JPH0566554A - Photomask - Google Patents

Abstract

PURPOSE:To increase the depth of exposure focus on a wafer in a photolithography process for a semiconductor device. CONSTITUTION:The photomask is so constituted that focusing on the upper and lower part of the high step of the wafer can be obtained by relatively shifting light shielding opaque patterns 12 and 15 of the photomask on an optical axis. Consequently, the simultaneous focusing on the upper and lower parts of the step on the substrate which has the relatively high step is enabled and pattern transfer can excellently be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask, and more particularly to a mask plate for an optical exposure apparatus used for manufacturing semiconductor devices and the like.

[0002]

2. Description of the Related Art In a VLSI semiconductor device produced in recent years, a large number of micron-order transistors and wirings are integrated on a silicon substrate. These fine patterns are formed by photo-exposure to form micron-order patterns by reducing (usually ⅕) the mask pattern transferred onto a photosensitive resin (resist) film coated on a semiconductor substrate. Technology is being used. Currently mass-produced 1MDRAM and 4MDR
The AM has a minimum line width of 1.2 μm and 0.8 μm, respectively. Most of the light exposure equipment (stepper) that produces these emits from an ultra-high pressure mercury lamp called g-line.
The 6 nm emission line is used, and the use of the 365 nm emission line, which is partly called the i line, emitted from the same lamp has started. 16M DRAM, 64MDR planned for future production
The minimum line width used in AM is 0.6 to 0.5 μ respectively.
m, 0.4 to 0.3 μm. In order to mass-produce these semiconductor devices, it is required to develop an optical exposure technique with higher resolution. In order to improve the resolution by shortening the wavelength of the exposure light, i line instead of g line, 248n
The use of a krypton / fluorine excimer laser of m. In addition, increasing the numerical aperture (NA) of the projection lens is also being considered. In these exposure devices, a mask in which an opaque pattern formed of a metal thin film is usually placed on a smooth transparent substrate such as quartz is irradiated with light from the back surface, and the light flux passing through the mask is reduced through a projection lens to reduce the substrate. Imaged above. In such a method, it is possible to increase the resolution by shortening the wavelength of the light used as the light source of the exposure apparatus or increasing the NA of the projection lens as described above. As the depth of the VLSI semiconductor device increases and the level of the step increases on the silicon substrate, it is an important issue to focus the transfer pattern on the entire area from the top to the bottom of the step at the same time. As described above, the pattern transfer of a VLSI semiconductor device having a high step difference is a serious problem in the conventional mask for light exposure in which an opaque pattern is formed on a smooth quartz substrate with a metal thin film or the like. There is a need for a light exposure mask that is easy and has high durability.

[0003]

SUMMARY OF THE INVENTION The present invention is for light exposure in which a pattern opaque to light is formed on a transparent substrate which is transparent to light such as visible light or ultraviolet light for pattern transfer. The photomask, wherein the opaque pattern portions are provided at positions of different heights on the transparent substrate. That is, the present invention provides an optical exposure mask capable of transferring a pattern of a high step VLSI semiconductor device by changing the focal plane by forming patterns at different heights on the optical axis. A reduction projection exposure apparatus used for manufacturing a VLSI semiconductor device reduces the pattern of a normal exposure mask to 1/5 and transfers it onto a silicon substrate. On the other hand, in a general reduction projection lens system, the vertical magnification (α) has the following relationship with the horizontal magnification (β). α = β ² (1) Therefore, for example, it is possible to simultaneously focus on the upper and lower steps of the silicon substrate having the step of 1 μm by providing the step of 25 μm on the exposure mask. Further, the effect of the invention can be obtained by providing the pattern on the mask above and below the transparent medium having a film thickness corresponding to the distance according to the equation (1) without forming such a step. In this case, when the reduction ratio is m and the refractive index of the transparent medium is n, the thickness T of the transparent medium required for focusing at the same time above and below the step of a μm on the silicon substrate is expressed by the following equation (2). .. T = (a × m ² ) / n (2) According to the present invention, the relative position on the optical axis of the pattern on the mask is changed to simultaneously focus on the upper and lower steps of the substrate having a relatively large step. be able to. Specifically, (i) as shown in FIGS. 4, 5, 6 and 7, the opaque pattern portions 12 and 15, 12a, 12b and 15 are formed.
a and 15b are provided directly above the transparent substrate 11 having a flat surface 11a and directly above the transparent layer 14 provided on the transparent substrate and transparent to light such as visible light or ultraviolet light for pattern transfer. It can be a photo mask made by
i) As shown in FIG. 9, the step lower surface 31a of the transparent substrate 31 in which the opaque pattern portions 22a and 22b have the step H
And (iii) as shown in FIG. 10, an opaque pattern portion 32 is formed on the step upper surface 31b from the step lower surface 31a of the transparent substrate 31 having the step H. (Iv) As shown in FIG. 11, the opaque pattern portions 42a and 42b have the stepped lower surface 44a and the stepped upper surface 44 of the transparent layer 44 having the step L.
b and a photomask provided on each of the b and (V) opaque pattern portions 5 as shown in FIG.
3, 54 and 55 are provided on the step lower surface 31a and the step upper surface 31b of the transparent substrate 31 having the step H, respectively,
And the lower surface 3 of the step of the transparent substrate 31 between the both 53 and 54
The photomask is provided so as to extend from 1a to the step upper surface 31b.

[0004]

【Example】

Embodiment 1 In FIG. 4, an opaque pattern portion is transparent directly above a transparent substrate having a flat surface and transparent to light such as visible light or ultraviolet light for pattern transfer provided on the transparent substrate. The 1st example of the present invention of a photomask provided directly on a layer is shown. To form a photomask, first, as shown in FIG. 1, a pattern transfer photoresist 13 is applied onto a quartz substrate 11 having a light shielding film 12. continue,
A desired pattern of the photoresist 13 is drawn by an electron beam drawing apparatus, a resist pattern (not shown) is obtained after development, and then the light-shielding film 12 is formed by a normal liquid bath etching method using the obtained resist pattern as a mask. By processing, the first opaque pattern 12 is formed. After that, the resist pattern is removed (see FIG. 2). Further, in order to change the relative position of the first opaque pattern 12 and the second opaque pattern which will be formed later, a transparent tank 14 is deposited, and then a second light-shielding film 15 is deposited and processed. An electron beam resist 16 for coating is applied (see FIG. 3). After that, the resist 16 is removed by an electron beam drawing device.
A desired pattern (not shown) is drawn, a resist pattern is obtained after development, and then the light-shielding film 15 is formed by a normal liquid layer etching method using the obtained resist pattern as a mask.
Are processed to form the second opaque pattern 15. After that, the resist pattern 15 is removed to obtain a desired mask (see FIG. 4). In addition, FIG. 5 shows the opaque pattern 1 on the upper and lower sides.
By connecting 5, 12 in the optical axis direction, the light-shielding film 1 after transfer
4 shows a modification of the first embodiment of the present invention in which the opaque patterns 15 and 12 can be connected above and below the step A in FIG. Further, FIG. 6 shows the first embodiment of the present invention in which the upper and lower opaque patterns 15 and 12 are slightly overlapped with each other, so that the opaque patterns 15 and 12 can be connected to each other above and below the step A in the light-shielding film 14 after transfer. The other modification of an example is shown. Also in FIG. 7, upper and lower opaque patterns 15a, 15b, 12
A further modified example of the first embodiment of the present invention in which the a and 12b are slightly overlapped to enable connection of opaque patterns above and below the step A in the light-shielding film 14 after the transfer is fairly excellent is shown. As described above, in the method shown in this embodiment, it is desirable that the film thickness of the transparent layer 14 between the first opaque pattern and the second opaque pattern is equal to the film thickness T (= A) shown in the equation (2). .. In the mask making process for the 1/5 reduced projection i-line (365 nm) stepper according to the present embodiment, a two-layer metal film of chromium oxide film / chrome (Cr) having a total film thickness of 100 nm is used as a light-shielding film on a transparent substrate made of quartz. A film was used, a positive type resist of 500 nm was used as a light-shielding film pattern forming resist, and the light-shielding film was etched by an ordinary liquid layer method to form a first opaque pattern. Transparent layer 1
For forming No. 4, a silicon oxide film (SiO ₂ ) having a refractive index of 1.45 was deposited by 17.24 μm by a known atmospheric pressure CVD method. Further, the transparent layer 14 has a total film thickness of 10 as a light shielding film.
A two-layer metal film of 0 nm chromium oxide film / chromium (Cr) is used, and a light-shielding film pattern forming resist is 500 n
Using a positive resist of m, etching of the light-shielding film was performed by an ordinary liquid layer method to form a second opaque pattern, and a photomask was completed. These individual process technologies are known in the IC manufacturing process. The above materials,
Numerical aperture (NA) = 0.45 using the mask manufactured in the process
The exposure test was performed using the i-line stepper. It was confirmed that 0.4 μm lines and spaces could not be transferred onto a substrate having a 1 μm step with the conventional mask, but this mask can transfer them well. In the manufacturing process of this embodiment, various materials and methods other than the above materials and methods can be used. The light-shielding film is molybdenum, tungsten,
It may be a metal film of cobalt, nickel, aluminum, etc., a silicon metal compound such as tungsten silicide (WSi ₂ ), molybdenum silicide (MoSi ₂ ), a silicon alloy film, or a semiconductor film of silicon. As the etching method, other than the usual liquid layer method, an appropriate method can be adopted depending on the material of the light shielding film. For example, with a metal film such as molybdenum, a pattern can be formed by reactive in-etching. The transparent film may be a spin-coatable silicon glass film, a silicon-phosphorus glass film, a silicon-phosphorus-boron glass film, or the like.

Embodiment 2 FIG. 9 shows a first embodiment of the present invention of a photomask in which opaque pattern portions are provided on the step lower surface and the step upper surface of a transparent substrate having steps, respectively. In order to form a photomask, first, as shown in FIG. 8, a light-shielding film 22 is deposited on a quartz substrate 31 provided with a step H in advance, and a pattern transfer photoresist (not shown) is applied.
A desired pattern is drawn by an electron beam drawing device to obtain a resist pattern 23 after development. Then, the resist pattern 23 thus obtained is used as a mask to process the light-shielding film 22 by a normal liquid layer etching method, and the first opaque pattern 2 is formed.
2a and 22b are formed. After that, the resist pattern 23
Are removed to complete the photomask (see FIG. 9).

Embodiment 3 In addition, in FIG. 10, when the transparent substrate 31 has the inclined portion 131, the step lower surface 31a and the step upper surface 31b of the inclined portion are connected by the opaque pattern 32 so that the step H after transfer is increased or decreased. 3 shows a third embodiment of the present invention in which an opaque pattern can be connected.

Embodiment 4 FIG. 11 shows a case where the transparent substrate 21 does not have an inclined portion, and opaque pattern portions 42a and 42b are provided on the step lower surface 44a and the step upper surface 44b of the transparent layer 44 having the step A, respectively. 4 shows a fourth embodiment of the present invention. By connecting the patterns in the optical axis direction as in the case of the first embodiment, it is possible to connect the opaque patterns above and below the step after transfer.

Embodiment 5 In FIG. 12, opaque pattern portions 53, 54 and 55 are provided on a step lower surface 31a and a step upper surface 31b of a transparent substrate 31 having a step H, respectively, and between the two, a transparent substrate is formed. A fifth embodiment of the present invention, which is provided extending from the lower surface of the step to the upper surface of the step, will be described. By connecting the patterns in the optical axis direction as in the case of the first embodiment, it is possible to connect the opaque patterns above and below the step after transfer. As described above, in the second, third, and fifth embodiments, the step provided on the transparent quartz substrate in advance is 25 steps of the step on the substrate according to the above equation (1).
It is desirable to be equal to twice. 1 according to the present embodiment
In the step of forming the mask for the 5 reduced projection i-line (365 nm) stepper, the step on the transparent substrate made of quartz was 25 μm, and the light-shielding film was a two-layer metal film of chromium oxide film / chrome (Cr) with a total film thickness of 100 nm. A 500 nm positive resist was used as the light-shielding film pattern forming resist, and the light-shielding film was etched by an ordinary liquid layer method to form an opaque pattern to complete a photomask. These individual process technologies are known in the IC manufacturing process. An exposure test was conducted using an i-line stepper with a numerical aperture (NA) = 0.45 using the mask manufactured by the above materials and steps. It was confirmed that good results similar to those of the first example were obtained. As the manufacturing process of the present embodiment, the above materials,
In addition to the method, various materials and methods can be used. The light-shielding film is molybdenum, tungsten, cobalt, nickel,
A metal film such as aluminum, tungsten silicide (WSi ₂ ), molybdenum silicide (MoSi
_It may be a silicon metal compound such as ₂ ), a silicon alloy film, or a semiconductor film such as silicon. As the etching method, other than the usual liquid layer method, an appropriate method can be adopted depending on the material of the light shielding film. For example, a metal film of molybdenum or the like can be patterned by reactive ion etching.

[0010]

As described above, according to the present invention, it is possible to focus at the same time above and below a step on a substrate having a relatively high step, the depth of focus of exposure can be increased, and good pattern transfer can be performed. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a structural explanatory view for explaining a first step of a manufacturing process of a photomask in a first embodiment of the present invention.

FIG. 2 is a structural explanatory view for explaining a second step of manufacturing process of the photomask in the above-mentioned embodiment.

FIG. 3 is a configuration explanatory view for explaining a third step of manufacturing process of the photomask in the above-mentioned embodiment.

FIG. 4 is a diagram illustrating the configuration of the photomask in the above embodiment.

FIG. 5 is a configuration explanatory view showing a first modified example of the photomask in the above-described embodiment.

FIG. 6 is a structural explanatory view showing a second modified example of the photomask in the above-mentioned embodiment.

FIG. 7 is a structural explanatory view showing a third modified example of the photomask in the above-mentioned embodiment.

FIG. 8 is a structural explanatory view for explaining the first step of the photomask manufacturing process in the second example of the present invention.

FIG. 9 is an explanatory diagram of a configuration of a photomask in the second embodiment.

FIG. 10 is a structural explanatory view of a photomask according to a third embodiment of the present invention.

FIG. 11 is a structural explanatory view of a photomask according to a fourth embodiment of the present invention.

FIG. 12 is a structural explanatory view of a photomask according to a fifth embodiment of the present invention.

[Explanation of symbols]

11, 21, 31 Transparent quartz substrate 12, 15, 22a, 22b, 32, 42a, 42b,
53,54,55 Opaque pattern 13,23 Electron beam resist 14 Transparent layer 16 Electron beam resist

Claims (6)

[Claims] 1. A mask for light exposure, which comprises a transparent substrate transparent to light such as visible light or ultraviolet light for pattern transfer, on which a pattern opaque to the light is formed.
A photomask, characterized in that opaque pattern portions are provided at positions of different heights on a transparent substrate. 2. The opaque pattern portion is provided directly on a transparent substrate having a flat surface and on a transparent layer provided on the transparent substrate and transparent to light such as visible light or ultraviolet light for pattern transfer. Photomask according to claim 1, each provided. 3. The photomask according to claim 1, wherein the opaque pattern portions are provided on the step lower surface and the step upper surface of the transparent substrate having the step, respectively. 4. The photomask according to claim 3, wherein the opaque pattern portion is provided so as to extend from the step lower surface to the step upper surface of the transparent substrate having the step. 5. The photomask according to claim 2, wherein opaque pattern portions are provided on the step lower surface and the step upper surface of the stepped transparent layer, respectively. 6. An opaque pattern portion is provided on each of a step lower surface and a step upper surface of a transparent substrate having a step, and is provided so as to extend from the step lower surface to the step upper surface of the transparent substrate between them. The photomask according to claim 1.