JP2003148925A - Depth measuring apparatus and film thickness measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the depth of a hole or groove with a high aspect ratio formed in a substrate and to measure the thickness of a film in real time. SOLUTION: This apparatus has a scanning beam, a stage 11 for supporting the substrate, and two or more light receiving element arranged in the direction corresponding to x-axial direction. In this device, the depth of a recessed part formed on the substrate is determined on the basis of the relative distance information outputted from a drive device 13 for changing the relative distance in the optical axial direction between the focal point of the scanning beam and the substrate and a distance detector 14 for detecting the relative distance between the focal point of the scanning beam and the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a depth measuring device for measuring the depth of grooves and holes and the height of steps using a confocal optical system. Further, the present invention relates to a film thickness measuring device for measuring the film thickness of an optically transparent film formed on a substrate by using a confocal optical system.

[0002]

2. Description of the Related Art Various grooves, holes and steps are formed on a semiconductor substrate during the process of manufacturing a semiconductor device. Since the depths of the grooves and holes formed in these semiconductor substrates are closely related to the performance of semiconductor devices and the manufacturing yield, there is a strong demand for strict definition. For example, if the depth of the trench for element isolation is insufficient, an undesired leak current increases, which not only lowers the device performance but also causes a reduction in manufacturing yield.
Therefore, in order to further improve the manufacturing yield of semiconductor devices, there is a strong demand for the development of an apparatus capable of accurately measuring the depth of grooves and holes formed in a semiconductor substrate during the manufacturing process.

As a device for measuring the depth of the trench groove and the contact hole and the height of the step, a microscope device utilizing a confocal optical system is conceivable. That is, since the confocal optical system has a high resolution in the height direction, that is, the optical axis direction, scanning is performed while slightly shifting the focal position of the objective lens in the optical axis direction, and the brightness information of the obtained image is obtained. It is assumed that the depth information of the groove or hole is obtained from the relationship with the scanning amount of the objective lens in the optical axis direction.

[0004]

A laser microscope apparatus proposed by the present applicant is known as an optical apparatus utilizing the unique characteristics of a confocal optical system. However, since the laser microscope optically detects the state of the sample surface by scanning the sample surface with a minute light spot, it is not possible to use the known laser microscope as it is. A practical device has not been realized as a depth measuring device for measuring the depth of a groove or a groove.
In addition, as the density of devices formed on semiconductor wafers has increased, the aspect ratio of grooves and holes has become even higher.
For example, in the case of a trench groove formed on an SOI wafer, it is necessary to form a groove having a high aspect ratio with a width of 1 μm and a depth of 6 μm. However, when the aspect ratio of the groove or hole becomes high, the light beam focused by the objective lens is eclipsed by the edge portion of the hole or groove, and the light beam with a sufficient light quantity does not enter the bottom of the groove. It is also assumed that an image signal having a high S / N ratio cannot be obtained.

Further, in the manufacturing process of semiconductor devices, various semiconductor films are formed on a substrate, and development of a film thickness device capable of measuring the film thickness of these semiconductor films in real time is strongly demanded. That is, if an apparatus capable of measuring the film thickness of the semiconductor film in real time is arranged in the semiconductor device manufacturing line, the manufacturing yield of the semiconductor device can be further improved.

Therefore, an object of the present invention is to provide a depth measuring device which can accurately measure the depth of a groove or hole having a high aspect ratio or the height of a step using a confocal optical system.

Further, another object of the present invention is to realize a film thickness measuring device capable of measuring the thickness of an optically transparent film in real time.

[0008]

A depth measuring device according to the present invention comprises:
A depth measuring device for optically measuring the depth of a recess formed in a substrate, comprising: a light source for generating a light beam; a first beam deflecting device for deflecting the light beam in the x direction; A second beam deflecting device for deflecting the deflected light beam in the y direction orthogonal to the x direction, and an objective for focusing the scanning beam emitted from the second beam deflecting device into a minute spot shape and projecting it toward the substrate. A linear image sensor having a lens, a stage for supporting the substrate, and a plurality of light receiving elements arranged in a direction corresponding to the x-axis direction, for receiving reflected light from the substrate, and scanning emitted from the objective lens. A driving device that changes the relative distance between the focal point of the beam and the substrate in the optical axis direction of the objective lens; a distance detection device that detects the relative distance between the focal point of the scanning beam and the substrate; image A signal processing circuit that determines the depth of a recess formed in the substrate based on an image output signal output from each light receiving element of the sensor and relative distance information output from the distance detecting device; A beam deflection frequency control device for controlling the beam deflection frequency of the beam deflection device and the second beam deflection device, and capturing a series of substrate images while changing the relative distance between the objective lens and the substrate. And the second beam deflecting device has the first lens in the first scanning range in the optical axis direction away from the substrate.
Beam deflection is performed at a deflection frequency of, and the beam is deflected at a second deflection frequency lower than the first deflection frequency in the second scanning range in which the objective lens is closer to the substrate than the first scanning range. Characterize.

In the present invention, the depth of a groove or hole or the height of a step is measured by effectively utilizing the characteristic of the confocal optical system having high resolution in the height direction. When the focal point of the scanning beam emitted from the objective lens coincides with the surface of the substrate or the bottom of the groove, a large amount of light is incident on each light receiving element of the linear image sensor, while the focal point of the scanning beam is on a part other than the reflecting surface. When incident, the output signal from the light receiving element becomes almost zero. In particular, even if the focal point of the scanning beam is slightly deviated from the substrate surface in the height direction (optical axis direction), the amount of light incident on the linear image sensor is significantly reduced. Using the characteristics of this confocal optical system, the substrate image is captured while changing the relative distance between the objective lens and the substrate, that is, while scanning in the optical axis direction of the objective lens. And
The height position where the focal point coincides with the surface of the substrate and the bottom surface of the hole is detected from the amount of reflected light entering each light receiving element of the linear image sensor, and the surface profile of the substrate is obtained from the detected height information. The depth of the recess is determined from the surface profile of. As a result, it is possible to detect the depth of holes, grooves, etc. formed in the substrate in real time.

In a preferred embodiment of the depth measuring apparatus according to the present invention, the signal processing circuit detects the height profile of the substrate surface based on the output signal from the linear image sensor and the output signal from the distance detecting apparatus. It has a depth profile detecting means and a depth determining means for determining the depth of the recess from the obtained height profile. In the present invention, a large amount of light is incident on each light receiving element of the linear image sensor when the position of the focusing point of the scanning beam coincides with the substrate surface or the bottom surface of the concave portion, and is incident on the light receiving element when the position of the focusing point deviates from the substrate surface. The height profile of the substrate surface is detected by utilizing the characteristic that the amount of light to be drastically reduced is determined, and the depth of the recess is determined from the detected height profile.

On the other hand, when the aspect ratio of the concave portion of the substrate is large, the scanning beam is eclipsed by the peripheral member of the concave portion, the light amount of the scanning beam penetrating to the bottom surface of the concave portion is remarkably reduced, and the detection sensitivity to the bottom surface of the concave portion is lowered. May occur. In order to solve this problem, the present invention captures a series of substrate images while moving the objective lens and the substrate so as to approach each other, and the first and second beam deflecting devices
The objective lens deflects the beam at a first deflection frequency in a scanning range in the first optical axis direction away from the substrate, and the objective lens moves closer to the substrate than in the first optical axis direction scanning range. Beam deflection is performed at a second deflection frequency lower than the first deflection frequency in the axial scanning range. The amount of charge accumulated in the linear image sensor is proportional to the product of the intensity of incident light and time. Therefore, if the beam scanning speed is slowed, a highly sensitive output signal can be obtained. However, if the surface of the substrate is scanned at a low scanning speed over the entire scanning area, the measurement time becomes too long and the requirement for real-time measurement cannot be met. Therefore, the beam scanning is performed at high speed in the first scanning range, and the beam scanning is performed at low speed in the second scanning range near the bottom of the recess. In this way, by switching the scanning speed in the depth direction, it is possible to perform depth measurement with high sensitivity even if the depth of the recess having a high aspect ratio is not too long.

The preferred embodiment of the depth measuring device of the present invention is x
A second beam deflecting device for deflecting the scanning beam deflected in the direction in the y direction orthogonal to the x direction, the substrate surface is two-dimensionally scanned, and the height profile detecting means are two-dimensionally arranged. The height determining means detects the height profile of the two-dimensional image of the surface of the substrate composed of different pixels, and the depth determining means determines the first and second two from the relationship between the height information of each pixel and the pixel frequency. The peak is obtained, and the difference in height between these two peaks is output as the depth of the recess. The depth determining means uses the height profile of the two-dimensional image to form a relationship between height and pixel frequency, that is, a histogram. In the obtained histogram, two peaks are generated, which are based on two surfaces, a surface defined by the reflected light from the upper surface of the substrate and a surface defined by the reflected light from the bottom surface of the recess. Therefore, the depth of the concave portion can be determined by obtaining the distance between these two peaks.

In a preferred embodiment of the depth measuring apparatus according to the present invention, an objective lens moving device for moving the objective lens in the optical axis direction is used as a driving device for changing the distance between the focal point of the scanning beam and the substrate. The relative distance between the focusing point of the scanning beam and the substrate is detected using the position information of the objective lens in the optical axis direction. As a method of changing the distance between the focusing point of the scanning beam and the substrate, there are a method of changing the position of the objective lens in the optical axis direction and a method of changing the height of the stage supporting the substrate. In this case, the position of the objective lens in the optical axis direction is
By using a motor and an encoder, there is an advantage that it can be defined relatively easily.

A film thickness measuring device according to the present invention is a film thickness measuring device for optically measuring the thickness of an optically transparent film formed on a substrate, which comprises a light source for generating a light beam and a light source. A first beam deflecting device for deflecting the beam in the x direction, a second beam deflecting device for deflecting the light beam deflected in the x direction in the y direction orthogonal to the x direction, and emitted from the second beam deflecting device. An objective lens that focuses the projected scanning beam into a minute spot and projects it toward the substrate, a stage that supports the substrate, and a plurality of light receiving elements arranged in a direction corresponding to the x-axis direction are provided. Linear image sensor for receiving the reflected light of the objective lens, a driving device for changing the relative distance in the optical axis direction of the objective lens between the focal point of the scanning beam emitted from the objective lens and the substrate, and the focusing of the scanning beam. Between the point and the substrate A distance detection device that detects a relative distance, a film formed on a substrate based on an image output signal output from each light receiving element of the linear image sensor and relative distance information output from the distance detection device. A signal processing circuit for determining the film thickness and a beam deflection frequency control device for controlling the beam deflection frequency of the first beam deflecting device and the second beam deflecting device are provided, and the objective lens and the substrate are brought close to each other. While capturing a series of substrate images, the first and second beam deflecting devices are
The objective lens deflects the beam at a first deflection frequency in a scanning range in the first optical axis direction away from the substrate, and the objective lens moves closer to the substrate than in the first optical axis direction scanning range. Beam deflection is performed at a second deflection frequency lower than the first deflection frequency in the axial scanning range.

In the semiconductor film formed on the substrate, the interface between the air and the semiconductor film constitutes a first reflecting surface, and the interface between the semiconductor film and the substrate has a refractive index of the semiconductor film and a refractive index of the substrate. Since a difference in refractive index is generated between the second reflective surface and the second reflective surface. Since the first reflecting surface and the second reflecting surface correspond to the substrate surface and the bottom surfaces of the holes and the grooves, respectively, the principle of depth measurement can be applied to the film thickness measurement as it is. That is, when the focus point of the scanning beam is located on the interface of the semiconductor film, a large amount of reflected light is incident on the light receiving element of the linear image sensor by the interface, so that the position of the focus point of the scanning beam in the optical axis direction is changed. However, by capturing an image, the film thickness profile of the semiconductor film formed on the substrate can be detected. Therefore, the film thickness can be easily determined by the film thickness determining means from the detected film thickness profile. Also in this case, the sample surface can be two-dimensionally scanned to form a two-dimensional film thickness profile of the film formed on the substrate. Then, from the obtained two-dimensional film thickness profile, two peak values can be obtained from the relationship between the pixel frequency and the thickness information, and the film thickness can be determined based on the distance between the peaks in the optical axis direction. Also in this film thickness measurement, the reflectance at the interface between the substrate and the semiconductor film formed thereon is relatively low. Therefore, by setting the beam deflection frequency near the interface to a low speed, the substrate and the semiconductor film The interface with and can be accurately detected.

[0016]

1 is a diagram showing the construction of an example of a depth measuring apparatus according to the present invention. A scanning beam is generated from the light source 1. In this example, a blue laser diode is used as the light source. The scanning beam is incident on the acousto-optic deflecting element 2 which is the first beam deflecting device. The acousto-optic deflector 2 deflects the scanning beam in the x direction at high speed. The beam emitted from the acousto-optic deflecting element 2 passes through the polarizing beam splitter 5 via the relay lenses 3 and 4, and enters the vibrating mirror 6. The vibrating mirror 6 deflects the incident beam in the y direction which is orthogonal to the x direction. The beam reflected by the oscillating mirror 6 enters the objective lens 10 through the relay lenses 7 and 8 and the quarter-wave plate 9 and is focused into a minute spot by the objective lens, and then is focused on the substrate 12 arranged on the stage 11. Incident. The substrate 12 to be measured can be a semiconductor wafer having trench grooves or contact holes formed therein, or a sample having an optically transparent layer formed therein. Of course, when used as a film thickness measuring device, the film thickness of each layer is simultaneously measured by one measurement operation, that is, one scanning in the optical axis direction, even for a sample in which a plurality of optically transparent layers are laminated. can do.

Since the scanning beam incident on the substrate 12 is focused by the objective lens 10 in the form of a minute spot, the substrate 12 is two-dimensionally scanned by the minute light spot. The objective lens 10 is the objective lens driving device 1
3 is connected to the optical axis 3 and moves stepwise for each scan in the optical axis direction, that is, the z direction orthogonal to the x and y directions.
The objective lens driving device 13 can be composed of, for example, a servo motor. Further, the position of the objective lens 10 in the optical axis direction can be measured by the encoder 14 connected to the servo motor. The relative distance between the focal point of the scanning beam and the substrate changes due to the movement of the objective lens in the optical axis direction. Therefore, the substrate 12 has a focal point position of 1
Two-dimensional scanning is sequentially performed by a scanning beam that changes in the optical axis direction at a predetermined pitch for each scan. The position information of the objective lens 10 detected by the encoder 14 is supplied to a signal processing circuit 19 to be described later and used for detecting the height profile of the substrate surface.

The beam reflected by the surface of the substrate is focused again by the objective lens 10, and the quarter wavelength plate 9 and the relay lens 8 are provided.
And 7, and then enters the vibrating mirror 6 and is descanned. The beam reflected by the vibrating mirror enters the polarization beam splitter 5. Since this reflected beam has passed through the quarter-wave plate 9 twice, its plane of polarization is rotated by 90 °. Therefore, the beam is reflected by the polarization beam splitter 5 and separated from the light beam traveling from the light source 1 to the substrate 12. The beam reflected by the polarization beam splitter is lens 1
It is focused by 5 and enters the linear image sensor 16. The linear image sensor 16 has a plurality of light receiving element arrays arranged in a line in a direction corresponding to the x direction. Since the beam incident on the linear image sensor 16 is descanned by the vibrating mirror 6, the light receiving surface of the linear image sensor 16 is scanned at high speed at the deflection frequency of the acoustooptic device 2. The charge accumulated in each light receiving element of the linear image sensor 16 is read out by the reading circuit 17
Under the control of the
And output to the signal processing circuit 19 line by line. Therefore, the image signal of the two-dimensional image of the substrate at each position in the optical axis direction of the objective lens is sequentially supplied to the signal processing circuit 19.

Next, the basic principle of the depth measuring method according to the present invention will be described. FIG. 2 is a diagram for explaining the basic principle of the depth measuring apparatus using the confocal optical system according to the present invention. The light beam from the point light source 21 is a half mirror 2.
2 and then enters the objective lens 23. Then, it is focused in a spot shape by the objective lens 23 and is incident on the substrate 24. At this time, when the focus point, that is, the focal point of the light beam is located on the substrate, the light reflected on the substrate surface is again focused by the objective lens 23, reflected by the half mirror 22, and passes through the opening 25a of the pinhole mask 25. Then photo detector 2
Focus on 6. Therefore, when the focus of the light beam from the light source is located on the substrate, a large amount of light is incident on the photodetector. On the other hand, as shown by the broken line in FIG. 2, when the focus of the light beam is formed on the front side or the rear side of the substrate 24, most of the reflected light from the substrate surface is blocked by the pinhole mask 25, and the light detection is performed. Only a small amount of light enters the container 26.
Therefore, the objective lens is moved in the optical axis direction or the position of the substrate stage is moved in the optical axis direction, and the focusing point of the light beam is moved along the depth direction of the hole or groove formed in the substrate. The peak value of the reflected light from the substrate surface and the peak value of the reflected light reflected from the bottom surface of the hole or groove formed in the substrate can be obtained by measuring the intensity of the reflected light from the substrate. Then, the depth of the hole or groove formed in the substrate can be determined by detecting the relative distance between the objective lens that generates the two peaks of the reflected light and the substrate.

FIG. 3 is a graph schematically showing the intensity of reflected light from the surface of the substrate and the bottom surface of the hole or groove when the objective lens is moved in the optical axis direction. In FIG. 3, the horizontal axis represents the moving position of the objective lens, and the vertical axis represents the intensity of the reflected light incident on the photodetector. It is assumed that the focus is located on the upper surface of the substrate at the position H1 of the objective lens. In this case, position H
The reflected light intensity at 1 becomes maximum, and the first peak occurs. Due to the characteristics of the confocal optical system, the amount of light incident on the photodetector is sharply reduced by only slightly shifting the focal position of the objective lens in the depth direction. Further, when the objective lens is moved toward the bottom of the hole, the focal point of the light beam is located on the bottom surface of the hole at the position H2. Since this bottom surface forms a reflecting surface, the reflected light intensity incident on the photodetector forms a second peak. Therefore, the depth of the hole or groove can be obtained from the peak distance d between the first peak and the second peak.

On the other hand, when the aspect ratio of the hole or groove becomes large, the scanning beam is eclipsed by the peripheral portion of the hole or groove, and the amount of light penetrating to the bottom surface becomes minute. As a result, the intensity of the reflected light from the bottom surface of the hole is significantly reduced, and the peak of the reflected light from the bottom surface cannot be accurately determined. Therefore, the present invention utilizes the charge storage capability of the linear image sensor. That is, the amount of charge accumulated in each light receiving element of the linear image sensor is proportional to the product of the intensity of incident light and the incident time. Therefore, by decreasing the scanning speed and increasing the incident time, it is possible to obtain a high-brightness output signal from each light-receiving element of the linear image sensor even if the intensity of reflected light from the bottom surface of the hole is low. The clear peak value of the reflected light can be detected. On the other hand, if the scanning speed of the light beam is reduced over the entire scan, the measurement time becomes too long and the requirement for real-time measurement cannot be met. Therefore, in the present invention, a series of substrate images are captured while moving the objective lens and the substrate so as to approach each other, and the first and second beam deflecting devices use the optical axis direction in which the objective lens is away from the substrate. Beam deflection is performed at a first deflection frequency in a first scanning range of, and the objective lens is lower than the first deflection frequency in a second scanning range closer to the substrate than the first optical axis direction scanning range. Beam deflection is performed at the second deflection frequency. That is, the beam scanning is performed at a high speed during a period of scanning near the surface of the substrate, and the beam scanning is performed at a low speed during a period of time when the focal point is near the bottom surface. in this way,
By switching the scanning speed according to the position of the hole in the depth direction, the bottom surface of the recess can be clearly detected only by slightly increasing the measurement time.

As another method, the light beam scanning in the x direction is performed at high speed as it is, and the reading frequency of the reading circuit 16 of the linear image sensor is set to the first scanning range and the second scanning range in the optical axis direction. Similar effects can be achieved by switching with. That is, the second near the bottom of the groove
The read frequency in the depth range is set to be slower than the read frequency in the first depth range near the substrate surface. By slowing the reading frequency, each light receiving element of the linear image sensor is scanned with the reflected beam a number of times before the charges are read out, which is equivalent to reducing the beam scanning speed. Even if the reflected light intensity is low, the linear image sensor can generate a high S / N output signal.

Next, the operation of the depth measuring device shown in FIG. 1 will be described. The controller 30 controls the entire apparatus. An x-direction drive control signal is supplied from the controller 30 to the acousto-optic deflection element drive circuit 31, and the x-direction scanning frequency of the acousto-optic deflection element 2 is controlled by the drive signal from the acousto-optic deflection element drive circuit. The ratio of the scanning frequency of the acousto-optic deflecting element in the first scanning range to the scanning frequency in the second scanning range under the control of the controller 30 can be set to 16: 1, for example. The controller 30 supplies an oscillating mirror drive signal to the oscillating mirror drive circuit 32, so that the oscillating mirror drive device 33 outputs y.
Controls the scanning frequency in the direction. Similar to the acousto-optic deflecting element, this vibrating mirror is also capable of switching the scanning speed between the first scanning range and the second scanning range, and the scanning speed ratio is set to be the same as that of the acousto-optical deflecting element. A read control signal is supplied from the controller 30 to the read circuit 17, and the charge accumulated in each light receiving element of the linear image sensor 16 is read by this read control signal. This reading frequency is set to the same frequency as the driving frequency of the acousto-optic deflecting element 2, for example. As with the acousto-optic deflector, the read frequency is also switched between the first scan range and the second scan range. Further, a drive signal is supplied from the controller 30 to the objective lens drive circuit 13, and the objective lens is moved so as to approach the substrate step by step for each y-direction scan.

Next, the relationship between the relative distance between the focal point of the scanning beam and the substrate and the output signal of the linear image sensor will be described. 4A to 4D show the relationship between the scanning position of the focal point of the scanning beam and the output signal of one scanning line read from the linear image sensor. 4A to 4D, the drawings on the left side show the position of the focusing point of the scanning beam with respect to the substrate 12 (the broken line shows the position of the focusing point),
The diagram on the right is a graph showing the output signal strength of the linear image sensor. In the diagram on the right side, the horizontal axis represents the scanning position in the x direction, and the vertical axis represents the output intensity of each light receiving element. Figure 4
A shows an example in which the focus point of the scanning beam is located above the substrate surface, FIG. 4B shows an example in which the focus point is located on the substrate surface, and FIG. 4C shows the focus point between the substrate surface and the bottom of the recess. FIG. 4D shows an example in which the focal point of the scanning beam is located on the bottom surface of the concave portion. When the focal point of the scanning beam is located above the substrate surface, the output signal from each light receiving element of the linear image sensor becomes substantially zero. On the other hand, as shown in FIG. 4B, when the focus point is located on the surface of the substrate, the output signal from the portion corresponding to the groove is almost zero, but the output signal of the light receiving element in a wide range other than the groove has high brightness. Shows. Further, as shown in FIG. 4C, when the focus point of the scanning beam moves to the lower side and the focus point is located between the surface of the substrate and the bottom surface of the groove, the reflected light from the substrate is very small because there is no reflective surface. The output signal from each light receiving element of the linear image sensor becomes substantially zero. When the focus point of the scanning beam further moves and the position of the focus point of the scanning beam in the optical axis direction coincides with the position of the bottom surface of the groove, as shown in FIG. 4D, the output from the light receiving element corresponding to the bottom surface portion. The signal represents a relatively high brightness, and the output signal from the light receiving element corresponding to the portion other than the bottom surface becomes substantially zero.

FIG. 5 is a diagram showing the configuration of an example of a signal processing circuit of the depth measuring and film thickness measuring apparatus according to the present invention.
The signal processing circuit detects the height profile of the substrate surface and a depth determining circuit 50 that determines the depth of the recess based on the height profile information output from the height profile detecting circuit 40 and the height profile detecting circuit. Equipped with.
The height profile detection circuit 40 has a comparator 41, a selector 42, a frame memory 43, and a height profile memory 44. The image signal A from the linear image sensor 16 amplified by the amplifier 18 is supplied to the comparator 41 and the selector 42. The output signal of the selector 42 is supplied to the frame memory 43, and the output signal B of the frame memory 43 is supplied to the other input of the comparator 41. Comparator 4
1 compares the image signal A from the linear image sensor with the signal B stored in the frame memory 43 (for example, the image signal obtained by the previous scan), and A> B
In case of A, a control signal of 1 is output, and in case of A <B, a control signal of 0 is output. These control signals are supplied to the selector 42 and the height profile memory 44, respectively. Similarly, the selector 42 inputs the image signal A from the linear image sensor and the signal B stored in the frame memory 43, outputs the image signal A when the control signal supplied from the comparator 41 is 1, and controls the same. When the signal is 0, the signal B stored in the frame memory is output. The frame memory 43 that stores the output signal from the selector has an address space corresponding to each pixel of the image signal, and stores the output signal from each light receiving element of the linear image sensor in the memory area corresponding to each pixel. Therefore, at the address position corresponding to each pixel of the frame memory, the highest reflected light intensity information among the reflected light intensities obtained by scanning at each position in the optical axis direction of the objective lens, that is, the reflected light on the substrate surface Will be stored respectively.

The height profile memory 44 stores the output signal of the encoder 14 indicating the position of the objective lens 10 in the optical axis direction, that is, the relative distance between the focal point of the scanning beam and the substrate.
Supply to. Like the frame memory 43, the height profile memory 44 also has an address space corresponding to each pixel of the image signal, and the address space of each pixel contains height information when the maximum reflected light intensity is received. Remember. A control signal from the comparator 41 is also supplied to the height profile memory 44, and when the control signal is 1, the encoder 14
The height information from is stored, and is not stored when the control signal is 0. As a result, height information that maximizes the intensity of the reflected light from the substrate surface, that is, the position in the optical axis direction, is stored in the memory area corresponding to each pixel of the height profile memory 44. Will store the surface profile of the substrate.

The height profile information of the substrate surface stored in the height profile memory 44 is the depth determining device 5.
Supply to 0. In the depth determining device 50, the relationship between the number of pixels shown in FIG. 6, that is, the frequency of pixels and the position of the objective lens in the optical axis direction is obtained. While moving the position of the objective lens in the optical axis direction step by step so as to approach the substrate, the substrate surface is moved to 2
When dimensionally scanned, the focus point of the scanning beam _first coincides with the substrate surface (position H ₁ ), and a large number of pixels receive reflected light of maximum intensity. Further, when the objective lens is moved closer to the substrate, the focal point of the scanning beam coincides with the bottom surface of the concave portion (position H ₂ ), and the pixels having the number of pixels corresponding to the area of the bottom surface emit the reflected light having the maximum intensity. Receive light. Therefore, a histogram showing the relationship between the position of the objective lens in the optical axis direction and the number of pixels is formed, and based on the obtained histogram, the distance between the positions H ₁ and H ₂ , which is the distance between two peaks of the pixel frequency, is formed. The depth of the recess can be obtained by measuring the distance d.

The optical system shown in FIG. 1 and the signal processing circuit shown in FIG. 5 can be applied to film thickness measurement. That is,
In the case of film thickness measurement, the interface between the air and the film becomes the first reflecting surface for the scanning beam, and the interface between the film and the underlying material layer or the substrate also becomes the second reflecting surface due to the difference in the refractive index. A characteristic similar to that shown in FIG. 6 is obtained. Therefore, in the film thickness measurement, the height profile detection circuit 40 of FIG. 5 becomes a film thickness profile detection circuit that detects the two-dimensional film thickness profile of the film, and the depth determination circuit 50
It functions as a film thickness determining circuit that determines the film thickness from the relationship between the height information and the number of pixels.

The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the substrate surface is two-dimensionally scanned, but even when the scanning beam is one-dimensionally scanned, it is possible to accurately detect the groove and hole of the substrate and the film thickness of the sample. This one-dimensional scanning measuring device can be realized by using the vibrating mirror which scans in the y direction of the measuring device shown in FIG. 1 as a fixed mirror. In this case, not only an acousto-optic device but also a vibrating mirror, a galvano mirror, or a polygon mirror can be used as a scanning device for one-dimensional scanning. In addition, the depth can be determined from the distance between two peaks in the one-dimensional height profile.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an example of a depth measuring apparatus and a film thickness measuring apparatus according to the present invention.

FIG. 2 is a diagram showing the principle of height measurement using a confocal optical system.

FIG. 3 is a diagram showing the relationship between the amount of movement of an objective lens and the intensity of reflected light.

FIG. 4 is a diagram showing a relationship between a position in the height direction of a focusing point of a scanning beam on a substrate having a groove formed therein and an output signal of a light receiving element.

FIG. 5 is a diagram showing a configuration of an example of a signal processing circuit.

FIG. 6 is a histogram showing the relationship between the position of the objective lens in the optical axis direction and the number of pixels.

[Explanation of symbols]

1 light source 2 Acousto-optic element 3,4,7,8 relay lens 5 Polarizing beam splitter 6 Vibration mirror 9 λ / 4 plate 10 Objective lens 11 stages 12 substrates 13 Objective lens moving device 14 encoder 15 Focusing lens 16 linear image sensor 17 Read circuit 18 amplifier 19 Signal processing circuit 30 controller

Continued front page    F term (reference) 2F065 AA06 AA24 AA25 AA30 AA51                       BB02 CC19 DD06 FF10 FF44                       FF49 FF67 GG06 GG22 HH04                       JJ02 JJ05 JJ25 LL00 LL04                       LL05 LL13 LL30 LL36 LL37                       LL57 LL62 LL65 MM16 MM26                       PP02 PP12 QQ23

Claims (9)

[Claims] 1. A depth measuring device for optically measuring the depth of a recess formed in a substrate, wherein a light source for generating a light beam and a first beam deflecting device for deflecting the light beam in the x direction. And a second beam deflecting device for deflecting the light beam deflected in the x direction in the y direction orthogonal to the x direction, and a scanning beam emitted from the second beam deflecting device is focused into a minute spot on the substrate. An objective lens for projecting toward, a stage for supporting the substrate, a plurality of light receiving elements arranged in a direction corresponding to the x-axis direction, a linear image sensor for receiving reflected light from the substrate, and the objective A drive device that changes the relative distance between the focal point of the scanning beam emitted from the lens and the substrate in the optical axis direction of the objective lens, and the distance detection that detects the relative distance between the focal point of the scanning beam and the substrate. Device and A signal processing circuit for determining the depth of a recess formed in the substrate based on an image output signal output from each light receiving element of the near image sensor and relative distance information output from the distance detecting device; A beam deflection frequency control device for controlling the beam deflection frequency of the first beam deflection device and the second beam deflection device, and capturing a series of substrate images while changing the relative distance between the objective lens and the substrate, The first and second beam deflecting devices perform beam deflection at a first deflection frequency in a scanning range in which the objective lens is away from the substrate in the first optical axis direction, and the objective lens is higher than the first scanning range. In the second scanning range approaching the substrate, the second scanning frequency lower than the first deflection frequency
Depth measuring device characterized by performing beam deflection at the deflection frequency of. 2. A depth measuring device for optically measuring the depth of a recess formed in a substrate, wherein a light source for generating a light beam and a first beam deflecting device for deflecting the light beam in the x direction. And a second beam deflecting device for deflecting the light beam deflected in the x direction in the y direction orthogonal to the x direction, and a scanning beam emitted from the second beam deflecting device is focused into a minute spot on the substrate. A linear image sensor having an objective lens for projecting toward it, a stage for supporting the substrate, and a plurality of light receiving elements arranged in a direction corresponding to the x-axis direction, for receiving reflected light from the substrate, and the linear image sensor. A read control circuit that controls the read frequency of the charges accumulated in each light receiving element of the image sensor, and the relative distance in the optical axis direction of the objective lens between the focusing point of the scanning beam emitted from the objective lens and the substrate are changed. Driving device, a distance detecting device for detecting a relative distance between the focusing point of the scanning beam and the substrate, an image output signal output from each light receiving element of the linear image sensor, and an output from the distance detecting device. And a signal processing circuit that determines the depth of the recess formed in the substrate based on relative distance information, capturing a series of substrate images while changing the relative distance between the objective lens and the substrate, The read control circuit of the linear image sensor reads the charge accumulated in the light receiving element at the first read frequency in the first scanning range in the optical axis direction in which the objective lens is away from the substrate, and the objective lens is the first scan range. Depth characterized in that the charge accumulated in the light receiving element is read at a second read frequency lower than the first read frequency in a second scan range closer to the substrate than in the scan range. measuring device. 3. The height profile in the optical axis direction of the substrate surface is generated by the signal processing circuit based on the image signal output from each light receiving element of the linear image sensor and the relative distance information output from the distance detection device. 3. The depth measuring device according to claim 1, further comprising height profile detecting means for detecting and depth determining means for determining the depth of the concave portion from the obtained height profile. 4. The depth measuring apparatus according to claim 3, wherein the depth determining means determines the surface height of the substrate and the height of the bottom surface of the recess from the height profile of the substrate surface, and determines the height of these substrates. Calculate the difference between the surface height and the height of the bottom of the recess,
A depth measuring device, which outputs the obtained difference as the depth of the recess. 5. The depth determining means determines the height of the substrate surface in the optical axis direction and the concave portion from the relationship between the height information in the optical axis direction of each pixel obtained from the height profile of the substrate surface and the number of pixels. The depth measuring device according to claim 4, wherein the height of the bottom surface is determined. 6. An objective lens moving device for moving the objective lens in the optical axis direction is used as a driving device for changing the distance between the focusing point of the scanning beam and the substrate, and position information of the objective lens in the optical axis direction is used. The depth measuring device according to claim 5, wherein the relative distance between the focal point of the scanning beam and the substrate is detected by using. 7. The substrate is a semiconductor wafer having a groove, a hole or a step formed therein, and the depth of the groove, the depth of the hole or the height of the step is measured. From 6
The depth measuring device according to any one of 1 to 6 above. 8. A film thickness measuring device for optically measuring the thickness of an optically transparent film formed on a substrate, wherein the light source generates a light beam and the light beam is deflected in the x direction. First
Beam deflecting device and a light beam deflected in the x direction
A second beam deflecting device that deflects in the y direction orthogonal to the direction, an objective lens that focuses the scanning beam emitted from the second beam deflecting device into a minute spot and projects it toward the substrate, and supports the substrate. A linear image sensor having a stage and a plurality of light receiving elements arranged in a direction corresponding to the x-axis direction, for receiving reflected light from the substrate, a focusing point of a scanning beam emitted from the objective lens, and the substrate. Between the driving device for changing the relative distance of the objective lens in the optical axis direction, the distance detecting device for detecting the relative distance between the focusing point of the scanning beam and the substrate, and the light receiving elements of the linear image sensor. A signal processing circuit for determining the film thickness of a film formed on the substrate based on the output image output signal and the relative distance information output from the distance detection device;
A beam deflection frequency controller for controlling the beam deflection frequency of the first beam deflector and the second beam deflector, and capturing a series of substrate images while changing the relative distance between the objective lens and the substrate. In the first and second beam deflecting devices, the objective lens deflects the beam at the first deflection frequency in the first scanning range in the optical axis direction away from the substrate, and the objective lens moves in the first scanning range. A film thickness measuring device, characterized in that beam deflection is performed at a second deflection frequency lower than the first deflection frequency in a second scanning range closer to the substrate. 9. A film thickness measuring device for optically measuring the thickness of an optically transparent film formed on a substrate, comprising a light source for generating a light beam and deflecting the light beam in the x direction. First
Beam deflecting device and a light beam deflected in the x direction
A second beam deflecting device that deflects in the y direction orthogonal to the direction, an objective lens that focuses the scanning beam emitted from the second beam deflecting device into a minute spot and projects it toward the substrate, and supports the substrate. A linear image sensor having a stage and a plurality of light-receiving elements arranged in a direction corresponding to the x-axis direction, which receives reflected light from the substrate, and a charge accumulated in each light-receiving element of the linear image sensor. A read control circuit for controlling the read frequency; and a drive device for changing the relative distance in the optical axis direction of the objective lens between the focal point of the scanning beam emitted from the objective lens and the substrate.
A distance detection device that detects a relative distance between the focusing point of the scanning beam and the substrate, an image output signal output from each light receiving element of the linear image sensor, and relative distance information output from the distance detection device. And a signal processing circuit for determining the film thickness of the film formed on the substrate based on the above, by capturing a series of substrate images while changing the relative distance between the objective lens and the substrate, The readout control circuit reads out the electric charge accumulated in the light receiving element at the first readout frequency in the first scanning range in the optical axis direction in which the objective lens is away from the substrate, and the objective lens is closer to the substrate than the first scanning range. The film thickness measuring device is characterized in that the electric charge accumulated in the light receiving element is read at a second reading frequency lower than the first reading frequency in the second scanning range approaching to.