JP3343113B2 - Exposure mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure mask, and more particularly to a lithography mask.

[0002]

2. Description of the Related Art Semiconductor integrated circuits are becoming ever more highly integrated and finer. When manufacturing the semiconductor integrated circuit,
Lithography technology is particularly important as a key to processing.

In the current lithography technology, a method of projecting and exposing a mask pattern onto an LSI substrate via a reduction optical system is mainly used. If a high-pressure mercury lamp is used as a light source, the minimum line width is about 0.5 μm. Is the limit. 0.5μ
Direct patterning technology using KrF excimer laser or electron beam and X-ray equal-size exposure technology are being developed for pattern dimensions of m or less. However, photolithography is required for mass production and process versatility. Expectations have become very high.

In such a situation, the light source is G
The use of various light sources such as X-rays, i-rays, excimer lasers, and X-rays is being studied.Development of new resists and new resist treatments such as REL are also being studied for resists. Research is also being conducted on the CEL image reverse method and the like.

[0005] On the other hand, for the mask manufacturing technology,
Though not fully reviewed, the 1982 IBM
A phase shift method has been proposed and attracted attention by Levenson et al.

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

This principle will be described with reference to FIG. In this method, as shown in FIG. 12A, chromium (Cr) formed on a quartz substrate 11 by a sputtering method or the like is used.
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. The amplitude of the light is canceled at the boundary between the two transmitting portions (FIG. 12C). As a result, the light intensity at the boundary between the two transmission portions becomes 0, and the pattern formed on the wafer can be separated from the two transmission portions as shown in FIG.

In this way, a 0.7 μm pattern was resolved by a 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 needs to have a relationship of d = λ / 2 (n−1) where n is the refractive index of the shifter material and λ is the exposure wavelength.

Further, Terazawa et al. Of Hitachi have further developed the technology of Levenson et al. And applied it to an isolated pattern as shown in FIG. In this method, in addition to the isolated pattern a, an auxiliary pattern b as a dummy which is not resolved alone is provided, and a shifter 13 for inverting the phase is provided in this portion. In this method, with an i-line stepper having NA = 0.42, an isolated space of 0.3 μm and 0.4 are used.
The contact hole having a diameter of μm was resolved, and the resolution was improved by about 30% as compared with the conventional method. However, the smaller the pattern size of the contact hole, the smaller the light intensity difference between the auxiliary pattern and the auxiliary pattern. Therefore, there is a limit that the light intensity transmitted through the transmission portion is weakened as a whole and no resolution is achieved.

Further, in the above-described method, a shifter is provided for every other transmission part for lines and spaces, and a mask layer is processed for an auxiliary pattern for isolated patterns, and Because of the arrangement, there is a problem that the alignment of the shifter with respect to the mask pattern and a selective processing technique are required, so that the number of steps is greatly increased and the manufacturing process of the mask is complicated.

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

FIG. 14 illustrates this principle. This mask is
As shown in FIG. 14A, a phase shifter formed so as to protrude around a mask pattern 12 made of a laminated film of chromium (Cr) and chromium oxide (Cr ₂ O ₃ ) formed on a quartz substrate 11. As shown in FIG. 14 (b), using a mask having a transparent film 13 as a mask, the phase of this portion is reversed, and the light having a phase of 0 ° and a phase of 180 ° cancel each other at both ends of the transmission portion, and the light The intensity is reduced and the contrast is improved (FIG. 14C). As a result, the light intensity at both ends of the transmissive portion becomes almost zero, and the pattern formed on the wafer can be separated from the two transmissive portions as shown in FIG.

This mask is formed as follows.

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

Next, as shown in FIG. 15B, using this resist pattern as a mask, this mask layer 1 is formed by a wet etching method or a reactive ion etching method.
2 is patterned, and the resist pattern R is peeled off.

Thereafter, as shown in FIG.
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 composed of a PMMA film pattern, as shown in FIG.

Finally, as shown in FIG.
Using the phase shifter 13 composed of the MMA film pattern as a mask, side etching of the mask
A mask formed so that the phase shifter 13 projects from 2 is completed.

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

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

When exposure is performed using such a mask,
Since the light passing through each opening has a phase inverted with respect to each other as shown by a broken line, the light intensity at a portion below the mask layer is greatly reduced, and the light as a whole is represented by a solid line. In view of the intensity distribution, it is possible to achieve resolution up to almost half the size as compared with the case where a conventional mask is used.

When the transmittance of the phase shifter is assumed to be 100% in the mask having such a structure 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, when an excimer stepper with NA = 0.42 as shown in FIG. 16 is used, the optimum shifter width of a 0.3 μm line and space is 0.04 μm (on a wafer) and a 0.25 μm line and space. The optimum shifter width of the space 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 could not be resolved conventionally can be obtained. Is also possible.

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

Such a shifter pattern must use either a permeable film or an anti-permeable film. However, the mask used in the manufacturing process of the VLSI must be in a state where there is no adhesion of dust, so that frequent cleaning is required. For this reason, the phase shift mask also needs to have a strength that can withstand repeated cleaning, but if a shifter is formed of a resist, it cannot be used at all in terms of strength.

[0026]

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

Further, there is no mask which can be used sufficiently in strength as a mask used in a process for manufacturing an VLSI.

The present invention has been made in view of the above circumstances, and has as its object to provide an exposure mask capable of improving the resolution limit of a transfer device and performing faithful pattern transfer with a constant light amount. I do.

[0029]

Therefore, in an exposure mask according to the present invention, a first mask pattern made of a light-shielding material disposed on a transparent substrate, and the first mask pattern on the first mask pattern are provided. A second mask pattern comprising a phase shifter disposed so as to protrude from an edge of the pattern, wherein the second mask pattern has a value obtained by dividing a pattern dimension by λ / NA of an exposure condition. Is 0.34
To 0.68, and the phase shifter is semi-transparent.

[0030]

As a result of examining the light image intensity distribution projected on the wafer by changing the shifter transmittance by simulation, a translucent film pattern having a predetermined transmittance is used instead 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.
With the above configuration, the resolution of the fine pattern becomes easy. Further, the patterning of the phase shifter can be performed once without performing the patterning separately from the light-shielding film pattern, so that the pattern control is easy.

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

Incidentally, an optical image depends on NA (numerical aperture of an optical system) and λ (wavelength).

However, when the pattern dimension w is normalized as shown in the following equation, γ = w / (λ / NA), optical images having the same normalized dimension γ are completely similar with a similarity ratio λ / NA. NA / λ represents a cutoff frequency in the spatial frequency domain, and its reciprocal λ / NA represents a cutoff frequency of 1
The frequency is equivalent to one division obtained by dividing the frequency by NA / λ. By dividing each pattern dimension by this λ / NA in this manner, the position occupied by the dimension in the spatial frequency domain can be normalized.

As a result of repeating various experiments using the standardized dimensions, the standardized dimensions (values divided by the exposure condition λ / NA) were obtained.
Is particularly effective for a mask pattern having a value of 0.61 or less. Therefore, a mask using a translucent film having a transmittance of 0 to 50% and a phase shift of 180 ° is used only for a mask pattern whose value divided by the exposure condition λ / NA is 0.61 or less. By forming a pattern, a phase shift effect can be easily obtained,
It is possible to resolve a pattern that cannot be resolved with a conventional mask. The transmissivity of the translucent film may be set to a value at which the contrast is optimal according to the pattern size.

Further, the present inventors conducted a simulation using a program for obtaining an optical image intensity distribution in order to obtain an optimum relationship between an amplitude transmittance and a shifter width in a line-and-space at equal intervals. . From this result, it was found that the amplitude transmittance of the shifter having the maximum contrast differs depending on the shifter width, and that the smaller the amplitude transmittance, the larger the shifter width. As a result, it was found that this phenomenon was common when the value obtained by dividing the pattern size of the mask pattern by the exposure condition λ / NA was 0.34 to 0.68. Therefore, by adjusting the transmittance of the shifter arbitrarily in each pattern dimension within this range, a large contrast improvement effect can be obtained with a shifter width in a range where sufficient precision for shifter processing can be obtained.

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

[0038]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a view showing a cross section of an exposure mask according to a first embodiment of the present invention.

This exposure mask is a quintuple mask. A 1.5 μm line-and-line made of a translucent film having a thickness of 0.25 μm and a transmittance of 6% is formed on the surface of the translucent quartz substrate 1. The 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 translucent film is made of p-TERPHENYL
And PMMA were mixed at a ratio of 1: 4, and the resulting mixture was dissolved in ethyl cellosolve acetate and spin-coated.
After adjusting the thickness to 25 μm, exposure and development were performed, and 1.
This is a line and space pattern having a width of 5 μm.

The exposure mask thus formed is mounted on a KrF excimer laser stepper having a projection lens with NA = 0.42, and the SAL6
Pattern transfer (λ = 248 nm, coherency σ =
0.5) and developed with a special developer.

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

Next, in order to determine the optimum shifter transmittance in the line-and-space pattern at equal intervals, a simulation was performed using a program for uniquely calculating 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), coherency σ = 0.5 was set. Here, as shown in FIG. 1, a translucent quartz substrate 11 is composed of three types of translucent films of three kinds of transmissivity T = 0% (chromium), T = 6%, and T = 20%. Using a mask pattern 2 having a line-and-space pattern having a width of 3 μm, a change in the light image intensity distribution with respect to each transmittance was examined.

FIGS. 2A to 2C show a pattern size of 0.3.
The transmittance of a μm line and space pattern is defined as T =
The light intensity distribution obtained as a result of performing a simulation by changing 0% (chromium), T = 6%, and T = 20% is shown. From this result, it can be seen that the valley portion of the light intensity distribution is almost 0 when T = 6%, and that the contrast is improved when T = 0%.

Further, the following equation C = (Imax-Imin)
/ (Imax + Imin) (Expression) Imax Light intensity of the peak of the light intensity distribution waveform Imin Light intensity of the valley of the light intensity distribution waveform C ... The contrast is calculated using the contrast, and FIG. 7 shows a change in contrast with respect to a change in transmittance of a pattern formed using the reduced dimensions. Curves 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), 0.2
The change in contrast with the change in transmittance at 39 (0.23 μm) and 0.34 (0.20 μm) is shown.

In the case of line and space, 0.37 μm
m, the contrast decreases as the transmittance of the shifter increases, but the pattern size is 0.25 μm.
, The transmittance is 16%, and the transmittance is 6% and 0.3 at 0.3 μm.
At 5 μm, the transmittance is 3% and the contrast is maximum.

From this result, it is found that a light-shielding film of chromium or the like is used for a pattern of 0.36 μm or more (normalized value of 0.61) or more, and the transmittance is reduced from 0% to 20% for a pattern smaller than 0.36 μm. It can be seen that the use of the adjusted translucent shifter makes it possible to resolve a fine pattern.

When the result of FIG. 3 is multiplied by λ / NA of each exposure condition, the transmittance of the translucent film which maximizes the contrast according to the pattern size under the exposure condition is obtained. Obtainable.

FIG. 3 shows that a light-shielding film such as chrome is used for a pattern having a standardized pattern size of 0.61 or more, and a translucent film is used for a smaller pattern. When the rate is set in the range of 0 to 50%,
It can be seen that the contrast can be improved. Here, the optimum transmittance is 50% at the normalized size of 0.39, 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 larger than 50%. You can see that.

Incidentally, a dye may be added to the translucent film to adjust the transmittance.

Embodiment 2 FIG. 4 is a sectional view showing a manufacturing process of an exposure mask according to a second embodiment of the present invention. This exposure mask forms a Cr film pattern with a thickness of 100 nm on the surface of a translucent quartz substrate 11 and has a phase shifter width of 0.6 μm consisting of a translucent film with a thickness of 0.25 μm and a transmittance of 30%. The shifter 121 is formed. First, FIG.
As shown in FIG. 2, p-TERPH is formed on the surface of the transparent quartz substrate 11 on which a Cr film pattern having a thickness of 100 nm is formed.
ENYL and PMMA were mixed at a ratio of 1: 4, and this was dissolved in ethyl cellosolve acetate and spin-coated.
The thickness is set to 0.25 μm. The amplitude transmittance of this phase shifter was 30%.

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

Then, as shown in FIG.
Development was performed with SK.

Thereafter, as shown in FIG. 4D, Cr was side-etched with a ceric ammonium nitrate solution to form a mask so that the shifter width became 0.6 μm on the mask.

The exposure mask thus formed is mounted on a KrF excimer laser stepper having a projection lens with NA = 0.42, and the SAL6
Pattern transfer (λ = 248 nm, coherency σ =
0.5) and developed with a special developer.

As a result, it is possible to obtain a resist pattern composed of a high-precision 0.25 μm and 0.3 μm wide line-and-space pattern that 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 at a pattern size of 0.3 μm is 0.2 μm on the mask, but ± 0.1 μm on the process.
A variation of about m occurs. The decrease in contrast caused by the error in the shifter width is considerably large at 0.05 as a relative value as shown in FIG.

On the other hand, the amplitude transmittance of the phase shifter 30
In the case of the optimal shifter width of 0.6 μm, the contrast is reduced by 0.00 as shown in FIG. 5B even with the same error of ± 0.1 μm.
5 and very small.

As described above, by lowering the transmittance of the shifter and increasing the shifter width, it is possible to suppress a decrease in contrast due to an error in the shifter width, and as a result, it is possible to provide a good resist pattern.

Next, as shown in FIG.
In order to obtain the optimum relationship between the amplitude transmittance in the AND space and the shifter width δ, a simulation was performed using a program for obtaining an optical image intensity distribution. Exposure conditions are KrF excimer laser light, NA = 0.42, λ = 248.
nm and coherency σ = 0.5. FIGS. 7A to 7E show combinations having the highest contrast when the amplitude transmittance and the shifter width are changed. From this result, it was found that the smaller the amplitude transmittance, the larger the shifter width.

FIG. 8 shows the change in the contrast of the light image intensity distribution when the amplitude transmittance is changed while the shifter width is fixed in the 0.3 μm line and space.

From this figure, it can be seen that the amplitude transmittance of the shifter at which the contrast is maximum differs depending on the shifter width.
FIG. 9 shows the measurement result of the relationship between the amplitude transmittance of the shifter and the shifter width when the contrast is maximized. From this figure, it is understood that the shifter width can be increased by decreasing the shifter amplitude transmittance.

FIG. 10 shows the change in the contrast of the light image intensity distribution when the amplitude transmittance is changed while the shifter width is fixed in the 0.25 μm line and space.

FIG. 11 shows the result of measuring the relationship between the amplitude transmittance of the shifter and the shifter width when the contrast is maximized. Also in this case, a 0.3 μm line and
Same as space.

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

The present invention has been described with reference to the embodiment. In the embodiment, the transparent film as the phase shifter has been described as a polymethyl methacrylate also used as a resist and a silicon oxide layer as an inorganic film.
The material is not limited to these, and may be a material having a high transmittance to light having a wavelength of 436 nm or less used as exposure light. For example, as the inorganic film, another material such as calcium fluoride (CaF), magnesium fluoride (MgF), and aluminum oxide (Al ₂ O ₃ ) may be used.

As the resist serving as the phase shifter, materials such as polymethyl methacrylate, polytrifluoroethyl-α-chloroacrylate, chloromethylated polystyrene, polydimethylglutarimide, and polymethylisopropenyl ketone can be considered. Further, the thickness of the pattern and the like can be appropriately changed according to the material and the lithography light.

Further, the materials of the light-transmitting substrate and the light-shielding film are not limited to those in the embodiments, but can be changed as appropriate.

In addition, the phase shifter layer does not necessarily have to perform a phase shift of 180 degrees. If the light intensity distribution of the pattern edge is sharply reduced in the vicinity of 180 degrees, the phase shifter is slightly increased. It may be off.

[0072]

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

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

[Brief description of the drawings]

FIG. 1 is a view 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 while 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 dimensions standardized by λ / NA.

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

FIG. 5 is a diagram showing a relationship between shifter width and contrast in the embodiment.

FIG. 6 is a view showing an exposure mask according to a third embodiment of the present invention.

FIG. 7 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. 8 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. 9 is a diagram showing the relationship between the amplitude transmittance of the shifter and the shifter width.

FIG. 10 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. 11 is a diagram showing a relationship between the amplitude transmittance of a shifter and a shifter width.

FIG. 12 is an explanatory diagram of a conventional phase shift method.

FIG. 13 is an explanatory diagram of a conventional phase shift method.

FIG. 14 is an explanatory diagram of a conventional phase shift method.

FIG. 15 is an explanatory diagram of a conventional phase shift method.

FIG. 16 is an explanatory diagram of a conventional phase shift method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Quartz substrate 2 ... Mask pattern 3 ... Cr pattern 4 ... Phase adjustment area 5 ... Silicon oxide film 6 ... Ion implantation layer 7 ... Semi-transparent layer 8 ... Silicon oxide film 11 ... Quartz substrate 12 ... Mask pattern 13 ... Transparent film

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroaki Ma 8-8 Shinsugita, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Works Co., Ltd. (56) References JP-A-3-45951 (JP, A) JP-A-3-242648 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (1)

(57) [Claims] A first mask pattern made of a light-shielding material provided on a transmissive substrate; and a first mask pattern provided on the first mask pattern so as to protrude from an edge of the first mask pattern. A second mask pattern comprising a phase shifter, wherein a value obtained by dividing a pattern dimension by λ / NA of an exposure condition is 0.34 to 0.68. An exposure mask, wherein the phase shifter is translucent.