JPH07319148A - Photomask and its production - Google Patents

Abstract

PURPOSE:To provide a halftone phase shift mask with which reflected light of sufficient intensity is obtainable in order to position a photomask from alignment marks and a process for producing such photomask. CONSTITUTION:This photomask has a transparent substrate 6 which is transparent to exposing light, translucent films which are formed in first regions including at least regions 4 forming the patterns to be transferred on the surface of this transparent substrate 6 and reflection films 1 which are formed in second regions including regions 5 for forming the alignment marks for the purpose of at least positioning of the mask among the regions exclusive of the first regions on the surface of the transparent substrate 6 and afford the reflectivity of the exposing light of >=2 times the reflectivity on the exposed transparent substrate 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for reduction projection exposure and a method for manufacturing the same.

[0002]

2. Description of the Related Art For reduction projection exposure, a wavelength of 365n is usually used.
m mercury i-line or the like is used. The size of the pattern is on the order of submicron due to the high integration of LSI.
The resolution limit of i-line is approaching. As a method for exceeding this resolution limit, a reduction projection exposure technique using a halftone phase shift mask has received attention.

FIG. 6 shows a schematic sectional view of a halftone phase shift mask and the amplitude and intensity of exposure light. The upper part of FIG. 6 shows a cross section of the halftone phase shift mask.
On a single surface of a transparent substrate 50 made of quartz or the like, a laminated layer 53 composed of a light absorption film 51 made of Cr or the like and a phase shifter 52 having a predetermined pattern is formed. The light absorption film 51 is configured to have a thickness showing a predetermined transmittance of 10 to 20%, for example. Phase shifter 52
Are, for example, SOG (spin on glass) film, SiO ₂
It is formed of a film or the like and has a thickness that gives a phase shift of about π (180 °).

The graph in the middle of FIG. 6 shows the amplitude of the exposure light just after passing through the halftone phase shift mask. Since most of the light is transmitted through the opening (light transmitting portion) of the stack 53,
The amplitude is relatively large. In the halftone portion where the stacked layer 53 is formed, the light absorption film 51 absorbs a part of the light, so that the amplitude is attenuated. Further, the phase shifter 52 delays the phase by 180 °. That is, it has an opposite phase to the light transmitted through the light transmitting portion.

The lower graph of FIG. 6 shows the light intensity at the wafer position. Light has the property of spreading by diffraction, but in the vicinity of the boundary between the light transmission part and the halftone part, lights of opposite phases are superimposed, so the intensity of the light is reduced to 0 slightly from the boundary line to the halftone part. Become.

As described above, by irradiating the portion that should be originally shielded with light having a weak antiphase, it is possible to make the light intensity change near the boundary steep and to improve the resolution.

Although the mask having the two-layer structure of the light absorption film 51 and the phase shifter 52 is described with reference to FIG. 6, a single layer film having a function of absorbing light and shifting the phase may be used. The single-layer film may be, for example, a chromium oxide film (CrO).
_x ), a chromium oxynitride film (CrO _x N _y ) or the like is used.

[0008]

For positioning the photomask, an alignment mark formed on the photomask at the same time as the mask pattern is usually used as a reference. The alignment mark is formed by patterning the photomask stack 53 shown in the upper part of FIG. The exposure light incident from above in the figure is reflected by the alignment mark. Positioning is performed by detecting this reflected light.

However, in the case of a single-layer halftone phase shift mask, since the difference in complex refractive index between the transparent substrate and the halftone layer is small, there is little reflection at the interface and the intensity of reflected light is small. Also, in the case of the two-layer photomask shown in the upper part of FIG.
Since the light absorption film 51 is formed to be extremely thin so that 20% is transmitted, the intensity of reflected light is small.

As described above, if the intensity of the reflected light from the alignment mark is low, it becomes difficult to position the photomask. An object of the present invention is to provide a halftone phase shift mask and a method of manufacturing the halftone phase shift mask, which can obtain reflected light having sufficient intensity for positioning a photomask from an alignment mark.

[0011]

A photomask of the present invention is formed on a transparent substrate which is transparent to exposure light and on a first region of the transparent substrate surface which includes at least a region for forming a pattern to be transferred. Of the semi-transparent film and the second region of the surface of the transparent substrate other than the first region, the second region including at least a region for forming an alignment mark for positioning the mask and exposed. And a reflection film that gives a reflectance of exposure light that is at least twice the reflectance of the transparent substrate.

[0012]

By forming the reflection film in the region where the alignment mark is formed and in the vicinity thereof, the reflectance of the exposure light in the vicinity of the alignment mark can be increased. Therefore, the intensity of the reflected light reflected from the alignment mark at the time of exposure becomes strong. By increasing the intensity of the reflected light from the alignment mark, the mask can be easily positioned.

[0013]

FIG. 1 shows an original plate of a halftone phase shift mask according to an embodiment of the present invention before forming a mask pattern. 1A is a cross-sectional view of the original plate, FIG. 1B is a plan view of one configuration example of the original plate, and FIG. 1C is a plan view of another configuration example.

As shown in FIGS. 1A and 1B, a reflective film 1 made of a material such as quartz having a high reflectance for light having a wavelength of the exposure light is provided around the periphery of the surface of the transparent substrate 6. Are formed. In order to easily position the mask, the reflectance of the reflective film 1 is preferably twice or more the reflectance of the transparent substrate 6. As the reflective film 1, for example, Cr, M
o, MoSi, W, WSi, Ge, Si, amorphous Si, Al, or other metals or metal compounds can be used. When using Cr, 50
A reflectance of 30-40% can be obtained at a thickness of nm.

On the reflective film 1 and the transparent substrate 6, a halftone film 2 is formed which can shift the phase of the exposure light and at the same time attenuate the intensity. The halftone film is formed of known chromium oxide, chromium oxynitride, or the like.
The thickness of the halftone film 2 is set so that the phase of light passing through the film is delayed by 180 ° with respect to light propagating in the air. Further, in order to improve the resolution on the wafer, it is preferable that the transmittance of the exposure light passing through the halftone film is about 5 to 20%.

If the order of laminating the reflective film 1 and the halftone film 2 is reversed, the effect of increasing the reflectance is small. The exposure light is emitted from the lower side of FIG. Therefore, when the reflective film 1 is formed on the halftone film 2, the intensity of the incident light and the reflected light is attenuated by the halftone film 2. Therefore, it is preferable to form the reflective film 1 directly on the transparent substrate 6 as shown in FIG.

A transfer pattern is formed in the central portion 4 of the transparent substrate 6 shown in FIG. 1B in a later step. In addition, an alignment mark is formed in a predetermined region 5 of the portion where the reflective film 1 is formed.

As shown in FIG. 1C, the reflective film 1 may be formed only in a region in the vicinity including at least a region 5 in which an alignment mark is to be formed. Next, a method of manufacturing the original plate shown in FIG. 1 will be described with reference to FIGS.

FIG. 2 shows a method of forming a reflective film on a desired region of a transparent substrate by sputtering. A target holder 8 to which a positive DC voltage is applied with respect to the ground potential is arranged at the bottom of the vacuum container 7. A target 11 made of a reflective film material to be formed is placed on the target holder 8. A transparent substrate 6 attached to a substrate holder (not shown) is arranged at a position facing the target holder 8 of the vacuum container 7.

A metal shielding plate 10 having an opening 9 provided in a region where a reflective film is to be formed is arranged in close contact with the film forming surface of the transparent substrate 6 or in the vicinity of the surface. Metal shield 10
The transparent substrate 6 is connected to the ground potential.

Sputter gas is introduced from the gas introducing / exhausting means 12 provided in the vacuum container 7 to generate plasma in the vacuum container 7. The atoms in the target 11 sputtered by the ions in the plasma pass through the opening 9 and reach the surface of the transparent substrate 6. In this way, the reflective film 1 can be deposited only on a desired region of the transparent substrate 6. Although the formation of the reflective film by sputtering is described with reference to FIG. 2, other film forming methods such as vapor deposition may be used.

FIG. 3 shows a method of forming a reflective film by the lift-off method. As shown in FIG. 3A, the transparent substrate 6
A resist film 15 is formed in a region other than the region where the upper reflective film is to be formed. As shown in FIG. 3B, the reflection films 1 and 1a are formed on the exposed surfaces of the resist film 15 and the transparent substrate 6 by vapor deposition, sputtering or the like. Figure 3
As shown in (C), the resist film 15 is removed with a remover. At this time, the reflective film 1 a deposited on the resist film 15 is peeled off together with the resist film 15. In this way, the reflective film 1 can be formed only in a desired region.

After forming the reflection film 1 in a desired region by the method shown in FIG. 2 or 3, the halftone film 2 is formed on the transparent substrate 6 and the reflection film 1 to obtain the halftone phase shown in FIG. A shift mask original plate can be manufactured.

Next, with reference to FIG. 4, a method for forming a transfer pattern and an alignment mark on the halftone phase shift mask original plate shown in FIG. 1 will be described. Figure 4
As shown in (A), a resist film 16 is applied onto the halftone film 2 of the halftone phase shift mask original plate.

As shown in FIG. 4B, an opening 17 corresponding to the transfer pattern is formed in the resist film 16 by photolithography. At the same time, an opening 18 corresponding to the alignment mark is formed in the area where the reflective film 1 is formed.

As shown in FIG. 4C, the resist film 16
Through the openings 17 and 18 using the mask as a mask.
Are partially etched. Further, the reflective film 1 is etched through the opening 18 until the transparent substrate 6 is partially exposed. If the etching is performed under the condition that the halftone film 2 and the reflective film 1 are both etched, the etching process can be simplified.

As shown in FIG. 4D, the resist film 16
To remove. In this way, the transfer pattern and the alignment mark can be formed on the original halftone phase shift mask plate.

When positioning the photomask, FIG.
In the step (C), positioning is performed with the alignment mark formed on the reflective film 1 through the opening 18 as a reference. Since the boundary line between the region where the reflective film 1 is formed and the region where only the halftone film 2 is formed is not used for positioning the photomask, the positional accuracy like the alignment mark is not required. Therefore, a method such as sputtering using a metal shielding plate as shown in FIG. 2 can be used.

In the above embodiment, the case where the single-layer halftone film is used has been described, but the halftone film may have a two-layer structure of the light absorption film and the phase shifter. Less than,
An example in which the halftone film has a two-layer structure will be described.

FIG. 5 is a sectional view of a halftone phase shift mask original plate having a two-layer structure of a halftone film. A light absorbing film 20 made of metal or the like is formed on almost the entire surface of the transparent substrate 6. The light absorbing film 20 has a thickness that absorbs a part of the exposure light and attenuates the transmitted light by a predetermined intensity in the central portion where the transfer pattern is formed. Further, the peripheral portion is formed thicker than the central portion. A phase shifter 21 having a predetermined thickness is formed on the light absorption film 20.

In the original plate shown in FIG. 5, the light absorption film 20 near the region where the alignment mark is formed is relatively thick. Therefore, stronger reflected light can be obtained from the alignment mark. Even in the original plate shown in FIG. 5, the light absorption film 20 may be thickly formed only in the vicinity of the region where the alignment mark is to be formed, as shown in FIG.

In the central portion where the transfer pattern is formed, the light transmittance is preferably 5 to 20%. For example,
When a Cr film is used as the light absorbing film, the thickness of the film is about 20 nm and
A transmittance of 20% is obtained. Further, when the thickness of the Cr film is 50 nm near the region where the alignment mark is formed, a reflectance of about 40% can be obtained. Also in this case, as in the case of using the single-layer film, it is preferable that the reflectance in the vicinity of the region where the alignment mark is formed is twice or more the reflectance of the transparent substrate.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0034]

As described above, according to the present invention,
Relatively strong reflected light can be obtained from the alignment mark of the halftone phase shift mask. For this reason,
The photomask can be easily positioned.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view of a halftone phase shift mask according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a sputtering apparatus for producing an original plate of a halftone phase shift mask according to an example of the present invention.

FIG. 3 is a cross-sectional view of a mask substrate for explaining a process of manufacturing an original plate of a halftone phase shift mask according to an example of the present invention.

FIG. 4 is a cross-sectional view of a mask substrate for explaining a process of forming a transfer pattern and an alignment mark on a master plate of a halftone phase shift mask according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a halftone phase shift mask according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view of a halftone phase shift mask according to a conventional example and a graph showing amplitude and intensity of exposure light.

[Explanation of symbols]

 1 Light Absorbing Film 2 Phase Shifter 4 Transfer Pattern Area 5 Alignment Mark Area 6 Transparent Substrate 7 Vacuum Container 8 Target Holder 9 Opening 10 Metal Shielding Plate 11 Target 12 Gas Injecting / Discharging Means 15 and 16 Resist Film 17 Transfer Pattern Opening 18 Alignment Mark opening 20 Light absorbing film 21 Phase shifter 50 Transparent substrate 51 Light absorbing film 52 Phase shifter 53 Laminate

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Kenichi Kawakami 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (6)

[Claims] 1. A transparent substrate transparent to exposure light, a semitransparent film formed on a first region of the transparent substrate surface including at least a region for forming a pattern to be transferred, and the transparent substrate surface. Of the area other than the first area, which is formed in a second area including at least an area for forming an alignment mark for positioning the mask, and is at least twice the reflectance of the exposed transparent substrate. And a reflection film that gives the reflectance of exposure light. 2. The reflection film is made of one material selected from the group consisting of chromium, molybdenum, molybdenum silicide, tungsten, tungsten silicide, germanium, silicon, amorphous silicon, and aluminum. 1. The photomask according to 1. 3. A transparent substrate transparent to exposure light, a light absorbing film formed on the surface of the transparent substrate and absorbing the exposure light, and at least a pattern to be transferred on the surface of the light absorbing film is formed. A phase shifter for delaying the phase of exposure light, the phase shifter being formed in a first region including a region, and the light absorption film for positioning at least a mask in a region other than the first region. The photomask formed in the second region including the region for forming the alignment mark is thicker than the thickness in the first region. 4. The photomask according to claim 3, wherein the reflectance of the exposure light in the second region is at least twice the reflectance of the exposure light with respect to the exposed transparent substrate. 5. A step of preparing a transparent substrate transparent to exposure light, and a step of forming a reflective film on the surface of the transparent substrate by causing component atoms of a reflective film material to fly to the surface of the transparent substrate. A method for producing a photomask including, wherein the reflecting film forming step shields component atoms of the reflecting film material flying to a region including at least a region for forming a pattern to be transferred on the transparent substrate surface. A method for producing a photomask for forming a reflective film. 6. A step of preparing a transparent substrate that is transparent to exposure light, and at least a second area of the surface of the transparent substrate, which includes an area for forming an alignment mark for positioning a mask, is exposed. Forming a resist film so as to cover at least a first region including a region for forming a pattern to be transferred, depositing a reflective film on the surface of the resist film and the transparent substrate, and the resist film And a step of removing the resist film together with the reflective film deposited on the photomask.