JP3395102B2 - Stencil mask for electron beam drawing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask for shaping an electron beam into a predetermined shape in a collective electron beam exposure apparatus for exposing and drawing a resist on a substrate such as a wafer.

[0002]

2. Description of the Related Art Conventionally, high-density semiconductor integrated circuits such as LSI, VLSI, and ASIC have been manufactured by applying a resist having sensitivity to ionizing radiation on a substrate to be processed such as a silicon wafer and using the resist as a stepper or aligner. After exposing the image of the mask pattern original plate with, to obtain a desired resist pattern by developing, using the resist pattern as a mask, the lithography process such as substrate etching, doping treatment, thin film formation, and lift-off was performed. .
The mask pattern original used to create the resist pattern is called a reticle in the stepper and a master mask without a mask in the aligner.Both are collectively called a photomask.Both of them are called exposure masks. A light-shielding film pattern having a light-shielding property is provided on the substrate, and the images of these light-shielding film patterns are exposed and transferred to the resist. Usually, in the case of a stepper, the image of the mask pattern original plate is reduced to 1/5 to 1/10, and in the case of an aligner, the image of the mask pattern original plate is exposed and transferred at a ratio of 1: 1. In recent years, the degree of integration of semiconductor integrated circuits has increased, and 64 Mbits has come to a practical level for DRAM, which is one of the memories, in particular.
The minimum dimension of M is about 0.30 μm, which is a region exceeding the resolution limit of the resist pattern in the conventional i-line stepper exposure method.

Therefore, in order to achieve resolution of 64 MDRAM level, the exposure light source has a shorter wavelength and the transfer lens has a higher N.
Various methods such as a super-resolution method represented by A method and an annular illumination method and a method using a phase shift mask that can use the conventional stepper exposure apparatus as they are are being studied.
In order to obtain a resolution higher than the level of MDRAM, electron beam direct writing method that does not use a photomask, in which an electron beam is shaped by a variable aperture and a desired resist pattern is obtained by directly irradiating the resist on a wafer, is also being studied. ing.
This is also called a variable shaped electron beam direct writing method. In this electron beam direct writing method, generally, as shown in FIG. 5, an electron beam (beam) 520 emitted from an electron gun 510 is
By passing the first rectangular aperture 530 and then the second rectangular aperture 531, the two sides that sandwich the right angle of the first rectangular aperture 530 and the second rectangular aperture 5
31 is shaped into a rectangular shape having a shape corresponding to two sides sandwiching the right angle, and the shaped large and small electron beams are reduced by a lens system and irradiated onto a predetermined position on the wafer.
Only a predetermined area of the resist is irradiated, and the irradiated resist is developed to obtain a desired resist pattern. 550 is an electron beam having a rectangular cross section.
Reference numeral 60 denotes an electron beam irradiation region. Incidentally, FIG.
[FIG. 3] is a schematic view for simplifying the description, and the lens system and others are omitted. The electron beam irradiation region 560 is also shown in a large size for easy understanding. However, in the case of this electron beam direct drawing method, a large number of electron beams shaped into large and small rectangles (rectangular electron beam 550) are irradiated to irradiate all predetermined regions, and irradiation drawing to the resist is performed. It took time and it was necessary to deal with it.

Therefore, as shown in FIG. 6, an electron beam direct writing method has been adopted in which the entire desired pattern is exposed at one time. In this method, the electron beam (beam) 620 emitted from the electron gun 610 is shaped into a rectangular shape by the first rectangular aperture 630, and the shaped electron beam is irradiated onto the mask 640 to correspond to the mask 640. After shaping the electron beam into a predetermined shape, the shaped electron beam 650 is reduced and projected by a lens system to irradiate a predetermined position on the wafer. That is, a predetermined shape corresponding to the mask 640 can be collectively irradiated onto the wafer, and the writing time can be shortened as compared with the electron beam writing method shown in FIG. This method is also referred to as a partial collective exposure type electron beam direct writing method.
Note that FIG. 6 is also a schematic diagram for simplifying the description, the lens system and the like are omitted, and an electron beam irradiation region 660 is shown.
Is also shown large for easy understanding. The mask 640 used here is for selectively passing the electron beam depending on the position of the mask, and is generally shown in FIG.
As shown in (a), a support 71 made of a silicon substrate
0 on one surface of the intermediate layer 72 such as silicon dioxide (SiO ₂ )
The silicon thin film 730 fixed through 0 is used, and the silicon thin film 730 has a through hole 731 corresponding to a predetermined pattern.
And the thick silicon substrate 710 also corresponds to the through hole 731 of the silicon thin film 730.
(Referred to as 1) is provided in a plurality of parts. Then, only the region corresponding to the through hole of the silicon thin film 730,
It is designed to allow the passage of electron beams. Hereinafter, this mask 640 is referred to as a stencil mask. Incidentally, FIG.
7B is a view seen from the B3 side of FIG. 7A, and FIG.
Shows the shape of the silicon thin film 730 in the window 711A region.

Thus, this stencil mask 640
In this example, the window (through hole) 711 is provided in the silicon substrate 710 which is thicker than the silicon thin film 730.
Conventionally, the shape of 1 is hot potassium hydroxide (KOH)
Or EPW (Ethylenediamine: Pitecarol: H ₂ O =
As shown in FIG. 8, it was formed into a substantially rectangular shape by etching using 17: 8: 3) as an etching solution, as shown in FIG. The etching speed with these etching solutions has anisotropy that differs depending on the direction of the silicon crystal structure. And, in general, since the surface of the silicon substrate is (100),
As shown in FIG. 8, a window having (111) faces on all sides is opened.

[0006]

As described above, the window portion of the stencil mask in the electron beam direct writing method shown in FIG. 6 is conventionally provided in a substantially rectangular shape for simplicity as shown in FIG. It was As a result, the in-plane stress of the silicon thin film in the area corresponding to the window area provided on the silicon substrate varies, and the accuracy of the pattern shape of the stencil mask transferred to the resist on the wafer and the position accuracy decrease. There was a problem of doing. Under the circumstances, the present invention devises the shape of the stencil mask used in the electron beam direct writing apparatus of the reduction transfer type on the resist on the wafer, and corresponds to the window area provided on the silicon substrate. The present invention intends to provide a silicon thin film having a small variation in the in-plane stress in the region to be filled. This improves the accuracy of the pattern shape of the stencil mask transferred to the resist on the wafer and the positional accuracy,
The present invention intends to meet the demand for further miniaturization in semiconductor devices such as LSI.

[0007]

The stencil mask for electron beam drawing of the present invention is formed by shaping an electron beam into a predetermined shape corresponding to the mask, and reducing the shaped electron beam by a lens system. A partial collective electron beam exposure apparatus for forming a latent image of a resist pattern having a predetermined pattern on a predetermined area by directly irradiating a predetermined area on a resist on a substrate such as a wafer directly with the electron beam. A mask used, in which a silicon thin film forming a mask portion was fixedly provided on one surface of a support made of a silicon substrate having a (100) surface as a surface, with an intermediate layer made of a silicon dioxide thin film interposed therebetween. The silicon thin film has through holes corresponding to a predetermined pattern for shaping the electron beam into a predetermined shape, and the support made of a silicon substrate corresponds to the through holes of the silicon thin film. The region is provided with at least one window formed of a through hole for passing an electron beam shaped by a silicon thin film, and the window is two sides parallel to the orientation flatness and orthogonal to the orientation flatness. It is characterized in that it is a substantially regular octagonal through hole having sides. Further, in the above, a conductive layer is provided on the upper surface of the silicon thin film.

[0008]

The present invention is constructed as described above,
It is possible to provide a stencil mask with less variation in the in-plane stress of the silicon thin film in the region corresponding to the window region provided on the support made of a silicon substrate, and as a result, the stencil transferred to the resist on the substrate such as the wafer. It is possible to improve the accuracy of the pattern shape of the mask and the position accuracy. Specifically, the support made of a silicon substrate has a substantially octagonal shape of a window formed of a through hole for passing an electron beam shaped by the silicon thin film in a region corresponding to the through hole of the silicon thin film. As compared with the conventional quadrangular shape shown in FIG. 8, it is assumed that the shape is closer to a circle, and the variation in the in-plane stress of the silicon thin film in the region corresponding to the window region provided in the support made of the silicon substrate is small. There is. The support made of a silicon substrate is a silicon substrate having a (100) plane on its surface, and the octagonal through-hole has two sides parallel to the orientation flatness and two sides orthogonal to the orientation flatness. By providing such a structure, it is possible to easily form a substantially octagonal window by etching. And
Since the intermediate layer is a silicon dioxide thin film, as will be described later, when a stencil mask is manufactured from a Si-SiO ₂ substrate in which an intermediate layer and a silicon thin film are sequentially laminated on a silicon substrate, an etching stop layer in window etching Silicon dioxide (SiO 2) as (stopper layer)
₂ ) Layers are available. Furthermore, by providing a conductive layer on the upper surface of the silicon thin film, it is possible to prevent the electron beam from being charged up in the silicon thin film.

[0009]

EXAMPLE An example of a stencil mask for electron beam drawing of the present invention will be described with reference to the drawings. FIG. 1A shows a sectional view of a stencil mask for electron beam writing according to the present embodiment, and FIG. 1B shows a window portion of a support made of a silicon substrate, which is a characteristic portion of FIG. 2A is a diagram showing a state seen from the A3 side, FIG. 1C is a plan view of the stencil mask, and a diagram seen from the A0 side of FIG.
FIG. 3 is a diagram showing the relationship between the shape of the window forming resist pattern and the shape of the window formed by etching when the window is formed by etching from the A3 side shown in FIG. 3A and 3B are cross-sectional views for explaining how to enter etching on each side shown in FIG. The cross-sectional view taken along line A1-A2 of FIG.
It is (a). Further, in FIG. 2, a solid line L1 shows a window forming resist pattern, and a dotted line L2 shows an etching shape. 1, 2 and 3, 1
00 is a stencil mask, 110 is a support, 111 is a window, 115 is orientation flatness, 120
Is an intermediate layer, 130 is a silicon thin film, 131 is a through hole, 1
Reference numeral 40 is a conductive layer, and 160 is a resist (silicon dioxide). The stencil mask 100 of this embodiment shapes an electron beam into a predetermined shape corresponding to the mask as shown in FIG.
Further, the electron beam shaped into the predetermined shape is reduced by a lens system, and the resist on the substrate such as a wafer is directly irradiated with the electron beam collectively in a predetermined area, whereby the predetermined area is predetermined. A mask used in a partial collective electron beam exposure apparatus that forms a latent image of a resist pattern made of a pattern, and an intermediate body 120 made of silicon dioxide (SiO ₂ ) and an electron beam are sequentially formed on a support 110 made of a silicon substrate. The through-hole 131 of the silicon thin film 130 is provided with a silicon thin film 130 having a through-hole corresponding to a predetermined pattern for shaping into a predetermined shape and a conductive layer 140 made of W (tungsten) for preventing charge-up. The support 110 in the region corresponding to is provided with a window 111 formed of an octagonal through hole for passing an electron beam. The support 110 is a silicon substrate having a (100) plane on its surface, and the octagonal through-hole has two sides parallel to the orientation flatness and two sides orthogonal to the orientation flatness. is there.

In this embodiment, the silicon thin film 130 is used.
Has a thickness of 625 μm, the intermediate layer 120 has a thickness of 1 μm, the silicon thin film has a thickness of 20 μm, and the conductive layer has a thickness of several Å. The silicon thin film 130 is a mask for shaping the electron beam (beam) shaped in a certain range region as shown in FIG. 6 so that its cross section has a predetermined shape.
Only the region of the through hole 131 is made to pass the electron beam, and the through hole 131
The electron beam is shaped without passing through the region other than the part. The thickness of the silicon thin film 130 is 20
It should be at least μm, but in terms of processing and strength,
The range of 20 μm to 25 μm is preferable. The support made of a silicon substrate supports the silicon thin film 130, and preferably has a thickness in the range of 600 μm to 650 μm. The intermediate layer 120 is used for the support 11 as described later.
It is provided so that the silicon thin film 130 side is not etched when a window is opened in 0.
O ₂ ).

FIG. 2 shows the relationship between the shape of a corrosion-resistant film (also called a resist) made of silicon nitride (SiN) and the etching shape when a substantially regular octagonal window is formed in the support 110. However, in order to open a substantially regular octagonal window, a corrosion-resistant film (resist 160) made of silicon nitride (SiN) is provided in a shape different from the regular octagon as shown in FIG. There is a need. This is because hot potassium hydroxide (KOH) or EPW (ethylenediamine: ethylenediamine: is used as an etching solution for forming a window (through hole) in a silicon substrate.
Since Pitecarol: H ₂ O = 17: 8: 3) is used,
This is because the way etching enters shows anisotropy that differs depending on the direction. The cross section of the (111) plane shown in FIG. 2 is etched as shown in FIG. 3A, and the cross section of the (100) plane shown in FIG.
As shown in (b), etching processing is performed. In the case of a silicon substrate having a (100) surface on its surface, which is used as a support, two sides parallel to the orientation flatness 115 of the window forming resist pattern (solid line L1),
And the etching surface along the two orthogonal sides is (111)
The surface and the etched surface along the other four sides are the (100) surface.

Next, the stencil mask 100 of this embodiment is used.
The manufacturing method of will be briefly described. First, (1
Support 11 made of a silicon substrate having a (00) surface as a surface
0, an intermediate layer 110 made of silicon dioxide (SiO ₂ ) was sequentially formed by thermal oxidation to a thickness of 1 μm, and a silicon thin film 130 was polished to a thickness of 20 μm. _{2 The} substrate 210 was prepared. (Fig. 4
(A)) The Si-SiO ₂ substrate 210 is provided with a silicon dioxide (SiO ₂ ) thin film as an intermediate layer 120 on one surface of a Si substrate 110A, and a silicon thin film (Si thin film) is further provided on the intermediate layer 120.
130 is provided. This Si-SiO ₂ substrate 2
10 for CVD (Chemical Vapor)
The SiO ₂ film 220 of about 0.5 μm is formed on the silicon thin film 130 by the deposition. (FIG. 4B) Next, with respect to the Si—SiO ₂ substrate 210 on which the SiO ₂ film 220 is formed, a SiN film 230 serving as a mask at the time of wet etching of the Si substrate 110A described later is formed by CVD to a thickness of 0.2 μm. Filmed on. (FIG. 4C) Next, the opening 231 of the SiN film 230 having the shape shown in FIG. 2 was formed on the surface on the side where the window was formed. (FIG. 4D) The opening 231 is formed by applying a resist on the SiN film 230, patterning the resist, and etching the SiN film 230 by dry etching with C ₂ F ₆ gas using the resist pattern as a mask. I went. Next, with respect to the silicon substrate 110A, the portion exposed from the opening 231 of the SiN film 230 is heated with hot potassium hydroxide (KO).
H) solution was used for etching to form the window 111 (FIG. 4E), the resist was removed with a predetermined solution, and the SiN film 230 was removed with a phosphoric acid solution. (FIG. 4 (f)) As a result, the window portion 11 has a shape similar to the shape of the dotted line portion shown in FIG.
1 was processed, and the processing of the support 110 shown in FIG. 1 was completed.

Next, a resist is coated on the SiO ₂ film 220 on the silicon thin film 130 when the SiO ₂ film 220 is etched, patterned into a predetermined shape, and exposed using CHF ₃ gas. _{The 2} film 220 was dry-etched to form a mask 220A made of a corrosion-resistant SiO ₂ film 220 for etching the silicon thin film 130 into a predetermined shape. (FIG. 4 (g)) Next, the silicon thin film 130 was dry-etched using SiCl ₄ gas using the mask 220A made of the SiO ₂ film 220 as a corrosion-resistant mask. (FIG. 4 (h)) After that, due to hydrofluoric acid, the exposed SiO ₂ film 220 and SiO that became an etching stop layer when the window 111 was formed
_{The two} films (intermediate layer) 120 were removed. (FIG. 4 (i)) Next, the conductive layer 140 made of W (tungsten) was formed to a thickness of several Å by sputtering. (Fig. 4
(J)) The conductive layer 140 is not particularly limited to W (tungsten), but may be Ta (tantalum), Au (gold), or the like. In this way, the stencil mask 100 shown in FIG. 1 for forming the electron beam into a desired shape was manufactured.

[0014]

As described above, according to the present invention, in the stencil mask used in the electron beam direct drawing apparatus of the type shown in FIG. 6 in which the shape of the stencil mask is reduced and transferred to the resist on the wafer, the silicon substrate as the support is By making the shape of the provided window region closer to a circle, it is possible to provide a stencil mask with less variation in the in-plane stress of the silicon thin film in the region corresponding to the window region. As a result, as compared with the conventional stencil mask having the rectangular window portion shown in FIG. 8, the accuracy of the pattern shape of the stencil mask transferred to the resist on the wafer and the positional accuracy are improved. As a result, the collective electron beam exposure apparatus can be used as a patterning device capable of coping with further miniaturization of a semiconductor device such as an LSI.

[Brief description of drawings]

FIG. 1 is a diagram showing a stencil mask of an embodiment.

FIG. 2 is a diagram for explaining the relationship between the shape of the window of the stencil mask of the example and the shape of the resist (SiN film) for forming the window.

FIG. 3 is a cross-sectional view for explaining how to etch a silicon substrate.

FIG. 4 is a process chart showing an example of a method for manufacturing a stencil mask of an embodiment.

FIG. 5 is a schematic diagram for explaining a variable shaping type electron beam exposure method.

FIG. 6 is a schematic diagram for explaining an electron beam exposure method of a partial batch exposure method.

FIG. 7 is a diagram for explaining a stencil mask.

FIG. 8 is a view showing a window portion of a conventional stencil mask.

[Explanation of symbols]

100 Stencil Mask 110 Support 110A Silicon Substrate 111 Window 115 Orientation Flatness 120 Intermediate Layer 130 Silicon Thin Film 131 Through Hole 140 Conductive Layer 160 Resist (SiN Film) 210 Si-SiO ₂ Substrate 220 Silicon Dioxide Film (Si
O ₂ film) 221 opening 220A mask 230 SiN film 231 opening 510 electron gun 520 electron beam 530 first rectangular aperture 531 second rectangular aperture 550 rectangular electron beam 560 electron beam irradiation area 610 electron gun 620 electron beam 630 Rectangular aperture 640 Mask (stencil mask) 650 Shaped electron beam 660 Electron beam irradiation area 710 Supports 711, 711A Window 720 Intermediate layer 730 Silicon thin film 731 Through hole

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Claims (2)

(57) [Claims] 1. An electron beam is shaped into a predetermined shape corresponding to a mask, and the electron beam shaped into the predetermined shape is reduced by a lens system so that a resist on a substrate such as a wafer is
By directly irradiating a predetermined area with an electron beam collectively,
A mask used in a partial collective electron beam exposure apparatus for forming a latent image of a resist pattern having a predetermined pattern in the predetermined region, the mask being formed on a surface of a support made of a silicon substrate having a (100) surface as a surface, A silicon thin film that forms a mask portion is fixedly provided through an intermediate layer made of a silicon dioxide thin film.The silicon thin film has through holes corresponding to a predetermined pattern for shaping an electron beam into a predetermined shape. And a support made of a silicon substrate is provided with at least one window formed of a through hole for passing an electron beam shaped by the silicon thin film in a region corresponding to the through hole of the silicon thin film, and The window is a substantially octagonal through hole having two sides parallel to the orientation flatness and two sides orthogonal to the orientation flatness. Child line drawing for the stencil mask. 2. The stencil mask for electron beam drawing according to claim 1, wherein a conductive layer is provided on the upper surface of the silicon thin film.