JP2006216598A - Mask for charged particle beam exposure and mask inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mask for charged particle beam exposure capable of performing automatic focus even in a mask of a multilayer film structure and highly accurately measuring mask distortion, and an inspection method thereof. <P>SOLUTION: The mask for charged particle beam exposure is provided with a strut section having a beam structure, a membrane section provided on the main surface of the strut section and consisting of a first thin film formed in such a way that a pattern to be transferred onto a substrate is divided into a plurality of collective exposure small regions, an intermediate layer made of a second thin film provided between the membrane section and the strut section, and a position mark provided on the main surface of the strut section. In the mask, the position mark has an eliminating section in which the first and second thin films are eliminated, and a projecting section having a laminate structure consisting of the first and second thin films, and the center point of the position mark is positioned at the eliminating section. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charged particle beam exposure mask and mask inspection method used in a charged particle beam projection exposure apparatus used for exposure of a semiconductor integrated circuit or the like, and in particular, can prevent a decrease in pattern transfer accuracy due to reticle distortion. The present invention relates to a charged particle beam exposure mask and a mask inspection method.

  Semiconductor integrated circuits are increasingly miniaturized, and more and more advanced technology is required in the manufacturing process for realizing them. Among these, charged particle beam projection exposure, particularly electron beam projection exposure technology, has attracted attention as a technology that replaces the ultraviolet exposure technology.

  As an example of the electron beam projection exposure technique, a stencil mask is irradiated with an electron beam having a size of about 1 mm on a mask and subjected to reduced exposure to one-fourth, whereby a side of 250 μm (a region exposed simultaneously) Has been proposed (for example, Patent Document 1). The stencil mask used here is composed of a large number of divided patterns obtained by dividing the entire pattern of one chip, and collective electron beam exposure is performed on each divided pattern. The mask is formed using a substrate having a multilayer structure such as an SOI substrate (consisting of a silicon thin film layer, an oxide film layer, and a silicon support substrate from the upper surface).

  In this method, if the position of the image of each subfield is shifted during exposure, the divided circuit pattern does not connect well on the wafer, resulting in a failure. One cause of the subfield misalignment is a subfield misalignment on the mask due to mask distortion or the like. Such a defect can be prevented by accurately grasping the positional deviation on the mask and correcting the mask stage position by the amount of the deviation. Alternatively, in the case of electron beam exposure, the image position can be finely adjusted by correcting the deflection of the electron beam in the projection optical system.

  In order to grasp the positional deviation of the subfield on such a mask, the position of a reference mark (position mark) provided outside the subfield is usually measured by a coordinate measuring device (for example, a light wave interference type coordinate measuring device). Is done. This is called, for example, “mask distortion measurement”.

7 and 8 are schematic views showing an example of a conventional position mark.
7A is a schematic plan view seen from above the mask, and FIG. 7B is a cross-sectional view taken along the line AA in FIG. 7A. 8A is a schematic plan view from above the position mark 16, FIG. 8B is a schematic cross-sectional view along the line BB of the position mark 16, and FIG. 8C is a modification thereof. 3 is a schematic plan view of a certain position mark 16. FIG.

  This mask is composed of a membrane portion 14 made of a silicon thin film layer, an oxide film layer (BOX layer) 24, and a multilayer substrate (SOI substrate) in which a silicon support substrate is laminated.

  The position mark 16 is formed on the strut portion 20 (the beam portion between the subfields 10) of the mask. When measuring the position of the position mark 16, the stage holding the mask is moved to scan the position mark 16 with illumination light for measurement, and the scattered light or reflected light is detected by the detector. At this time, the coordinate measuring apparatus is focused on the plane of the scanning start point (the mask surface outside the position mark 16). When the scanning illumination light moves on the protruding edge of the position mark 16, the illumination light is greatly scattered at the edge portion 26 (scattered light L1), so that the signal intensity detected by the detector changes greatly. The position of the position mark 16 can be detected from the change in signal intensity. That is, in this method, position measurement is performed mainly by recognizing the pattern of the recess 22.

Although the recess 22 of the position mark 16 illustrated in FIG. 8A is continuous in an annular shape, a plurality of divided recesses 23 may be provided as illustrated in FIG. 8C (Patent Document 2). ).
JP-A-9-139344 JP 2004-172175 A

  However, the position mark formed on the multilayer substrate causes the following problems. That is, the reflected light from each layer is strengthened or weakened by interference. In the cross-sectional structure shown in FIG. 8B, illumination light from above is applied to the uppermost membrane portion 14 (L2), a part of the light is reflected on the surface (L7), and the rest is transmitted. A part of the light (L3) transmitted through the membrane part is reflected at the boundary with the oxide film layer 24 (L6) and the rest is transmitted (L4). A part (L5) of the light (L4) incident on the oxide film layer 24 is reflected at the interface with the strut 20 which is a silicon support substrate. In practice, more complex multiple reflections can occur.

  The phase of the reflected light (L5, L6, and L7) at such a multilayer film boundary varies depending on the film thickness of each layer. It strengthens in the same phase and weakens in the opposite phase. In coordinate position measurement, if reflected light (or scattered light) interferes, a change in signal intensity cannot be measured accurately. As a result, auto focus may not be possible, and it becomes difficult to detect the focus position.

FIG. 9 is a schematic diagram for explaining the relationship between the thickness of the silicon membrane and the intensity of reflected light. That is, as shown in FIG. 2B, a membrane having a thickness d made of silicon (Si) is provided on a silicon (Si) substrate via a SiO ₂ film having a thickness of 1 micrometer. explain. At this time, the relationship between the reflected light R and the thickness d of the membrane portion is as shown in FIG. That is, only by changing the film thickness of the membrane part made of silicon material by about 40 nanometers, the intensity of the reflected light R changes as much as about 50% from the maximum value of about 60% to the minimum value of about 10%, and the focus Position detection and position measurement become difficult.

  In addition, when detecting the position mark 16, the scattered light (L1) from the edge portion 26 is affected by the interference of the reflected light from each layer, so that it is difficult to detect the position of the position mark 16 accurately.

  The present invention provides a charged particle beam exposure mask capable of autofocusing and capable of measuring mask distortion with high accuracy even in a multilayer film mask, and an inspection method thereof.

In order to achieve the above object, according to one aspect of the present invention,
A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
A position mark provided on the main surface of the strut portion;
With
The position mark includes a removed portion from which the first and second thin films are removed, and a convex portion having a laminated structure composed of the first and second thin films, and the center point of the position mark is the point A charged particle beam exposure mask is provided which is located in the removal portion.

According to another aspect of the present invention,
A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
A position mark provided on the main surface of the strut portion;
With
A charged particle beam exposure mask is provided, wherein the position mark has a removal portion from which the first and second thin films have been removed and a convex portion made of the second thin film.

According to yet another aspect of the present invention,
A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
A position mark provided on the main surface of the strut portion;
With
A charged particle beam exposure mask is provided in which the position mark has a removal portion from which the first and second thin films have been removed and a recess provided in the strut portion.

  Here, the first thin film may be made of silicon, the second thin film may be made of silicon oxide, and the strut portion may be made of silicon.

Moreover, the side surface of the said convex part shall have a taper angle.
Further, the size of the removal unit may be larger than the sum of the spot size of the illumination light for focus of the coordinate measuring device that measures the position mark and the alignment accuracy of the coordinate measuring device.

Meanwhile, according to yet another aspect of the present invention,
A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure subregions;
An intermediate layer comprising a second thin film provided between the membrane part and the strut part;
On the main surface of the strut portion, a position mark provided with at least a removal portion from which the first and second thin films have been removed,
An inspection method for inspecting a charged particle beam exposure mask comprising:
A charged particle beam exposure mask inspection method is provided, wherein focusing is performed at the removal portion of the position mark.

Here, after the focus is adjusted in the removal unit, the focus position can be changed by giving an arbitrary offset amount to the focus position.
Further, after focusing at the removal unit, the lower surface edge of the convex portion can be detected with the focus position maintained.

  According to the present invention, when measuring mask distortion using a coordinate measuring apparatus, focus position alignment can be performed with high accuracy and position mark position measurement accuracy can be further improved. As a result, the mask distortion can be corrected accurately and a high-performance semiconductor device can be provided, which has a great industrial advantage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing a part of a charged particle beam exposure mask according to an embodiment of the present invention. That is, FIG. 4A is a plan view of the position mark 17 provided on the mask, and FIG. 4B is a schematic cross-sectional view taken along the line CC.

  The mask of this embodiment can also be formed using an SOI substrate that is a multilayer film. The membrane part 14 consists of semiconductor thin films, such as a silicon | silicone, for example, The thickness is 0.1 micrometer-several micrometers, for example. The strut portion 20 is made of, for example, a silicon material, and has a thickness of, for example, about 0.7 millimeters in order to maintain the mechanical strength of the reticle. Further, the width of the strut portion 20 is, for example, about 0.05 mm. The membrane part 14 and the strut part 20 have a structure fixed by an intermediate layer 24 made of a semiconductor oxide film. The thickness of the intermediate layer 24 can be, for example, about 0.1 μm to several 1 μm.

  The feature of the position mark 17 in this specific example is that the semiconductor thin film and the oxide film in the central part are removed while leaving the convex part 30. A removal portion 39 from which these two-layer structures are removed is provided on the strut portion 20. The size of the removal unit 39 is preferably equal to or greater than the sum of the spot size 37 of the illumination light used when auto-focusing is performed by the coordinate measuring device and the alignment accuracy of the coordinate measuring device. The outer shape of the removal unit 39 is preferably, for example, a rectangle, and one side thereof is 10 to 100 micrometers. In FIG. 1A, the spot size 37 is represented by a circle, but is not limited to a circle, and may be, for example, a rectangular shape.

  When the focus measurement is performed by the coordinate measuring apparatus, it is performed within the area of the removal unit 39. In this case, the focus position is adjusted with respect to the opening surface 38 of the strut portion 20. Here, the irradiation light is L10, and the reflected light from the opening surface 38 is L11. In the conventional structure described above with reference to FIG. 6, since the focus position is adjusted on the upper surface of the multilayer film, it is strongly influenced by interference of reflected light. On the other hand, in this specific example, it is understood that the multilayer film layer is formed only by the convex portion 30 in the spot size 37, and the reflected light from the multilayer film layer can be greatly reduced. In this specific example, the influence of interference due to reflected light can be greatly suppressed, so that the focus position can be accurately determined without causing weakening of the reflected light or scattered light signal. In addition, when it is desired to focus on the upper surface of the membrane portion 14 instead of the strut portion surface 38 (that is, the position mark bottom surface), the focus position may be shifted by the digging depth (H). That is, it is only necessary to apply a focus offset.

As explained above,
In the case of this specific example, by accurately focusing on the lower surface edge or the upper surface edge of the convex portion 30 (using a focus offset as necessary), the influence of interference can be reduced and accurate position mark position detection is possible. It becomes.

Next, a second specific example of the present invention will be described.
FIG. 2 is a schematic cross-sectional view of a position mark in the mask of the second specific example of the present invention. In this figure, elements similar to those described above with reference to FIG.

  When weakening due to the multilayer film occurs not only in autofocus but also in the position mark position detection signal, it is necessary to detect the position of the focus position in accordance with the bottom surface of the position mark, that is, the lower edge of the convex portion 31. is there.

  In this case, it is necessary to prevent the detection light beam from being blocked by the convex portion at the lower edge. Therefore, as shown in FIG. 2, it is preferable to provide a taper angle by inclining the side surface of the convex portion 31. The taper angle α is determined by the numerical aperture (NA) of the coordinate measuring apparatus, and if the illumination light is prevented from being irradiated as much as possible on the upper surface of the convex portion 31 of the position mark, the detection light is scattered and shielded by the upper surface and side surfaces of the convex portion 31. This prevents the position detection accuracy of the lower surface edge. That is, the focus position is the lower surface 38 of the position mark, and the bottom edge of the convex portion 31 can be detected with high accuracy.

FIG. 3 is a schematic cross-sectional view of a position mask in the third concrete example mask of the present invention. In this specific example, the convex portion 32 is configured only by an oxide film layer (BOX layer). By doing so, there is no semiconductor thin film corresponding to the membrane part 14 in the convex part 32, and interference of reflected light due to the multilayer film structure can be suppressed.
FIG. 4 is a schematic view illustrating the relationship between the thickness of the oxide film and the intensity of reflected light.
That is, as shown in FIG. 4B, when the thickness of the oxide film (SiO ₂ ) is d, the intensity of the reflected light R changes as shown in FIG.
It can be seen that the change in the intensity of the reflected light R in this example is significantly suppressed as compared to the intensity change in the reflected light R described above with reference to FIG. That is, as illustrated in FIG. 4A, even if the thickness d of the oxide film varies, the intensity variation of the reflected light R is in the range from the maximum value of about 35 percent to the minimum value of about 10 percent. The fluctuation range is 25%. This fluctuation range is about half of the film thickness fluctuation of the membrane part described above with reference to FIG. In general, the variation in film thickness of the oxide film layer formed by thermal oxidation is very small, so that the amount of change in the intensity of reflected light is further suppressed.

  As a result, even when the upper surface of the convex portion 32 is focused, it is possible to detect the mark with the automatic focusing reliably. In addition, when the focus is set on the lower surface edge of the convex portion 32, the thickness of the convex portion 32 is thin, so that the influence of detection light shielding and scattering is small, and the position detection accuracy of the lower surface edge can be increased.

  FIG. 5 is a schematic cross-sectional view of a position mark in the mask of the fourth specific example of the present invention. Also in this figure, elements similar to those described above with reference to FIGS. 1 to 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  Also in this specific example, the convex portion 33 is composed of only an oxide film layer (BOX layer), and the side surface of the convex portion 33 is inclined to provide a taper angle. In this way, as described above with reference to the second specific example, it is possible to more effectively eliminate light shielding and scattering when the lower surface edge is focused, and it is possible to detect the position with higher accuracy.

  FIG. 6 is a schematic cross-sectional view of a position mask in the mask of the fifth specific example of the present invention. In this figure, the same elements as those described above with reference to FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The feature of the position mark in this specific example is that a recess is provided in the strut portion after removing the semiconductor thin film and the oxide film. In this way, since it is equivalent to a position mark made of a single material, shielding and scattering due to light interference when focusing on the upper surface edge can be eliminated, and more accurate position detection can be achieved.

  As described above, according to the embodiment of the present invention, it is possible to prevent the focus position from being mistaken and improve the measurement accuracy by suppressing the interference of light accompanying the multilayer structure when detecting the mark position. Further, the signal strength for detecting the position mark position can be increased, and the measurement accuracy can be improved. As a result, it is possible to stably manufacture a high-performance semiconductor device with a small alignment deviation.

The embodiments of the present invention have been described with reference to specific examples. However, the present invention is not limited to these specific examples.
That is, even if those skilled in the art add design changes to the elements constituting the mask and mask inspection method of the present invention, they are included in the scope of the present invention as long as they have the gist of the present invention. .

It is a schematic diagram showing a part of the mask for charged particle beam exposure concerning the Example of this invention, (a) is a top view of the position mark 17 provided in the mask, (b) is CC line It is the schematic cross section along. It is a schematic cross section of the position mark in the mask of the 2nd example of this invention. It is a schematic cross section of the position mark in the mask of the 3rd example of this invention. It is a schematic diagram which illustrates the relationship between the thickness of an oxide film, and the intensity | strength of reflected light. It is a schematic cross section of the position mark in the mask of the 4th example of this invention. It is a schematic cross section of the position mark in the mask of the 5th example of this invention. It is a schematic diagram which shows the conventional mask for charged particle beam exposure, (a) is a top view, (b) is sectional drawing. It is a schematic diagram which shows the position mark of the conventional mask for charged particle beam exposure, (a) is a top view of a position mark, (b) is sectional drawing, (c) is a top view of a modification. It is a schematic diagram for demonstrating the relationship between the thickness of a silicon membrane, and the intensity | strength of reflected light.

Explanation of symbols

10 Small exposure area (subfield)
DESCRIPTION OF SYMBOLS 12 Membrane-membrane perforated part 14 Membrane part 16 Position mark 17 Position mark 20 Strut part 22 Concave part 23 Concave part 24 Intermediate layer 26 Edge part 30 Convex part 31, 33 Convex part (taper)
32 Convex (semiconductor oxide film)
34 Recess (Strut)
37 Illumination light spot size 38 Position mark bottom 39 Removal part

Claims (8)

A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
A position mark provided on the main surface of the strut portion;
With
The position mark includes a removed portion from which the first and second thin films are removed, and a convex portion having a laminated structure composed of the first and second thin films, and the center point of the position mark is the point A charged particle beam exposure mask which is located in a removal portion. A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
A position mark provided on the main surface of the strut portion;
With
The charged particle beam exposure mask, wherein the position mark includes a removal portion from which the first and second thin films are removed, and a convex portion made of the second thin film. A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
A position mark provided on the main surface of the strut portion;
With
The charged particle beam exposure mask, wherein the position mark includes a removal portion from which the first and second thin films have been removed, and a recess provided in the strut portion.   The charged particle beam exposure mask according to claim 1, wherein a side surface of the convex portion has a taper angle.   The size of the removal unit is larger than the sum of the spot size of the illumination light for focus of the coordinate measuring device that measures the position mark and the alignment accuracy of the coordinate measuring device. The charged particle beam exposure mask according to any one of the above. A strut portion having a beam structure;
A membrane portion comprising a first thin film provided on the main surface of the strut portion and formed by dividing a pattern to be transferred onto the substrate into a plurality of batch exposure small regions;
An intermediate layer composed of a second thin film provided between the membrane part and the strut part;
On the main surface of the strut portion, a position mark provided with at least a removal portion from which the first and second thin films have been removed,
An inspection method for inspecting a charged particle beam exposure mask comprising:
A charged particle beam exposure mask inspection method comprising: focusing at the removal portion of the position mark.   7. The charged particle beam exposure mask inspection method according to claim 6, wherein the focus position is changed by giving an arbitrary offset amount to the focus position after focusing in the removing section.   7. The charged particle beam exposure mask inspection method according to claim 6, wherein after the focus is adjusted in the removing unit, the lower surface edge of the convex portion is detected at the focus position.

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