JPH0561183A - Exposing mask - Google Patents

Abstract

PURPOSE:To improve the resolution threshold of a transfer device and to allow faithful pattern transfer at a specified light quantity by using translucent film patterns in place of light shielding film patterns. CONSTITUTION:The exposing mask which has a light transparent substrate 1 and the mask patterns 2 constituting of a light shieldable material disposed on the light transparent substrate 1 is so constituted as to include the translucent film patterns constituted as to vary the optical path length to exposing light. Namely, the translucent film patterns are used in place of the light shielding film patterns as the mask patterns 2 having the sizes in a certain range. The translucent film patterns having a prescribed transmittance are preferably used if the value obtd. by dividing the pattern size of the mask patterns 2 by l/NA of the exposing conditions is <=0.61 and the opaque patterns of nearly 0 transmittance are used if the above-mentioned value is >=0.61. Further, the amplitude transmittance of the translucent film patterns is adjusted according to the sizes of the mask patterns 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to exposure masks, and more particularly to lithographic masks.

[0002]

2. Description of the Related Art Semiconductor integrated circuits are becoming highly integrated and miniaturized. When manufacturing the semiconductor integrated circuit,
Lithography technology is particularly important as a cornerstone of processing.

In the current lithographic technology, a method of projecting and exposing a mask pattern on an LSI substrate through a reduction optical system is mainly used, but if a high pressure mercury lamp is used as a light source, the minimum line width is about 0.5 μm. Is the limit. 0.5
Direct patterning technology using KrF excimer laser or electron beam and X-ray same-magnification exposure technology are being developed for pattern dimensions of less than μm, but due to reasons such as mass productivity and process versatility, optical lithography Expectations for are very high.

Under these circumstances, the G
Of various light sources such as X-ray, i-line, excimer laser, and X-ray is being considered, and development of a new resist and a new resist treatment such as REL are also being considered for the resist. Research is also proceeding on the CEL image reverse method and the like.

On the other hand, regarding the mask manufacturing technique,
Though not fully examined, 1982 IBM
Levenson et al. Of the company proposed a phase shift method and received attention.

The phase shift method is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through a mask.

This principle will be described with reference to FIG. In this method, as shown in FIG. 20 (a), chromium (Cr) formed on the quartz substrate 11 by a sputtering method or the like.
Alternatively, a mask in which a transparent film 13 is formed on one of a pair of adjacent transparent portions of a mask pattern 12 made of chromium oxide (Cr ₂ O ₃ ) is used, and the phase of this portion is inverted as shown in FIG. 20 (b). The amplitude of the light is canceled at the boundary between the two transmission parts (FIG. 20 (c)). As a result, the light intensity at the boundary between the two transmissive portions becomes 0, and the pattern formed on the wafer can be separated from the two transmissive portions as shown in FIG. In this way, the 0.7 μm pattern was resolved by the g-line stepper with NA = 0.28, and the resolution was improved by about 40%. At this time, in order to invert the phase, the film thickness d of the phase shifter is d = λ / 2 where n is the refractive index of the shifter material and λ is the exposure wavelength.
The relationship of (n-1) is required.

Terazawa et al. Of Hitachi further developed the technique of Levenson et al. And applied it to an isolated pattern as shown in the principle of FIG. In this method, in addition to the isolated pattern a, an auxiliary pattern b as a dummy that is not resolved by itself is provided, and a shifter 13 for inverting the phase is provided at this portion. In this method, an i-line stepper with NA = 0.42, an isolated space of 0.3 .mu.m and 0.
A 4 μm diameter contact hole was resolved, and the resolution was improved by about 30% compared to the conventional method. However, with respect to the contact hole, the smaller the pattern size is, the smaller the difference in light intensity with the auxiliary pattern is. Therefore, there is a limit that the light intensity transmitted through the transmissive portion is weakened as a whole and is not resolved.

Furthermore, in the above-described method, shifters are installed for every other transmissive portion for lines and spaces, and for isolated patterns, a mask layer is processed for an auxiliary pattern and shifters are used. Since the arrangement is performed, there is a problem that the shifter is aligned with the mask pattern and a selective processing technique is required, which significantly increases the number of steps and complicates the mask manufacturing process.

In view of such a problem, further, Nitayama et al. Of Toshiba have proposed a phase shift mask structure in which a phase shifter is provided around a transmission portion or a light shielding portion.

FIG. 22 shows this principle. This mask is
As shown in FIG. 22 (a), a phase shifter formed so as to project around a mask pattern 12 formed of a laminated film of chromium (Cr) and chromium oxide (Cr ₂ O ₃ ) formed on a quartz substrate 11. As shown in Fig. 22 (b), the phase of this part is reversed by using a mask with a transparent film as No. 13, and the amplitude of the light cancels out the light of phase 0 ° and phase 180 ° at both ends of the transmitting part. The intensity is reduced and the contrast is improved (FIG. 22 (c)). As a result, the light intensity at both ends of the transmissive part becomes almost zero, and the pattern formed on the wafer can be separated from the two transmissive parts as shown in FIG. 22 (d).

This mask is formed as follows.

First, as shown in FIG. 23 (a), the quartz substrate 1
A laminated film 12 of chromium (Cr) and chromium oxide (Cr ₂ O ₃ ) is deposited on the substrate 1 by a sputtering method or the like to a thickness of about 100 nm,
A resist is applied on this, electron beam drawing is performed, and development is performed to pattern the resist pattern R.

Then, as shown in FIG. 23B, the mask layer 1 is formed by wet etching or reactive ion etching using the resist pattern as a mask.
2 is patterned, and the resist pattern R is removed by peeling.

After this, as shown in FIG. 23 (c), the PMM
A film 13 is applied and back exposure is performed to form a latent image 13S.

Then, development is performed to form a phase shifter 13 having a PMMA film pattern, as shown in FIG.

Finally, as shown in FIG. 23 (e), this P
Side etching of the mask layer 12 is performed by using the phase shifter 13 having the MMA film pattern as a mask to form the mask layer 1
A mask formed so that the phase shifter 13 overhangs from 2 is completed.

In this mask, PMMA serves as a phase shifter, but PMMA has a high transmittance and a sharp resist profile, so that it serves as a good phase shifter.

Further, according to this method, since the phase shifter pattern can be formed in a self-aligning manner, mask alignment and selective processing steps are not required, and the pattern can be easily formed.

When exposure is performed using such a mask,
The light passing through each opening has their phases inverted as shown by the broken line, so the light intensity at the lower part of the mask layer is significantly reduced, and the light as a whole is shown by the solid line. In view of the intensity distribution, it is possible to resolve up to approximately half the size of the conventional mask.

When the transmittance of the phase shifter in the mask having such a structure is assumed to be 100% and the shifter width is optimized, the optimum shifter width having the largest contrast improving effect differs depending on the pattern size. I understood. For example, as shown in FIG. 19, when an excimer stepper with NA = 0.42 is used, the optimum shifter width for a line and space of 0.3 μm is 0.04 μm (on the wafer) and 0.25 μm for a line and space. -The optimum space shifter width is 0.06 μm (on the wafer).

As described above, by setting the optimum shifter width having the largest contrast improving effect in accordance with the pattern size, the maximum contrast improving effect can be obtained and the resolution of a fine pattern which cannot be resolved by the conventional technique. Will also be possible.

However, in this method, since a finer shifter pattern is provided on the fine pattern, there is a problem that the shifter width is difficult to control and the processing is extremely difficult.

Further, such a shifter pattern must use either a permeable film or an anti-permeable film. However, since the mask used in the VLSI manufacturing process must be free from dust, it must be cleaned frequently. For this reason, the phase shift mask also needs to have a strength sufficient to withstand repeated cleaning, but if the shifter is formed of a resist, it cannot be put to practical use in terms of strength.

[0025]

As described above, in the conventional photolithographic mask using the phase shift method, since a finer shifter pattern is provided on the fine pattern, it is difficult to control the shifter width and perform alignment. However, there was a problem that processing was difficult.

Further, as a mask used in the VLSI manufacturing process, there has been no one that can be sufficiently used in terms of strength.

The present invention has been made in view of the above circumstances, and provides an exposure mask capable of improving the resolution limit of a transfer device and performing faithful pattern transfer with a constant amount of light, and a manufacturing method thereof. The purpose is to

[0028]

Therefore, in the first exposure mask of the present invention, a semitransparent film pattern is used instead of the light shielding film pattern in the mask pattern having a certain range of dimensions. Desirably, the amplitude transmittance of the semitransparent film pattern is adjusted according to the size of the mask pattern.

Further, desirably, the semitransparent film pattern is composed of a plurality of regions having different amplitude transmittances divided into a plurality of fine regions which are not resolved by exposure light.

Desirably, the semitransparent film pattern is constructed so that the amplitude transmittance is adjusted by the occupation area ratio of the fine region.

Desirably, the semitransparent film pattern includes a region whose amplitude transmittance is changed by ion implantation.

In the second exposure mask of the present invention, the shift film having different optical path lengths with respect to the exposure light, the mask substrate formed on the upper or lower layer of this film, and the predetermined exposure light are provided. It is configured to have a laminated structure with a translucent film as a transmittance adjusting layer configured to have transmittance.

In the third aspect of the present invention, by adjusting the amplitude transmittance of the material forming the phase shifter, the shifter width effective for improving the contrast is increased and the precision required for the shifter width is relaxed. ing. That is, when the value obtained by dividing the pattern dimension of the mask pattern by λ / NA of the exposure condition is 0.34 to 0.68, the amplitude transmittance of the phase shifter is set to 100% or less, and the phase shifter width affects the adjacent pattern. It is designed so that it can be selected so large that it does not reach. It is desirable to make the shifter width large enough,
The amplitude transmittance of the phase shifter is selected so that the contrast becomes maximum according to the pattern size.

[0034]

As a result of examining the light image intensity distribution projected on the wafer by changing the shifter transmittance by simulation, it is possible to use a semitransparent film pattern having a predetermined transmittance in place of the light shielding film pattern. It was found that the contrast was improved. The present invention has been made in view of this point, and with the above configuration, resolution of a fine pattern is facilitated. Further, since the patterning of the phase shifter can be performed once without performing the patterning of the light shielding film pattern, the pattern control is easy.

Desirably, the resolution can be improved by adjusting the amplitude transmittance of the semitransparent film pattern according to the size of the mask pattern.

Further, by using a fine semitransparent film pattern having a constant transmittance and having a resolution equal to or lower than the resolution of the exposure optical system so that the occupied area transmittance is different, the amplitude transmission according to the pattern size is actually performed. The rate pattern can be easily formed.

In the second exposure mask of the present invention, the shift film having different optical path lengths with respect to the exposure light, the mask substrate formed on the upper or lower layer of the film, and the predetermined exposure light are provided. Since it has a laminated structure with a translucent film as a transmittance adjusting layer configured to have a transmittance of 1, the film for shifting the phase and the film for adjusting the transmittance are independently selected. In addition to being able to easily form, it is possible to appropriately select materials including materials other than resin, such as a silicon oxide film or spin-on-glass for the shift layer that shifts the phase. It is possible to obtain a pattern having strength enough to withstand repeated washing as in the case of using.

The optical image depends on NA (numerical aperture of optical system) and λ (wavelength).

However, when the pattern size w is standardized as follows: γ = w / (λ / NA) Optical images having the same standardized size γ are completely similar at the similarity ratio λ / NA. NA / λ represents a cutoff frequency in the spatial frequency domain, and its reciprocal λ / NA is a frequency corresponding to one division obtained by dividing the cutoff frequency by 1 and NA / λ. Thus, each pattern dimension is set to this λ / N
By dividing by A, the position occupied by the dimension in the spatial frequency domain can be standardized.

As a result of repeating various experiments using this standardized dimension, the standardized dimension (value divided by λ / NA of exposure conditions)
It was found to be particularly effective for a mask pattern having a value of 0.61 or less. Therefore, a mask is formed using a semitransparent film having a transmittance of 0 to 50% and a phase shift of 180 ° only for a mask pattern whose value divided by λ / NA of the exposure condition is 0.61 or less. By forming a pattern, the phase shift effect can be easily obtained,
It is possible to resolve a pattern that cannot be resolved by a conventional mask. The transmissivity of the semitransparent film may be selected such that the contrast is optimum according to the pattern size.

The inventors of the present invention performed a simulation using a program for obtaining an optical image intensity distribution in order to obtain the optimum relationship between the amplitude transmittance and the shifter width in a line-and-space at equal intervals. .. From this result, it was found that the amplitude transmittance of the shifter where the contrast becomes maximum depends on the shifter width, and the width of the shifter can be increased as the amplitude transmittance is decreased. As a result, as a result of this phenomenon, the value obtained by dividing the pattern size of the mask pattern by λ / NA of the exposure condition is 0.34 to 0.68.
It turned out to be common at the time. Therefore, by adjusting the transmittance of the shifter arbitrarily in each pattern dimension within this range, a large contrast improving effect can be obtained with a shifter width within a range in which sufficient accuracy can be obtained for shifter processing.

Further, if the shifter width is made sufficiently large and the amplitude transmittance of the phase shifter is selected so that the contrast becomes maximum according to the pattern size, the manufacturing becomes extremely easy.

[0043]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Example 1 FIG. 1 is a diagram showing a cross section of an exposure mask of Example 1 of the present invention.

This exposure mask is a quintuple mask, and a line and line of 1.5 μm width made of a semitransparent film having a film thickness of 0.25 μm and a transmittance of 6% is formed on the surface of the transparent quartz substrate 1. A mask pattern 2 composed of a space pattern is provided. This line-and-space is transferred onto the wafer and has a line-and-space width of 0.3 μm.
It becomes a space pattern.

This semitransparent film is made of p-TERPHENYL.
And PMMA were mixed at a ratio of 1: 4, and this was dissolved in ethyl cellosolve acetate and spin-coated to give a film thickness of 0.
After adjusting the thickness to 25 μm, exposure and development are performed, and
It is a line-and-space pattern with a width of 3 μm.

The exposure mask thus formed is mounted on a KrF excimer laser stepper having a projection lens with NA = 0.42, and SAL6 is mounted on a silicon substrate.
Pattern transfer (λ = 248 nm, coherency σ =) to a wafer coated with a negative resist called 01.
0.5) was carried out, and it was developed with a dedicated developer.

As a result, it is possible to obtain a highly accurate resist pattern consisting of a line-and-space pattern having a width of 0.3 μm, which cannot be resolved by the conventional exposure mask.

Next, in order to obtain the optimum shifter transmittance in the line-and-space pattern at equal intervals, simulation was performed using a program for independently obtaining the light image intensity distribution. The result is shown in FIG.

The exposure conditions are KrF excimer laser light, NA = 0.42, λ = 248 nm (λ / NA = 0.5).
9) and coherency σ = 0.5. Here, as in the case shown in FIG. 1, there are three types of translucent films having transmissivity T = 0% (chromium), T = 6%, and T = 20% formed on a transparent quartz substrate 11. The change in the light image intensity distribution with respect to each transmittance was examined by using a mask pattern 2 having a line-and-space pattern having a width of 3 μm.

2 (a) to 2 (c) show the pattern size 0.
The transmittance of the line and space pattern of 3 μm is T
The light intensity distributions obtained as a result of performing simulation by changing = 0% (chromium), T = 6%, and T = 20% are shown. From this result, it can be seen that the valley portion of the light intensity distribution is almost 0 when T = 6%, and the contrast is improved more than when T = 0%.

Further, the following formula C = (I _max −I _min ) / (I _max + I _min ) ... (Formula) I _max ... Light intensity of peak of light intensity distribution waveform I _min ... of valley of light intensity distribution waveform The contrast was calculated using the light intensity C ... Contrast, and FIG. 3 shows the change in the contrast with respect to the change in the transmittance of the pattern formed using the dimensions standardized by λ / NA. Curve a,
b, c, d, e, f, g and h are 0.68 (0.40 μm
), 0.63 (0.37 μm), 0.61 (0.36)
μm), 0.59 (0.35 μm), 0.51 (0.3
μm), 0.42 (0.25 μm), 0.39 (0.2
3 shows the change in contrast with respect to the change in transmittance at 3 μm) and 0.34 (0.20 μm).

0.37μ in case of line and space
For patterns of m or more, the contrast decreases as the shifter transmittance increases, but the pattern size is 0.25 μm.
, Transmittance 16%, 0.3 μm transmittance 6%, 0.
At 35 μm, the transmittance is 3% and the contrast is maximum.

From this result, a light-shielding film of chromium or the like is used for a pattern of 0.36 μm (a normalized value of 0.61) or more, and the transmittance is reduced from 0% to 20% for a pattern smaller than that. It is understood that the fine pattern can be resolved by using the adjusted semitransparent shifter.

If the result of FIG. 3 is multiplied by λ / NA under each exposure condition, the transmissivity of the semitransparent film that maximizes the contrast according to the pattern dimension under the exposure condition is obtained. Obtainable.

Further, from FIG. 3, a light-shielding film such as chromium is used for a pattern having a standardized pattern size of 0.61 or more, and a semi-transparent film is used for a pattern having a smaller pattern size. When the rate is set in the range of 0-50%,
It can be seen that the contrast can be improved. Here, when the standardized dimension is 0.39, the optimum transmittance is 50%, and at 0.34 smaller than 0.39, there is no effect even if the transmittance is adjusted, and there is no effect even if the transmittance is greater than 50%. I understand.

A dye may be added to this semitransparent film to adjust the transmittance.

Second Embodiment Next, a second embodiment of the present invention will be described in detail.

FIGS. 4A and 4B are views showing the main part of the exposure mask of the second embodiment of the present invention.

As this exposure mask, a pattern having a resolution limit of the exposure optical system or less is used, and the amplitude transmittance is controlled by adjusting the density (area occupancy ratio) according to the size of the mask pattern. It is characterized in that the resolution limit is improved by setting the optimum amplitude transmittance.

This exposure mask has an exposure light wavelength of 436.
Used in the nm range, the exposure light that has passed through the semi-permeable membrane pattern as a phase shifter has its phase inverted by 180 degrees and is combined with the exposure light that does not pass through the semi-permeable membrane pattern, and the light intensity at the pattern boundary Is sharpened.

Next, the manufacturing process of this exposure mask will be described.

First, as shown in FIG. 5A, the surface of a transparent fused silica substrate 1 having a size of 5 inches square and a thickness of 2.4 mm was sputtered to form a C film having a thickness of 0.035 μm.
A semitransparent film composed of the r film 3 is deposited.

Then, as shown in FIG. 5B, a resist R is applied and patterned by a photolithography process using EB exposure.

Thereafter, as shown in FIG. 5C, a Cr film is formed by reactive ion etching using the resist pattern R as a mask and a reactive gas containing CH ₂ Cl ₂ and O ₂ gas as main components. 3 is patterned, and then the substrate 1 is etched by about 0.42 μm by dry etching using a gas containing CF ₄ as a main component to form a groove T. Here, the region 4 not carved by this etching becomes the phase adjustment region. The engraving amount of the substrate 1 at this time complies with the following equation.

(N ₁ −1) × d ₁ / λ + (n ₂ −1) × d ₂ /λ=0.5 n ₁ : Refractive index of Cr d ₁ : Thickness of Cr n ₂ : Refraction of quartz substrate Rate d ₂ : Engraved amount of quartz substrate Further, as shown in FIG. 5 (d), the resist pattern R is formed by immersing in a mixed solution of sulfuric acid and hydrogen peroxide solution.
Only selectively remove.

After that, as shown in FIG. 5 (e), the Cr film 3
Pattern R2 for processing a fine pattern
To form.

Then, as shown in FIG. 5 (f), the semi-transparent film made of the Cr film 3 is patterned by dry etching using CH ₂ Cl ₂ and O ₂ as main components using the resist pattern R 2 as a mask, Then, the silicon oxide film 5 is selectively formed in the region surrounded by the resist pattern by the liquid phase growth method. Here, the thickness of the silicon oxide film 5 is C
The phase difference between the exposure light transmitted through the r film 3 and the exposure light transmitted through the silicon oxide film 5 is set to zero.

Finally, the resist R2 is stripped with an organic solvent or an acid to complete the exposure mask (FIG. 5 (g)).

The phase shifter of the exposure mask thus formed adjusts the area occupancy ratio between the fine pattern of the Cr film 3 and the silicon oxide film 5 according to the pattern size so as to obtain an optimized pattern. ing.

The film thickness was determined on the assumption that the exposure light used for the exposure of this exposure mask has a wavelength of 436 nm.

The exposure mask thus formed was mounted on a g-line stepper having a projection lens with NA = 0.42, and a 0.5 μm-thick novolak-based positive resist applied on the substrate to be processed. When PR-1024 was exposed, a pattern of 0.3 μm was obtained with extremely high precision and reproducibility.

Further, here, the Cr film 3 as a semitransparent film is used.
Since the desired amplitude transmissivity is obtained by adjusting the area occupancy of the fine pattern of the silicon oxide film 5 and the silicon oxide film 5, it is easy to control the amplitude transmissivity according to the pattern size.

In the above embodiment, the Cr film 3 and the silicon oxide film 5 are different from each other and a step is formed, but a combination of materials having a close refractive index such as a chromium oxide film and a silicon oxide film should be used. If so, the step can be eliminated and the optical characteristics can be further improved. Further, the semitransparent film is not limited to Cr, and other metal materials or other materials may be used. That is, any material may be used by setting a thin film thickness and the like. Also, the transparent film is not limited to silicon oxide, but may be calcium fluoride (CaF), magnesium fluoride (Mg).
Other materials such as F) and aluminum oxide (Al ₂ O ₃ ) may be used.

Third Embodiment Next, a third embodiment of the present invention will be described in detail.

In this example, attention is paid to the fact that the transmittance can be changed little by little by ion implantation, and the feature is that the amplitude transmittance is finely adjusted.

30 Ke on the surface of a transparent substrate made of fused silica
A silicon ion is ion-implanted at an acceleration voltage of V and a wavelength of 4
The transmittance at 36 nm was measured. The result is shown in Fig. 6 (a).
Shown in. Here, the horizontal axis is the implantation ion dose amount, and the vertical axis is the transmittance. As can be seen from this figure, the transmittance monotonously decreases with an increase in the dose amount. This exposure mask is used in a region where the wavelength of the exposure light is 436 nm, and the exposure light transmitted through the semi-transparent film pattern as the phase shifter has its phase inverted by 180 degrees and does not pass through the semi-transparent film pattern. The light intensity becomes sharp at the pattern boundary.

Next, the manufacturing process of this exposure mask will be described.

First, as shown in FIG. 7 (a), a dose amount of 7.0 × 10 ¹⁷ / is uniformly distributed over the entire surface of a translucent fused quartz substrate 1 having a size of 5 inches square and a thickness of 2.4 mm. cm ² Acceleration voltage 30 KeV Silicon ion ion implantation semi-transparent layer 6
To form. As a result, the wavelength of the semitransparent layer 6 is 436.
The transmittance for the exposure light of nm is 6%.

Thereafter, as shown in FIG. 7B, a resist R is applied and patterned by a photolithography process using EB exposure.

Thereafter, as shown in FIG. 7C, a depth of about 0.47 μm is obtained by reactive ion etching using the resist pattern R as a mask and a reactive gas containing CF ₄ gas as a main component. Etching is performed to form the trench T. Here, the region 4 not carved by this etching becomes the phase adjustment region.

The exposure mask thus formed was attached to a g-line stepper having a projection lens with NA = 0.42, and a 0.5 μm-thick novolac positive resist applied on the substrate to be processed. When PR-1024 was exposed, a pattern of 0.3 μm was obtained with extremely high precision and reproducibility.

The phase shifter of the exposure mask thus formed changes the dose amount or accelerating voltage according to the pattern size, or the focused ion beam method (FI).
It is also possible to form a fine ion-implanted region by drawing according to step B) so as to obtain an optimized pattern.

Although silicon ions are implanted in the above-mentioned embodiment, it is not limited to silicon ions and can be changed as appropriate. However, when Au is implanted under the same implantation conditions as shown in FIG. 6 (a), the transmittance saturates at 80% even if the dose amount is increased as shown in FIG. 6 (b). Cannot be adjusted. Therefore, it is necessary to select the ions and the implantation energy so that the characteristics that the transmittance monotonously changes with the dose amount of the implanted ions are obtained.

Fourth Embodiment Next, a fourth embodiment of the present invention will be described in detail.

In this example, the semitransparent layer is selectively formed by performing ion implantation through the resist pattern.

Next, the manufacturing process of this exposure mask will be described.

First, as shown in FIG. 7 (a), a resist R is applied to a translucent fused quartz substrate 1 having a size of 5 inches square and a thickness of 2.4 mm, and a photolithography process using EB exposure is performed. Then, this is patterned, and silicon ions are uniformly implanted into the entire surface through the resist pattern R to form a semitransparent layer 7 as shown in FIG. 7B. At this time, if the resist pattern R in the pattern area is adjusted for each transfer pattern size, the transmittance can be controlled to a desired value for each area.

Next, the silicon oxide film 8 is formed by the liquid phase growth method.
Are selectively formed in the region surrounded by the resist pattern. Here, the silicon oxide film 8 and the semitransparent layer 7 have a phase difference of 180 degrees with the exposure light transmitted through the transparent substrate.
(Fig. 7 (c)).

Finally, the resist R is peeled off with an organic solvent or acid to complete the exposure mask (FIG. 7 (d)).

The phase shifter of the exposure mask thus formed has a silicon oxide film 8 depending on the pattern size.
The area occupancy of the fine pattern forming the laminated structure of the transparent layer 7 and the semi-transparent layer 7 is adjusted so that an optimized pattern is obtained.

Fifth Embodiment Next, a fifth embodiment of the present invention will be described in detail.

FIG. 9 is a diagram showing a cross section of an exposure mask according to the fifth embodiment of the present invention.

This exposure mask is a transparent quartz substrate 2
A light-shielding film 22 such as chrome is used for a pattern having a standardized pattern size of 0.61 or more, and a semi-transparent film is used for a smaller pattern. 23, the transmissivity of this semitransparent film is set in the range of 0 to 50%.

At this time, all the patterns on the mask surface are formed with extremely good contrast, and the resolution is greatly increased.

Sixth Embodiment Next, a sixth embodiment of the present invention will be described in detail.

FIG. 10 is a diagram showing a cross section of an exposure mask according to the sixth embodiment of the present invention.

In this exposure mask, a chrome light-shielding film (not shown) is used for a pattern of 0.37 μm (normalized value: 0.61) or more, and a transmittance is set for a pattern smaller than that. By using a semitransparent pattern adjusted from 0% to 20%, it is possible to resolve a fine pattern.

That is, this exposure mask is a semi-chromium thin film formed on the surface of the transparent quartz substrate 31 so as to have an amplitude transmittance of 25% (light intensity transmittance of 6.25%). It is characterized in that it is composed of a transparent film 32 and a transparent silicon oxide film 33 which is formed on the upper layer of the semitransparent film 32 and serves as a phase shifter. 180 ° out of phase.

The phase of the exposure light transmitted through this transparent silicon oxide film 33 used as the phase shifter is inverted by 180 degrees,
It is combined with the exposure light that does not pass through the phase shifter 33 so that the light intensity becomes sharp at the pattern boundary.

Next, the manufacturing process of this exposure mask will be described.

First, as shown in FIG. 11 (a), a semitransparent film 32 made of a Cr thin film is formed on the surface of a transparent quartz substrate 1 by a sputtering method. A silicon oxide film 33 to be a phase shifter is deposited. Here, the film thickness of the silicon oxide film 33 as the phase shifter is such that the phase shifts by 180 °.

Then, as shown in FIG. 11B, a resist 34 is applied and patterned by a photolithography process using EB exposure. Using this as a mask, a reactive gas containing CF ₄ gas as a main component is used. The silicon oxide film 34 is patterned by reactive ion etching using.

Further, as shown in FIG. 11 (c), CH ₂
The semitransparent film 32 made of a Cr thin film is patterned by dry etching containing Cl ₂ and O ₂ as main components, and the resist 34 is stripped with an organic solvent or an acid to complete an exposure mask.

Since the phase shifter of the exposure mask thus formed has a pattern formed by the semitransparent film 32 and the silicon oxide film 33 which is an inorganic film, it is repeatedly washed in the VLSI manufacturing process. In such a case, it has sufficient strength to withstand this cleaning, and has a long life and high reliability.

The film thickness was determined on the assumption that the exposure light used for the exposure of this exposure mask has a wavelength of 436 nm.

The thickness of the silicon oxide film in the portion acting as the phase shifter is set to be λ / 2 (n-1). Here, λ is the wavelength of the exposure light, and n is the refractive index of the silicon oxide film.

The exposure mask thus formed was mounted on a g-line stepper having a projection lens with NA = 0.42, and a 0.5 μm-thick novolak-based positive resist applied on the substrate to be processed. When PR-1024 was exposed, a 0.3 μm pattern was obtained with extremely high precision and reproducibility.

By the way, the resolution was about 0.4 μm at most when exposed by the conventional exposure mask formed in exactly the same manner as in the above example except that this phase shifter layer was not formed. From these comparisons, it can be seen that the exposure mask of the embodiment of the present invention and the exposure method using the same can provide a pattern with extremely high accuracy.

The semitransparent film is not limited to Cr, and other metal materials or other materials may be used. That is, any material may be used by setting a thin film thickness and the like. Also, the transparent film is not limited to silicon oxide, but calcium fluoride (Ca
Other materials such as F), magnesium fluoride (MgF), aluminum oxide (Al ₂ O ₃ ) may be used.

Further, it is possible to form an antireflection film of magnesium fluoride or the like on the upper or lower layer of the pattern of this exposure mask by the sputtering method or the like.

Embodiment 7 FIG. 12 is a sectional view showing the steps of manufacturing an exposure mask according to the seventh embodiment of the present invention. In this exposure mask, a Cr film pattern having a film thickness of 100 nm is formed on the surface of a transparent quartz substrate 11 and a phase shifter having a film thickness of 0.25 μm and a translucency of 30% and a shifter width of 0.6 μm. Shifter 121
Is formed. First, Fig. 1
As shown in FIG. 2 (a), p-TER is formed on the surface of the translucent quartz substrate 11 on which a Cr film pattern having a film thickness of 100 nm is formed.
PHENYL and PMMA are mixed at a ratio of 1: 4, and a solution obtained by dissolving this in ethyl cellosolve acetate is spin-coated to give a film thickness of 0.25 μm. The amplitude transmittance of this phase shifter was 30%.

Next, as shown in FIG.
Backside exposure is performed with a mercury lamp of 300 nm.

Then, as shown in FIG. 12 (c), development was carried out with the dedicated developer TSK.

Thereafter, as shown in FIG. 12 (d), side masking of Cr was performed with a ceric ammonium nitrate solution so that the shifter width was 0.6 μm on the mask to form a mask.

The exposure mask thus formed is mounted on a KrF excimer laser stepper having a projection lens with NA = 0.42, and SAL6 is mounted on a silicon substrate.
Pattern transfer (λ = 248 nm, coherency σ =) to a wafer coated with a negative resist called 01.
0.5) was carried out, and it was developed with a dedicated developer.

As a result, it is possible to obtain a highly accurate resist pattern consisting of line and space patterns of 0.25 μm and 0.3 μm width, which cannot be resolved by the conventional exposure mask.

In the conventional case where the amplitude transmittance of the shifter is 100%, the optimum shifter width in the pattern dimension of 0.3 μm is 0.2 μm on the mask, but ± 0.1 in the process.
A variation of about μm will occur. The decrease in contrast caused by the error in the shifter width is a relatively large value of 0.05 as shown in FIG. 13 (a).

On the other hand, the amplitude transmittance of the phase shifter is 30
%, The decrease in contrast is as small as 0.005 as shown in FIG. 13 (b) even with the same error of ± 0.1 μm.

By thus decreasing the transmittance of the shifter and increasing the shifter width, it is possible to suppress the reduction in contrast due to the shifter width error, and as a result, it is possible to provide a good resist pattern.

Next, as shown in FIG. 14, in order to obtain the optimum amplitude transmissivity and the shifter width δ in the line-and-space at equal intervals, a simulation is performed using a program for obtaining the light image intensity distribution. went. The exposure conditions are KrF excimer laser light, NA = 0.42, λ = 24.
It was set to 8 nm and coherency σ = 0.5. The combinations with the highest contrast when the amplitude transmittance and the shifter width are changed are shown in FIGS. 15 (a) to 15 (e). From this result, it was found that the shifter width can be increased as the amplitude transmittance is decreased.

FIG. 16 shows the change in contrast of the light image intensity distribution when the shifter width is fixed and the amplitude transmittance is changed in a line and space of 0.3 μm.

From this figure, it can be seen that the amplitude transmittance of the shifter having the maximum contrast varies depending on the shifter width.
FIG. 17 shows the result of measurement of the relationship between the amplitude transmittance of the shifter and the shifter width when the contrast becomes maximum.
From this figure, it is understood that the shifter width can be increased by decreasing the shifter amplitude transmittance.

FIG. 18 shows the change in contrast of the light image intensity distribution when the shifter width is fixed and the amplitude transmittance is changed in a line and space of 0.25 μm.

FIG. 19 shows the result of measurement of the relationship between the amplitude transmittance of the shifter and the shifter width when the contrast becomes maximum. In this case as well, the line and
It was similar to the space.

As a result of repeating such an experiment, the phenomenon is that the pattern size of the mask pattern is changed to λ /
It was found that when the value divided by NA was 0.34 to 0.68, it was common. Therefore, by adjusting the transmittance of the shifter arbitrarily in each pattern dimension within this range, a large contrast improving effect can be obtained with a shifter width within a range in which sufficient accuracy can be obtained for shifter processing.

The present invention has been described above with reference to the embodiments. In the embodiments, the transparent film as the phase shifter is the polymethyl methacrylate also used as the resist and the silicon oxide layer as the inorganic film.
The material is not limited to these, and any material having a high transmittance for light having a wavelength of 436 nm or less used as exposure light may be used. For example, other materials such as calcium fluoride (CaF), magnesium fluoride (MgF), aluminum oxide (Al ₂ O ₃ ) may be used as the inorganic film. Further, as the resist that becomes the phase shifter,
Polymethylmethacrylate, polytrifluoroethyl-
Materials such as α-chloroacrylate, chloromethylated polystyrene, polydimethylglutarimide, polymethylisopropenyl ketone, etc. are considered. Further, the thickness of the pattern and the like can be appropriately changed depending on the material and the lithography light.

The materials for the transparent substrate and the light-shielding film are not limited to the examples, and can be changed as appropriate.

In addition, the phase shifter layer does not necessarily have to perform a phase shift of 180 degrees, and 180 degrees may be used as long as it sharply lowers the light intensity distribution of the pattern edge in the vicinity of 180 degrees. It may be off.

[0130]

As described above, according to the exposure mask of the present invention, the contrast is improved by using the semitransparent film pattern instead of the light shielding film pattern.
The resolution can be improved.

According to the second exposure mask of the present invention,
A shift film configured to have different optical path lengths for exposure light, a mask substrate formed on the upper or lower layer of the film, and a transmittance adjusting layer configured to have a predetermined transmittance for exposure light. Since it has a laminated structure with the semi-transparent film, it is possible to independently select the film that shifts the phase and the film that adjusts the transmittance, and obtain an exposure mask with high strength for cleaning and the like. be able to.

In the third aspect of the present invention, by adjusting the amplitude transmittance of the material forming the phase shifter, the shifter width effective for improving the contrast is increased and the precision required for the shifter width is relaxed. Therefore, a mask with high precision and high contrast can be easily formed.

As described above, according to the exposure mask of the present invention, it is possible to form a pattern with high accuracy and faithfulness to the pattern without depending on the pattern density.

[Brief description of drawings]

FIG. 1 is a diagram showing an exposure mask according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a light intensity distribution obtained as a result of performing a simulation by changing the transmittance of the exposure mask.

FIG. 3 is a diagram showing a change in contrast with respect to a change in transmittance formed using a dimension standardized by λ / NA.

FIG. 4 is a diagram showing an exposure mask according to a second embodiment of the present invention.

FIG. 5 is a manufacturing process diagram of the same exposure mask.

FIG. 6 is a diagram showing a relationship between injection conditions and transmittance.

FIG. 7 is a diagram showing a process of manufacturing an exposure mask according to a third embodiment of the present invention.

FIG. 8 is a view showing a manufacturing process of an exposure mask according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a fifth embodiment of the present invention.

FIG. 10 is a diagram showing an exposure mask according to a sixth embodiment of the present invention.

FIG. 11 is a manufacturing process diagram of the same exposure mask.

FIG. 12 is a diagram showing a process of manufacturing an exposure mask according to a seventh embodiment of the present invention.

FIG. 13 is a diagram showing a relationship between shifter width and contrast in the example.

FIG. 14 is a diagram showing an exposure mask according to an eighth embodiment of the present invention.

FIG. 15 is a diagram showing the relationship between the amplitude transmittance of the shifter and the contrast of the light intensity distribution with respect to the shifter width.

FIG. 16 is a diagram showing the relationship between the amplitude transmittance of the shifter and the contrast of the light intensity distribution with respect to the shifter width.

FIG. 17 is a diagram showing the relationship between the amplitude transmittance of the shifter and the shifter width.

FIG. 18 is a diagram showing the relationship between the amplitude transmittance of the shifter and the contrast of the light intensity distribution with respect to the shifter width.

FIG. 19 is a diagram showing the relationship between the amplitude transmittance of the shifter and the shifter width.

FIG. 20 is an explanatory diagram of a conventional phase shift method.

FIG. 21 is an explanatory diagram of a conventional phase shift method.

FIG. 22 is an explanatory diagram of a conventional phase shift method.

FIG. 23 is an explanatory diagram of a conventional phase shift method.

FIG. 24 is an explanatory diagram of a conventional phase shift method.

[Explanation of symbols]

 1 quartz substrate 2 mask pattern 3 Cr pattern 4 phase adjustment region 5 silicon oxide film 6 ion implantation layer 7 semitransparent layer 8 silicon oxide film 11 quartz substrate 12 mask pattern, 13 transparent film 21 quartz substrate 22 light shielding film 23 semitransparent film 31 Quartz substrate 32 semi-transparent film, 33 silicon oxide film.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 14, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

When the transmittance of the phase shifter in the mask having such a structure is assumed to be 100% and the shifter width is optimized, the optimum shifter width having the largest contrast improving effect differs depending on the pattern size. I understood. For example, as shown in FIG. 24, when an excimer stepper with NA = 0.42 is used, the optimum shifter width for a line and space of 0.3 μm is 0.04 μm (on the wafer) and 0.25 μm for a line and space. -The optimum space shifter width is 0.06 μm (on the wafer).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0046

[Correction method] Change

[Correction content]

This semitransparent film is made of p-TERPHENYL.
And PMMA were mixed at a ratio of 1: 4, and this was dissolved in ethyl cellosolve acetate and spin-coated to give a film thickness of 0.
After making it 25 μm, it is exposed and developed.
It is a line and space pattern with a width of 5 μm.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0088

[Correction method] Change

[Correction content]

First, as shown in FIG. 8A, a resist R is applied to a translucent fused silica substrate 1 having a size of 5 inches square and a thickness of 2.4 mm, and a photolithography process using EB exposure is performed. Then, this is patterned, and silicon ions are uniformly implanted into the entire surface through the resist pattern R to form a semitransparent layer 7 as shown in FIG. 8 (b). At this time, if the resist pattern R in the pattern area is adjusted for each transfer pattern size, the transmittance can be controlled to a desired value for each area.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0089

[Correction method] Change

[Correction content]

Next, the silicon oxide film 8 is formed by the liquid phase growth method.
Are selectively formed in the region surrounded by the resist pattern. Here, the silicon oxide film 8 and the semitransparent layer 7 have a phase difference of 180 degrees with the exposure light transmitted through the transparent substrate.
(Fig. 8 (c)).

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0090

[Correction method] Change

[Correction content]

Finally, the resist R is peeled off with an organic solvent or an acid to complete the exposure mask (FIG. 8 (d)).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroaki Inter-inventor Hiromu Komukai-shi, Kawasaki-shi, Kanagawa 1 Toshiba Research Institute, Inc. (72) Inventor Haruki Komano Komukai-shi Toshiba-cho, Kawasaki-shi, Kanagawa Toshiba Research Institute, Inc.

Claims (8)

[Claims] 1. An exposure mask comprising a light-transmissive substrate and a mask pattern made of a light-shielding material provided on the light-transmissive substrate, wherein the mask patterns have different optical path lengths with respect to the exposure light. An exposure mask, characterized in that it comprises a semi-transparent film pattern constructed as described above. 2. A semitransparent film pattern having a predetermined transmittance is used for a mask pattern having a value of 0.61 or less obtained by dividing a pattern dimension of the mask pattern by λ / NA of an exposure condition, The pattern size of the mask pattern is λ / N of the exposure condition.
The mask for exposure according to claim 1, wherein an opaque film pattern having a transmittance of almost 0 is used for a mask pattern whose value divided by A is 0.61 or more. . 3. The exposure mask according to claim 1, wherein the translucent film pattern has an amplitude transmittance determined according to its pattern size. 4. The exposure according to claim 1, wherein the semitransparent film pattern has a plurality of regions having different amplitude transmittances, which are divided into fine regions that are not resolved by exposure light. Mask. 5. The exposure mask according to claim 4, wherein the semi-transparent film pattern is configured to control the amplitude transmittance according to the occupied area ratio of the fine region. 6. The exposure mask according to claim 4, wherein the translucent film pattern includes a region whose amplitude transmittance is changed by ion implantation. 7. An exposure mask comprising a light-transmissive substrate and a mask pattern made of a light-shielding material, which is disposed on the light-transmissive substrate, and has different optical path lengths with respect to the exposure light. A shift film, a mask substrate formed on the upper or lower layer of the film, and a semi-transparent film as a transmittance adjusting layer configured to have a predetermined transmittance for exposure light are laminated. An exposure mask that is characterized by 8. A light-transmitting substrate, a mask pattern made of a light-shielding material provided on the light-transmitting substrate, and arranged around the mask pattern so as to have different optical path lengths for exposure light. And a phase shifter having an exposure condition of λ / N
When the value divided by A becomes 0.34 to 0.68, the amplitude shift factor of the phase shifter is set to 100% or less, and the phase shifter width is determined to be large according to the amplitude shift factor. Exposure mask.