JPH0714783A - Plasma cvd equipment - Google Patents

Abstract

PURPOSE:To provide a plasma CVD equipment in which the plasma can be controlled such that the molecules generated in the plasma in the vicinity of a substrate, on which a thin film is formed, can be measured highly accurately while keeping the quantity thereof at an optimal level. CONSTITUTION:The plasma CVD equipment comprises a CVD chamber 22 for holding a substrate on which a thin film is formed by plasma CVD, a laser light source 21, a detecting means 25 producing a detection output corresponding to the quantity of received light, a multiple reflection means disposed at a fixed position and reflecting the laser light emitted from the laser light source along a predetermined path through a CVD chamber to the detecting means thus measuring the absorptivity of substance present on the optical path, and means for adjusting the surface of substrate in the CVD chamber by a desired amount with respect to a reflection path in the approaching or separating direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma CVD apparatus for producing a thin film or the like, and more particularly to a plasma CVD apparatus capable of performing optimum plasma control.

[0002]

2. Description of the Related Art For example, one of the methods for forming a thin film on a substrate such as a semiconductor is chemical vapor deposition (CVD).
There is a method called por deposition). This CVD is used in the epitaxial growth method of silicon, and a thin film is formed by growing silicon obtained from a source gas on a substrate.

On the other hand, there is plasma CVD as a technique for forming an amorphous silicon thin film. The plasma CVD apparatus is an apparatus for performing this plasma CVD, and is an apparatus for forming a thin film by utilizing a vapor phase reaction of active species in low temperature plasma. Amorphous silicon is used for solar cells, electrophotographic photosensitive materials, thin film transistors, sensors,
Further, it is used for forming a semiconductor protective film and the like.

By the way, when a thin film is formed on a substrate by a plasma CVD apparatus, it is very important to measure the generated molecules in the immediate vicinity of the substrate surface and perform precise plasma control. For example, in the formation of a hydrogenated amorphous silicon film, in order to form a thin film uniformly and efficiently, it is necessary to increase the concentration of the precursor SiH ₃ (silyl) radical in the vicinity of the substrate surface to an optimum state. This is because plasma control must be performed.

Therefore, the spatial distribution of the produced molecules in the plasma is measured, and conventional methods for that purpose include the laser-induced fluorescence method and the absorption method. The laser-induced fluorescence method is a method of measuring molecules generated by irradiating laser light into plasma and collecting and detecting fluorescence generated in the laser light irradiation portion. In this case, a desired spatial position is measured. When measuring the generated molecule at
This can be easily performed by changing the relative position relationship of the irradiation position of the laser light in the plasma and the condensing lens for condensing and guiding the fluorescence generated at the laser light irradiation portion to the detector.

However, the laser-induced fluorescence method cannot be said to be suitable for measuring the produced molecules in the measurement object space having a dilute gas concentration distribution, and much less as a measurement method used for controlling plasma. There are many.

On the other hand, the absorption method is a method of measuring the produced molecules from the amount of light after irradiation of the irradiated laser light, and even if a few produced molecules are present in a dilute gas, the laser is generated at a desired spatial position. By making the optical path a multiple reflection path, it becomes possible to increase the optical path length, which makes it possible to multiply the measured value virtually and measure the molecular weight of the product. Therefore, the measured value can be used for controlling the plasma.

However, the measurement does not have to be fixed in any space, and it is necessary that the measurement be performed in the vicinity of the surface of the substrate. When the position of the spatial region to be measured is determined in this way, this absorption method is not as easy as the laser-induced fluorescence method.

This is because it is necessary to increase the optical path length when measuring the molecules produced in a dilute system such as the plasma CVD method. For that purpose, it is generally necessary to use a multiple reflection cell. Is.

That is, in the multiple reflection cell, since it is necessary to repeatedly reflect the laser light several tens of times between the three concave mirrors, the optical arrangement is changed to change the measurement position after the adjustment. Readjustment is extremely difficult. Therefore, if it is necessary to measure the produced molecule by the absorption method, the optical system should be fixed in place,
It was common to move the measurement object.

Under such circumstances, it is necessary to control the SiH ₃ (silyl) radical concentration near the substrate in order to form a high quality film, for example, when forming a hydrogenated amorphous silicon film. In some cases, the distance from the substrate to the measurement point is calculated by calculation based on the geometrical arrangement on the drawing (that is, on the design).

[0012]

As described above, when it is necessary to measure the produced molecule by the absorption method, the optical system is fixed at a fixed position and the object to be measured is moved. And, like when forming a hydrogenated amorphous silicon film,
When it is necessary to control the SiH ₃ radical concentration near the substrate in order to form a high quality film, the optical system that is the measurement system is fixed at a fixed position, and the substrate is brought close to the laser optical path of the measurement system. The position of the substrate is set so that the laser beam of the measurement system passes near the substrate, plasma CVD is performed, and the generated molecules near the substrate are measured to control the plasma.

In this case, the distance between the substrate and the optical path is calculated by the geometrical arrangement relationship in design, and the distance of the measurement point from the substrate is calculated by this. Therefore, the position of the measurement point from the substrate is only an estimated value calculated on the desk, and there is no way to confirm what it actually looks like.

As described above, when it is necessary to measure the produced molecules in the plasma by the absorption method, it is not known conventionally which part (the position with respect to the substrate) in the plasma, so that the measurement in the target region is performed. There is no guarantee that
Therefore, there is no guarantee that optimum plasma control can be performed.

Therefore, the object of the present invention is to
The target position on the substrate surface for thin film deposition (position that is very close to the substrate surface) can be set so that the optical path can pass through with certainty, which makes it possible to measure the amount of absorption at the target measurement point for the substrate, which is optimal. It is an object of the present invention to provide a plasma CVD apparatus capable of precise plasma control.

[0016]

In order to achieve the above object, the present invention is configured as follows. That is, a CVD chamber for holding a substrate on which a thin film is to be formed and forming a thin film on this substrate by a plasma vapor deposition method, a laser light source, and a detection means for generating a detection output corresponding to the received light amount, The laser light is arranged at a position and is emitted after the laser light incident from the laser light source is reflected by following a predetermined reflection path passing through the inside of the CVD chamber, and the emitted light is detected. Multiple reflection means for measuring the amount of absorption by the substance on the laser optical path by receiving light by the means, and position adjustment for adjusting the desired amount of the substrate surface in the CVD chamber in the contact and separation direction with respect to the reflection path. And means.

[0017]

The present apparatus having such a structure is constructed so that the optical path of the multiple reflection means passes through the CVD chamber, holds the substrate, and forms a thin film on the substrate by CVD.
The chamber is constructed so that the surface of the substrate can be moved and adjusted by a desired amount in the contact and separation directions with respect to the optical path of the multiple reflection means.
Then, the laser light is made incident on the multiple reflection means from the laser light source, and the light emitted by following the reflection optical path of the multiple reflection means passes through the CVD chamber while repeatedly passing therethrough. Therefore, the optical path length in the CVD chamber becomes sufficiently long, and the light emitted from the multiple reflection means can be measured by reflecting the light absorption amount by the dilute generated molecules generated from the raw material gas in the CVD chamber. It becomes a level of light. When this light is detected by the detection means, the detection output can accurately measure the amount of produced molecules in the plasma on the optical path.

When a thin film is formed on a substrate, it is necessary to know the amount of produced molecules in plasma in a region very close to the surface of the substrate and perform plasma control so as to optimize the amount. In this apparatus, the position of the CVD chamber is adjusted in advance before the start of CVD so that the optical path of the multiple reflection means comes to a position very close to the surface of the thin film formation target substrate in the CVD chamber. In this, the position of the CVD chamber is adjusted by the position adjusting means while making the laser light incident on the multiple reflection means so that the thin film formation target substrate first blocks the optical path. As a result, the output of the detecting means disappears, so the position of the CVD chamber is adjusted by the position adjusting means, and the adjustment is advanced to the state where the output of the detecting means is generated. With this as a reference position, C is set so that the thin film formation target substrate may be separated from the optical path, though slightly.
The position of the VD chamber is adjusted by the position adjusting means.

By doing so, the target substrate for thin film formation can be positioned slightly away from the optical path, and the distance relationship between the optical path and the substrate can be accurately determined from the amount of movement from the reference position. Therefore, it becomes possible to measure the amount of produced molecules in the plasma in a region very close to the surface of the substrate on which the thin film is to be formed, and control the plasma so as to optimize the amount.

As described above, after the laser light is passed through the multiple reflection means (multiple reflection cell) to be actually measured, the position of the CVD chamber is adjusted by using the position adjustment means (movable stage) to obtain the laser light intensity. Change the position of the thin film formation target substrate, and further move the CVD chamber to determine the measurement point, so that the generated molecules generated in the plasma in the region very close to the surface of the thin film formation target substrate It is possible to control the plasma so that the amount can be optimized, and thus it is possible to provide a plasma CVD apparatus capable of easily forming a thin film of high quality and uniform thickness.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention arranges flanges having concave mirrors for forming a multiple reflection cell via bellows on both sides of a CVD chamber, and the flanges are fixed on a pedestal to form a C
The VD chamber is placed on a movable stage,
The laser light is passed through the multiple reflection cell, the laser light is received by the detector, and the position of the substrate is determined by the strength of the signal.
The position of the measurement point can be specified by moving the movable stage, the details of which will be described below.

Embodiments of the present invention will be described with reference to the drawings. In order to explain the details of the present invention in detail, first, the function of the multiple reflection cell will be described with reference to FIG. The multiple reflection cell is arranged so that the optical path passes through the inside of the CVD chamber, and has a structure as shown in FIG. Figure 1
In FIG. 1, 1 is a convex lens, 2 is a window, 3 is a cell body, 4, 5 and 6 are concave mirrors, 7 is a window, 8 is a convex lens, and 9, 10 and 11 are concave mirrors 4, 5 and 6, respectively, which are micrometer heads. Is. In addition, the arrow in the figure indicates the optical path of the laser light.

The cell body 3 has a cylindrical shape, and windows 2 and 7 are provided on one end surface thereof. Also, the cell body 3
Inside the windows 2 and 7 on the one end face side.
A concave mirror 4 is disposed in the middle of the above, and the concave mirror 4 is supported from the outside of the cell body 3 by a micrometer head 9 attached to one end surface of the cell body 3 so that the position can be adjusted. Further, outside the cell body 3, a convex lens 1 is arranged with its optical axis aligned with the window 2, and a convex lens 8 is arranged with its optical axis aligned with the window 7. Further, concave mirrors 5 and 6 are arranged on the other end face side in the cell body 3.

The convex lens 1 is a lens on the light incident side,
The convex lens 8 is a lens on the exit side. The concave mirror 5 is for reflecting the light that has entered the cell body 3 from the window 2 through the convex lens 1 toward the concave mirror 4, and the tilt is adjusted by the micrometer head 10 attached to the other end surface of the cell body 3. Is supported by possible.

The concave mirror 6 is for reflecting the light reflected by the concave mirror 4 to the window 7.
A tilt is adjustable by a micrometer head 11 attached to the other end surface of the cell body 3.

In such a multiple reflection cell, the curvatures of the concave mirrors 4, 5 and 6 are designed to be equal to the distances between the concave mirror 4 and the concave mirror 5 and between the concave mirror 4 and the concave mirror 6.
Further, since it is for measuring the generated molecules in the vicinity of the surface of the substrate on which the thin film is to be formed, the laser beam passage optical path which enters the window 2, is reflected by the concave mirrors 4, 5, 6 and reaches the window 7 is the CVD chamber. It is set as a path passing through a plane parallel to the surface of the substrate to be thin film-formed, which is held inside.

In the multiple reflection cell configured as described above, the laser beam converted into a parallel beam passes through the window 2 by the convex lens 1 into the cell body 3 and is condensed on an extension line of the mirror surface of the concave mirror 4. The concave mirror 5
Is reflected by. The laser light reflected by the concave mirror 5 is condensed and reflected at the center of the concave mirror 4 and guided to the concave mirror 6. Then, the laser light reflected by the concave mirror 6 passes through the window 7 and is emitted from the cell body 3, and is normally returned to a parallel beam by the convex lens 8 and the like.

The above is the simplest example in which two passes are realized by using multiple reflection cells. However, in order to increase the optical path length (increase the number of passes), the horizontal tilt angles of the concave mirrors 5 and 6 are set. , And can be realized by finely adjusting with the micrometer heads 10 and 11.

An embodiment of the plasma CVD apparatus of the present invention is shown in FIG. The present plasma CVD apparatus has a structure in which a CVD chamber is arranged in the middle of the multiple reflection cell as described above, the multiple reflection cell portion is fixed in a fixed position, and the CVD chamber portion intersects the laser optical path of the multiple reflection cell. The configuration is such that movement adjustment is possible in any direction, and the details will be described below.

In the figure, 21 is a laser light source, 22 is a CVD chamber, 23 and 24 are flanges having a concave mirror inside,
25 is a detector, 26 is a digital oscilloscope, 27 is a movable stage, 28 is an optical base (rigid body), 29, 30
Is an optical laboratory table, 31 and 32 are optical surface plates, 33 and 34 are bellows, 35 and 36 are bellows support jigs, 37 and 3.
Reference numeral 8 is a transparent quartz tube, 39 is an evacuation tube for the CVD chamber 22, and 40 is a support for the CVD chamber.

The optical base 28 is a rigid body, and the optical laboratory benches 29, 30 are provided on the optical base 28.
The optical laboratory benches 29, 30 are spaced apart and have a flat upper surface. A movable stage 27 is provided on the optical base 28 so as to be located between the optical experiment stands 29 and 30, and a CVD chamber support stand 40 is provided on the movable stage 27. The movable stage 27 is capable of moving up and down with precision, and has a measuring device for measuring the amount of movement, which enables precise adjustment of the height position of the CVD chamber support 40 and measurement of the amount of movement. Is. Optical test bench 2
Optical surface plates 31 and 32 are provided on the plates 9 and 30, respectively.

A CVD chamber 22 is provided on the CVD chamber support 40. The CVD chamber 22 holds a substrate on which a thin film is to be formed, heats the substrate, and plasma-discharges the substrate to perform CVD. Further, a vacuum exhaust pipe 39 is attached to the CVD chamber 22, and the vacuum exhaust pipe 3 is attached.
The inside of the CVD chamber 22 can be evacuated by evacuating from 9, and the necessary amount of the source gas can be supplied by evacuating while supplying the source gas into the CVD chamber 22. The CVD chamber 22 has a tubular shape, and flanges are formed on both ends. Then, the bellows 33 and 34 are connected at their one ends using this flange.

The optical laboratory table 29 is provided with a laser light source 21, a detector 25, and a bellows support jig 35 on an optical surface plate 31, and the other end of the bellows 33 is one end of the bellows support jig 35. It is connected to the. The bellows support jigs 35 and 36 are cylindrical, and both ends of the cylinder are flanges, and the other end of the bellows 33 is connected to one end side flange of the bellows support jig 35 to be held in a predetermined state. . A cylindrical transparent quartz tube 37 is connected to the other end side flange of the bellows support jig 35, and the other end of the transparent quartz tube 37 is closed by a flange 23 having a concave mirror inside.

Further, the bellows 34 on the other end side of the CVD chamber 22 is connected to one end of a cylindrical bellows support jig 36 provided on an optical surface plate 31 on the optical laboratory table 30 and held in a predetermined state. Bellows support jig 36
One end of a cylindrical transparent quartz tube 38 is connected to the other end of the.
The other end of the transparent quartz tube 38 is closed by a flange 24 having a concave mirror inside.

The flange 23 provided on the other end of the transparent quartz tube 37 has a concave mirror inside, which corresponds to the concave mirror 4 of the multi-cell described in FIG. As shown in FIG. 1, there are windows corresponding to the windows 2 and 7 since they are on the entrance and exit sides. The position can be adjusted by the micrometer head 9 in the optical axis direction of the concave mirror.

Further, the concave mirrors attached to the flange 24 correspond to the concave mirrors 5 and 6 in FIG. 1, and their tilt angles can be adjusted by the micrometer heads 10 and 11.

As mentioned above, the concave mirrors attached to the flanges 23 and 24 are in place on the optical benches 29 and 30, while the CVD chamber 22 is in the movable stage 2.
7, the height position can be adjusted up and down. Then, the laser light for measurement is made to enter from the laser light source and the flange 2
Multiple reflection is carried out by the concave mirrors attached to 3, 24, and the detector 25 is made to enter through the exit window of the flange 23 for detection. The above-mentioned multiple reflection path passes through the position of the CVD chamber 22.

In this apparatus, the height position of the CVD chamber 22 is adjusted with respect to the multiple reflection path (laser optical path) that has been adjusted and set to a fixed position, so that the multiple reflection path is at a desired position on the substrate. The bellows 33, 34 are provided in order to secure the degree of freedom with respect to the fixed-position fixed flanges 23, 24 holding the concave mirror in a fixed position and to keep the inside in an airtight structure in order to adjust so that they can pass through. Using the bellows support jigs 35, 3 on the optical laboratory benches 29, 30
6 is connected.

FIG. 3 shows the geometrical arrangement relationship of the electrodes in the CVD chamber 22 and the substrate on which the thin film is to be formed. 4 in the figure
1 is an RF electrode (high frequency electrode) for applying high frequency power, 4
Reference numeral 2 denotes a substrate heating heater arranged to face the RF electrode 41, and 43 denotes a substrate mounted on the substrate heating heater 42, which is a substrate on which a thin film is to be formed. Reference numeral 44 represents a laser optical path. RF electrode 41 and substrate heater 42
Are arranged so as to face each other via the laser light path 44 in the multiple reflection cell, and are configured to be able to move forward and backward with respect to the laser light path 44.

In the above-mentioned configuration, the optical laboratory bench 29
Upper laser light source (for example, He-Ne laser light source) 2
CV having multiple reflection cells by oscillating laser light from 1
It is introduced into the D chamber 22. That is, the laser light source 21
When the laser light is incident from the entrance window of the flange 23, the incident laser light passes through the CVD chamber 22, is reflected by the concave mirror of the flange 24, passes through the CVD chamber 22 again, and the flange 23
Of the concave mirror of the flange 24, reflected again here, passes through the CVD chamber 22 again, and is reflected by the concave mirror of the flange 24.
It again passes through the inside of the CVD chamber 22 and exits from the exit window of the flange 23 and enters the detector 25, where the amount of light is detected.

The laser light guided into the CVD chamber 22 in this way is reflected a predetermined number of times (usually two passes) in the multiple reflection cell constituted by the flange 23 and the flange 24, and the CVD chamber is again shown. Since the light is emitted to the outside of 22, the intensity of the laser light can be detected by the detector 25 (for example, a power meter or the like) and converted into an electric signal to detect the light amount.

At the initial stage, the output of the detector 25 is input to the digital oscilloscope 26 or the like to measure the output voltage,
While monitoring, the CVD chamber 22 is positioned so that the optical path of the laser beam comes close to the surface of the substrate in the CVD chamber 22.

This is done as follows. Detector 25
When the movable stage 27 is moved up and down while monitoring the output signal of, the CVD chamber 22 placed on the movable stage 27 also moves up and down, so that the substrate 43 mounted in the CVD chamber 22 also moves up and down. As a result, the laser beam path 44 that was initially set is transferred to the substrate 43.
There is an area blocked by.

Since the laser light does not reach the detector 25 when the substrate 43 blocks the laser light path 44, the output signal from the detector 25 becomes almost zero (only a minute output due to scattered light such as stray light). Become.

As described above, when the CVD chamber 22 is moved up and down while monitoring the output signal from the detector 25, the laser optical path 44 is blocked or opened, so that the output signal changes. The height of the CVD chamber at the time of change corresponds to the position where the surface of the substrate 43 and the laser optical path 44 coincide with each other.

In this state, the generated molecules in the plasma cannot be measured, so the height of the CVD chamber 22 is slightly changed from this state. That is, the position of the substrate is set to be farther from the laser optical path 44, though slightly. As a result, it becomes possible to measure the generated molecules in the immediate vicinity of the surface of the substrate 43.

For example, the substrate 4 in the CVD chamber 22
3 and the RF electrode 41 are configured as shown in FIG. 3, after aligning the surface of the substrate 43 with the laser optical path 44, the CVD chamber 22 is slightly moved upward to make the substrate 43 It is possible to measure the generated molecules in the immediate vicinity of the surface.

Since the movable stage 27 is capable of fine movement adjustment and its moving amount can be accurately measured by a measuring instrument, the position where the output is generated again near the height position where the output of the detector 25 disappears. By fine adjustment, and fine adjustment of the height position in the direction away from the laser optical path 44 with reference to this position, the distance relationship between the laser optical path 44 and the surface of the substrate 43 from the adjustment amount (movement amount). Will be able to be grasped accurately.

Therefore, after accurately grasping the positional relationship between the laser optical path 44 and the surface of the substrate 43, the source gas is subjected to CVD.
While supplying plasma into the chamber 22, plasma CVD is performed, and in parallel with this, a detection output signal of the light amount of the laser light incident on the detector 25 via the laser optical path 44 is obtained,
By utilizing this for plasma control in the CVD chamber 22, it becomes possible to perform precise plasma control corresponding to the concentration of generated molecules in the plasma near the extreme surface of the substrate 43.

As described above, the present apparatus holds the substrate on which the thin film is to be formed, the CVD chamber for forming the thin film on this substrate by the plasma vapor deposition method, the laser light source, and the detection output corresponding to the received light amount. A detector that produces
A multi-reflection cell that is arranged at a fixed position, reflects the laser light incident from the laser light source along a predetermined reflection path passing through the CVD chamber, and then emits the laser light; and the substrate inside the CVD chamber. The surface is configured to include a movable stage that adjusts the position in the contact and separation directions with respect to the reflection path, and the movable stage is used after passing the laser light through the multiple reflection cell that is the actual measurement target. Since the position of the thin film formation target substrate is determined by observing the change in the laser light intensity by adjusting the position of the CVD chamber, the CVD chamber is further moved to determine the measurement point.
It becomes possible to measure the amount of produced molecules in plasma in a region very close to the surface of the substrate on which the thin film is to be formed and perform plasma control so as to optimize the amount. Therefore, it becomes possible to easily form a thin film having high quality and uniform thickness. It should be noted that the present invention is not limited to the above-described embodiments, but can be implemented by being modified appropriately within the scope of the invention.

[0051]

As described above, according to the present invention, the optical path of the multiple reflection cell is set to a fixed position, and a mechanism for adjusting the position with respect to the optical path is attached to the CVD chamber arranged in this optical path, and the inside of the multiple reflection cell is By positioning the substrate to be a thin film deposition target in the CVD chamber with respect to the optical path while monitoring the output signal from the reciprocating laser light, it is possible to measure the generated molecules in the immediate vicinity of the substrate surface. . This is very important when forming a thin film in a plasma CVD apparatus, for example,
In the formation of the hydrogenated amorphous silicon film, it is necessary to increase the concentration of SiH ₃ (silyl) radical which is a precursor of the hydrogenated amorphous silicon film in the vicinity of the substrate surface. For that purpose, plasma control must be performed. Therefore, it becomes possible to realize a plasma CVD apparatus having an effective monitor and control function.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention,
The figure which shows the schematic structure of the multiple reflection cell used for this invention.

FIG. 2 is a diagram for explaining an embodiment of the present invention,
The schematic block diagram which shows the Example of this invention.

FIG. 3 is a diagram for explaining an embodiment of the present invention,
The figure for demonstrating the arrangement structure of an electrode etc. in a CVD chamber used for the apparatus of this invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Convex lens 2 ... Window, 3, 7 ... Cell main body 4, 5, 6 ... Concave mirror 8 ... Convex lens 9, 10, 11 ... Micrometer head 21 attached to each of the concave mirrors 4, 5, 6 21 ... Laser 22 ... CVD chamber 23 , 24 ... Flange having concave mirror inside 25 ... Detector 26 ... Digital oscilloscope 27 ... Movable stage 28 ... Optical base (rigid body) 29, 30 ... Optical laboratory bench 31, 32 ... Optical surface plate 33, 34 ... Bellows 35, 36 ... Bellows support jig 37, 38 ... Transparent quartz tube 39 ... Vacuum exhaust tube for CVD chamber 22 ... CVD chamber support 41 ... RF electrode 42 ... Substrate heating heater 43 ... Substrate 44 ... Laser optical path.

Claims (1)

[Claims] 1. Holding a substrate on which a thin film is to be formed,
A CVD chamber for forming a thin film on this substrate by a plasma vapor deposition method, a laser light source, and a detection means for generating a detection output corresponding to the amount of received light are arranged at a fixed position and are incident from the laser light source. The laser light is reflected by a predetermined reflection path that passes through the inside of the CVD chamber, and then emitted.
The multiple reflection means for measuring the amount of absorption by the substance on the laser optical path by allowing the emitted light to be received by the detection means, and the substrate surface in the CVD chamber are brought into contact with and separated from the reflection path. And a position adjusting means for adjusting a desired position.