JPH074938A - Surface-state inspection apparatus - Google Patents

Abstract

PURPOSE:To obtain an inspection apparatus for surface state whose inspection accuracy is sufficient and which can reduce the number of inspection processes sharply by a method wherein a line mirror is arranged between an objective lens and a sample and in a position exposed to a laser beam. CONSTITUTION:A line mirror 33 and a second beam splitter 27 are arranged between an objective lens 25 and a sample 29, an incident laser beam P2 is divided into two directions by the beam splitter 27, the sample 29 is irradiated with the laser beam P2 on one side, and the mirror 33 is irradiated with the laser beam P2 on the other side. Consequently, a beam of interference light P3 of a beam of reflected light P3 from the surface of the sample 29 with a beam of reflected light P3 from the mirror 33 can be detected by a photodetector 32, and the surface state (the unevenness) of the sample 29 can be observed with good accuracy on the basis of the optical intensity of the beam of interference light. In addition, since the lengthwise direction of the mirror 33 coincides with the main scanning direction of the incident laser beam P2, the surface state can be observed continuously along a scanning track, and the number of inspection processes can be reduced sharply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface condition inspection device, and more particularly to an LSI (large scale integ
rated circuit) A surface condition inspection device suitable for inspecting the flatness of each layer of a chip. Generally, in an LSI chip having a multi-layer structure, the flatness of the surface deteriorates as the number of stacked layers increases, and this may cause inconvenience especially when pattern formation is performed by an optical projection method.

In the optical projection method, a mask pattern is projected on a resist on the surface of a chip. However, the depth of focus of an optical system tends to become shallower as the pattern line width becomes smaller. Therefore, if the unevenness of the chip surface is large enough to deviate from the depth of focus, the pattern image projected on the chip surface will be blurred and accurate pattern formation will be difficult.

[0003]

2. Description of the Related Art As a technique for inspecting the flatness of the surface of a chip, the applicant of the present invention has previously referred to a "surface defect inspection device" (Japanese Patent Laid-Open No. Sho 5).
9-92306). This device
A laser beam reflected from the sample surface (hereinafter referred to as “reflected light”) is split into two beams by a half mirror, the first beam is received by a first photodetector, and the second beam is passed through a pinhole. The second photodetector receives light, and the first
The output of the photo detector of is to the reference input of the comparator,
The output of the second photodetector is applied to the comparison input of the same comparator.

According to this, the average level of the sample surface can be represented by a signal corresponding to the amount of reflected light from a relatively wide range of the sample surface, and the comparator operation, that is, the relatively narrow range of the sample surface. It is possible to quantitatively measure the deviation of the level of from the above average level.

[0005]

However, such a conventional surface state inspection device is useful for pinpoint level inspection of the sample surface, but for inspection of surface flatness, The test must be repeated for each point. Therefore, there is still room for improvement in terms of reduction of inspection man-hours. [Purpose] Therefore, an object of the present invention is to provide an excellent surface condition inspection apparatus which has a sufficient inspection accuracy and can significantly reduce the inspection man-hours.

[0006]

In order to achieve the above object, the present invention has an optical system 3 including an objective lens 1 and a first beam splitter 2 as shown in FIG. The surface of the sample 5 is irradiated with the laser beam 4 via the, and the reflected light 6 from the surface of the sample 5 is guided to the photodetector 8 through the imaging lens 7, and based on the output signal of the photodetector 8. In the device for inspecting the surface state of the sample 5 by using the objective lens 1, the width of the laser beam 4 narrowed by the objective lens 1 is narrower in the lateral direction (horizontal direction in the drawing) and longer in the longitudinal direction (in the drawing). A line mirror 9 whose direction (passing through the front and back sides) of the laser beam 4 coincides with the scanning direction of the laser beam 4, and the line mirror 9 is exposed to the laser beam 4 between the objective lens 1 and the sample 5. Place it in place, and then the line mirror It is characterized in that the second beam splitter 10 is disposed between the sample 5 and.

[0007]

FIG. 1B is a conceptual diagram of the behavior of the laser light in the vicinity of the line mirror 9, the second beam splitter 10 and the sample 5. The incident laser beam 4 first passes through the second beam splitter 10 and reaches the sample 5, and the second laser beam 4 a reflects the second laser beam 10 and reaches the line mirror 9. It is divided into light 4b.
Then, after these two laser beams 4a and 4b are respectively reflected by the sample 5 and the line mirror 9, again,
The first reflected laser light (hereinafter "first reflected light") 4a 'and the second reflected laser light (hereinafter "second reflected light") 4b'
Becomes the reverse path of the incident light, and the two reflected lights 4a ′, 4
Interfering light having a light intensity corresponding to the path length difference b'is observed by the photodetector 8.

That is, the distance La from the second beam splitter 10 to the sample and the second beam splitter 10
Since the signal corresponding to the difference ΔL from the distance Lb from the line mirror 9 to the line mirror 9 is output from the photodetector 8, the surface state (degree of unevenness) of the sample 5 can be inspected based on this signal. Further, since the longitudinal direction of the line mirror 9 (direction penetrating the front and back of the drawing) and the scanning direction of the laser beam 4 are coincident with each other, the surface condition of the sample 5 can be continuously inspected along the scanning line, and the spot condition can be obtained. It is possible to significantly reduce the inspection man-hours compared to other inspections.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 10 are views showing an embodiment of the surface condition inspection apparatus according to the present invention. First, the configuration will be described. Figure 2
Is a block diagram of the optical system of the present embodiment, and 20 is a laser beam P
₁ , a beam expander 22 that expands the beam diameter of the laser light P ₁ (P ₂ is the expanded laser light), and a beam splitter 23 that bends the optical axis of the laser light P ₂ (hereinafter referred to as “first Beam splitter "), 24 is a rotary polygonal mirror that mainly scans the laser light P ₂ while rotating at a constant speed V in a predetermined direction, 25 is an objective lens (also called a scan lens) that narrows down the laser light P ₂ , and 26 is glass. Etc., 27 is a second beam splitter, 28 is a scanning locus of the laser beam P ₂ drawn on the surface of a sample 29 such as an LSI chip, 30 is a reflected laser beam from the sample 29 (hereinafter referred to as “reflected light”). ) An image forming lens disposed on the optical axis of P ₃ , 31 is a pinhole plate having a pinhole 31a having a diameter smaller than the beam diameter of the reflected light P ₃ which has passed through the image forming lens 30, and 32 is the pinhole 31a. Passed through A photodetector for outputting an electrical signal corresponding to the light intensity of the light P _3.

Here, a line mirror 33 having a fine width is attached (or formed by vapor deposition) to the transparent body 26. The reflecting surface of the line mirror 33 is directed toward the second beam splitter 27 side, and the longitudinal direction of the line mirror 33 coincides with the main scanning direction of the laser beam P ₂ (direction of the scanning locus 28). The width of the line mirror 33 in the lateral direction is smaller than the beam diameter of the laser light P ₂ narrowed down by the objective lens 25.

FIG. 3 is an overall block diagram of this embodiment. The signal output from the optical system of FIG. 2 (the signal from the photodetector 32) is amplified by an amplifier 40 and then A / D converted. It is converted into a digital signal by a device (not shown) and written in a designated address of the frame memory 41. Note that the addressing of the frame memory 41 is performed by the controller 42, and the controller 42 uses the sample (reference numeral 29 in FIG. 2).
The sub-scan is performed by controlling the movement of the table 43 on which the reference (see) is placed, and the addressing is performed in synchronization with the sub-scan. The contents of the frame memory 41 are sequentially read and sent to the defect discrimination logic unit 44, and compared with a predetermined discrimination reference value to judge the concavo-convex state of the sample surface, and the judgment result is displayed or outputted by the output unit 45. Hard copied.

Next, the operation will be described. 4 is a configuration diagram of a main part including the line mirror 33 and the second beam splitter, and FIG. 5 is an enlarged conceptual diagram thereof. Laser light P ₂
Since the beam width of the beam is wider than the width of the line mirror 33 in the lateral direction, most of the beam passes through the transparent body 26 and reaches the second beam splitter 27. Light that passes through (hereinafter referred to as “first laser light”) P ₂ a And reflected light (hereinafter referred to as “second laser light”) P ₂ b.

First laser beam P ₂ a Is reflected by the surface of the sample 29 and the first reflected laser light (hereinafter referred to as “first reflected light”) P ₃ a And the second laser beam P ₂ b Of the second reflected laser light (hereinafter referred to as “first reflected light”) P ₃ b after being reflected by the line mirror 33. , And both travel in the opposite direction on the incoming path. That is, the reflected light P
₃ is the first reflected light P ₃ a And the second reflected light P ₃ b Of the two reflected light P ₃ a , P ₃ b from the second beam splitter 27 to the sample 2
A signal corresponding to the difference ΔL between the distance La up to 9 and the distance Lb from the second beam splitter 27 to the line mirror 33 is extracted from the photodetector (see reference numeral 32 in FIG. 2).

For example, as shown in FIG. 6, when the surface of the sample 29 has a convex portion 29a of height Lc, the distance La from the second beam splitter 27 to the sample 29 is the normal scanning position. As a result of decreasing the distance Lc with respect to "a" or increasing it in the case of a concave portion, the output signal of the photodetector (see reference numeral 32 in FIG. 2) changes as shown in FIG. 7 (interference waveform). Will be done.

As described above, in the present embodiment, the line mirror 33 and the second beam splitter 27 are arranged between the objective lens 25 and the sample 29, and the incident laser light P ₂ is emitted to the second position.
Of the laser beam P ₂ a While irradiating the sample 29 with the other laser beam P ₂ b Since the line mirror 33 is irradiated with the light, the reflected light P ₃ a from the surface of the sample 29 is reflected. And the reflected light P ₃ b from the line mirror 33 The interference light (P ₃ ) with the light can be detected by the photodetector 32, and the surface state (concavities and convexities) of the sample 29 can be accurately observed from the light intensity of the interference light.

Moreover, since the longitudinal direction of the line mirror 33 and the (main) scanning direction of the laser beam P ₂ coincide with each other, continuous observation along the scanning locus is possible, and the number of inspection steps is greatly reduced. can do. FIG. 8 is an image diagram showing the contents stored in the frame memory 41.
It is the figure developed dimensionally. The three interference fringes shown for convenience respectively correspond to the unevenness on the sample surface. The height can be known from the striped pattern, and a product that does not meet the standard can be identified as a defective product.

In the above embodiment, the photo detector 32
As shown in FIG. 9, the pinhole plate 30 provided in front of is for cutting out the central portion of the optical axis of the reflected light P ₃ , and narrows down the beam axis of the laser light P ₂ irradiating the surface of the sample 29. This is to obtain the same effect (improvement of resolution). In addition, although the second beam splitter 27 is a single component in the above embodiment, the invention is not limited to this. As shown in FIG. 10, a glass having a line mirror 33 attached (or vapor-deposited) on one surface thereof is used. On the other side of the transparent body 26 'such as the second beam splitter 2
You may make it attach 7 '.

[0018]

According to the present invention, since it is configured as described above, it is possible to provide an excellent surface condition inspection apparatus with sufficient inspection accuracy and capable of greatly reducing the inspection man-hours.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an optical system of an example.

FIG. 3 is a configuration diagram including a signal processing system according to an embodiment.

FIG. 4 is a configuration diagram of a main part of an embodiment.

FIG. 5 is a conceptual diagram of a main part of one embodiment.

FIG. 6 is a measurement conceptual diagram of an example.

FIG. 7 is a relationship diagram between the surface state of the sample and the output signal of the photodetector in one example.

FIG. 8 is an image diagram of stored contents of a frame memory according to an embodiment.

FIG. 9 is a configuration diagram of a pinhole plate according to an embodiment.

FIG. 10 is another configuration diagram of the second beam splitter of the embodiment.

[Explanation of symbols]

 1: Objective Lens 2: First Beam Splitter 3: Optical System Including 4: Laser Light 5: Sample 6: Reflected Light 7: Imaging Lens 8: Photodetector 9: Line Mirror 10: Second Beam Splitter

Claims (3)

[Claims] 1. A surface of a sample (5) is irradiated with a laser beam (4) through an optical system (3) including an objective lens (1) and a first beam splitter (2) to obtain the sample (5). The reflected light (6) from the surface of the sample is guided to the photodetector (8) through the imaging lens (7), and the sample (5) is output based on the output signal of the photodetector (8).
In the device for inspecting the surface state of the laser beam (4), the width of the laser beam (4) narrowed by the objective lens (1) is narrower than the beam diameter of the laser beam (4) and the longitudinal direction of the laser beam (4) is smaller. A line mirror (9) that coincides with the scanning direction is provided, and the line mirror (9) is arranged between the objective lens (1) and the sample (5) and at a location exposed to the laser light (4). Further, a surface state inspection device characterized in that a second beam splitter (10) is arranged between the line mirror (9) and the sample (5). 2. The pinhole is arranged immediately before the photodetector, and the diameter of the pinhole is substantially equal to or smaller than the width of the line mirror in the lateral direction. Surface condition inspection device. 3. The surface state inspection apparatus according to claim 1, wherein the line mirror is attached to one surface of the transparent body, and the second beam splitter is attached to the other surface of the transparent body.