JPH11202469A - Mask for reduction projection exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mask for reduction projection exposure which facilitates the manufacture of an auxiliary pattern and practicizes an auxiliary pattern method. SOLUTION: A half-tone phase shift film 103 is formed entirely over one surface of a transparent substrate 101 and a light shield film 102 is formed on the half-tone phase shift film 103 corresponding to the main pattern of the center part of the substrate. Further, a main pattern is formed by boring a light shield film 102 and the half-tone phase shift film 103 at the center part of the substrate and the half-tone phase shift film 103 at the periphery of the main pattern 1 is bored to form the auxiliary pattern 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a line-and-
The present invention relates to a reduction projection exposure mask for forming a space pattern.

[0002]

2. Description of the Related Art At present, in a line-and-space pattern (a repetitive pattern having a constant pitch of lines and spaces), a sufficient depth of focus can be obtained by practical use of a modified illumination method. That is, a pattern having periodicity such as a gate and a wiring pattern of a DRAM can be formed stably even with a considerably small dimension.

The modified illumination method is a method in which the shape of an effective light source formed by a fly-eye lens is changed (for example, a ring shape), and all light incident on a mask is oblique. In a normal image formation state, three light beams of the 0th-order diffracted light and ± 1st-order diffracted light of the mask are collected by a lens (imaging of three light beams interference). In the modified illumination method, one of the ± 1st-order diffracted lights of the light obliquely incident on the mask does not enter the projection lens, and forms an image with two light fluxes of the 0th-order light and ± 1st-order diffracted light (two-beam interference). Imaging).

Comparing these two imaging states with the best focus, the contrast is lower in the modified illumination method in which one of the ± 1st-order diffracted lights is discarded. However, considering the angle of incidence on the image plane (semiconductor substrate), the image formed by two-beam interference is の of the three-beam interference. Therefore, blurring of the image when the focus is shifted is reduced, and the depth of focus can be increased. However, there is no effect of the modified illumination method on an isolated pattern in which clear diffracted light does not occur, and increasing the depth of focus of the isolated pattern is an important problem.

In order to increase the depth of focus of an isolated pattern, an auxiliary pattern method has been proposed. The auxiliary pattern method is a method of arranging a pattern equal to or less than the resolution limit of an exposure apparatus around a pattern to be transferred onto a semiconductor substrate (hereinafter, referred to as a main pattern). Due to this auxiliary pattern, although not perfect, the pattern has periodicity, and diffracted light is generated. Therefore, by using the auxiliary pattern mask under the deformation proof condition, the depth of focus of the isolated pattern is increased.

In this auxiliary pattern method, the position and size of the auxiliary pattern affect the depth of focus of the main pattern. There is an optimum value where the distance between the auxiliary pattern and the main pattern is substantially equal to or slightly larger than the size of the main pattern. Also, the larger the auxiliary pattern size, the larger the depth of focus of the main pattern. However, if the auxiliary pattern size is too large, the auxiliary pattern itself is transferred onto the semiconductor substrate.

Therefore, the size of the auxiliary pattern is limited to about 2/3 of the main pattern. Therefore, difficulty in manufacturing a mask is pointed out as a problem of the auxiliary pattern method.

Although the mask pattern is drawn by an electron beam drawing apparatus, it is known that the linearity is reduced for a fine pattern of 1 μm or less due to the proximity effect. The proximity effect refers to a phenomenon in which a pattern changes in size due to the influence of another pattern in the periphery. In electron beam writing, the proximity effect occurs due to reflected electrons from a semiconductor substrate or generated heat. For example, 0.2 μm
Auxiliary patterns of about 0.15 μm are arranged in the hole pattern. These are 1 μm main pattern and 0.75 μm auxiliary pattern on a 5-fold mask. In this case, under the condition that the size is matched to the main pattern, the size of the auxiliary pattern is reduced by about 0.05 to 0.1 μm. Various means for correcting the proximity effect have been proposed as means for reducing the proximity effect.

[0009] For example, Photomask and X-ray mask technology 3 (Procedures of SPIE vol. 2793, page 22)
~ 33, 1996 (Photomask and X
-Ray Mask Technology III,
Proceedings of SPIE, vol2
793, p. 22-33, 1996) is a technology that is currently expected.

The ghost method is a method in which a slight amount of exposure is performed on a pattern portion obtained by inverting the original drawing pattern, thereby eliminating the difference in pattern density. However, the correction of the proximity effect in mask writing is still an experimental stage, and there is a problem that the pattern formation is not stable.

[0011]

By the way, especially in electron beam lithography, since the entire mask is drawn by connecting fields of several millimeters square, fine patterns such as auxiliary patterns are formed at the connection between the fields. When the pattern is located,
It is also known that the shape is extremely deformed.

Therefore, it is difficult to produce an auxiliary pattern due to the influence of the dimensional linearity and the field connection error (batting error) of the device.
The auxiliary pattern method has not been put to practical use yet.

An object of the present invention is to provide a reduced projection exposure mask which facilitates the production of an auxiliary pattern and makes the auxiliary pattern method practical.

[0014]

In order to achieve the above object, a reduced projection exposure mask according to the present invention is a reduced projection exposure mask having a main pattern and an auxiliary pattern. By arranging the auxiliary pattern in the periphery and making the periphery of the auxiliary pattern a halftone phase shift region, the transfer of the auxiliary pattern is prevented.

An auxiliary pattern of the same size is arranged around the main pattern, and light having a phase difference of 180 degrees is leaked in a halftone phase shift area around the auxiliary pattern, thereby preventing transfer of the auxiliary pattern. It is something to do.

Further, the size of the auxiliary pattern is enlarged,
The transfer of the auxiliary pattern is prevented by increasing the transmittance of the halftone phase shift area around the auxiliary pattern.

Further, a multilayer coating mirror in which two materials having different refractive indexes are alternately laminated on a semiconductor substrate is formed, and a pattern of a reflection region and an absorption region is formed by a heavy metal X-ray absorbing material. The periphery is an X-ray mask in which only the main pattern is transferred by using the absorption region and the periphery of the auxiliary pattern as the halftone phase shift region.

The X-ray mask is a reflection type or transmission type X-ray mask.

According to the present invention, the transfer of the auxiliary pattern is reduced by making the periphery of the auxiliary pattern a halftone phase shift region in the auxiliary pattern mask, thereby facilitating the production of the auxiliary pattern.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1A is a plan view showing a reduced projection exposure mask according to Embodiment 1 of the present invention, and FIG.
FIG. 2 is a vertical sectional view taken along line AA of FIG.

As shown in the drawing, the reduced projection exposure mask according to the present invention is basically a reduced projection exposure mask having an in-pattern 1 and an auxiliary pattern 2, and is arranged around the main pattern 1 as a center. By arranging the auxiliary pattern 2 and making the periphery of the auxiliary pattern 2 a halftone phase shift area, the transfer of the auxiliary pattern is prevented.

Next, a specific example of a reduced projection exposure mask according to the present invention will be described as an embodiment with reference to the drawings.

The exposure apparatus used in the embodiment of the present invention comprises:
A KrF excimer laser exposure apparatus with a reduction ratio of 1/5, NA 0.5, σ = 0.8, and 70% annular illumination (70% of the effective light source is shielded from light). The pattern formed on the semiconductor substrate will be described as a hole of 0.18 μm.

In the mask for reduction projection exposure according to the first embodiment of the present invention shown in FIG. 1, an auxiliary pattern 2 of the same size is arranged around a main pattern 1 and a halftone phase shift area around the auxiliary pattern 2 is used. By leaking light having a phase difference of 180 degrees, the transfer of the auxiliary pattern 2 is prevented.

That is, as shown in FIG. 1, the mask M for reduction projection exposure according to the first embodiment of the present invention
1, a halftone phase shift film 103 is formed on the entire surface, and a light shielding film 102 is formed on the halftone phase shift film 103 corresponding to the main pattern 1 in the center of the substrate. Further, an opening is provided in the light-shielding film 102 and the halftone phase shift film 103 in the center of the substrate to form the main pattern 1
The auxiliary pattern 2 is formed by providing an opening in the halftone phase shift film 103 around the main pattern 1.

The main pattern 1 shown in FIG. 1 is a hole of 0.9 μm above the mask, and auxiliary patterns 2 of the same size are arranged around the main pattern 1 at a 1.8 μm pitch. The peripheral portion of 0.45 μm of the main pattern 1 is a light shielding area. On the other hand, the periphery of the auxiliary pattern 2 is a halftone phase shift area.

The transmission intensity T of the halftone phase shift area
Is 0.12 (the transmission intensity of the transparent substrate 101 is 1),
The phase difference θ is 180 degrees. Here, this transmittance is determined as follows in order to prevent the transfer of the auxiliary pattern 2. √ (T) = (Auxiliary pattern area) / (Halftone area) = 1/3 T = 0.11

At this time, the average amplitude of the light transmitted through the auxiliary pattern 2 is 0, and the transfer of the auxiliary pattern 2 can be effectively prevented. However, this is a condition for reducing the average amplitude in the auxiliary pattern 2 portion. When the size of the auxiliary pattern 2 increases, the peak light intensity of the auxiliary pattern 2 increases. Therefore, it is necessary to further leak light in the halftone region, reduce the peak intensity, and prevent the auxiliary pattern 2 from being transferred.

As shown in FIG. 1B, the mask structure has a two-layer structure in which a halftone phase shift film 102 and a light shielding film 103 are sequentially formed on a transparent substrate 101. As a material of the transparent substrate 101, synthetic quartz is generally used.
As a material of the halftone phase shift film 103 for the KrF excimer laser, molybdenum oxynitride silicide and chromium fluoride are used. As a material of the halftone phase shift film 103 in the embodiment,
Using a 110 nm-thick molybdenum oxynitride silicide, a transmittance of 11% for a KrF excimer laser,
A halftone phase shift film 103 having a phase difference of 180 degrees is formed. In addition, chromium (30 nm) and chromium oxide (30 nm) are used as the material of the light shielding film 102. This chromium oxide is an antireflection film for preventing light reflected on the semiconductor substrate from being reflected on the surface of the photomask and returning to the semiconductor substrate again, similarly to a normal photomask.

The method of manufacturing the reduced projection exposure mask M according to the first embodiment of the present invention is the same as the method of manufacturing a normal halftone phase shift mask. FIG. 2 is a cross-sectional view illustrating a method of manufacturing the reduction projection exposure mask M according to the first embodiment of the present invention in the order of steps.

First, as shown in FIG. 2A, a halftone phase shift film 102 and a light shielding film 103 are sequentially formed on the entire surface of the transparent substrate 1, and a resist film 105 is applied on the light shielding film 103. Then, the main pattern 1 and the auxiliary pattern 2 are drawn on the resist film 105.

Next, as shown in FIG.
03 is etched by dry etching using a chlorine-based gas, and thereafter, the halftone phase shift film 102 is etched by dry etching using a fluorine-based gas while changing the etching chamber.

Next, as shown in FIG. 2C, after the resist film 105 is once removed, a new resist 105 is again formed.
Apply the film. Further, a pattern for making the periphery of the auxiliary pattern 2 a halftone phase shift region is drawn while avoiding the main pattern portion in the central portion of the substrate, and the resist film 105 is left only in the main pattern portion in the central portion of the substrate.

Next, as shown in FIG. 2D, a resist film 105 remaining only in the main pattern portion at the center of the substrate is formed.
Is used as a mask, around the auxiliary pattern 2 (0.
The light-shielding film 103 (45 μm) is removed by wet etching (aqueous cerium ammonium nitrate solution).

Finally, the resist film 105 remaining only in the main pattern portion at the center of the substrate is removed.

The above manufacturing method is the same as the manufacturing method of the halftone phase shift mask having the light shielding region of the light shielding film around the mask, but the pattern of the second drawing is different.

In the first embodiment of the present invention, an auxiliary pattern 2 having the same dimensions as the main pattern 1 is formed around the main pattern 1 first. Therefore, all the first drawing patterns have the same periodic pattern. for that reason,
The influence of the proximity effect at the time of mask drawing is eliminated, and the dimensional accuracy of the pattern is improved. By giving the pattern periodicity in this manner, an image of two-beam interference can be formed under a deformed illumination condition, and the depth of focus can be increased.

The transfer of the auxiliary pattern 1 is prevented by the halftone phase shift area. In the halftone phase shift region, light having a phase of 180 degrees is transmitted and interferes with light of the transparent auxiliary pattern portion to reduce the light intensity.

FIG. 3 is a diagram showing the light intensity distribution at the position AA in FIG. 1 in the mask for reduction projection exposure according to the embodiment of the present invention.

In FIG. 3, the x-axis is a position on the image plane, and the center of the main pattern 1 is located at x = 0 nm. The y-axis is called relative light intensity, which is a standard value when the light intensity of a sufficiently wide area without a pattern is set to 1.

As shown in FIG. 3, the light intensity of the auxiliary pattern 2 is lower than that of the main pattern 1 due to the effect of the peripheral halftone phase shift region. As a method of predicting a resist pattern from a light intensity distribution, there is generally a simple resist development model called an exposure threshold model. This is a model assuming that a portion having a certain intensity (hereinafter, this intensity is referred to as Ith) or more in a light intensity distribution is removed by development, and a portion having Ith or less is not melted even if developed.

According to the simulation result of the present invention (FIG. 3), Ith is 0.098. Since the peak intensity of the auxiliary pattern portion is 0.075, the auxiliary pattern 2 is not transferred onto the resist.

Next, the effect of increasing the depth of focus of the reduced projection exposure mask according to the embodiment of the present invention will be described. Here, the contrast is defined as follows from the light intensity distribution as shown in FIG. Contrast = Imax / Iedge Here, Imax is the maximum light intensity of the main pattern portion at each focal position, and Iedge is the light intensity at the pattern edge position at the best focus. This Ied
The use of ge corresponds to setting the exposure amount so that the pattern size of the photosensitive resin becomes the target size at the best focus.

FIG. 4 is a diagram showing the relationship between the contrast and the focus position in the reduced projection exposure mask according to the embodiment of the present invention and the ordinary reduced projection exposure mask. The level of the contrast defined here at which a pattern can be formed depends on the resist performance. Usually, the contrast at the lower limit of the resolution of the pattern is in the range of 1.7 to 1.3. Here, if the depth of focus is set to a contrast of 1.4 or more, the normal mask has a depth of focus of ± 0.30 μm, but the reduced projection exposure mask according to the embodiment of the present invention has a depth of focus of ± 0.45 μm. It can be seen that it expands to.

(Embodiment 2) FIG. 5 (a) is a plan view showing a reduced projection exposure mask according to Embodiment 2 of the present invention, and FIG. 5 (b) is a line AA of FIG. 5 (a). It is a longitudinal cross-sectional view.

The second embodiment of the present invention shown in FIG. 5 is an application example where the auxiliary pattern dimension (main pattern dimension) is large and the transfer of the auxiliary pattern cannot be prevented unless the transmittance of the halftone phase shift area is increased. That is, by increasing the size of the auxiliary pattern 2 and increasing the transmittance of the halftone phase shift region around the auxiliary pattern 2,
The transfer of the auxiliary pattern 2 is prevented.

In the second embodiment of the present invention shown in FIG. 5, the main pattern 1 has a hole of 0.2 μm and the auxiliary pattern 2
Is 0.2 μm, and all of these patterns are 0.4 μm.
They are arranged at a pitch of μm. Then, the transmittance of the halftone phase shift film 103 is set to 25%, and 0.05 μm around the auxiliary pattern 2 (0.25 μm above the mask) is used as a light shielding region.

In the second embodiment of the present invention, the auxiliary pattern 2
Is large, the light of the strong opposite phase does not leak around the auxiliary pattern 2, so that the peak light intensity of the auxiliary pattern 2 cannot be kept small.

In the second embodiment of the present invention, a light intensity distribution simulation is performed by varying the transmittance while setting the size of the halftone phase shift region to 0.1 μm, and the peak light intensity of the auxiliary pattern portion is Ith (the main pattern is 0). .2 μm
(Light intensity level)
It is set at 5%. Further, the width W of the halftone phase shift film 103 in the halftone phase shift region is set in consideration of the mask manufacturing stability.

That is, when the transmittance is high, since the dimensional change of the halftone region affects the size of the main pattern 1 when the halftone region is close to the main pattern 1, the halftone region is separated from the main pattern 1 to some extent. It is desirable. If the width W of the halftone phase shift film 103 in the halftone phase shift region is too small,
There is a possibility that the transfer of the auxiliary pattern 2 cannot be prevented due to variations in the mask manufacturing error (0.05 μm on the mask: 0.01 μm on the semiconductor substrate). Therefore, in the second embodiment, W is set to 0.05 μm (0.25 μm on the mask).

FIG. 6 is a diagram showing the light intensity distribution of the reduced projection exposure mask according to the second embodiment of the present invention shown in FIG. In FIG. 6, the center of the main pattern 1 is located at x = 0 μm.

As is clear from FIG. 6, the peak light intensity of the auxiliary pattern 2 is sufficiently low even in the mask for reduction projection exposure according to the second embodiment of the present invention shown in FIG. Will not be transcribed.

(Embodiment 3) FIG. 7 shows a reduced projection exposure mask according to a third embodiment of the present invention. The reduced projection exposure mask according to the third embodiment of the present invention is a reduced projection X-ray mask. It is intended for a reflective mask for exposure.

As shown in FIG. 7, a multilayer coating mirror 111 in which two materials having different refractive indexes are alternately laminated on a silicon substrate 110 is formed, and a reflection region is formed by a heavy metal X-ray absorbing material such as tungsten or gold. The pattern of the absorption region is formed.

Even in such an X-ray mask, only the main pattern 1 can be transferred by making the periphery of the main pattern 1 an absorption area and the periphery of the auxiliary pattern 2 a halftone phase shift area. The half-tone phase shift film 112 for X-rays is formed by forming a heavy metal having a predetermined thickness different from that used for the light shielding material 113. For example, tantalum (Ta,
In the case where processing is performed by dry etching using a gas containing chlorine), the halftone phase shift film 112 is selectively formed by using tungsten silicide (processing is performed by dry etching of a gas mainly containing fluorine). Processing becomes possible. Further, there is a transmission type mask as the X-ray mask, but the present invention can be similarly applied to a transmission type X-ray mask.

[0056]

As described above, according to the present invention, the transferability of the auxiliary pattern can be reduced by forming the periphery of the auxiliary pattern as a halftone phase shift area, and the production of the auxiliary pattern is facilitated. Thus, the auxiliary pattern method can be put to practical use.

[Brief description of the drawings]

FIG. 1A is a plan view showing a reduced projection exposure mask according to a first embodiment of the present invention, and FIG.
It is a line longitudinal cross-sectional view.

FIG. 2 is a cross-sectional view showing a method for manufacturing a reduced projection exposure mask M according to Embodiment 1 of the present invention in the order of steps.

FIG. 3 is a diagram showing a light intensity distribution at a position AA in FIG. 1 in the reduced projection exposure mask according to the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a contrast and a focus position in a reduced projection exposure mask according to an embodiment of the present invention and a normal reduced projection exposure mask.

FIG. 5A is a plan view showing a reduced projection exposure mask according to a second embodiment of the present invention, and FIG. 5B is a vertical sectional view taken along line AA of FIG.

FIG. 6 is a view showing a light intensity distribution of a reduced projection exposure mask according to the second embodiment of the present invention shown in FIG. 5;

FIG. 7 is a cross-sectional view illustrating a reduced projection exposure mask according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main pattern 2 Auxiliary pattern 101 Transparent substrate 102 Light shielding film 103 Halftone phase shift film 105 Resist film 110 Silicon substrate 111 Multilayer coating mirror 112 Halftone phase shift film 113 Absorbing material

Claims (5)

[Claims] 1. A reduction projection exposure mask having a main pattern and an auxiliary pattern, wherein the auxiliary pattern is arranged around the main pattern as a center, and the periphery of the auxiliary pattern is a halftone phase shift area. Wherein the auxiliary pattern is prevented from being transferred. 2. An auxiliary pattern having the same size is arranged around the main pattern, and light having a phase difference of 180 degrees is leaked in a halftone phase shift area around the auxiliary pattern, thereby preventing transfer of the auxiliary pattern. The reduced projection exposure mask according to claim 1, wherein 3. The transfer of the auxiliary pattern is prevented by enlarging the size of the auxiliary pattern and increasing the transmittance of a halftone phase shift area around the auxiliary pattern. The reduced projection exposure mask according to claim 1. 4. A multi-layer coated mirror in which two materials having different refractive indexes are alternately laminated on a semiconductor substrate,
Further, a pattern of a reflection region and an absorption region is formed by a heavy metal X-ray absorbing material, and the periphery of the main pattern is the absorption region and the periphery of the auxiliary pattern is the halftone phase shift region, so that only the main pattern is transferred. The reduced projection exposure mask according to claim 1, wherein the mask is an X-ray mask configured as described above. 5. The reduction projection exposure mask according to claim 4, wherein the X-ray mask is a reflection type or transmission type X-ray mask.