METHOD FOR EMISSIVITY-CORRECTED PYROMETRY

Abstract

A method for coating a substrate with at least one layer. During deposition of the layer, at least one optical measuring device repeatedly determines successive measurement value pairs on the layer, each containing an emission value corresponding to the radiation power measured at a light wavelength and a reflectance value, which is also measured at a light wavelength. Actual values of a substrate temperature are calculated based on the measurement value pairs and a previously determined correction value. The actual values are used to control a temperature-control device for controlling the substrate temperature to a desired value. To improve the determination of the correction factor, during the measurement and within a plurality of measurement intervals, at least two measurement value pairs are measured and, for each of the measurement intervals, a temperature-dependent factor is determined that is used for the calculation of the correction value.

Claims

1. A method for coating a substrate (22) with at least one layer (23 to 31), the method comprising: depositing the at least one layer (23 to 31) on the substrate (22); while depositing the at least one layer (23 to 31), repeatedly measuring by at least one optical measuring device (11, 12) successive measurement value pairs {U.sub.E,n, U.sub.R,n} on the at least one layer (23 to 31), each measurement value pair containing an emission value U.sub.E corresponding to a radiation power measured at a light wavelength, and a reflectance value U.sub.R, which is also measured at the light wavelength; calculating temperature values T.sub.C of the at least one layer (23 to 31) on the substrate (22) from the measurement value pairs {U.sub.E,n, U.sub.R,n} using equations: $U_E=A.Math.e^{\frac{B}{T}}.Math.\left(1-.Math..Math.U_R\right)\mathrm{and}$ $U_E=C\left(T\right)-C\left(T\right).Math..Math..Math.U_R,$ wherein: A is a first calibration parameter, B is a second calibration parameter in which B<0, is a reflectance normalization calibration parameter which relates the reflectance value U.sub.R and a physical reflectance R, where 0R1, is a correction value, and C(T) is a temperature-dependent factor that satisfies $C\left(T\right)=A.Math.e^{\frac{B}{T}}$ wherein at least two of the measurement value pairs {U.sub.E,n, U.sub.R,n} are each measured during a measurement duration within a plurality of measurement intervals t.sub.i, 1ik; determining the temperature-dependent factor C.sub.i(T.sub.i) for each of the measurement intervals t.sub.i; and calculating the correction value based on the temperature-dependent factor C.sub.i(T.sub.i) determined for each of the measurement intervals t.sub.i.

2. (canceled)

3. The method of claim 1, wherein for each of the measurement intervals t.sub.i, the temperature-dependent factor C.sub.i(T.sub.i) is determined by a regression of the emission values U.sub.E measured within the measurement interval t.sub.i, and plotted against the reflectance values U.sub.R measured within the measurement interval t.sub.i.

4. The method of claim 1, further comprising forming normalized emission values U.sub.E,n from the emission values U.sub.E,n recorded in at least some of the measurement intervals t.sub.i by, for each of the at least some of the measurement intervals t.sub.i, dividing each of the emission values U.sub.E,n measured within the measurement interval t.sub.i by the respective temperature-dependent factor C.sub.i(T.sub.i) determined for the measurement interval t.sub.i in accordance with $U_{E,n}^{}=\frac{U_{E,n}}{C_i\left(T_i\right)}=\left(1-.Math..Math.U_{R,n}\right)$

5. The method of claim 4, wherein the correction value is formed from a gradient of a compensation curve through the normalized emission values U.sub.E,n.

6. The method of claim 1, wherein the correction value is obtained by adapting first temperature values T.sub.i to second temperature values T.sub.i, wherein each of the first temperature values T.sub.i is calculated from the respective temperature-dependent factors C.sub.i(T.sub.i) in accordance with T.sub.i=B, and wherein each of the second temperature values T.sub.i are calculated from the respective measurement value pairs {U.sub.E,n, U.sub.R,n}, in accordance with T.sub.i=B.

7. The method of claim 1, wherein an interval-specific correction value (.sub.i) is determined for each of the measurement intervals t.sub.i, and an average value is formed from the interval-specific correction values (.sub.i).

8. The method of claim 1, wherein respective time progressions of the emission values U.sub.E and the reflectance values U.sub.R are periodic with a period length, wherein a temporal duration of each of the measurement intervals t.sub.i is less than a quarter of the period length, and wherein a total duration of all of the measurement intervals t.sub.i is greater than the quarter of the period length or a multiple of the period length.

9. The method of claim 1, wherein at least one of: the measurement duration or a number of measurement intervals t.sub.i used to determine the correction value is kept constant; or the correction value changes over time.

10. The method of claim 1, wherein at least one of: the correction value is optimized continuously during the deposition of the at least one layer (23 to 31) on the substrate (22), the correction value is updated with each newly determined measurement value pair {U.sub.E,n, U.sub.R,n} or a constant number of the measurement value pairs {U.sub.E,n, U.sub.R,n} or a number of the measurement value pairs {U.sub.E,n, U.sub.R,n} that varies within a predetermined range is used to calculate the correction value .

11. The method of claim 1, further comprising utilizing the temperature values (T.sub.C) to regulate a temperature control device (5, 6) for controlling a temperature of the substrate (22) with respect to a setpoint s.

12. A measuring device, comprising: one or more optical measuring devices (11, 12) configured to repeatedly measure successive measurement value pairs {U.sub.E,n, U.sub.R,n} in an apparatus for depositing at least one layer (23 to 31), each measurement value pair {U.sub.E,n, U.sub.R,n} containing an emission value U.sub.E and a reflectance value U.sub.R; and a computing device (15) configured to calculate temperature values T.sub.C of a surface of the at least one layer (23 to 31) using a correction value , wherein the computing device (15) is programmed to determine the correction value in accordance with the method of claim 1.

13. A device for depositing at least one layer (23 to 31) on a substrate (22), the device comprising: a reactor housing (1); a process chamber (8) formed within the reactor housing (1); a gas inlet element (2) arranged in the reactor housing (1), through which process gases are fed into the process chamber (8); a susceptor (4) having a surface facing towards the process chamber (8), wherein the substrate (22) is arranged on the surface of the susceptor (4); a heating device (5) for heating the susceptor (4); one or more optical measuring devices (11, 12) for repeatedly measuring an emission value U.sub.E and a reflectance value U.sub.R of the at least one layer (23 to 31) of the substrate (22) facing towards the process chamber (8); a control device for regulating a temperature of the substrate (22) using the emission values U.sub.E and reflectance values U.sub.R measured by the at least one or more optical measuring devices (11, 12); and a computing device (15) configured to calculate temperature values T.sub.C of the at least one layer (23 to 31) using a correction value , wherein the computing device (15) is programmed to determine the correction value in accordance with the method of claim 1.

14. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In the following text, an exemplary embodiment of the method is explained in detail with reference to accompanying figures. In the drawing:

[0049] FIG. 1 is a schematic illustration of a device for carrying out the method;

[0050] FIG. 2 is a schematic illustration of the section along line II-II in FIG. 1 on the susceptor 4, on which substrates 7 are arranged, and measurement points 13, with which emission values U.sub.E,i and reflectance values U.sub.R,i may be measured by means of a reflectance measuring device 11 and an emissivity measuring device 12;

[0051] FIG. 3 is a schematic illustration of the structure of a multilayer structure 21 on a silicon substrate 22;

[0052] FIG. 4 shows the progression over time of the measured value of the emission U.sub.E and the measured value of the reflectance U.sub.R, wherein t.sub.k denotes a total measurement time over which measurement value pairs, each consisting of an emission value U.sub.E and a reflectance value U.sub.R, are measured in several measurement intervals i with a duration t.sub.i;

[0053] FIG. 5 shows an example of the temporal progression of a true temperature over the entire measurement time t.sub.k, corresponding to the total duration of five measurement intervals t.sub.1 to t.sub.5 as a dashed line;

[0054] FIG. 6 is a schematic illustration of a method with which a temperature-dependent factor C.sub.i(T.sub.i) is obtained from at least two, in the exemplary embodiment three, measurement value pairs {U.sub.E, U.sub.R} of a measurement interval i by deducting the emission values U.sub.E over the reflectance values U.sub.R and drawing a compensation curve through the measurement points, for which the point of intersection of the compensation curve is determined with the ordinate placed through the zero point of the abscissa, the parameters and are obtained from the hatched gradient triangle shown there, since is known and C.sub.i(T.sub.i) is obtained from the y-axis distance, can be calculated;

[0055] FIG. 7 shows the schematic representation according to FIG. 6 to illustrate a first exemplary embodiment, in which all measurement values of all measurement intervals i are shown in a diagram, to illustrate that the measurement points of various measurement intervals i lead to compensation straight lines with various gradients and various intersection points with the ordinate, parameter results from the hatched gradient triangle shown there;

[0056] FIG. 8 shows the representation according to FIG. 6, in which all measured values of all measurement intervals are shown in a diagram, but instead of an emission value U.sub.E a normalized emission value U.sub.E is used, calculated by dividing the measured emission value U.sub.E by a normalization factor C.sub.i(T.sub.i) and drawing a compensation curve through the point cloud obtained in this way, which intersects the ordinate at the value 1 and whose slope is the product of a calibration parameter and a correction value ;

[0057] FIG. 9 shows the schematic representation according to FIG. 5 to illustrate a second embodiment, but instead of showing the progression of the true temperature of the substrate, represents the temperatures T.sub.i calculated from the factors C.sub.i(T.sub.i) for each measurement interval i according to FIG. 6;

[0058] FIG. 10 shows a representation according to FIG. 9, wherein the calculated temperature T.sub.i is assigned in the middle of each time interval, and a connecting curve through the calculated temperatures T.sub.i is shown, which may also consist of a polygon, and the distances of the temperature T.sub.n calculated for each measuring point n from the calculated temperature T.sub.i of the measurement interval i are shown, which are to be minimized in an optimization process;

[0059] FIG. 11 shows a flow chart of the method.

DETAILED DESCRIPTION

[0060] The CVD reactor shown in FIGS. 1 and 2 has a reactor housing 1, a heating device 5 arranged therein, a susceptor 4 arranged above the heating device 5, and a gas inlet element 2 for introducing, for example, TMGa, TMAI, NH.sub.3, AsH.sub.3, PH.sub.3 and H.sub.2.

[0061] The susceptor 4 is driven in rotation about a vertical axis of rotation A with the aid of a rotary drive device 14. For this purpose, a drive shaft 9 is connected on the one hand to the rotary drive device 14 and on the other hand to the underside of the susceptor 4. Substrates 7 lie on the horizontal surface of the susceptor 4 facing away from the heating device 5. Substrate holders 6 are provided, on which the substrates 7 lie. The substrates 7 are located radially outside the axis of rotation A and are held in position by substrate receptacles.

[0062] Two measuring devices may be provided. An emissivity measuring device 12 may be formed by a pyrometer. A reflectance measuring device 11 may also be formed by a pyrometer. A beam splitter 10 may be provided, with which an input beam can be divided between the two measuring devices 12, 11. The beam path is incident on the substrate 7 at a measuring point 13. FIG. 2 suggests that the measuring point 13 migrates over all of the substrates 7 during a rotation of the susceptor 4.

[0063] FIG. 3 shows a multi-layer structure 21 which is deposited one layer after the other in a plurality of successive coating steps in a coating process. First, a nucleation layer 23 of AlN or InN is deposited on the silicon substrate 22. A first AlGaN layer 24 is then deposited on the nucleation layer 23, followed by a second AlGaN layer 25 and a third AlGaN layer 26. The three AlGaN layers 24 to 26 form transition layers. The aluminium content of the transition layers may decrease incrementally.

[0064] A first buffer layer 27 of GaN is then deposited on the transition layers 24 to 26. The layer may be C-doped. A second buffer layer 28, also of GaN, which may be undoped, is then deposited on the first buffer layer 27.

[0065] When one of the layers 23 to 31 is deposited on the substrate 22, measurement value pairs {U.sub.E,n, U.sub.R,n} are measured at one measurement point 13 each with the aid of the reflectance measuring device 11 and the emissivity measuring device 12 on the top of the substrate 7 facing the process chamber 8. These pairs of measured values are stored in a storage device of a computing device 15. The two measuring devices 11 and 12 may be arranged in a common measuring head, and the optical measuring device designed in this way may include a computing device 15. The computing device 15 may be accommodated in a housing arranged outside the reactor housing 1. A light source may also be accommodated there, the light of which is guided to the measuring head with a light guide. The measuring head may also have a further light guide, with which light is guided to the housing 1, where an optical measuring device is arranged, which performs the function of both the reflectance measuring device and that of the emissivity measuring device.

[0066] The current temperature T.sub.C of the substrate 7 may be determined according to Planck's law of radiation. For the sake of simplicity, Wien's approximation is used for this purpose below:

[00004]$\begin{array}{cc}{U}_E=.Math.A.Math.e^{\frac{B}{T}}& \left(1\right)\end{array}$$\mathrm{where}$$\begin{array}{cc}=1-.Math..Math.U_R& \left(1a\right)\end{array}$

[0067] FIG. 4 schematically shows the progression over time of both the emission value U.sub.E and the reflectance value U.sub.R. Due to the reflections inside the deposited layer, the measurement signal oscillates with increasing layer thickness, i.e. with increasing time t.

[0068] In order to compensate for residual oscillations due to scattered light effects or the like, the calibration parameter referred to above is inserted, yielding the following relationship:

[00005]$\begin{array}{cc}{U}_E=A.Math.e^{\frac{B}{T}}.Math.\left(1-.Math..Math.U_R\right),& \left(2\right)\end{array}$$\begin{array}{cc}{U}_E=C\left(T\right)-C\left(T\right).Math..Math..Math.U_R& \left(3\right)\end{array}$

where the following factor plays a role that is significant for the invention:

[00006]$\begin{array}{cc}C\left(T\right)=A.Math.e^{\frac{B}{T}}.& \left(4\right)\end{array}$

[0069] In the method according to the invention, measurement value pairs are obtained during the deposition of one of the layers represented in FIG. 3 and in particular one of the layers 23 to 28 during a time t.sub.k. FIG. 5 shows, by way of example, a true temperature progression of a temperature of the substrate which is not constant over time, which rises slightly and falls slightly at a later time. The total time t.sub.k, during which the measurement is carried out, is divided into a plurality of measurement intervals i with measurement times t.sub.i, in the exemplary embodiment t.sub.1, t.sub.2, t.sub.3, t.sub.4 and t.sub.5. During each measurement interval i or measurement times t.sub.1, t.sub.2, t.sub.3, t.sub.4 and t.sub.5, three pairs of measurement values {U.sub.E,1, U.sub.R,1} are obtained, each pair of measurement values containing an emission value U.sub.E and a reflectance value U.sub.R.

[0070] FIG. 6 shows a representation in which the measurement value pairs {U.sub.E, U.sub.R} of one of the measurement intervals t.sub.i are shown as measurement points in a coordinate system U.sub.E versus U.sub.R. Equation 2 shows that the correction value embodies the unknown contribution to the gradient of a straight line. From equation 3, it is apparent that the factor C(T) can be determined by the point of intersection of the compensation curve through the ordinate of the coordinate system.

[0071] A correction value .sub.i assigned to the measurement interval i and a factor C.sub.i can thus be found for each measurement interval i by means of a linear regression. A temperature T.sub.i of each measurement interval i can in turn be obtained from the factor C.sub.i according to equation 4 (see FIG. 9).

[0072] If, as shown in FIG. 7, all measurement points of all measurement intervals i were represented in a diagram, compensation curves with different gradients and different intersection points with the ordinate would form. FIG. 7 shows that there are individual correction values .sub.i and factors C.sub.i for each of the measurement intervals i based on the temperature profile shown in FIG. 5.

[0073] In order to be able to evaluate the relationships between the emission values U.sub.E and reflectance values U.sub.R in a joint representation, according to a first exemplary embodiment of the invention, the emission value U.sub.E is normalized by dividing the measured emission value U.sub.E by the factor C.sub.i of the respective measurement interval i. The normalized emission values U.sub.E,i obtained in this way for all measurement value pairs are shown in FIG. 8. The formal relationship between the normalized emission value U.sub.E, a unified correction value and the reflectance values U.sub.R,n and the emission values U.sub.E,n is as follows:

[00007]$\begin{array}{cc}{U}_E^{}=\frac{U_{E,n}}{C_i\left(T_i\right)}=1-.Math.{}_k.Math.U_{R,n}.& \left(5a\right)\end{array}$

[0074] The point cloud shown in FIG. 8 can thus be used to represent the linear relationship resulting from equation 5a. The correction value may be determined from the gradient of the compensation curve, which is obtained according to FIG. 4 from measurement values recorded over at least one period length, but which is divided into several measurement intervals.

[0075] This correction value is used to calculate the temperatures T from the relationships according to equation 2 or equation 3, which are used in the regulation as the actual value of a substrate temperature, for example in order to deposit one of the layers shown in FIG. 3, wherein U.sub.E and U.sub.R are the current values of the emission value and the reflectance value, respectively.

[0076] A second exemplary embodiment of the invention is explained with reference to FIGS. 9 and 10.

[0077] FIG. 9 shows a representation similar to FIG. 5, but instead of the true temperature, which is technically difficult to measure, the temperatures T.sub.i that can be calculated from the method step explained with reference to FIG. 6 are plotted. The temperatures T.sub.i are determined directly from the factor C.sub.i as follows:

[00008]$\begin{array}{cc}{T}_i=\frac{B}{\ln \left(\frac{C_i\left(T_i\right)}{A}\right)}.& \left(6\right)\end{array}$

[0078] Following this, a compensating curve is drawn by the temperatures T.sub.i approximately through the temporal midpoints of the measurement intervals i. This compensating curve is shown in FIG. 10 as a dashed line between the midpoints of the measurement intervals i. It is evident that the mean temperatures T.sub.i of the measurement intervals i calculated with C.sub.i(T.sub.i) deviate from the temperatures T.sub.n calculated individually according to the following equation.

[00009]$\begin{array}{cc}{T}_n^{}=\frac{B}{\ln \left(U_{E,n}\right)-\ln \left(A.Math.\left(1-a.Math..Math.U_{R,n}\right)\right)}& \left(7\right)\end{array}$

[0079] By means of an optimization calculation, for example as follows:

[00010]$\begin{array}{cc}\frac{d}{d}.Math.{\left(T_n^{}-T_i\right)}^2& \left(8\right)\end{array}$

a value can be calculated for the correction value by varying the correction value in equation 7 until the resulting measured temperature value T/matches the temperature curve from C.sub.i(T.sub.i) as closely as possible.

[0080] In the exemplary embodiment shown in FIG. 10, a polygon may also be plotted through the calculated temperatures T.sub.i as the compensation curve. In other embodiments, an exponential curve, a sinusoidal curve, or a combination of such curves may be used.

[0081] According to a third exemplary embodiment of the invention, individual correction values .sub.i are first calculated for each measurement interval i, as described above with reference to FIG. 6. A mean value is then calculated from these correction values .sub.i.

[0082] Further embodiments in connection with the methods of the first, second or third exemplary embodiments described above may have the following properties:

[0083] Besides the calculation of C.sub.i(T.sub.i) and T.sub.i from a time interval t.sub.i for a given data point U.sub.Ei or U.sub.Ri, C.sub.i(T.sub.i) and T.sub.i can also be determined from two or more time intervals t.sub.i, t.sub.i+1, . . . , that lie before and after a specific measurement value pair. The valid values C; (T.sub.i) and T.sub.i are then the mean values from the calculation over several time intervals.

[0084] In a preferred variant of the invention or the exemplary embodiments, the number of measurement intervals or the measurement duration is kept constant. When calculating the correction value in this variant, only the most recent measurement value pairs are used. If the set of measurement value pairs is supplemented by a new measurement value pair, the oldest measurement value pair in each case is removed from the set. With this method, a measuring window that varies over time is established, during which the measurement values needed for the correction value are determined. The correction value is updated with each measurement.

[0085] In addition, a sliding fit may be applied through all C.sub.i(T.sub.i) (possibly with a weighting on the most recent measurement data) to enable the values used for the calculation of U.sub.E to be determined as accurately as possible. Depending on the type of temperature change to be expected, this fit may be linear, polynomial, exponential, sinusoidal or a combination of these functions. The appropriate function may also be selected automatically depending on the signal form.

[0086] In order to reduce the noise of the data originating from the calculation over the time intervals t.sub.i, particularly erroneous data can be rejected.

[0087] Here, both T.sub.i and Y.sub.i can be used as a figure of merit. [0088] i. T.sub.i can be compared to the mean temperature in the time interval t.sub.x where t.sub.i>t.sub.x>t.sub.k (possibly measured with an incorrect value). If the difference is too large, for example greater than 10 C., then the corresponding data point is rejected and not used for further calculations. The temperature comparison can also be made with the maximum temperature measured in time interval t.sub.x, which is typically closer to the real temperature than the mean value. [0089] ii. It is usually known from experience in which range .sub.k can lie for a given system and a given process. For example, this can be the value range 0.95 to 0.98. Value pairs with a .sub.i outside this range can be rejected. If there is no empirical value, the comparison between the classically calculated .sub.k,class. without taking temperature changes into account and the .sub.k calculated as described here can return the maximum allowed offset |.sub.k,class..sub.k| from .sub.i. The allowed offset may also be a multiple of |Y.sub.k,class..sub.k|.

[0090] When performing a fit over the longer time interval t.sub.k, values with a particularly large deviation can be rejected. This is possible in the first, second and third embodiments.

[0091] Data from data points with minimum and maximum reflection (or maximum and minimum emission signal) can be excluded from the calculation. Due to the small change in reflectance and emissivity, these data points are particularly susceptible to noise.

[0092] A further possibility of improving noise is the use of several measurement locations or measurement zones (FIG. 2). In general, a measuring zone must be selected sufficiently small, since the residual oscillation of the temperature signal is averaged out due to different layer thicknesses over a wafer, but the resulting signal is incorrect. However, the .sub.k calculation can be carried out over several measurement zones or locations at the same time. These measurement zones may be on the same wafer or on several wafers. Another advantage is that more frequent recalculations than once per revolution are possible. Since it is to be expected that .sub.k is constant for all measurement zones and locations if layer growth is sufficiently homogeneous, the mean value of .sub.k from the various measurement zones can be taken as a valid value.

[0093] As described, it is possible for .sub.k to vary over the course of the process. With the method presented here, .sub.k can be adjusted continuously. However, a sudden change in .sub.k is not to be expected. Therefore, the continuous change of .sub.k can be smoothed with a suitable filter method (e.g. a low-pass filter).

[0094] In the method of the third exemplary embodiment, a continuous fit may also be used instead of a simple averaging in order to predict the change in .sub.k. This fit may be linear, polynomial, exponential, sinusoidal or a combination of these functions depending on the expected change. The appropriate function may also be selected automatically depending on the signal form.

[0095] This procedure may also be used in the methods of the first and second exemplary embodiments. In such cases, .sub.k is replaced with a time-dependent function .sub.k(t). [0096] i. In the case of a temperature step in the process or a pause in growth, this must be taken into account in the temporal function .sub.k(t); for example, by deleting the values that are not to be used and shifting the time axis so that there is no longer a pause in the data.

[0097] According to the method of the first exemplary embodiment, the y-intercept of the linear fit of the data U.sub.E(U.sub.R) is ideally equal to 1. If the deviation is greater than a value to be defined, the specific value for .sub.k can be declared invalid. Then the value for .sub.k used previously is to be used further.

[0098] A .sub.k can be specified at the beginning of the process if not enough data is available. This may originate, for example, from empirical values or the previous process result. This value is then the basis for rejecting, serves as the basis for a filter or serves as the starting point for a fit.

[0099] In the case of a large temperature change (for example between two layers), the data U.sub.E (U.sub.R) cannot be used. This can be done automatically by rejection of the data points or manually by recipe control and/or detection of the change in the temperature setpoint. A continuous calculation of .sub.k with exclusion of this data is possible with the data before and after the temperature change.

[0100] .sub.k can also be calculated by all three methods simultaneously. A valid .sub.k can be selected using the methods described previously. If there are several valid values, an averaging or a previously specified prioritization of the methods can define the value.

[0101] Since both .sub.i and T.sub.i (and thus C (T.sub.i)) are variable over time, an iterative function might also be used in the method of the second exemplary embodiment to determine the optimal (temporal) profile of .sub.i and T.sub.i. .sub.k could then be determined from this time profile. [0102] a. The iterative procedure may be such that T.sub.i is recalculated after each .sub.k Or .sub.k(t) calculation, taking .sub.k Or .sub.k(t) into account. [0103] b. The progression of C (Tt) from the method of the second exemplary embodiment can be used to carry out an optimized calculation according to the method of the first or third embodiments. The progression of C (Tt) is then taken into account in the linear fit.

[0104] The length of the time interval t.sub.k may be determined automatically in order to map exactly one or a multiple of the oscillation period.

[0105] The error in the gradient caused by the temperature change can be determined from the difference, depending on whether U.sub.E or U.sub.R is rising or falling (over a whole oscillation period). This allows the calculation to be corrected in each t.sub.i interval.

[0106] The temperature change can be estimated from the difference between T.sub.i and T.sub.i+1. With a constant temperature change, T.sub.i and T.sub.i+1 will be shifted in the same direction if the calculation is not made at the reversal point of U.sub.E and U.sub.R. This can then be used iteratively to correct the calculation of T.sub.i and T.sub.i+1.

[0107] The preceding notes are intended to serve as an explanation of the inventions reported as a whole in the application, which further develop the state of the art at least with the following feature combinations, also each on their own merits, wherein two, several or all of said feature combinations may also be combined, specifically:

[0108] A method that is characterized in that at least two measurement value pairs {U.sub.E,n, U.sub.R,n} are measured during a measurement period within a multiplicity k of measurement intervals t.sub.i and a temperature-dependent factor C.sub.i(T.sub.i) is determined for each of the measurement intervals t.sub.i, which factor is used for the calculation of the correction value .

[0109] A method that is characterized in that the factor C.sub.i(T.sub.i) is a product of a first calibration parameter A with the value of the exponential function of a quotient of a second calibration parameter B and a temperature T.sub.i.

[0110] A method that is characterized in that the factor C.sub.i(T.sub.i) is obtained by a regression of the emission values U.sub.E each plotted against the reflectance values U.sub.R or using an optimization method.

[0111] A method that is characterized in that normalized emission values U.sub.E are formed from the emission values U.sub.E recorded in at least some of the measurement intervals by dividing by the respective factor C.sub.i(T.sub.i), and the correction value is calculated by a regression over the normalized emission values U.sub.E plotted against the reflectance values U.sub.R or by an optimization process.

[0112] A method that is characterized in that the correction value is formed from the gradient of a compensation curve through the normalized emission values U.sub.E.

[0113] A method that is characterized in that a correction value is obtained by adapting temperature values T.sub.i obtained from the factors C.sub.i(T.sub.i) to temperature values T.sub.i calculated from the respective measurement value pairs {U.sub.E,n, U.sub.R,n}.

[0114] A method that is characterized in that a correction value .sub.i is determined for each of the measurement intervals t.sub.i and a mean value is formed from these correction values .sub.i over the measurement period.

[0115] A method that is characterized in that the emission value U.sub.E and the reflectance value U.sub.R change periodically during the deposition of layers 23 to 31 or a multilayer structure 21 consisting of several layers 23 to 31 with a period length, wherein the temporal duration of a measurement interval t.sub.i is less than a quarter or a tenth of the period length, and that the total duration of all measurement intervals t.sub.i is greater than a quarter of the period length or a multiple of the period length.

[0116] A method that is characterized in that the measurement duration or the number of measurement intervals t.sub.i used to determine the correction value is kept constant and/or that the correction value changes over time.

[0117] A method that is characterized in that the correction value is continuously optimized during the deposition of one or more layers on the substrate and/or that the correction value is updated with each newly determined measurement value pair {U.sub.E,n, U.sub.R,n}, and/or that a constant number or a number of measured value pairs that varies within a predetermined range is used to calculate the correction value .

[0118] A method that is characterized in that the temperature value T.sub.C is an actual value with which a temperature control device 5, 6 for controlling the temperature of the substrate 22 is regulated with respect to a setpoint s.

[0119] A measuring device that is characterized in that the computing device 15 is programmed in such a way that the correction value is determined according to a method according to any one of the above methods.

[0120] A device that is characterized in that the measuring device is embodied according to the above measuring device.

[0121] All disclosed features are essential to the invention (by themselves, but also in combination with one another). In the disclosure of the application the disclosure content of the associated/attached priority documents (copy of the previous application) is hereby also included in its entirety, also for the purpose of including features of these documents in claims of the present application. The subclaims, even without the features of a referenced claim, characterize with their features independent inventive developments of the prior art, in particular for making divisional applications on the basis of these claims. The invention specified in each claim can additionally have one or more of the features specified in the above description, in particular with reference numbers and/or specified in the list of reference numbers. The invention also relates to configurations in which individual features mentioned in the above description are not implemented, in particular if they are clearly superfluous for the respective intended use or can be replaced by other technically equivalent means.

LIST OF REFERENCE SYMBOLS

[0122] 1 Reactor housing [0123] 2 Gas inlet element [0124] 3 Gas supply line [0125] 4 Susceptor [0126] 5 Heating device [0127] 6 Substrate holder [0128] 6 Gas cushion [0129] 7 Substrate [0130] 8 Process chamber [0131] 9 Drive shaft [0132] 10 Beam splitter [0133] 11 Reflectance measuring device [0134] 12 Emission measuring device [0135] 13 Measuring point [0136] 14 Rotary drive device [0137] 15 Computing device [0138] 21 Multilayer structure [0139] 22 Substrate [0140] 23 Nucleation layer [0141] 24 Transition layer [0142] 25 Transition layer [0143] 26 Transition layer [0144] 27 Buffer layer [0145] 28 Buffer layer [0146] 29 Boundary layer, two-dimensional electron gas [0147] 30 Barrier layer [0148] 31 Cover layer [0149] Correction value [0150] .sub.i Correction value of a measurement interval [0151] Wavelength [0152] Calibration parameter [0153] A Axis of rotation [0154] A Calibration parameter [0155] B Calibration parameter [0156] U.sub.E Emission value [0157] U.sub.E Normalized emission value [0158] U.sub.R Reflectance value [0159] U.sub.E,n Emission value [0160] U.sub.R,n Reflectance value [0161] T.sub.C Corrected temperature, temperature actual value [0162] T.sub.M Measurement temperature [0163] T.sub.S Temperature setpoint [0164] t.sub.i Time interval [0165] i Index of a measurement interval [0166] n Index of a measurement pair [0167] k Number of measurement intervals [0168] t.sub.k Total measurement time [0169] S Setpoint