JPH0472223B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a negative photoresist used for producing active elements, wiring patterns, etc. in forming semiconductor devices and the like. (Prior Art) In recent years, as semiconductor devices have become more highly integrated, there has been a demand for technology that can form fine resist patterns with high aspect ratios in the manufacturing process of these devices. In particular, when forming multilayer wiring, the wiring formed on the substrate forms a step between it and the substrate surface, and such a step forms a new resist pattern to form the next wiring on this substrate. It may be harmful in some cases. By the way, when forming a resist pattern on a substrate having such a step difference, the film thickness must be thick enough to cover the step difference (for example, 1.5~
2.0μm) It is necessary to form a resist. However, the reduction projection exposure machines that are currently mainly used tend to have large numerical apertures in their lenses in order to obtain high-resolution resist patterns, and therefore cannot achieve a large depth of focus.
For this reason, it has been difficult to pattern a thick resist film with high resolution using such an exposure machine. In addition, for the purpose of obtaining a high-resolution resist pattern, short wavelength light, such as 200 ~
Resists are exposed using deep ultraviolet rays of 300 nm, but since many commonly used resists have absorption in this wavelength range, it is difficult to achieve high resolution when the resist film is thick. It becomes difficult to pattern the image. A two-layer resist process has been proposed as a processing technique that eliminates the above-mentioned drawbacks and can obtain a fine resist pattern with a high aspect ratio even from a thick resistor. Hereinafter, this two-layer resist process will be briefly explained with reference to the manufacturing process diagrams shown in FIGS. 6A to 6C. Note that these figures are shown as cross-sectional views schematically showing a part of the wafer. In the two-layer resist process, the step 1 on the substrate 11 is
A resist pattern is obtained using a lower layer resist 15 formed to have a thick film thickness to absorb 3 and achieve planarization, and an upper layer resist 17 formed on this lower layer resist and containing silicon. The film thickness of this upper layer resist 17 is usually about 0.2 to 0.5 μm (see FIG. 6A), and this upper layer resist 17 is patterned by a suitable method such as a light exposure method to obtain a resist pattern 17a (see FIG. 6A). (See FIG. 6B.) Next, using this resist pattern 17a as an etching mask, the lower resist 15 is removed by oxygen (O ₂ )-reactive ion etching (RIE). As a result, the pattern of the upper resist layer can be transferred to the lower resist layer, and a fine two-layer resist pattern 19 with a high aspect ratio can be obtained (see FIG. 6C). Various resists have been proposed for use in such two-layer resist processes, but
Hereinafter, the resist used particularly as the upper layer resist will be explained. As a resist for such an upper layer, for example, there are references in the literature (Journal of the Electrochemical Society).
Electrochemical Society) 130 [9] P.1962
(1983)). According to this document, trimethylsilylstyrene (referred to as SiSt) is used as a silicon-containing photoresist.
A copolymer with chloromethylstyrene (referred to as CMS) is used, and the copolymerization ratio is
90:10 copolymer P( _SiSt90 - _CMS10 )
It has been reported that both O ₂ -RIE resistance and sensitivity to far ultraviolet rays are excellent. According to this report, P.
When O ₂ -RIE is applied to (SiSt ₉₀ - CMS ₁₀ ), the amount that is etched until the film thickness decreases to an extremely small value of several Å/min (hereinafter referred to as the initial etching amount) ) is said to be 220 to 290 Å. In addition, the sensitivity to far ultraviolet light (gelation initiation exposure amount D ⁱ _g ) is 60 mJ/
It is said to be cm ² . (Problem to be solved by the invention) However, in the conventional photoresist as described above, the initial etching amount is 220 to 290 Å/min.
Because of the large size, there was a problem that the etching process latitude could not be widened. Specifically, when this resist is used as an etching mask, the amount of initial etching is large, so it must be formed to a certain degree of thickness.
On the other hand, if the film thickness of this upper resist layer is made thicker than necessary, it becomes impossible to obtain a resist pattern that is fine and has a high aspect ratio. Therefore,
Increasing the thickness of the upper resist layer also has its own limits. For this reason, the film thickness of the lower resist layer cannot be made very thick. Also, the sensitivity to far ultraviolet light (D ⁱ _g ) is 60mJ/cm ²
There was a problem that high throughput could not be obtained because of the low The purpose of this invention is to solve the above-mentioned problems,
An object of the present invention is to provide a negative photoresist having O ₂ -RIE resistance and excellent sensitivity. (Means for solving the problem) In order to achieve this objective, according to the negative photoresist of the present invention, the following formula (1) is used. It is characterized by containing poly(allyl silsesquioxane) having a weight average molecular weight of about 3,000 to about 50,000 represented by: and bisazide. This poly(allylsilsesquioxane) is a polymer of allylsilsesquioxane, for example, an oligomer obtained by hydrolyzing allyltrichlorosilane or allyltrialkoxy, and a tertiary polymer such as triethylamine or tri-n-butylamine. It can be obtained by condensation polymerization with grade amine. Furthermore, since there are various bisazides that have different absorption wavelengths when irradiated with light, the wavelength at which the negative resist of the present invention is sensitive can be changed by selectively using a bisazide.
In carrying out the present invention, if a resist is to be exposed to short wavelength light, such as deep ultraviolet rays, for the purpose of obtaining a high-resolution resist pattern, the above-mentioned bisazide may be A bisazide that is photodecomposed by deep ultraviolet light of approximately 200 to 300 nm may be used. Furthermore, it is preferred that the bisazide be added in an amount of about 5 to 14% by weight based on the aforementioned poly(allyl silsesquioxane). (Function) The negative photoresist of the present invention contains bisazide and relatively low molecular weight poly(allyl silsesquioxane). Azides eliminate nitrogen molecules by light to generate nitrene, which is added to double bonds, or
It is known to generate crosslinks between base polymers in a photoresist by drawing out active hydrogens present at benzyl positions, allyl positions, etc. Furthermore, the above-mentioned poly(allylsilsesquioxane)
Since there are many allyl groups in the molecule that participate in crosslinking with nitrene, these and nitrene form a highly dense crosslinked structure. Therefore, a highly sensitive negative resist can be obtained in which the poly(allyl silsesquioxane) has a relatively low molecular weight and the amount of bisazide added is small. Further, since no crosslinked structure appears in the portions that are not irradiated with light, these portions are removed in the development step, and a resist pattern is therefore formed. Furthermore, since a high-density crosslinked structure appears in the light-irradiated area, this area cannot swell during development, thus promoting the formation of a fine resist pattern. In addition, this poly(allyl silsesquioxane) has a high silicon content of 30% by weight in its molecule, and when viewed from a compositional perspective, the ratio of oxygen to silicon atoms is 3/3.
Since it has a diatomic composition, which is close to that of silicon dioxide, the O ₂ -RIE resistance of poly(allylsylcerquioxane) is expected to be close to that of silicon dioxide. (Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, although the following description of the present invention is given using specific preferable numerical conditions within the scope of the present invention, these are merely illustrative, and the present invention is not limited to only these conditions. That is clear. First, the following formula (1) Bisazide is added to poly(allyl silsesquioxane) having a weight average molecular weight of about 3,000 to about 50,000 represented by, and this is dissolved in an organic solvent such as chlorobenzene to a predetermined concentration.
A resist solution of a negative photoresist of this invention was prepared. Incidentally, this poly(allylsilsesquioxane) can be obtained, for example, by condensing and polymerizing an oligomer obtained by hydrolyzing allyltrichlorosilane or allyltrialkoxy with a tertiary amine such as triethylamine or tri-n-butylamine. . Also, the reason for using poly(allylsilsesquioxane) with a weight average molecular weight of about 3,000 to about 50,000 is that it is liquid-like when the molecular weight is lower than this range, and gel-like when the molecular weight is larger than this range. This is because, in either case, the material is unsuitable as a material constituting a photoresist. Furthermore, since there are various bisazides that have different absorption wavelengths when irradiated with light, it is possible to change the photosensitive wavelength of the negative photoresist of the present invention by selectively using bisazides. . The following embodiments will be explained using a negative type photoresist that is exposed to deep ultraviolet rays. In such a case, the above-mentioned bisazide may be replaced with a bisazide that is photodecomposed by deep ultraviolet light having a wavelength of about 200 to 300 nm. For example, alkyl azides exhibit absorption at wavelengths of approximately 300 nm or less and are known to be photodegraded by such deep ultraviolet light. It can be used by adding it to the negative photoresist of this invention.
Specific examples include 2,6-bis(4'azidobenzylidene)-4-methylcyclohexanone, 2,
Aromatic bisazides in which the azide group is directly bonded to the aromatic ring, such as 6-bis(4'-azidobenzylidene)cyclohexanone, etc., 1,3-diazide-1, in which the azide group is not bonded to the aromatic ring, etc. 3
-Dimethyl-1,3-diphenyldisiloxane and other bisazides. Sensitivity experiment to deep ultraviolet light First, experimental results regarding the sensitivity of the negative photoresist of the present invention to deep ultraviolet light will be explained. Example 1 After hydrolyzing allyltrichlorosilane,
5g of poly(allyl silsesquioxane) obtained by condensation polymerization with a weight average molecular weight of _W 3000,
After dissolving 250 mg of 2,6-bis(4'azidobenzylidene)-4-methylcyclohexanone in 28 g of chlorobenzene, this solution was filtered through a membrane filter having a pore size of 0.2 μm to prepare a resist solution. This resist solution was spin-coated onto each of six previously prepared substrates, and then soft-baked at a temperature of 60° C. for 30 minutes to obtain six sample wafers each having a resist film with a thickness of 0.5 μm. The resist film thickness at this time is defined as the initial film thickness. By changing the dose amount for these sample wafers,
Exposure is performed through a quartz mask having test patterns that allow formation of various line widths. This exposure was carried out using a 500W Xe-Hg lamp and deep ultraviolet light with wavelengths longer than 280 nm removed by a CM-250 cold mirror. After exposure, these sample wafers were developed in a mixed solvent of isopropanol/cyclohexano at a ratio of 10/1.5 (volume ratio) for 35 seconds, and then,
A 5 second rinse was performed in isopropanol. Next, these sample wafers were heated at a temperature of 100°C.
Post-bake was performed for 15 minutes. The film thickness of each resist pattern formed on multiple sample wafers through such processing is
Each of the 3 μm line patterns in this pattern was measured to obtain the remaining film thickness of each sample wafer. The value (residual film rate) obtained by normalizing these remaining film thicknesses by the above-mentioned initial film thickness is plotted on the vertical axis, and the value obtained by taking the common logarithm of the dose amount for the sample wafer is plotted on the horizontal axis. A characteristic curve diagram plotting the film ratio is shown in FIG. Example 2 5 g of poly(allylsilsesquioxane) with a weight average molecular weight _W 8000 and 500 mg of 2,6-bis(4'-azidobenzylidene)-4-methylcyclohexanone as used in Example 1 were added. After dissolving in 28g of chlorobenzene, this solution was
A resist solution was prepared by filtering through a membrane filter having a pore size of 0.2 μm. A sample wafer was prepared in the same manner as in Example 1, except that the development time was changed to 45 seconds, and a characteristic curve of the remaining film rate versus dose was determined. This result is the second
As shown in the figure. Example 3 5 g of poly(allyl silsesquioxane) with a weight average molecular weight _W 8000 and 2,6-bis(4'-azidobenzylidene)cyclohexanone
After dissolving 250 mg of chlorobenzene in 28 g of chlorobenzene, this solution was filtered through a membrane filter having a pore size of 0.2 μm to prepare a resist solution. A sample wafer was prepared in the same manner as in Example 1, except that the development time was changed to 45 seconds, and a characteristic curve of the remaining film rate versus dose was determined. This result is the third
As shown in the figure. Example 4 5 g of poly(allylsilsesquioxane) with a weight average molecular weight _W 8000 and 500 mg of 1,3-diazide-1,3-dimethyl-1,3-diphenyldisiloxane were dissolved in 28 g of chlorobenzene. After that, this solution was filtered through a membrane filter having a pore size of 0.2 μm to prepare a resist solution. A sample wafer was prepared in the same manner as in Example 1 except that the developer was a mixed solvent of isopropanol/cyclohexanone at a ratio of 10/1 (volume ratio) and the development time was 32 seconds. The characteristic curve of the rate was obtained. The results are shown in FIG. Attached Table 1 shows the materials and experimental conditions used in Examples 1 to 4, and the sensitivity determined from the characteristic curve diagrams obtained in each example (dose amount D ^0.5 _o at which the residual film rate is 50%).
and are shown respectively. As can be understood by comparing Example 1 and Example 2, when the same type of bisazide is added to the resist of this invention, the sensitivity improves as the amount added increases. In Example 2, a sensitivity of 11 mJ/cm ² was obtained. or,
If the amount of bisazide added is further increased, an improvement in sensitivity is expected, but a problem arises due to the solubility of bisazide in organic solvents. For example, in Example 2, when a film was formed on a substrate using a resist containing 15% by weight of this bisazide based on poly(allyl silsesquioxane), the bisazide was precipitated during baking before exposure and a resist pattern was formed. This resulted in an unsuitable film. or,
In Example 4, when a film was formed on a substrate using a resist containing 15% by weight of this bisazide,
During contact exposure, statesking occurred when the mask and wafer were stuck together. The cause of statesking is 1,3-diazide-1,3
This is thought to be because -dimethyl-1,3-diphenyldisiloxane is an oily substance. Therefore, it is preferable to add bisazide, which is one of the constituent components of the negative photoresist of the present invention, in an amount of about 5 to 14% by weight, preferably 5 to 10% by weight, based on the poly(allyl silsesquioxane). be. The reason why the lower limit of the amount added is set to 5% by weight is that if the amount added is smaller than this, the desired sensitivity cannot be obtained. O ₂ −RIE resistance experiment Next, the O _{2 −RIE} resistance experiment of the negative photoresist of this invention.
- Explain the experimental results regarding RIE resistance. Example After the resist solution prepared in Example 2 was spin-coated onto a silicon substrate, soft baking was performed at a temperature of 60° C. for 30 minutes to obtain a resist film with a thickness of 0.5 μm. Subsequently, exposure was performed using the same light source as in Example 2 through a quartz mask blank at a dose of 20 mJ/cm ² . Next, development and post-baking were performed under the same conditions as in Example 2 to obtain a sample wafer. Next, this sample wafer was divided into four parts, and O ₂ -RIE was performed on three of the wafer parts for 10 minutes, one for 20 minutes, and one for 30 minutes. The etching conditions were an RF power density of 0.08 W/cm ² , a gas pressure of 5 Pa, and a gas flow rate of 20 sccm. Figure 5 shows the characteristics shown by plotting the amount of resist film loss against the etching time, with the vertical axis representing the amount of resist film loss on each sample wafer portion etched during each etching time, and the horizontal axis representing the etching time. 5 is a curve diagram, and the characteristic curve diagram shown in FIG. 5 shows the O ₂ -RIE resistance of the resist prepared in Example 2. Example Using the resist prepared in Example 4, the same treatment as in Example was performed to investigate the O ₂ -RIE resistance of this resist. However, in this example, the dose was 80 mJ/cm ² , and the development process was carried out under the same conditions as in Example 4. The characteristic curve diagram shown in FIG. 5 shows the O ₂ -RIE resistance of the resist prepared in Example 4. Comparative Example For comparison, for example, a sample used as a lower resist in a two-layer resist process on a silicon substrate
AZ-2400 (Product name of Shitspray's resist.)
After coating, hard baking was performed at a temperature of 220°C for 1 hour to obtain a resist film with a thickness of 2 μm. The wafer having this resist film was divided into four parts, and each wafer portion was etched under the same conditions as the O ₂ -RIE conditions used in the example, to investigate the O ₂ -RIE resistance of this resist film. The characteristic curve diagram shown in Figure 5 is O ₂ -RIE of AZ resist.
It shows resistance. In addition, this AZ resist is used in the above-mentioned etching process after 25 minutes from the start of etching.
After a few minutes, everything was etched away. As can be understood from the characteristic curve diagram of the example and comparative example shown in FIG. 5,
The etching amount until the etching rate becomes substantially zero (initial etching amount) is 140 Å for the resist used in the example, 100 Å for the resist used in the example, and both The value was also about half that of conventional silicon-containing photoresists. Therefore, when the negative photoresist of the present invention is used as an upper layer resist in a two-layer resist process, the purpose can be achieved even if it is formed to a sufficiently thin film thickness. Experiment on Forming a Two-Layered Resist Pattern Hereinafter, the results of an experiment in forming a resist pattern using the negative photoresist of the present invention as an upper layer resist in a two-layer resist process will be explained. Example: After coating AZ-2400 on a silicon substrate, 220
Hard baking was performed at a temperature of 1 hour to obtain a lower resist film with a thickness of 3 μm. Subsequently, the resist solution prepared in Example 1 was spin-coated onto this lower resist film, and then soft baked at a temperature of 60° C. for 30 minutes to obtain an upper resist film with a thickness of 0.3 μm. Next, exposure was carried out at a dose of 40 mJ/cm ² using the light source already described in Example 1 through a predetermined quartz mask. Subsequently, development and baking were performed under the same developing conditions and post-baking conditions as in Example 1 to obtain a resist pattern of an upper layer resist. Next, using this upper layer resist pattern as an etching mask, RF radiation is applied to the lower layer resist.
The power density is 0.08W/ ^cm2 , the gas pressure is 5Pa,
O ₂ -RIE was performed for 50 minutes at a gas flow rate of 20 sccm. When the two-layer resist was observed using a SEM (scanning electron microscope) after etching, the thickness was 3 μm.
It was found that a two-layer resist pattern with a line width of 0.5 μm, that is, an aspect ratio of 6, which was approximately equal to the design value of the mask used, was obtained. Example AZ-2400 was placed on a silicon substrate in the same manner as in the example.
was formed to a thickness of 2.0 μm, and the resist prepared in Example 2 was applied as an upper layer resist on this AZ-2400.
It was formed to a film thickness of 0.35 μm. Next, a two-layer resist pattern was formed in the same manner as in the example.
In this example, the exposure dose for the upper resist layer was 20 mJ/cm ² and the development time was the same as in Example 2. Further, the conditions for O ₂ -RIE were the same as in the example except that the etching time was 35 minutes. When the two-layer resist was observed after etching using a SEM, it was found that a two-layer resist pattern with a thickness of 2.1 μm and a line and space of 0.5 μm was obtained. Example AZ-2400 was placed on a silicon substrate in the same manner as in the example.
was formed to a thickness of 2.0 μm, and the resist prepared in Example 4 was applied as an upper layer resist on this AZ-2400.
It was formed to a film thickness of 0.25 μm. Next, a two-layer resist pattern is formed in the same manner as in the example.
In this example, the exposure dose for the upper resist layer was 60 mJ/cm ² and the development time was the same as in Example 4. Further, the conditions for O ₂ -RIE were the same as in the example except that the etching time was 35 minutes. When the two-layer resist was observed after etching using a SEM, it was found that a two-layer resist pattern with a thickness of 2.1 μm and a line and space of 0.5 μm was obtained. As is clear from the experimental results of Examples to Examples, the negative photoresist of the present invention has an O ₂
-Excellent RIE resistance. Therefore, it can be seen that when the resist of the present invention is used as an upper layer resist, it can withstand use as an etching mask even if the resist is thinner than the conventional resist.
Furthermore, it is possible to increase the film thickness of the lower resist layer compared to the conventional method. Incidentally, the present invention is not limited to each of the embodiments described above. For example, although the above-mentioned embodiment has been described as a negative-tone photoresist for deep ultraviolet light, other types of photoresists can be obtained by adding a bisazide that photodecomposes at a wavelength different from that of the embodiment. It is also possible to obtain a resist that can be exposed in the wavelength range of . Even in such a case, it is possible to obtain a negative photoresist with a resist pattern having a high crosslinking density and excellent O ₂ -RIE resistance. (Effects of the Invention) As is clear from the above explanation, the negative photoresist of the present invention contains poly(allyl silsesquioxane) having a large number of allyl groups that participate in the crosslinking reaction and bisazide. If the bisazide in this resist is, for example, bisazide that can be photodecomposed by deep ultraviolet light,
Exposure to deep ultraviolet light to obtain a 50% film retention rate
It is extremely sensitive as it can be performed at a dose of 11mJ/cm ² . Therefore, a resist pattern can be formed with high throughput. Furthermore, since a high crosslinking density appears, a resist pattern with high resolution of, for example, submicron order can be obtained. Moreover, for the negative resist of this invention, O ₂ −
When RIE was applied, the etching amount (initial etching amount) until the etching rate became substantially zero was 100 to 140 Å. This value is approximately half that of conventional silicon-containing photoresists. Therefore, the etching process latitude can be widened. Therefore, a negative photoresist having O ₂ RIE resistance and excellent sensitivity can be provided. Therefore, the negative photoresist of this invention is
For example, in the manufacturing process of large-scale integrated circuits, it can be used as an upper layer resist in a two-layer resist process to form a resist pattern with a high aspect ratio and on the submicron order on a substrate with complex and large steps. It is something. 【table】

[Brief explanation of the drawing]

1 to 4 are characteristic curve diagrams showing the sensitivity to far ultraviolet light of the negative photoresists explained in the first to fourth embodiments of the present invention, and FIG. FIG. 6 is a characteristic curve diagram showing the O ₂ -RIE resistance of each of the negative photoresists described in the examples and the resist of the comparative example.
Figures A to C are manufacturing process diagrams for explaining a conventional two-layer resist process and for explaining the present invention. 11...Substrate, 13...Step, 15...Lower layer resist, 17...Upper layer resist, 17a...Upper layer resist pattern, 19...Two layer resist pattern.

Claims (1)

[Claims] 1 The following formula (1) A negative photoresist characterized by containing poly(allyl silsesquioxane) having a weight average molecular weight of 3,000 to 50,000 represented by the formula and bisazide. 2. The negative photoresist according to claim 1, wherein the bisazide is a bisazide that is photodecomposed by deep ultraviolet light having a wavelength of 200 to 300 nm. 3. The negative photoresist according to claim 1, wherein the bisazide is added in an amount of 5 to 14% by weight based on the poly(allyl silsesquioxane).