JPH0950112A - Phase shift mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an upper shifter type phase shift mask which suppresses the fluctuation in the thickness of a phase shift film induced by a difference in level of a light shielding film in an element region, exhibits a sufficient light shielding characteristic in the periphery of the element region and has an excellent phase shift effect. SOLUTION: This phase shifter mask has the first patterns of the light shielding film 108 and the second patterns of the phase shift film 109 laminated on the first patterns on a transparent substrate 101. The phase shifter mask has the peripheral regions where the film thickness of the light shielding film 108 is large and the element region where the film thickness of the light shielding film 108 is small in order to suppress the fluctuation in the thickness of the phase shift film induced by the difference in level of the light shielding film 108 on the transparent substrate 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift mask, and more particularly to a phase shift mask capable of forming a fine pattern in a photomask used for manufacturing a VLSI or the like.

[0002]

2. Description of the Related Art A phase shift mask having a light-shielding film for forming at least a first pattern and a phase shift film for forming a second pattern on a transparent substrate is known to be effective for forming a fine pattern. ing. The following two types of phase shift masks are generally known. That is, (1) a so-called upper shifter type phase shift obtained by first providing a light-shielding film on the entire surface of a transparent substrate, plate-making these on a predetermined pattern, and then providing a phase-shifting film on the entire surface and making the plate. A mask,
(2) A so-called bottom obtained by forming a phase shift film and a light shielding film on the entire surface in this order on a transparent substrate, then processing the shielding film into a predetermined pattern, and then patterning the phase shift film. And a shifter type phase shift mask.

Comparing the two, the former is more advantageous for the following reasons.

(1) In the latter case, a so-called optical waveguide effect occurs, and complicated pattern data adjustment is necessary to cancel it, but in the former case, this is not necessary. (2) In the former, the processing process for the phase shift film, which is a process specific to the phase shift mask, can be added after the normal chrome mask process, whereas in the latter, it must be inserted between the chrome processes.
Therefore, in the former case, the light-shielding film process may be the same as the conventional process, whereas in the latter case, the light-shielding film process needs to be partially reviewed because of the existence of the phase shift film.

[0005]

However, the upper shifter type phase shift mask also has the following drawbacks. That is, when forming the phase shift film on the patterned light shielding film, there is a problem that the phase shift film cannot be formed uniformly due to the influence of the step of the light shielding film pattern. The unevenness of the steps of the phase shift film makes the amount of phase shift of the transmitted exposure light uneven and significantly deteriorates the performance as a phase shift mask.

In order to eliminate the unevenness of the film thickness of the phase shift film and obtain a phase shift mask in which the phase angle is accurately adjusted, it is necessary to reduce the film thickness of the light shielding film and reduce the step difference of the light shielding film. Is. However, when the film thickness of the light-shielding film is reduced, the light-shielding performance is deteriorated, and when performing step-and-repeat exposure, a multiple exposure area in which adjacent shots (ranges transferred in one exposure) overlap each other on the wafer Since the problem of reduction in contrast due to exposure occurs, it is difficult to solve the above problem by reducing the film thickness of the light shielding film.

As the light-shielding film, a chromium film formed by sputtering is generally used, and the relationship between the thickness of the chromium film and its transmittance is shown in FIG. The normally required light-shielding performance is that the transmittance is 0.1% or less. From this, it is understood that the light-shielding film is required to have a thickness of at least 60 nm or more. Further, in general, the light shielding film may be required to have an antireflection function. In this case, an antireflection film is required in addition to the chromium film, and the thickness of the light shielding film is 1
It is usually 00 nm or more.

On the other hand, when the phase shift film is formed on the light-shielding film pattern having a step, generally, a step equal to or close to the step of the light-shielding film pattern has a surface of the phase shift film. Will also occur. Further, depending on the film forming method of the phase shift film (shifter film), it is observed that the film has a taper toward the opening of the light shielding film as shown in FIG. In this case, the amount of phase shift is not constant in the opening, which reduces the effect of the phase shift mask.

A silicon oxide film is generally used as the phase shift film, but when the silicon oxide film has a film thickness variation of 60 nm equivalent to the above-mentioned chromium step in the opening, the amount of phase shift is increased. Variation of about 30 ° in i-line lithography and 4 in KrF excimer laser lithography.
It will be close to 5 °. Further, when the variation in film thickness is 100 nm including the antireflection film, it becomes about 50 ° in i-line lithography and about 70 ° in KrF excimer laser lithography, which makes it unusable as a phase shift mask.

On the contrary, the allowable range of fluctuation of the phase shift amount is ±
When the angle is 10 °, the variation in film thickness allowed for the phase shift film made of silicon oxide is about 20 n in i-line lithography.
m, about 14 in KrF excimer laser lithography
Only nm. For this reason, the allowable step difference of the light-shielding film pattern depends on the film forming method of the shifter film, but unless the special film forming method is adopted, it is considerably smaller than the above-mentioned 60 nm, and as is clear from FIG. However, the light blocking performance will be low.

The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a phase shift film caused by a step of a patterned light shielding film in a region where a phase shift effect is required. In the area where the variation of the film thickness is suppressed and a sufficient light blocking rate is required,
An object of the present invention is to provide an upper shifter type phase shift mask that exhibits sufficient light shielding characteristics and has an excellent phase shift effect.

[0012]

According to the present invention, there are provided a region in which the light-shielding film has a large film thickness and thus a large step, and a high light-shielding performance, and a region in which a film thickness is small and therefore a small step and a low light-shielding performance. By providing it, the above-mentioned problem is solved. In addition, as the configuration of the light-shielding film, by providing a region having a large number of layers and thus a large step difference and a high light-shielding performance and a region having a small number of layers and thus a small step difference and a low light-shielding performance, the same as described above is achieved. It solves the problem.

Generally, in a pattern requiring a phase shift effect, such as a fine pattern in an element region, a phase shift layer introduces a phase difference of a half wavelength (180 °) between adjacent openings. Is important,
Even if the light blocking performance of the light blocking layer between the openings is not high, a sufficient phase shift effect can be expected. On the other hand, a phase shift effect is required in a region where high light shielding performance is required for the light shielding layer, such as a region where multiple exposure is performed in step and repeat exposure in the peripheral portion of the element region. There is no fine pattern. Therefore, it is possible to sufficiently divide into a region in which the light shielding performance is prioritized and a region in which the phase shift effect is prioritized in advance.

Specifically, after forming a normal light-shielding film pattern on a transparent substrate, a resist mask for exposing the light-shielding film pattern in a region where the light-shielding performance may be sacrificed is formed through a second lithography process. To do. Here, the exposed portion of the light-shielding film is etched by a predetermined amount to be thin, and then the remaining resist is removed to obtain two regions having different film thicknesses and different light-shielding capabilities. At this time, if it is difficult to control the etching depth, the light-shielding film is a multilayer film made of different materials in advance,
It is also possible for only certain layers of material to be etched during the etching described above. With this method, the film thickness and the light shielding performance of the two regions can be controlled more strictly.

Further, the light-shielding film pattern is thinly formed in all regions on the transparent substrate, the phase shift film pattern is formed, and then a third layer having a sufficient light-shielding property is formed thereon. The above-mentioned object can also be achieved by plate-making.

That is, the phase shift mask of the present invention is
In a phase shift mask having at least a first pattern of a light shielding film and a second pattern of a phase shift film laminated on the first pattern on a transparent substrate, a film thickness of the light shielding film on the transparent substrate is It is characterized by the existence of a large area and a small area.

In this case, the region where the light-shielding film has a large thickness is
It is desirable to include an area that is subjected to multiple exposure in step-and-repeat exposure.

Another phase shift mask of the present invention is
In a phase shift mask having at least a first pattern of a light-shielding film and a second pattern of a phase-shifting film laminated on the first pattern on a transparent substrate, the light-shielding film is composed of a multilayer film composed of a plurality of layers. On the transparent substrate, there are an area having a large number of layers forming the multilayer film and an area having a small number of one layer.

In this case, it is desirable that the region where the number of layers of the light shielding film is large includes a region which is subjected to multiple exposure in step and repeat exposure.

Still another phase shift mask of the present invention is a phase shift mask having at least a first pattern of a light shielding film and a second pattern of a phase shift film laminated on the first pattern on a transparent substrate. In the second
It is characterized in that it has a light-shielding third pattern on the pattern.

In this case, it is desirable that the area where the third pattern is formed includes an area that is subjected to multiple exposure in step and repeat exposure.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The phase shift mask of the present invention will be specifically described below with reference to the drawings based on its manufacturing method. [Embodiment 1] An embodiment of a phase shift mask for i-line exposure according to the present invention will be described below with reference to process diagrams showing the manufacturing method of FIGS. First, as shown in FIG.
A chromium light-shielding film 102 having a film thickness of 100 nm is formed under the following conditions on a synthetic quartz substrate 101 for a photomask having an inch square and a thickness of 0.25 inch.

Film forming method: DC magnetron sputtering target: Metal chromium Film forming gas and flow rate: Argon 80 sccm + Nitrogen 20 s
ccm film forming pressure: about 5 mTorr current: 6 amperes Note that the light shielding film 102 thus formed has a wavelength of 36.
The transmittance at 5 nm was about 0% when the transparent substrate 101 was set to 100%.

Next, as shown in FIG. 1B, an electron beam resist 103 is applied onto this blank and patterned by a usual electron beam lithography method, as shown in FIG. A resist pattern 104 is obtained. Using this resist pattern 104 as a mask, the chromium light-shielding film 102 whose surface is exposed is selectively etched with a cerium nitrate-based wet etchant. The etching time at this time was 40 seconds. Further, after etching is completed, the remaining resist pattern 104 is removed,
A light shielding film pattern 105 as shown in FIG. 1D is obtained.

After the substrate is thoroughly washed, FIG.
As shown in (e), the electron beam resist 106 is applied again, and the chrome light-shielding film 10 in the inner portion of the element region is formed by ordinary electron beam lithography as shown in (f) of the figure.
A resist pattern 107 for exposing 5 is obtained.

Then, using the above wet etchant, 75% of the above etching time, that is,
The chromium light-shielding film 105 in the region exposed only for 30 seconds is etched to provide a region with a small film thickness. The film thickness of the chromium light-shielding film 105 in this small film thickness region was about 25 nm. After that, the remaining resist is removed to obtain the light shielding film 108 having two regions having different thicknesses according to the present invention as shown in FIG.

Next, as shown in FIG. 2 (h), a commercially available spin-on glass (for example, O manufactured by Tokyo Ohka Co., Ltd.)
(CD) is spin-coated to a thickness of 385 nm, dried and baked in air at 250 ° C., and the phase shift amount is about 1
The 80 ° phase shift film 109 is obtained. Subsequently, FIG.
As shown in (i), a normal photoresist 1 is formed on this.
10 is applied and patterned by a lithography method using a laser beam pattern drawing apparatus to form a resist pattern 111 as shown in FIG. Next, using the resist pattern 111 as a mask, the exposed phase shift film 109 is selectively etched by a normal dry etching method, and then the remaining resist pattern 111 is removed, as shown in FIG. The phase shift mask 112 of the present invention is obtained.

[Embodiment 2] Next, an embodiment of another phase shift mask for i-line exposure according to the present invention will be described with reference to process diagrams showing the manufacturing method of FIG. As shown in FIG.
On the transparent substrate 201, a light-shielding film composed of two layers 202 and 203 is sequentially formed under the following conditions (1) and (2). Note that the two layers 202 and 203 were formed at once without being taken out from the vacuum device.

Condition (1) Film forming method: DC magnetron sputtering target: Metal chromium Film forming gas and flow rate: Argon 95 sccm + carbon tetrafluoride 5 sccm Film forming pressure: Approximately 5 mTorr Current: 6 amperes Condition (2) Film forming method: DC Magnetron sputtering target: metal from Film forming gas and flow rate: Argon 80 sccm + Nitrogen 20 s
ccm film forming pressure: about 5 mTorr current: 6 amperes Here, the first layer 202 had a thickness of about 20 nm and the second layer 203 had a thickness of about 100 nm. Next, as shown in FIG. 3B, a conventional electron beam resist 204 is applied on the light-shielding film, and as shown in FIG. 3C, this is patterned by a conventional electron beam lithography. A resist pattern 205 is obtained. Then, the light shielding film exposed from the resist pattern 205 is dry-etched under the following conditions.

Etching Method: High Frequency Reactive Ion Etching Gas and Flow Rate: Dichloromethane 50 sccm + Oxygen 20 sccm Pressure: Approximately 300 mTorr Power: 250 W Note that this dry etching can remove both of the two layers 202 and 203 forming the light shielding film. Further, the remaining resist is removed to obtain a light shielding film pattern 206 as shown in FIG.

Next, after thoroughly cleaning this substrate, FIG.
As shown in (e), the electron beam resist 207 is applied again, and as shown in (f) in the figure, this is patterned so that the light-shielding film is exposed only in the element region 208. continue,
The second layer 2 of the light-shielding film is formed by using a cerium nitrate-based wet etchant (for example, MR-ES manufactured by Inktech Co., Ltd.).
03 is selectively etched and the remaining resist is removed to obtain a light shielding film pattern 209 of the present invention as shown in FIG. The first layer 202 formed under the above condition (1) has a very low dissolution rate in the above wet etchant and is not substantially etched. Therefore, only the film 203 is removed and the film 202 remains.

Thereafter, as in the first embodiment, a phase shift film made of spion glass is formed and patterned, and the phase shift mask 210 of the present invention as shown in FIG. 3 (h).
Get.

[Embodiment 3] Finally, an embodiment of the third phase shift mask for i-line exposure according to the present invention will be described with reference to the process charts showing the manufacturing method of FIG. As shown in FIG. 4A, a chromium light-shielding film 302 having a film thickness of 30 nm is formed on a 6-inch square and 0.25-inch thick synthetic quartz substrate 301 for a photomask under the following conditions.

Film forming method: DC magnetron sputtering target: Metal chromium Film forming gas and flow rate: Argon 80 sccm + Nitrogen 20 s
ccm film-forming pressure: about 5 mTorr current: 6 amperes Note that the light-shielding film 302 thus formed has a wavelength of 36.
The transmittance at 5 nm was about 7% when the transparent substrate 301 was set to 100%.

Next, the light shielding film 302 is patterned in the same manner as in Example 1 to obtain a light shielding film pattern 303 as shown in FIG. 4 (b). Then, similarly to the first embodiment, a shifter film made of spin-on-glass is formed on this and patterned to obtain a shifter pattern 304 as shown in FIG. 4C.

On the shifter pattern 304, as shown in FIG.
As shown in (d), a common electron beam resist 305 is applied on the entire surface, and this is applied by a conventional method so that the shift film 304 is exposed only in the outer portion 306 of the element region as shown in FIG. Pattern. Further, a second light-shielding film 307 is formed thereon, as shown in FIG. 4F, under the same conditions as the above-described film-forming conditions for the light-shielding film 302. The film thickness of the second light shielding film 307 at this time was about 100 nm. Finally, the resist 305 is lifted off and the second light-shielding film 307 on the element region is removed, whereby the phase shift mask 308 of the present invention as shown in FIG.
Get.

The phase shift mask of the present invention has been described above based on some embodiments, but the present invention is not limited to these embodiments and various modifications can be made.

[0038]

As is apparent from the above description, the phase shift mask of the present invention comprises a so-called light-shielding film for forming a first pattern on a transparent bright substrate and a so-called light-shielding film after the light-shielding film has been patterned. A phase shift mask having at least a so-called phase shift film for forming a second pattern laminated on the transparent substrate, wherein a region having a large thickness and a region having a small thickness of the light shielding film are present on the transparent substrate, or The light-shielding film is a multilayer film composed of a plurality of layers, and is characterized in that there are a region having a large number of layers and a region having a small number of layers constituting the multilayer film on the transparent substrate, and the phase shift effect is In the required region, the variation in the film thickness of the phase shift film caused by the step of the patterned light shielding film is suppressed, and in the region where a sufficient light shielding rate is required,
It shows a sufficient light-shielding property. Therefore, in the upper shifter type phase shift mask, an excellent phase shift effect can be brought out.

[Brief description of drawings]

FIG. 1 is a part of a process chart showing a method for manufacturing a phase shift mask according to a first embodiment of the present invention.

FIG. 2 is the rest of the process drawing showing the method for manufacturing the phase shift mask of the first embodiment.

FIG. 3 is a process drawing showing the method of manufacturing the phase shift mask of the second embodiment.

FIG. 4 is a process drawing showing the manufacturing method of the phase shift mask of Example 3;

FIG. 5 is a diagram showing the relationship between the film thickness of a chromium film used as a light-shielding film and the transmittance.

FIG. 6 is a diagram for explaining a defect caused by a step of the light shielding film of the upper shifter type phase shift mask.

[Explanation of symbols]

 Reference numeral 101 ... Synthetic quartz substrate for photomask 102 ... Chrome light shielding film 103 ... Electron beam resist 104 ... Resist pattern 105 ... Light shielding film pattern 106 ... Electron beam resist 107 ... Resist pattern 108 ... Light shielding film 109 having two regions having different thicknesses 109 ... Phase shift film 110 ... Photoresist 111 ... Resist pattern 112 ... Phase shift mask 201 ... Transparent substrate 202 ... First layer 203 forming light-shielding film ... Second layer forming light-shielding film 204 ... Electron beam resist 205 ... Resist pattern 206 ... Shading film pattern 207 ... Electron beam resist 208 ... Element region 209 ... Shading film pattern 210 ... Phase shift mask 301 ... Photomask synthetic quartz substrate 302 ... Chromium shading film 303 ... Shading film pattern 304 ... Shifter pattern 305 ... Electron beam Regis 306 ... outer portion 307: second light-shielding film 308 ... phase shift mask element region

Claims (6)

[Claims] 1. A phase shift mask having at least a first pattern of a light shielding film and a second pattern of a phase shift film laminated on the first pattern on a transparent substrate, wherein the light shielding is provided on the transparent substrate. A phase shift mask having a region where the film thickness is large and a region where the film thickness is small. 2. The phase shift mask according to claim 1, wherein the region where the light-shielding film has a large film thickness includes a region which is subjected to multiple exposure in step and repeat exposure. 3. A phase shift mask having at least a first pattern of a light-shielding film and a second pattern of a phase-shifting film laminated on the first pattern on a transparent substrate, wherein the light-shielding film is composed of a plurality of layers. A phase shift mask comprising a multi-layered film of the following, wherein there are a region having a large number of layers and a region having a small number of one layer on the transparent substrate. 4. The phase shift mask according to claim 3, wherein the region where the number of layers of the light shielding film is large includes a region which is subjected to multiple exposure in step and repeat exposure. 5. A phase shift mask having at least a first pattern of a light-shielding film and a second pattern of a phase-shifting film laminated on the first pattern on a transparent substrate, wherein light is shielded on the second pattern. A phase shift mask, which has a third pattern having a positive property. 6. The phase shift mask according to claim 5, wherein the region in which the third pattern is formed includes a region which is subjected to multiple exposure in step and repeat exposure.