Production of photomask

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a method for producing a photomask.

【0002】

[Conventional technology]

Conventional blank masks used in the manufacture of photomasks have a two-layer structure in which a light-shielding film is attached on a transparent substrate. Quartz is mainly used as the transparent substrate material used for the blank mask, and chromium is mainly used as the light-shielding film material. The chromium film thickness of the blank mask is usually about 110 nm, and is formed by vacuum deposition or sputtering.

【0003】

Next, a method of forming a photomask will be described. First, a resist for an electron beam (hereinafter referred to as "EB" (EB: Electron Beam)) is mainly used as a protective film material required for processing a blank mask to a photomask. The film thickness of this EB resist is about 500 nm, and it is applied to a blank mask by a spin-on method. The EB resist is patterned by EB drawing and development.

【0004】

Then, based on this resist mask, the light-shielding film is patterned by wet etching. The wet etching method includes a dipping method and a spray method. It is also desirable that the ratio of the resist film thickness to the chromium film thickness be 3: 1.

【0005】

[Problems to be Solved by the Invention]

As described above, when the wet etching method is used for processing the photomask, the undercut due to the side etching occurs in both of the above two methods by 0.1 μm or more, and the chrome film pattern size becomes thinner than the resist pattern size. This undercut is a phenomenon in which the etching solution wraps around under the resist film from the edge of the window opening portion and the etching proceeds in the lateral direction as shown in FIG. 8, which is a diagram used to explain the problems of the prior art. Is. In FIG. 8, 1 is a transparent substrate, 2 is a chromium film, and 3 is a resist.

【0006】

When the chrome film pattern size becomes as thin as about 1 μm, the dimensional accuracy of the photomask deteriorates due to this undercut, and it is applied to the OPC (Optical Proximity Correction) mask pattern by the conventional technique shown in Fig. 7 (b). As shown, the corner roundness of the pattern becomes noticeable. Note that FIG. 7 (c) is a diagram showing a design OPC mask pattern, and in FIG. 7 (c), 4 shows an OPC mask pattern.

【0007】

However, in lithography using i-line and g-line, the minimum size of the chromium film pattern is about 2 μm, and even if wet etching is used, the desired pattern size can be sufficiently supported. Although photomask accuracy has been obtained, in photolithography using a KrF excimer laser, there is a problem that the dimensional accuracy of the photomask cannot be obtained because the minimum size of the chromium film pattern is about 1 μm.

【0008】

In order to miniaturize the light-shielding pattern (mainly the chromium film pattern), a technique using a dry etching method such as plasma or sputtering instead of wet etching has been proposed. The dry etching method has an advantage that it can be suppressed by an undercut of 0.05 μm or less and a pattern that matches the resist mask is formed, and is superior to the wet etching method.

【0009】

However, due to the poor dry etching resistance of the resist for EB, the two points that the resist film is greatly reduced and the resolution of the resist is low in order to form the chrome film pattern according to the resist mask affect the patterning of the chrome film. However, even if it can be processed, there is a problem that the dimensional accuracy of the photomask required for KrF excimer lithography cannot be obtained.

【0010】

An object of the present invention is to provide a technique for improving the dimensional accuracy of a photomask.

【0011】

[Means for solving problems]

In the method for producing a photomask of the present invention according to claim 1, a resist for electron beam is formed on the surface of the light-shielding film of a blank mask in which a light-shielding film is formed on a transparent substrate so that the film thickness is 280 nm to 350 nm. The resist is patterned by drawing and developing an electron beam, and then the light-shielding film is etched using the patterned resist as a mask.

【0012】

The method for producing a photomask of the present invention according to claim 2 is a resist for an electron beam on the surface of the light-shielding film of a blank mask in which a chromium film having a film thickness of 60 nm to 70 nm is formed as a light-shielding film on a transparent substrate. The resist is patterned by forming, drawing and developing an electron beam, and then the light-shielding film is etched using the patterned resist as a mask.

【0013】

The method for producing a photomask of the present invention according to claim 3 is a resist for an electron beam on the surface of the light-shielding film of a blank mask in which a chromium film having a film thickness of 60 nm to 70 nm is formed as a light-shielding film on a transparent substrate. The resist is patterned by drawing and developing an electron beam to form a film having a film thickness of 280 nm to 350 nm, and then the light-shielding film is etched using the patterned resist as a mask. is there.

【0014】

Further, in the method for producing a photomask of the present invention according to claim 4, the exposure amount of the electron beam exposure is 2.3 μC / cm.²To 2.6 μC / cm²The method for producing a photomask according to claim 1 or 3, wherein the photomask is characterized in that.

【0015】

Further, the method for producing a photomask of the present invention according to claim 5, wherein the light-shielding film is etched by dry etching, and the photomask according to any one of claims 1 to 4 is produced. The method.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail based on the embodiments.

【0017】

FIG. 1 is a manufacturing process diagram of a photomask according to an embodiment of the present invention, FIG. 2 is a correlation diagram between the chromium film thickness and the transmittance at each exposure wavelength, and FIG. 3 is a case where the resist film thickness is changed. It is a diagram showing the characteristics of the exposure amount and the line width dimension (CD: Critical Dimension) shift amount (deviation of the measured data with respect to the design data). Is defined as resist sensitivity (practical sensitivity) and plotted. FIG. 5 is a correlation diagram between resist film thickness and dimensional linearity limit value, and FIG. 6 is a correlation between resist film thickness and in-plane dimensional accuracy. It is a relational diagram, and FIG. 7A is a diagram showing an example of application to the OPC mask pattern of the present invention. Further, in FIG. 1, 1 is a transparent substrate, 2 is a chromium film, and 3 is a resist for EB.

【0018】

In Fig. 7, the resist used was "ZEP810S" manufactured by Nippon Zeon Corporation. In Fig. 7 (a), the resist film thickness was 300 nm, the chromium film thickness was 60 nm, and the exposure amount was 2.3 (1.15 ×). 2) μC / cm²In FIG. 7 (b), the resist film thickness is 500 nm, the chromium film thickness is 110 nm, and the exposure amount is 3.30 (1.65 × 2) μC / cm.²The case where the etching is performed by wet etching is shown.

【0019】

The present invention shortens the dry etching time by making the chromium film thickness as thin as possible, and reduces the loss of the resist film due to dry etching. As shown in FIG. 2, as the wavelength is shortened, the chrome film thin film becomes easier when the KrF excimer laser is used for EB drawing with the same transmittance setting. If the transmittance required for the performance of the light-shielding film is set to 0.5% or less without a sudden optical change, the chromium film thickness can be reduced to 60 nm when using a KrF excimer laser.

【0020】

Further, as shown in FIG. 4, the resist film thickness and the sensitivity have a substantially linear relationship, and a highly sensitive resist pattern can be easily obtained by thinning the resist. Therefore, the resist film thickness should be as large as possible. It needs to be thin.

【0021】

Since it is desirable that the dimensional linearity limit value is 1.000 μm or less, the optimum film thickness of the resist is about 280 nm to 350 nm, which is the dimensional linearity limit value of 1.000 μm or less, as shown in FIG. Further, if the resist used at this time is an EB resist, it is effective.

【0022】

The optimum value of the EB exposure amount when the optimum resist film thickness is 280 nm to 350 nm is 2.3 μC / cm as shown in FIG.²To 2.6 μC / cm²Will be. In fine pattern formation, it is necessary to correct the deterioration of dimensional linearity (resolution margin) by increasing the EB exposure amount, but since the thin film resist has high sensitivity, there is a sufficient margin in the correction exposure amount.

【0023】

Further, as shown in FIG. 6, the in-plane dimensional accuracy behaves the same as the dimensional linearity, the resolution margin is large, and the in-plane dimensional accuracy is 0.020 μm or less in a resist pattern (film thickness 280 nm to 350 nm) having a good pattern shape. can do.

【0024】

Further, since the chrome film thickness is thinned, the tapered shape of the chrome pattern is suppressed, and the edge roughness can be reduced by using dry etching.

【0025】

Hereinafter, the manufacturing process of the photomask according to the embodiment of the present invention will be described with reference to FIG. First, a chromium film 2 is formed on the transparent substrate 1 by sputtering, vacuum deposition, etc. at about 60 nm, and then a resist 3 is applied at 300 nm (FIG. 1 (a)). The resist 3 must have excellent etching resistance when etching the chromium film 2. In this embodiment, "ZEP810S" manufactured by Nippon Zeon Corporation was used.

【0026】

Next, in the EB drawing step, the light-shielding region is not drawn, and the transmission region is irradiated with an electron beam set to a required charge amount capable of completely removing the resist 3. There are two types of resist 3, negative type and positive type. Fig. 1 shows the case where a positive type resist is used. The part irradiated with the electron beam is dissolved in the developing solution, and the chromium film 2 is a part. Is exposed (Fig. 1 (b)).

【0027】

After development, dry etching of the exposed chromium film 2 is performed. For etching, a parallel plate type reactive ion etching method (RIE) was used. Etching gas is CCl₄(Tetrachloromethane) and O₂Mixed gas with (oxygen) or CH₂Cl₂(Dichloromethane) and O₂Flow ratio of mixed gas with (oxygen) is 25 sccm (CCl)₄Or CH₂Cl₂): 75sccm (O₂) Was controlled and used. The RF power is 200W (it can be used within 500W), the pressure is 0.250 Torr (33.25Pa), and the discharge frequency is 13.56MHz.

【0028】

The selectivity of chromium (Cr) and quartz under the above conditions is 25 to 30, and the etching rate of Cr is 55 nm / min. Further, the resist 3 acts as a protective film against etching, and only the chromium film 2 in the portion not covered by the resist is removed, and the transparent substrate 1 is partially exposed (FIG. 1 (c)). When a chlorine-based gas is used for the dry etching of the chromium film 2, the dry etching resistance of the resist 3 is sufficient.

【0029】

Next, after etching the chromium film 2, the entire surface of the resist 3 is removed (FIG. 1 (d)). The resist is peeled off by immersing it in a chemical solution in the order of dimethylformamide, acetone, and sulfuric acid hydrogen peroxide. In this case, the resistance of the transparent substrate 1 and the chromium film 2 to the chemical solution is sufficient.

【0030】

In this embodiment, as a result of patterning the chromium film 2 having a film thickness of about 60 nm using a resist having a film thickness of 300 nm, a good rectangular patterning shape as shown in FIG. 7A was obtained. However, in the case of a thinner resist film thickness (250 nm), the resist film thickness at the time of etching becomes insufficient, so that the corner portion becomes a round shape and the pattern shape deteriorates.

【0031】

In this case, not only the dimensional linearity is poor as shown in FIG. 5, but also the in-plane dimensional accuracy is poor as shown in FIG. From this, a resist having a film thickness of 280 nm to 350 nm can ensure dimensional linearity and in-plane dimensional accuracy.

【0032】

[Effect of the invention]

As described in detail above, a high-sensitivity and high-resolution resist pattern can be obtained by thinning the resist using the present invention according to claim 1, claim 3 or claim 4. In particular, in the combination of the chromium film thickness of 60 nm and the resist film thickness of 280 nm to 350 nm, the dimensional linearity can be up to 1 μm or less. Since the thin film resist of 280 nm to 350 nm has high sensitivity, there is a sufficient margin for the corrected exposure amount.

【0033】

Further, by using the present invention according to claim 2, claim 3 or claim 4, the chromium film is thinned to a thickness of 60 nm to 70 nm, so that the transmittance of the chromium film is 0.5% without a sudden optical change. While maintaining the following, the etching time can be shortened, and the loss of the resist film during dry etching can be reduced.

【0034】

Further, by using the present invention according to claim 5 and using dry etching for etching the light-shielding film, the edge roughness is reduced, and by making the chrome film thickness thinner than before, the taper is reduced and the shape of the chrome pattern is reduced. Since the corner round (roundness) of the pattern did not progress due to the improvement in the thickness of the resist and the thin film thickness of the resist, a good pattern shape was obtained.

[Simple explanation of drawings]

[Figure 1]

It is a manufacturing process diagram of the photomask of one Embodiment of this invention.

[Figure 2]

It is a correlation diagram of the chromium film thickness and the transmittance at each exposure wavelength.

[Fig. 3]

It is a figure which shows the characteristic of the exposure amount and the CD shift amount when the resist film thickness is changed.

[Fig. 4]

FIG. 3 is a diagram in which the EB exposure amount at which the CD shift amount is zero is plotted.

[Fig. 5]

It is a correlation diagram of a resist film thickness and a dimensional linearity limit value.

[Fig. 6]

It is a relationship diagram of a resist film thickness and in-plane dimensional accuracy.

[Fig. 7]

(a) is a diagram showing an application example to the mask pattern of the present invention, (b) is an application example to the mask pattern of the prior art, and (c) is a diagram showing a design mask pattern.

[Fig. 8]

It is a figure which provides the explanation of the problem of the prior art.

[Explanation of symbols]

1 Transparent substrate 2 Chrome film 3 resist 4 OPC pattern