JP3333502B2 - Phase shift 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 used for manufacturing a semiconductor integrated circuit and the like, and more particularly to a phase shift mask whose resolution is improved by utilizing a phase shift method.

[0002]

2. Description of the Related Art In recent years, semiconductor integrated circuits have continued to be highly integrated and miniaturized, and in the manufacture thereof, lithography is important as a key to fine processing. In the lithography technology, for example, for a light source, g-line, i-line,
The use of various light sources such as excimer lasers and X-rays is being studied, and new resist materials suitable for each light source are being developed for resist materials. Further, researches on resist processing techniques such as a multilayer resist method, a CEL (Contrast Enhancement Layer) method, and an image reverse method have been advanced.

On the other hand, regarding the mask manufacturing technology,
Although not sufficiently studied so far, a phase shift method has recently been proposed (MDLevenson, N. et al.
S.Viswanathan and RASimpson: IEEE Trans.ED-29 (1
982) 1828).

FIG. 20 shows the principle of the phase shift method. this
The phase shift method proposed by Levenson et al. Is effective for simple repetitive patterns such as line and space because of its principle.However, when a complex pattern is formed, the phase of light transmitted through the adjacent openings is reduced. Since a portion having the same phase is generated, the effect as the phase shift method is significantly reduced.

When the conventional phase shift method is applied to an electronic device such as a DRAM, it is effective in a portion having a large number of simple repetitive patterns such as a cell array portion, but is effective in a portion derived from the cell array portion to a peripheral circuit (such as a sense amplifier). )
In many cases, a complicated pattern arrangement is used, and if a conventional phase shift method is applied to this portion, the pattern must be rewritten so that the phase shifter can be easily arranged. For this reason, the conventional phase shift method has great restrictions in design.

On the other hand, the shifter material of the phase shift mask has the following problems. Until now proposed highly permeable to the phase shifter has a resist (PMMA, etc.) or a CVD method or a sputtering method in forming the SiO ₂ film, SiO ₂ film formed by a coating such as SOG, a portion to be a shifter by etching Some are engraved. Among these methods, the method of forming a shifter layer by etching is based on the fact that the transmitted light intensity between the phase shifter and the normal opening differs depending on the shape of etching, residue, etc., and the resolution pattern formed by the phase shifter and the normal opening However, there is a problem that non-uniformity occurs. Further, even if the phase shifter is formed of a material having a high transmittance, it cannot be avoided that the intensity of light passing through the substrate opening and the intensity of the light passing through the phase shifter are different.

[0007]

As described above, conventionally, a method of forming a phase shifter by etching includes the values of the light intensity transmitted through the opening of the substrate and the light intensity transmitted through the phase shifter due to the shape of etching, residue, and the like. Was different. For this reason, the resolution pattern formed by the phase shifter portion and the opening of the transparent substrate becomes non-uniform, causing a problem that an exposure pattern is not formed as desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to make the light intensity transmitted through the substrate opening close to the light intensity transmitted through the phase shifter. An object of the present invention is to provide a phase shift mask capable of improving the uniformity of a resolution pattern formed by an opening in a transparent substrate.

[0009]

(Structure) In order to solve the above-mentioned problem, the present invention employs the following structure.

That is, the present invention provides a phase shifter in which a light-shielding film having a desired opening pattern is formed on a light-transmitting substrate, and a phase shift material for shifting the phase of transmitted light is formed in a part of the opening pattern. In the mask, a buffer film made of the same material as the phase shift material is formed on both the transmission part made of the opening pattern in which the phase shift material is not formed and the shifter part made of the opening pattern in which the phase shift material is formed. The thickness of the buffer film is adjusted so that the transmittance of light passing through the section and the shifter section becomes substantially equal.

[0011] than the features specifically, the present invention, SiO ₂ film was formed by the phase shifter having a high permeability resist (PMMA, etc.) or a CVD method or a sputtering method, SiO ₂ film or the like formed by a coating such as SOG The same material as the phase shifter is formed on the entire surface (the area including the substrate opening and the phase shifter) of the mask formed by the film formation of the phase shift mask and formed through a normal phase shift mask manufacturing process. Form by process. By selecting the film thickness of the same material as the phase shifter formed on the entire surface as in the following equation (the value of the film thickness is determined by the exposure wavelength and the refractive index of the phase shifter material),
The light intensity transmitted through the substrate opening and the light intensity transmitted through the phase shifter can be made equal.

[0012] _{h = (λ / 4n s)} {m-n s / (n s -1)} where, n _s: the shifter refractive index, lambda: the exposure wavelength, m: is an integer.

As a result, a desired pattern can be formed without causing non-uniformity in the resolution pattern formed by the phase shifter and the opening of the transparent substrate. According to the above equation, the film thickness h becomes a negative value depending on the value of m, but this is unreasonable in manufacturing the mask. Therefore, m should be selected so that h ≧ 0. Further, it is desirable that the film thickness h be as small as possible, that is, the value of m should be a small value, from the relation of the throughput in manufacturing the mask. But h
Is too small, a uniform and highly accurate film cannot be formed because the film formation time is short. It is considered that the value of m is suitably from 6 to 9 from the throughput of mask production and the stability of film formation.

Further, when a mask pattern and a phase shift pattern are formed on the light transmitting substrate, and the deviation of the phase rotation angle of the light transmitted through the phase shift material from a desired value is within ± 10 °, the phase shift pattern The ratio of the light intensity transmitted through the opening where the phase shift pattern is formed to the light intensity transmitted through the opening where no is formed is 0.99.
A material having a refractive index of 1.01 to 1.01, more preferably 0.995 to 1.005 is used as the phase shift material.

(Function) In the present invention, the phase shifter is formed by applying a highly transmissive resist, a SiO ₂ film formed by a CVD method or a sputtering method, or a SiO ₂ film formed by applying SOG or the like.
When the phase shifter and the transparent substrate are formed by film formation such as _two films, multiple reflection occurs at the interface between the phase shifter and the transparent substrate unless the refractive indices for the exposure wavelength of the phase shifter and the transparent substrate are strictly adjusted, and as shown in FIG. Light intensity I transmitted through the opening
The value of the light intensity I _s transmitted through _q phase shifter varies. This means that the size of the resolution pattern formed by the phase shifter and the opening of the substrate becomes non-uniform. This problem can be solved by equalizing the refractive indices of the phase shifter and the transparent substrate. However, it is almost impossible to make the refractive indices exactly the same as long as the phase shifter film is formed.

Therefore, in the present invention, by forming the same buffer film as the phase shifter material in both the substrate opening and the phase shifter, multiple reflections are actively generated in both the substrate opening and the phase shifter. By making the effects of these multiple reflections equal, non-uniformity does not occur in the resolution pattern dimensions formed by the phase shifter and the substrate opening. The reason why the effects of multiple reflections are equal is to adjust the thickness of the buffer film optimally as described later. Here, a method of preventing the phase shifter from being formed by film formation so that the effects of multiple reflections are equal on the entire surface of the mask and that the resolution pattern dimension formed by the phase shifter portion and the substrate opening does not become non-uniform. The principle will be described.

Consider multiple reflection in the shifter in the two-layer structure of the transparent substrate / shifter shown in FIG. n _q , n
_s is the refractive index at the exposure wavelength of the transparent substrate and the phase shifter, respectively, the amplitude transmittance for the incident light from the transparent substrate to the phase shifter is t ₁ , the amplitude reflectance from the phase shifter to the transparent substrate is r ₁ , The amplitude transmittance and the amplitude reflectance from the phase shifter to the air are defined as t ₂ and r ₂ , respectively. The thickness of the shifter is h. When light having a wavelength λ and an amplitude a ₀ enters a transparent substrate at an angle φ ₀ and exits into the air, L ₁ , L ₂ ,
The amplitudes of L ₃ are a ₀ t ₁ t ₂ , a ₀ t ₁ t ₂ r ₁ r ₂ ,
_{a 0 t 1 t 2 (r} 1 r 2) 2 ... a because the complex amplitudes of the interference wave combined these added _{is, a t = a 0 t 1} t 2 + a 0 t 1 t 2 (r 1 r 2 ) given by _{exp (iδ) + a 0 t} 1 t 2 (r 1 r 2) 2 exp (i2δ) + ... = a 0 t 1 t 2 / (1-r 1 r 2 exp (iδ)) ... (1) Can be

Here, the phase difference δ between adjacent light fluxes is shown in FIG.
It is more δ = k {(AB + BC ) n s -AP} = (4πhn / λ) cos φ 1 ... (2).

The intensity of the interference light is _{therefore, I t = | a t |} 2 = a 0 2 t 1 2 t 2 2 / {1+ (r 1 r 2) 2 -2r 1 r 2 cos δ} ... (3) Here, r ₁ , r ₂ , t ₁ , and t ₂ are perpendicular incidence (φ ₁ =
0) _{When, r 1 = (n q -n} s) / (n q + n s) r 2 = (1-n s) / (1 + n s) t 1 = 2n q / (n s + n q) t 2 = because it is _{2n s / (1 + n s} ) ... (4), the ratio of transmitted light intensity I _t to incident intensity I _a = _{a o} ² is

(Equation 1) Next, since [delta] is (2) from equation _{δ = 4πhn s / λ ... (} 6), the [delta] of the light phase with respect to the opening that is not in contact arrangement the shifter transmits only shift shifter theta (6) δθ the equation _{= (4πn s / λ) ·} λ / {2 (n s -1)} · θ / π = {2n s / (n s -1)} θ ... (7) substrate opening and the phase shifter portion In order to make the intensity of light transmitted through the phase shifter equal, the same material as that of the phase shifter is formed on the entire surface by the phase angle δθ. At this time, I _t / I _a expressed by the equation (5)
Since equal in substrate opening and the phase shifter portion, cos (δπ + δθ) = cos δθ ∴θ = {(n s -1) / 2n s} {m- (n s / (n s -1))} π ... (8) (6) (7) (8) h = from equation _{(λ / 4n s) {m-} (n s / (n s -1))} (m = 1,2,3 ...) ... (9) Therefore, if a film of the same material as the phase shifter having a film thickness h that satisfies the expression (9) is formed on the entire surface, the influence of multiple reflection at the substrate opening and the phase shifter becomes the same, and the transmitted light intensity of each Are equal.

Next, consider the allowable range of the refractive index of the shifter material when a film of the same material as the phase shifter is not formed on the entire surface. In this case, the difference in light intensity transmitted through the substrate opening and the phase shifter portion is within 1% is allowable range of the light intensity of the substrate _{opening, | (I s -I q)} / I q) | ≦ 0. 01… (10) From equations (5) and (10)

(Equation 2)

Now, assuming that the allowable range of the deviation of the phase shifter film thickness from 180 ° is ± 10 °, 170 ° ≦ δ ≦ 190 ° (12) The refractive index _nq of the transparent substrate is uniform according to the exposure wavelength λ. Therefore, the shifter refractive index n _s that simultaneously satisfies the expressions (8) and (9) is a desirable value in view of the multiple reflection at the shifter substrate interface and the shift amount of the shifter film thickness from 180 °. You should choose a material with a high refractive index value.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 shows the structure of a phase shift mask according to a first embodiment of the present invention.
(A) is a plan view, (b) and (c) are views AA 'of (a).
It is sectional drawing. First, in FIG. 1B, a light-shielding film pattern 2 is formed on a transparent substrate 1. The material of the transparent substrate 1 is, for example, quartz, and the material of the light shielding film 2 is, for example, chromium oxide. Further, a phase shifter 3 having a thickness tt = λ / 2 ( _ns− 1) × φ / 180 (13) is formed in a region having an opening on the transparent substrate 1. Here, λ: exposure wavelength, n _s : refractive index of the phase shifter at the exposure wavelength, φ:
This is the phase difference from the light transmitted through the transparent opening 101.

The thickness of the phase shifter 3 formed in one opening is the same in the region of the opening. As a material of the phase shifter 3, for example, an SiO ₂ film formed by a liquid phase growth method, a sputtering method, a coating method, a CVD method, or the like can be considered.

Now, the exposure light is i-line (λ = 365 nm),
If the phase shifter material is a SiO ₂ film formed in a liquid phase, the refractive index of the phase shifter at the i-line wavelength is ns = 1.44.
Since the phase difference is 6, when the phase difference between the light transmitted through the phase shifter 3 and the light transmitted through the transparent opening 101 is desired to be 180 °, the thickness of the phase shifter 3 may be set to 409 nm according to Expression (13). You can see that. Similarly, it can be seen that the phase shifter 3 having a thickness of 204.5 nm is required to have a phase difference of 90 ° and the phase shifter 3 having a thickness of 613.5 nm is required to have a phase difference of 270 °. At this time, the allowable range of the film thickness error of the phase shifter 3 is within ± 10% of the desired film thickness.

As described above, in the conventional Levenson-type phase shift method, since the phase shift mask is formed only by the phases of 0 ° and 180 °, the combination in which the phases of adjacent patterns are different is (0 °, 180 °). There was only one type, and thus the design had great restrictions. Therefore, FIG.
By adding a new 90 ° and 270 ° phase shifter as shown in (b), combinations of adjacent patterns having different phases are (0 °, 90 °), (0 °, 180 °), (0 °, 2 °).
70 °) (90 °, 180 °) (90 °, 270 °)
(180 °, 270 °), which greatly reduces design constraints.

FIG. 1B shows an example in which the phase shifter 3 is formed on the transparent substrate 1, but the phase shifter shown in FIG.
It may be formed by engraving as shown in FIG. In this case, the amount of engraving is represented by Expression (13), and it goes without saying that n _s is the refractive index of the transparent substrate at the exposure wavelength. At this time, the allowable range of the engraving amount error is within ± 10% of the desired engraving amount.

As described above, conventionally, 180 ° shifters are alternately arranged in a repetitive pattern such as line and space in order to enhance the effect of the Levenson-type phase shift method. However, when a shifter is arranged in the opening as in this reference example, a sufficient effect as a phase shift method can be obtained by disposing a shifter of, for example, 0 °, 90 °, 180 °, or 270 °. Further, the degree of freedom in design increases.

As a specific arrangement, (0 °, 180 °) is required for a pattern portion requiring periodic or high resolution, such as a memory cell array pattern of a high density memory element.
°) phase combination (relative phase difference 180 °)
For other patterns, combinations of adjacent patterns having different phases (0 °, 90 °), (0 °, 180 °),
(0 °, 270 °), (90 °, 180 °), (90
°, 270 °), (180 °, 270 °) (relative phase difference 90 ° or 180 °), the cell array section can obtain a high resolving power.
In other parts, design constraints are relaxed.

(Second Embodiment) FIG. 2 is a sectional view showing a manufacturing process of a phase shift mask according to a second embodiment of the present invention. In this embodiment, a method for manufacturing a phase shift mask using a liquid phase growth method will be described.

First, as shown in FIG. 2A, a pattern made of a light shielding film 11 is formed on a transparent substrate 10. As the transparent substrate 10, for example, a quartz substrate is used, and as the light-shielding film 11, for example, chromium oxide having a thickness of 100 nm is used.

Next, as shown in FIG. 2B, the resist is formed so that the resist 12 is formed on the transparent substrate opening 110 where the shifter is not formed and the transparent substrate opening 112 where the 180 ° shifter is formed. Perform patterning. That is, an opening in which a phase shifter whose fractional part is 0.44 or more and 0.55 or less when the phase is divided by 180 ° is defined as a cutout pattern. For patterning the resist, an electron beam or optical lithography may be used.

Next, a liquid phase in which silicon oxide is dissolved in supersaturation
A transparent substrate is immersed inside, and as shown in FIG.
A silicon oxide film 13 is grown in the opening. Let it grow at this time
The thickness of the silicon oxide film 13 depends on the light transmitted through the phase shifter.
The phase difference of the light transmitted through the transparent substrate is close to 90 °
Film thickness. At this time, the tolerance of the thickness error of the phase shifter
The range is within ± 10% of the desired film thickness. Now, exposure light
Is the i-line (λ = 365 nm), using the liquid phase growth method
The refractive index of the silicon oxide formed at the i-line wavelength is n _s= 1.
446, the silicon oxide film 13 formed at this time is
The film thickness becomes a value close to 204.5 nm.

Next, as shown in FIG. 2D, the resist 12 is peeled off by using the SH method or the Asher method.
Next, as shown in FIG. 2E, the resist is patterned so that the resist 14 is formed on the transparent substrate opening 110 where the shifter is not formed and the transparent substrate opening 111 where the 90 ° shifter is formed. That is, the phase is set to 180
An opening where a phase shifter having a value a _i of 0.94 <a _i when divided by ° is formed as a cutout pattern. For patterning the resist, an electron beam or optical lithography may be used.

Next, a liquid phase in which silicon oxide is dissolved in supersaturation
A transparent substrate is immersed inside, and as shown in FIG.
A silicon oxide film 15 is grown in the opening. Let it grow at this time
The thickness of the silicon oxide film 15 depends on the light transmitted through the phase shifter.
The phase difference of the light transmitted through the transparent substrate is close to 180 °
Film thickness. At this time, the tolerance of the thickness error of the phase shifter
The range is within ± 10% of the desired film thickness. Now, exposure light
Is the i-line (λ = 365 nm), using the liquid phase growth method
The refractive index of the silicon oxide formed at the i-line wavelength is n _s= 1.
446, the thickness of the silicon oxide film formed at this time
Is a value close to 409 nm. Then, as shown in FIG.
As shown in the figure, the resist is
And peel off.

As a result, a phase shifter (90 °) having a thickness of 204.5 nm is formed in the substrate opening 111 by the first growth of the silicon oxide film 13, and the second silicon oxide film 15 is formed.
A phase shifter (180 °) having a thickness of 409 nm is formed in the substrate opening 112 by the growth of the silicon oxide film 13, and a film thickness of 61 is formed in the substrate opening 113 by the first and second growths of the silicon oxide films 13 and 15.
A 3.5 nm phase shifter (270 °) will be formed.

As described above, when the method of manufacturing the phase shift mask of the present embodiment is used, the thickness of the phase shifter becomes 9
Although there are three types, 0 °, 180 °, and 270 °, the resist patterning on the mask after the formation of the light-shielding film pattern is performed only twice, and the mask manufacturing process can be shortened. Furthermore, a 90 ° phase shifter (ie, a phase shifter with a small thickness)
Therefore, during the second resist patterning on the mask (FIG. 2E), the influence of the step on the base (the step between the phase shifter and the light-shielding film) can be minimized.

(Third Embodiment) FIG. 3 is a sectional view showing a manufacturing process of a phase shift mask according to a third embodiment of the present invention. In this embodiment, a method of applying a liquid silicon oxide film (eg, SOG), a method of manufacturing a phase shift mask using a sputtering method, or a CVD method will be described.

First, as shown in FIG. 3A, a pattern made of a light shielding film 17 is formed on a transparent substrate 16. As the transparent substrate 16, for example, a quartz substrate is used, and as the light-shielding film 17, for example, chromium oxide having a thickness of 100 nm is used.

Next, as shown in FIG. 3B, a silicon oxide film 18 is formed on the entire surface of the mask by using a method of applying a liquid silicon oxide film (eg, SOG), a sputtering method, or a CVD method. The thickness of the silicon oxide film 18 formed at this time is such that the phase difference between the light transmitted through the phase shifter and the light transmitted through the transparent substrate is close to 90 °. At this time, the allowable range of the thickness error of the phase shifter is ±
It is within 10%. Now, the exposure light is changed to i-line (λ = 365n).
m), i of silicon oxide formed using the CVD method
Since the refractive index of a line wavelength is n _s = 1.446, thickness of the silicon oxide film 18 formed at this time becomes a value close to 204.5Nm.

Next, as shown in FIG.
Transparent substrate openings 117 and 270 °
The resist is patterned so that the resist 19 is formed on the transparent substrate opening 119 forming the shifter. That is, the fractional part when the phase is divided by 180 ° is 0.1.
An opening in which a phase shifter having a size of 44 or more and 0.55 or less is formed as a blanking pattern. For patterning the resist, an electron beam or optical lithography may be used.

Next, as shown in FIG. 3D, the silicon oxide film on the transparent substrate opening 116 where the shifter is not formed and the transparent substrate opening 118 where the 180 ° shifter is formed are removed by etching. This etching may be performed using either an isotropic or anisotropic method.

Next, as shown in FIG. 3E, a silicon oxide film 20 is formed on the entire surface of the mask by a method of applying a liquid silicon oxide film (eg, SOG), a sputtering method, or a CVD method. The thickness of the silicon oxide film 20 formed at this time is such that the phase difference between the light transmitted through the phase shifter and the light transmitted through the transparent substrate is close to 180 °. At this time, the allowable range of the film thickness error of the phase shifter is within ± 10% of the desired film thickness. Now, the exposure light is changed to i-line (λ = 365).
nm), the refractive index at the i-line wavelength of silicon oxide formed by the CVD method is n _s = 1.446, so that the thickness of the silicon oxide film 20 formed at this time has a value close to 409 nm. Become.

Next, as shown in FIG.
° shifter forming transparent substrate openings 118 and 270 °
The resist is patterned so that the resist 21 is formed on the transparent substrate opening 119 forming the shifter. That is, the value a _i when the phase is divided by 180 ° is 0.
An opening where a phase shifter satisfying 94 < _ai is formed is defined as a cutout pattern. For patterning the resist, an electron beam or optical lithography may be used.

Next, as shown in FIG. 3G, the silicon oxide film on the transparent substrate opening 116 where the shifter is not formed and the transparent substrate opening 117 where the 90 ° shifter is formed are removed by etching. This etching may be performed using either an isotropic or anisotropic method. After that, the resist is peeled off using the SH method, the Asher method, or the like.

Even in such a reference example, the resist patterning on the mask after the formation of the light-shielding film pattern is performed only twice, and the film thickness of the phase shifter is 90 °, 180 °, and 90 °.
Three types of 270 ° can be formed, and the same effect as in the second reference example can be obtained.

(Fourth Embodiment) FIG. 4 is a sectional view showing a method of manufacturing a phase shift mask according to a fourth embodiment of the present invention. In this embodiment, a method for manufacturing a phase shift mask using an etching method will be described.

First, as shown in FIG. 4A, a pattern made of a light shielding film 27 is formed on a transparent substrate 26. As the transparent substrate 26, for example, a quartz substrate is used, and as the light shielding film 27, for example, chromium oxide having a thickness of 100 nm is used.

Next, as shown in FIG. 4B, the resist is formed so that the resist 28 is formed on the transparent substrate opening 120 where the shifter is not formed and the transparent substrate opening 122 where the 180 ° shifter is formed. Perform patterning. For patterning the resist, an electron beam or optical lithography may be used. That is, the fractional part when the phase is divided by 180 ° is 0.44 to 0.5.
An opening in which 5 or less phase shifters are formed is defined as a blanking pattern.

Next, as shown in FIG. 4C, the transparent substrate 26 is carved by etching. This etching may be performed using either an isotropic or anisotropic method.
At this time, the depth of engraving by etching is such that the phase difference between the light transmitted through the engraved portion and the light transmitted through the transparent substrate 26 is 90 °.
The film thickness should be close to At this time, the allowable range of the engraving depth is within ± 10% of the desired engraving amount.
Now, the exposure light is i-line (λ = 365 nm) and the transparent substrate 26 is exposed.
Is quartz, the refractive index of the quartz at the i-line wavelength is n _s =
Since it is 1.446, the digging depth at this time is 20
The value is close to 4.5 nm. After that, as shown in FIG. 4D, the resist 28 is peeled off by using the SH method or the Asher method.

Next, as shown in FIG. 4E, a resist is formed so that the resist 29 is formed on the transparent substrate opening 120 where the shifter is not formed and the transparent substrate opening 121 where the 90 ° shifter is formed. Perform patterning. That is,
The value a _i obtained by dividing the phase by 180 ° is 0.94 <a _i
The opening in which the phase shifter to be formed is formed is defined as a cutout pattern. For patterning the resist, an electron beam or optical lithography may be used.

Next, as shown in FIG. 4F, the transparent substrate 26 is carved by etching. For this etching, either an isotropic or anisotropic method may be used. At this time, the depth of the engraving by etching is such that the phase difference between the light transmitted through the engraved portion and the light transmitted through the transparent substrate 26 is one.
The film thickness is set to be close to 80 °. At this time, the allowable range of the engraving depth is within ± 10% of the desired engraving amount. Now, assuming that the exposure light is i-line (λ = 365 nm) and the transparent substrate 26 is quartz, the refractive index of the quartz at the i-line wavelength is n.
_{Since s} = 1.446, the digging depth at this time is 4
The value is close to 09 nm. Thereafter, as shown in FIG. 4G, the resist 29 is peeled off by using the SH method, the Asher method, or the like.

As a result, a phase shifter (90 °) having a digging depth of 204.5 nm is formed in the substrate opening 121 by the first etching, and a digging depth is formed in the substrate opening 122 by the second etching. A 409 nm phase shifter (180 °) is formed, and the first and second etchings dig into the substrate opening 123 to a depth of 613.5 nm.
Is formed (270 °).

As described above, when the method of manufacturing the phase shift mask according to the present embodiment is used, the thickness of the phase shifter becomes 9
Although there are three types, 0 °, 180 °, and 270 °, the resist patterning on the mask after the formation of the light-shielding film pattern is performed only twice, and the mask manufacturing process can be shortened. Further, since the phase shifter of 90 ° (that is, the phase shifter having a shallow engraving) is formed first, at the time of the second resist patterning on the mask (FIG. 4E), the step of the base (phase shifter and light shielding film) ) Can be minimized.

(Fifth Embodiment) FIG. 5 is a plan view showing an arrangement example of a phase shifter of a phase shift mask according to a fifth embodiment of the present invention. FIG. 6 shows an arrangement example of a conventional phase shifter for comparison. In each figure, a dotted line surrounds a cell array region having a periodic pattern and a sense amplifier region having a non-periodic pattern.

In the conventional example shown in FIG. 6, the shifters are arranged in the openings only with phases of 0 ° and 180 °. In a portion of a periodic pattern such as a cell array portion, if there is a shifter having a film thickness of 180 °, it can be arranged so that the phases of light transmitted through adjacent openings are different. However, in a section derived from the cell array section (here, a sense amplifier section is taken as an example), there are portions (p, q in the figure) in which the phases of light transmitted through adjacent openings are the same. . In these portions, since the effect of the phase shift method is significantly reduced, it is necessary to increase the size or rewrite the pattern so that the phase of light passing through adjacent openings differs. Therefore, 0
When the shifter is arranged in the opening only by the phase of 180 ° and 180 °, it can be said that there is a great restriction in design.

On the other hand, in the present embodiment shown in FIG.
An example of a shifter arrangement in the case of using 90 ° and 270 ° phase shifters in addition to the 180 ° and 180 ° phases is shown. When the four types of phases 0 °, 90 °, 180 °, and 270 ° are used as described above, if the phases of light transmitted through adjacent openings are to be made different, the phase difference is 90 ° or 180 °.
Becomes As can be seen from FIG. 17, the phase difference of light transmitted through the adjacent openings is 180 ° because the resolution is higher.
In a portion of a simple repetition pattern such as a cell array portion, it is desirable to arrange shifters at 0 °, 180 °, 0 °, 180 °,. This is because, for example, the cell portion of a DRAM often has a three-dimensional structure such as a trench or a stack, and accordingly, a higher resolution is required.

Further, in the present reference example, a phase such as 90 ° or 270 ° is provided in a portion where the phase of light transmitted through an adjacent opening in the sense amplifier section is conventionally the same. According to this arrangement method, the phase of the light transmitted through the adjacent openings in the sense amplifier portion becomes different, and the effect of the phase shift method can be provided.
Therefore, unlike the conventional phase shift method, the number of portions where the phases of the light passing through the adjacent openings are the same is reduced, and the size of these portions is increased, or the phase of the light passing through the adjacent openings is reduced. Design constraints such as rewriting patterns differently are reduced.

(Sixth Embodiment) FIG. 7 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to a sixth embodiment of the present invention. FIG. 7A shows a conventional example, in which 0 °,
The shifter is arranged in the opening only at a phase of 180 °.
Thus, the conventional Levenson-type phase shift method uses 0 °,
Since the phase shift mask is formed only by the combination of the phases of 180 °, there is only one combination (0 °, 180 °) in which the phases of the adjacent patterns are different. Therefore, the patterns s and q in FIG. No matter which phase of 0 ° or 180 ° is arranged, adjacent patterns have the same phase. Therefore, the effect of the phase shift method is significantly reduced in this portion.

Therefore, in this reference example, as shown in FIG.
New 90 ° and 270 ° phase shifters are combined with the patterns s and q. Accordingly, combinations of adjacent patterns having different phases are (0 °, 90 °), (0 °, 18
0 °), (0 °, 270 °), (90 °, 180 °),
(90 °, 270 °) and (180 °, 270 °), and the adjacent patterns have different phases, and the effect as the phase shift method is produced.

(Seventh Embodiment) FIG. 8 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to a seventh embodiment of the present invention. In this reference example, a region surrounded by any two parallel openings where a phase shifter is arranged so that the relative phase difference of light transmitted through adjacent openings is close to 180 ° (dotted line in the drawing) In the area DA), an opening is formed in a direction along the two surrounding openings. Further, the number of openings in an arbitrary cross section (AA ′ cross section) perpendicular to the direction along the two surrounding openings is an even number (two in the figure). In this case, the phase shifter is arranged so that the relative phase of the light transmitted through the adjacent openings is close to 180 °.

By arranging in this manner, the relative phase of the light transmitted through the adjacent openings is always close to 180 °, and the effect as the phase shift method is sufficiently exhibited. A high resolution can be obtained for the pattern thus obtained.

(Eighth Embodiment) FIG. 9 is a plan view showing a phase shifter arrangement example of a phase shift mask according to an eighth embodiment of the present invention. In this reference example, a region surrounded by any two parallel openings where a phase shifter is arranged so that the relative phase difference of light transmitted through adjacent openings is close to 180 ° (dotted line in the drawing) In the region DB), an opening is formed in a direction along the two surrounding openings. Further, the number of openings in an arbitrary section (BB ′ section) perpendicular to the direction along the two surrounding openings is an even number (three in the figure). In this case, the phase shifter is arranged so that the relative phase of the light transmitted through the adjacent openings is close to 90 °.

By arranging in this manner, the relative phase of the light transmitted through the adjacent openings is always close to 90 °, and the effect as the phase shift method is sufficiently exhibited. A high resolution can be obtained for the pattern thus obtained.

(Ninth Reference Example) FIG. 10 shows a ninth embodiment of the present invention.
FIG. 11 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to the reference example. In this reference example, a region surrounded by any two parallel openings where a phase shifter is arranged so that the relative phase difference of light transmitted through adjacent openings is close to 180 ° (dotted line in the drawing) In the region DC), an opening is formed in a direction along the two surrounding openings.
Furthermore, the number of openings in an arbitrary cross section perpendicular to the direction along the two surrounding openings is even and odd. That is, the number is even (two in the figure) in the C1-C1 'section, and odd (one and three in the figure) in the C2-C2' and C3-C3 'sections.

As described above, when there is one even-numbered portion and a plurality of odd-numbered portions, first, the relative phase of the light transmitted through the adjacent openings of the even-numbered portions is set close to 180 ° (that is, C1).
In the -C1 'section, Q1 is set to a value of 180 ° and R1 is set to a value close to 0 °). Then, in the other openings, the relative phase of light transmitted through the adjacent openings is set to be close to 90 ° (that is, the relative phase is close to 90 °). P1 is set to a value close to 90 ° or 270 ° in the C2-C2 ′ section and the C3-C3 ′ section).

By arranging in this manner, the relative phase of the light transmitted through the adjacent openings is always close to 180 ° or 90 °, and the effect as the phase shift method is sufficiently exhibited. A high resolution can be obtained for the pattern formed by using.

(Tenth Embodiment) FIG. 11 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to a tenth embodiment of the present invention. In this reference example, a region surrounded by any two parallel openings where a phase shifter is arranged so that the relative phase difference of light transmitted through adjacent openings is close to 180 ° (dotted line in the drawing) In the area DD) of FIG.
An opening is formed in a direction along the opening surrounding the book. Furthermore, the number of openings in an arbitrary cross section perpendicular to the direction along the two surrounding openings is even and odd. That is, D1-D1 'section, D2-
The number is even (two in the figure) in the section D2 ', and odd (three in the figure) in the section D3-D3'.

When there is one odd-numbered portion and a plurality of even-numbered portions, a plurality of even-numbered portions (D1-D in FIG.
The relative phase of the light transmitted through the adjacent opening in one of the sections (1 ′ section and D2-D2 ′ section) (referred to as D1-D1 ′ section in the drawing) is set to be close to 180 ° ( That is, Q2 is 180 in the D1-D1 'section.
° and R2 are values close to 0 °). Next, the relative phase of the light transmitted through the adjacent openings in the even-numbered portions (D2-D2 'cross section in the figure) is made close to 180 ° (that is, P2 is set to 180 ° in the D2-D2' cross section).
Value close to). At this time, the relative phase difference between P2 and Q2 is 0 °, and the effect of the phase shift method cannot be obtained in this portion. Therefore, either P2 or Q2 is set to a value close to 90 ° or 270 °. As a result, the relative phase difference between P2 and Q2 becomes 90 °, and the effect of the phase shift method can be obtained also in this portion.

By arranging in this manner, the relative phase of the light transmitted through the adjacent openings is always close to 180 ° or 90 °. 180 ° relative phase
17, a portion having a relative phase of 180 ° is formed, and the effect of the phase shift method is more fully exhibited over the entire mask than in the case of a relative phase of 90 ° (see FIG. 17). 180 than 90 °
° is more effective as a phase shift method), and a pattern formed using the present mask can obtain high resolution.

Next, an embodiment of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 12 shows a first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a structure of a phase shift mask according to the embodiment. A light-shielding film pattern 51 is formed on a transparent substrate 50. As a material of the transparent substrate 50, for example, quartz,
As a material of the light shielding film 51, for example, chromium oxide or the like was used. The thickness λ / 2 is applied to the region of the quartz substrate 50 having the opening.
(N _s -1) phase shifters 52 (lambda:: exposure wavelength, n _s the refractive index of the phase shifter at the exposure wavelength) is formed. As a material of the phase shifter 52, for example, SiO ₂ formed by a liquid phase growth method, a sputtering method, or a CVD method is used.
A film or the like was used.

Up to this point, the structure is the same as the conventional structure.
In this embodiment, further, the film formation method is the same as that of the phase shifter 52.
The same material (buffer film) 53 as the formed phase shifter 52
Of the light from both the quartz opening 501 and the phase shifter 502
It is formed uniformly in the area including the transmission part. At this time,
Depending on the method, it may be formed on a light-shielding film.
The buffer film 53 formed on the film 51 is transferred during exposure.
It does not affect. Buffer film 5 of the same material as this phase shifter
3 has an exposure wavelength λ and a refractive index n of the phase shifter. _sDecided
And given by:

[0074] _{h = (λ / 4n s)} {m-n s / (n s -1)} ... (14) However, n _s: the shifter refractive index, lambda: the exposure wavelength, m: is an integer.

Assume that the exposure light is i-line (λ = 365 nm),
When the phase shifter material and SiO ₂ film formed by the liquid phase, the refractive index of the i-line wavelength of the phase shifter is n _s = 1.44
6, the thickness of the phase shifter 52 is 409 nm, and the thickness of the buffer film 53 of the same material as the phase shifter is 11.1 nm when m = 5.

That is, in order to form the phase shift mask for the i-line by using the liquid phase growth method, after forming the light shielding film pattern 51 on the quartz substrate 50, the 409 nm phase shifter 52 is formed by using the liquid phase growth method. Then, the buffer film 53 of the same material as the 11.1 nm phase shifter 52 may be formed on both the quartz opening 501 and the phase shifter 502 using the same method. The allowable range of the deviation of the thickness of the buffer film 53 from the desired value is within ± 10% of the desired value.

[0077] i-line exposure light in FIG. 13, when a SiO ₂ film phase shifter using a liquid-phase growth method, shows the phase angle δ dependence of the ratio I _s of the transmitted light to incident intensity. From the figure,
I _s When the [delta] = 0 ° whereas a 92.793%, [delta]
= 180 °, it is 93.109%. This is because, when the phase shift mask for i-line is formed using the liquid phase growth method, the method of the present embodiment (a method of uniformly forming the same film as the phase shifter on both the quartz opening and the phase shifter). It can be seen that the intensity of light transmitted through the phase shifter becomes 0.316% higher than the intensity of light transmitted through the quartz opening if no is used.

To correct this, the light intensity transmitted through the phase shifter and the light transmitted through the quartz opening are made equal, and the phase of the light transmitted through the phase shifter and the phase of the light transmitted through the quartz opening are adjusted. To make the phases 180 degrees different,
As shown in FIG. 13, it can be seen that the film thickness h corresponding to the phase angle δ should be formed uniformly on both the quartz opening and the phase shifter.

The exposure light is i-line (λ = 365 nm) and the phase shift
SiO with lid material formed in liquid phase _TwoMembrane (n_s= 1.4
46) and the film thickness h and the integer m shown in the present embodiment when
FIG. 14 shows the relationship between the values of. According to the value of m from FIG.
Is a negative value of the film thickness h, which is unreasonable for mask fabrication.
It is. Therefore, m should be selected so that h ≧ 0.
It is. In addition, there is a throughput
Therefore, it is desirable that the film thickness h be as small as possible.

For example, when SiO ₂ of the phase shifter for i-line is formed in the liquid phase (film formation rate: about 100 nm / h), FIG.
In the case of m = 10 from 4, the film formation time is about 12% longer than that of a normal phase shift mask. On the other hand, if the value of h is too small, a uniform and highly accurate film cannot be formed because the film formation time is short. When forming a phase shifter in a liquid phase, it is known that the film uniformity is low when the film thickness is 20 nm or less. That is, the lower limit of the value of m is determined by the stability of the film thickness, and the lower limit varies depending on the mask manufacturing process. From the above, when forming the phase shift mask for the i-line in the liquid phase, it is considered that the value of m is suitably from 6 to 9 as shown in FIG.

As described above, according to the present embodiment, the same material as the phase shifter is formed on the entire surface (opening of the transparent substrate and the phase shifter) of the mask formed through the normal phase shift mask manufacturing process. By selecting the film thickness of this material (the thickness value is determined by the exposure wavelength and the refractive index of the phase shifter material), the light intensity transmitted through the transparent substrate opening and the light intensity transmitted through the phase shifter are made equal. be able to. As a result, a desired pattern can be formed without causing non-uniformity in the resolution pattern formed by the phase shifter and the transparent substrate opening.

(Second Embodiment) FIG. 15 is a diagram for explaining a method of selecting a shifter material having an optimum refractive index according to a second embodiment of the present invention. When the method of forming the same film as the phase shifter on both the quartz opening and the phase shifter is not used as shown in the first embodiment, the transmission light intensity of the quartz opening and the transmission light intensity of the phase shifter are not measured. The refractive index of the shifter material (i.e., a suitable shifter material) must be chosen such that the difference is within an acceptable range. If the difference between the transmitted light intensity of the quartz opening and the transmitted light intensity of the phase shifter is within 1% of the light intensity of the quartz opening, the above-mentioned (11)
It looks like an expression.

If the allowable range of the deviation of the phase shifter film thickness from 180 ° is ± 10 °, the above equation (12) is obtained.

FIG. 4 shows the dependence of I _s / I _{q on} the phase shifter refractive index n _s when using a KrF excimer laser. The value of I _s / I _q that satisfies the expression (12) is indicated by the hatched portion in FIG. Now, the refractive index of the shifter in which the difference between the transmitted light intensity of the quartz opening and the transmitted light intensity of the phase shifter is within 1% of the light intensity of the quartz opening must satisfy the following relationship. is there.

[0085] _{1.46 ≦ n s ≦ 1.55 ... (} 15) Next, the allowable range of the difference in transmitted light intensity of the transmitted light intensity and phase shifter portion of the quartz opening a more stringent 0.05%,

(Equation 3)

[0086] Also, the phase shifter film thickness of 180 °
Assuming that the allowable range of the amount of deviation from
2)

FIG. 15 shows the dependence of I _s / I _{q on} the phase shifter refractive index n _s when using a KrF excimer laser. The value of I _s / I _q that satisfies the expression (9) is indicated by the hatched portion in FIG. Now, the difference between the transmitted light intensity of the quartz opening and the transmitted light intensity of the phase shifter is one of the light intensity of the quartz opening.
It is necessary that the refractive index of the shifter whose allowable range is within% is to satisfy the following relationship.

[0088] _{1.48 ≦ n s ≦ 1.53 ... (} 17) Here, ± tolerance of the difference in transmitted light intensity and the transmitted light intensity of the phase shifter portion of the quartz opening of the light intensity of the quartz opening 1 %, Preferably within ± 0.5%.
This will be described with reference to FIG. FIG. 16 shows the dependence of the resist size on the deviation from the desired value of the transmitted light intensity. From FIG. 16, it can be seen that the allowable range of deviation of the transmitted light intensity from the desired value is ± 1% in order to obtain a depth of focus of ± 0.5 μm or more required for device prototype. In addition, from FIG. 16, it can be seen that in order to obtain a depth of focus of ± 1.0 μm or more required for manufacturing a commercial device, the allowable range of deviation of the transmitted light intensity from a desired value is ± 0.5%.

As described above, according to this embodiment, when the method of forming the same film as the phase shifter on both the transparent substrate opening and the phase shifter is not used, the transmitted light intensity of the quartz opening and the phase shifter By selecting the refractive index of the shifter material (that is, a suitable shifter material) so that the difference in transmitted light intensity is within an allowable range, the resolution pattern formed by the phase shifter portion and the opening of the transparent substrate may have non-uniformity. The pattern can be formed as desired without any occurrence.

[0090]

As described in detail above, the present invention (Claims 1 to 5)
According to 4), the phase shifter is arranged in a phase combination of 0 °, 90 °, 180 °, and 270 ° (the relative phase difference of the light transmitted through the adjacent patterns is 90 ° or 180 °), thereby achieving a phase shift. Thus, it is possible to realize a phase shift mask that can reduce the design constraints of the mask while maintaining a sufficient resolution in the method.

According to the present invention (claim 5), a buffer film made of the same material as the phase shift material is formed in both the transmission portion and the shifter portion, and the thickness of the buffer film is set optimally. A phase shift mask that can approach the light intensity transmitted through the substrate opening and the light intensity transmitted through the phase shifter, and can improve the uniformity of the resolution pattern formed by the phase shifter and the opening of the transparent substrate. It can be realized.

[Brief description of the drawings]

FIGS. 1A and 1B are a plan view and a cross-sectional view illustrating a structure of a phase shift mask according to a first reference example.

FIG. 2 is a cross-sectional view illustrating a process of manufacturing a phase shift mask according to a second reference example.

FIG. 3 is a cross-sectional view showing a process of manufacturing a phase shift mask according to a third reference example.

FIG. 4 is a cross-sectional view illustrating a process of manufacturing a phase shift mask according to a fourth reference example.

FIG. 5 is a plan view showing a phase shifter arrangement example of a phase shift mask according to a fifth reference example.

FIG. 6 is a plan view showing a shifter arrangement example of a conventional phase shift mask for comparison.

FIG. 7 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to a sixth reference example.

FIG. 8 is a plan view showing a phase shifter arrangement example of a phase shift mask according to a seventh reference example.

FIG. 9 is a plan view showing a phase shifter arrangement example of a phase shift mask according to an eighth reference example.

FIG. 10 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to a ninth reference example.

FIG. 11 is a plan view showing an example of a phase shifter arrangement of a phase shift mask according to a tenth reference example.

FIG. 12 is a sectional view showing the structure of the phase shift mask according to the first embodiment.

FIG. 13 is a characteristic diagram illustrating a relationship between a phase angle and transmittance in the first embodiment.

FIG. 14 is a characteristic diagram showing a relationship between a film thickness and an integer value in the first embodiment.

FIG. 15 is a view for explaining a method of selecting a shifter material having an optimum refractive index in the second embodiment.

FIG. 16 is a graph showing the dependence of the transmitted light intensity of a resist dimension on a deviation from a desired value.

FIG. 17 is a characteristic diagram for explaining the operation of the present invention and showing the relationship between the defocus value and the contrast.

FIG. 18 is a view for explaining the operation of the present invention, and shows a state in which the value of the light intensity Iq transmitted through the opening of the substrate and the value of the light intensity Is transmitted through the phase shifter are different.

FIG. 19 is a view for explaining the operation of the present invention and shows a state of multiple reflection in a shifter in a two-layer structure of a transparent substrate / shifter.

FIG. 20 illustrates the principle of the phase shift method.

[Description of Signs] 1,10,16,26,50 ... Transparent substrate 2,11,17,27,51,52 ... Light shielding film 3,13,15,18,20 ... Phase shifter 12,14,19,21 , 28, 29 ... resist 53 ... buffer film 101, 110-113, 116-123 ... transparent opening

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP 5-158219 (JP, A) JP 5-142750 (JP, A) JP 4-340962 (JP, A) JP 3- 59555 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (1)

(57) [Claims] 1. A phase shift mask in which a light-shielding film having a desired opening pattern is formed on a light-transmitting substrate, and a phase shift material for shifting a phase with respect to transmitted light is formed in a part of the opening pattern. A buffer film made of the same material as that of the phase shift material is formed on both the transmission part having the opening pattern in which the phase shift material is not formed and the shifter part having the opening pattern in which the phase shift material is formed. A thickness of the buffer film is adjusted so that transmittances of light passing through the portions are substantially equal.