 at the first drying rotation speed r21. The resist formed on the main surface of the substrate is formed on the side surface of the substrate after the resist film thickness and in-plane uniformity of the resist film thickness hardly change due to other than thermal factors (subsequent (dry) rotation). In order to force the dried resist to dry, the substrate rotation speed is increased to the second drying rotation speed r22, and a drying process is performed in which the substrate is rotated for the second drying rotation time t22.

  On the other hand, the resist coating method according to the conventional technique includes a drying process in which the substrate is rotated at the drying rotation speed R2 and then the drying rotation time T2 is rotated after the uniformizing process in which the main rotation time T1 is rotated at the main rotation speed R1. Is what you do.

  Here, when comparing the drying rotation time in the drying process in both resist coating according to the present invention and the conventional technique, the present invention may be completed earlier than the conventional technique by "T2-t21-t22" time. This improves productivity. This productivity improvement effect becomes remarkable when a polymer resist having a reason such as difficulty in drying is used, and the productivity can be improved by about 25 to 45%.

  The polymer type resist applied to the mask blank is an electromagnetic radiation collapsed or crosslinked type resist having an average molecular weight of about 50000 or more. For example, a polymer type resist, which is a commercially available resist. , ZEP series (manufactured by Nippon Zeon Co., Ltd.), PBS series (manufactured by Chisso Corporation), EBR series (manufactured by Toray Industries, Inc.), OEBR series (manufactured by Tokyo Ohka Kogyo Co., Ltd.) and the like.

  In particular, in the case of a chemically amplified resist that is weak against chemical contaminants, the time in the resist film formation process, particularly the time in an incompletely dry state that is easily affected by the environment, is compared with the conventional method. Since the pre-baking process can be performed earlier by “T2-t21-t22” time, the risk of the resist function (sensitivity stability) being impaired is reduced.

  Here, the chemically amplified resist is, for example, FEP series (Fuji Film Arch), SAL series (Shipley), AZDX, AZEX series (Hoechst), OEBR series (Tokyo Ohka Kogyo), NEB. Series (manufactured by Sumitomo Chemical Co., Ltd.).

  When the drying process is completed at the first drying rotation time t21 hours, the resist is not completely dried at this point, so that the transport means comes into contact with the side surface of the substrate when transporting to the pre-baking apparatus. This is not preferable because a mask blank with a resist film in which a defect due to resist stringing, that is, a local film thickness abnormality occurs, is obtained. Further, even if the drying process is performed for up to T2 hours, the resist formed on the side surface of the substrate is not completely dried, and is in a dry state, because the resist adheres to the gripping means of the transport means. Dust generation occurs, and the surface defect of the mask blank cannot be prevented.

  The mask blank referred to in the present invention refers to both a transmission type mask blank and a reflection type mask blank, and these structures have an optical pattern on the substrate to cause an optical change with respect to the exposure light, and transfer patterns to be transferred to the transfer target. And a resist film.

The transmissive mask blanks use a translucent substrate as a substrate. An optical change with respect to exposure light means that a light shielding film that blocks exposure light or a phase shift film that changes the phase of exposure light (a halftone film having a light shielding function and a phase shift function is included in the phase shift film). Including).
Accordingly, the transmissive mask blank includes a photomask blank on which a light shielding film is formed, a phase shift mask blank on which a phase shift film (including a halftone film) is formed, and the like.

  The reflective mask blank is a mask blank having a low thermal expansion coefficient as a substrate and having a light reflecting multilayer film and a light absorber film serving as a transfer pattern on the substrate.

  In addition to the above-described films, the mask blanks of the present invention include a resist underlayer anti-reflective coating (BARC), a resist upper anti-reflective coating (TARL), and a resist upper protective layer. A film such as a conductive film may be formed.

  In addition, the heat treatment process for heat-treating the resist film includes a pre-bake process for heat-treating the resist film and a cooling process for cooling treatment. The pre-baking temperature, the heating rate, the cooling temperature, and the cooling rate are appropriately set according to the resist type.

  Hereinafter, the manufacturing method of the mask blank of this invention is demonstrated in detail by an Example.

<Example 1>
In the case of using a polymer resist, a chromium film and a chromium oxide film are sequentially laminated by sputtering on a synthetic quartz glass substrate having a substrate size of 152.4 mm × 152.4 mm and a thickness of 6.25 mm. Photomask blanks on which an antireflection film was formed were obtained.
ZEP7000 (manufactured by Nippon Zeon Co., Ltd.), which is a polymer-type electron beam drawing resist, was spin-coated on the obtained photomask blanks using the above-described spin coating apparatus under the following coating conditions to form a resist film. The resist concentration was adjusted so that the average film thickness was 4000 mm.
Uniformization process Main rotation speed R1: 1100rpm
Main rotation time T1: 10 sec
Drying process First drying speed r21: 250 rpm
First drying rotation time t21: 80 sec
Second drying speed r22: 1000 rpm
Second drying rotation time t22: 5 sec
Air velocity of the airflow hitting the main surface of the substrate: 2 m / sec (from the start of rotation of the substrate to the stop of rotation)
In the above, the resist film uniformly applied on the main surface of the substrate by the homogenizing step is dried by the air current from above the substrate while the substrate is rotated at the first drying rotation speed for the first drying rotation time. Higher than the first drying speed after being dried until the film thickness of the resist film and the in-plane uniformity of the film thickness are almost unchanged due to the action and the drying action due to the rotation of the substrate. The substrate was rotated at the second drying rotational speed, and the resist film formed on the side surface of the substrate was forced to dry mainly by the drying action by the rotation of the substrate.
Thereafter, the side surface of the substrate was gripped by a transport means, transported to a pre-baking device and a cooling device, and subjected to a predetermined heat treatment to produce a photomask blank with a resist film.

The in-plane uniformity of the film thickness was measured for the resist film of the produced photomask blank.
As a result, the in-plane uniformity of the resist film thickness was 30 mm. The in-plane uniformity of the resist film thickness is a spectral reflection type film thickness meter (manufactured by Nanometrics Japan Co., Ltd .: AFT6100M) with 11 × 11 = 121 points arranged uniformly in the entire effective area 132 mm × 132 mm at the center of the substrate. To measure the in-plane film thickness distribution (film thickness data at each measurement point), and from this in-plane film thickness distribution data, (maximum film thickness value) − (minimum film thickness value) = ( In-plane film thickness uniformity).
Further, when defects on the resist film surface were inspected by a defect inspection apparatus (manufactured by Hitachi Electronics Engineering Co., Ltd .: GM1000), no surface defects due to resist film peeling existed.

<Comparative Example 1>
Photomask blanks with a resist film having an average film thickness of 4000 mm were produced in the same manner as in Example 1 except that the rotation conditions in the drying step of Example 1 were changed to the following conditions.
Drying speed R2: 250 rpm
Drying rotation time T2: 150 sec
And the in-plane uniformity of film thickness was measured about the resist film of the produced photomask blanks.
As a result, the in-plane uniformity of the resist film thickness was 30 mm.
Further, when the defect on the resist film surface was inspected by a defect inspection apparatus (manufactured by Hitachi Engineering Co., Ltd .: GM1000), a surface defect due to peeling of the resist film attached to the conveying means was found.

When Example 1 and Comparative Example 1 were compared, in the drying process after the homogenization process, the substrate was rotated at a first drying rotation speed lower than the main rotation speed in the homogenization process, thereby forming a uniform film. Since the film thickness and the in-plane uniformity of the film thickness are hardly changed, the in-plane film thickness uniformity obtained is the same regardless of the subsequent second drying speed. Although both did not change to 30 mm, Example 1 was able to shorten the drying process time by 65 seconds compared with Comparative Example 1, and the productivity was improved by about 43%.
Further, in Example 1 in which the resist formed on the side surface of the substrate was forcibly dried by rotating the substrate at the second drying speed, the resist film on the side surface of the substrate was completely dried. Although there is no surface defect due to the resist film peeling, the substrate is rotated at the second drying speed, and in Comparative Example 1, the resist film on the side surface of the substrate is not dried, and the surface defect due to the resist film peeling from the side surface of the substrate It was observed.
As described above, in order to improve productivity and prevent defects on the resist film surface, a uniform film thickness is first formed on the main surface of the substrate by the uniformizing process after the drying process after the uniformizing process. The substrate is rotated at a first drying rotation speed lower than the main rotation speed until the film thickness and in-plane uniformity of the film thickness hardly change, and the resist film is formed on the main surface of the substrate. After the resist formed on the substrate is dried, the resist is rotated at a second drying rotational speed higher than the first drying rotational speed, and the resist formed on the side surface of the substrate is mainly forced using the drying action by the rotation of the substrate. It can be seen that it is sufficient to dry it.

<Comparative example 2>
As Comparative Example 2, a photomask blank with a resist film in which the second drying rotation speed was not performed in the drying process of Example 1 was produced. In this example, because the resist is not completely dry, when the substrate is transported to the pre-baking device, the transport means comes into contact with the side surface of the substrate, causing a defect (local thickness abnormality) due to resist stringing. Thus, a photomask blank with a resist film was obtained.

<Example 2>
In the case of using chemically amplified resist The resist of Example 1 was changed to a chemically amplified electron beam drawing resist (OEBR-CAP209: manufactured by Tokyo Ohka Kogyo Co., Ltd.), and the resist concentration was adjusted so that the average film thickness was 4000 mm. Then, spin coating was performed under the following coating conditions to form a resist film.
Uniformization process Main rotation speed R1: 1500rpm
Main rotation time T1: 5 sec
Drying process First drying speed r21: 300rpm
First drying rotation time t21: 50 sec
Second drying speed r22: 1000 rpm
Second drying rotation time t22: 5 sec
Air velocity of the airflow hitting the main surface of the substrate: 2 m / sec (from the start of rotation of the substrate to the stop of rotation)
Other conditions were the same as in Example 1, and a photomask blank with a resist film having an average film thickness of 4000 mm was produced.
Note that the resist film uniformly applied on the main surface of the substrate by the homogenizing process in the same manner as in the first embodiment described above is the upper portion of the substrate while the substrate is rotated at the first drying rotation speed for the first drying rotation time. After drying until the in-plane uniformity of the film thickness and thickness of the resist film that has become a uniform film by the homogenization process is almost unchanged due to the drying action by the air current from the substrate and the drying action by the rotation of the substrate The substrate was rotated at a second drying rotational speed higher than the first drying rotational speed, and the resist film formed on the side surface of the substrate was forcibly dried mainly by a drying action by the rotation of the substrate.
And about the produced resist film of the photomask blanks, the in-plane uniformity of the film thickness was measured similarly to Example 1.
As a result, the in-plane uniformity of the resist film thickness was 30 mm.
Further, when defects on the resist film surface were inspected by a defect inspection apparatus (manufactured by Hitachi Engineering Co., Ltd .: GM1000), no surface defects due to resist film peeling existed.

<Comparative Example 3>
Photomask blanks with a resist film having an average film thickness of 4000 mm were produced in the same manner as in Example 2 except that the rotation conditions in the drying step in Example 2 were changed to the following conditions.
Drying process Drying speed R2: 300rpm
Drying time T2: 90sec
And about the produced resist film of the photomask blanks, the in-plane uniformity of the film thickness was measured in the same manner as in Example 1.
As a result, the in-plane uniformity of the resist film thickness was 30 mm.
Further, when defects on the surface of the resist film were inspected by a defect inspection apparatus (Hitachi Electronics Engineering Co., Ltd .: GM1000), surface defects due to peeling of the resist film attached to the conveying means were found.

When Example 2 and Comparative Example 3 were compared, in the drying process after the homogenizing process, the substrate was rotated at a first drying speed lower than the main rotating speed in the homogenizing process, resulting in a uniform film. Since the resist film thickness and the in-plane uniformity of the film thickness are almost unchanged, the obtained in-plane film thickness uniformity is obtained regardless of the subsequent second drying speed. Although both were the same as 30 mm, Example 2 was able to shorten the drying process time by 35 seconds compared with Comparative Example 3, and the productivity was improved by about 39%.
Further, in Example 2 in which the resist formed on the side surface of the substrate was forcibly dried by rotating the substrate at the second drying speed, the resist film on the side surface of the substrate was completely dried. Although there is no surface defect due to the resist film peeling, the substrate is rotated at the second drying speed, and in Comparative Example 3, the resist film on the side surface of the substrate is not dried, and the surface defect due to the resist film peeling from the side surface of the substrate It was observed.
As described above, in order to improve productivity and prevent defects on the resist film surface, a uniform film is formed on the main surface of the substrate by performing a drying process after the homogenizing process first. The substrate is rotated at a first drying rotation speed lower than the main rotation speed until the film thickness and in-plane uniformity of the film thickness hardly change, and the main surface of the substrate is formed. After drying the resist formed above, it is rotated at a second drying speed higher than the first drying speed, and the resist formed on the side surface of the substrate is mainly utilized by the drying action by the rotation of the substrate. It turns out that it should be forced to dry.

<Comparative example 4>
As Comparative Example 4, when the second drying rotation speed was not performed in the drying process in Example 1, the substrate was not completely dried, and therefore, when transported to the pre-baking apparatus, the side surface of the substrate was contacted by the transport means. Thus, a photomask blank with a resist film in which a defect (local thickness abnormality) due to resist stringing occurred was obtained.

<Stability evaluation test for resist function>
Next, in order to evaluate the stability of the resist function in the chemically amplified resist, only the spin coating process in the mask blank manufacturing process is performed in an atmosphere with an ammonia concentration of 12 ppm, and the heat treatment process is performed in a sealed pre-baking device and a cooling device. A mask blank with a resist film was prepared in the same manner as in Example 2 and Comparative Example 3 except that the process was performed in a nitrogen atmosphere.
Immediately thereafter, exposure processing, development processing, post-baking processing, and etching processing were performed to form a 300-500 nm line-and-space resist pattern, and cross-sectional observation was performed with an SEM (scanning electron microscope).
As a result, in the case of Example 2, the pattern edge was not jagged and the pattern cross section was vertical, which was very good.
On the other hand, in Comparative Example 3, the pattern edge was observed to be jagged. This is presumably because the chemically amplified resist was contaminated with chemical contaminants (ammonia) in the spin coating process, the resist function deteriorated, and pattern resolution failure occurred.
<Example 3>
After forming the resist film by spin coating in Example 1, before performing the predetermined heat treatment, dissolve the resist film formed at an unnecessary portion of the peripheral portion of the substrate using a solvent capable of dissolving the resist film. Removed.
The method of removing the resist film formed on the peripheral edge of the substrate is to cover the substrate surface with a cover member, supply the solvent from above the cover member while rotating the substrate covered with the cover member, and remove the solvent from the cover member. The resist film was removed by supplying to an unnecessary part through a solvent supply path provided in the predetermined part.
In the obtained photomask blank, since the resist film at the peripheral edge of the substrate was removed, dust generation due to the peeling of the resist film from the peripheral edge of the substrate was prevented, and surface defects of the mask blank could be prevented.

It is a structural diagram showing a resist coating apparatus. It is a figure which shows the relationship between the rotation time in a resist coating method, and rotation speed.

Explanation of symbols

1 substrate 2 chuck 3 resist 4 nozzle 5 motor 7 cup

Claims (8)

After dropping a resist solution on the main surface of a mask blank substrate having a predetermined size, the substrate is rotated at a predetermined main rotation speed and a predetermined main rotation time, and the dropped resist is mainly used. A homogenization step for forming a film having a uniform film thickness on the main surface of the substrate;
After the uniformizing step, the substrate is rotated at a predetermined drying rotation number and a predetermined drying rotation time, and a drying step mainly for drying the resist having the uniform film thickness,
After the drying step, a heat treatment step of heat treating the resist film applied and formed on the main surface of the substrate;
A mask blank manufacturing method comprising:
The homogenization step is a step of reducing the in-plane uniformity of the resist film thickness formed on the main surface of the substrate to 50 mm or less,
In the drying step, the resist that is a film having a uniform film thickness on the main surface of the substrate by the uniformizing process is used until the in-plane uniformity of the film thickness and film thickness hardly changes. The substrate is rotated at a first drying rotation speed lower than the main rotation speed to dry the resist formed on the main surface of the substrate, and then the substrate is rotated at a second drying rotation speed higher than the first drying rotation speed. A method for manufacturing a mask blank, comprising rotating the substrate to dry the resist formed on the side surface of the substrate. The drying step is a step of allowing the airflow to strike the resist formed on the main surface of the substrate from above the main surface of the substrate, and drying the resist by a drying action by the airflow and a drying action by rotation of the substrate. 2. The method for producing a mask blank according to claim 1, wherein: The method for manufacturing a mask blank according to claim 1 or 2, wherein the first drying speed is 50 to 450 rpm, and the second drying speed is 700 rpm or more. The resist mask blank manufacturing method according to any one of claims 1 to 3, characterized in that a polymer resist. The resist mask blank manufacturing method according to any one of claims 1 to 3, characterized in that a chemically amplified resist. After the resist film is formed on the main surface of the mask blank substrate, an unnecessary film removing step of dissolving and removing the resist film by supplying a solvent to the resist film formed at an unnecessary portion in the peripheral portion of the substrate The method of manufacturing a mask blank according to any one of claims 1 to 5 , wherein: The unnecessary film removing step covers the main surface of the substrate with a cover member, and supplies the solvent to a solvent supply path formed in the cover member while rotating the substrate and the cover member together, thereby removing unnecessary portions. 7. A method of manufacturing a mask blank according to claim 6 , wherein a solvent is supplied to the resist film to dissolve and remove unnecessary portions of the resist film. 8. The method of manufacturing a mask blank according to claim 6 , wherein the resist film is heat-treated after the unnecessary film removing step.

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