METHOD OF FORMING A PHOTORESIST PATTERN

Abstract: A method of forming a photoresist pattern contains steps that a photoresist coating film (2) of naphthoquinone diazide sulfonate of novolak is formed on a substrate layer (1), the photoresist coating film (2) is exposed by selectively irradiating with near ultraviolet radiation (10) of 300 to 450 nm through a photomask (3), the exposed photoresist coating film (2) is developed with an either negative type or positive type developing solution. The resultant photoresist pattern (5) or (6) is usable for manufacturing a highly integrated circuit such as LSI which needs fine processing.

Description: The present invention relates to a method of forming a photoresist pattern. The photoresist pattern is specifically used for manufacturing semiconductor devices with a submicrometer resolution. In the semiconductor technical field, there is a glowing need for higher integration of semiconductor devices. Accordingly, there is a severe technical demand for the production of fine photoresist patterns. One of the fine processing methods employs ionization radiation such as electron beams, X-rays, shortwavelength ultraviolet radiation and the like so as to form the photoresist pattern, and thereafter precisely transfer the photoresist pattern onto underlying layers, e.g., substrates by dry-etching treatment in which ion or plasma has been filled. As a transfer apparatus for forming a photoresist pattern for a fine process, as an optical reduction type transfer apparatus (aligner) has been mainly used because the equipment of its properties of high resolution and high accuracy for alignment. As a light source of this type of transfer apparatus, g-line emitted from the mercury vaper lamp and being in a region of near ultraviolet region is most expected in view of lower absorption in the optical system and higher light outputs. However, as a positive type photoresist for photolithography using the near ultraviolet radiation, due to high resolution and dry etching resistance, a photoresist is used which is obtained by mixing novolak resin and naphthoquinone diazide of a photosensitive material. Further, as a negative type photoresist, a photoresist obtained by mixing polyvinyl phenol and bisazide is used. This resist has high sensitivity at the i-line (365 nm). However, as to the light of the g-line (436 nm) being most expected as a light source of the optical reduction type transfer apparatus, the sensitivity of the above negative type photoresist is low. Further, the positive type photoresists have difficulty in maintaining good line width control over the topography because of the reflective notching caused by reflected light from the substrate. If the negative and positive type photoresist patterns are able to be formed only by selecting developing solutions, it is possible to select a method by which the negative or positive type photoresist pattern can be easily obtained in accordance with the photoresist pattern. As a result, various merits are achieved in the manufacturing of semiconductor devices. It is therefore an object of the present invention to provide a method of forming a negative type photoresist pattern by using properly the negative type developing solution and for forming a constant line width pattern even over the substrate topography. The object of the invention may be accomplished by providing a method of forming a photoresist pattern according to the following steps. A coating film of naphthoquinone diazide sulfonate of novolak as a photoresist coating film is firstly formed on a substrate or other underlying layer. Then, this coating film is exposed by irradiating with near ultraviolet radiation of from 300 to 450 nm through a photomask of a desirable pattern which is to be copied to the coating film. If the light wavelength is above 450 nm, the resist is not sensitized. Accordingly, the light source having the above wavelength region is used. Subsequently, when the negative pattern is formed, the irradiated coating film is developed with a negative type developing solution. Through such treating steps, it is possible to form the desired negative type photoresist pattern on an underlying layer. In Microelectronic Engineering, vol. 1, no. 4, Dec. 1983, p. 269 - 293, there is discloses that negative film relief images can be obtained from diazoquinone/novolak photoresists by using neutral organic solvents for the developing step. US-A- 3 046 114 relates to aromatic hydrocarbons, such as benzene and xylene, as developers for naphthoquinone diazide systems. The method of forming a photoresist pattern comprises the steps of: forming a photoresist coating film (2) naphthoquinone diazide sulfonate of novolak on an underlying layer (1), exposing the photoresist coating film (2) by selectively irradiating with ultraviolet radiation (10) of 300 to 450 nm through a photomask (3) developing the exposed photoresist coating film (2) with a negative type developing solution containing one or more solvents selected from the group of halogen-containing solvents, thereby removing an unexposed portion of the photoresist coating film (2). The negative type developing solution is preferably a solution which is made by mixing the nonpolar halogen-containing solvent with one or more solutions selected from the group consisting of cyclohexane, n-hexane and petroleum ether. In a preferred embodiment of the present invention, the halogen-containing solvent consists of one or more sovents selected from the group consisting of monochlorobenzene, trichloroethylene, chloroform, dichloromethane and dichloroethane. As described above, the present invention is able to form the photoresist coating film of naphthoquinone diazide sulfonate of novolak, expose the photoresist coating film by irradiating with near ultraviolet radiation, and selectively use a negative type halogen-containing developing solution for the exposed photoresist coating film in accordance with a desirable pattern to be formed. These and other feature and advantages of the present invention will become readily apparent from the following detailed description of embodiments of the present invention, particularly when taken in connection with accompanying drawings wherein like reference numerals designate like or functionally equivalent parts throughout, and wherein; Figs. 1A to 1C are sectional views illustrating steps of forming a negative type photoresist pattern according to the present invention. A detailed description will now be made of preferred embodiments according to the invention. It should be understood that the invention is not restricted to the specific embodiments of materials, numerical datum, but it provides the similar effects as those obtained by substituting the other materials, numerical datum. Example I Referring to Figs. 1A to 1C, naphthoquinone diazide sulfonate of novolak (referred as "NQN") was dissolved into methyl cellosolve acetate at the rate of 10 to 40 weight %, this solution was then filtered through a filter (not shown) having a throughole diameter of 0.2 µm and applied onto a silicon wafer 1, thereby forming the coating film 2 having a thickness of 0.7 µm by way of a spin coating method. This silicon wafer 1 functions as a base or underlying layer. Then, this silicon wafer 1 having a photoresist coating film 2 of NQN was prebaked at a temperature of 70°C for about 30 minutes. Thereafter, the resist coating film 2 of NQN was treated by exposing with the g-line of a 250 W mercury lamp of the 1/5 optical reduction type aligner (not shown in detail). The exposure dose was 50 mJ/cm². Accordingly, a photomask pattern 3 was transferred onto the NQN coating film 2. Thereafter, the wafer 1 having the exposed NQN coating film 2 was interbaked at a temperature range of 60 to 130°C, preferably 100°C for approximately 30 minutes. Such an interbaking treatment to the exposed NQN coating film 2 increases its sensitivity without lowering its resolution. According to this example, this NQN coating film 2 was developed for 35 seconds by employing a mixutre type developing solution containing a volume rate of 10 : 1 of monochloro benzene and cyclohexane. The temperature of this developing solution was 23°C. Subsequently, the coating film 2 was rinsed in cyclohexane for 10 seconds, so that concaves (not shown) were formed in unexposed surface portions of the substrate or wafer 1, to which no ultraviolet radiation 10 had been projected because these portions were located under the photomask 3. Thus, a negative type photoresist pattern 5 was fabricated. It could be recognized that such a negative type photoresist pattern 5 could have clean, sharp and rectangular sectional plane and also resolved to a 0.6 µm line and space pattern by observing with a scanning electron microscope. Example II In this example, a substrate consisting of a silicon water and an alminum layer formed thereon instead of the silicon wafer 1 as described in Fig. 1 was employed and the same film forming process as in the Example I was conducted. As a result of this example, the recognition could be made in that the resultant photoresist pattern was resolved to a 0.7 µm line and space pattern by observing with the scanning electron microscope. Example III (heat resistance experiments) The photoresist pattern fabricated according to the example I was baked at a temperature of 150°C for 30 minutes. The edge portion of the baked photoresist pattern was not deformed when observed by the scanning electron microscope. For the sake of comparison, Az-1350J (i.e., the photoresist commercially available from Shipley corporation) was applied to the same substrate under the same conditions to form the conventional photoresist pattern. When the conventional photoresist pattern was baked at a temperature of 150°C, the edge portion thereof was deformed so that the sectional plane of the photoresist pattern was rounded. Example IV Naphthoquinone diazide sulfonate of novolak (NQN) was dissolved into methyl cellosolve acetate at the rate of 25 weight %, this solution was then filtered through a filter having a throughhole diameter of 0.2 µm and applied onto the silicon wafer in a coating thickness of 0.8 µm by using a spin coating method. Then, this silicon wafer having a photoresist coating of NQN was prebaked at a temperature of 60°C for about 30 minutes. After this prebaking, the resist coating of NQN was treated by contact-exposing with a 250 W mercury lamp. The dose amount was 100 mJ/cm². The exposed film was developed by using trichloroethylene at a temperature of 23°C for 30 seconds and rinsed with cyclohexane at a temperature of 23°C for 15 seconds. Then a negative type photoresist pattern was obtained. It could be recognized that the negative type photoresist pattern was resolved to a 1.0µm line and space pattern, and the thickness of the remaining coating film after development was 0.8 µm. Example V A coating of naphthoquinone diazide sulfonate of novolak (NQN) was formed and exposed as described in Example V. The coating was developed by using a solution containing 3 parts by weight of chloroform and 1 part by weight of cyclohexane at a temperature of 23°C for 15 seconds, and rinsed with cyclohexane for 15 seconds. Then, a negative type photoresist pattern was obtained. It could be recognized that the negative type photoresist pattern was resolved to a 1.0 µm line and space pattern. The thickness of the remaining coating film after the development was 0.78 µm. Example VI Referring back to figures 1A to 1C, a silicon (Si) wafer 1 was prepared as a substrate. Naphthoquinone diazide sulfonate of novolak (abbreviated as "NQN") as a photoresist material was used. This NQN was dissolved into methyl cellosolve acetate at a rate of 10 to 40 weight %. This solution was then filtered through a filter having a throughhole diameter of 0.2 µm and applied onto the silicon wafer 1, whereby the wafer 1 is coated by a film having a thickness of approximately 1µm. Then, this silicon wafer 1 having a photo resist coating film 2 of NQN was prebaked at a temperature of 70°C for about 30 minutes. After this baking, the resist film 2 of NQN was exposed through a photoresist mask 3 having a desired mask pattern by a 1/5 optical reduction type transfer apparatus (NA : 0.35) equipped with g-line of 350 W mercury lamp as a light source. The dose time within one exposure process was determined as 450 msec. After this exposure, the resist film 2 formed on the substrate 1 was interbaked at a temperature on the order of 100°C for approximately 30 minutes, and then developed. This development was firstly conducted at a temperature of 23°C for 50 seconds by use of a mixed solution having a 10 : 1.5 volume ratio of monochloro benzene and cyclohexane as the first developing solution. As a result, a negative type photoresist pattern 5 was obtained (see Fig. 1C). It was recognized that the negative type pattern 5 could be resolved to a 0.6 µm line and space pattern by observing with the scanning type electron microscope. Example VII In this example, the resultant photoresist coating film as described in Example VII was contact-exposed with a mercury (Hg) lamp of 250 W. The exposure time was selected to be 10 seconds. After the heating treatment of the exposed photoresist at a temperature of 100°C for 30 minutes, the photoresist was developed at a temperature of 23°C for 50 seconds using the mixed developing solution containing 1 : 0.15 volume ratio of monochlorobenzene and isopropyl alcohol, thereby a negative type photoresist pattern being obtained. It could be recognized that the negative type photoresist pattern was resolved to a 0.5 µm line and space pattern by observing with the scanning electron microscope. As is understood from the above mentioned Examples, in case of forming the negative type photoresist patterns, there is an advantage that the photoresist patterns of high resolution are obtained since the NQN film does not swell with the developing solution. Another advantage is that, in case of forming the photoresist patterns on the reflective and/or stepped surface of the underlying layer, the mask patterns are precisely transferred onto the photoresist coating film, thereby forming the correct, clean and sharp photoresist patterns, since the light absorption coefficient of the NQN film to the exposure radiation of the wavelength range of 300 to 450 nm is large and therefore the sensitivity of the NQN film is high and then the patterning precision is not influenced by the light reflected from the surface of the underlying layer. A further advantage is that the edge portions of the photoresist patterns are not deformed when baked at a temperature of the order of 200°C since the NQN film has better heat resistance at a temperature of the order of 200°C. A still further advantage is that the underlying layer having formed thereon the photoresist patterns can be subjected to the plasma etching treatment, since the NQN material has excellent resistance to the dryetching. Comparison Example I The conventional photoresist of AZ-1305J (commercially available from Shipley corporation) was coated over a silicon wafer with a coating thickness of 1.0 µm so as to form a photoresist film. Subsequently, the photoresist film was prebaked at a temperature of 80°C for 20 minutes, and thereafter exposed under the exposure dose of 80 mJ/cm² by the same reduction type projection apparatus as in the Example I. When the exposed film was developed for 60 seconds by use of monochloro-benzene at a temperature of 23°C as a developing solution, both the exposed portion and unexposed portion of the resist film were not dissolved, so that no photoresist pattern could be formed. This is because quinon diazide of AZ-1350J as a photosensitive agent might be converted into indene carboxylic acid, whereas naphthoquinone and a photosensitive agent were not dissolved by the nonpolar solvent such as monochloro-benzene, so that no photoresist pattern could be formed. Comparison Example II A photoresist coating film of AZ-1350J was formed on an aluminum substrate under the same conditions as in the comparison example I, and then exposed. When the exposed photoresist film was developed with an alkaline developing solution, the photoresist pattern having a linewidth more than or equal to 1 µm could be fabricated, but the pattern having a linewidth less than 1 µm, i.e., submicrometer could not be formed. Comparison Example III AZ-1350J (photoresist commercially available from Shipley corporation) was applied onto a silicon wafer in a coating thickness of 1 µm to form a photoresist coating film was exposed as described in Example VI. The exposed resist was developed by using a solution containing the AZ developing solution diluted with water at a ratio of 1 : 1 at a temperature of 23°C for 20 seconds. A positive type photoresist pattern was obtained. Observing this resist pattern, it could be recognized that a 1.0 µm line and space pattern was obtained. Then, a sample obtained by the same exposure conditions was developed with monochlorobenzene at a temperature of 23°C for 2 minutes. However, no resist pattern was formed. Furthermore, another sample resist film obtained by the same exposure conditions was developed with a developing solution mixed 1 part by weight of isoamyl acetate with 1 part weight of isopropyl alcohol at a temperature of 23°C, but no pattern was formed either. And furthermore, this resist coating film was developed only with isoamyl acetate solution. As a result, the resist was dissolved over the wafer surface, and no pattern was formed. As apparent from the above Examples and comparison Example, when the coating film made of naphthoquinone diazide sulfonate of novolak (NQN) was exposed with near ultraviolet radiation, negative type photoresist can be merely determined by selection of the developing solution for the exposed photoresist. The reason is considered as follows. Quinon diazide group of NQN is decomposed by the near ultraviolet radiation, and converted into carboxylic acid. Then, polarity appears in the exposed region of NQN. The polar region is not dissolved in monochloro benzene which is a nonpolar solvent. As a result, the negative type photoresist pattern is formed by the insoluble polar region. As described in the comparison Examples, in AZ-1350J which is a mixture of novolak and naphthoquinone diazide, a change of naphthoquinone diazide into calboxylic acid is the same as that of NQN. However, it could be considered that a change of polarity throughout this photoresist is small. Actually, it is impossible to form the photoresist pattern by using the difference of this polarity. Comparison Example IV Using the same photoresist coating film on the silicon substrate as obtained in the Example I, the development was performed with various types of the developing solutions. The results of the development are shown in a table 1. In the first to third development examples, the dissolution of the exposed portion of the photoresist coating film was done relatively faster than that of the unexposed portions thereof. The photoresist coating film represents the positive type property. A thickness of the remaining film was thinner than 0.1 µm. In the fourth development example, the unexposed portion of the photoresist coating film was not completely dissolved, whereas a thickness of the exposed portion thereof was approximately 0.1 µm. The developing solutions used in the first to fourth development examples represent the positive type property. However, no photoresist pattern could be formed. While the present invention has been described using a specific embodiment, it should be understood that further modifications and changes can be made without departing from the scope of the present invention. As the negative type developing solutions, nonpolar halogen-containing solvents such as monochloro benzene , dichloro benzene, trichloro benzene, trichloro ethylene may be used. Mixed solutions of one or more nonpolar solvents selected from the above-mentioned group and one or more solvents selected from the group consisting of cyclohexane, n-hexane, petroleum ether and the other desired solvents may be used as the developing solutions. Furthermore, the coating film need not be directly coated on the substrate, but on other underlying layer. Finally, it is also possible to employ as the exposure light, electron beams, x-rays or the like having other wavelength than 300 to 450 nm. As previously described in detail, according to the method of forming the photoresist pattern of the invention, a negative type photoresist pattern can be formed by selecting only the developing solution because the naphthoquinone diazide sulfonate of novolak is used, and exposed to near ultraviolet radiation in the wavelength range of 300 to 450 nm. Accordingly, the photoresist pattern of the present invention is preferably used for manufacturing highly integrated circuit such as LSI which needs the fine processing, e.g., submicrometer processing.

Claims: A method of forming a photoresist pattern comprising the steps of : forming a photoresist coating film (2) naphthoquinone diazide sulfonate of novolak on an underlying layer (1), exposing the photoresist coating film (2) by selectively irradiating with ultraviolet radiation (10) of 300 to 450 nm through a photomask (3) developing the exposed photoresist coating film (2) with a negative type developing solution containing one or more solvents selected from the group of halogen-containing solvents, thereby removing an unexposed portion of the photoresist coating film (2). A method of forming a photoresist pattern as claimed in claim 1, wherein the halogen-containing solvent is monochloro benzene. A method of forming a photoresist pattern as claimed in claim 1, wherein the exposed photoresist coating film (2) is interbaked at a temperature of 60 to 130°C before the coating film (2) is treated by the developing.

Inventors: ASANO, TAKATERU FUJI CHEMICALS IND. CO., LTD., ITOH, TOSHIO OKI ELECTRIC IND. CO., LTD., KAWAZU, RYUJI OKI ELECTRIC IND. CO., LTD, KOBAYASHI, KENJI FUJI CHEMICALS IND. CO., LTD., YAMASHITA, YOSHIO OKI ELECTRIC IND. CO., LTD
Applicants: FUJI CHEMICALS INDUSTRIAL CO., LTD., OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1986
Main classification: G03F7
IPC codes: G03F7