JPH04153652A - Production of photomask having phase shifter layer - Google Patents

Abstract

PURPOSE:To easily produce a phase shifter layer having high quality by immersing a photomask into a supersatd. aq. soln. of silicon oxide contg. hydrogen silicofluoride and silica gel as essential components and depositing a silicon oxide film at a prescribed film thickness. CONSTITUTION:The aq. hydrogen silicofluoride soln. prepd. by putting the silica gel (SiO2) into the aq. soln. of the hydrogen silicofluoride (H2SiF6) and forming the soln. as the supersatd. aq. soln. can form the denser films as the concn. is higher in a 0.5 to 5mol/l range. This supersatd. aq. soln. is heated to the deposition temp. (usually 35 deg.C) and an initiator is added thereto. The SiO2 in the soln. deposits on a glass substrate 5 and forms an SiO2 film 9 when a chromium reticule is immersed into such soln. after the SiO2 in the soln. is made into the state of the supersatd. aq. soln. 8. The silicon oxide film having the uniform film thickness and no pinholes is formed with the simple equipment in this way.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a photomask (reticle) used for manufacturing high-density integrated circuits such as LSI and VLSI, and in particular, The present invention relates to a method of manufacturing a photomask having a phase soft layer when forming a pattern with high precision.

：Conventional technology 2 Semiconductor integrated circuits such as IC, LSI, and VLSI are manufactured using a so-called process in which a resist is applied onto a substrate to be processed such as an Sl wafer, a desired pattern is exposed using a stepper, etc., and then developed and etched. It is manufactured by repeating the lithography process.

Photomasks called reticles used in such lithography processes are used to improve the performance of semiconductor integrated circuits.
There is a tendency for higher precision to be required with higher integration. The line width of device patterns formed using these reticles is 1.2 μm and 4 μm for IM bit DRAM.
0.8μm for M-bit DRAM, 16M-bit DRAM
For M, there is a demand for further miniaturization of 0.5 μm, and various exposure methods are being researched to meet these demands.

However, for example, a 64 Mbit DRAM class device requires a pattern with a line width of 0.35 μm, which requires a conventional stepper using a reticle! In the optical method, there is a limit to the resolution of the resist pattern, for example,
A new type of reticle called a phase shift mask has been proposed, as disclosed in Japanese Patent Publication No. 173744 and Japanese Patent Publication No. 62-59296. Phase shift lithography using a phase shift reticle is a technique that improves the resolution and contrast of a projected image by manipulating the phase of light that passes through the reticle.

(Phase Shift) The IJ sogerafy will be briefly explained according to the drawings. Fig. 3 is a diagram showing the principle of the phase shift method, and Fig. 4 is a diagram showing the conventional method.
) are cross-sectional views of the reticle, Figures 3(b) and 4(b)
is the amplitude of the light on the reticle, Figures 3 (C) and 4 (C)
) is the amplitude of the light on the wafer, Fig. 3(d) and Fig. 4(
d) shows the light intensity on the wafer, 1 is the substrate,
2 is a light shielding film, 3 is a phase shifter, and 4 is incident light.

In the conventional method, as shown in FIG. 4(a), a light-shielding film 2 made of chromium or the like is formed on a substrate 1 made of glass or the like, and a light-transmitting part in a predetermined pattern is formed. However, in the case of IJ Sogerahui (phase shift), Fig. 3 (
As shown in a), a phase shifter 3 made of a transparent film for inverting the phase (phase difference of 180°) is provided on one of the adjacent light transmitting portions on the reticle. Therefore, in the conventional method, the amplitude of the light on the reticle is
The light beams on the wafer are in phase as shown in b), and the amplitudes of the lights on the wafer are also in phase as shown in Figure 4(c).
While it is not possible to separate the patterns on the wafer as shown in Figure 4(d), in phase shift lithography, the light transmitted through the phase shifter is separated as shown in Figure 3(b).
), since the adjacent patterns are set in opposite phases to each other, the light intensity becomes zero at the pattern boundary, and the adjacent patterns can be clearly separated as shown in Figure 3(d). I can do it. In this way, in the phase shift IJ sogerafy, patterns that could not be separated in the past can be separated, and the degree of understanding can be improved.

[Issues that Hathu tries to solve]

By the way, in phase shift lithography, wavelength 365
Since light of nm(III) or 248 film m<KrFX ximer laser) is used for pattern transfer, a material having light transmittance close to 100% for these wavelengths is required as a phase shifter material.

On the other hand, if the film thickness of the phase shifter with the refractive index n is d, and the wavelength of the light used is λ, then there is d between n, d, and λ.
=λ/2(n-1), for example, the refractive index is 1.
In the case of one-line exposure using a SiO2 phase shifter of 46 mm, a phase shifter film thickness of 3967 is required. There are not many phase shifter materials that have a thickness of 3,967 m and a light transmittance close to 100%, and the materials currently used are polymer resin films such as electron beam resists that have a high light transmittance. Alternatively, an SIO2 film made by the S○G (spin-on-glass) coating method, which is often used as an insulating film material in semiconductors, or an S+Oa film made by vacuum technology such as evaporation, sputtering, or CVD (chemical vapor deposition). It's nothing more than that.

However, in the above-mentioned materials, the polymer resin film:
However, it has a problem in that it is extremely weak in terms of chemical resistance, light resistance, mechanical strength, etc., and although it can be used in the laboratory, it cannot be put to practical use.

In addition, since the SOG method is formed by coating, there is a large difference in film thickness between the center and the periphery on a rectangular photomask substrate, and a baking process is required. , Warping of the glass substrate, misalignment of the chrome light-shielding pattern, and pattern peeling due to stress changes in the pattern. In the case of low-temperature firing below 400°C, the chemical resistance, light resistance, etc. of the formed 5102 film, Mechanical strength was insufficient and there was a problem in practical use. Also,
The 5iOa film formed using vacuum technology requires expensive vacuum film forming equipment and has a thickness of around 0.4 μm51.
02 had problems such as difficulty in controlling stress, adhesion to the substrate being a problem with fine phase shifters, and insufficient coverage of Sigh at the edges of the chrome pattern with sputtering.

The present invention was made in view of this situation, and
The purpose is to provide a method for manufacturing a phase shift reticle having a phase shifter layer that is different from conventional phase shifter layers, is easier to manufacture, and has a higher quality phase shifter layer.

[Means to solve the problem]

In view of the above-mentioned problems, the present inventor has developed a film using a liquid phase film formation method.
As a result of various studies on 102 film formation methods, we found that a specific liquid phase film formation method produces dense and high quality 5iC)2 for phase shifters.
The inventors have discovered that a film can be formed at low temperatures and with good coverage over light-shielding patterns made of chromium or the like, and have completed the present invention based on this knowledge.

Hereinafter, a method for manufacturing a photomask having a phase shifter layer according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the manufacturing process of a phase shift reticle according to the present invention, and as shown in FIG. Prepare.

Although chromium is used as an example of the light-shielding film, other materials commonly used as photomask light-shielding films, such as chromium oxide, chromium oxynitride, tungsten, and molybdenum silicide, can be similarly applied. Furthermore, since high precision is required for the substrate 5, quartz glass having a small coefficient of thermal expansion is generally used, but low thermal expansion glass, soda lime glass, etc. can also be used.

Next, as shown in the same figure (b), an immersion tank 7 made of a hydrofluoric acid-resistant material such as Teflon is prepared, and a dipping tank 7 made of a hydrofluoric acid-resistant material such as Teflon is prepared.
Silica gel (SiO2) is added to an aqueous solution of H=SiF, ) to make a saturated aqueous solution. The hydrosilicofluoric acid aqueous solution is 0.5
Mol/i! ~5 mol/l is appropriate; within this range, the higher the concentration, the denser the film can be formed. The amount of silica gel required for saturation varies depending on the temperature and concentration of the H=SiFg aqueous solution, but for example, in the case of a 2 mol/1 Hz SiF6 aqueous solution at 20° C., 20 g of silica gel becomes a saturated aqueous solution.

This saturated aqueous solution is heated to the precipitation temperature (usually 35°C),
After adding an initiator such as calcium chloride or boric acid (H, BO3) to make the S+Oi in the solution into a supersaturated aqueous solution 8, when the chrome reticle prepared in Figure (a) is immersed, the S iO2 in the solution is deposited on a glass substrate and S
This becomes an iO2 film 9. The initiator reacts with the nHF present in the aqueous solution of H2SIFg and silica gel to change the equilibrium state, and S10. This serves to promote the precipitation of 5102 by bringing it into a saturated state. The above precipitation is explained by the following reaction formula.

The aqueous solution of H=S+Fg is in an equilibrium state expressed by equation (1).

S+Fa--+(2+x)H2O,l::S+02'
XH2O"41'l"+6F-"' (1) When silica gel is added to this solution, the equilibrium reaction shown by equation (2) begins to coexist in the solution, and as the amount of silica gel added, this equation (2) changes. Become more dominant.

4H"=55iF6-+5i02-"3 [S+F,・
S+F, E-+2820...(2) Next, if H, BO, is added to the solution where the equilibrium reactions of equations (1) and (2) coexist, H, BO, becomes H in the solution.
It reacts with F and reaches the equilibrium state of the following equations (3) and (4) via an HF adduct.

11.8G, -3HF:: 1(BF3(OH)-
2) 120...(3) HBF3 (Kano)
-HF, =: HBF, -8,0...(4) In other words, the addition of H2B○ causes a simple shift in chemical equilibrium due to the reaction with HF, resulting in the equilibrium reaction of equations (1) and (2). Both are changed to SiC and to the depositing side.

Now, returning to Figure (b), the precipitation rate of the 5102 film is affected by the liquid temperature and the amounts of H and BO added, but generally 100
~1000 people/hour is used. In order to simplify the diagram, the state in which S10 is precipitated only on the glass surface on the chromium pattern side of the glass substrate 5 is shown in FIGS. Emissions occur on all exposed glass surfaces in aqueous solution. Therefore 810
．． It is necessary to mask in advance the parts that do not need to be folded out. It is also possible to immerse a plurality of glass substrates at the same time, or to immerse two substrates back to back with the chrome pattern on the outside.

After forming the 8102 film 9 of a predetermined thickness by the liquid phase film forming method as described above, it was thoroughly washed with water and dried, as shown in the same figure (C).
As shown in (d) of the same figure, an ionizing radiation resist layer 10 such as polymethyl methacrylate is formed on a chrome reticle having a 5in2 film 9, and as shown in (d) of the same figure, a resist layer l
A resist pattern 13 is formed by drawing a predetermined pattern using ionizing radiation 11 from an electron beam exposure device or the like, developing and rinsing, as shown in FIG. 3(e).

Next, after performing heat treatment and descum treatment as necessary, as shown in IK (f), the transparent film portion exposed from the opening of the resist pattern 13 is wet-etched with hydrofluoric acid. A phase shifter pattern 12 is formed. Note that the phase shifter pattern 12 can be formed by dry etching instead of wet etching, but in that case, it is necessary to use a resist with high dry etching resistance for the resist layer 10.

Next, as shown in the figure, the remaining resist is removed by ashing with oxygen plasma 14. Note that, instead of the dry method using oxygen plasma, the resist can also be removed by a wet method using a stripping solution or acid specifically for the resist.

Through the above steps, a phase shifter 1 as shown in the hole in the figure is obtained.
A phase shift mask having 2 is completed.

The above is a case where a phase shifter pattern is formed by patterning a 5102 film formed by a liquid phase film formation method using an etching method. The resist film is left on the part of the ROM reticle where the phase shifter is not provided, and the 5i02 film is deposited using the liquid phase deposition method described above only on the part of the reticle exposed from the resist pattern to form the phase shifter layer on the desired part. It can also be configured to form.

Dual action: According to the present invention, a silicon oxide film (SiO
2) is formed at a low temperature of 40℃ or less, so it has high accuracy.
The positioning accuracy of the chrome reticle can be maintained as it is, and the coverage is also good), so it can be used for complex, minute or detailed applications. ;64MD
It has two major features: it can form a silicon oxide shifter layer with a uniform thickness and no pinholes even on a rectangular reticle having a chromium pattern larger than that of a RAM.

Further, the photomask manufacturing method of the present invention has the advantage that a silicon oxide film can be formed with simple and common equipment, and expensive equipment such as a dedicated spinner or sputtering method used in conventional SOG is not required.

J Example: Examples of the present invention will be described below.

Example 1 Hydrosilicofluoric acid 2 mol/! Silica gel 2 in aqueous solution 101 of
After mixing 0.0g and heating this solution to 35°C, 0.
5 mol/i' [acid was added to make a supersaturated aqueous solution, and then a reticle having a chrome pattern on a quartz glass substrate was immersed in this supersaturated aqueous solution for 9 hours to obtain a desired film thickness on the reticle having a chrome pattern. 3102 was isolated. After that, the reticle with 5iOz precipitated was washed with water and dried, and then an electron beam resist CMS was applied to the chrome pattern side.
(manufactured by Tosoh Corporation) was applied, exposed to electron beam, developed, and rinsed to form a resist pattern at a predetermined position. Next, after wet-etching the unnecessary SiO2 film with hydrofluoric acid, the remaining resist was removed with oxygen plasma to complete a reticle with a 4,500-meter SiO2 film phase shifter.

Example 2 A resist solution of chloromethylated polystyrene was applied by spin coating onto a photomask in which a chromium pattern 6 was formed on a quartz glass substrate 5 as shown in FIG. 2(a), as shown in FIG. A uniform resist film 15 having a thickness of 0.7 μm was obtained by coating and heating and drying.

Next, as shown in FIG. 3C, pattern exposure was performed at predetermined positions while detecting alignment marks on the photomask using an electron beam 16 of an electron beam drawing device with an acceleration voltage of 20 kV. Note that this pattern exposure may be performed by light or ion beam exposure instead of electron beam exposure. After exposure, this substrate was developed and rinsed with the same solvent as described above to obtain a resist pattern 17 as shown in FIG. 4(d).

Subsequently, heat treatment and discum treatment were performed, and then this substrate was immersed in the same solution as in Example 1, in which silica gel was supersaturated in hydrosilicic acid and boric acid was added, as shown in FIG. Next, 5iO218 was precipitated to a thickness of 415 nm in the area where the resist film 17 was not present. The refractive index of 5102 obtained by this liquid phase film formation method is 1.44.

Finally, the remaining resist 17 was heated to 2 Torr.

Ashing and removal was performed using 400 W oxygen plasma to obtain a phase shift mask having a phase shifter layer 18 made of S]02, as shown in FIG. 2(f).

〔Effect of the invention〕

According to the method of manufacturing a photomask having a phase shifter layer according to the present invention, the silicon oxide film (SiO2 film) is formed by the liquid phase deposition method at a low temperature of 40°C or less, so it is highly accurate and the positional accuracy of the ROM reticle is maintained as it is. In addition, because of its good coverage, it is possible to form a silicon oxide shifter layer uniformly and without pinholes even on a rectangular reticle with a complex and fine chromium pattern of 64M DRAM or larger. Has characteristics.

Furthermore, the photomask manufacturing method of the present invention has the advantage that a silicon oxide film can be formed with simple equipment and does not require expensive equipment such as a dedicated spinner or sputtering method used in conventional SOG. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the steps of one embodiment of the method for manufacturing a photomask having a phase shifter layer according to the present invention, and FIG.
The figures are cross-sectional views showing the steps of another embodiment, FIG. 3 is a view showing the principle of the phase shift method, and FIG. 4 is a view showing the conventional method. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Light shielding film, 3... Phase shifter, 4... Incident light, 5... Glass substrate, 6... Chrome pattern, 7... Immersion tank, 8...・Supersaturated aqueous solution, 9
...5102 film, 10... resist layer, 11...
Ionizing radiation, 12... Phase shifter pattern, 13.
...Resist pattern, 14...Oxygen plasma, 15
...Resist film, 16...Electron beam, 17...
Resist pattern, 18...Phase shifter layer Applicant: Dai Nippon Printing Co., Ltd. Agent Patent attorney: Hiroshi Nirasawa (7 others) Figure 2

Claims (3)

[Claims] (1) A photomask with a light-shielding film on a glass substrate is immersed in a supersaturated aqueous solution of silicon oxide containing hydrofluorosilicic acid and silica gel as main components, and a silicon oxide film is deposited to a predetermined thickness using a liquid phase deposition method. 1. A method for manufacturing a photomask having a phase shifter layer, the method comprising depositing the phase shifter layer to form the phase shifter layer. (2) The method for forming the phase shifter layer is characterized in that a silicon oxide film is selectively deposited only on the necessary portions of a photomask having a light-shielding film on a glass substrate to form a phase shifter layer. A method of manufacturing a photomask having the phase shifter layer described above. (3) As a method for forming the phase shifter layer, a silicon oxide film is deposited to a predetermined thickness on the glass portion of a photomask having a light-shielding film on a glass substrate, and then unnecessary portions of the silicon oxide film are removed by etching. A method for manufacturing a photomask having a phase shifter layer according to claim 1.