Method for emissivity-corrected pyrometry

Abstract

A substrate is coated with a multilayer structure which has layers of a first portion and layers of a second portion that are deposited on the layers of the first portion. During the deposition of at least one layer of the second portion, at least one optical measuring apparatus measures an emissivity value and a reflectance value on the broad side of the substrate, which broad side comprises the layer. Using a previously determined correction value, an actual value of a temperature of the broad side of the substrate is calculated and, using the actual value, a heating apparatus is controlled in order to control the temperature of the substrate to match a target value of the temperature of the broad side of the substrate. The correction value is determined during the deposition of the first portion, which is carried out immediately before the deposition of the second portion.

Claims

1. A method for emissivity-corrected pyrometry when coating a substrate (22) with a multilayer structure (21) in a process chamber (8) of a chemical vapor deposition (CVD) reactor, wherein a first portion (18) of the multilayer structure (21) includes first layers (23-28) and a second portion (19) deposited on the first portion (18) includes second layers (30, 31), the method comprising: depositing with the CVD reactor the first portion (18) on the substrate (22); during the deposition of one of the first layers (23-28) of the first portion (18) and prior to the deposition of the second layers (30, 31) of the second portion (19), determining by a computing device (15) a correction value (), wherein immediately before the determination of the correction value (), the substrate (22) is heated to a temporally constantly maintained measured temperature (TM), at which the correction value () is determined; depositing with the CVD reactor the second portion (19), wherein the deposition of the first portion (18) is carried out immediately before the deposition of the second portion (19); during the deposition of a first one of the second layers (30, 31) of the second portion (19), measuring with at least one optical measuring device (10, 11) an emissivity value (E) and a reflectance value (R) from a surface of the first one of the second layers (30, 31), wherein a time sequence of emissivity values and a time sequence of reflectance values each exhibits an oscillating pattern, and the time sequence of reflectance values is phase shifted with respect to the time sequence of emissivity values; calculating by the computing device (15) an actual value (T.sub.C) of a temperature of the substrate (22) from the emissivity value (E) and the reflectance value (R) using the correction value (); and controlling a heating device (5) to adjust the temperature of the substrate (22) to match a target value (T.sub.S) using the actual value (T.sub.C).

2. The method of claim 1, wherein at least one of: (i) the first layers (23-28) of the first portion (18) of the multilayer structure (21) includes a plurality of buffer or transition layers, or (ii) the second layers (30, 31) of the second portion (19) of the multilayer structure (21) includes at least one barrier layer (30).

3. The method of claim 1, wherein the measurement of one or more of the emissivity value (E) or the reflectance value (R) comprises measuring light with a wavelength () in a range between 800 nm and 1000 nm.

4. The method of claim 1, wherein the substrate (22) is non-transparent to light with a wavelength () at which one or more of the emissivity value (E) or the reflectance value (R) is measured, and at least the second layers (30, 31) in the second portion (19) are transparent or semi-transparent.

5. The method of claim 1, further comprising during the determination of the correction value (), heating the substrate (22) with a constant heat output from the heating device (5) without regulating the temperature of the substrate (22).

6. The method of claim 1, wherein the time series of the emissivity values and the time series of the reflectance values oscillate in accordance with a period, and wherein a temporal length of a value determination phase (17, 17), during which the correction value () is determined, is between a quarter of the period and an entirety of the period.

7. The method of claim 1, wherein the determination of the correction value () is carried out during a plurality of correction value determination phases (17, 17) that are performed one after another, wherein an intermediate correction value is determined in each of the correction value determination phases (17, 17), and wherein the correction value () is determined using the intermediate correction values.

8. The method of claim 1, wherein at least one of: (i) the substrate (22) is a silicon substrate, or (ii) the multilayer structure (21) includes layers of elements from main group III and main group V.

9. The method of claim 1, wherein the first layers (23-28) of the first portion (18) of the multilayer structure (21) include one or more buffer or transition layers, during whose deposition the correction value () is determined, and wherein the one or more buffer or transition layers contains one or more of gallium, nitrogen or aluminium.

10. The method of claim 1, wherein the second layers (30, 31) of the second portion (19) of the multilayer structure (21) include a barrier layer (10) formed by an AlGaN layer or an AlInN layer.

11. The method of claim 1, wherein a composition of at least one of the first layers (23-26) of the first portion (18) is similar to a composition of at least one of the second layers (30) of the second portion (19).

12. The method of claim 1, wherein the substrate (22) is part of a plurality of substrates (22) contained in a reactor housing (1) of a chemical vapor deposition (CVD) reactor, the method further comprising simultaneously performing the method of claim 1 on each of the substrates (22).

13. The method of claim 1, further comprising: determining an intermediate correction value during the deposition of the second portion (19); and optimizing the correction value () based on the intermediate correction value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following text, an exemplary embodiment of the invention will be explained with reference to accompanying drawings. In the drawings:

(2) FIG. 1 depicts a schematic representation of a cross-section of an apparatus for performing the method,

(3) FIG. 2 depicts schematically a cross-section according to the line II-II in FIG. 1,

(4) FIG. 3 depicts an exemplary embodiment of a multilayer structure 21 deposited on a silicon substrate 22,

(5) FIG. 4 depicts schematically a temporal curve of the reflectance value R and the emissivity value E during a correction value determination phase and the temperature calculated therefrom without correction, and

(6) FIG. 5 depicts in the manner of the representation according to FIG. 4 the curve of reflectance value R, emissivity value E, and the corrected temperature calculated therefrom during deposition of the active region of the multilayer structure with correction. The temperature is represented here as weakly oscillating. Ideally, the temporal curve of the temperature has no or only minor fluctuations, and would thus be a straight line in the diagram.

DETAILED DESCRIPTION

(7) The CVD reactor represented 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 feeding in for example TMGa, TMAl, NH.sub.3, AsH.sub.3, PH.sub.3 and H.sub.2. The susceptor 4 is rotated 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 both to the rotary drive device 14 and to the underside of the susceptor 4.

(8) Substrates 7 are positioned 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 lie radially outside the axis of rotation, a, and are held in position by substrate holders 6.

(9) Two measuring apparatuses may be provided. An emissivity measuring device 10 can be formed by a pyrometer. A reflectance measuring device 11 can also be formed by a pyrometer. A beam splitter 12 may be provided, with an input beam can be divided onto the two measuring apparatuses 10, 11. The beam path meets the substrate 7 at a measurement point 13. FIG. 2 indicates that the measurement point 13 passes over all of the substrates 7 during a revolution of the susceptor 4.

(10) FIG. 3 shows a multilayer structure 21 with layers that are deposited one after another in several consecutive coating steps in a coating process. First, a nucleation layer 23 of AlN or InN is deposited on the silicon substrate 22. Then, a first AlGaN layer 24 is deposited on the nucleation layer 23, followed by a second AlGaN layer 25 and on this a third AlGaN layer 26. The three AlGaN layers 24 to 26 constitute transition layers. The aluminium content of the transition layers may be reduced incrementally.

(11) Then, a first buffer layer 27 of GaN is deposited on the transition layers 24 to 26. The layer may be C-doped. Then, a second buffer layer 28, also of GaN, which may be undoped, is deposited on the first buffer layer 27.

(12) The region of the multilayer structure 21, starting with the nucleation layer 23 and extending as far as the top region of the second buffer layer 28 is designated the first portion 18 of the multilayer structure 21. The top region of the buffer layer 28, which does not belong to the first portion 18, has a minimum thickness of about 100 nm.

(13) A barrier layer 30 of AlGaN or AlInN is deposited on the second buffer layer 28. At least the bottom region of the barrier layer 30, of which the thickness may be about one tenth the thickness of the second buffer layer 28, is designated the second portion 19 of multilayer structure 21, similarly to the top region of the second buffer layer 28.

(14) In FIG. 3, two regions designated with reference numerals 17, 17 are represented, during which the correction values are calculated. In the illustration according to FIG. 3, these correction value determination phases 17, 17 are separated spatially from each other and from the second portion 19. During deposition of the multilayer structure, the correction value determination phases 17, 17 are separated temporally from each other and from the start of the deposition of the second portion 19. An optional optimization of the correction value may still be carried out during the time of the deposition of the second portion 19, that is to say while the correction value is being used.

(15) Then, a cover layer 31 of P-doped GaN is deposited on the barrier layer 30. However, the cover layer 30 and the second buffer layer 28 may also be counted as part of the second portion 19 of the multilayer structure 21.

(16) An actual value T.sub.C of a substrate temperature is calculated during the deposition of the first portion 18. This may be done according to the following formula:

(17) $\begin{array}{cc}{T}_C=\frac{B}{\log E-A+\log \left(1-R\right)}& \left(3\right)\end{array}$

(18) However, the actual value T.sub.C may also be calculated according to the following formula:

(19) $\begin{array}{cc}{T}_C=\frac{B}{\log E-A+\log \left(1-.Math.R\right)}& \left(5\right)\end{array}$

(20) The terms in the formulas shown above represent the following variables: T.sub.C: Emissivity-corrected temperature E: Calibrated signal of the measurement of the thermal emission (linear relationship between measurement signal and incident radiation) R: Calibrated signal of the reflectance measurement (linear relationship between measurement signal and incident radiation) T.sub.cal, S.sub.cal: Calibration parameters for determining the raw temperature R.sub.cal: Calibration parameter of the reflectance measurement : Wavelength of pyrometer and reflectance measurement c.sub.2: Second radiation constant

(21) Parameters A and B as well as the correction value are adapted or calculated.

(22) The reflectance of the layer is measured with the emissivity measuring device 10. Because of the constantly growing layer and changing reflections and layer thicknesses, the emissivity value E has an oscillating pattern, shown schematically in FIG. 4. The reflectance value R measured with the reflectance measuring device 11 also has an oscillating pattern for the same reasons. The actual value T.sub.C of the substrate temperature calculated therefrom also has an oscillating pattern. The actual value T.sub.C is used to regulate the substrate temperature against a target value T.sub.S. This is why the physical temperature T of the substrate 7, which is represented in FIG. 4, also has an oscillating pattern. The period length of the oscillation curve is about 100 to 200 seconds with a wavelength of 950 nm and a refraction index n of about 3.

(23) A correction value or multiple intermediate correction values are calculated in one or more correction value determination phases 17, 17 during the deposition of the first portion. The length of a correction value determination phase 17, 17 is at least equal to the time of one quarter of a period length. The temperature T of the substrate surface is regulated against a target value before the correction value determination phase 17, 17. Because of the oscillation of the emissivity E and the reflectance R, as represented in FIG. 4, the temperature oscillates. The physical substrate temperature T is kept constant immediately before the correction value determination phase 17, 17 by interrupting the regulation. The temperature T reaches a steady state. In the correction value determination phase 17, 17, the heating device 5 is not regulated, but is energized with constant power. The measured value of emissivity E and reflectance R oscillates. But the temperature T remains constant. With the aid of the computing device 15, in particular using the formula (5), a correction value is varied in such manner that the calculated temperature T.sub.C varies as little as possible. In this context, calibration parameters A and B are determined at the same time.

(24) The calculation of correction value may also be carried out after the correction value determination phase 17, 17. The essential point is that measurement values are recorded in the correction value determination phase with which the calculation can be carried out.

(25) If multiple correction value determination phases 17, 17 are provided, the correction value can be optimized incrementally.

(26) For the deposition of a boundary layer 29 between the top buffer layer 28 and barrier layer 30 located above it, in a second portion of the multilayer structure 19, also in a correction phase, the actual value of the substrate temperature is calculated according to formula (5). The physical temperature T of the substrate surface then progresses approximately as shown in FIG. 5. The oscillation has a smaller amplitude than that of the oscillation of the temperature curve illustrated in FIG. 4. Ideally, the temperature curve no longer has any oscillation at all. Therefore, it is provided in particular that an emissivity-corrected pyrometry is carried out during the deposition of the buffer layer 28 and the barrier layer 30 in order to determine the actual value of the temperature of the substrate surface, wherein the correction value was obtained immediately beforehand, during the same deposition process.

(27) FIG. 2 shows a total of six substrates 7. For each substrate 7, an individually assigned correction value can be calculated, which is then used during the deposition of the second portion 19 of the multilayer structure 21.

(28) The above explanations are intended to explain all the inventions included overall in the filing, each of which also advances the state of the art, at least through the following feature combinations, wherein two, more, or all of these feature combinations can also be combined, specifically:

(29) A method which is characterized in that the correction value is determined during the deposition of the first portion, that takes place immediately before the deposition of the second portion 19.

(30) A method which is characterized in that the first portion 18 of the multilayer structure 21 includes a multiplicity of buffer- or transition layers 23 to 28, and/or that the second portion 19 of the multilayer structure 21 has least one barrier layer 30.

(31) A method which is characterized in that the measurement of the emissivity value E and/or of the reflectance value R is carried out at a wavelength A in a range between 800 nm and 1000 nm, and/or that the substrate 22 is opaque for light with wavelength A, at which the emissivity value E and/or the reflectance value R is measured, and the layers of the first portion and the second portion 19, but at least some layers in the region of the first and second portion 19 are transparent or semi-transparent.

(32) A method which is characterized in that immediately before the determination of the correction value the substrate 22 is heated to a temporally constantly maintained, measured temperature T.sub.M, at which the correction value is determined, and/or that the substrate 22 is heated without temperature regulation with constant heat output during a correction value determination phase 17, 17.

(33) A method which is characterized in that the emissivity value E and the reflectance value R changes periodically during the deposition of the multilayer structure 21, wherein the temporal length correction value determination phase 17, 17 is at least equal to a quarter of the period and/or maximally one half or an entire period, and/or maximally 100 seconds.

(34) A method which is characterized in that the determination of the correction value is carried out in a number of correction value determination phases 17, 17, each being completed temporally consecutively after a pause, wherein an intermediate correction value is determined in each case, wherein the correction value is calculated using the intermediate correction values, and/or an intermediate correction value is determined in order to optimize the correction value during the deposition of the second portion 19.

(35) A method which is characterized in that the substrate 22 is a silicon substrate and/or that the multilayer structure 21 contains layers of elements from main groups III and V, and/or that the one or more buffer or transition layers 23 to 28, during whose deposition the correction value is determined, contains gallium, nitrogen and/or aluminium, and/or that the barrier layer 10 is an AlGaN layer or an AlInN layer, and/or that the first portion 18 includes at least one layer 23 to 26 that is similar to at least one layer 30 of the second portion 29 in terms of its composition.

(36) A method which is characterized in that in a reactor housing 1 of a CVD reactor multiple substrates 22 on a susceptor 4 which is heated by a heating device 5 are coated simultaneously with a multilayer structure 21, wherein an individual correction value is calculated for each of the substrates 22, and an individual actual value T.sub.C of a temperature of the substrate 22 is calculated with the individual correction value .

(37) An apparatus which is characterized in that the computing device 15 is programmed in such manner that the correction value is determined during the deposition of a first portion 18 of the multilayer structure 21 on the substrate 22, immediately before the deposition of the second portion 19 of the multilayer structure 21 on the first layer arrangement.

(38) All disclosed features (individually, but also in combination with each other) are essential to the invention. The content of disclosure of the associated/accompanying priority documents (copy of the previous application) is herewith also incorporated in the disclosure of the application in its entirety, also for the purpose of including features of these documents in claims of the present application. Even without the features of a referenced claim, the subordinate claims with their features characterize stand-alone inventive further developments of the state of the art, in particular with a view to filing divisional applications on the basis of these claims. The invention described in each claim may additionally include one or more of the features presented in the preceding description, in particular those designated with reference numerals and/or presented in the list of reference signs. The invention also relates to design forms in which some of the features specified in the preceding description are not realized, in particular to the extent that they are evidently not essential for the respective intended use or can be replaced by other means with technically equivalent function.

LIST OF REFERENCE SIGNS

(39) 1 Reactor housing 2 Gas inlet element 3 Gas supply line 4 Susceptor 5 Heating device 6 Substrate holder 7 Substrate 8 Process chamber 9 Drive shaft 10 Emissivity value measuring device 11 Reflectance value measuring device 12 Beam splitter 13 Measurement point 14 Rotary drive device 15 Computing device 17 Correction value determination phase 17 Correction value determination phase 18 First portion of the multilayer structure 19 Correction phase, second portion of the multilayer structure 21 Multilayer structure 22 Substrate 23 Nucleation layer 24 Transition layer 25 Transition layer 26 Transition layer 27 Buffer layer 28 Buffer layer 29 Boundary layer, two-dimensional electron gas 30 Barrier layer 31 Cover layer Correction value Wavelength a Axis of rotation A Calibration parameter B Calibration parameter E Emissivity value R Reflectance value T.sub.C Corrected temperature, temperature actual value T.sub.M Measured temperature T.sub.S Temperature target value T Physical temperature