JP2740898B2 - X-ray exposure mask and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-precision mask for X-ray exposure used for manufacturing a semiconductor integrated circuit and the like.

[Prior Art] FIG. 8 shows a cross section of a conventional X-ray exposure mask. An X-ray absorber 1 and an alignment mark 2 forming an exposure pattern are provided on a membrane 3. The membrane 3 is supported on a Si frame 4 reinforced by a reinforcing frame 5. Generally, heavy metals such as Au, Ta, and W are used for the X-ray absorber 1. The membrane 3 is a thin film of an inorganic substance such as SiC, SiN, and BN, and has a thickness of several μm. The Si frame is formed by removing a central portion of the wafer by etching. Its thickness is 0.
About 4 to 2 mm is generally used.

9 to 12 show plan views of a conventional X-ray exposure mask. However, in these figures, the illustration of the X-ray absorber is omitted, and only the region 6 having the exposure pattern is shown. In each figure, the lower Si of the membrane
Only the portion where is removed by etching is shown as a membrane 3A.

The shape of the membrane 3A is generally circular or octagonal as shown in FIGS. 9 and 10, and the exposure pattern and the alignment mark 2 are on the same membrane 3A. Generally, the thickness of the membrane is from 1 to several μm, and the membrane is deformed by several tens μm even when a pressure of several mmH ₂ O is applied. With a mask of such a shape, the gap between the wafer and the mask should be 10 to 30μ.
When set in the range of m, the membrane is greatly deformed and vibrates due to the pressure fluctuation between the wafer and the mask. Therefore, even if an attempt is made to set a gap, a gap detection signal oscillates, making it difficult to set the gap. In order to reduce such pressure fluctuations, it is necessary to reduce the distance between the wafer and the mask at a very low speed, and the alignment time becomes very long, which is not practical.

FIG. 11 and FIG. 12 are intended to solve this disadvantage. In FIG. 11, the inner periphery of the Si frame is brought close to the alignment mark 2 to reduce the vibration of the membrane as much as possible. However, in practice, there is a limit in the accuracy of processing and removal of the Si frame.
And the inner periphery of the frame is usually about 1 to 2 mm apart.
The pattern area is about 20mm square and the space between the wafer and mask is
When the thickness is 20 to 30 μm, the pressure between the mask and the wafer fluctuates by several mmH ₂ O even if the distance between the wafer and the mask slightly changes. This pressure fluctuation causes a problem that the membrane vibrates and a gap detection signal cannot be obtained. In order to suppress this problem, it is necessary to make the gap setting speed between the mask and the wafer extremely slow, and it takes a long time to set and align the gap, which is not practical.

In the example of FIG. 12, in order to solve this problem, the pattern exposure area and the alignment mark area are separated. Ie
The alignment mark portion of the Si wafer is removed by etching, and a membrane portion 3B on which the alignment mark is formed is provided independently of the membrane portion 3A on which the exposure pattern is formed. With such a configuration, since the membrane in the alignment mark area is small, vibration of the membrane hardly occurs, and almost no time is required for gap setting and alignment. However, in this case, the alignment mark cannot be provided on the scribe line, the chip arrangement on the wafer becomes extremely complicated, and there is a problem that the yield is reduced during the production of the semiconductor integrated circuit.

[Problem to be Solved by the Invention] An object of the present invention is to solve the above-mentioned conventional problems and to generate a slight pressure fluctuation generated between a mask and a wafer when setting a gap between a mask and a wafer and performing alignment. An object of the present invention is to provide a high-precision X-ray mask in which alignment marks are provided in the vicinity of a pattern region by suppressing vibration of a mask membrane and forming a window in which marks are provided on a scribe line.

[Means for Solving the Problems] In the X-ray exposure mask according to the present invention, a heavy metal pattern that absorbs X-rays is present on a membrane of a light element that transmits X-rays, and the membrane is held by a frame having high rigidity. In the X-ray exposure mask described above, the membrane has a quadrilateral exposure pattern region, and an alignment mark region having a shape protruding outside the quadrilateral in a direction perpendicular to the sides of the quadrilateral of the exposure pattern region, The alignment mark is formed in the alignment mark area.

The manufacturing method of the present invention corresponds to a step of forming an etching protective film on a surface of a Si wafer having a (100) plane orientation opposite to an exposure pattern side, and a quadrilateral exposure pattern region of the etching protective film. At the boundary between the portion and the portion corresponding to the alignment mark region having a shape projecting outside the quadrilateral at right angles to the sides of the quadrilateral of the exposure pattern region, an etching protection region projecting inside the quadrilateral A step of removing a portion corresponding to the exposed region of the etching protection film and a portion corresponding to the alignment mark region while leaving the etching protection region, and etching the Si wafer by wet etching to obtain {110} surface, {100} Using the difference in the etching rate of the {111} plane with respect to the plane to make the edge portion between the exposure area and the alignment mark area a right angle.

[Operation] According to the present invention, since the alignment mark area is surrounded by the Si frame with a narrow width and is integrated with the exposure area,
The alignment mark can be provided in the vicinity of the exposure region, and the alignment accuracy can be improved. Further, since the alignment mark can be provided on the scribe line, the yield of the semiconductor integrated circuit can be improved. Furthermore, since the alignment mark arrangement is relatively free, hybrid exposure with light exposure and electron beam exposure becomes possible.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

Example 1 SiN layers were formed on both front and back surfaces of a Si wafer having a (100) plane orientation by a normal method. The SiN layer on the surface serves as a membrane for an X-ray exposure mask. After forming an X-ray absorber and alignment marks thereon, the Si wafer was processed into a Si frame.

FIG. 1 (A) shows an example of the mask back surface shape before frame processing for forming the X-ray mask of the present invention, and FIG. 1 (B).
Is an enlarged view of a part thereof. Reference numeral 7 denotes a protective film that functions as an etching mask during wet etching, in this case, SiN formed on the back surface of the wafer when the membrane is formed. 4A is the silicon exposed by removing the etching protection film 7.
Plane. As shown in the figure, in the present embodiment, a portion corresponding to the central exposure pattern region of the protective film 7 is removed in a square shape, and a narrow region 7A at the center of each side of the square is aligned with the alignment mark. The area has been removed.
The protrusions 7B on both sides of the region 7A are etching protection regions for making the edges of the exposure region and the alignment mark region perpendicular to each other by etching the back surface of the Si wafer. At this time, it is preferable that the plane perpendicular to the plane of FIG. 1 be parallel to the {110} plane of the Si wafer through each side of the square forming the exposure pattern area. After the protective film 7 has the shape shown in FIG.
The back surface of the Si wafer was wet-etched with a normal etching solution.

FIG. 2 shows a state after etching the back surface of the mask. FIG. 2 (A) shows the same part as FIG. 1 (B), and FIG. 2 (B) shows a cross section along the line AA 'in FIG. 2 (A). Due to the difference in etching rate depending on the plane orientation, the etching protection region 7B is removed by etching, and the edges of the exposure region and the alignment mark region are at right angles. The inclined surface of the Si frame 4 is a {111} surface.

FIG. 3 shows a plan view of the X-ray exposure mask thus formed. The exposure pattern is not shown. The edges of the exposure area and the alignment mark area are at right angles, and the alignment mark 2 is between narrow parallel frames and is supported by a rigid body. For this reason, the membrane in this portion hardly vibrates due to the pressure fluctuation applied to the membrane.

In order to examine the displacement of the alignment mark area, a mask having a membrane having the shape shown in FIG. 4 was manufactured. In the case where the membrane width of the alignment mark area is approximately 2 mm and the size of the membrane in the exposure area is 24 mm square, the etching protection area 7B
Since the etching of the Si wafer was performed without providing the edge, the edges of the exposure area and the alignment mark area form an angle of 45 °. FIG. 5 is a partially enlarged view of FIG. 4, where points A, B, C, D, E, F, and G
Indicates the position where the vibration of the membrane was measured. Sixth
The figure shows the relationship between the distance from the center of the membrane and the amount of displacement of the membrane. The curves (a, b, c, d, e) show the mask-wafer spacing from 30 to 10 μm and 35 to 15 μm, respectively.
The displacement amount when the mask is changed from 40 μm to 20 μm, from 45 μm to 25 μm, and from 50 μm to 30 μm. When the initial gap is as large as 50 μm, the displacement is small. When the initial gap is 30 μm, when the gap is changed to 10 μm, a displacement of approximately 20 μm occurs at point A in the exposure area. At points F and G in the alignment mark area, the amount of displacement is within 1 μm. In the curve of E having an initial gap of 50 μm, the displacement amount is within 2 μm even at the point A, and the displacement amount is within 1 μm at the points E, F and G.

As described above, the deformation of the membrane decreases as it goes deeper into the alignment mark area. Usually, the mask-wafer interval used in X-ray exposure is 20 to 30 μm, and the amount of displacement at the points F and G is almost negligible. Moreover, the displacement amount shown in FIG. 6 is a value when the edge is set to 45 °, and as shown in FIGS. 2 and 3, if the edge is made a right angle,
The displacement of the membrane is further reduced.

By using the frame of the present invention having a structure having a right-angled edge, the problem of the vibration of the alignment mark was almost eliminated, and the gap setting time at the time of alignment could be greatly reduced.

Embodiment 2 FIG. 7 (A) shows another example of the shape of the back surface of the mask before forming the frame for forming the X-ray mask of the present invention. FIG. 2B is an enlarged view of a part of FIG.
This embodiment differs from the embodiment shown in FIG. 1 only in that the etching protection region 7C has a wedge shape in this embodiment. The etching protection region 7C is removed by etching, the boundary between the exposure region and the alignment mark region becomes the same as that shown in FIGS. 2 and 3, and the edges of the exposure region and the alignment mark region are at right angles. The edges of the exposure area and the alignment mark area are at right angles, and the alignment mark 2
Is between narrow parallel frames and is supported by a rigid body. For this reason, the membrane in this portion hardly vibrates due to the pressure fluctuation applied to the membrane.

The shape of the etching protection region is not limited to those shown in the first and second embodiments, and various shapes of etching protection regions are possible by considering the etching rate ratio between the (111) plane and the (100) and (110) planes. is there. More specifically, there may be mentioned one in which a rectangular etching protection area is provided on the alignment mark area side, and one in which a rectangular etching protection area is provided in each of the alignment mark area and the exposure area.

[Effect of the Invention] As described above, the alignment mark area has a narrow width and is
By being surrounded by the frame and being integrated with the exposure area, alignment marks can be provided in the vicinity of the exposure area, improving alignment accuracy and providing alignment marks on the scribe line. The yield of the circuit can be improved. Furthermore, since the alignment mark arrangement is relatively free, hybrid exposure with light exposure and electron beam exposure becomes possible.

In the alignment, since the alignment mark area is surrounded by the Si frame with a narrow width, even if the gap between the mask and the wafer is set, the membrane in the alignment mark area does not vibrate, and the alignment can be performed in a short time.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the shape of the back surface of the mask before frame processing in the present invention, FIG. 2 is a diagram showing the shape of an alignment mark area after etching, and FIG. 3 is a diagram of an X-ray exposure mask according to the present invention. FIG. 4 is a plan view, FIG. 4 is a view showing the shape of the membrane, FIG. 5 is a partially enlarged view of the membrane, FIG. 6 is a view showing the relationship between the displacement of the membrane and the measurement position, and FIG. FIG. 8 is a view showing another example of the shape of the back surface of the previous mask, FIG. 8 is a sectional view of a conventional X-ray exposure mask, and FIGS. 9 to 12 are plan views of the conventional X-ray exposure mask. DESCRIPTION OF SYMBOLS 1 ... Absorber, 2 ... Alignment mark, 3 ... Membrane, 4 ... Si frame, 4A ... Si surface from which etching protection film was removed, 5 ... Reinforcement frame, 6 ... Exposure area, 7 ... Protective film, 7A: alignment mark area, 7B, 7C: etching protection area.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-65621 (JP, A) JP-A-1-102926 (JP, A) Full-scale operation 63-44438 (JP, U) 32017 (JP, U)

Claims (2)

(57) [Claims] (1) X-rays are applied on a light element membrane that transmits X-rays.
In an X-ray exposure mask in which a heavy metal pattern that absorbs rays is present and the membrane is held by a rigid frame, the membrane has a quadrilateral exposure pattern area,
It has an alignment mark area of a shape protruding outside the quadrilateral in a direction perpendicular to the quadrilateral side of the exposure pattern area, wherein the alignment mark is formed in the alignment mark area. X-ray exposure mask. 2. A step of forming an etching protection film on a surface of a Si wafer having a (100) plane orientation facing the exposure pattern side, and the etching protection film corresponds to a quadrilateral exposure pattern region. At the boundary between the portion and the portion corresponding to the alignment mark region having a shape projecting outside the quadrilateral at right angles to the sides of the quadrilateral of the exposure pattern region, etching protection projecting into the quadrilateral is provided. Providing a region, removing the portion corresponding to the exposure region and the portion corresponding to the alignment mark region of the etching protection film while leaving the etching protection region, etching the Si wafer by wet etching,
Using the difference in the etching rate of the {111} plane with respect to the {110} plane and the {100} plane to make the edge of the exposure area and the alignment mark area perpendicular to each other. Manufacturing method of mask.