JPH0980737A - Phase shift photomask and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a phase shift photomask having high accuracy and high quality capable of exactly matching phase difference with 180 deg. while directly reading this difference and eliminating the need for examining the wet etching liquid resistance of a resist. SOLUTION: The phase shifter layers of the parts corresponding to the apertures in a part of light shielding patterns 2 are dry-etched (Fig, (j)) and thereafter, the phase shift layers 4 of the parts corresponding to all the apertures of the light shielding patterns 2 are sideetched by wet etching (Fig. (1)), in the process for producing the phase shift mask constituted by forming, successively from a substrate side, an etching stopper layer 5, the phase shift patterns 4 and the light shielding patterns 2 in this order on a transparent substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift photomask and a method for manufacturing the same, and particularly to an LSI and an ultra LS.
I, ASIC, etc., which has a phase shifter layer or phase shift, which is used for manufacturing high-density semiconductor integrated circuits, devices requiring ultra-fine processing, holograms requiring phase change of light, optical communication, etc. And a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, high-density semiconductor integrated circuits such as LSI, VLSI, and ASIC are manufactured by coating a resist having sensitivity to ionizing radiation on a substrate to be processed such as a silicon wafer and using the resist as a stepper or aligner. And then processed into a desired pattern, and using the pattern as a mask, a lithography process such as substrate etching and doping, thin film formation, and lift-off is used.

The original plate of the pattern used in the pattern forming process on the substrate to be processed is called a reticle in the stepper and a mask in the aligner. Both of them have a light-shielding pattern formed on the transparent substrate. Since the pattern is transferred by using light, it is collectively referred to as a photomask here. In addition, the pattern on the photomask is usually formed in a size equal to or 5 times the size of the pattern transferred onto the substrate to be processed.

In recent years, the degree of integration of semiconductor integrated circuits has increased,
In particular, DRAM, which is one of the memories, is being integrated up to 64 Mb. Since the minimum pattern size of the 64 Mb DRAM is 0.35 to 0.20 μm on the substrate to be processed, there is an increasing demand for miniaturization of the size of the photomask which is the original plate of the pattern and improvement in accuracy.

The size of the photomask in the above 64 Mb DRAM is 1.75 to 1.00 μ even if it is five times larger.
m. These patterns are the resolution limit of the resist pattern in the conventional stepper exposure method.

As a method of forming these patterns,
Shorter wavelength of exposure light source, higher NA of transfer lens (numerical aperture)
And the super-resolution method represented by the annular illumination method and the electron beam direct writing without using a photomask are being studied. However, the above method involves cost increase such as modification of the exposure apparatus or introduction of a new apparatus.

To solve these problems, for example, JP-A-58-173744 and JP-A-62-5929.
As shown in Japanese Patent No. 6 and the like, a new photomask called a phase shift photomask has been proposed.

In a phase shift photomask, a light-shielding film is patterned on a transparent substrate so as to have a desired transmissive portion, but unlike a conventional photomask, a phase shifter layer is provided at an alternating transmissive portion. It is on. The phase shifter layer is adjusted so that the phase is inverted by about 180 ° at the wavelength of the ionizing radiation to be transmitted. Ionizing radiation incident from behind the substrate passes through the transparent substrate,
Although the light is transmitted through the transmissive portion where the light-shielding film does not exist, the transmitted light is divided into light that is transmitted through the phase shifter layer and light that is not transmitted through the adjacent light transmissive portions. At this time, the electromagnetic field strengths from the adjacent transmissive parts, which are obtained when the distances between the transmissive parts adjacent to each other are very close and the dimensions of each transmissive part are very small, are in opposite phases to each other, and the relative light intensity is relatively high. There will be a part of zero. Therefore, the contrast of the light intensity is sufficiently obtained as compared with the conventional photomask, and the resolution can be improved.

Thus, the phase shift photomask is
As compared with the conventional photomask, it is very effective in resolving a fine pattern, so various structures have been studied. Although each structure has a direction in which the intended pattern is not oriented, the Levenson type, which is the most effective in improving the critical resolution among phase shift photomasks,
A method for manufacturing the phase shift photomask will be described.

As shown in FIG. 3A, an etching stopper layer 5 for preventing the transparent substrate 1 from being etched when the phase shifter layer 4 to be formed later is etched on the transparent substrate 1 by sputtering or CVD. Film is formed by the method. Next, a phase shifter layer 4 having a thickness adjusted so as to invert the phase of the wavelength of the ionizing radiation transmitted at the time of transfer by 180 ° is formed by sputtering, CVD or spin coating, and the light shielding film 2 is further formed. Spatter or C
The film is formed by the VD method. Finally, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a spin coating method and subjected to a heat drying treatment to form a resist layer 3 having a thickness of about 0.1 to 1.0 μm. The heat treatment varies depending on the type of resist and the equipment used, but the temperature is 80 to 20
The temperature is 0 ° C., and the time varies depending on the device, but is 20 to 60 minutes in the case of an oven and 1 to 30 minutes in the case of a hot plate.

Next, as shown in FIG. 3 (b), a pattern is drawn on the resist layer 3 with an ionizing radiation 6 by an electron beam exposure or a laser exposure apparatus according to a conventional method, and thereafter, development and rinsing are performed, and FIG. As shown in c), a desired resist pattern is formed. At this time, the developing and rinsing liquids are determined by the type of the applied resist layer 3. The same applies to each time. Next, heat treatment or descum treatment is performed as necessary.

After that, as shown in FIG. 3D, the light-shielding film 2 exposed from the openings of the patterned resist layer 3 is removed by dry etching or wet etching according to a conventional method. Next, as shown in FIG. 3 (e), the patterned resist layer 3 is removed by ashing or solvent removal by a conventional plasma containing oxygen as a main component. Here, if necessary, the substrate is cleaned and the light-shielding film 2 is inspected and corrected by using a normal photomask cleaning, inspection and correction device.

Then, as shown in FIG.
The resist layer 3 is applied again in the same manner as when the resist layer 3 is spin-coated in (a). Next, as shown in FIG. 3G, pattern drawing is performed with ionizing radiation 6 as in FIG. 3B, and development similar to that in FIG. 3C is performed as shown in FIG. Then, a rinsing process is performed to form a desired resist pattern. Next, a heating process or a descum process is performed as needed.

At this time, since the purpose is to etch the phase shifter layer 4 under the opening of the lower light-shielding film 2, the patterned resist layer 3 is positioned on the phase shifter layer 4 which does not require etching. I have to do it. Therefore, the ionizing radiation 6 in FIG.
At the time of pattern drawing, alignment drawing must be performed so that the patterned resist layer 3 is aligned with the patterned light-shielding film 2.

Next, as shown in FIG. 4 (i), the phase shifter layer 4 exposed from the opening of the patterned resist layer 3 is dry-etched by the etching gas plasma 7 to form the patterned phase shifter layer 4. Form. At this time, the etching gas plasma 7 that etches the phase shifter layer 4 is removed from the etching stopper layer 5 by the etching gas plasma 7.
Blocked by, without etching the transparent substrate 1,
Only the phase shifter layer 4 formed in (a) is etched.

Here, there is a structural problem of the lower shifter type phase shift photomask as described above. FIG. 4
As shown in (j), the light-shielding film 2 is formed on the phase shifter layer 4.
(When the device is installed on the stepper, the substrate 1 is turned upside down, so the light shielding part 2 is turned down.). for that reason,
The exposure light transmitted through the transparent substrate 1 is affected by the side wall of the engraved phase shifter layer 4, and a difference appears in the size of the transfer pattern between the engraved portion and the non-engraved portion.
However, this problem can be solved at present by putting a side etching in the engraved phase shifter layer 4 portion. Therefore, as shown in FIG. 4K, the engraved phase shifter layer 4 is side-etched.
Here, since the side etching is difficult to perform by dry etching, a wet etching method using hydrofluoric acid which is a conventional method is used.

Thereafter, the patterned resist layer 3
Is removed by ashing or solvent stripping with a plasma containing oxygen as a main component, and a phase shift photomask having a phase shifter layer 4 is produced as shown in FIG.

[0018]

However, there are two problems in such a conventional method of performing side etching. First, the resist may not be able to withstand the etching solution used for side etching, and the resist resistance to the etching solution must be taken into consideration.
The other is that the resist remains until the final step and the phase difference cannot be measured unless the resist is peeled off. Also, even if there is a phase error as a result of the measurement, there is no resist, so the process can be performed again. This is something that cannot be done.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to perform a manufacturing process while directly reading a phase difference and accurately adjust the phase difference to 180 °. It is an object of the present invention to provide a method for producing a high-precision and high-quality phase shift photomask, which does not require consideration of the wet etching solution resistance, and a phase shift photomask obtained by the method.

[0020]

The manufacturing method of the present invention solves the problems of the prior art, and is performed without increasing the number of steps of manufacturing a conventional phase shift photomask as shown in FIGS. Is something that can be done. The manufacturing method of the present invention will be described below.

First, when the phase shifter layer is formed, the thickness of the phase shifter layer may be thicker by 0.15 μm at the maximum than the thickness at which the phase difference with respect to air is 180 ° at the wavelength for the purpose of pattern transfer. It becomes important. During the dry etching, the phase shifter layer is etched up to the vicinity of the etching stopper layer so that the thickness of the remaining phase shifter layer is equal to or less than the target side etching amount, and then the resist is stripped. Wet etching is performed on the substrate after the resist is removed, and side etching is performed. At this time, since the etching continues to proceed in the vertical direction only in the light-shielding pattern openings that have not been dry-etched, the relative phase difference between the light-shielding pattern openings that have been dry-etched and the light-shielding pattern openings that have not been dry-etched is directly read. While performing the wet etching process, the phase difference can be accurately adjusted to 180 °. Also, since the resist is peeled off during wet etching,
There is no need to study the wet etchant resistance of the resist.

That is, in the phase shift photomask of the present invention, in the phase shift photomask in which the etching stopper layer, the phase shifter pattern and the light shielding pattern are formed in this order on the transparent substrate from the substrate side, all the openings of the light shielding pattern are formed. It is characterized in that the phase shifter portion of the portion corresponding to is side-etched.

In this case, the thickness from the etching stopper layer of the phase shifter portion to the light-shielding layer is thicker by 0.15 μm at the maximum than the thickness which causes a phase difference of 180 ° with respect to air at the pattern transfer wavelength. It is what

Further, the method for producing a phase shift photomask of the present invention is a method for producing a phase shift photomask, which comprises an etching stopper layer, a phase shifter pattern and a light shielding pattern formed in this order on a transparent substrate from the substrate side. A method characterized by dry etching the phase shifter layer in a portion corresponding to part of the opening of the pattern, and then performing side etching by wet etching on the phase shifter layer in a portion corresponding to all the openings of the light shielding pattern. Is.

In this case, the relative phase difference at the pattern transfer wavelength between the portion of the phase shifter layer that has been wet-etched after dry etching and the portion of the phase shifter layer that has been wet-etched without dry etching is 180. It is desirable that the angle be ± 10 °.

The etching solution for wet etching is hydrofluoric acid, a hydrofluoric acid solution such as buffered hydrofluoric acid, an alkaline solution such as sodium hydroxide or potassium hydroxide, or
An acidic solution such as phosphoric acid can be used.

In the manufacturing method of the present invention, the phase shifter layer is etched up to the vicinity of the etching stopper layer so that the thickness of the remaining phase shifter layer during dry etching is less than or equal to the target side etching amount, and then, Insert side etching that is good for wet etching. At this time, in the vertical direction of the dry-etched portion, the etching is stopped by the etching stopper layer and stopped, and only the lateral side etching proceeds. Further, although the portion which is not dry-etched is also wet-etched at the same time, this portion is isotropically etched simultaneously in the vertical and horizontal directions, unlike the portion which is dry-etched.

Here, when the phase shifter layer is formed, its thickness is such that the phase difference with respect to air is 180 ° at a wavelength for the purpose of pattern transfer.
In view of problems such as the mixing of foreign matter, it is important that the thickness is 0.15 μm at maximum. As described above, since the wet etching continues in the vertical direction in the portion not dry-etched, the relative phase difference between the portion not dry-etched and the portion not dry-etched approaches 180 °. In addition, since the phase difference is finally adjusted by wet etching and there is no resist at the final step of wet etching, it is possible to perform the process while directly reading the phase difference and accurately adjust it to 180 °.

Further, in this method, since the resist is peeled off during the wet etching, it is not necessary to study the resistance of the resist to the wet etching solution.

If the phase shifter layer is 0.15 μm or more thicker than the thickness that causes a phase difference of 180 ° with respect to the air at the pattern transfer wavelength, the side etching amount must be large, so that the side etching is performed. This is not suitable because the eaves portion of the light shielding layer becomes large, and problems such as peeling and chipping of the light shielding layer and mixing of foreign matter occur.

From the above, according to the manufacturing method of the present invention, a phase shift photomask can be accurately manufactured regardless of the resistance of the resist to the etching solution and with almost no increase in the conventional phase shift photomask manufacturing process. be able to.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for manufacturing a phase shift photomask of the present invention and a phase shift photomask manufactured by the method will be specifically described with reference to Examples. FIG.
As shown in (a), when the phase shifter layer 4 to be formed later is etched on the optically polished transparent substrate 1 made of synthetic quartz glass for a photomask, the transparent substrate 1 is prevented from being etched. Aluminum oxide, for the purpose of
An etching stopper layer 5 containing tin oxide or hafnium oxide as a main component is formed by sputtering to a thickness of about 100 nm. Next, the SOG (spin-on-glass) is made to have a thickness of about 0.4 so that the phase is inverted by 180 ° at the wavelength (365 nm) of the i-line stepper, which is the mainstream in the current transfer.
About 0 μm and the amount of side etching this time is 0.06 μm
The phase shifter layer 4 having a combined thickness was formed by a spin coating method or the like, and then vacuum or heat drying and heat baking were performed. At this time, drying is performed at 200 ° C. for 3 minutes and baking is performed at 400
The temperature was set to 2 ° C. for 2 hours. Further, the light-shielding film 2 used in the conventional photomask is formed thereon by a conventional method. Finally, a positive resist (Hoechst AZ-5200)
Was uniformly applied by a spin coating method, and heat-dried to form a resist layer 3 having a thickness of about 0.5 μm. The heat drying treatment was carried out at 150 ° C. for about 20 minutes using a hot plate.

Next, as shown in FIG. 1B, a pattern was drawn on the resist layer 3 by an electron beam exposure apparatus according to a conventional method. At this time, the exposure is performed with an acceleration voltage of 20 keV,
The exposure amount was 10 μC / cm ² . Then, dip-develop at room temperature for 1 minute with a water-soluble alkaline developer containing tetramethylammonium hydroxide as a main component,
Rinsing was performed with pure water, and a desired resist pattern was formed as shown in FIG. Next, the resist layer 3
In order to improve the adhesion between the light-shielding film 2 and the light-shielding film 2, heat treatment was performed in an oven at 120 ° C. for 30 minutes.

After that, as shown in FIG. 1D, the light-shielding film 2 exposed from the opening of the patterned resist layer 3 was removed by a wet etching method. Here, as the wet etching, spray etching was performed with an aqueous solution containing cerium ammonium nitrate as a main component at room temperature for 1 minute, and then rinsed with pure water.

Next, as shown in FIG. 1 (e), the patterned resist layer 3 was removed by solvent removal. here,
Stripping is performed with a stripping solution containing ethanolamine as the main component.
It was carried out under ultrasonic waves at 3 ° C. for 3 minutes, and then rinsed with pure water. Here, after the resist layer 3 was peeled off, the substrate was cleaned and the light-shielding film 2 was inspected and corrected by using a normal photomask cleaning, inspection and correction device.

Subsequently, as shown in FIG. 1 (f), a positive resist (AZ-5200 manufactured by Hoechst Co., Ltd.) is uniformly applied again on the patterned light-shielding film 2 by a spin-coating method, followed by heat-drying treatment. Then, a resist layer 3 having a thickness of about 0.7 μm was formed. The heat drying treatment was performed at 150 ° C. for 20 minutes using a hot plate.

Next, as shown in FIG. 1G, alignment drawing was performed by an electron beam exposure apparatus according to a conventional method.
At this time, the exposure is performed with an acceleration voltage of 20 keV and an exposure amount of 10
It was performed at μC / cm ² .

Then, as shown in FIG. 2 (h), dip development is carried out at room temperature for 1 minute with a water-soluble alkali developing solution containing tetramethylammonium hydroxide as a main component,
Rinsing was performed with running pure water to form a desired resist pattern. Moreover, if necessary, descum treatment was performed with oxygen plasma. If descum treatment is required, use a parallel plate electrode type RIE dry etching device with 0.2 mTo
It was treated with rr, O ₂ -100 sccm, 0.1 W / cm ² for 1 minute.

Next, as shown in FIG. 2I, the phase shifter layer 4 was etched by the dry etching method.
The conditions are 0.1 mTorr, CHF ₃ -93 sccm, and a parallel plate electrode type RIE dry etching apparatus.
O ₂ −7 sccm, 0.2 W / cm ² was used. At that time, as shown in FIG. 2 (j), the etching amount was such that the phase shifter layer 4 was left by a thickness of about 0.03 μm from the etching stopper layer 5.

After that, as shown in FIG. 2K, the patterned resist layer 3 is removed by solvent removal. Here, the peeling was performed under ultrasonic waves at 60 ° C. for 3 minutes with a peeling solution containing ethanolamine as a main component, and then rinsed with pure water.

Finally, as shown in FIG. 2 (l), side etching of the phase shifter layer 4 was performed by using a wet etching method under conditions of 10 wt% sodium hydroxide aqueous solution at 40 ° C. for 10 minutes. . The side etching amount at this time is about 0.06 μm. After the etching is completed, the relative phase difference between the portion where the dry etching is performed and the portion where the dry etching is not performed is 1
A phase shift photomask precisely adjusted to 80 ° was produced.

Although one embodiment of the manufacturing method of the present invention has been described above, this is one example and does not limit the materials, devices, conditions or the like to be used. Further, in particular, the dry etching conditions are strongly influenced by the dry etching apparatus, the structure of the etching chamber, and the like. The wet etching condition is also not limited to this condition because it is influenced by the etching area and the amount of the etching solution.

[0043]

As is apparent from the above description, according to the phase shift photomask of the present invention and the method of manufacturing the same,
After dry etching the part of the phase shifter layer corresponding to the openings of the light-shielding pattern, side etching is performed on the part of the phase shifter layer corresponding to all the openings of the light-shielding pattern by wet etching. The phase difference can be adjusted by wet etching, and since there is no resist layer in the wet etching in the final step, the phase difference can be accurately adjusted to 180 ° by performing the etching process while directly reading the phase difference.
Further, in this method, since the resist layer is peeled off, there is no need to study the wet etching solution resistance of the resist. From the above, according to the present invention, a phase shift photomask can be accurately manufactured regardless of the resistance of the resist to the etching solution and with almost no increase in the conventional phase shift photomask manufacturing process.

[Brief description of drawings]

FIG. 1 is a diagram showing part of a process chart for explaining one embodiment of a method for manufacturing a phase shift photomask of the present invention.

FIG. 2 is a view showing the rest of the process chart for explaining one embodiment of the method for manufacturing a phase shift photomask of the present invention.

FIG. 3 is a diagram showing part of a process chart for explaining a conventional method for manufacturing a phase shift photomask.

FIG. 4 is a view showing the rest of the process drawing for explaining the conventional method for manufacturing a phase shift photomask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent substrate (synthetic quartz glass) 2 ... Light-shielding film (chrome etc.) 3 ... Resist layer 4 ... Phase shifter layer 5 ... Etching stopper layer 6 ... Ionizing radiation 7 ... Etching gas plasma

Claims (5)

[Claims] 1. A phase shift photomask comprising a transparent substrate and an etching stopper layer, a phase shifter pattern, and a light-shielding pattern formed in this order from the substrate side, and a phase shifter portion corresponding to all openings of the light-shielding pattern. A phase shift photomask characterized by being side-etched. 2. The thickness from the etching stopper layer of the phase shifter portion to the light shielding layer is thicker by 0.15 μm at the maximum than a thickness which causes a phase difference of 180 ° with respect to air at a pattern transfer wavelength. The phase shift photomask according to claim 1. 3. A method of manufacturing a phase shift photomask, which comprises an etching stopper layer, a phase shifter pattern, and a light-shielding pattern formed in this order on a transparent substrate from the substrate side. A method of manufacturing a phase shift photomask, comprising dry etching the phase shifter layer, and then side etching the portion of the phase shifter layer corresponding to all the openings of the light shielding pattern by wet etching. 4. A relative phase difference at a pattern transfer wavelength of 180 ° between a portion of a phase shifter layer that is wet-etched after dry etching and a portion of a phase shifter layer that is wet-etched without dry etching. The method for producing a phase shift photomask according to claim 3, wherein the angle is ± 10 °. 5. An etching solution for performing the wet etching is a hydrofluoric acid solution such as hydrofluoric acid or buffered hydrofluoric acid, an alkaline solution such as sodium hydroxide or potassium hydroxide, or
The method for producing a phase shift photomask according to claim 3, wherein the method is an acidic solution of phosphoric acid or the like.