JPH0154691B2 - - Google Patents

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A Industrial field of application B Overview of disclosure C Prior art D Problem to be solved by the invention E Means for solving the problem F Example F ₁ Example of resist material F ₂ Outline of the method of the present invention F ₃ Effects of exposure (Figures 1, 2 and 3) _F4 Specific Example G Effect of the invention A Field of industrial application The present invention relates to a method for processing a mask having a two-layer resist structure, and more specifically relates to a method for processing a mask having a two-layer resist structure. The present invention relates to a method for enhancing the opacity of an imaging mask based on. The present invention also relates to a method for processing masks of two-layer resist structure, all developable with water-soluble bases.

B. SUMMARY OF THE DISCLOSURE The mask processing method of the present invention enhances the opacity of novolak resin based masks. The method uses water-soluble base-developable, 200 to
A lower layer of deep UV resist sensitive to wavelengths in the range below 280 nm is applied on the substrate, then an upper resist layer based on novolak resin is applied, the upper resist layer is imagewise exposed, and then Develop it and use it as an image-forming mask. This imaging mask is then subjected to a treatment of exposure to ultraviolet light having a wavelength in the range of 280 to 310 nm, or a combination of heating and plasma curing, followed by a treatment of 200 nm through the imaging mask. The lower resist layer is exposed to ultraviolet light having wavelengths between and below 280 nm, and the lower resist layer is developed to form an image that corresponds to the image on the imaging mask. If the substrate is provided with a lower resist layer of water-soluble base-developable material and is provided thereon with an upper resist layer of water-soluble base-developable material,
An entirely water-soluble resist system is obtained.

C. Prior Art Mask technology with a two-layer resist structure is known to be insensitive to underlying surface irregularities and to form a resist image with a high aspect ratio (ratio of mask thickness to minimum line width). This technique is used in subtractive etching and lift-off metallization processes. The basis of this technology is the Tokuko Sho 61-13746
As disclosed in the issue of
(UV) The image of the novolak resist is used as a mask when the resist layer is uniformly exposed to deep UV light. An important aspect of the two-layer resist structure mask technology is that it is currently known for forming high aspect ratio resist images with micron and sub-micron dimensions that are insensitive to surface irregularities without the use of reactive ion etching. The fact is that it is the only way. This technique is desirable because reactive ion etching processes are complex, costly, and difficult to maintain reproducible control.

Novolac resins mixed with certain sensitizers are useful in resist formulations and are used in mask technology for two-layer resist structures. These resists are used in the upper resist layer as described in US Pat. No. 4,078,569. This US patent discloses a resist that is sensitive to electron beams or deep ultraviolet radiation. A major limitation of the two-layer resist process using novolak resin-based resists is that the novolak resin-based resists are not completely opaque in the deep UV region. This material has a significant transmission "window" between 240 and 280 nm. Therefore, because of this transmission window, the light transmitted through the novolak resin-based resist limits the overall contrast that can be obtained with a two-layer resist process. Therefore, thin films thicker than 0.5 μm are required, which limits resolution. As a result, the aspect ratio also decreases, and interlayer adhesion is adversely affected, making the selection of far-UV resists more difficult.
When exposing a two-layer resist with an electron beam,
Because the thin upper resist layer reduces proximity effects,
Increased resolution allows formation of small features.

Two methods are currently used to overcome the drawbacks of this two-layer resist mask. The first method involves carefully filtering the wavelengths of deep UV light to remove wavelengths greater than 240 nm. This method is sensitive to wavelengths below 240 nm.
Limited to UV resist. These far-UV resists sensitive below 240 nm are low-sensitivity acrylate resins. A second method is to add materials to the novolak resin that increase opacity at 240-280 nm.

The method of filtering wavelengths above 240 nm has several drawbacks. When using this filter technique, the light output is relatively low, so much of the available radiation is wasted and the exposure time must be increased. Furthermore, filter devices are expensive.

The second method, which involves adding materials to the novolak resin that absorb wavelengths between 240 and 280 nm, is less desirable than the first method. These additional materials degrade the lithographic properties of the resist.
This is because such additives change the solubility and optical properties of the resist thin film. Some of these additives also reduce the lifetime of resist solutions used in thin film production. Therefore, in a far-UV light exposure type two-layer resist mask using an upper resist layer based on novolak resin, it is possible to effectively increase the opacity of the upper novolak resist layer to far-UV light. is desirable.

Polymethyl methacrylate (PMMA) is used as a far-UV photoresist, and this is used as a near-UV photoresist.
For example, the two-layer resist mask technology covered with a novolak resist as a photoresist was developed by Tokko Sho.
It is generally known as disclosed in No. 61-13746. In this technique, the upper novolak resist is imagewise exposed and then developed. Since the upper novolak resist must act as a contact mask for the exposure of the lower PMMA photoresist, the image area of novolak resin remaining after development must strongly absorb wavelengths in the radiation range to which PMMA is sensitive. It won't happen. In this case, the lower PMMA deep UV photoresist exposed through the upper novolak resist mask becomes the ultimate photoresist pattern on the underlying substrate. However, Japanese Patent Publication No. 61-13746 does not teach a technique for increasing the opacity of the upper novolak resist layer as the present invention does.

D. Problems to be Solved by the Invention In view of the shortcomings of the prior art, it is an object of the present invention to increase the opacity of novolak resists so that high-resolution images can be produced effectively.

E Means for Solving the Problems Simply put, the present invention provides a method for exposing and developing a two-layer mask using an upper resist layer based on a novolac resin, after the upper resist layer is exposed and developed. Before exposing the lower far-UV resist layer, an intermediate treatment is performed to increase the opacity of the upper resist layer (image-forming resist layer).

As this intermediate treatment for promoting opacity, the exposed and developed upper image-forming resist layer is
Exposure to ultraviolet light in the wavelength range of 310 nm or a combination of heating and plasma curing treatment.

According to the present invention, it is possible to obtain a two-layer resist mask that can be treated entirely with a water-soluble base. The upper and lower layers must each be sensitive to different wavelengths.

F Example Referring to FIGS. 1-3, the light absorption effect of novolac resins upon exposure to UV light in the wavelength range of 240-280 nm is illustrated. FIG. 1 shows a case in which a novolac resin is included, and FIGS. 2 and 3 show cases in which a sensitizer (described later) is further included. As you can see from the graph,
After UV exposure at wavelengths of 280-310 nm according to the present invention, thin films become significantly opaque, or windowed, to wavelengths below about 300 nm.

Examples of F ₁ resist materials Suitable examples of water-soluble base-developable novolak resins which can be used in the present invention include, for example, phenolic or alkyl (C ₁ -C ₆ ) substituted and halogen substituted phenols (e.g. cresol, etc.), resorcinol. , or pyrogal and acetaldehyde, acetone, acrolein, benzaldehyde, 1,
Condensation products with aldehydes or aldehyde precursors, such as 3,5-trioxane, and novolak resins, such as addition polymers of hydroxy styrene. Resins that can be developed with suitable water-soluble bases are approximately
It has a molecular weight of 300 to about 100,000, preferably 300 to 20,000.

The composition of the novolak resins that can be used to form the novolak resin-based upper resist layer used in these embodiments of the invention generally increases the sensitivity to exposing radiation, as disclosed in U.S. Pat. No. 3046121, No. 3106465, No.
3201239, 3666473, 1,2 photosensitizers such as 1-oxo-2-diazonaphthalene-5-sulfonic acid esters of 2,3,4-trihydroxybenzophenone; -Diazonaphthoquinone-5-sulfonic acid type photosensitizers are generally included. This type of UV photoresist based on a suitable commercially available novolak resin
AZ1350 (sold by Azoplate),
HPR204 (trade name of a resist consisting of a novolac resin and a diazoquinone photosensitizer) and HPR204 (trade name of a resist consisting of a novolac resin and a diazoquinone photosensitizer, sold by Hunt Chemical). Other resists using different combinations of novolac resins and other photosensitizers can also be used in the present invention if desired. For example, the example of FIG. 2 used a novolac resin containing a polyolefin sulfone sensitizer such as the polymethylallyl ether-methyl pentene sulfone bipolymer described in U.S. Pat. No. 4,398,001. Commercial examples of this class of novolak compositions are
RE5000P (trade name of an electron beam resist made of novolac resin and poly-2-methyl pentane sulfone sold by Hitachi Chemical).

Suitable materials that can be used as the lower deep UV resist layer used in the masks of the present invention are those that are soluble in water-soluble base developers.

Exemplary materials developable with aqueous base developers that can be used in the present invention as the lower deep UV resist layer include methacrylate terpolymers, such as terpolymers of methyl methacrylate, methacrylic acid, and methacrylic anhydride (e.g., U.S. Pat.
3087659), aliphatic imide polymers such as polydimethyl glutarimide, other acrylic acid polymers, polymethyl methacrylate-methacrylic acid polymers, itaconic acid polymers such as poly-dimethyl itaconic acid, and (Hydroxystyrene).

If necessary, azido-polyvinyl phenol (for example, disclosed in U.S. Pat. Nos. 4,268,603, 4,148,655, etc.) (R93000N and
RE2000N), diazoquinone phenolic resin or novolac resin (A21350 from Azoplate)
Positive and negative resist materials can be used, such as.

When exposing the upper resist layer, the lower resist layer can be dyed, for example, with a dye, if desired. Suitable properties of this dye are thermal stability and the ability to absorb the wavelength of the UV light used to expose the upper resist. Suitable specific examples include coumarin dyes such as Coumarin 6, Coumarin 7 and Coumarin 30 sold by Kodak.

Suitable resist materials that can be used to form the upper resist layer in all water-soluble base developable two-layer resist mask embodiments of the present invention include polymeric materials that can be used in combination with sensitizers or photoactive components. It is. Suitable polymeric materials are selected from novolak resins, polyvinyl phenol-based polymers, or polymers that can be converted to polyvinyl phenol by irradiation or a combination of irradiation and heat treatment when a photoactive component is added to the polymer. can. These are about 300 to about 500 nm
Sensitive to wavelengths in the range of .

Particular examples include novolac resins sensitized with diazoquinone derivatives. Examples of suitable resist materials comprising polyvinyl phenol and bis aryl azide are described in US Pat. No. 4,268,603. An example of a polymer that converts to polyvinyl phenol upon irradiation and heat treatment in the presence of an aryl onium salt photoactive component is poly(P-tart.
butoxycarbonyloxystyrene), poly(tert-butyl P-vinylbenzoate), poly(P-tert-butoxycarbonyloxy-2-
methylstyrene), poly(tert-butyl P-isopropenyloxyacetate) and poly(tert-butyl methacrylate), such as those disclosed in US Pat. No. 4,491,628.

All aqueous developable two-layer resists of the present invention.
Suitable resist materials for the underlayer that can be used in mask embodiments are polymers selected from the following groups, including at least a covalent portion thereof: These resist materials are sensitive to UV wavelengths of about 200 to about 280 nm.

(1) Polymers containing carboxylic acid groups that, upon irradiation, become developable with water-soluble bases, such as terpolymers of methyl methacrylate, methacrylic acid, and methacrylic anhydride.

(2) Anhydride (anhydride) is hydrolyzed by irradiation, or after irradiation, anhydride is hydrolyzed in the presence of a water-soluble base developer to form methacrylic anhydride and acrylic anhydride. Polymers containing acid-giving acid anhydride groups, such as copolymers.

(3) Polymers containing imide groups that are developable with water-soluble bases such as polyglutarimide and polymaleimide upon irradiation.

(4) By irradiation, O-nitrobenzaldehyde derivatives, photo-Fries reaction (photo-Fries) as disclosed in U.S. Pat.
polymers capable of generating phenolic or hydroxyl groups, such as the "t-boc"series;

Various sensitizers can be used to enhance the photosensitivity of polymers suitable for use in the present invention. The use of sensitizers is not necessary in many cases. This is because, with the exception of the onium salt-"t-box" polymers of group (4), the water-soluble base developable polymers are themselves photosensitive.

The lower resist layer of the two-layer resist mask may be a resist material developed with an organic solvent, such as polymethyl methacrylate (PMMA) polymer, polymethyl isopropenyl ketone, poly-t-butyl methacrylate, and other resist materials. The use of polymethacrylate copolymers is also considered, but these resist materials are not preferred when using novolac resin-based opacification of the upper resist layer to achieve high-resolution, sharp images. . That is, as described below with respect to FIG. 2 and Example 2, when opaqueizing the upper novolak resist layer, heat treatment can be used in combination with UV exposure at 280 to 310 nm to increase the efficiency of the opaque process. Alternatively, heat treatment can be performed before exposing the lower resist layer to stabilize the exposed and developed upper novolak resist layer. After the resist layer is developed, the novolac resin remaining on the lower resist layer (novolac residue left in the developed area without being completely removed) undergoes a crosslinking reaction, forming methyl resin at the boundary between the upper resist layer and the lower resist layer. This produces crosslinked novolac residues that are insoluble in organic solvents such as isobutyl ketone (MIBK), resulting in the inability to obtain high-resolution, sharp images. Therefore, in this case, it is necessary to either not use heat treatment or to perform an additional removal step such as plasma etching to remove the novolac residue, and if heat treatment is used, the process Make it complicated. Experiments have shown that when a resist material that can be developed with a water-soluble basic solvent is used as the lower resist layer, no residue is generated at the boundary even when heat treatment is involved, and a clear image with high resolution can be obtained. did. This means that if a resist material such as a water-soluble basic solvent developable terpolymer is used as the lower resist layer, the interface will be in the form of a mixture with the lower resist material exposed to far-UV light. This is believed to be due to the formation of novolak residues, which make the mixture soluble in water-soluble basic solvents. The upper novolak resist in the unexposed areas is not mixed as described above and remains on top of the lower resist layer after development of the lower resist layer.

_F2 Overview of the Method of the Invention Using the materials described above, mask materials that can be used in embodiments of the invention can be easily prepared.

Specifically, on a substrate, such as a surface-oxidized silicon wafer, resist material for the lower resist layer is first deposited, preferably from about 0.5 to about 5 μm, using conventional coating techniques such as spin coating. was coated to a uniform thickness of 1 to 3 μm and dried. This was followed by coating an upper resist layer with a thickness of about 0.3 to about 1.5 μm, preferably 0.5 to 1.0 μm, over the lower resist layer. A suitable technique for applying the upper resist layer is spin coating, followed by drying.

After the mask material of the present invention was formed, it was imagewise exposed to radiation to which the upper resist layer was sensitive, using a chromium-coated glass master as an image. The appropriate wavelength of the radiation used for this exposure is approximately 300nm.
to about 450nm or less, preferably from 350nm to 440nm
The range is up to Suitable radiation sources that can be used for exposure to wavelengths in this range include mercury vapor lamps, mercury-xenon lamps, and the like. Alternatively, the upper resist layer can be imagewise exposed to electron beam radiation or to X-rays.

After exposure of the upper resist layer, the mask material is PH
is developed with a water-soluble base developer having a 12 to about 13. Suitable examples of water-soluble base developers that can be used in the present invention include potassium hydroxide, sodium hydroxide, tetramethyl ammonium hydroxide, sodium silicate, sodium phosphate, and the like. These developers are commercially available from Azoplate as AZ Developer and from Shipley as Microporit 2401. As a result of exposure, the exposed areas of the upper resist layer become soluble in the aqueous base developer and are removed by contact with the developer, exposing the lower resist layer in these removed areas. . Naturally, in the areas removed by this development, either the upper resist layer is a positive resist or the upper resist layer is a negative resist.
Depends on the resist.

As a result of this exposure and development of the upper resist layer, a mask image corresponding to the original resist image is formed in the upper resist layer and serves as an imaging mask for the lower resist layer.

The next step, which is to enhance the opacity of the developed upper mask layer (imaging mask) to deep UV radiation, involves applying the resulting image mask at a temperature of approximately 20° C. to 200° C., at a wavelength of 280 to 320 nm. Preferably
Exposure to radiation having a wavelength of 280-310 nm.
For example, a full exposure is used. Suitable sources for radiation in this wavelength range are mercury-xenon and mercury vapor lamps. This exposure reduces the remaining image area of the upper resist layer to deep UV exposure, i.e.
It was found that the area becomes opaque to ultraviolet light. A suitable exposure dose for this exposure step is about 1 to about 20, preferably 5 to 20 joules/cm ² .

The first exposure step for opacification as described above, i.e.
After exposure to UV radiation with a wavelength of 280-310 nm, a second imagewise exposure step is performed. The radiation suitable for this exposure is the radiation to which the underlying resist layer is sensitive.
The appropriate wavelength of radiation for this exposure is 200 to
It is less than 280 nm, preferably in the range of 200 to 240 nm. Suitable radiation sources with wavelengths in this range include mercury arc lamps and the like.

As a result of this exposure, the lower resist layer is developable in a developer. Suitable water-soluble base developers for the lower resist layer are those with a PH of 12.5 to 13.5. Exemplary aqueous base developers that can be used include aqueous solutions of sodium hydroxide, potassium hydroxide, tetramethyammonium hydroxide, sodium phosphate, and sodium silicate. Appropriate times and temperatures for this development are about 1 minute to about 10 minutes, and about 10 minutes, respectively.
The temperature is between 10°C and 25°C.

As a result of the above-described processing, a mask is formed on the substrate.

Effect of F ₃ Exposure Referring to the figures, the improvement in opacity (absorption ε) by the method of the invention is shown, for example when using a novolak resin as the upper resist layer.

The data in Figure 1 uses a low power lamp (250W),
The images were obtained using fairly long exposure times of about 5 to 30 minutes. However, using higher power lamp designs, the processing time can be reduced by approximately a factor of 10. High speed exposure equipment is available to reduce processing time.

FIG. 2 shows that a similar change can be induced thermally using a novolac/polyolefin sulfone sensitizer resist. Therefore, the processing time can be further reduced by combining UV exposure and heat treatment.

FIG. 3 shows the effect of the method of the invention on a thin film (0.5 .mu.m) of resist consisting of a novolac resin (a cresol-formaldehyde condensate having a molecular weight of 6000) and a naphthoquinone diazide photosensitizer.

When the novolak resist used in Figure 3 with a thickness of 0.5 μm is used as a mask and processed (this intermediate treatment uses a filter to remove wavelengths below 280 nm, it is processed at a wavelength of 300 nm)
Acrylic terpolymers (70:15 molar ratio of methyl ^methacrylate , methacrylic anhydride and methacrylic acid: A deep UV resist consisting of a ternary copolymer of No. 15) was exposed to ultraviolet light at wavelengths between 200 and less than 280 μm (see US Pat. No. 4,087,569).
The contrast resulting from this exposure was determined by measuring the dissolution rate of the masked and unmasked portions of the film in a developer consisting of 2-ethoxyethanol. Samples using masks that were intermediately treated with radiation at wavelengths between 280 and 310 nm showed a 32% increase in contrast (ratio of solubility between exposed and unexposed areas) compared to untreated samples. Figure 1 (resin), Figure 2 (resin and polyolefin sulfone sensitizer) and Figure 3 (resin and naphthoquinone diazide sensitizer) show that this effect is a result of the properties of the resin, and all similar to novolak. This can generally be said about resist systems.

When implementing the above-described embodiments of the present invention, the masking ability of novolak resists to deep UV light is improved. This improvement occurs without changing the lithographic performance of the resist. Moreover, there is no need to use expensive and inefficient filter devices.

Although embodiments of the present invention are specific to the examples and materials disclosed herein, opacification may by itself be approximately
It is applicable to any two-layer resist mask technique that uses a novolak resist as a mask for exposure of a lower resist layer sensitive to wavelengths below 200-280 nm.

When novolac is used for the upper resist layer and a resist that can be developed with a water-soluble base is used for the lower resist layer, the lower resist layer can be developed immediately after exposure without additional processing such as heat treatment. However, if necessary, after exposure of the lower resist layer,
100℃ to approx. 200℃ to stabilize the upper resist layer.
Baking heat treatment can be carried out at a temperature of 120 to 150°C, preferably for about 1 to 10 minutes, preferably 5 to 10 minutes. Full surface for opacity
Instead of UV exposure curing, plasma curing treatment can also be used in combination with heat treatment. This process is described in U.S. Patent No. 4187331, 1981 Journal of Vac. Sci. & Tech.
Moran (J.Moran) and G. Taylor (G.
This is known as a plasma hardening process for resist layers, as disclosed in the paper by John Taylor. For plasma curing techniques, U.S. Patent No.
See also US Pat. No. 4,253,388. Because the mask layer is typically 1.0 microns or less thick, plasma curing methods are more effective for embodiments of the present invention than curing methods reported in the literature. When a combination of heating and plasma curing is used instead of full-surface UV exposure for opacity, the opacity effect of baking and the opacity effect of plasma curing are combined, as shown in Figure 2, and the opacity effect is sufficient. It was found that a good opacity can be obtained.

_F4 Specific Examples In the following description, all parts, percentages, ratios, etc. are expressed in units of weight unless otherwise specified.

Example 1 A silicon wafer with a thermally grown oxide layer 5000 Å thick was coated with an acrylic terpolymer resist (methyl methacrylate, methacrylic anhydride and methacrylic acid in a molar ratio of 70:
15:15 terpolymer) followed by a 1.7 μm layer of diazoquinone/novolac photoresist.
Covered with a 0.5 μm layer and baked at 80°C for 30 minutes. The upper resist layer was patterned by exposure using a GCA6000 step-and-repeat camera (commercially available from GCA). The resist was then developed in a 0.2N KOH aqueous solution for 1.5 minutes at a temperature of 23°C. This patterned upper resist layer was exposed to UV at wavelengths of 280-310nm using a Microlite 100m with a 280nm cut-off filter.
(sold by Fusion Semiconductor Systems Inc.). The UV treatment time was 800 seconds. Following this, the lower far
UV resist 200~200 using the camera mentioned above.
It was exposed to light at a wavelength of 240 nm and developed in a dilute solution of tetramethylammonium hydroxide (approximately 1% by weight). Good quality submicron (0.8 micron)
image was obtained.

Comparative Example 1 The same silicone material was treated in the same manner as in Example 1 except that 280 to 310 nm UV exposure treatment was not used.
In the case of wafers, resolution was limited to about 1.2 or 1.1 μm. There were almost no 1 micron images, and no submicron images were obtained.

Example 2 A silicon wafer with a 5000 Å thick thermally grown oxide layer was prepared as shown in Example 1.
Coated with 1.7μm acrylic terpolymer and heated at 200℃
Baking treatment was performed. Example 1 Layers of each wafer
It was coated with a layer of diazoquinone/novolak photoresist such as . image-wise exposing the novolak photoresist layer with an exposure dose of 75 mJ/ ^cm2 ;
Developed with 0.20N KOH aqueous solution developer.

The wafer with the patterned and developed novolak resist layer was then exposed to 300 nm radiation (35 mW/cm ² ) was exposed for 600 seconds to make the novolak resin image opaque to the 240-280 nm region.

One wafer thus obtained was thermally treated at 150°C for 10 minutes, and the other wafer was similarly heat-treated and then further heat-treated at 180°C for 5 minutes.

The lower resist layer is then passed through the patterned upper novolak resist layer using a Microlite 100m radiation source.
Exposure was made to a wavelength of 200 to 250 nm (230 nm) with an exposure dose of 1500 mJ/cm ² . The acrylic terpolymer resist layer of each of the samples thus obtained was then treated with a 1:1.15 (by volume) diluted aqueous solution of 0.32N tetramethyl ammonium hydroxide (Allied Corporation). Acculith produced
LM1600). Clear images with no novolak resin residue at the borders were obtained in each case.

The above results show that the UV of novolak resin resist
When UV exposure is combined with subsequent heat treatment to improve optical opacity, the underlying acrylic terpolymer resist layer can be clearly developed, yet can be easily developed using a non-staining water-based base developer. It is shown that the residue at the border can be clearly removed by developing the acrylic terpolymer deep UV resist layer on the side.

Comparative Example 2 A polymethyl methacrylate (PMMA) resist layer was used on a silicon wafer instead of an acrylic terpolymer resist layer as the lower resist layer, and the PMMA was heated at 160 °C for 30 minutes, and then the upper diazoquinone/ A novolak resist layer was applied. The novolak resist layer on each of the silicon wafers was then imagewise exposed and developed as described in Example 2.

One silicon wafer (sample 1) developed in this way was thermally treated at 150°C for 10 minutes, and then
silicon wafer (sample 2) at 150℃ for 10
minutes, followed by thermal treatment at 180° C. for 5 minutes.

The lower PMMA resist layer was then exposed using a Microlite 100m radiation source through the patterned upper novolak resin resist layer as described in Example 2 at 150 mJ/
Exposure was at a wavelength of 230 nm with an exposure dose of cm ² .

The exposed PMMA resist layer of Sample 1 was developed in methyl isobutyl ketone (MIBK) for 75 seconds to remove the exposed areas of PMMA. However, in the image area, PMMA
Residue remained at the interface between the layer and the novolac layer.

Even after developing with MIBK for an additional 25 seconds, the residue at the border could not be removed. It was found that using isopropyl alcohol (IPA) as a cleaning solution did not remove the residue at the interface.

Sample 2 was also exposed as described above.
Develop the PMMA resist layer in MIBK for 90 seconds.
Although the PMMA was removed, very high levels of interfacial residue remained.

G Effects of the Invention According to the present invention, a clear mask image with high resolution can be easily, economically, and efficiently realized in a mask with a two-layer resist structure using an upper resist layer based on novolak resin. be able to.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the absorption rate of novolak resin and wavelength when the irradiation time is changed. FIG. 2 is a graph showing the relationship between absorption coefficient and wavelength of a resist composed of a novolac resin and a polyolefin sulfone sensitizer. FIG. 3 is a graph of absorption versus wavelength for a novolak photoresist comprising a novolak resin and a diazoquinone sensitizer.

Claims (1)

[Scope of Claims] 1 (a) A lower resist layer developable with a water-soluble base sensitive to ultraviolet rays having a wavelength of 200 nm to less than 280 nm and an upper resist layer based on a novolak resin are formed on a substrate. (b) imagewise exposing the upper resist layer; (c) developing the upper resist layer to convert it into an imaging mask;
(e) exposing the lower resist layer to ultraviolet light having a wavelength of 200 nm to less than 280 nm through the imaging mask; and (f) developing the lower resist layer to form an image that corresponds to the image of the imaging mask.