JPH05134391A - Mask for exposing - Google Patents

Abstract

PURPOSE:To enable the transfer of patterns with high accuracy to a wafer, the surface of which is not flat by disposing transfer patterns on the front or rear surface of a transparent substrate according to the shape of the exposing surface of an object to be exposed. CONSTITUTION:Metallic thin film layers 2b are provided on the rear surface of the substrate 1 in the regions corresponding to projecting parts and metallic thin film layers 2a are provided atop the substrate 1 in the regions corresponding to recessed parts according to the rugged shapes generated by a deposition layer 7 of the wafer 4. Further, the substrate 11 covering the metallic thin film layers 2a is disposed on the substrate 1. The objective surface of a short focal length with the rear surface of the substrate 1 as the objective surface is, therefore, obtd. in the projecting parts and the objective surface of a long focal length with the rear surface of the substrate 11 as an objective surface is obtd. in the recessed parts. As a result, exposing is eventually executed on the always optimum image surface with the resist 5 on the wafer 4 and the pattern transfer is executed with high accuracy.

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 in a photolithography process which is a part of a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art FIG. 4 is a view showing a structure of an exposure mask used in forming a pattern of a conventional semiconductor device, in which a transparent substrate 1 made of quartz or the like is covered with a metal thin film 2 such as chromium to form a pattern. There is. Then, at the time of exposure, the pattern formed on this mask is transferred onto a wafer (not shown).

Next, the principle of exposure will be described. As shown in FIG. 5, when the wafer 4 is irradiated with the light transmitted through the mask by the projection (convex) lens 3 of the exposure apparatus, the pattern defined by the metal thin film 2 is transferred to the wafer 4.

Here, assuming that the projection lens 3 is a single lens, the optical distance between the target surface (pattern forming surface of the mask 4) and the lens 3 surface (hereinafter referred to as target distance) is Do, and Since the target distance Do is on the opposite side of the lens 3, it has a negative value, and on the other hand, it is the optical distance (hereinafter referred to as image forming distance) Di between the image forming surface (the surface of the wafer 4) and the lens 3 surface. The distance Di can generally be negative when the image plane is located on the same side as the target surface with respect to the projection lens, but it is assumed to be a positive value depending on the design state of the exposure apparatus. There is a simple relationship represented by the following formula between the target distance Do and the image formation distance Di, where F is a focal length which is a positive value, and 1 is a positive value.

1 / Do = 1 / Di-1 / F

The above-mentioned optical distance is equal to the physical distance increased by the refractive index of the substance, and since the refractive index is the same for air, the optical distance in air is equal to the physical distance. For other materials, the index of refraction depends on the wavelength of the light and in most cases will differ from the physical distance.

In practice, however, the lenses of the exposure apparatus are often complex systems consisting of a plurality of lenses having different shapes. Therefore, the target distance Do and the imaging distance Di
The formula that expresses the relation of is very complicated. However, the imaging distance Di is defined as a function of the target distance Do and the lens parameter F as follows.

Di = f {Do, lens parameter}

In order to obtain a good transferred image on the wafer, the position of the wafer must be carefully adjusted. More specifically, as shown in FIG. 7, when the wafer 4 is covered with a general resist 5 having a thickness t, the image plane 6 is one third of the resist thickness t from the surface of the wafer 4. It is a well-known fact that optimum transcription is performed when it is located at a site corresponding to the distance (1 / 3t). Therefore, the height of the wafer 4 must be adjusted so as to achieve this optimum transfer condition.

[0010]

The conventional exposure mask is constructed as described above, and the pattern is transferred by focusing on the predetermined depth position of the resist formed on the wafer substrate surface. However, the wafer substrate often goes through various steps in the manufacturing process and does not remain flat but has some irregularities.

Explaining with reference to FIG. 5, a deposition layer 7 having a thickness T such as an insulating film or a CVD layer is partially formed on the surface of the wafer 4, and in the case of such a wafer substrate, it is described above. As described above, in order to realize the optimum transfer condition, the image plane is changed along the uneven shape, and, for example, in the portion where the deposition layer 7 is formed, at the position 6b of T + 1 / 3t from the surface of the wafer 4,
Further, in the portion where the deposition layer 7 is not formed, it is necessary to align at the position 6a which is 1 / 3t from the surface of the wafer 4.

However, in the conventional exposure mask,
Since the target surface is flat, the position of the image plane obtained on the wafer surface is also flat. Conventionally, in such a situation, an image plane which is located between the image planes 6a and 6b is selected. I was exposed to light. Therefore, in such a method, there is a problem that the image plane projected on the wafer is not located at an optimum position and high-precision transfer cannot be performed.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an exposure mask capable of performing highly accurate transfer even to a wafer having an uneven surface. ..

[0014]

An exposure mask according to the present invention has a transfer pattern arranged on the upper surface or the lower surface of a transparent substrate according to the shape of the exposed surface of an object to be exposed.

Further, a second light-transmissive substrate is partially formed on one main surface of the transparent substrate according to the exposure surface shape of the object to be exposed, and the transfer pattern is formed on the substrate and the second substrate. Are arranged on the same main surface side.

Further, transfer patterns are formed on the upper and lower surfaces of the transparent substrate, a second transparent substrate is provided on the upper surface of the substrate, and the transfer pattern is further formed on the substrate.

[0017]

In the present invention, the transfer pattern is arranged on the upper surface or the lower surface of the transparent substrate according to the shape of the exposed surface of the object to be exposed. can get.

Since the second transparent substrate is partially provided on the one main surface side of the transparent substrate according to the shape of the exposed surface of the object to be exposed and the transfer pattern is arranged, the second substrate thickness An image plane having a different focal length can be obtained.

Further, since the transfer patterns are formed on the upper and lower surfaces of the transparent substrate, and the second transparent substrate is provided on the upper surface of the substrate, and the transfer patterns are further formed on the substrate, three or more transfer patterns are formed. A plurality of image planes having different focal lengths can be obtained.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An exposure mask according to an embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the same reference numerals as those in FIG. 4 denote the same or corresponding parts, and 2a denotes the upper surface of the quartz substrate 1 or the first groove 12a of the quartz substrate 12 having the pattern forming groove 12a on the upper surface. It is a metal thin film, for example, a metal such as chromium is used.
2b is the lower surface of the quartz substrate 1 or the quartz substrate 1
A second metal thin film arranged on the lower surface of 2 and a second quartz substrate 11 arranged on the first metal thin film 2a.

Next, the exposure principle will be described. As shown in FIG. 2, using the exposure mask of FIG. 1B, the light transmitted through the mask is projected onto the wafer 4 by the projection (convex) lens 3 of the exposure apparatus.
When it is irradiated with, the pattern defined by the metal thin film 2 is transferred to the wafer 4.

At this time, since the mask has the two-layer metal patterns 2a and 2b arranged on the front surface and the back surface of the substrate 1, the mask has two spatially arranged target surfaces, that is, the lower surface of the substrate 1, And, there are two target surfaces of the lower surface of the substrate 11. Therefore, the imaging distance Di1 corresponds to the target distance Do1, and the imaging distance Di0 corresponds to the target distance Do0.
And any imaging distance Di corresponds to a different target distance Do. Here, the two target surfaces are Do1 and Do2,
If the corresponding image planes are Di1 and Di2, the following relationship holds.

Di1 = f {Do1, lens parameter} Di2 = f {Do2, lens parameter} Do1-Do2 = ΔDo Di1-Di2 = ΔDi

In order to obtain an ideal image, the distance difference ΔDi between the image planes must be equal to the height of the uneven shape on the wafer substrate 4. Here, the distance difference ΔDi in the image plane is defined by the distance difference ΔDo in the target surface and the lens parameter. The lens parameter is a constant value in a constant exposure apparatus. Therefore, the distance difference ΔDi in the image plane is defined by the distance difference ΔDo in the target surface for a particular exposure apparatus. This distance difference .DELTA.D0 is defined by the physical layer thickness between the two metal thin film layers of the mask and the refractive index of said layers. Therefore, by selecting a predetermined material having a constant refractive index and setting the layer thickness between the two metal thin film layers to an appropriate value, the distance difference ΔD having an arbitrary value can be obtained.
o can be realized. As a result, the distance difference ΔDi of any image plane can be realized, and therefore the wafer substrate 4
It is possible to obtain a mask having a target surface (imaging surface) corresponding to the above-mentioned uneven shape.

Further, in the above structure, the refractive index of the material between the two metal thin film layers 2a and 2b needs to be extremely close to the refractive index of the mask surface, otherwise, internal refraction in the contact area between these two materials is required. May reduce the quality of imaging. In this case, as shown in FIG. 1 (b), a groove is provided on the upper surface of the transparent substrate 12, the metal thin film 2a is embedded in the groove, and the transparent substrate 12 and the transparent substrate 11 are brought into close contact with each other. It is possible to suppress deterioration of imaging quality.

As shown in FIG. 1 (a), a single substrate 1
In the mask having the metal thin films 2a and 2b on both surfaces, the target surface is the front surface and the back surface of the substrate, and the distance difference ΔDo in the target surface and the distance difference ΔDi in the image forming surface are caused by the thickness of the substrate 1 itself and its refractive index. Will be defined.

As described above, according to this embodiment, the metal thin film layer 2b is provided on the lower surface of the substrate 1 in the region corresponding to the convex portion according to the concave-convex shape generated by the deposition layer 7 of the wafer 4, and corresponds to the concave portion. In the region, a metal thin film layer 2a is provided on the upper surface of the substrate 1,
Further, since the substrate 11 covering the metal thin film layer 2a is arranged on the substrate 1, a target surface having a short focal length with the lower surface of the substrate 1 as a target surface can be obtained in the convex portion, and the lower surface of the substrate 11 in the concave portion. A target surface having a long focal length, which is the target surface, is obtained. Therefore, the resist 5 on the wafer 4 is always exposed on the optimum image surface, and highly accurate pattern transfer can be performed.

Further, the metal thin film layer 2a on the surface of the substrate 12 is embedded in the substrate 12, and the transparent substrate 11 is provided in close contact therewith, so that imaging by internal refraction in the contact region between the metal thin film layers 2a and 2b is performed. It is possible to prevent deterioration of quality.

Next, a second embodiment of the present invention will be described. In order to obtain different target surfaces in this embodiment, FIG.
As shown in (a), an auxiliary transparent substrate 13 for shortening the focal length is formed on the lower surface of the substrate 1, and the metal thin film layer 2 is formed on each of them.
c and 2d are arranged, and the auxiliary substrate 1
By adjusting the layer thickness of 3, it is possible to easily obtain a mask having a desired distance difference ΔDo. In this case, a plurality of auxiliary substrates having different layer thicknesses may be provided on the substrate 1 to form a mask having three or more different focal lengths.

Further, FIG. 3 (b) shows a modification of FIG. 1 (c). In addition to the structure shown in FIG. 1 (c), a metal thin film 2e is embedded on the upper surface of the substrate 11, and a transparent substrate is further formed thereon. In this way, it is possible to obtain a mask having three different focal lengths whose target surfaces are the lower surface of the substrate 12, the lower surface of the substrate 12, and the lower surface of the substrate 14. It is possible to deal with a wafer having two or more steps, and a wafer having more steps can be exposed by further stacking such a structure.

[0031]

As described above, according to the exposure mask of the present invention, the transfer pattern is arranged on the upper surface or the lower surface of the transparent substrate according to the shape of the exposed surface of the object to be exposed. A target surface having a different focal length can be obtained depending on the arrangement surface of the pattern, or a second transparent substrate is partially provided on one main surface side of the transparent substrate according to the shape of the exposed surface of the exposed object to form a transfer pattern. Since I was supposed to place
A target surface having a different focal length depending on the thickness of the second substrate can be obtained, and the image-forming surface changes according to the uneven shape of the surface of the object to be exposed, so that highly accurate pattern transfer can be performed. There is an effect that can be.

Further, the transfer patterns are formed on the upper and lower surfaces of the transparent substrate, and the second transparent substrate is provided on the upper surface of the substrate, and the transfer patterns are further formed on the substrate. It is possible to obtain a plurality of image forming planes having different focal lengths, and it is possible to easily and highly accurately transfer a pattern to an object to be exposed having a complicated uneven shape.

[Brief description of drawings]

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

FIG. 2 is a conceptual diagram when performing exposure using an exposure mask according to an embodiment of the present invention.

FIG. 3 is a view showing the arrangement of an exposure mask according to another embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional exposure mask.

FIG. 5 is a conceptual diagram when performing exposure using a conventional exposure mask.

FIG. 6 is a diagram for explaining an optimum position of an exposure formation surface by using a wafer on which a photoresist is formed.

FIG. 7 is a diagram for explaining a problem of a conventional exposure mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Metal thin film 3 Projection lens 4 Wafer 5 Photoresist 6 Image plane 7 Deposition layer 11, 12, 14 Transparent substrate 13 Auxiliary substrate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 21/027

Claims (5)

[Claims] 1. An exposure mask in which a light-blocking transfer pattern is formed on a light-transmissive substrate surface, wherein the light-blocking transfer pattern is an upper surface or a lower surface of the substrate depending on an exposed surface shape of an object to be exposed. An exposure mask, which is formed on. 2. The exposure mask according to claim 1, further comprising a second light-transmissive substrate that covers the transfer pattern formed on the upper surface of the substrate. 3. The exposure mask according to claim 2, wherein the transfer pattern formed on the upper surface of the substrate is embedded in a recess on the upper surface of the substrate, and the upper surface of the substrate and the lower surface of the second substrate are in close contact with each other. An exposure mask that is characterized by 4. The exposure mask according to claim 3, wherein a metal pattern is provided on an upper surface of the second light transmissive substrate. 5. An exposure mask in which a light-shielding transfer pattern is formed on a surface of a light-transmissive substrate, wherein the substrate has a main surface on one side thereof partially depending on a shape of an exposed surface of an object to be exposed. An exposure mask having a formed second light-transmissive substrate, wherein the light-shielding transfer pattern is arranged on the same main surface side of the substrate and the second substrate, respectively.