JPH05333270A - Appearance inspection microscoptic device - Google Patents

Abstract

PURPOSE:To perform visual inspection with high accuracy and also to reduce observer's fatigue regardless of the direction of a mark for inspection. CONSTITUTION:At least two kinds of marks (MX, MY) provided on a specimen 4 in a state where they face different directions are respectively observed through an objective lens 5. The device is provided with an image rotating optical member 8 arranged on an observing optical path in order to rotate a luminous flux from the objective lens 5 around an optical axis, and adjusting means 12-15 adjusting the rotating amount of the luminous flux by the image rotating optical member 8 according to the direction of the mark in order to form the observed images of the two kinds of marks in the nearly same direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visual inspection microscope apparatus, and more particularly to a microscope apparatus suitable for visual inspection of overlay accuracy of patterns formed on a semiconductor wafer or a liquid crystal substrate.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor wafer or a liquid crystal substrate, a plurality of pattern layers are formed on the substrate by repeating pattern baking, etching and the like. These pattern layers should be accurately superposed in a predetermined positional relationship, but the superposition state as designed may not always be obtained due to the misalignment during printing.

Therefore, in order to inspect whether or not the state of superposition of a new pattern layer formed on the underlying pattern layer is within the range of permissible accuracy, visual inspection using an appearance inspection microscope device is performed. It is being appreciated. This type of visual inspection is carried out by observing an inspection mark specially formed on a test object such as a wafer or a liquid crystal substrate. The inspection mark is provided on each of the plurality of pattern layers to be overlaid, and the inspection mark of the new pattern layer is formed in a predetermined positional relationship with the inspection mark of the underlying pattern layer. Then, by observing the positional deviation between the inspection marks, the overlay accuracy of the entire test object can be determined. The inspection marks are provided at a plurality of positions on the surface of the object to be inspected, and for example, scale marks are known as the shape thereof, and the overlay accuracy in the X direction is determined by observing the scale marks extending in the X direction. Then, the overlay accuracy in the Y direction can be determined by observing the scale mark extending in the Y direction orthogonal to the scale mark.

At the time of visual inspection, an object to be inspected is placed on a stage of a microscope, and an observer observes an enlarged image of an inspection mark through a microscope optical system. The stage moves so that the inspection marks distributed at a plurality of locations on the test object are sequentially brought into the field of view of the microscope.

[0005]

In the visual inspection of a wafer, one wafer is usually 3 to 10 on the wafer.
For the chips, the X-direction and Y-direction scale marks existing on each chip are continuously observed at a time interval of 2 to 6 seconds per mark. In the conventional visual inspection as described above,
For the inspection mark in the X direction, the observer determines the overlay accuracy of the patterns while observing the scale mark extending in the horizontal direction, and for the inspection mark in the Y direction, the observer extends the scale in the vertical direction. It was necessary to judge the overlay accuracy of the patterns while observing the marks. Therefore, continuous observation of the inspection marks in the horizontal direction and the vertical direction, which are alternately displayed, is extremely painful for the observer, and the eyes are extremely tired.

Further, when observing an image formed by a microscope,
Since the ability of the human eye to evenly separate eyes, such as graduation marks, is superior to the vertical direction in the horizontal direction, the vertical direction is better than the horizontal direction (X direction) when determining the overlay accuracy. There is a problem that the determination accuracy in the direction (Y direction) is poor. The present invention has been made to solve such conventional problems, and enables a visual inspection with high accuracy regardless of the direction of the inspection mark, and an appearance inspection microscope capable of reducing fatigue of an observer. The purpose is to provide a device.

[0007]

An appearance inspection microscope apparatus according to the present invention as set forth in claim 1 has at least two types of marks (MX, MY) provided on a test object in different directions.
And an image rotation optical member (8) arranged on an observation optical path for rotating a light beam from the objective lens around the optical axis, and the two types described above. Adjusting means (13) for adjusting the rotation amount of the light flux by the image rotating optical member according to the direction of the mark so that the observed images of the mark are formed in substantially the same direction.
~ 15) and.

According to a second aspect of the present invention, the image rotating optical member is composed of a plurality of image rotating prisms (81, 82) having different amounts of rotation of light beams, and the plurality of image rotating prisms are selected by the adjusting means. It is configured to be switched and arranged on the observation optical path. In the invention according to claim 3, the adjusting means is a storage section (15) capable of storing the coordinate position and direction of the mark on the object to be inspected.
A drive device (12) for relatively moving the object and the objective lens so that the mark sequentially faces the observation position by the objective lens according to the stored coordinate position; and the image rotating optical member according to the stored direction. Drive to adjust (1
3) and have.

According to a fourth aspect of the present invention, the adjusting means further includes a controller (1) for completing the adjustment of the image rotation optical member by the drive unit during the relative movement by the drive unit.
Having 4). Further, in the invention of claim 5, there is provided means (20) for displaying the rotation state of the light flux by the adjusting means.

[0010]

[Operation] Since the image rotating optical member (8) rotates the observation light beam around the optical axis according to the directions of the two types of marks (MX, MY), the two types of marks are always observed in the directions that are easy to observe. be able to. By switching a plurality of image rotation prisms (81, 82) having different amounts of rotation of the light flux, it is possible to switch instantaneously with good responsiveness according to the direction of the mark to be observed.

According to the coordinate position of the mark stored in the storage unit, the object and the objective lens are moved relative to each other so that the mark sequentially faces the observation position by the objective lens, and at the same time, the observation light flux is changed in accordance with the stored mark direction. If the rotation is adjusted, the mark can be automatically set up and the direction can be adjusted, so that the work can be efficiently performed and highly accurate determination can be performed.

By displaying the rotation state of the luminous flux,
It is possible to recognize in which direction the mark currently being observed is.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In FIG. 1 showing the basic configuration of the present embodiment, an object to be inspected 4 such as a wafer placed on a stage 2 is an observation optical system including an objective lens 5, a mirror 6, relay lenses 7, 9 and an eyepiece lens 10. Observed through. The observation optical system is provided with an image rotating optical member 8 between the relay lenses 7 and 9 for rotating the observation light beam around the optical axis 3 by a predetermined amount.

Stage 2 is X-in the plane perpendicular to the plane of the drawing.
It is driven by the driving device 12 in a known configuration that is movable in the Y direction. Further, a drive unit 13 for adjusting the rotation amount of the light flux by the image rotation optical member 8 is provided, and these drive device 12 and drive unit 13 are controlled by a command from the control unit 14. The storage unit 15 stores the coordinate position and direction of the inspection mark on the wafer 4, and supplies storage data to the control unit in response to a request from the control unit 14. This memory 15
The control unit 14 controls the drive unit 12 and the drive unit 13 based on the data from the.

Details of the inspection marks provided on the wafer 4 will be described with reference to FIGS. As shown in FIG. 2, a plurality of chip regions are arranged in a matrix on the surface of the wafer 4. Such a chip region is formed through a manufacturing process such as development and etching after the mask pattern is transferred to the photoresist coated on the wafer 4 by using an exposure device such as a stepper. By repeating these manufacturing processes (photoresist application, pattern transfer, development, etching), a plurality of layers of circuit patterns are superimposed on each chip region, and thus a semiconductor integrated circuit is manufactured. An alignment mark (not shown) provided in each chip area is used in order to accurately superimpose a new n + 1th layer circuit pattern on the underlying nth layer circuit pattern.

Further, an inspection mark MX in the X direction and an inspection mark MY in the Y direction are provided at the same time as the circuit pattern in each chip area. Both inspection marks MX, M
Y is for visually inspecting the overlapping state of the circuit patterns, and each has a scale shape as shown in an enlarged view in FIGS. 3 (a) and 3 (b). In the wafer that has completed the manufacturing process up to the nth layer, the inspection mark MX in the X direction formed in each chip area is the scale MX-1 previously formed in the previous manufacturing process and And the graduation MX-2 formed in the same step as the circuit pattern of the n-th layer provided in. Base scale MX-1
Is composed of a plurality of rectangular elements repeated at a constant pitch in the X direction, and has a symmetrical shape centered on the longest central rectangular element. In addition, the scale of the n + 1th layer MX-2 is
It consists of scale elements with a width smaller than the rectangular elements of the base scale MX-1, and is arranged in the X direction at a constant pitch slightly smaller than the base scale MX-1.

The inspection mark MY in the Y direction also has the same structure as the inspection mark MX in the X direction, and has a top and bottom symmetrical shape having a base scale MY-1 and an (n + 1) th layer scale MY-2 which are long in the Y direction. Is. When ideal overlay accuracy is obtained in both the XY directions between the circuit pattern of the nth layer and the circuit pattern of the (n + 1) th layer, the inspection mark in the X direction.
For both the MX and Y direction inspection marks MY,
The center line of the rectangular element in the center of the background scale and the center line of the central scale element of the scale of the (n + 1) th layer match (state in FIG. 3). If the positional relationship of the inspection marks is determined in this way, it is possible to determine the quality of the overlay only by reading the location where the center line of the rectangular element and the center line of the scale element match. For example, if the allowable range of the overlay error is set to "within 2 scales to the left and right from the central rectangular element", in the case of the inspection mark MX in the X direction formed as shown in FIG. Since the center lines coincide with each other on the second scale (indicated by an arrow), it is determined that the defective chip is out of the allowable range of overlay error.

Next, the image rotating optical member 8 and the driving unit 13
The configuration will be described in detail with reference to FIGS. The image rotation optical member 8 includes two image rotation prisms (trapezoidal prisms) 81,
Has 82. One of the image rotation prisms 81 rotates the incident light beam by 180 degrees when it is arranged in the observation light path and emits it, and the other image rotation prism 82 emits the incident light beam by 90 degrees when it is arranged in the observation light path. Just rotate and eject. That is, as shown in FIG. 7, the image rotating prism 81 is attached to the prism fixing member 83 so that the trapezoidal bottom surface is perpendicular to the horizontal plane, and the image rotating prism 82 is inclined so that the trapezoidal bottom surface is inclined by 45 degrees with respect to the horizontal plane. It is installed.

The prism fixing member 83 is movable along a linear guide 21 extending in the direction of arrow a in FIG.
It is fixed to 4 and by moving the moving table 84 in the horizontal direction, two prisms for image rotation 81, 82 in the direction orthogonal to the optical axis are obtained.
It is possible to integrally displace. The linear guide 21 is fixed on a U-shaped lens support member 22 fixed to the microscope body. The pair of relay lenses 7 and 9 shown in FIG. 1 are fitted and fixed in through holes 23 and 24 provided in both vertical walls of the lens support member 22, respectively.

Below the lens support member 22, there is disposed a trapezoidal cam 26 movable along a linear motion guide 25 extending in the direction of arrow b in FIG. The side surface of the trapezoidal cam 26 is formed as a cam surface, and its head is equal to the distance between the optical axes of the two image-rotating prisms 81 and 82. Prism fixing member
A rotating roller 85 provided on 83 rolls on the cam surface of the trapezoidal cam, and a spring 86 urges the prism fixing member 83 to maintain the contact between the rotating roller 85 and the cam surface.

The reciprocating movement of the trapezoidal cam 26 along the linear guide 25 can be instantaneously achieved by the air cylinder 27. The air cylinder 27 is provided with speed controllers 29 and 30 that control the flow rate of air,
14 selectively supplies air to these speed controllers 29, 30 via a solenoid valve 28. Next, the operation of this embodiment will be described.

Prior to the visual inspection, the operator selects a chip area to be inspected and registers the coordinate position and direction of the inspection mark in the chip area in the storage unit 15. This registration is possible by inputting the coordinate position and direction of the inspection mark based on the design data for a predetermined number of chip areas. In the manufacturing line, the operation of observing a large number of wafers having the same pattern one after another is repeated. In such a case, the coordinate position of the inspection mark on the first wafer may be detected by the microscope and registered in the storage unit. That is, when the stage on which the first wafer is placed is moved by the operation of the observer and the target inspection mark is located in the center of the observation field of view, the reading value of the encoder provided on the stage is changed to the direction of the mark. Register with.

In this embodiment, the chip area C ₀ located at the center of the wafer and the chip areas C ₁ , C _{2 at} the left and right ends of the chip area C ₀ ,
And the five mark chip areas C ₃ and C _{4 at} the upper and lower ends, the inspection marks MX and Y in the X direction.
The coordinate position and direction of the direction inspection mark MY are registered in the storage unit. When the wafer 4 is placed on the stage 2, the control unit 14 reads the data of the first inspection mark from the storage unit 15 and operates the drive unit 12 according to the coordinate position to move the stage 2. At the same time, the control unit 14 determines the direction of the inspection mark and operates the drive unit 13 to switch the image rotation optical member 8.
That is, if the mark is the inspection mark MX in the X direction, the image rotating prism 81 is arranged on the optical axis of the observation light beam, and if it is the Y direction inspection mark MY, the image rotating prism 82 is arranged. Operate the solenoid valve 28 so that it is placed on the optical axis of the observation light flux, and use the air cylinder 27 to move the trapezoidal cam 2
Move 6

Therefore, when the inspection mark moved on the optical axis of the objective lens 5 is the inspection mark MX in the X direction, since this mark is originally a horizontal scale, the image rotation prism 81 is Only horizontal reversal is performed, and it is observed as a horizontal scale through the screen of the eyepiece lens 10 or the display unit 20. Moreover, the inspection mark moved on the optical axis of the objective lens 5 is the inspection mark MY in the Y direction.
, The mark is a graduation in the vertical direction, so that the mark is rotated 90 degrees by the image rotation prism 82 and converted to the horizontal direction. As a result, it is observed as a horizontal scale on the screen of the eyepiece 10 or the display unit 20.

When the observation of one inspection mark is completed,
The operator indicates the "next mark" to the control unit 14. The control unit 14 reads the data of the second inspection mark from the storage unit 15, moves the stage 2 and switches the image rotation optical member 8 at the same time to set the horizontal scale of the second inspection mark. Enables the observation of. Five chip areas C ₀ , C ₁ , C ₂ , C ₃ and C ₄ Both marks MX, M
The same operation is repeated until the observation of Y is completed.

The display unit 20 inputs data from the control unit 14 and displays the position state of the image rotating optical member with respect to the mark currently being observed. When observing the horizontal inspection mark MX in the horizontal direction, for example, "MODE: -X-" is displayed, and when observing the vertical inspection mark MY in the horizontal direction, "MODE: -X-" is displayed. : -Y- ”is displayed. In the present embodiment, the configuration of the image rotating optical member that switches between the two image rotating prisms has good responsiveness and facilitates quick positioning for switching, which is useful from the viewpoint of improving the efficiency of inspection.

The image is rotated by 180 degrees with respect to the horizontal inspection mark by the image rotating prism 81. In this case, however, since the image rotation is not essential, a separate optical path length correction is necessary. You may substitute by the optical element of. Further, when there are inspection marks in the diagonal direction or the like other than the horizontal direction and the vertical direction, an image rotation prism corresponding to the angle may be further arranged and switching may be performed between them.

As a modification of the image rotating optical member in the present embodiment, a single image rotating prism is always arranged on the observation optical path and is rotated around the optical axis according to the direction of the inspection mark. You may comprise.

[0029]

As described above, according to the present invention, the positional deviation amount of the pattern represented by the inspection mark in the observation visual field can be
Since it is possible to always observe in the horizontal direction, it is possible to improve the measurement accuracy. In addition, since the inspection marks oriented in various directions on the object to be inspected are always aligned in the same direction, the operator's eye fatigue in continuous observation can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a basic configuration of a visual inspection microscope apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view schematically showing a surface of a wafer used as a test object.

FIG. 3 is an enlarged view showing an example of X-direction and Y-direction inspection marks on a test object.

FIG. 4 is an enlarged view showing an example of an X-direction inspection mark.

FIG. 5 is an exploded perspective view showing detailed structures of an image rotating optical member and a driving unit in the embodiment of the present invention.

6 is a cross-sectional view of an image rotation optical member and a drive unit shown in FIG.

7A and 7B are a front view and a plan view of an image rotation prism.

[Explanation of symbols]

 2 ... Stage 4 ... Object to be inspected 5 ... Objective lens 8 ... Image rotation optical member 12 ... Drive device 13 ... Drive unit 14 ... Control 15 ... Memory unit MX ... X direction inspection mark MY ... Y direction inspection mark 81, 82 ... Image rotation prism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akitoshi Kawai 471 Nagaodai-cho, Sakae-ku, Yokohama-shi, Kanagawa Incorporated Nikon Yokohama Works (72) Inventor Osamu Yamashita 471 Nagaodai-cho, Sakae-ku, Yokohama, Kanagawa Expression company Nikon Yokohama Works (72) Inventor, Yoshihiko Inoue, Kusu-cho, Asa-gun, Yamaguchi, 192-3 Kamimoto, Higashi-mangura, Yamaguchi NEC (72) Inventor, Minoru Kato Kusu-cho, Asa-gun, Yamaguchi 192, Kamimoto, Higashimangura, Yamada-3, Yamaguchi NEC Corporation

Claims (5)

[Claims] 1. A visual inspection microscope apparatus for observing at least two types of marks provided on a test object in different directions through an objective lens, wherein a light beam from the objective lens is rotated around an optical axis. The image rotation optical member arranged on the observation optical path for rotation and the light flux by the image rotation optical member according to the direction of the mark so that the observation images of the two types of marks are formed in substantially the same direction. And a means for adjusting the amount of rotation of the appearance inspection microscope apparatus. 2. The image rotating optical member has a plurality of image rotating prisms having different amounts of rotation of light beams, and the adjusting means selectively arranges the plurality of image rotating prisms on the observation optical path. The visual inspection microscope apparatus according to claim 1, wherein the apparatus is a visual inspection microscope apparatus. 3. The adjusting unit sequentially stores a storage unit capable of storing a coordinate position and a direction of the mark on the test object, and the mark sequentially faces an observation position of the objective lens according to the stored coordinate position. The appearance inspection microscope according to claim 1, further comprising: a driving device that relatively moves the object to be inspected and the objective lens, and a driving unit that adjusts the image rotating optical member according to the stored direction. apparatus. 4. The external appearance according to claim 3, wherein the adjusting unit further includes a control unit that completes adjustment of the image rotation optical member by the drive unit during relative movement by the drive unit. Inspection microscope device. 5. The appearance inspection microscope apparatus according to claim 1, further comprising means for displaying a rotation state of the light flux by the adjusting means.