JPH1123236A - Apparatus for measuring substrate spacing and method for measuring substrate spacing - Google Patents

Abstract

(57) Abstract: The present invention relates to a substrate spacing measuring device and a substrate spacing measuring method for measuring a substrate spacing between two substrates joined via a spacer, and relates to a case where upper and lower substrates have different sizes. It is an object of the present invention to reliably perform interval measurement even if there is any. A substrate gap (1) is provided between two substrates (12, 14) joined by a metal pillar (16) with a small substrate gap (18).
8, a light projecting device 20 </ b> A that receives incident light having a parallel light beam and a uniform light intensity distribution from one of the light emitting devices 8, a light receiving device 22 </ b> A that detects light intensity of light emitted from the other of the substrate gaps 18,
A moving device 30 for moving the light projecting device 20A in a direction perpendicular to the surface direction of each of the substrates 12 and 14, and a distance between the substrate intervals 18 based on the light intensity detected by the light receiving device 22A and the moving amount of the light projecting device 20A. An interval measurement circuit 32 for measurement is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a distance between substrates and a method for measuring a distance between substrates, and more particularly to an apparatus and a method for measuring the distance between two substrates joined via a spacer. Related to the measurement method. 2. Description of the Related Art In recent years, the development of semiconductor technology, particularly the improvement of high-frequency characteristics of compound semiconductors, has been remarkable, and the application to not only the microwave band but also the millimeter wave band is becoming a reality.

The use of a compound semiconductor for a device in the millimeter-wave band has a great advantage in that the device can be reduced in size, but it is necessary to reduce the price of the device in order to promote its spread. However, since the compound semiconductor substrate is expensive, it is necessary to reduce the area of the compound semiconductor substrate used in order to reduce the cost of the device. Therefore, only the necessary parts (active elements and the like) are made of a compound semiconductor, the other parts (matching circuits and the like) are formed on an inexpensive silicon substrate, and these two substrates are bonded with metal bumps and the like ( A method has been proposed in which the use area of a compound semiconductor is minimized by flip-chip bonding to reduce the apparatus cost.

[0003]

2. Description of the Related Art By the way, substrates bonded by flip-chip bonding are located very close to each other (actually, about several microns to several tens of microns). In a circuit with a very high frequency, the characteristic impedance of the transmission line on the substrate changes due to the influence of the nearby ground plane or the like. Therefore, in order to set the characteristic impedance of the transmission line on the substrate to a desired value, it is necessary to set the interval between the two substrates to a designed value, and for that purpose, a method of measuring the interval between the substrates is required.

FIG. 7 shows a conventional method of measuring the distance between substrates. In the figure, an upper substrate 1 is a compound semiconductor substrate, and is disposed on a lower substrate 2 which is a silicon substrate via a metal pillar 3. As a result, the upper substrate 1 and the lower substrate 2 face each other with a predetermined interval 4 therebetween. Conventionally, a microscope 5 is used as a means for measuring the distance of the interval 4. Specifically, a scale is provided on the objective lens of the microscope 5, and the microscope 5 is located on the side of the interval 4 formed by the upper substrate 1 and the lower substrate 2, and the microscope 5 observes the interval 4 and A method of reading a distance using a scale has been used.

[0005]

However, the distance 4
In the method of observing and measuring with a microscope 5 from the lateral direction,
As shown in FIG. 13, when the area of the lower substrate 2 is larger than the area of the upper substrate 1 (actually, in most cases), the lower substrate 2 becomes an obstacle and the eyepiece of the microscope 5 Cannot be brought close to the interval 4 to a position where focusing can be performed. For this reason, the distance measurement method using the microscope 5 has a problem that it is practically impossible to measure the distance between the substrates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides a substrate spacing measuring apparatus and a substrate spacing measuring method capable of reliably performing a spacing measurement even when upper and lower substrates have different sizes. The purpose is to provide.

[0007]

The above-mentioned object can be attained by taking the following means. In the apparatus for measuring a substrate interval according to the first aspect of the present invention, a parallel light beam and a uniform light intensity distribution are incident from one of the intervals between two substrates joined at a small interval by a spacer. A light projecting device for injecting light, a light receiving device for detecting light intensity of outgoing light emitted from the other of the intervals, and a state in which the incident light is incident on the interval, in a direction perpendicular to the surface direction of the substrate. Incident light changing means for changing the light intensity, the light intensity detected by the light receiving device, and a measuring means for measuring the distance of the interval based on the amount of change of the incident light by the incident light changing means, Is what you do.

According to a second aspect of the present invention, in the apparatus for measuring a substrate interval according to the first aspect, the incident light changing means moves the light projecting device in a direction perpendicular to a surface direction of the substrate. It is a moving mechanism that causes the movement. According to a third aspect of the present invention, in the apparatus for measuring a substrate interval according to the first or second aspect, the light projecting device is configured such that an optical axis is directed downward in a direction perpendicular to a surface direction of the substrate. A light source, and a first prism that performs optical path conversion so that light emitted from the light source is directed toward the space, and the light receiving device is configured such that an optical axis thereof is directed downward perpendicular to a surface direction of the substrate. And a second prism that performs optical path conversion so that outgoing light emitted from the other side of the space is directed to the light receiving element.

According to a fourth aspect of the present invention, in the apparatus for measuring a substrate interval according to any one of the first to third aspects, in addition to the light projecting device, a bias light for causing a bias light to enter the interval is provided. A light projection device is provided. According to a fifth aspect of the present invention, in the apparatus for measuring the distance between the substrates according to the first aspect, the incident light changing means changes the amount of incident light incident on the distance in a direction perpendicular to a surface direction of the substrate. It is characterized in that the shutter is changed.

Further, in the method for measuring the distance between the substrates according to the invention of claim 6, between the two substrates joined at a small distance by a spacer, the light is projected from one of the distances using a light projecting device. Parallel light rays and incident light having a uniform light intensity distribution are made incident, and while the incident state of the incident light to the space is changed in a direction perpendicular to the surface direction of the substrate, the light emitted from the other of the spaces is emitted. The light intensity of the emitted light is detected by a light receiving device, and the distance of the interval is measured based on the light intensity detected by the light receiving device and the amount of change of the incident light by the incident light changing means. .

Each of the above means operates as follows.
According to the first and sixth aspects of the present invention, the incident light changing means changes the incident state of the incident light emitted from the light projecting device to the interval in a direction perpendicular to the plane direction of the substrate, The light intensity of the incident light that enters the space between the two substrates changes.

Therefore, the light intensity detected by the light receiving device is correlated with the amount of movement of the light source. Specifically, the position of the light projecting device at which the light intensity starts to change and the light intensity received are zero. The distance from the position of the light emitting device at the time of becoming becomes the distance of the interval. Based on this principle, the measuring means measures the distance of the interval from the light intensity detected by the light receiving device and the amount of change of the incident light by the incident light changing means.

According to the second aspect of the present invention, the incident light changing means is constituted by the moving mechanism for moving the light projecting device in a direction perpendicular to the plane direction of the substrate, so that the distance can be easily changed by the moving operation. The intensity of light to be incident on the light source can be changed. According to the third aspect of the invention, by moving the first prism in a direction perpendicular to the plane direction of the substrate, the amount of light incident at intervals changes as in the case of the first aspect. Therefore, the distance of the gap can be measured by detecting the light intensity of the light emitted from the gap by the light receiving device.

According to the fourth aspect of the present invention, the sensitivity of the light receiving device can be improved by providing the bias light projecting device for injecting the bias light within the interval in addition to the light projecting device. . That is, a light-receiving element such as a photodiode usually has such characteristics that the linearity is deteriorated when the input light is near zero, the output change with respect to the input change is small, and the sensitivity is deteriorated. Instead, by providing a bias light projecting device and applying a bias, the sensitivity of the light receiving element can be increased, and the measurement accuracy can be improved.

Further, according to the fifth aspect of the invention, instead of moving the light projecting device itself, the intensity of light incident on the space can be changed by moving the shutter disposed between the light source and the space. . Therefore, the distance of the gap can be measured based on the amount of movement of the shutter and the detection result of the light receiving device.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a measuring device 10A (hereinafter simply referred to as a measuring device 10) of a substrate interval according to a first embodiment of the present invention.
A). The upper substrate 12
It is made of a compound semiconductor such as GaAs, and has active elements and the like. A predetermined position facing the lower substrate 14 described later has a height of 20 microns by plating or the like.
Au pillars having a diameter of about 40 microns (hereinafter referred to as metal pillars 16)
Is formed.

The lower substrate 14 is a substrate made of a material such as alumina or silicon, and a required circuit pattern such as a matching circuit is formed on the lower substrate 14 by a method such as vacuum deposition and photolithography. The upper substrate 12 and the lower substrate 14 configured as described above are flip-chip bonded via the metal pillars 16, whereby the upper substrate 12
And the lower substrate 14 are integrated.

As described above, only the necessary parts such as the active elements are collectively formed on the upper substrate 12 with the compound semiconductor, and the other matching circuits and the like are formed on the lower substrate 1 made of inexpensive silicon or the like.
4 and the two substrates 12 and 14 are flip-chip bonded with metal pillars 16 to minimize the use area of the compound semiconductor (that is, the area of the upper substrate 12) and reduce the cost. It becomes possible. still,
The metal pillar 16 also has a function of electrically connecting the upper substrate 12 and the lower substrate 14.

By joining the upper substrate 12 and the lower substrate 14 as described above, a metal column 16 functioning as a spacer is provided between the upper substrate 12 and the lower substrate 14 as shown in the figure. A substrate spacing 18 (dimension d) is formed. The bonded substrates 12 and 14 are very close to each other, and specifically, the substrate spacing 18 is about several microns to several tens of microns.

As described above, in a circuit having a high frequency such as a millimeter wave band, the characteristic impedance of the transmission line on each of the substrates 12 and 14 changes due to the influence of an adjacent ground plane or the like. Therefore, in order to set the characteristic impedance of the transmission lines on the substrates 12 and 14 to a desired value, it is necessary to set the interval between the two substrates 12 and 14 to a designed value. Therefore, in the present embodiment, the substrate spacing 1 formed between the upper substrate 12 and the lower substrate 14 joined via the metal pillars 16 as described above.
Measure 8.

A light projecting device 20A and a light receiving device 22A are provided on both sides of the space between the substrates 12 and 14 bonded together. The light projecting device 20A includes a light source 24 and a first lens system 26. Further, the light receiving device 22A includes the light receiving element 3
4 and a second lens system 28. In the present embodiment, a filament lamp is used as the light source 24, and the light emitted from the light source 24 is transmitted to the first lens system 26.
Are used as parallel rays. Incidentally, a laser diode can be used as the light source 24, and in this case, the first lens system 26 becomes unnecessary.

The light projecting device 20A is connected to a moving device 30 (incident light changing means). When the moving device 30 is driven, the light projecting device 20A is perpendicular to the surface directions of the substrates 12 and 14. It is configured to be movable in the direction (vertical direction in the figure). When performing this movement, the movement position of the light source 24 provided in the light emitting device 20A is
It is desirable to set the position apart from 2,14.

That is, the moving position of the light source 24 is
4, the light source 24 may come into contact with the lower substrate 14 in a state where the light source 24 has moved to the lowest position. Thus, the light source 2
When the lower substrate 14 and the lower substrate 14 come into contact with each other, a gap is formed between the incident light output from the light source 24 and the lower substrate 14, giving an error to the measurement result (as a practical problem,
It is difficult to emit a parallel light beam from a portion where the light source 24 contacts the lower substrate 14). Therefore, as shown in FIG.
4 is desirably arranged outside the lower substrate 14.

As shown in FIG. 2, the incident light incident on the substrate space 18 is basically a parallel light beam and has a constant light intensity. Therefore, even if the distance between the substrate interval 18 and the light source 24 or the distance between the substrate interval 18 and the light receiving element 34 is large, the measurement of the substrate interval 18 is possible without focusing as in the case of microscopic observation. Thereby, even if there is an area difference between the upper substrate 12 and the lower substrate 14, the measurement of the substrate interval 18 can be performed reliably.

The light source 24 is connected to a moving device 30 (for example,
It is possible to perform the movement with a resolution of 1 micron or less using a micrometer. FIG. 3 shows an example in which the output of the light receiving element 34 when the light source 24 is moved is recorded.
As shown in the figure, since the light source 24 moves away from the substrate interval 18 as it moves, the intensity of light detected by the light receiving element 34 decreases. This decrease in light intensity has a characteristic of decreasing substantially linearly.

Therefore, the distance between the position of the light source 24 when the light intensity is the highest (indicated by A in FIG. 3) and the position where the light intensity is the lowest (indicated by B in FIG. 3) is the distance 18 between the substrates.
Is the distance d. Thus, by observing the change in the output of the light receiving element 34, the distance between the substrates can be known. The output of the light receiving element 34 and the light source 24 by the moving device 30
Is transmitted to the interval measurement circuit 32. Therefore, the interval measuring circuit 32 obtains the position A of the light source 24 having the highest light intensity and the position B of the light source 24 having the lowest light intensity based on the above-described principle, and determines the distance between the positions A and B. By calculating, the board spacing 18
Is determined.

The above-described measuring method basically uses the light source 2
The spot diameter (diameter of the light beam) of No. 4 is the distance d of the substrate interval 18.
However, even when the spot diameter is smaller than the distance d of the substrate interval 18, the output of the light receiving element 34 when the light source 24 is moved is analyzed to obtain the distance of the substrate interval 18. It is possible to calculate d. This analysis method is shown in FIGS.

As shown here, when the diameter e of the light source 50 is smaller than the distance d of the substrate interval 18 (e <d), as the light source is moved, the output of the light receiving element 34 becomes a profile as shown in FIG. Becomes That is, the area between the position A and the position B shown in FIG. 11 is a range where all the incident light from the light source 50 is received by the light receiving element 34. This range is equal to the distance d of the substrate interval 18, and therefore, even when the diameter e of the light source 50 is smaller than the distance d of the substrate interval 18, the distance from the output of the light receiving element 34 to the distance of the substrate interval 18. d can be determined.

Next, a description will be given of a measuring apparatus 10B according to a second embodiment of the present invention. FIG. 4 is a main part configuration diagram of a measuring apparatus 10B according to the second embodiment. In FIG. 4, the same components as those of the measuring apparatus 10A according to the first embodiment shown in FIG. In the measuring device 10B according to the present embodiment, the light emitting device 20
B is a light source 24 configured so that the optical axis is perpendicular to the plane direction of the substrates 12 and 14, and a first prism that performs optical path conversion so that light emitted from the light source 24 is directed toward the substrate interval 18. 36.

The light receiving device 22B has an optical axis
The light receiving element 34 is configured to be vertically downward with respect to the plane directions of the light emitting elements 2 and 14, and a second prism 38 that performs optical path conversion so that light emitted from the substrate gap 18 is directed to the light receiving element 34. ing. Each prism 36, 3
In 8, a metal such as Al is vapor-deposited on the reflection surfaces 40 and 42 that reflect light to be mirror surfaces. In addition, prism 3
The angle θ between the reflection surfaces 40 and 42 of the 6, 38 is set to 45 degrees.

In the measuring apparatus 10B according to the present embodiment, the first
By providing the second prism 36 and the second prism 36, the arrangement position of the light source 24 and the arrangement position of the light
The light source 24 and the light receiving element 34 can be arranged at a position above and spaced apart from the light sources 2 and 14, so that the arrangement positions of the light source 24 and the light receiving element 34 can be given flexibility. In addition, since it is not necessary to make incident light emitted from the light source 24 directly enter the substrate gap 18,
Since the incident light can be made incident from a position substantially close to the substrate interval 18, light loss can be suppressed and measurement accuracy can be improved.

In this embodiment, the light source 24 itself is fixed, and the light intensity of the incident light incident on the substrate interval 18 is reduced by moving the first prism 36 in the horizontal direction in FIG. It is configured to change.
Therefore, since it is not necessary to move the light source 24 having a complicated structure by providing the wiring and the first lens system 26, the structure of the measuring device 10B is simplified and the moving device 30 is provided.
Can be reduced in size.

Incidentally, the specific method of obtaining the distance d of the substrate interval 18 is the same as the method described above with reference to FIG. 3 in the first embodiment, and therefore the description thereof is omitted. Also in the present embodiment, the measurement method described with reference to FIGS. 10 and 11 can be applied. Next, a measuring apparatus 10C according to a third embodiment of the present invention will be described.

FIG. 5 shows a measuring apparatus 10C according to a third embodiment.
FIG. In FIG. 5, the same components as those of the measuring device 10B according to the second embodiment shown in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted. The measuring apparatus 10C according to the present embodiment includes a microscope 4 instead of the light receiving element 34.
4 is provided. This microscope 4
4, a not-shown micrometer is provided.
The configuration is such that the distance of the observed image can be measured.
Further, the light source 24 has a fixed configuration unlike the above-described embodiments.

In this embodiment, the substrate spacing 18 is directly measured by a micrometer provided in the microscope 44 by observing the substrate spacing 18 through the second prism 38 with the objective lens of the microscope 44. As described above, even in the configuration using the microscope 44, the use of the prism 38 makes it possible to make the objective lens of the microscope 44 substantially close to the substrate interval 18 unlike the related art, and the upper and lower substrates 12 and 14.
Can be measured even if the area of the substrate is different.

Next, a description will be given of a measuring apparatus 10D according to a fourth embodiment of the present invention. FIG. 6 is a main part configuration diagram of a measuring apparatus 10C according to the fourth embodiment. In FIG. 6, the same components as those of the measuring apparatus 10B according to the second embodiment shown in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted. The measuring device 10D according to the present embodiment includes a light emitting device 20B.
In addition to the above, a bias light source 46 (bias light projecting device) for inputting bias light into the substrate interval 18 is provided. Thereby, the sensitivity of the light receiving device 20B can be improved.

That is, the light receiving element 34 is usually constituted by an element such as a photodiode. The light receiving element 34 such as a photodiode has a characteristic that its linearity deteriorates when input light is near zero. I have. As described above, when the linearity of the input light near zero is deteriorated, the change of the output with respect to the change of the input is small, the sensitivity is deteriorated, and the accuracy of the distance measurement is reduced.

Therefore, in this embodiment, a so-called bias is applied to the incident light by providing a bias light source 46 in addition to the light projecting device 20B, thereby increasing the sensitivity of the light receiving element 34. Thus, the light receiving element 34
, The measurement accuracy of the substrate interval 18 can be improved. Next, a measuring apparatus 10E according to a fifth embodiment of the present invention will be described.

FIG. 7 shows a measuring apparatus 10E according to a fifth embodiment.
FIG. In FIG. 7, the same components as those of the measuring apparatus 10B according to the second embodiment shown in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted. The measuring apparatus 10E according to the present embodiment uses a shutter 48 as incident light changing means,
The amount of incident light incident on the substrate is changed in a direction perpendicular to the surface direction of the substrates 12 and.

As in this embodiment, by using the shutter 48 as the incident light changing means, the shutter 48 disposed between the light source 24 and the substrate interval 18 can be moved instead of moving the light projecting device 20C itself. The substrate spacing 1
8 can be changed. Therefore, the interval measurement circuit 32 can measure the distance d of the substrate gap 18 based on the amount of movement of the shutter 48 and the detection result of the light receiving device 22B. FIG. 8 shows a measuring apparatus which is a modification of the fifth embodiment, in which the configuration of the fifth embodiment is applied to the measuring apparatus 10A shown in FIG. For this purpose, the present embodiment can be applied to a configuration in which the prisms 36 and 38 are not used.

FIG. 9 shows a measuring apparatus 10E according to the fifth embodiment.
5 shows an example in which the output of the light receiving element 34 when the shutter 48 is moved is recorded. In the figure, the shutter 48 is gradually opened from the state where the incident light from the light source 24 is completely blocked by the shutter
8 shows an example in which incident light is incident. In the figure, a position A is a state where the shutter 48 is closed. Therefore, the output of the light receiving element 34 is zero. By gradually opening the shutter 48 from the position A, the incident light from the light source 24 is incident on the substrate interval 18 and the output of the light receiving element 34 gradually increases accordingly.

After the shutter 48 is moved to the distance d of the substrate interval 18 (that is, after the shutter 48 is moved to the position B), the incident light from the light source 24 is incident on the entire surface of the substrate interval 18 so that the light is received. The output of element 34 is constant. Therefore, the distance between the position of the shutter 48 when the light intensity is the lowest (shown by A in FIG. 9) and the position where the light intensity becomes the highest (shown by B in FIG. 9) is the distance d of the substrate interval 18. Becomes Thus, by observing the change in the output of the light receiving element 34, the distance between the substrates can be known.

[0043]

As described above, according to the present invention, it is possible to measure the distance between two substrates located very close to each other with high accuracy. Therefore, in an electronic circuit in the millimeter-wave band designed on the assumption that there is a ground plane at a close position, the high-frequency characteristics as designed are reproduced by confirming the board spacing after (or during) manufacturing. (Because the distance between the two substrates greatly affects the high-frequency characteristics).

As a result, the present invention greatly contributes to improving the performance (improving the reproducibility) of the high-frequency semiconductor device.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a substrate spacing measuring device and a substrate spacing measuring method according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a movement amount of a light source and an output of a light receiving element (part 1).

FIG. 3 is a diagram illustrating the relationship between the movement amount of a light source and the output of a light receiving element (part 2).

FIG. 4 is a view for explaining a substrate spacing measuring apparatus according to a second embodiment of the present invention.

FIG. 5 is a view for explaining an apparatus for measuring a distance between substrates according to a third embodiment of the present invention.

FIG. 6 is a view for explaining a substrate spacing measuring apparatus according to a fourth embodiment of the present invention.

FIG. 7 is a view for explaining an apparatus for measuring a distance between substrates according to a fifth embodiment of the present invention (part 1).

FIG. 8 is a view for explaining an apparatus for measuring a distance between substrates which is a modification of the fifth embodiment of the present invention.

FIG. 9 is a diagram illustrating a relationship between an output of a light receiving element and a movement amount of a shutter according to a fifth embodiment of the present invention.

FIG. 10 is a view for explaining a substrate spacing measuring apparatus according to a sixth embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between an output of a light receiving element and a moving amount of a light source according to a sixth embodiment of the present invention.

FIG. 12 is a view for explaining a substrate spacing measuring device and a substrate spacing measuring method, which are examples of the related art (part 1).

FIG. 13 is a view for explaining a substrate spacing measuring apparatus and a substrate spacing measuring method as an example of the related art (part 2).

[Explanation of symbols]

 10A to 10F Measuring device 12 Upper substrate 14 Lower substrate 16 Metal column 18 Substrate spacing 20A to 20C Light emitting device 22, 22B Light receiving device 24, 50 Light source 26 First lens system 28 Second lens system 30 Moving device 32 Interval Measuring circuit 34 Light receiving element 36 First prism 38 Second prism 40, 42 Reflecting surface 44 Microscope 46 Light source for bias 47 Shutter

Claims (6)

[Claims] 1. A light projecting device that, between two substrates joined at a small interval by a spacer, enters parallel light and incident light having a uniform light intensity distribution from one of the intervals, A light-receiving device that detects the light intensity of outgoing light emitted from the other of the intervals; an incident light changing unit that changes an incident state of the incident light into the interval in a direction perpendicular to a surface direction of the substrate; An apparatus for measuring a distance between substrates, comprising: a measuring means for measuring a distance of the distance based on a light intensity detected by a light receiving device and a change amount of incident light by the incident light changing means. 2. The apparatus according to claim 1, wherein said incident light changing means is a moving mechanism for moving said light projecting device in a direction perpendicular to a surface direction of said substrate. Measuring device for substrate spacing. 3. The apparatus for measuring the distance between substrates according to claim 1, wherein the light projecting device comprises: a light source configured so that an optical axis thereof is perpendicular to a surface direction of the substrate; A first prism that performs optical path conversion so that the emitted light of the substrate goes toward the distance, and the light receiving device is configured such that the optical axis is directed downward and perpendicular to the surface direction of the substrate. And a second prism for performing optical path conversion so that light emitted from the other of the intervals goes toward the light receiving element. 4. The apparatus for measuring a distance between substrates according to claim 1, further comprising a bias light projecting device for causing a bias light to enter the space in addition to the light projecting device. Measuring device for substrate spacing. 5. The apparatus for measuring a distance between substrates according to claim 1, wherein the incident light changing means is a shutter for changing the amount of incident light incident on the distance in a direction perpendicular to a surface direction of the substrate. An apparatus for measuring the distance between substrates. 6. A parallel light beam and a uniform light intensity distribution are made incident from one of said spaces by using a light projecting device between two substrates joined by a spacer at a minute space. While changing the state of incidence of the incident light on the space in a direction perpendicular to the surface direction of the substrate, the light intensity of outgoing light emitted from the other of the spaces is detected by a light receiving device, and the light receiving device is A method for measuring a distance between substrates, wherein the distance between the substrates is measured based on a light intensity to be detected and a change amount of incident light by the incident light changing means.