JPH1115128A - Photomask and pattern formation using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photomask improved in the resolution of isolated patterns and congested patterns and a method for formation of patterns. SOLUTION: Alternate type phase shift parts 8 of the photomask comprise the laminated films of a halftone film 2 and a light shielding film 3 and halftone type phase shift parts 9 comprise the halftone film 2. As a result, the resolution characteristic of both patterns and the tolerance of the process are improved in the mask in which the coarsely arranged and densely arranged patterns exist and the production yield of the element is improved. The fining of the pattern is embodied and the shortening of the element area is embodied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a photomask which has been subjected to a process of changing the phase of illumination light in order to form a fine pattern such as a semiconductor element, and a pattern forming method using the same.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, a lithography technique is used as a method of transferring a fine pattern onto a wafer. In the lithography technique, a projection exposure apparatus is used. As one of the conventional techniques for improving the resolving power of this exposure apparatus, there is a method of introducing a phase difference into light transmitted through a mask. For example, in Japanese Patent Publication No. 62-50811, a transparent film for changing the phase is formed on at least one of the transparent portions on both sides sandwiching the opaque portion. According to this method, the resolution can be significantly increased without changing the projection lens of the projection exposure apparatus. This method is called an alternate phase shift mask. Also, Japanese Patent Application Laid-Open No. 62-067
In 547, as a means for improving the resolution of a single transmissive portion, a transmissive portion having a resolution equal to or less than the resolution limit where the phase of transmitted light is inverted is provided on both sides of the single transmissive portion. This is called an auxiliary pattern type phase shift mask. In addition, Japanese Patent Application Laid-Open No.
In 6854, as a means for improving the resolution of the single transparent pattern, the periphery of the single transparent pattern is made translucent, that is, the light shielding portion of the conventional mask is made translucent, and a slight light passing through the translucent portion, The phase of light passing through the transparent pattern is inverted. That is, light less than the sensitivity of the resist for transferring the pattern is allowed to pass through the translucent film, and the phase of this light and the light passing through the transparent pattern are inverted. Since the light that has passed through the translucent film has a phase inverted with respect to the light that has passed through the transparent pattern, which is the main pattern, the phase is inverted at the boundary and the light intensity at the boundary approaches zero. As a result, the ratio of the intensity of the light that has passed through the transparent pattern and the intensity of the light at the boundary of the pattern becomes relatively large, and a light intensity distribution having a higher contrast than the conventional method can be obtained. This is called a halftone phase shift mask.

[0003] As a method for improving the resolution of an isolated pattern and a dense pattern with the same mask, Japanese Patent Application Laid-Open No. H06-1 is disclosed.
No. 23961 discloses a method of achieving the functions of an alternate phase shift mask and a halftone phase shift mask with the same mask.

In this method, as shown in FIG. 7, an alternate type phase shift unit 79 and a halftone type phase shift unit 80 are mixed on the same mask. However, in this method, since the same phase shift layer 72 is used for both, if the phase difference between the transmitted lights 75 and 76 in the alternate type phase shift unit 79 is adjusted to 180 degrees, the transmission of the halftone phase shift unit 80 It is difficult to adjust the phase difference between the lights 77 and 78 to 180 degrees.

That is, since the transmitted lights 76 and 78 have the same optical path, there is no phase change. Since the transmitted light 75 passes through the shifter 72, the phase difference is 180 degrees. However, transmitted light 7
Since the light 7 passes through the shifter 72 and the translucent film 73, a phase change in the translucent film 73 is applied, resulting in a phase difference of more than 180 degrees, and it is difficult to obtain a sufficient phase shift effect. Reference numeral 71 denotes an etching stop layer.

In Japanese Patent Application Laid-Open No. 07-306522, FIG.
As shown in the figure, since the alternate type phase shift unit is formed without using the light shielding film using the halftone film 84, the transmitted light 85 and 86 are inverted in phase, but the transmitted light 89 is changed to 85. In contrast, the transmitted light 8
5 has a tendency to cancel, and acts to amplify the transmitted light 86. Therefore, there is a problem that a difference in light intensity occurs between the transmitted lights 85 and 86 and the pattern becomes asymmetric.

In Japanese Patent Application Laid-Open No. 06-161091, FIG.
As a method for solving the problem of the structure shown in FIG. 8, as shown in FIG. 8, a phase shift film 91 is arranged so as to overlap with the halftone film 94 to avoid asymmetry between the transmitted lights 95 and 96. However, in this method, the misalignment of the pattern between the shift film 91 and the halftone film 94 causes the asymmetry of the pattern, and this is a serious problem particularly when resolving an ultra-fine pattern.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide the same mask with the functions of an alternate phase shift mask and a halftone type phase shift mask so that the resolution of an isolated pattern and a dense pattern can be improved with the same mask. Another object of the present invention is to provide a photomask capable of solving the problems of the conventional method and a pattern forming method using the same, in order to put mixed phase shift masks into practical use.

[0009]

In order to achieve the above object, a photomask according to the present invention comprises a semi-transparent film having a halftone phase shift portion provided on a transparent substrate, and an alternate type phase shift portion having a transparent substrate. It is composed of a laminated film of a semi-transparent film and a light-shielding film which are sequentially provided above.

A photomask can be prepared by the following method. A translucent film is formed on a transparent substrate so that the phase of the transmitted light of the exposure light is inverted, and an original plate on which a light-shielding film is formed is used. The part is etched and processed into a desired pattern.

Next, a desired portion of the light-shielding film on the semi-transparent film is removed by etching to form a halftone type phase shift mask region. Next, in the region where the light shielding film remains,
When the patterns where the transparent substrates are exposed are adjacent to each other, one of the transparent substrates is etched to a desired depth so that the phase of the exposure light passing through the adjacent pattern is inverted, and the alternate type phase A shift mask region was formed.

An isolated transparent area is arranged in the halftone type phase shift mask area, and mainly a minimum resolution pattern is arranged.

In the alternate phase shift mask area, a minimum resolution pattern that is repeatedly arranged is formed.

For a large pattern having a sufficient resolution, a transparent pattern is arranged in a region where the light shielding film is arranged.

The relationship between the pattern size on the mask and the size of the pattern transferred on the wafer was adjusted as follows. Since the mask is a five-fold mask, the mask is five times larger.
The size is doubled, but here, for convenience, it is described in terms of the pattern size on the wafer. Adding an offset to the design pattern size on the mask as compared to the pattern size to be transferred onto the wafer is referred to as applying a mask bias. When a halftone phase shift mask is used, it is necessary to apply a mask bias in order to prevent transfer of a light intensity peak generated in a pattern other than a pattern to be transferred. In the present invention, the mask bias is adjusted by using the mask patterns of the halftone type phase shift mask region and the alternate type phase shift mask region. Specifically, the bias amount was adjusted according to the transmittance of the halftone portion.
The bias amount in the halftone portion was adjusted to be larger than the bias amount in the alternate portion. Thereby, the transfer of the sub-peak in the halftone portion could be avoided.

By using the above mask structure and manufacturing method, the optical characteristics of the alternate type phase shift mask portion and the halftone type phase shift mask portion can obtain substantially the same characteristics as when each is formed as a single function mask alone. . Therefore, the effect of improving both resolution characteristics is sufficiently obtained, and a single pattern and a dense pattern can be resolved with a single mask with high resolution characteristics.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

Reference Example 1 A reference example will be described with reference to FIG. Fig. 2 (a)
Is a cross-sectional view of a conventional mask, 1 is a glass substrate, and 2 is a translucent phase shift film. The translucent phase shift film 2 has M
An oSiO film was used. Thickness t of translucent phase shift film 2
Is such that t = λ / (n−1) × {(1 / a) + m} (where λ is the wavelength and n is the translucent phase shift film 2
, 1.3 ≦ a ≦ 4, m is an integer). Also,
At this time, the transmittance of the exposure light was 6%. Transparent patterns 5 and 5 'were arranged. The dimensions of the transparent patterns 5 and 5 ′ were 0.3 μm square, and the pattern interval was 0.2 μm.
(All the pattern dimensions on the mask are shown in terms of the dimensions on the wafer.) That is, the hole patterns were arranged very close. The characteristics of the projection optical system of the reduction projection exposure apparatus used were a reduction ratio of 1/5, a lens NA of 0.55, an exposure wavelength of 248 nm, and a light source coherency σ of 0.3. The condition of the optical system is not limited to this. FIG. 2B shows the amplitude distribution of the light transmitted through the mask. The light that has passed through the transparent patterns 5 and 5 'has a positive sign, whereas the light that has passed through the translucent film phase shift film 2 has its phase inverted and has a negative sign. When this light is projected on the wafer through the lens, as shown in FIG. 2 (c), the transparent patterns 5 and 5 '
And the light intensity during this period becomes large, and it becomes difficult to separate and resolve the two holes. As a result of transferring a hole pattern to a positive resist formed on a wafer by a normal method by a normal method, the film thickness was reduced between the two hole patterns, and a normal pattern could not be formed. As described above, the conventional translucent film phase shift mask has excellent resolution characteristics of an isolated pattern, but when the patterns are close to each other, it is difficult to separate and resolve the pattern similarly to the conventional Cr mask. On the other hand, the mask of the present invention is excellent in the resolution of an isolated pattern and the separation and resolution of a close pattern.

(Embodiment 1) The first embodiment of the present invention is
This will be described with reference to the drawings. FIG. 1A is a sectional view of a mask of the present invention. 1 is a glass substrate, 2 is a translucent phase shift film, and 3 is a light shielding film. The conditions such as the material, thickness and transmittance of the translucent film 2 are the same as those of the above-mentioned conventional method. The light shielding film 3 is a Cr film, but is not limited to this. Area 5 is an alternate phase shift section, and area 9 is a halftone phase shift section. The exposure light 4 and the exposure light 5 that have passed through the transparent portion in the alternate phase shift portion 8 have phases inverted from each other as shown in FIG. Therefore, as shown in FIG. 1 (c), the light intensity distribution becomes steep, and mutually exhibit good separation and resolution characteristics. Further, as shown in FIG. 1B, the exposure light 6 that has passed through the translucent film 2 in the halftone phase shift section 9 has a phase inverted from that of the exposure light 7 that has passed through the transparent section. 1 (c)
As shown in (1), the exposure light 7 that has passed through the transparent portion acts to suppress the spread of the bottom of the light intensity distribution, and a sharp light intensity distribution can be obtained.

FIG. 3 shows a manufacturing process of the present mask. FIG.
As shown in (a), a mask blank is prepared in which a translucent phase shift film 32 is formed on a transparent substrate 31 and a light shielding film 33 is further formed thereon. Here, the transparent substrate 3
1 is quartz, and the translucent phase shift film 32 is MoSiO.
A film was used, the transmittance was 6%, and a Cr film was used as the light-shielding film 33, but the invention is not limited to this. The translucent phase shift film 32 only needs to have an optical characteristic capable of inverting the phase difference of the transmitted light and achieving a desired transmittance. A single-layer film or a multi-layer film can be applied.

Next, as shown in FIG. 3B, desired openings 34, 35 and 36 are processed using a resist pattern as a mask. Next, as shown in FIG. 3C, in order to form a halftone phase shift region 39, a resist film 3 is formed.
7 was used as a mask, the light-shielding film 33 was removed, and then the resist film 37 was removed. Thereby, as shown in FIG. 3D, a halftone phase shift region 39 and an alternate phase shift region 40 were formed.

Next, as shown in FIG. 3E, the apertures 34, 35 formed in the alternate phase shift region 40 are formed.
An opening is formed in the resist such that one of the openings (here, the opening 34) is exposed.

Next, as shown in FIG. 3F, the quartz substrate 31 is etched using the resist as a mask, and the opening 3 is formed.
4 'was formed. The etching depth of the quartz substrate 31 was adjusted so that the phase of the exposure light passing through the openings 35 and 34 'was inverted. The specific etching depth Z is Z = λ /
(N-1) × {(1 / a) + m} (where λ is the wavelength of the exposure light, n is the refractive index of the quartz substrate, 1.3
≦ a ≦ 4, m is an integer). Through the above steps, a composite mask in which the alternate phase shift region 40 and the halftone phase shift region 39 are mixed can be formed.

Using this mask, a pattern was transferred by a projection exposure apparatus. The projection exposure apparatus used a reduction ratio of 1/5, an exposure wavelength λ of 248 nm, a projection lens NA of 0.55, and an illumination system coherency σ of 0.3. The pattern size of the mask was adjusted so that a hole having a diameter of 0.24 μm was formed on the wafer.

FIG. 4 is a plan view of the mask. The patterns 43, 44, and 45 composed of transparent portions on the mask are square patterns, the mask bias amount is +0.04 μm, and the pattern is 0.28.
μm □ (5 times the size on the mask). The mask bias of the square patterns 44 and 45 arranged in the alternate phase shift region 42 is +0.01 μm,
0.25 μm square. The patterns are densely arranged,
It is arranged at a pitch of 0.48 μm in both the X and Y directions.
Pattern 4 arranged in halftone phase shift area 41
Reference numeral 3 denotes a so-called isolated pattern, and the minimum pattern pitch is 0.7 μm. For comparison, a halftone type phase shift mask having the same pattern and an alternate type phase shift mask were prepared. In the case of the alternate type, the isolated pattern did not particularly use the auxiliary pattern. As a result of pattern transfer on the entire surface using a halftone type phase shift mask, the isolated pattern showed good resolution characteristics, and the focus margin, which indicates the transfer process margin, was 1 μm. However, patterns that are densely and repeatedly arranged are deformed with each other, and a phenomenon that they are sometimes connected occurs, and a good pattern cannot be formed. Further, in the case where the entire surface is an alternate phase shift mask, although the densely arranged pattern can be formed well, the depth of focus of the isolated pattern is small and it has been difficult to put it to practical use.

On the other hand, as a result of forming a pattern using the composite type mask of the present invention, the isolated pattern arranged in the halftone phase shift region shows good resolution characteristics, and also has a focus margin showing a transfer process margin. 1 μm could be secured.

In addition, a densely arranged pattern arranged in the alternate phase shift region can be formed satisfactorily, and the focus latitude is also 1.
2 μm could be secured. As described above, an isolated pattern and a densely arranged pattern could be formed with good resolution characteristics using one mask.

(Embodiment 2) The second embodiment of the present invention is
FIG. 6 and FIG. Here, an example in which the present invention is applied to formation of a wiring connection hole (contact hole) in a manufacturing process of a semiconductor memory element will be described. FIG. 6 is a diagram showing an arrangement of patterns in a main process of FIG. 5; 56 is an active region, 53 is a gate electrode,
Reference numeral 51 denotes a gate electrode lead-out hole, and reference numerals 52, 54, and 55 denote source / drain electrode lead-out holes. Region A is a region where contact holes are sparsely arranged, and region B is a region where contact layers are densely arranged. In the region B, contact holes are densely arranged in the vertical direction. By arranging as many holes as possible in the same region, electrical contact resistance can be reduced, and a higher operating speed can be realized. . Therefore, it is effective to reduce the arrangement pitch of the patterns as much as possible. Here, an alternate phase shift structure is applied to this portion. In addition, area B
Applied a halftone type phase shift structure.

FIG. 6 schematically shows a plan view of the mask used. Reference numeral 65 denotes a light-shielding region, reference numeral 61 denotes a halftone phase shift region, reference numeral 63 denotes a transparent region, reference numeral 65 denotes a transparent region, and reference numeral 65 denotes a transparent region. It is. The digging depth is the same as the condition shown in the first embodiment.

Also, so-called side etching is performed so that etching proceeds in the lateral direction from the edge of the Cr film,
A reduction in the amount of transmitted light due to scattering of transmitted light due to the overlap of the r edge portion and the edge portion of the substrate digging groove is prevented.

The exposure light passing through the halftone portion 61 and the exposure light passing through the transparent portion 63 are adjusted so that the phases thereof are inverted, so that the effect of the halftone phase shift can be obtained. .

The boundary between the halftone area and the light-shielding portion was set as follows. When the distance 66 between the transparent pattern in the halftone area and the halftone boundary is D1, D1 = k1.lambda. / NA (where NA is the number of apertures in the projection lens, .lamda. Is the exposure wavelength, and k1.gtoreq.1.5). ).

The distance of the transparent pattern in the alternate phase shift region from the halftone boundary was also set to D1. As a result of using this mask in this step,
A good pattern can be formed regardless of the density of the pattern arrangement,
The focus latitude and the exposure latitude, which indicate the latitude of the lithography process, can be improved, and the manufacturing yield of the device has been improved. Further, since the patterns can be densely arranged, the occupied area of the functional element itself can be reduced, and the element area can be reduced.

Further, in order to further improve the resolution of the isolated pattern, a transparent auxiliary pattern having a size smaller than the resolution is arranged around the transparent isolated main pattern in the halftone area.

FIG. 10 shows an example of the pattern arrangement. The distance 109 between the centers of the isolated main pattern 103 and the auxiliary pattern 106 is
When the center-to-center distance 109 is D2, D2 = k2 · λ / NA
(However, NA is the number of apertures in the projection lens, λ is the exposure wavelength,
1.35 <k2 ≦ 1.9). In addition, auxiliary pattern 1
06 is W1 = k · λ / NA (where NA is the number of apertures in the projection lens, λ is the exposure wavelength, and 0.07 ≦ k ≦ 0.
25).

As a result of using this mask, the resolution and the depth of focus are further improved as compared with the case where there is no auxiliary pattern.
The depth of focus almost equal to the depth of focus obtained with densely arranged holes in the alternate area could be obtained even with an isolated pattern.

Further, a phenomenon that the outermost pattern size of the dense pattern arrangement in the alternate area is reduced in resolution has occurred. However, as a result of disposing the auxiliary patterns 107 and 108 as shown in FIG. Could be improved.
For example, the transparent auxiliary pattern 107 is arranged on the outer peripheral side of the densely arranged transparent main pattern 104 on which the shifter is arranged. A transparent auxiliary pattern 108 in which a shifter is arranged is arranged on the outer periphery of the densely arranged transparent main pattern 105 in which no shifter is arranged. When the center-to-center distance 110 between the main pattern and the auxiliary pattern is D3, D3 = k3.lambda. / NA (where NA is the number of apertures of the projection lens, .lambda. Is the exposure wavelength, and 0.7 <k3.ltoreq.0.9). did. As a result, it was possible to prevent the pattern collapse of the densely arranged outer peripheral portion.

In an actual element, it is also effective to arrange a dummy pattern which does not affect the operation of the element, as the outermost peripheral pattern, instead of arranging the auxiliary pattern as described above.

[0038]

According to the present invention, it is possible to realize a mask in which a halftone type phase shift region and an alternate type phase shift region are mixed, and in a mask in which a pattern is arranged densely and sparsely, both masks are used. The resolution characteristics of the pattern can be improved. Using the mask of the present invention, the pattern of this mask is transferred to a semiconductor substrate coated with a photoresist film by using a reduction projection exposure apparatus to produce a semiconductor device. The improvement of the light tolerance was realized, and the production yield of the device was improved. In addition, the effect of improving the resolution can be effectively used, and the pattern can be miniaturized as compared with the conventional mask, and the element area can be reduced.

[Brief description of the drawings]

FIG. 1A is a sectional view of a photomask according to the present invention, and FIG.
It is an amplitude distribution diagram of transmitted light, and (c) is a light intensity distribution diagram of a projected image.

2A is a cross-sectional view of a halftone phase mask of a conventional example, FIG. 2B is an amplitude distribution diagram of transmitted light, and FIG. 2C is a light intensity distribution diagram of a projected image.

FIG. 3 is a cross-sectional view of the photomask for illustrating a manufacturing process of the photomask according to the present invention.

FIG. 4 is a plan view of a photomask according to the present invention.

FIG. 5 is a plan view of a main part of a semiconductor element including a wiring connection hole.

FIG. 6 is a plan view of a photomask for wiring connection holes according to the present invention.

FIG. 7 shows a cross-sectional view of a conventional photomask.

FIG. 8 shows a cross-sectional view of a conventional photomask.

FIG. 9 shows a cross-sectional view of a conventional photomask.

FIG. 10 shows a plan view of a photomask according to the present invention.

[Explanation of symbols]

1, 31, 70 ° glass substrate, 2, 32, 71, 8
4, 94 translucent film, 91, 71 ° phase shifter, 3, 3
3, 74 ° light shielding film, 4, 5, 6, 7, 75, 76, 7
7, 78, 85, 86, 87, 88, 89, 95, 9
6, 97, 98 ° transmitted light, 9, 39, 41, 80 °
Halftone type phase shift region, 8, 40, 42, 7
9, {alternate type phase shift region, 62} light shielding region, 56} active region, 53 {gate electrode, 51}
{Gate electrode lead holes, 52, 54, 55} Source / drain electrode lead holes.

Claims (8)

[Claims] A substrate that is transparent to the exposure light; a groove provided on the substrate, the phase of the exposure light being inverted depending on the presence or absence thereof; and a predetermined portion on the substrate and around the groove. A translucent film that has a lower transmittance to the exposure light than the substrate, and the phase of the exposure light is inverted depending on the presence or absence thereof; and the translucent film so that the substrate is exposed. A first opening provided in a first region of the film; a light-shielding film provided on a second region of the translucent film and having a lower transmittance to the exposure light than the translucent film; And a second opening provided in the light-shielding film and the translucent film so that the substrate is exposed. 2. A plurality of first openings and a plurality of second openings are provided, respectively, and the density of the plurality of first openings and the density of the second openings are different from each other. The photomask according to claim 1, wherein: 3. A step of preparing an original plate on which a translucent film having an inverted phase of transmitted light of exposure light is formed on a transparent substrate of a mask and on which a light-shielding film is formed; Etching a part of the translucent film and processing it into a desired pattern; etching a part of the light shielding film on the translucent film and processing the light shielding film into a desired pattern; Etching a part of the transparent substrate to a depth at which the phase of the exposure light passing through the transparent substrate is inverted. 4. A translucent film formed on a transparent substrate, wherein the phase of transmitted light is inverted depending on the presence or absence of the translucent film, and the translucent film is exposed in a first region where the translucent film is exposed. A third region in which the transparent substrate is exposed, in a third region in which the translucent film is formed on the transparent substrate, and a light-shielding film is formed thereon; And transferring a pattern to a wafer using a photomask including a region where the transparent substrate is etched to a desired depth so that the phase of the region 4 and the exposure light passing through the fourth region are inverted. Characteristic pattern forming method. 5. The distance D between the end of the first area and the end of the second area is D = k.lambda. / NA (where NA is the number of apertures in the projection lens, and λ is the exposure wavelength). 5. The pattern forming method according to claim 4, wherein k ≧ 1.5). 6. A distance D between an end of the third region and an end of the fourth region is D = k.lambda. / NA (where NA is the number of apertures in the projection lens, and λ is the exposure wavelength). 5. The pattern forming method according to claim 4, wherein k ≧ 1.5). 7. A mask bias amount given as an offset to a design size of a pattern on the photomask with respect to a pattern size to be transferred to the wafer is equal to the second region in the first region. 5. The pattern forming method according to claim 4, wherein the pattern is different from the pattern formed by the fourth region and the etched region in the third region. 6. 8. A mask bias amount given as an offset to a design dimension on a mask with respect to a pattern size to be transferred to the wafer, the mask bias amount of the pattern comprising the second region in the first region. 5. The pattern forming method according to claim 4, wherein the pattern is larger than a pattern formed by the fourth region and the etched region in the third region.