JP2010153697A - Semiconductor device and method of detecting alignment mark - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that sufficient contrast cannot be obtained associated with a decrease in a difference in the reflection factor of alignment light from a body of a mark and the periphery of the mark, when a film for forming an alignment mark becomes thin. <P>SOLUTION: By forming recesses and projections for constituting a diffraction grating having a two-dimensional shape in either the body of the mark for forming an alignment pattern or the periphery of the mark, diffracted light from the diffraction grating and non-diffracted light are used to enhance light intensity contrast. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor device having an alignment pattern for optical image recognition and a method for detecting an alignment mark using the alignment pattern.

  Usually, in the manufacturing process of a semiconductor device, for example, in-line monitoring such as measurement of film thickness after film formation is performed, but in order to detect the position of a measurement pattern for automatic measurement, alignment marks are usually used. Is used. In this case, an alignment mark is formed using the manufacturing process before the measurement process, irradiated with white light, and imaged using the intensity contrast of reflected light between the alignment mark area and its peripheral area, In general, the position is determined by a matching method.

  For example, when measuring the film thickness of the insulating film embedded in the STI trench after the STI formation, an alignment mark is formed in the silicon nitride film patterning process that becomes the trench forming mask, and the reflected light intensity contrast due to the presence or absence of the silicon nitride film is determined. We are using. However, as the miniaturization of semiconductor devices progresses, the thickness of the silicon nitride film becomes thinner, and a sufficient reflected light intensity contrast cannot be obtained, resulting in a situation where alignment errors frequently occur.

  On the other hand, Patent Document 1 discloses an alignment mark that can improve reflected light intensity contrast. The alignment mark disclosed in Patent Document 1 includes an alignment mark main body portion and a peripheral region provided in the periphery thereof, and a diffuse reflection layer made of aluminum is provided in the peripheral region. Here, the diffuse reflection layer is composed of, for example, a fine pattern of stripes, dots, or lattices.

  In this configuration, the mark body with a smooth surface with no irregularities reflects the alignment light almost completely specularly, while the diffuse reflection layer provided in the peripheral area diffuses and reflects so that it reflects from the peripheral area. The brightness of the reflected light reaching the image recognition device is extremely low compared to the brightness of the reflected light from the mark main body. As a result, the difference in luminance between the reflected light from the mark main body and the reflected light from the surrounding fine pattern increases, and the image recognition apparatus can perform highly accurate and stable detection and recognition.

JP 2000-182914 A

  However, in the technique disclosed in Patent Document 1, in order to diffusely reflect (diffuse reflection) on the surface, actually, after forming a stripe pattern or a rectangular dot pattern, as shown in FIG. It is necessary to form a film on the surface and make the surface curved. However, in the manufacturing process of a semiconductor device having a fine pattern, from the viewpoint of lithography, the surface is usually flattened by a CMP technique and is often difficult to apply.

  On the other hand, when the alignment mark is formed in the silicon nitride film patterning process that becomes a groove forming mask in order to measure the film thickness of the insulating film embedded in the STI groove after the STI formation, when the silicon nitride film becomes thin Since the wavelength of the alignment light is longer than the film thickness, most of the light is reflected. That is, as the miniaturization of the semiconductor device proceeds, the thickness of the film forming the alignment mark becomes thinner, and light can easily pass through the film. For this reason, in many cases, sufficient contrast cannot be obtained for the reflected light indicating the boundary of the alignment mark.

  The present invention is to obtain a sufficient light intensity contrast even when the thickness of the film forming the alignment mark is reduced.

  The present invention divides one part of the alignment mark forming part and its peripheral part into fine patterns periodically arranged in a semiconductor device, and uses interference between reflected light on the surface of the fine pattern By doing so, a semiconductor device and an alignment mark that can obtain a stable reflected light intensity contrast at the detection level of the alignment mark detection device without being affected by changes in the manufacturing conditions of the semiconductor device, and can obtain high alignment accuracy. The detection method is provided.

  Specifically, according to the first aspect of the present invention, in the semiconductor device having an alignment pattern including an alignment mark for optical image recognition provided on a semiconductor substrate, the alignment pattern forms the alignment mark. A mark body portion and a mark periphery portion around the alignment mark, and irregularities constituting a diffraction grating are formed on either the mark body portion or the mark periphery portion, and the reflecting surface is substantially flat in each case A semiconductor device characterized by this can be obtained. The diffraction grating forms a two-dimensionally arranged pattern.

  According to a second aspect of the present invention, in the method for detecting an alignment mark using an alignment pattern having a mark main body part for forming an alignment mark and a mark peripheral part provided around the mark main body part, the mark A diffraction grating is formed on one of the main body and the periphery of the mark, and the 0th-order light out of the reflected light is reflected from the portion where the diffraction grating is formed, and is reflected from the portion where the diffraction grating is not formed. By detecting light, a method for detecting an alignment mark can be obtained, wherein the alignment mark is detected.

  According to the present invention, the alignment pattern is formed by providing a periodic pattern having a flat reflecting surface formed by selective etching in either one of the mark main body portion and the mark peripheral portion. By reducing the light intensity of the reflected light in a specific direction due to the interference between the reflected lights at the light source, the light intensity contrast of the reflected light in the specific direction in the region without the periodic pattern can be obtained. High alignment accuracy can be secured without being influenced.

(First embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1A is a plan view showing an installation example of an alignment pattern of an inline monitor used in a shallow trench isolation formation process of a semiconductor device according to an embodiment of the present invention. 1B is an enlarged view of the rectangular frame in FIG. 1A, and FIG. 1C is a schematic cross-sectional view taken along line XX in FIG. 1B.

  This alignment pattern includes a mark body portion 17 and a mark peripheral portion 15, and the silicon nitride film 13 in the mark peripheral portion 15 is divided into minute rectangular patterns periodically arranged as shown in FIG. 1B.

  FIG. 1C shows a cross section of the alignment pattern formed by the shallow trench isolation formation process. As shown in the figure, a silicon oxide film 12 and a silicon nitride film 13 are sequentially deposited on the surface of the silicon substrate 11, and a part of the silicon nitride film 13 is selectively etched away by a normal lithographic process. A trench for shallow trench isolation is formed by etching the silicon oxide film 12 and the silicon substrate 11 in a region exposed by using the silicon nitride film 13 as a mask. After that, an insulating film is formed on the surface of the silicon substrate 11 and a trench for shallow trench isolation is buried, and then the surface of the silicon substrate 11 is polished by CMP to obtain the structure of FIG. 1C. At this time, since the silicon nitride film 13 has a low polishing rate, it functions as a polishing stopper, and as a result, the surface of the silicon substrate 11 becomes flat as shown in FIG. 1C.

  That is, the minute rectangular patterns periodically arranged on the mark peripheral portion 15 function as a two-dimensional diffraction grating. Similar effects can be obtained even if a fine line and space pattern is used.

  Since the minute rectangular patterns are periodically arranged in the region where the diffraction grating is provided in this manner, the reflected lights on the flat surfaces of the silicon substrate 11 and the silicon nitride film 13 of the respective rectangular patterns are reflected on each other. Since there is a reflection angle that interferes with each other and increases the light intensity, and a reflection angle that weakens each other, zero-order light that reflects in the normal reflection angle direction and primary light in a direction that forms a specific angle with it.

  At this time, the light intensity of the reflected light in this region can be reduced by arranging the light detector in the direction of the 0th-order light and adjusting so that the reflected light of the first-order or higher light does not enter the light detector. On the other hand, the light interference as described above does not occur in the region without the diffraction grating. As a result, it can be expected that the reflected light intensity contrast between the region with and without the minute rectangular pattern arrangement is about 50%. At this time, the surfaces of the silicon substrate 11 and the silicon nitride film 13 which are light reflecting surfaces need to be substantially flat.

  On the other hand, since the characteristics of the diffraction grating are determined only by the arrangement pitch of the minute pattern, it is controlled by the mask pattern used in the lithography process, and the influence of various film thicknesses forming the alignment pattern can be reduced. The influence of changes in the manufacturing conditions of the apparatus can be kept small.

  As described above, even if there is a change in the manufacturing conditions of the semiconductor device by using the alignment pattern according to the present invention, and even when the pattern surface is flat when using the alignment pattern, the region where the diffraction grating is located Since the desired reflected light intensity contrast can be ensured stably and weakly with respect to the reflected light intensity in a region having no reflected light intensity, image recognition of the alignment mark can be performed reliably.

  FIG. 1D is a histogram showing the intensity of light reflected vertically in the alignment pattern of FIG. 1A and reflected in the vertical direction, and the intensity of light detected in each area divided into FIG. 1A. It is. The horizontal axis is the light intensity, and the vertical axis is the frequency. It can be seen that two distribution peaks of a bright region with a high light intensity and a weak dark region are observed, and the difference in light intensity, that is, contrast is obtained. The alignment mark can be recognized by giving a light intensity threshold value for light / dark determination to the detected light intensity at each coordinate.

  In the present embodiment, an example in which a diffraction grating is arranged in the mark peripheral portion 15 has been described. However, even if a diffraction grating is provided in the mark main body 17, similar effects can be obtained.

  It is desirable that the width of the pattern portion of the diffraction grating in the alignment pattern according to the embodiment is 0.3 μm to 1.2 μm, and the space portion is an interval of 0.3 μm to 1.2 μm.

(Second Embodiment)
FIG. 2 is a diagram for explaining an alignment pattern according to the second embodiment of the present invention. 2A shows an installation example of an alignment pattern formed in the metal wiring forming process of the semiconductor device, FIG. 2B is an enlarged view of the rectangular frame in FIG. 2A, and FIG. . This embodiment is used during pattern transfer exposure in a lithography process. The alignment pattern has a mark main body 17 and a mark peripheral portion 15, and the mark peripheral portion 15 is divided into minute rectangles arranged two-dimensionally at a fine pitch to form a diffraction grating. On the other hand, the mark main body 17 has no diffraction grating.

  As shown in FIG. 2C, the diffraction grating is formed by selectively etching a laminated film of a tungsten nitride film 22, a tungsten film 23, and a silicon nitride film 24 sequentially deposited on the silicon oxide film 21 in a general lithography process. A silicon oxide film 25 is deposited on the diffraction grating pattern, and the surface of the tungsten film 23 which is the main light reflecting surface of the diffraction grating and the surface of the silicon nitride film 24 and the surface of the silicon oxide film 25 which are the upper layers thereof are both. There is a feature in that the surface is substantially flat, and no irregularities are formed on the surfaces of the tungsten film 23, the silicon nitride film 24, and the silicon oxide film 25.

  The diffraction grating pattern formed by the laminated film of the tungsten nitride film 22, the tungsten film 23, and the silicon nitride film 24 formed on the silicon oxide film 21 is a minute rectangle in which the surface of the tungsten film 23 is substantially flat and periodically arranged. Since it consists of a pattern, the reflected lights on the surface of the tungsten film 23 interfere with each other and function as a diffraction grating. At this time, since the characteristics of the diffraction grating are substantially determined by the arrangement pitch of the periodically arranged micro rectangular patterns, even if the film thickness of the tungsten nitride film 22 and the tungsten film 23 constituting the diffraction grating is reduced, the alignment is almost completed. It does not affect the performance of the pattern. In addition, an alignment pattern that functions stably when the surface is flat is obtained without being affected by the thickness of the silicon oxide film 25 formed on the alignment pattern.

  It is desirable that the width of the pattern portion of the diffraction grating in the alignment pattern according to the above embodiment is 0.3 μm to 1.2 μm and the space portion is 0.3 μm to 1.2 μm.

  The present invention can be used for forming an alignment pattern of a semiconductor device such as a DRAM.

It is a top view which shows the whole structure of the alignment mark which concerns on the 1st Embodiment of this invention. It is a top view which expands and shows a part of FIG. 1A. It is sectional drawing which follows the XX line of FIG. 1B. It is a figure which shows the relationship between the reflected light from a mark main-body part, and the brightness | luminance of the reflected light from a mark peripheral part. It is a top view which shows the whole structure of the alignment mark which concerns on the 2nd Embodiment of this invention. It is a top view which expands and shows a part of FIG. 2A. It is sectional drawing which follows the XX line of FIG. 2A.

Explanation of symbols

15 Mark peripheral portion 17 Mark body portion 11 Silicon substrate 12 Silicon oxide film 13 Silicon nitride film 21 Silicon oxide film 22 Tungsten nitride film 23 Tungsten film 24 Silicon nitride film 25 Silicon oxide film

Claims (8)

  In a semiconductor device having an alignment pattern including an alignment mark for optical image recognition provided on a semiconductor substrate, the alignment pattern has a mark body portion that forms the alignment mark and a mark peripheral portion around the alignment mark, Irregularities constituting a diffraction grating are formed on one of the mark main body and the mark peripheral part, and the reflecting surface of each is a substantially flat surface.   2. The semiconductor device according to claim 1, wherein the diffraction grating forms a two-dimensionally arranged pattern.   3. The semiconductor device according to claim 2, wherein the two-dimensionally arranged pattern includes a plurality of rectangular regions.   2. The semiconductor device according to claim 1, wherein the diffraction grating is formed by a line and space pattern.   5. The semiconductor device according to claim 1, wherein the diffraction grating is provided in a peripheral portion of the mark.   6. The semiconductor according to claim 2, wherein a pattern portion of the diffraction grating is 0.3 μm to 1.2 μm, and a space portion of the diffraction grating is 0.3 μm to 1.2 μm. apparatus.   In the method of detecting an alignment mark using an alignment pattern having a mark main body part that forms an alignment mark and a mark peripheral part provided around the mark main body part, either the mark main body part or the mark peripheral part The alignment mark is formed by detecting a zero-order light out of the reflected light from a portion where the diffraction grating is formed and detecting the reflected light from a portion where the diffraction grating is not formed. A method for detecting an alignment mark, comprising detecting the alignment mark.   8. The method of detecting an alignment pattern according to claim 7, wherein the diffraction grating divided into rectangular shapes is formed on the mark body and the alignment mark is detected.

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