Abstract:
A method and apparatus are provided to directly and accurately detect a temperature of a semiconductor layer at the time of depositing and film-forming the semiconductor layer. First wavelength laser light having light transmissivity attenuated in a first temperature range and second wavelength laser light having light transmissivity attenuated in a second temperature range are applied to the semiconductor layer. A light receiving unit receives light passing through the semiconductor layer. An attenuation range of the laser light transmissivity is detected when the temperature of the semiconductor layer is increased and the detection light quantity of the first wavelength laser light is attenuated. As the temperature continues to increase and the detection light quantity of the second wavelength laser light exceeds an attenuation start point, the temperature of the semiconductor layer is calculated based on a detection light quantity at a predetermined measurement time and the attenuation range.

Description:
RELATED APPLICATION 
       [0001]    The present application claims the benefit under 35 U.S.C. §371 of International Patent Application No. PCT/JP2011/067678, having an internal filing date of Aug. 2, 2011, the content of which is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present invention relates to a method and an apparatus for measuring the temperature of a semiconductor layer by which, when a semiconductor layer of a light-emitting diode or other semiconductor devices is formed by deposition, the temperature or surface roughness of the semiconductor layer can be measured during or after deposition. 
       BACKGROUND 
       [0003]    Semiconductors such as AlN, GaAs, GaN, InP, Si and SiC can be formed by deposition. Examples of deposition techniques include chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). In such a deposition technique, a film can be formed such that a substrate is placed in an evacuated chamber and source molecules are supplied in the form of a source gas onto the substrate to deposit a crystal layer on the surface of the substrate. 
         [0004]    In deposition techniques of this type, the temperature of the substrate in the chamber has to be accurately controlled in order to form a high purity, high density, reproducible semiconductor crystal layer at a constant deposition rate. To this end, a monitor for measuring the temperature of the substrate in the chamber is provided along with a heater for heating the substrate, so that the heating temperature of the heater can be controlled based on the temperature measured by the monitor. 
         [0005]    Conventionally, as described in Patent Literatures 1 and 2 cited below, a pyrometer for monitoring an infrared light that will be emitted from the surface of the heated substrate has been used as the monitor. The pyrometer is disposed outside a window of the chamber so that the infrared light emitted from the surface of the substrate or the surface of the semiconductor layer during deposition can be detected by the pyrometer through the glass window. However, the temperature monitoring by the pyrometer has the following problems. 
         [0006]    When the infrared light emitted from the surface of the heated substrate passes through the semiconductor layer during deposition, a light passing through the semiconductor layer interferes with a light reflected inside the semiconductor layer to cause minor fluctuations of the detection output from the pyrometer, and moreover, the degree of interference varies with a change in the film thickness of the semiconductor layer during deposition. Conventionally, this problem has been solved by disposing a light emitting device outside the chamber, applying a laser light to the semiconductor layer during deposition through the glass window of the chamber, and monitoring a laser light passing through the semiconductor layer. Since the laser light passing through the semiconductor layer also interferes with a laser light reflected inside the semiconductor layer, as with the case of the infrared lights, the output fluctuations of the monitored laser light due to the interference can be used for calibration to eliminate or reduce the interference with the infrared light to be detected by the pyrometer. 
         [0007]    However, even if the interference with the infrared light to be detected by the pyrometer can be avoided, the temperature monitoring is performed by the pyrometer at a place away from the surface of the substrate, generally, outside of the chamber through a glass window. Since not only a long distance but also the glass window exists between the substrate surface from which heat is actually emitted and the monitoring spot, it is inevitable that an error will arise between the temperature measured by the pyrometer and the actual temperature of the substrate surface. 
         [0008]    If the semiconductor layer growing on the surface of the substrate is transparent, moreover, the pyrometer actually measures the temperature of the substrate surface through the transparent semiconductor layer. Thus, it is difficult to directly and accurately measure the temperature of the growing semiconductor layer itself by a measuring method with a pyrometer. 
         [0009]    Patent Literature 1 cited below further discloses the use of a thermocouple monitor for measuring the temperature of the substrate at its back side. However, since the thermocouple monitor is disposed on the back side of the substrate, it is impossible to accurately measure the actual temperature of the substrate surface. In addition, since the thermocouple monitor cannot readily respond to a temperature change in the chamber because of its large heat capacity, it is difficult to accurately measure the temperature of the substrate. 
         [0010]    Patent Literature 3 cited below further discloses a technique of irradiating a light from a halogen lamp on a wafer to be measured and calculating the surface temperature of the wafer from transmittance, reflectance and wavelength of the light. 
         [0011]    However, since transmittance and reflectance of light vary greatly depending on various factors such as surface roughness of the wafer, it is difficult to determine the temperature of the object to be measured with high accuracy only from transmittance and reflectance of a single light. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention is to solve the above-mentioned problems of the prior art and has an object to provide a method and an apparatus for measuring the temperature of a semiconductor layer by and with which the temperature of the semiconductor layer can be accurately determined during or after deposition onto a substrate, enabling deposition of a high-quality semiconductor layer. 
         [0013]    It is another object of the present invention to provide a method and an apparatus for measuring a temperature of a semiconductor layer by which a change in the temperature of the semiconductor layer can be immediately detected by monitoring a change in the quantity of light passing through the semiconductor layer. 
         [0014]    It is still another object of the present invention to provide a method and an apparatus for measuring a temperature of a semiconductor layer by which whether a change in the detected light quantity is due to a change in the temperature of the semiconductor layer or other factors can be determined based on a change in the light quantity detected by applying lights of different wavelengths to the semiconductor layer. 
         [0015]    According to a first aspect of the present invention, a temperature measuring method for measuring a temperature of a semiconductor layer during deposition in a chamber comprises using a first wavelength light whose transmittance to the semiconductor layer starts to decrease as the temperature of the semiconductor layer rises and reaches a first range and a second wavelength light whose transmittance to the semiconductor layer starts to decrease as the temperature of the semiconductor layer reaches a second range that is higher than the first range, applying the first wavelength light and the second wavelength light to the semiconductor layer along a common path and detecting quantities of the first wavelength light and the second wavelength light with a light detecting device facing the semiconductor layer, and when the detected quantity of the second wavelength light starts to decrease after the temperature of the semiconductor layer exceeds the first range during which the detected quantity of the first wavelength light decreases, calculating a current temperature of the semiconductor layer within the second range from a current detected quantity of the second wavelength light and a decrease in the detected quantity of the first wavelength light. 
         [0016]    In the temperature measuring method of the present invention, the current temperature of the semiconductor layer can be calculated such that (a maximum temperature of the second range)+(a temperature difference of the second range)×{(a decrease in the detected quantity of the second wavelength light from a decrease starting point to a current point)/(the decrease in the detected quantity of the first wavelength light)}. 
         [0017]    In the temperature measuring method of the present invention, moreover, a temperature of the semiconductor layer during deposition can be calculated from the current detected quantity of the second wavelength light acquired during deposition of the semiconductor layer onto the substrate, and the decrease in the detected quantity of the first wavelength light, and where a heating temperature of the substrate can be controlled to keep the calculated temperature within the second range. 
         [0018]    In the temperature measuring method of the present invention, when the semiconductor layer is being deposited on the substrate with source molecules supplied onto a heated transparent substrate in the chamber, the first wavelength light and the second wavelength light can be applied to a surface of the semiconductor layer and a diffuse reflected light passing through the semiconductor layer and a diffuse reflected light reflected from the surface of the semiconductor layer can be detected with the light detecting device facing the surface of the semiconductor layer. 
         [0019]    In the temperature measuring method of the present invention, the temperature of the semiconductor layer can also be measured by detecting an infrared light emitted from the semiconductor layer with a temperature change measuring device, and a measurement error of the temperature change measuring device can be corrected based on the calculated current temperature within the second range. 
         [0020]    According to a second aspect of the present invention, a temperature measuring method for measuring a temperature of a semiconductor layer during deposition in a chamber comprises using a first wavelength light whose transmittance to the semiconductor layer starts to decrease as the temperature of the semiconductor layer rises and reaches a first range and a second wavelength light whose transmittance to the semiconductor layer starts to decrease as the temperature of the semiconductor layer reaches a second range that is higher than the first range, applying the first wavelength light and the second wavelength light to the semiconductor layer along a common path and detecting quantities of the first wavelength light and the second wavelength light with a light detecting device facing the semiconductor layer, and when a change in the detected quantity of the second wavelength light is observed by monitoring the detected quantity of the second wavelength light after the temperature of the semiconductor layer exceeds the first range during which the detected quantity of the first wavelength light decreases, determining whether the change in the detected quantity of the second wavelength light is due to a change in the temperature of the semiconductor layer or other factors based on a current change in the detected quantity of the first wavelength light. 
         [0021]    In the temperature measuring method of the present invention, when a change in the detected quantity of the first wavelength light is observed along with the change in the detected quantity of the second wavelength light, it can be determined that the change in the detected quantity of the second wavelength light is due to a factor other than a change in the temperature of the semiconductor layer. 
         [0022]    In this case, it is also possible to calculate a surface roughness of the semiconductor layer from at least one of the change in the detected quantity of the first wavelength light or the change in the detected quantity of the second wavelength light. 
         [0023]    In the temperature measuring method of the present invention, moreover, when a change in the detected quantity of the first wavelength light is not observed along with the change in the detected quantity of the second wavelength light, it can be determined that the change in the detected quantity of the second wavelength light is due to a change in the temperature of the semiconductor layer. 
         [0024]    In the temperature measuring method of the present invention, when the semiconductor layer is being deposited on the substrate with source molecules supplied onto a heated transparent substrate in the chamber, the first wavelength light and the second wavelength light can be applied to a surface of the semiconductor layer and a diffuse reflected light passing through the semiconductor layer and a diffuse reflected light reflected from the surface of the semiconductor layer can be detected with the light detecting device facing the surface of the semiconductor layer. 
         [0025]    According to a third aspect of the present invention, a temperature measuring apparatus for measuring a temperature of a semiconductor layer during deposition in a chamber comprises a light emitting device for applying a first wavelength light whose transmittance to the semiconductor layer starts to decrease as the temperature of the semiconductor layer rises and reaches a first range and a second wavelength light whose transmittance to the semiconductor layer starts to decrease as the temperature of the semiconductor layer reaches a second range that is higher than the first range, a light detecting device for detecting the first wavelength light and the second wavelength light, the light emitting device and the light detecting device facing a surface of the semiconductor layer, enabling the first wavelength light and the second wavelength light to be applied to the surface along a common path and a diffuse reflected light passing through the semiconductor layer and a diffuse reflected light reflected from the surface to be detected by the light detecting device, and a controller for calculating the temperature of the semiconductor layer from quantities of the first wavelength light and the second wavelength light detected by the light detecting device. 
         [0026]    In the temperature measuring apparatus of the present invention, for example, when the detected quantity of the second wavelength light starts to decrease after the temperature of the semiconductor layer exceeds the first range during which the detected quantity of the first wavelength light decreases, the controller can calculate a current temperature of the semiconductor layer within the second range from a current detected quantity of the second wavelength light and a decrease in the detected quantity of the first wavelength light. 
         [0027]    Alternatively, when a change in the detected quantity of the second wavelength light is observed by monitoring the detected quantity of the second wavelength light after the temperature of the semiconductor layer exceeds the first range during which the detected quantity of the first wavelength light decreases, the controller can determine whether the change in the detected quantity of the second wavelength light is due to a change in the temperature of the semiconductor layer or other factors based on a current change in the detected quantity of the first wavelength light. 
         [0028]    Moreover, when there is a change in both the detected quantity of the second wavelength light and the detected quantity of the first wavelength light, the controller can calculate a surface roughness of the semiconductor layer from at least one of the change in the detected quantity of the first wavelength light or the change in the detected quantity of the second wavelength light. 
         [0029]    With the temperature measuring method and apparatus according to the present invention, the temperature of the semiconductor layer can be immediately determined by applying lights of different wavelengths to the semiconductor layer during or after deposition. 
         [0030]    Moreover, whether a change in the detected light quantity is due to a change in the temperature of the semiconductor layer or other factors can be determined based on a change in the light quantity detected by applying lights of different wavelengths to the semiconductor layer. This makes it possible to determine whether there is a change in the surface roughness of the semiconductor layer during deposition and also to determine the degree of surface roughness. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0031]      FIG. 1  is a schematic explanatory drawing showing the configuration of a film deposition apparatus and a temperature measuring apparatus according to a first embodiment of the present invention; 
           [0032]      FIG. 2  is an explanatory drawing showing details of a light emitting device in the temperature measuring apparatus; 
           [0033]      FIG. 3  is an explanatory drawing showing details of a light detecting device in the temperature measuring apparatus; 
           [0034]      FIG. 4  is an enlarged explanatory drawing showing a substrate and a semiconductor layer during or after deposition in the film deposition apparatus; 
           [0035]      FIG. 5  is a diagram showing a relationship between the wavelengths of light applied to the semiconductor layer, the light transmittance and the temperature of the semiconductor layer; 
           [0036]      FIG. 6  is a diagram showing a relationship between the transmission quantity of light applied to the semiconductor layer and the temperature of the semiconductor layer; 
           [0037]      FIG. 7  is a diagram showing a relationship between the transmission quantity of two lights of different wavelengths applied to the semiconductor layer and the temperature of the semiconductor layer; 
           [0038]      FIG. 8  is a diagram showing a change in the transmittance of two lights of different wavelengths when the temperature of the semiconductor layer is being controlled; 
           [0039]      FIG. 9  is a diagram showing a case where a factor other than temperature change has caused a change in the transmittance of the semiconductor layer; and 
           [0040]      FIG. 10  is a diagram showing a case where a change in the temperature of the semiconductor layer has caused a change in the transmittance. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0041]      FIG. 1  is an explanatory drawing showing a film deposition apparatus  1  and a temperature measuring apparatus  20  according to a first embodiment of the present invention,  FIG. 2  shows details of a light emitting device, and  FIG. 3  shows details of a light detecting device. 
         [0042]    In  FIG. 1 , the film deposition apparatus  1  for depositing a semiconductor layer by chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) is illustrated in a schematic drawing. 
         [0043]    The film deposition apparatus  1  has a chamber  2  that can be evacuated during deposition. A table  3  is disposed in the chamber  2 , and a heater  3   a  is incorporated in the table  3  as a heating device. A feed port  4  is connected to the chamber  2 , through which a source gas  5  containing elements (source molecules) for deposition of a semiconductor layer  7  is supplied to the surface of the table  3 , thereby depositing the semiconductor layer  7  on the surface of a substrate  6  disposed on the table  3 . 
         [0044]    The chamber  2  has a first window  8  and a second window  9 . Transparent plates such as glass plate are inserted in the first window  8  and the second window  9  so that the inside can be observed through the transparent plate, but the interior space of the chamber  2  is separated from the exterior space by the transparent plate. 
         [0045]    Outside the first window  8 , a pyrometer  10  is provided as an example of a temperature change measuring device. The pyrometer  10  has a light receiver  11  and a processing circuit  12  which processes light output received by the light receiver  11 . The light receiver  11  of the pyrometer  10  is located outside the first window  8  at a normal angle to the surface of the substrate  6 , looking through the transparent plate inserted in the first window  8 . The axis of the light receiver  11  lies on a perpendicular line Lv extending perpendicularly from the center of the surface of the substrate  6 , and where a light receiving element inside the light receiver  11  is facing the surface of the substrate  6  with its optical axis parallel to the perpendicular line Lv. 
         [0046]    When the table  3  and the substrate  6  are heated by the heater  3   a,  an infrared light emitted from the heated surface of the table  3  passes through the transparent substrate  6  and the semiconductor layer  7  during deposition and is received by the light receiver  11  through the first window  8 . The light output received by the light receiver  11  is sent to the processing circuit  12 , so that the surface temperature of the substrate  6 , more precisely, the surface temperature of the table  3  can be determined from the wavelength of the received infrared light. 
         [0047]    Outside the chamber  2 , a light emitting device  21  is provided as a constituent part of the temperature measuring apparatus  20  according to the embodiment of the present invention. The light emitting device  21  is located outside the second window  9  of the chamber  2 , facing the surface of the substrate  6 . 
         [0048]    As shown in  FIG. 2 , the light emitting device  21  has a first laser beam source  22  which emits a laser beam L 1  of a first wavelength and a second laser beam source  23  which emits a laser beam L 2  of a second wavelength. The laser beam L 1  emitted from the first laser beam source  22  is converted to a collimated light through a collimator lens  22   a  and then passes through a half mirror  25 . The laser beam L 2  emitted from the second light source  23  is converted to a collimated light through a collimator lens  23   a  and then reflected by a mirror  24  to the half mirror  25 . 
         [0049]    In the light emitting device  21 , the first laser beam source  22  and the second laser beam source  23  are alternately turned on and off so that the first laser beam L 1  and the second laser beam L 2  can be alternately applied to the substrate  6  and the semiconductor layer  7  along a common path Ld. 
         [0050]    The substrate  6  is made of a transparent materials such a sapphire wafer. In this context, “transparent” means having a total light transmittance of 80% or above as optical property, ideally, a total light transmittance of 95% or above. As shown in  FIG. 4 , a bottom surface  6   a  of the substrate  6  is slightly rough, diffusing the reflected light at its surface. When the light transmission of the semiconductor layer  7  is high, the laser beam irradiated along the path Ld can be diffusely reflected from the bottom surface  6   a  after passing through the semiconductor layer  7  and the substrate  6 . The diffuse reflected light R 1  from the bottom surface  6   a  passes through the substrate  6  and the semiconductor layer  7 , and a component of the diffuse reflected light R 1  directed along the perpendicular line Lv can be received by the light receiver  11 . 
         [0051]    Since the laser beam travelling along the path Ld enters the surface  7   a  of the semiconductor layer  7  at an incidence angle θ, the light specularly reflected from the surface  7   a  at the reflection angle θ cannot be received by the light receiver  11 . However, if the laser beam is diffusely reflected from the surface  7   a  of the semiconductor layer  7 , a component part of the diffuse reflected light R 2  directed along the perpendicular line Lv can be received by the light receiver  11 . 
         [0052]    The angle θ which the path Ld makes with the perpendicular line Lv is greater than 0 degree and less than 90 degrees. 
         [0053]    The light receiver  11  is not only used for the pyrometer  10  to receive an infrared light but also serves as a light detecting device which receives a laser light diffusely reflected from the bottom surface  6   a  and the surface  7   a.  In the light receiver  11 , the infrared light emitted from the heated substrate  6  and the semiconductor layer  7  and the diffuse reflected lights R 1 , R 2  of the laser beam reflected from the substrate  6  and the semiconductor layer  7  can be detected alternately in time. Moreover, light detection signals at the light receiver  11  are divided in synchronization with the emission of the two laser beam sources  22 ,  23 , so that the first laser beam L 1  and the second laser beam L 2  can be detected at different times. Therefore, in the light receiver  11 , the infrared light, the first laser beam L 1  and the second laser beam L 2  can be separately detected without interfering with each other. 
         [0054]    Alternatively, a light detecting device  16  which receives a laser beam may be provided separately from the light receiver  11  of the pyrometer  10  which receives an infrared light, and the light receiver  11  and the light detecting device  16  may be arranged side by side outside the first window  8 . 
         [0055]    In this case, as shown in  FIG. 3 , the light detecting device  16  may be configured to include a first light receiving element  13 , a condenser lens  13   a  for concentrating a reflected light to the first light receiving element  13 , a second light receiving element  14 , a condenser lens  14   a  for concentrating a reflected light to the second light receiving element  14 , and a wavelength filter  15 . In the light detecting device  16 , the diffuse reflected lights R 1 , R 2  entering along the perpendicular line Lv can be split by the wavelength filter  15 , so that the diffuse reflected light of the first laser beam L 1  can be received by the first light receiving element  13  while the diffuse reflected light of the second laser beam can be received by the second light receiving element  14 . 
         [0056]    When using the light detecting device  16  shown in  FIG. 3 , even if the first laser beam source  22  and the second laser beam sources  23  are simultaneously activated to continuously emit light in the light emitting device  21  shown in  FIG. 2 , the diffuse reflected light of the first laser beam L 1  and the diffuse reflected light of the second laser beam L 2  can be separated from each other with the wavelength filter  15 , so that the laser lights of different wavelengths can be separately received by the first light receiving element  13  and the second light receiving element  14 . 
         [0057]    As shown in  FIG. 1 , the film deposition apparatus  1 , the pyrometer  10  and the light emitting device  21  are controlled by a central controller  30 . The central controller  30  comprises a microcomputer, a memory and so on. A heating controller  31  receives an instruction from the central controller  30  and controls electric supply to the heater  3   a,  thereby controlling the heating temperature of the table  3 . A laser emission controller  32  receives an instruction from the central controller  30  and controls the light emitting device  21 . 
         [0058]    An output signal of the pyrometer  10  is sent to a temperature detecting device  33 . The temperature detecting device  33  receives the output signal, which is correlated to the infrared light emitted from the table  3 , determines the surface temperature of the table  3  from the wavelength of the infrared light or the like, and sends its temperature information to the central controller  30 . In addition, the diffuse reflected light R 1  of the laser beam diffusely reflected from the bottom surface  6   a  of the substrate  6  and the diffuse reflected light R 2  of the laser beam diffusely reflected from the surface  7   a  of the semiconductor layer  7  are received by the light receiver  11  or the light detecting device  16  shown in  FIG. 3 , and an output signal correlated to the amount of light detected is also sent to the temperature detecting device  33 , and its information is sent to the central controller  30 . 
         [0059]    Next will be described the principle of the method for measuring the temperature of the semiconductor layer using the measuring apparatus  20 . 
         [0060]    In the film deposition apparatus  1  shown in  FIG. 1 , the source gas  5  is introduced into the chamber  2  while the table  3  and the substrate  6  are being heated by the heater  3   a,  whereby the semiconductor layer  7  grows on the surface of the transparent substrate  6 , as shown in  FIG. 4 . 
         [0061]    The semiconductor layer  7  deposited on the surface of the substrate  6  serves as a monolayer in a light-emitting diode or other types of semiconductor elements and includes AlN, GaAs, GaN, InP, Si or SiC, for example. 
         [0062]    In such semiconductor layers, the light transmittance varies depending on the wavelength of light and the temperature of the semiconductor layer. In  FIG. 5 , the abscissa represents the wavelength λx of light applied to the semiconductor layer, while the ordinate represents the light transmittance in the semiconductor layer. In  FIG. 5 , the temperature of the same semiconductor layer is varied stepwise from T 1  to T 6  (T 1 &lt;T 2 &lt;T 3 &lt;T 4 &lt;T 5 &lt;T 6 ). As shown in  FIG. 5 , when the light applied to the semiconductor layer has a given wavelength λx, the light transmittance decreases with an increase in the temperature. In addition, as the temperature of the semiconductor layer increases, the temperature at which the transmittance starts to decrease varies depending on the wavelength λx of the light applied to the semiconductor layer. 
         [0063]    As a comparative example of the temperature measuring method according to the embodiment of the present invention,  FIG. 6  shows a temperature measuring method in which a single laser beam of a given wavelength λ1 is applied along the path Ld during deposition of the semiconductor layer  7  onto the surface of the substrate  6  in the film deposition apparatus  1 . In  FIG. 6 , the abscissa represents the temperature of the semiconductor layer  7 , while the ordinate represents the change in the detected light quantity when the diffusely reflected light of the laser beam from the bottom surface  6   a  of the substrate  6  and the surface  7   a  of the semiconductor layer  7  is received by the light receiver  11 . 
         [0064]    As shown in  FIG. 6 , the changes in curve (i) represent a relationship between the change in the temperature of the semiconductor layer  7  and the light quantity detected by the light receiver  11  in an almost ideal condition without any diffuse reflected light R 2  from the surface  7   a  of the semiconductor layer  7  or the like. 
         [0065]    As indicated by the changes in curve (i), when the temperature of the semiconductor layer  7  is low, the semiconductor layer  7  has a high light transmission, so that the diffuse reflected light R 1  reflected from the bottom surface  6   a  of the substrate  6  as shown in  FIG. 4  passes through the semiconductor layer  7  at a high rate. Consequently, a large quantity of the diffuse reflected light of the laser beam can be received by the light receiver  11 , and the detected light quantity becomes D2. When the temperature of the semiconductor layer  7  rises and reaches T 1 , the light transmittance of the semiconductor layer  7  starts to decrease, so that the quantity of the diffuse reflected light received by the light receiver  11  starts to decrease from D2. When the temperature of the semiconductor layer  7  rises to T 2 , the light transmittance of the semiconductor layer  7  becomes minimum, so that the detected quantity of the diffuse reflected light received by the light receiver  11  decreases to D1. 
         [0066]    In this description, a point (a) where the quantity of the diffuse reflected light detected by the light receiver  11  starts to decrease with an increase in the temperature of the semiconductor layer  7  is referred to as the “decrease starting point” and the detected light quantity D2 at the decrease starting point (a) is referred to as the “maximum detected light quantity”. On the other hand, a point (b) where the decrease in the quantity of the diffuse reflected light detected by the light receiver  11  ends is referred to as the “decrease ending point” and the detected light quantity D1 at the decrease ending point (b) is referred to as the “minimum detected light quantity”. 
         [0067]    In an actual film deposition process of the semiconductor layer  7 , the optical properties of the substrate  6  and the semiconductor layer  7  easily vary depending on temperature conditions as well as the direction and roughness of the surface  7   a  of the semiconductor layer  7  easily vary. In addition, when the substrate  6  is placed in the chamber  2 , an error easily arises in the angle between the surface  6   a  of the substrate  6  and the perpendicular line Lv. As the properties of diffused reflection of the laser beam vary with these various conditions, even if the light transmittance of the same semiconductor layer  7  is measured by using the same laser beam of wavelength λ1, the change in the light quantity detected by the light receiver  11  cannot follow the ideal curve (i) shown in  FIG. 6 , but will include the offset quantities δ1 and δ2, as shown by the dotted curve (ii). 
         [0068]    However, even if the conditions for diffused reflection of the laser beam from the substrate  6  or the semiconductor layer  7  vary, the relationship between the wavelength and the transmittance of light and the relationship with the current temperature remain the same as long as a laser beam of the same wavelength is irradiated on a semiconductor layer of the same material, as shown in  FIG. 5 . Accordingly, the temperature of the semiconductor layer  7  is T 1  not only at the decrease starting point (a) of the curve (i) but also at a decrease starting point (c) of the curve (ii), and the temperature of the semiconductor layer  7  is T 2  not only at the decrease ending point (b) of the curve (i) but also at a decrease ending point (d) of the curve (ii). 
         [0069]    In other words, although the light transmittance of the semiconductor layer  7  does not vary as long as the temperature and the wavelength remain the same, the quantity of the diffused reflected light of the laser beam detected by the light receiver  11  varies according to various optical conditions other than the transmittance such as diffused reflection conditions. 
         [0070]    In the temperature measuring method using a single laser beam of a wavelength λ1, if the curve shown in  FIG. 6  is obtained by increasing the temperature of the semiconductor layer  7  during deposition to a value higher than the temperature T 2  corresponding to the decrease ending point, as shown in  FIG. 6 , then, the temperature of the semiconductor layer  7  between T 1  and T 2  can be calculated by monitoring a detected light quantity Da. Once a relationship between the maximum value D2, the minimum value D1 and the temperatures T 2 , T 1  in the variation of the curve (i) is found by raising the temperature of the semiconductor layer  7  above T 2 , for example, the current temperature Tx of the semiconductor layer  7  can be calculated from the monitored value Da of the detected light quantity according to the following equation: 
         [0000]        Tx=T 1+( T 2− T 1)×{( D 2− Da )/( D 2 −D 1)}.
 
         [0071]    However, if the temperature is not raised to T 2  or the relationship between (T 2 −T 1 ) and (D2−D1) is unknown, the temperature Tx between T 2  and T 1  cannot be calculated from the monitored value of the temperature during deposition, so that it is impossible to perform the control to keep the temperature of the semiconductor layer  7  at Tx. 
         [0072]    In the method for measuring the temperature of the semiconductor layer using the measuring apparatus  20  according to the embodiment of the present invention, however, since at least two types of laser beams having different wavelengths are used, the temperature Tx between T 2  and T 1  can be calculated from the monitored value of the light quantity of the laser beam detected by the light receiver  11  without raising the temperature of the semiconductor layer  7  above T 2 . 
         [0073]    In the film deposition apparatus  1  shown in  FIG. 1 , the first laser beam L 1  is emitted from the first laser beam source  22  of the light emitting device  21  shown in  FIG. 2 , while the second laser beam L 2  is emitted from the second light source  23 , and these laser beams L 1 , L 2  are applied to the semiconductor layer  7  along the same path Ld. 
         [0074]    A curve (iii) shown in  FIG. 7  represents a relationship between the detected light quantity and the temperature of the semiconductor layer  7  when the first laser beam L 1  is applied to the semiconductor layer  7  placed on the substrate  6  and the diffuse reflected lights R 1 , R 2  are received by the light receiver  11 , while a curve (iv) represents a relationship between the detected light quantity and the temperature of the semiconductor layer  7  when the second laser beam L 2  is applied to the semiconductor layer  7  placed on the substrate  6  and the diffuse reflected lights R 1 , R 2  are received by the light receiver  11 . 
         [0075]    The wavelength of the first laser beam L 1  is selected such that the temperature of the semiconductor layer  7  is T 3  at a decrease starting point (e) and T 4  at a decrease ending point (f). The wavelength of the second laser beam L 2  is selected such that the temperature is T 5  at a decrease starting point (g) and T 6  at a decrease ending point (h). The range from the temperature T 3  to T 4  is a first temperature range in which the light transmission quantity of the first laser beam L 1  decreases, while the range from the temperature T 5  to T 6  is a second temperature range in which the light transmission quantity of the second laser beam L 2  decreases. The second temperature range is higher than the first temperature range. 
         [0076]    As shown in  FIG. 5 , depending on the type of material, the semiconductor layer  7  has a certain relationship between the transmittance and the wavelength for each temperature, so that the first temperature range can be set by selecting the wavelength of the first laser beam L 1  depending on the material of the semiconductor layer  7 , and in the same fashion the second temperature range can be set by selecting the wavelength of the second laser beam L 2  depending on the material. 
         [0077]    Since the first laser beam L 1  and the second laser beam L 2  are applied to the semiconductor layer  7  along the same path Ld, the first laser beam L 1  and the second laser beam L 2  are equally subjected to the influence of transmission and reflection properties of light, e.g., the influence of the diffused reflection from the bottom surface  6   a  of the substrate  6 , the influence of the surface roughness at the surface  7  of the semiconductor layer  7 , and the error in the angle between the surface  7   a  of the semiconductor layer  7  and the perpendicular line Lv. Consequently, the ratio of the changes δ1, δ2 in the detected light quantity shown in  FIG. 6  does not vary between the first laser beam L 1  and the second laser beam L 2 . 
         [0078]    Therefore, if the light emitting device  21  has the same emission intensity for both the first laser beam L 1  and the second laser beam L 2  and the light receiver  11  has the same photosensitivity for both the first laser beam L 1  and the second laser beam L 2 , both maximum of detected light quantity associated with the first laser beam L 1  and the second laser beam L 2  become D4, as shown in  FIG. 7 , and in the same way, the decrease of light quantity of the first laser beam L 1  and the decrease of light quantity of the second laser beam L 2  are equal and become (D4−D3). 
         [0079]    In practice, however, since the emission intensity differs between the two laser beams and the light reception sensitivity also differs between these laser beams, it is necessary to perform some calibrations before performing the film deposition in the apparatus  1 . 
         [0080]    An example of calibration is such that the substrate  6 , on which a sample of the semiconductor layer has been previously deposited, is placed on the table  3  in the chamber  2 , and where the temperature of the substrate  6 , as well as that of the semiconductor layer  7  is gradually increased under monitoring with the pyrometer  10 , while the first laser beam L 1  and the second laser beam L 2  are applied to the sample of the semiconductor layer. A change in the detected light quantity of the first laser beam L 1  is measured as the temperature exceeds the first temperature range (T 3 -T 4 ), and a change in the detected light quantity of the second laser beam L 2  is measured as the temperature exceeds the second temperature range (T 5 -T 6 ). Based on these measured values, software or hardware adjustments are performed such that a decrease in the detected light quantity of the first laser beam L 1  in the first temperature range becomes equal to a decrease in the detected light quantity of the second laser beam L 2  in the second temperature range. 
         [0081]    Another example of calibration is as follows. In the case where the semiconductor layer  7  has not been deposited on the transparent substrate  6  in the chamber  2 , the laser beam is emitted from the first laser beam source  22  shown in  FIG. 2  and the diffused reflection of the first laser beam L 1  from the bottom surface  6   a  of the substrate  6  and from the surface of the substrate  6  is detected by the light receiver  11 . Then, the laser beam is emitted from the second laser beam source  23  and the diffused reflection of the second laser beam L 2  from the bottom surface  6   a  of the substrate  6  and from the surface of the substrate  6  is detected by the light receiver  11 . Finally, the calibration is performed by software or hardware adjustments such that the light quantity detected when the laser beam is emitted from the first laser beam source  22  becomes equal to the light quantity detected when the laser beam is emitted from the second laser beam source  23 . 
         [0082]    In the film deposition apparatus  1  thus calibrated, the temperature Ty in the second temperature range between the temperatures T 5  and T 6  can be immediately calculated from the monitored value of the light quantity of the laser beam detected by the light receiver  11 , where the temperature of the semiconductor layer  7  need not be raised above T 6  shown in  FIG. 7 . 
         [0083]    As shown in  FIG. 7 , as the temperature of the semiconductor layer  7  rises, the detected light quantity of the first laser beam L 1  passes through the decrease starting point (e) and reaches the decrease ending point (f), as indicated by the curve (iii). At this point, the detected light quantity of the second laser beam L 2  has not yet started to decrease, as shown by the curve (iv). When the detected light quantity of the first laser beam L 1  has passed through the decrease ending point (f), the decrease (D4−D3) in the detected light quantity of the first laser beam L 1  can be determined by the processing circuit  12  of the light receiver  11  and sent to the central controller  30  for storage through the temperature detecting device  33 . 
         [0084]    Thereafter, as the temperature of the semiconductor layer  7  rises, the detected light quantity of the second laser beam L 2  reaches the decrease starting point (g) and starts to decrease. At this time, since the decrease (D4−D3) in the detected light quantity of the first laser beam L 1  has been already found, the temperature Ty of the semiconductor layer  7  can be calculated by the central controller  30  from a monitored value Db that is obtained when the detected light quantity of the second laser beam L 2  has passed through the decrease starting point (g) but not yet reached the decrease ending point (h) and the decrease (D4−D3) in the first laser beam L 1  according to the following equation: 
         [0000]        Ty=T 5+( T 6− T 5)×{( D 4− Db )/( D 4− D 3)}.
 
         [0085]    That is, the current temperature of the semiconductor layer  7  can be calculated such that (the maximum temperature of the second range)+(the temperature difference of the second range)×{(the decrease in the transmission quantity of the second wavelength light from the decrease starting point to the current point)/(the decrease in the detected quantity of the first wavelength light)}. 
         [0086]    Accordingly, as the temperature of the semiconductor layer  7  rises, the temperature of the semiconductor layer  7  can be controlled to be the temperature Ty between the temperatures T 5  and T 6  by monitoring the temperature after the second laser beam L 2  has passed through the decrease starting point (g). 
         [0087]    The relationship between the light transmittance and the current temperature in the case where the second laser beam L 2  is irradiated on the semiconductor layer  7  can be established depending on the relationship between the material of the semiconductor and the wavelength of the laser beam L 2 . When the semiconductor layer  7  is made of GaN (gallium nitride) and the wavelength of the second laser beam L 2  is 445 nm, for example, the temperature T 5  at the decrease starting point (g) can be set at about 800° C. and the temperature T 6  at the decrease ending point (h) can be set at about 900° C. In this case, the temperature at which occurs the deposition of the semiconductor layer  7  can always be controlled to be a certain temperature between 800° C. and 900° C. 
         [0088]    It should be noted that the wavelength of the first laser beam L 1  can be selected from a relatively wide range as long as the temperature T 4  at the decrease ending point (f) is lower than the temperature T 5  at the decrease starting point (g) of the second laser beam L 2 . 
         [0089]    In the film deposition apparatus  1  shown in  FIG. 1 , the temperature of the semiconductor layer  7  is indirectly measured such that the infrared light emitted from the substrate  6  and the surface of the semiconductor layer  7  is detected by the pyrometer  10 , which is an example of the temperature change measuring device, and an output signal correlated to the infrared light is sent to the temperature detecting device  33 . The temperature information acquired by the detection of the infrared light at the pyrometer  10  can be corrected by comparing the temperature information with the temperature calculated by using the first laser beam L 1  and the second laser beam L 2 . It is also possible to perform the temperature control with higher accuracy based on the temperature calculated by using the first laser beam L 1  and the second laser beam L 2  and the temperature information acquired by the detection of the infrared light. 
         [0090]      FIG. 8  shows a temperature control method for controlling the temperature of the semiconductor layer  7  to be a certain temperature Ty within the second temperature range (T 6 -T 5 ) during deposition of the semiconductor layer  7  in the chamber  1 . 
         [0091]    In  FIG. 8 , a dotted line T represents a change in the temperature of the semiconductor layer  7  during deposition onto the substrate  6 . A curve (v) represents a change in the light quantity of the first laser beam L 1  detected by the light receiver  11 , while a curve (vi) represents a change in the light quantity of the second laser beam L 2  detected by the light receiver  11 . 
         [0092]    When the semiconductor layer  7  is being deposited with the source gas  5  introduced into the chamber  2 , the heater  3   a  is controlled to raise the temperature T of the semiconductor layer  7 . The detected light quantity of the first laser beam L 1  reaches a decrease starting point (k) at a time τa and then reaches a decrease ending point (m), and thus, a decrease (D6−D5) of the first laser beam L 1  can be determined when the temperature of the semiconductor layer  7  exceeds the first temperature range. 
         [0093]    Once the detected light quantity of the second laser beam L 2  passes through a decrease starting point (n) along with a further rise in the temperature of the substrate  6  and the semiconductor layer  7 , it becomes possible to immediately calculate the actual temperature of the semiconductor layer  7  from the monitored value of the received light quantity of the second laser beam L 2  by the light receiver  11  and the previously determined decrease (D6−D5) of the first laser beam L 1 . Accordingly, once the detected light quantity of the second laser beam L 2  reaches Dc between D6 and D5 at a time Tb, the temperature of the semiconductor layer  7  can be maintained at an optimum temperature Ty for deposition in the second temperature range (T 5 -T 6 ) by controlling the heater  3   a  with the heating controller  31  and keeping the monitored value of the detected light quantity at Dc. 
         [0094]    As shown in  FIG. 8 , once the decrease (D6−D5) in the detected light quantity of the first laser beam L 1  is determined, the temperature of the semiconductor layer  7  can be maintained at the optimum temperature Ty for deposition by monitoring the detected light quantity of the second laser beam L 2  without the need to raise the temperature of the semiconductor layer  7  above the second temperature range. 
         [0095]      FIGS. 9 and 10  show a case where although the temperature of the semiconductor layer  7  is being controlled to be the optimum value Ty after the time τb, a change has occurred in the light quantity detected by the light receiving element  11 . 
         [0096]    In the case shown in  FIG. 9 , the detected light quantity of the second laser beam L 2  does not stay at Dc and varies as indicated by a during the temperature control after the time Tb. At the same time, the detected light quantity of the first laser beam L 1  does not stay at the minimum value D5, either, and has a change β similar to α. When the detected light quantity of the first laser beam L 1  and the detected light quantity of the second laser beam L 2  vary in a similar manner, as described above, it can be determined that a change has occurred in the laser beam incidence reflection conditions of the semiconductor layer  7 , e.g., that a change has occurred in the diffuse reflected light R 2  because of a change in the surface roughness at the surface  7   a  of the semiconductor layer  7 . 
         [0097]    On the other hand, if the detected light quantity of the second laser beam L 2  has a change α but the detected light quantity of the first laser beam L 1  does not show any changes after the decrease ending point (m), as shown in  FIG. 10 , it can be determined that this change is not due to a variation of the light transmission conditions or reflection conditions for the two laser beams of different wavelengths, but due to a real change of temperature Tz at the semiconductor layer  7 . 
         [0098]    That is, once the detected light quantity of the first laser beam L 1  passes through the decrease ending point (m), it becomes possible to determine whether a change has occurred in the temperature of the semiconductor layer  7  or an optical change has occurred in the semiconductor layer  7  by monitoring both the detected light quantity of the first laser beam L 1  and the detected light quantity of the second laser beam L 2 . 
         [0099]    For instance, the diffuse reflected light R 2  from the surface  7   a  may increase because of surface roughness caused by partial evaporation of the surface  7   a  during the deposition of the semiconductor layer  7 , but this phenomenon can be detected by the foregoing monitoring, and the occurrence of surface roughness at the surface  7   a  can be suppressed by controlling the introduction amount of the source gas  5  and the heating temperature. It is also possible to purposely impart surface roughness to the surface  7   a  of the semiconductor layer  7  by controlling them. 
         [0100]    In addition, if a relationship between at least one of a change a in the detected light quantity of the first laser beam L 1  or a change  13  in the detected light quantity of the second laser beam L 2  and the degree of surface roughness or an acceptable range of surface roughness at the surface  7   a  of the semiconductor layer  7  has been previously found and its function is stored in the central controller  30 , the surface roughness at the surface  7   a  of the semiconductor layer  7  can be calculated when the changes α, β appear in the detected light quantity, as shown in  FIG. 9 . For example, the degree of surface roughness at the surface  7   a  of the semiconductor layer  7  can be determined from a ratio of the maximum value D6 of the detected light quantity to the magnitude of the changes α, β or a ratio of the change (D6-D5) in the detected light quantity to the magnitude of the changes α, β. With this, the degree of actual surface roughness can be estimated numerically or used for relatively rough determination of whether the surface roughness is within an acceptable range or not. 
         [0101]    In the temperature measuring apparatus and method according to the present invention, it is also possible that the light detecting device  10  is opposed to the surface of the substrate  6  in the same manner as in  FIG. 1 , whereas the light emitting device  21  which emits the laser beams L 1 , L 2  of different wavelengths is opposed to the bottom surface of the substrate  6 . In this case, after having entered the bottom surface  6   a  of the substrate  6  and passed through the substrate  6  and the semiconductor layer  7 , the first laser beam L 1  and the second laser beam L 2  can be received by the light receiver  11 . 
         [0102]    Also in this case, the temperature of the semiconductor layer  7  can be measured as needed despite any optical changes other than a change in the light transmittance of the semiconductor layer such as the surface roughness at the surface of the semiconductor layer  7 , which are canceled by using the laser beams L 1  and L 2  of different wavelengths, as in the first embodiment. 
       REFERENCE SIGNS LIST 
       [0103]      1  Film Deposition Apparatus 
         [0104]      2  Chamber 
         [0105]      3  Table 
         [0106]      6  Substrate 
         [0107]      7  Semiconductor Layer 
         [0108]      8  First Window 
         [0109]      9  Second Window 
         [0110]      10  Pyrometer 
         [0111]      11  Light Receiver 
         [0112]      13  First Light Receiving Element 
         [0113]      14  Second Light Receiving Element 
         [0114]      15  Wavelength Filter 
         [0115]      16  Light Detecting Device 
         [0116]      20  Temperature Measuring Apparatus 
         [0117]      21  Light Emitting Device 
         [0118]      22  First Laser Beam Source 
         [0119]      23  Second Laser Beam Source 
         [0120]    L 1  Laser Beam of First Wavelength 
         [0121]    L 2  Laser Beam of Second Wavelength 
         [0122]    T 3 -T 4  First Temperature Range 
         [0123]    T 5 -T 6  Second Temperature Range 
         [0124]    (e), (g) Decrease Starting Point 
         [0125]    (f), (h) Decrease Ending Point