JP2008010548A - Alignment mark, and position measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alignment mark and a position measurement method that can highly accurately measure position coordinates without taking time. <P>SOLUTION: The alignment mark is provided with slopes in a bilaterally-symmetrical forward-tapered-shape in either of a height direction and a depth direction. When a focusing movement range of a focus lens is between the top and the bottom of the alignment mark; it is possible to detect a point where the luminance profile change becomes maximum, and a point where the luminance profile change becomes minimum, so as to measure the center position of the alignment mark from there. Consequently, it is possible to simply execute alignment at high speed without highly accurately controlling a focus lens position, and without requiring an advanced image processing function. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an alignment mark used for alignment and a position measurement method.

  In a reduction projection type exposure apparatus for manufacturing semiconductor devices, a reticle circuit pattern is projected onto a wafer by a projection lens and exposed. At this time, prior to the projection exposure, the wafer surface is observed using a measuring device (detection means) to detect an alignment mark on the wafer formed in advance, and the reticle and wafer are aligned based on the detection result. So-called alignment is performed.

  At this time, the alignment accuracy largely depends on the optical performance of the measuring apparatus. For this reason, the performance of the measuring apparatus is an important factor in the exposure apparatus. Recently, various exposure apparatuses for manufacturing highly integrated semiconductor devices using a phase shift mask, modified illumination, or the like have been proposed. In such an exposure apparatus, higher alignment accuracy is required.

  Conventionally, in an exposure apparatus for manufacturing a semiconductor element, wafer position information is obtained by observing an alignment mark provided on the wafer. As an observation method at this time, the following three methods are mainly used. (1-a) a system that uses non-exposure light and does not pass through the projection lens system (OFF-AXIS system), (11) a system that uses exposure light and passes through the projection lens system (exposure light TTL system), (1-c) A system using non-exposure light and passing through a projection lens system (non-exposure light TTL system).

  For example, in an alignment system using a non-exposure light TTL observation device, an optical image of an alignment mark on a wafer surface is formed on an image sensor such as a CCD camera, and image information obtained from the image sensor is processed. Thus, a method for detecting the position of the alignment mark has been proposed. (See Patent Document 1)

  In addition, an optical image of the alignment mark is formed by a CCD camera, image information obtained by the CCD camera is binarized, and a template matching process using the position coordinates of a specific image pattern in the binarized image as a template is performed. There has been proposed a position detection device that detects the position of the alignment mark. (See Patent Document 2)

Further, in a microscope system provided with an optical lens, alignment is performed by detecting at least two mark positions. At this time, after measuring the position of the alignment mark, the measured value is compared with the design value, the difference is calculated, and correction is performed. As a correction method, a method of calculating the difference amount by software and feeding back the corrected coordinate system to hardware is generally used. (See Patent Document 3)
JP-A-3-61802 JP-A-62-232504 JP 2000-269121 A

  However, when high-precision alignment is attempted using optical means, focusing is performed by moving the focus lens in the optical axis direction, so the alignment accuracy depends on the feed accuracy of the focus lens, and is required. There is a problem in that the time required for the alignment increases in proportion to the accuracy to be performed.

  Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide an alignment mark and a position measurement method that can measure position coordinates with high accuracy without requiring time. To do.

  The present invention according to claim 1 is characterized in that the alignment mark having a step has a forward tapered slope in either the height or depth direction, and the cross-sectional shape of the alignment mark is symmetrical. Is an alignment mark.

  According to a second aspect of the present invention, there is provided a reticle or wafer provided with the alignment mark according to the first aspect.

  According to a third aspect of the present invention, there is provided a position measurement method for detecting an image of an alignment mark provided on a predetermined surface by optical means, and measuring position information of the alignment mark using the detected image. A position measurement method using the alignment mark according to claim 1.

  The present invention according to claim 4 is an alignment method using the position measurement method according to claim 3.

The alignment mark of the present invention is characterized in that it has a symmetrically tapered forward tapered slope in either the height or depth direction, so that the focusing lens has a focusing movement range at the top of the step of the alignment mark. Between the bottom and the bottom, it is possible to detect the point at which the change in the luminance profile is maximum and the point at which the change is minimum, and the center position of the alignment mark can be measured therefrom.
For this reason, the position of the focus lens can be controlled with high accuracy and an advanced image processing function is not required, and alignment can be performed at high speed and simply. Therefore, there is an excellent effect that the coordinate position can be measured at high speed regardless of the focus position of the measuring apparatus.

  Hereinafter, the alignment mark of the present invention will be described with reference to FIGS.

  The alignment mark according to the present invention has a step, and is provided with a forward tapered inclined surface that is symmetrical in either the height or depth direction. Here, the forward tapered slope is not limited to a slope where the top and bottom of the step are connected by a straight line, but may be a slope connected by a continuous line (for example, an arc). Further, the step of the alignment mark is caused by the alignment mark having a convex shape or a concave shape, and is not limited to either one (FIGS. 2B and 3B). .

  The planar shape of the alignment mark is not particularly limited as long as position information can be easily obtained. In addition, since the position information of both X and Y can be measured simultaneously with one mark, the mark shape is preferably 90-degree rotational symmetry. Examples of such a shape include a cross shape (FIG. 2A) and a square shape (FIG. 3A).

  Hereinafter, a position measurement method using the alignment mark (FIGS. 2 and 3) of the present invention will be described with reference to FIG. 4 while comparing with a position measurement method using a conventional alignment mark (FIG. 1).

<Measurement of mark center position of alignment mark using optical means>
First, the focus lens is moved in the optical axis direction to change the focus position with respect to the alignment mark.

  Next, while changing the focus position, an alignment mark is imaged on an optical imaging device such as a CCD camera, and a brightness profile is obtained, thereby obtaining a brightness profile of the image at each focus position. Here, the luminance profile is a gray level distribution of pixels in a designated image region, and generally changes in the luminance profile become large at the edge portion of the mark, indicating an extreme value (maximum value or minimum value). In other words, as a means for obtaining the edge portion of the alignment mark, after removing noise components by smoothing the brightness profile of the mark in advance, the differential processing is performed to obtain the maximum value and the minimum value, and the alignment mark edge portion is obtained. Can be determined.

  FIG. 4 shows a relationship diagram between the focus position and the luminance profile. In FIG. 4, a solid line is a luminance profile (a gray level distribution of pixels in a designated image region), and a dotted line is a differentiation of the luminance profile. At this time, the luminance profile of the image becomes an extreme value at the edge portion of the alignment mark. For this reason, P1 and P2 which are the edge portions of the alignment mark are first determined for an image having a certain luminance or higher (the focus positions 1, 2, 4 and 5 in FIG. 4A are insufficient in luminance). , P1 and P2 cannot be obtained), a luminance profile is obtained, and the point where the change is maximum is P1, and the point where the change is minimum is P2.

FIG. 4A shows the luminance profile (solid line) and the change (dotted line) of the image at each focus position in the conventional alignment mark as shown in FIG.
FIG. 4B shows the luminance profile (solid line) and its change (dotted line) of the image at each focus position in the alignment mark of the present invention as shown in FIGS.

  As shown in FIG. 4, the change in the luminance profile (the change in the luminance profile is the difference between the luminance profiles shown by the solid line in FIG. 4 and the waveform shown by the dotted line in FIG. 4) is maximized. When the point is P1 and the minimum point is P2, the center position of the alignment mark (hereinafter referred to as the mark center position) is the midpoint of P1 and P2, that is, (P1 + P2) because the cross-sectional shape of the alignment mark is symmetrical. / 2. Therefore, the mark center position can be measured from the two points P1 and P2.

  In the case of the conventional alignment mark shown in FIG. 1, since the cross-sectional shape is substantially vertical, P1 and P2 can be detected only at the best focus position, that is, at the focus position 3 in FIG. For this reason, it is necessary to focus on the focus position 3 in order to measure the mark center position. Therefore, since the position of the focus lens is controlled with high accuracy and an advanced image processing function is required, alignment takes a lot of time.

  On the other hand, in the case of the alignment mark according to the present invention as shown in FIG. 2, since the cross-sectional shape is a forward tapered slope, if the movement range of the focus lens is between the top and bottom of the pattern, FIG. ), P1 and P2 can be detected. For this reason, a strict focus position is not required to measure the mark center position. Therefore, the position of the focus lens can be controlled with high accuracy and an advanced image processing function is not required, and alignment can be performed at high speed and simply.

  Hereinafter, an example of an alignment method using the position measurement method of the present invention will be described with reference to FIGS.

  First, the alignment mark of the present invention is provided on a reticle or wafer (hereinafter, measured object). At this time, the position of the alignment mark placed on the object to be measured is not particularly limited, and may be provided at an arbitrary position on the object to be measured. Further, the alignment marks arranged on the object to be measured are arranged at at least two arbitrary positions. (Hereinafter, for example, as shown in FIG. 6, one of the alignment points on the object to be measured is point A and the other is point B)

  Next, a measurement algorithm for obtaining position information of an object to be measured using the alignment mark will be described. FIG. 5 is a flowchart showing a procedure for obtaining position information of the object to be measured. First, after the object to be measured is transported onto the stage of the coordinate measuring apparatus, the coordinates of the mark center positions of the alignment marks provided in at least two places on the object to be measured are measured.

Specifically, first, it is moved to the vicinity of point A by a coordinate measuring device having a stage system capable of angle and positioning with an optical lens.
Next, the mark center position at point A is measured using the position measurement method of the present invention described above, and the measured value at point A is stored in a storage device such as a memory.

  Next, it moves to the vicinity of the point B, and in the same manner as the case of the point A, the mark center position of the point B is measured by the position measuring method of the present invention described above, and the measured value of the point B is stored in a storage device such as a memory. To do.

  Next, the measured values at the points A and B are compared with the coordinate values A ′ and B ′ of the coordinate measuring device at each point to calculate an angle deviation amount Δθ. (Fig. 6)

  Next, the stage of the coordinate measuring apparatus is rotated by an amount corresponding to the calculated Δθ, the coordinate system based on the measured values is made to coincide with the coordinate system of the system, and the alignment is completed.

  The alignment mark and the position measurement method of the present invention can be widely used in scenes that require alignment, and are particularly useful for manufacturing processes of various semiconductor devices that require highly accurate alignment.

It is a schematic diagram of the conventional alignment mark, (a) is a top view, (b) is sectional drawing. It is a schematic diagram of the alignment mark of this invention, (a) is a top view, (b) is sectional drawing. It is a schematic diagram of the alignment mark of this invention, (a) is a top view, (b) is sectional drawing. It is a figure explaining the method of calculating | requiring a mark center position from the mark image luminance profile when the position of a focus lens is changed, (a) is based on a conventional mark, (b) It is based on the mark of this invention. It is a flowchart explaining the alignment method using the position measuring method of this invention. It is explanatory drawing which shows the specific example of the alignment method using the to-be-measured object which arranged the alignment mark of this invention.

Explanation of symbols

10 ... Alignment mark

Claims (4)

In alignment marks with steps,
It has a forward tapered slope in either the height or depth direction,
An alignment mark characterized in that the cross-sectional shape of the alignment mark is symmetrical.   A reticle or wafer comprising the alignment mark according to claim 1. Detecting an image of the alignment mark provided on the predetermined surface by optical means;
In a position measuring method for measuring position information of the alignment mark using a detected image,
A position measurement method using the alignment mark according to claim 1.   An alignment method using the position measurement method according to claim 3.

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