JPH0513307B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resist pattern forming method using a perfluoroalkyl group-containing polymer sensitive to electron beams or X-rays as a resist material. Traditionally, photolithography using ultraviolet light with a wavelength of 2,500 to 4,000 Å has been used for lithography in the production of semiconductor integrated circuits, but in recent years, with the increasing density and integration of semiconductor integrated circuits, Lithography technology using electron beams, X-rays, etc. is attracting attention and is being put into practical use. These lithography techniques form a fine resist pattern using electron beams or X-rays, use this as a mask for etching, and transfer the pattern onto a substrate. For etching, wet etching has traditionally been used, but because of its limitations in transfer accuracy,
Dry etching methods with higher transfer accuracy are being adopted. Therefore, a practical resist material used for microfabrication at the submicron level must have high sensitivity and resolution to electron beams and X-rays, and be resistant to dry etching. As a result of intensive research into negative-type resist materials that satisfy these performance requirements, the present inventors discovered that a polymer with a special chemical structure containing perfluoroalkyl groups had satisfactory performance. This led to the invention. That is, the present invention is a resist pattern forming method characterized by using a perfluoroalkyl group-containing polymer represented by the following general formula () as a resist material in resist pattern formation using electron beams or X-rays. . (In the formula, Rf represents a perfluoroalkyl group having 2 to 20 carbon atoms, R ¹ and R ² represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms,
X and Y each represent the number of each monomer unit in the polymer, and the value of X/X+Y is in the range of 0.01 to 1.0. ) The perfluoroalkyl group-containing polymer represented by the general formula () of the resist material used in the present invention can be produced, for example, by the method shown below. That is, a perfluoroalkyl iodonium salt represented by the general formula () (In the formula, Rf is the same as above, φ is a substituted or unsubstituted phenyl group, R is a perfluoroalkyl group, lower alkyl group, or hydroxyl group having 1 to 5 carbon atoms) and is represented by the general formula () polymer consisting of repeating units (In the formula, R ¹ and R ² represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.) According to this method, the desired polymer can be obtained during the reaction without causing side effects such as main chain cleavage or crosslinking of the base polymer consisting of repeating units represented by the general formula (). As the resist material used in the present invention, the following can be exemplified. The molecular weight of the resist material used in the present invention is preferably in the range of several thousand to several million. If the molecular weight is less than several thousand, the mechanical strength and heat resistance of the film formed from the resist material will be poor. In addition, if the viscosity exceeds several million, the viscosity of the resist material solution becomes too high when forming a film using the resist material, making it difficult to control the film thickness to a predetermined thickness, and making handling difficult. may cause difficulties.
In addition, its molecular weight distribution can be selected depending on the purpose, and the weight average molecular weight / number average molecular weight (hereinafter referred to as
The value expressed by w/n can range from a narrow range of 1.0 to 1.1 to a wide range of 20 to 50. w/n is 1.0~
Resist materials with a w/n value below the range of 1.1 are practically impossible to synthesize, and resist materials with a w/n value of 20 to 50 or more cannot be drawn on a film made of the resist material using electron beams or X-rays. However, the resolution of the formed pattern becomes insufficient. A method for forming a film made of a resist material on a substrate is to apply a solution in which the resist material is dissolved in an appropriate solvent onto the substrate using a spin coating method, and then evaporate the solvent by heat treatment. One example is a method of removing it. The concentration of the resist material solution must be selected in consideration of the thickness of the film to be formed, ease of handling, etc. The temperature for the heat treatment is preferably selected within the range of 50° C. lower than the boiling point of the selected solvent and lower than the temperature at which the resist material is thermally decomposed. If the temperature is less than 50° C. lower than the boiling point of the solvent, the solvent will not be removed sufficiently even if the heat treatment time is increased. Further, the time for the heat treatment is determined depending on the temperature, but it is usually preferably in the range of 1 minute to 2 hours. If the heat treatment time is less than 1 minute, the solvent cannot be removed sufficiently. Moreover, if the time exceeds 2 hours, the productivity of semiconductor integrated circuits will drop significantly. The thickness of the resist material film thus formed on the substrate may normally be about 0.1 to 2 μm.
If the thickness of the resist material film is less than 0.1 μm, parts of the substrate are likely to be exposed due to thickness unevenness. Moreover, if the thickness exceeds 2 μm, the resolution of the formed pattern will be poor. Substrates used in the present invention include, for example, a single silicon substrate doped with impurities, a semiconductor substrate such as a thin layer of silicon oxide on this substrate, or a chromium film or chromium oxide film on a transparent glass plate. Examples include a mask substrate such as a laminated one. The resist material made of the polymer represented by the general formula () used in the present invention undergoes a crosslinking reaction when irradiated with electron beams or X-rays. This is presumed to be because the perfluoroalkyl group directly connected to the benzene ring is cleaved by these radiations, and the active species generated by this reaction promotes a crosslinking reaction between polymer molecules. . In other words, the fluorine atom present in the perfluoroalkyl group makes it more sensitive to electron beams and It is presumed that the benzene ring present therein provides good dry etching resistance. Therefore, the value of X/X+Y in general formula () must be 0.01 or more. If this value is less than 0.01, not only the sensitivity but also the crosslinking density after radiation irradiation will be insufficient. As described above, the resist material used in the present invention is a negative type resist material that is sensitive to electron beams or X-rays, so in order to form a resist pattern using it, it is necessary to A method is used in which a desired pattern is irradiated with electron beams or X-rays, and then the resist material in unirradiated areas is selectively removed. A method for selectively removing the resist material in the unirradiated areas is to immerse the resist film together with the substrate after irradiation in a solvent that is said to be a good solvent for the polymer represented by the general formula (). good. Examples of such good solvents include benzene, toluene, xylene, chloroform, THF,
Examples include dioxane, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, ethyl cellosolve, and ethyl acetate. Further, a mixed solvent in which a poor solvent is added to a good solvent can also be used for this purpose within a range that can dissolve the resist material in the non-irradiated areas. Examples of the poor solvent include methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol, and acetone. The resist material used in the present invention has excellent sensitivity and resolution to electron beams or X-rays. Sensitivity (hereinafter referred to as S value) refers to the final value of residual film thickness at 50% of the final value of residual film thickness that reaches saturation with respect to an increase in radiation dose in a sensitivity curve diagram depicting the relationship between radiation dose and residual film thickness. It is indicated by the value of the irradiation amount corresponding to the remaining film thickness in %, and the smaller the value, the higher the sensitivity.
In addition, resolution (hereinafter referred to as γ value) is 1/, where d ₁ and d ₂ are the irradiation doses at the points where the remaining film thickness is zero and the final value, respectively, on the tangent line corresponding to the S value of the sensitivity curve. It is indicated by the value of log ₁₀ (d ₂ / d ₁ ), and the higher the value, the higher the resolution.
Published on March 24th, see pages 139-140. ] That is, S of the resist material used in the present invention
The value and γ value are several μc/
cm ² to several tens of μc/cm ² and 1.0 to 2.0, 100 for X-rays
The values are ˜200 mJ/cm ² and 1.0 to 2.0, and have practically sufficient sensitivity and resolution. Therefore, according to the method of the present invention, a clear resist pattern can be formed efficiently. Hereinafter, specific examples of the present invention will be explained in more detail with reference to Synthesis Examples and Examples. Synthesis example 1 Weight average molecular weight 4.04 in a 100ml eggplant flask
×10 ⁴ , weight average molecular weight (w)/number average molecular weight (n) = 1.08 poly α-methylstyrene 20g
(17.0 mmol in monomer unit) and chloroform
Dissolved in 38ml. While stirring the solution, 25 ml of acetonitrile was added dropwise to form a homogeneous solution. Furthermore, 1.37 ml (17.0 mmol) of pyridine was added to this. A condenser was attached to the flask, and the flask was placed in a 75°C oil bath to raise the temperature. After stirring for 5 minutes, pentafluoroethyl phenyl iodonium trifluoromethanesulfonate was added little by little, and the entire amount was added over 10 minutes. After the addition, the reaction was continued for an additional 10 minutes while stirring at the same temperature. After the reaction, the reaction solution was passed through a short column filled with silica gel, and chloroform was used as a developing solvent. After concentrating the effluent, the concentrated solution was poured into 500 ml of methanol to precipitate a polymer. The polymer was collected by filtration and dried by vacuum drying to obtain 1.92 g of a white polymer. It was confirmed by the following method that the obtained polymer had the structure of the following formula. 1 Infrared spectrum (KBr method) The spectrum of the polymer obtained in this synthesis example is
1330, 1285, 1205, 1130, 1090, 1025, 990,
Absorption that does not exist in the raw material polyα-methylstyrene appeared at each position of 970, 830, 790, and 725 cm ⁻¹ . 2 ¹⁹ F-NMR (CDCl ₃ solvent, chemical shift internal standard CFCl ₃ ) Absorption by fluorine atoms of the polymer obtained in this synthesis example at each position of -85ppm (t.3F) -115ppm (m.2F) appeared. The perfluoroethylation rate (X/X+Y) was measured using benzotrifluoride as an internal standard and found to be 0.24. 3. Thermal Decomposition Products When the white polymer obtained in this synthesis example was heated, it began to decompose at about 200°C. When the decomposition products were analyzed by mass spectroscopy, all of them were α-methylstyrene.

[Formula] and perfluoroethylated α-methylstyrene

It was [formula]. this thing is in this polymer

[Formula] and

Indicates the existence of a repeating unit represented by the formula. In addition, observation by high performance liquid chromatography revealed that the obtained polymer had a molecular weight distribution almost equivalent to that of the raw material polymer. Synthesis Example 2 The pentafluoroethyl phenyl iodonium trifluoromethanesulfonate used in Synthesis Example 1 was changed from 8.01g to 2.00g (4.25mmol).
It was carried out in the same manner as in Synthesis Example 1 to obtain 1.81 g of a white polymer. Infrared spectrum of the obtained polymer, ¹⁹ F−
The NMR absorption position was the same as that obtained in Synthesis Example 1. In addition, all of the thermal decomposition products are α-methylstyrene and perfluoroethylated α-
methylstyrene

It was [formula]. Incidentally, the perfluoroethylation rate was measured to be 0.046 by ¹⁹ F-NMR. Synthesis example 3 Weight average molecular weight as poly α-methylstyrene
2.7×10 ⁵ , w/n=1.07,
The procedure was repeated in the same manner as in Synthesis Example 1, except that chloroform was changed to 39 ml and acetonitrile was changed to 24 ml.
I got g. Infrared spectrum of the obtained polymer, ¹⁹ F
-NMR absorption position was the same as that obtained in Synthesis Example 1. In addition, all of the thermal decomposition products are α-
Methylstyrene and perfluoroethylated α
-Methylstyrene

It was [formula]. Incidentally, the perfluoroethylation rate was measured to be 0.16 by ¹⁹ F-NMR. Synthesis Example 4 3.00 g (25.4 mmol in monomer units) of polyα-methylstyrene similar to that used in Synthesis Example 1 was placed in a 200 ml eggplant-shaped flask and dissolved in 58 ml of chloroform. While stirring this solution, 38.7 ml of acetonitrile was added dropwise to form a homogeneous solution. Furthermore, 2.05 ml (25.4 mmol) of pyridine was added to this. A condenser was attached to the flask, and the flask was placed in a 75°C oil bath to raise the temperature. After stirring for 5 minutes, perfluoro-n-butylphenyl iodonium trifluoromethanesulfonate was added little by little, and the entire amount was added over 10 minutes. After the addition, the reaction was continued for an additional 10 minutes while stirring at the same temperature. After the reaction, the reaction solution was passed through a short column filled with silica gel, and chloroform was used as a developing solvent. After concentrating the effluent, the concentrated solution was poured into 600 ml of methanol to precipitate a polymer. The polymer was collected by filtration and dried by vacuum drying to obtain 4.02 g of a white polymer. It was confirmed by the following method that the obtained polymer had the structure of the following formula. 1 Infrared spectrum (KBr method) The spectrum of the polymer obtained in this synthesis example is
1345, 1230, 1130, 1085, 1000, 980, 865, 840,
At each position of 810, 740, 720 cm ^-1 ,
Absorption not present in methylstyrene appeared. 2 ¹⁹ F-NMR (CDCl ₃ solvent, chemical shift internal standard CFCl ₃ ) -81.7ppm (t.3F) -111.6ppm (m.2F) -123.6ppm (m.2F) -126.2ppm (m.2F) each Absorption by fluorine atoms of the polymer obtained in this synthesis example appeared at this position. The perfluoro-n-butylation rate (X/X+Y) was measured using benzotrifluoride as an internal standard and found to be 0.34. 3. Thermal Decomposition Products When the white polymer obtained in this synthesis example was heated, it began to decompose at about 200°C. When the decomposition products were analyzed by mass spectroscopy, all of them were α-methylstyrene.

[Formula] and perfluoro-n-butylated α-methylstyrene

It was [formula]. this child In this polymer,

[Formula] and

Indicates the existence of a repeating unit represented by the formula. In addition, observation by high performance liquid chromatography revealed that the obtained polymer had a molecular weight distribution almost equivalent to that of the raw material polymer. Synthesis Example 5 151 mg (1.28 mmol in monomer units) of polyα-methylstyrene similar to that used in Synthesis Example 1 was placed in a 25 ml eggplant-shaped flask and dissolved in 3 ml of chloroform. While stirring this solution, 2 ml of acetonitrile was added dropwise to form a homogeneous solution. Furthermore, 0.10 ml (1.28 mmol) of pyridine was added to this. Attach a condenser to the flask and set the flask to 75
It was placed in an oil bath at ℃ to raise the temperature. After stirring for 5 minutes,
686 mg (1.27 mmol) of heptafluoroisopropyl-p-fluorophenyl iodonium trifluoromethanesulfonate was added little by little, and the entire amount was added over 10 minutes. After addition, while stirring at the same temperature,
The reaction was continued for an additional 10 minutes. After the reaction, the reaction solution was passed through a short column filled with silica gel, and chloroform was used as a developing solvent. After concentrating the effluent,
The concentrated solution was poured into 50 ml of methanol to precipitate a polymer. The polymer was collected by filtration and dried by vacuum drying to obtain 130 mg of a white polymer. It was confirmed by the following method that the obtained polymer had the structure of the following formula. 1 Infrared spectrum (KBr method) The spectrum of the polymer obtained in this synthesis example is
1295, 1275, 1215, 1160, 975, 950, 820, 715cm
Absorption that does not exist in the raw material polyα-methylstyrene appeared at each position of ^-1 . 2 ¹⁹ F-NMR (CDCl ₃ solvent, chemical shift internal standard CFCl ₃ ) Absorption by fluorine atoms of the polymer obtained in this synthesis example appears at each position of -76.2ppm (6F) -183.0ppm (1F). Ta. The heptafluoroisopropylation rate (X/X+Y) was measured using benzotrifluoride as an internal standard and found to be 0.14. 3. Thermal Decomposition Products When the white polymer obtained in this synthesis example was heated, it began to decompose at about 200°C. When the decomposition products were analyzed by mass spectroscopy, all of them were α-methylstyrene.

[Formula] and hepetafluoroisopropylated α-methylstyrene

It was [formula]. This means that in this polymer,

[Formula] and

Indicates the existence of a repeating unit represented by the formula. Note that the polymer obtained by observation by high performance liquid chromatography was found to have a molecular weight distribution almost equivalent to that of the raw material polymer. Synthesis Example 6 Poly-4-vinyltoluene (weight average molecular weight 7.2×10 ⁴ , w/
Synthesis Example 1 was repeated except that 2.0 g of Mn=1.06) was used, and 1.96 g of a white polymer was obtained. Analysis similar to Synthesis Example 1 (infrared spectrum, ¹⁹ F−
As a result of NMR (analysis of thermal decomposition products), it was found that the obtained polymer had the following structure. Example 1 1.0 g of pentafluoroethylated polyα-methylstyrene obtained in Synthesis Example 1 was dissolved in 10 ml of xylene, the solution was applied onto a silicon wafer, and the wafer was heated in a dryer at 120°C for 25 minutes. Prebaked for a minute. In this way, a 0.54 μm pentafluoroethylated polyα-methylstyrene thin film was formed on the silicon wafer. Next, desired portions of the prebaked coating film were irradiated with an electron beam at an accelerating voltage of 20 Kv at various doses. Thereafter, development was performed using xylene as a developer to dissolve and remove the portions that had not been irradiated with the electron beam, thereby forming a resist pattern on the wafer. A sensitivity curve diagram depicting the relationship between the electron beam dose (horizontal axis) and the remaining coating film thickness (vertical axis) at this time is shown in FIG. The S value and γ value read from FIG. 1 were 1.5×10 ⁻⁵ C/cm ² and 1.5, respectively. Examples 2 to 6 The polymers obtained in Synthesis Examples 2 to 6 were made into a xylene solution in the same manner as in Example 1, applied onto a wafer, and prebaked to form a coating film with the thickness shown in Table 1. Ta. Thereafter, in the same manner as in Example 1, electron beams were irradiated at various doses and development was performed with xylene.
Sensitivity curve diagrams depicting the relationship between the electron beam dose (horizontal axis) and the coating film residual thickness (vertical axis) at this time are shown in FIGS. 2 to 6. The S value and γ value read from FIGS. 2 to 6 were as shown in Table 2.

[Table] Table 2 S value (C/cm ² ) γ value Example 2 1.9×10 ^-5 1.6 Example 3 2.0×10 ^-6 1.6 Example 4 2.6×10 ^-5 1.1 Example 5 2.0×10 ^{- 5} 1.3 Example 6 4.8×10 ^-6 1.5 Example 7 The polymer obtained in Synthesis Example 3 was made into a xylene solution in the same manner as in Example 1, applied onto a wafer, prebaked, and made into a 0.55 μm thick solution. A coating film was formed. Then, desired portions of the coating film were irradiated with X-rays having a wavelength of several angstroms at various exposure doses.
After that, it is developed using a xylene developer and
The non-irradiated portions were dissolved and removed to form a resist pattern on the wafer. A sensitivity curve diagram depicting the relationship between the amount of X-ray exposure and the remaining thickness of the coating film at this time is shown in FIG. The S value and γ value read from FIG. 7 were 160 mJ/cm ² and 1.6, respectively. Comparative example 1 Weight average molecular weight 4.04×10 ^-4 , w/n=1.08
5.1 g of polyα-methylstyrene is added to 50 g of xylene.
After applying the solution onto a silicon wafer, the wafer was prebaked in a dryer at 120° C. for 25 minutes. In this way, a 0.58 μm polyα-methylstyrene thin film was formed on the silicon wafer. after that,
As in Example 1, electron beams were irradiated at various doses and developed with a mixed solvent of 100 ml of xylene and 100 ml of methanol. A sensitivity curve diagram depicting the relationship between the electron beam dose (horizontal axis) and the remaining coating film thickness (vertical axis) at this time is shown in FIG. As shown in FIG. 8, it was found that polyα-methylstyrene into which no perfluoroalkyl group had been introduced was degraded by electron beams.

[Brief explanation of the drawing]

Figures 1 to 6 are sensitivity curve diagrams depicting the relationship between the electron beam dose and residual film thickness obtained in Examples 1 to 6, respectively, and Figure 7 is a sensitivity curve diagram depicting the relationship between the X-ray exposure amount and residual film thickness obtained in Example 7. A sensitivity curve diagram depicting the relationship with film thickness, and FIG. 8 is a sensitivity curve diagram depicting the relationship between the electron beam dose obtained in Comparative Example 1 and the remaining film thickness.

Claims (1)

[Scope of Claims] 1. A resist pattern forming method using a perfluoroalkyl group-containing polymer represented by the following general formula as a resist material in resist pattern formation using electron beams or X-rays. (In the formula, Rf represents a perfluoroalkyl group having 2 to 20 carbon atoms, R ¹ and R ² represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms,
X and Y each represent the number of each monomer unit in the polymer, and the value of X/X+Y is in the range of 0.01 to 1.0. )