JP2000294608A - Method and device for projecting surface picture image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for projecting a surface picture image with which a desired layer is stably brought into focus without vibrating the focus. SOLUTION: In a projecting device for a surface picture image with which a picture image of the entire surface of a plate-like object 1 is obtained by relatively moving projection means 21, 53 and 56, that project a part of the surface of the plate-like object, along the surface of the plate-like object and then uniting projected picture images at each position, surface-height detecting means 31-37 that measure height of a plurality of points of the surface of the plate-like object, a surface shape data storage means 39 that calculates a surface shape of the plate-like object based on the measured height of a plurality of points and stores it, a focusing means 10 that varies a focus condition of the projecting means on the surface of the plate-like object, and a focus control means 12 that controls the focusing means 10 correspondent to the surface shape of the plate-like object stored in the surface shape data storage means when the projecting means is relatively moved along the surface of the plate-like object, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface image projection apparatus and a surface image projection method for projecting an image of the surface of a plate-shaped object, and more particularly to a surface image projection device formed on a surface of a semiconductor wafer (hereinafter simply referred to as a wafer). The present invention relates to a focus adjustment technique in an optical semiconductor wafer inspection apparatus (inspection machine) for imaging a surface image of a die (chip) and inspecting the presence or absence of a defect.

[0002]

2. Description of the Related Art In recent years, semiconductor devices have tended to become more and more multilayered in accordance with the improvement in integration, and the production process of semiconductor devices has increased to several hundreds. Since the final yield of a semiconductor device is determined by the accumulation of defects occurring in each step, it is important to manage the occurrence of defects in each step to be low. Therefore, at the time when each layer is formed, an image on the surface of the wafer is optically captured to inspect for defects.

A microscope is used to optically capture an image of the surface of a wafer. Previously, the inspector visually observed the image of the wafer surface projected by the microscope to determine the presence or absence of a defect, but now the projected image of the microscope is composed of a one-dimensional or two-dimensional image sensor. Defects are automatically detected by image processing after image signals are captured by an imaging device and digitized. An apparatus for this is an apparatus called an inspection machine.

FIG. 1 is a view showing a semiconductor wafer 1 on which a die 2 is formed. The wafer 1 has a thin plate shape, on which a number of dies 2 are formed as shown. There is a space 3 between each die 2 where no circuit pattern is formed,
When the die 2 is completed, a groove is formed in the space 3 with a dicer to separate each die, and the separated dies are attached to a package and assembled.

[0005] In recent years, patterns formed in semiconductor devices have been miniaturized with the improvement in the degree of integration, and the resolution is not sufficient if an image of one entire die is captured by one two-dimensional image sensor. Similarly, in the case of a one-dimensional image sensor, the resolution is not sufficient if one one-dimensional image sensor scans once to capture an image of the entire die.
Therefore, usually, as shown in FIG. 1, the die is divided into a plurality of stripes having a width of one one-dimensional image sensor capable of obtaining a sufficient resolution, and an image of each stripe is divided into one stripe.
It has been captured in the first scan.

In detecting a defect, there is a case where an image serving as a master is compared with an image actually captured. However, usually, the same stripe of each die is continuously scanned along a locus 4 as shown in FIG. A comparison is made between the same portions of adjacent or nearby dies to determine that they are defective if they differ. FIG.
FIG. 3 is a diagram illustrating a configuration of an optical system of the inspection machine. The pattern of each die formed on the wafer surface is very fine, and a microscope system is used to project an image of the surface. As shown in FIG. 2, the wafer 1 is placed on a stage 10 that can move up and down (in the Z-axis direction). The stage 10 is provided in an XY moving mechanism 11 that can move in a horizontal plane (XY plane), and the wafer 1 can move in three XYZ directions. Actually, the stage 10 can be rotated even in the plane perpendicular to the inclination of the mounting surface or the Z axis, but is omitted here. The movement of the stage 10 in the Z-axis direction is controlled by the stage Z movement control unit 12, and the movement of the stage 10 in the X-axis direction and the Y-axis direction by the XY movement mechanism 11 is controlled by the stage XY movement control unit 13.

The illumination light from the white light source 30 is
, An image of the light source 30 is formed at the position of the aperture stop 28. The illumination light that has passed through the aperture stop 28
7. The light passes through the field stop 26 and the lens 25, is reflected by the semi-transparent mirror (half mirror) 23, passes through the half mirror 23, and irradiates the surface of the wafer 1 with the objective lens 21. Light emitted from one point on the wafer 1 is converged by the objective lens 21,
The image sensor 24 passes through the half mirrors 22 and 23
Imaged on top. The above is the basic configuration of the illumination system and the imaging system of the microscope system. In order to obtain high resolution, it is necessary to use an objective lens 21 having a large NA (numerical aperture), and the depth of focus is several μm or less depending on the objective lens used.

The wafer 1 has a thin plate shape, is not perfectly flat, and warps when a pattern is formed thereon. Therefore, the height of the wafer 1 placed on the stage 10 differs slightly depending on the position on the wafer. Although the amount of change in the height is at most 100 μm or less, a good projected image cannot be obtained over the entire surface of the wafer because the depth of focus is extremely narrow as described above. Therefore, an automatic focus adjustment (autofocus) mechanism is provided. The autofocus mechanism includes the astigmatism method, knife edge method, and eccentric auxiliary beam method (ske
The inspection machine shown in FIG. 2 is provided with an autofocus mechanism based on the astigmatism method.

The laser beam emitted from the semiconductor laser 33 passes through the lens 32, is reflected by the half mirror 31, and enters the half mirror 31. Half mirror 22
Is a dichroic mirror that reflects only light near the wavelength of the semiconductor laser. The light of the semiconductor laser reflected by the half mirror 22 is converged by the objective lens 21 into a small spot on the surface of the wafer 1. The light of the semiconductor laser reflected on the surface of the wafer 1 passes through the objective lens 21, is reflected on the half mirror 22, and is reflected on the half mirror 31.
Passes through the lens 34 and the cylindrical lens 35 and enters the four-divided element 36.

FIG. 3 is a diagram for explaining an autofocus mechanism based on the astigmatism method. As shown in (1) of FIG.
The light converged to a small spot on the surface of the wafer 1 is reflected on the surface of the wafer 1 and emits a light beam as if there is a point light source on the wafer 1. This light beam passes through the objective lens 21 and is converged by the lens 34 to a position indicated by P. This light beam is further converged by the cylindrical lens 35 to a position indicated by Q only one component.
Since the other component is converged to the position indicated by P, the converging position of the light beam differs depending on the direction, as shown in the drawing, and converges linearly in one direction at the position of Q, and perpendicular to the line at the position of P. And converges in a line extending in the direction, and has a circular cross section at an intermediate position. Here, the four-divided element 36 is arranged at a position where the middle cross section becomes circular so that the dead zone between the four elements is 45 degrees with respect to the lines of the positions P and Q. If the convergence position of the light of the semiconductor laser on the wafer 1 shifts in the direction perpendicular to the wafer 1, the position of the light source shifts in the optical axis direction, and the light beam on the four-division element 36 changes as shown by the dotted line. I do. That is, when the light beam is converged to a position short of the surface of the wafer 1, it becomes an ellipse extending in the directions of the A and C elements,
When the light is converged on the front side of the surface of the wafer 1, an ellipse extends in the directions of the B and D elements. Therefore, the differential amplifier 38
Then, when the difference signal between the sum of the outputs of the A and C elements and the sum of the B and D elements is calculated, the output AF signal changes as shown in (2), so that the AF signal becomes zero. The state indicates a state where the spot is converged on the surface of the wafer 1, that is, a state where the spot is focused. In the range indicated by R, A
Since the F signal changes according to the focus shift, the AF signal
If feedback control is performed so that the stage 10 is moved up and down in response to a signal, the focus is always in a focused state. For example, if the AF signal is positive, the stage 10 is moved upward. If the AF signal is negative, the stage 10 is moved downward. If the AF signal is zero, the stage 10 is not moved. In other words, the AF signal indicates a deviation from the focus position.

Here, the astigmatism method has been described. However, even with other methods, it is possible to similarly control the focus to always be in a focused state, and to detect a deviation from the focus position. In any case, use a light source such as a semiconductor laser separate from the illumination for the autofocus mechanism,
The light source spot converges on the wafer. In the above example, the focus was adjusted by moving the stage up and down,
It is also possible to adjust the focus by moving the entire microscope or the objective lens up and down. In any case, by using the autofocus mechanism, it is possible to always project a focused clear image regardless of the position (surface shape) of the wafer surface.

[0012]

As described above, when any of the autofocus mechanisms is used, it is necessary to use a light source such as a semiconductor laser other than the illumination and to converge the light source spot on the wafer. is there. Recent semiconductor devices are:
Although the line width is about 0.2 μm, the light from the light source used for the autofocus mechanism has a relatively long wavelength, and the diameter of the spot converged on the wafer is several times to ten and several times the line width. is there. FIG. 4 is a diagram showing a state of the spot 20 of the light beam for autofocus converged on the wafer.

As shown in FIG. 4, the surface of the die formed on the wafer has irregularities in accordance with the pattern, and the irregularities change at a smaller pitch than the spot 20 of the light beam. Therefore, focusing by the autofocus mechanism is performed by averaging the surface heights in the range where the light beam spot 20 is irradiated.
For example, if the surface is a transparent layer, it will be focused on a position determined by the reflection intensity of the light beam, which is the average of all the reflections from the opaque metal wiring layer below it, etc. There has been a problem that a layer other than the layer is focused. In particular, a confocal microscope has recently been used as an optical system of an inspection machine as will be described later. However, when a confocal microscope is used, it is desirable to use a confocal microscope when a pattern is formed on the surface of a wafer. It is possible to capture an image of only the layer with a height of, but since the light beam reflected by each layer is focused on the average position, there was a problem that the layer to be inspected could not be focused .

Further, the autofocus mechanism always detects the focus state and performs feedback control, and there is a problem that the image is always deteriorated due to a delay of the feedback system, and the projected image is deteriorated. .
Furthermore, the spot of the light beam is large compared to the pattern of the die, but the diameter is still several μm or less, so when there is a defect in the irradiated position or when the height is different from other parts, other spots may be used. There has been a problem that the focus of the part is largely out of focus.

An object of the present invention is to solve such a problem, and it is an object of the present invention to realize a surface image projection apparatus and method capable of performing stable focusing on a desired layer without focus vibration.

[0016]

In order to achieve the above object, a surface image projection apparatus and method according to the present invention measure and store the surface shape of a plate-like object in advance, and focus on the surface in accordance with the surface shape. Control. That is, the surface image projection device of the present invention relatively moves the projection unit that projects a part of the surface of the plate-shaped object along the surface of the plate-shaped object,
A surface image projection apparatus that obtains an image of the entire surface of a plate-shaped object by combining projected images at respective positions, and a surface height detection unit that measures heights of a plurality of positions on the surface of the plate-shaped object, Surface shape data storage means for calculating and storing the surface shape of the plate-like object from a plurality of heights; focus adjusting means for changing the focus state of the projection means with respect to the surface of the plate-like object; And a focus control means for controlling the focus adjustment means in accordance with the surface shape of the plate-like object stored in the surface shape data storage means when relatively moving along the surface.

Further, in the surface image projection method of the present invention, while projecting a part of the surface of the plate-shaped object, the surface image is relatively moved along the surface of the plate-shaped object, and the projected images at the respective positions are combined to form the plate-shaped object. A surface image projection method for obtaining an image of the entire surface of an object, comprising: a surface height detection step of measuring a plurality of heights of a surface of the plate-like object; and a surface of the plate-like object from the measured heights of the plurality of places. Surface shape data storage step of calculating and storing the shape, comprising a scanning step of projecting a part of the surface of the plate-like object while relatively moving along the surface of the plate-like object,
In the scanning step, the focus state is changed according to the stored surface shape of the plate-shaped object.

The inventor of the present invention has found that the thickness of each layer formed on a wafer has a small error, the height variation is mainly caused by the height variation of the wafer surface, and the height variation of the wafer surface is gradual. It was noted that accurate measurement can be performed by measuring the height of a portion having no pattern other than the formation of the die. According to the surface image projecting apparatus and method of the present invention, the surface shape of the plate-like object calculated from the measured heights of the plurality of points on the surface of the plate-like object is stored in advance, and along the surface shape during scanning, Focus is controlled, it is possible to focus on a desired layer without being affected by minute irregularities on the surface, and vibration is not generated because it is not feedback control.

When a confocal microscope is used as a projection means and an optical sensor for detecting a projected image is provided, a desired layer can be projected. However, according to the present invention, after focusing on that layer, Since the focus is adjusted only in accordance with the height variation of the plate-like object, it is possible to scan while focusing on the layer. In this case, the operator indicates the layer to be projected by focusing on the layer to be projected.

The present invention can be applied to a case where one-dimensional and two-dimensional image sensors are used as usual without using a confocal microscope. When projecting a semiconductor wafer, the height of the wafer can be measured without being affected by the pattern by measuring the height of a portion around the die formed on the semiconductor wafer where no pattern is formed.

[0021]

FIG. 5 is a diagram showing a configuration of an optical system of an inspection machine according to an embodiment of the present invention. The inspection machine of the embodiment uses a confocal microscope and uses the height measuring mechanism based on the astigmatism method described with reference to FIGS. 2 and 3 as a mechanism for measuring the height of the wafer 1. Therefore, the description of the height measuring mechanism composed of the elements denoted by reference numerals 31 to 37 is omitted here.

Light from a white light source 57 passes through a condenser lens 56 and is reflected by a beam splitter 53 to illuminate a spinning disk 52. Spinning disc 5
Reference numeral 2 denotes a rotating disk provided with a large number of apertures 58. The image of the aperture 58, ie, the aperture 58
Passes through the lens 51 and the half mirror 22.
Is converged as a spot on the wafer 1 by the objective lens 21, and an image of the aperture 58 is formed on the wafer 1. The light beam applied to the wafer is reflected and converged on the corresponding aperture 58 through the opposite optical path.
The light that has passed through the aperture 58 is transmitted to the beam splitter 53.
And is converged on the optical sensor 55 by the lens 54. As the spinning disk 52 rotates, the image of the aperture 58 on the wafer 1 scans sequentially within the field of view. If the intensity distribution is obtained by synthesizing the signal of the optical sensor 57 at each position, 2
A two-dimensional image is obtained.

The light reflected at the spot of the light beam irradiated on the wafer 1 is converged on the corresponding aperture 58, so that the reflected light from other portions is cut off, and a clear contrast is obtained. A high image is obtained. Also,
When the position of the spot is shifted in the optical axis direction, the light spreads and almost all the light reflected at the widened portion is transmitted through the aperture 58.
, It is possible to capture an image of only the layer converged on the spot.

As described above, if a height measuring mechanism based on the astigmatism method composed of the elements denoted by reference numerals 31 to 37 is used, a change in height can be detected by the AF signal. In the present embodiment, an analog / digital (A / D) converter 3 that converts the AF signal output from the signal processing circuit 37 into a digital signal
8, a surface shape data storage unit 39 for storing height distribution data output from the A / D converter 38 at the time of surface shape measurement, and storing surface shape data calculated based on the stored data; A focus instruction unit 40 is newly provided for instructing the layer capturing an image to perform a scan while adjusting the focus and maintaining the focus position. The stage Z movement control unit 12 for controlling the movement of the stage 10 in the vertical direction (Z direction) and the stage XY movement control unit 13 for controlling the movement of the stage 10 in the horizontal direction (XY direction) are the same as those in the related art. It is realized by software of a control computer together with the data storage unit 39.

FIG. 6 is a flowchart showing a process for obtaining a surface image of a die on a wafer in the embodiment. Hereinafter, the processing will be described according to this flowchart. In step 101, the wafer 1 is placed on the stage 10,
Using a TV camera or the like (not shown), alignment for adjusting the arrangement direction of the dies is performed.

In step 102, the stage 10 is moved to XY
After moving within the plane, the height is measured at a plurality of locations on the wafer 1 and stored in the surface shape data storage unit 39. This height measurement is performed, for example, on a portion indicated by a cross indicated by reference numeral 6 in (1) of FIG. This portion is a portion to be grooved by a dicer between the dies 2 arranged on the wafer 1, and since no circuit pattern is formed, the surface is a flat surface without any irregularities as it is on the surface of the wafer 1. It is possible to measure the height accurately. The measurement is performed by scanning in the X direction such that the space between the dies 2 is below the optical axis of the objective lens, that is, the spot of the laser beam of the height measuring mechanism is irradiated on the space between the dies 2. , The digital value of the AF signal at the measurement position is stored. This scanning is performed by changing the position in the Y direction. As described above, the height of the portion marked with a cross in FIG. 7A can be measured.

In step 103, the surface shape data storage section 39 calculates and stores the height distribution of the entire surface of the wafer 1 from the heights of a plurality of locations on the wafer measured in step 102. For example, as shown in FIG. 7 (2), nine points are measured at a certain Y coordinate, and a continuous height change is obtained from the measured data by interpolation using a spline function or the like. . Such an operation is performed on the entire surface of the wafer 1 to calculate the surface shape data of the wafer 1.

In step 104, the operator looks at an image of a certain portion, and focuses on a layer from which an image is desired to be obtained. This focus adjustment can be performed by adjusting the stage Z movement control unit 1 even if a separately provided stage movement mechanism in the Z-axis direction is adjusted.
2 may be adjusted by adjusting the data value given from the outside.
When the adjustment is completed, a key operation of the focus instruction unit 40 indicates that the adjustment has been completed.

In step 105, the XY coordinates of the stage are changed so that the upper left position of the wafer 1 in FIG. 7 becomes the scanning start position. At this time, the position of the stage 10 in the Z-axis direction is changed from the surface shape data stored in the surface shape data storage unit 39 by the difference between the height at the position where the instruction in step 104 is performed and the upper left position of the wafer 1. Let it. In step 106, the stage XY movement control unit 13 outputs a signal for performing scanning while sequentially changing the X coordinate. When scanning from the left end to the right end is completed, the stage XY movement control unit 13 changes the Y coordinate and performs scanning in the reverse direction. The movement of the stage 10 is controlled so as to repeat such an operation. At this time, the height data at each scanning position is output to the stage Z movement control unit 12 from the surface shape data stored in the surface shape data storage unit 39, and the height of the stage 10 is changed by the height data. Thus, the focus of the optical system is always adjusted to the layer specified by the operator. With the above processing, a surface image of the entire surface of the wafer is obtained.

In this embodiment, an inspection machine is used. The read image data is compared with master data and image data of an adjacent die to detect a defect position, and further analyzes the image data for the defect position. Although various processes such as classification of the type of defect are performed, they are not directly related to the present invention, and thus detailed description is omitted here. Although the embodiment using the optical system of the confocal microscope has been described above, the present invention is not limited to the configuration using the confocal microscope, but uses an ordinary one-dimensional image sensor or two-dimensional image sensor. The present invention is also applicable to such a configuration.

[0031]

As described above, according to the present invention,
It is possible to focus on a desired layer without being affected by minute irregularities on the surface, and since it is not feedback control, a good image without vibration can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating scanning for obtaining a surface image of a die (semiconductor chip) formed on a semiconductor wafer.

FIG. 2 is a diagram showing a configuration of an optical system of a conventional inspection machine for obtaining a surface image of a die formed on a semiconductor wafer.

FIG. 3 is a diagram illustrating an autofocus mechanism based on an astigmatism method in a conventional example.

FIG. 4 is a diagram showing a state of a wafer surface and a spot of a light beam of an autofocus mechanism.

FIG. 5 is a diagram illustrating a configuration of an optical system of the inspection machine according to the embodiment of the present invention.

FIG. 6 is a flowchart showing a process for obtaining a surface image of a die on a wafer in the embodiment.

FIG. 7 is a diagram showing an example of a location where height measurement of a wafer surface is performed and surface shape data in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Plate object (semiconductor wafer) 10 ... Stage 12 ... Stage Z movement control part 13 ... Stage XY movement control part 21 ... Objective lens 33 ... Semiconductor laser 34 ... Lens 35 ... Cylindrical lens 36 ... Four-division element 39 ... Surface shape Data storage means 40: Focus instruction unit

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[Procedure amendment]

[Submission date] February 17, 2000 (2000.2.1
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

The laser beam emitted from the semiconductor laser 33 passes through the lens 32, is reflected by the half mirror 31, and enters the half mirror 22 . Half mirror 22
Is a dichroic mirror that reflects only light near the wavelength of the semiconductor laser. The light of the semiconductor laser reflected by the half mirror 22 is converged by the objective lens 21 into a small spot on the surface of the wafer 1. The light of the semiconductor laser reflected on the surface of the wafer 1 passes through the objective lens 21, is reflected on the half mirror 22, and is reflected on the half mirror 31.
Passes through the lens 34 and the cylindrical lens 35 and enters the four-divided element 36.

Claims (10)

[Claims] 1. A projection means for projecting a part of the surface of a plate-shaped object is relatively moved along the surface of the plate-shaped object, and a projection image at each position is adjusted to adjust the entire surface of the plate-shaped object. A surface image projection device that obtains an image, comprising: a surface height detection unit that measures heights of a plurality of locations on a surface of the plate-like object; and a surface shape of the plate-like object from the measured heights of the plurality of locations. Surface shape data storing means for calculating and storing; focus adjusting means for changing a focus state of the projecting means with respect to the surface of the plate-like object; and when the projecting means is relatively moved along the surface of the plate-like object. A focus control unit for controlling the focus adjustment unit according to the surface shape of the plate-shaped object stored in the surface shape data storage unit. 2. The surface image projection device according to claim 1, wherein the optical sensor is an image sensor for detecting a one-dimensional image, and the projection unit is relatively moved along a surface of the plate-like object. A surface image projection device that obtains a two-dimensional image by synthesizing a one-dimensional image at the time of the image formation. 3. The surface image projection device according to claim 1, wherein the projection unit is a confocal microscope. 4. The surface image projection device according to claim 1, further comprising a two-dimensional image sensor for detecting a projection image. 5. The surface image projection device according to claim 1, wherein the plate-like object is a semiconductor wafer. 6. The surface image projection device according to claim 5, wherein the surface height detecting means determines a height of a portion around the die formed on the semiconductor wafer where a pattern is not formed. Surface image projection device to measure. 7. The surface image projection device according to claim 1, wherein the plate-like object is a semiconductor wafer, the projection unit is a confocal microscope, an optical sensor for detecting a projection image, and the projection. A surface image projection apparatus comprising a focus instructing means for instructing a layer to be focused on the semiconductor wafer when the means is relatively moved along the surface of the plate-like object. 8. While projecting a part of the surface of the plate-like object,
A surface image projection method of relatively moving along the surface of the plate-shaped object to obtain an image of the entire surface of the plate-shaped object by combining the projected images at each position, wherein a plurality of positions on the surface of the plate-shaped object Surface height detection step of measuring the height of the surface, surface shape data storage step of calculating and storing the surface shape of the plate-like object from the measured heights of the plurality of locations, and along the surface of the plate-like object A step of projecting a part of the surface of the plate-like object while relatively moving the plate-like object. In the scanning step, a focus state is changed according to the stored surface shape of the plate-like object. Surface image projection method. 9. The surface image projection method according to claim 8, wherein the plate-like object is a semiconductor wafer, and in the surface height detecting step, a pattern around a die formed on the semiconductor wafer. Surface image projection method for measuring the height of a portion where no surface is formed. 10. The surface image projection method according to claim 8, wherein the plate-like object is a semiconductor wafer, and the projection optical system has a confocal microscope and an optical sensor for detecting a projection image. A focus position specifying step of specifying a layer to be focused on the semiconductor wafer before the scanning step.