CN115838966A - Molecular beam epitaxial growth process optimization method of pHEMT device - Google Patents
Molecular beam epitaxial growth process optimization method of pHEMT device Download PDFInfo
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Abstract
The invention provides a molecular beam epitaxial growth process optimization method of a pHEMT device, and relates to the technical field of semiconductor manufacturing. The method comprises the following steps: determining a rotation speed range of a sample frame rotation speed capable of being used for molecular beam epitaxial growth; n different rotation speeds R are selected in the rotation speed range i (ii) a For pHEMT devices and each speed R i Calculating the value of the corresponding evaluation function; the rotation speed corresponding to the minimum evaluation function value among the calculated evaluation function values is determined and is used as the rotation speed of the sample holder when the pHEMT device is epitaxially grown by using the molecular beam. Establishing an evaluation function aiming at the rotation speed of the sample holder according to the epitaxial layer structure of the target device, wherein the evaluation function and the channel layerThe uniformity of the doping concentration is correlated, and the minimum value of the evaluation function is obtained through calculation aiming at the selectable rotating speed, so that the corresponding rotating speed of the sample frame can be quickly selected when the doping uniformity of the channel layer is optimal, and the time cost and the material cost are greatly saved.
Description
Technical Field
The invention relates to the technical field of semiconductor manufacturing, in particular to a molecular beam epitaxial growth process optimization method of a pHEMT device.
Background
In mass production of Molecular Beam Epitaxy (MBE), a plurality of substrates are generally simultaneously carried on one substrate pallet for batch molecular beam epitaxy, thereby improving production efficiency and reducing production costs. In this case, the in-wafer uniformity of the epitaxial layer on the substrate wafer and the wafer-to-wafer uniformity are key indicators in mass production, and the quality of the uniformity directly affects the yield of the subsequent device manufacturing process.
Compound semiconductor-based pseudomorphic high electron mobility transistor (pHEMT) devices are typically fabricated by molecular beam epitaxy, and the doping concentration of the channel layer of the pseudomorphic hemt device directly affects the pinch-off voltage of the device, which is a very important performance parameter of the pHEMT device. In the molecular beam epitaxial growth process of the pseudomorphic high electron mobility transistor device, the doping uniformity of the planar doping layer and the thickness uniformity of the isolation layer influence the doping concentration uniformity of the channel layer. Since the flow rates of molecular beams ejected from a source furnace (for example, a Si furnace) for providing a dopant and a source furnace (for example, a Ga furnace and an Al furnace) for providing a molecular beam required for an isolation layer are not uniformly distributed on a substrate support plate during the growth of an epitaxial layer in a molecular beam epitaxy apparatus, in order to improve the uniformity of an epitaxial wafer, a sample holder carrying the substrate support plate needs to be rotated at a constant speed during the growth of the epitaxial layer, so that the equivalent beam flow rates of various molecular beam sources actually reaching the substrate are relatively uniform over a period of time.
However, in the prior art, in order to improve the uniformity of epitaxial wafer growth, the rotation speed of the sample holder can only be performed by multiple groping tests, which greatly increases the production test cost.
Disclosure of Invention
The invention aims to provide a molecular beam epitaxial growth process optimization method of a pHEMT device to solve the problem of optimization of molecular beam epitaxial growth uniformity of the pHEMT device, aiming at the defects of the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention provides a molecular beam epitaxial growth process optimization method of a pHEMT device, wherein the structure of the pHEMT device comprises a lower plane doping layer, a lower isolating layer, a channel layer, an upper isolating layer and an upper plane doping layer which are sequentially stacked from bottom to top, and the method comprises the following steps:
determining a rotation speed range of a sample frame rotation speed capable of being used for molecular beam epitaxial growth;
n different rotation speeds R are selected in the rotation speed range i ，R i In revolutions per minute, where i =1, 2, ·, N, and N is an integer greater than 5;
for pHEMT devices and each selected rotation speed R i Calculating a corresponding evaluation function F i The value of (a) is,
wherein ,T j to representS j The absolute value of the difference between the integer and its nearest neighbor,
，j=1, 2, 3, 4, 5，t 1 represents the time required for the molecular beam epitaxial growth of the lower planar doping layer,t 2 showing the time required for the molecular beam epitaxial growth of the lower spacer layer,t 3 Shows the time required for the molecular beam epitaxial growth of the channel layer,t 4 Represents the time required for the molecular beam epitaxial growth of the upper spacer layer, andt 5 represents the time required for the molecular beam epitaxial growth of the upper planar doping layer,t j in minutes, a and B are empirically determined weighting coefficients, a and B satisfying the following conditions: 0.3<A<3，0.3<B<3；
The rotation speed corresponding to the minimum evaluation function value among the calculated evaluation function values is determined and is used as the rotation speed of the sample holder when the pHEMT device is epitaxially grown by using the molecular beam.
Optionally, the rotation speed range is: greater than or equal to 15 revolutions per minute and less than or equal to 35 revolutions per minute.
Optionally, N rotation speeds R different from each other i Each of which is an integer.
Optionally, N =21.
Optionally, after the pHEMT device is grown by using the determined rotation speed of the sample holder to obtain the pHEMT epitaxial wafer, selecting a plurality of point locations on the pHEMT epitaxial wafer, and performing an epitaxial layer thickness test and a pinch-off voltage test at the plurality of point locations, where the epitaxial layer thickness test is used to obtain the thickness of the lower isolation layer and the upper isolation layer and the thickness T of the upper isolation layer and the lower isolation layer at each of the plurality of point locations n The pinch-off voltage test is used for obtaining a pinch-off voltage value V of each point location in the plurality of point locations p ；
Assume that the current values of the weighting factor A and the weighting factor B are A 0 and B0 The weighting coefficient A and the weighting coefficient B are corrected according to the following specifications to obtain a corresponding correction value A 1 and B1 And using the corrected weighting coefficient A when growing the pHEMT device next time 1 And a weighting factor B 1 To calculate an evaluation function F i ：
Calculating a correlation coefficient between a pinch-off voltage absolute value array and the thickness and array, the pinch-off voltage absolute value array being pinch-off voltage values V obtained by measurement at the plurality of points p Is an array of absolute values of, the thickness sum array being the thickness sum T obtained from the measurements at the plurality of points n Formed into an array, if the correlation coefficient is less than-0.6
，
If the correlation coefficient is greater than 0.6, then->
，/>
If the absolute value of the correlation coefficient is less than or equal to 0.6, then->
，/>
, wherein ,a 1 represents the correction magnification of the weighting factor A, and 1<a 1 <1.5；a 2 Represents a modified reduction factor of the weighting factor A, and is 0.6<a 2 <1；b 1 Represents the correction magnification of the weighting factor B, and 1<b 1 <1.5；b 2 Represents a modified reduction factor of the weighting factor B, and is 0.6<b 2 <1。
Optionally, the correlation coefficient is a pearson correlation coefficient.
Optionally, the plurality of points are distributed along a radial direction passing through the center of the pHEMT epitaxial wafer, the radial direction being the following direction: when the pHEMT epitaxial wafer is positioned on the molecular beam epitaxial growth substrate support plate, the direction is determined by the connecting line of the center of the pHEMT epitaxial wafer and the center of the molecular beam epitaxial growth substrate support plate.
Optionally, the plurality of points includes a plurality of points equally spaced in a radial direction.
Optionally, the number of the plurality of point locations is 5.
Optionally, the substrate for growing the pHEMT device is a GaAs substrate, the lower planar doping layer and the upper planar doping layer are Si planar doping layers, the lower isolation layer and the upper isolation layer are AlGaAs isolation layers, and the channel layer is an InGaAs channel layer.
The beneficial effects of the invention include:
the molecular beam epitaxial growth process optimization method of the pHEMT device provided by the invention comprises the following steps: determining a rotation speed range of a sample frame rotation speed capable of being used for molecular beam epitaxial growth; within the range of rotation speedSelecting N rotation speeds R different from each other i ，R i In revolutions per minute, where i =1, 2, ·, N, and N is an integer greater than 5; for pHEMT devices and each selected rotation speed R i Calculating a corresponding evaluation function F i The value of (a) is,
, wherein ,T j representS j The absolute value of the difference with its nearest neighbor integer, <' > or>
，j=1, 2, 3, 4, 5，t 1 Represents the time required for the molecular beam epitaxial growth of the lower planar doping layer,t 2 showing the time required for the molecular beam epitaxial growth of the lower spacer layer,t 3 The time required for the molecular beam epitaxial growth of the channel layer,t 4 Represents the time required for the molecular beam epitaxial growth of the upper spacer layer, andt 5 represents the time required for the molecular beam epitaxial growth of the upper planar doping layer,t j in minutes, a and B are empirically determined weighting coefficients, a and B satisfying the following conditions: 0.3<A<3，0.3<B<3; the rotation speed corresponding to the minimum evaluation function value among the calculated evaluation function values is determined and is used as the rotation speed of the sample holder when the pHEMT device is epitaxially grown by using the molecular beam. According to the specific epitaxial layer structure of the target device, an evaluation function for the rotation speed of the sample frame is established, the evaluation function is associated with the uniformity of the doping concentration of the channel layer, the minimum value of the evaluation function is obtained through calculation aiming at the selectable rotation speed, the corresponding rotation speed of the sample frame can be quickly selected when the uniformity of the doping concentration of the channel layer is optimal, repeated tests are not needed, and time cost and material cost are greatly saved.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method for optimizing a molecular beam epitaxial growth process of a pHEMT device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a pHEMT device provided by an embodiment of the present invention;
fig. 3 is a schematic plan view of a growth chamber of a molecular beam epitaxy apparatus according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Compound semiconductor-based pseudomorphic high electron mobility transistor (pHEMT) devices are typically fabricated by molecular beam epitaxial growth, and the doping concentration of the channel layer of the pseudomorphic hemt device directly affects the pinch-off voltage of the device, which is a very important performance parameter of the pHEMT device. In the molecular beam epitaxial growth process of the pseudomorphic high electron mobility transistor device, the doping uniformity of the planar doping layer and the thickness uniformity of the isolation layer influence the doping concentration uniformity of the channel layer. Since the flow rates of molecular beams ejected from a source furnace (for example, a Si furnace) for providing a dopant and a source furnace (for example, a Ga furnace and an Al furnace) for providing a molecular beam required for an isolation layer are not uniformly distributed on a substrate support plate during the growth of an epitaxial layer in a molecular beam epitaxy apparatus, in order to improve the uniformity of an epitaxial wafer, a sample holder carrying the substrate support plate needs to be rotated at a constant speed during the growth of the epitaxial layer, so that the equivalent beam flow rates of various molecular beam sources actually reaching the substrate are relatively uniform over a period of time. However, in the prior art, in order to improve the uniformity of epitaxial wafer growth, the rotation speed of the sample holder can only be performed by multiple groping tests, which greatly increases the production test cost. It is therefore desirable to propose a molecular beam epitaxy process optimization method for pHEMT devices to enable a fast determination of the optimal rotation rate of the sample holder.
FIG. 1 is a schematic flow chart of a method for optimizing a molecular beam epitaxial growth process of a pHEMT device according to an embodiment of the present invention; fig. 2 shows a schematic structural diagram of a pHEMT device according to an embodiment of the present invention.
As shown in fig. 2, the pHEMT device according to the embodiment of the present invention includes a lower planar doping layer 202, a lower isolation layer 203, a channel layer 204, an upper isolation layer 205, and an upper planar doping layer 206, which are sequentially stacked from bottom to top. It should be understood that the structure of the pHEMT device may also include: a substrate 200, a buffer layer 201 between the substrate 200 and the lower planar doping layer 202, a schottky layer 207 above the upper planar doping layer 206. Although not shown in fig. 2, the structure of the pHEMT device may also include other structural layers associated with the device structure, such as cap layers and the like.
Alternatively, for example, in the case where the substrate 200 on which the pHEMT device is grown is a GaAs substrate, the lower planar doping layer 202 and the upper planar doping layer 206 may both be Si planar doping layers (planar doping layers with silicon as a dopant), the lower isolation layer 203 and the upper isolation layer 205 may both be AlGaAs isolation layers, and the channel layer 204 may be an InGaAs channel layer.
As shown in fig. 1, an embodiment of the present invention provides a method for optimizing a molecular beam epitaxy growth process of a pHEMT device, where the method includes:
and 101, determining a rotating speed range of the rotating speed of the sample holder capable of being used for molecular beam epitaxial growth.
For a certain molecular beam epitaxial growth apparatus, a rotation speed range of a rotation speed of the sample holder that can be used for molecular beam epitaxial growth can be empirically determined. The rotating speed of the sample frame is too low, so that the uniformity of the epitaxial wafer is difficult to improve; the rotating speed of the sample holder is too high, so that the substrate sheet slides in the substrate supporting plate easily in the molecular beam epitaxial growth process, and the surface quality of the epitaxial wafer is further deteriorated and even broken. Alternatively, for example, the range of rotational speeds of the sample holder rotational speed may be selected as: greater than or equal to 15 revolutions per minute and less than or equal to 35 revolutions per minute. For example, the sample holder rotation speed may take any integer number within the above range.
102, selecting N different rotating speeds R in the rotating speed range i 。
R i In revolutions per minute, where i =1, 2, ·, N, and N is an integer greater than 5.
Optionally, N rotation speeds R different from each other i Each of which is an integer. For example, in the speed range: when the number of revolutions R is 15 or more and 35 or less, N may be 21, for example, and N revolutions R i Can be as follows: 15 rpm, 16 rpm, 17 rpm, 18 rpm, 19 rpm, 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, 31 rpm, 32 rpm, 33 rpm, 34 rpm, 35 rpm.
Evaluation function F i The expression of (a) is as follows:
wherein ,T j to representS j The absolute value of the difference between the integer and its nearest neighbor,
，j=1, 2, 3, 4, 5，t 1 represents the time required for the molecular beam epitaxial growth of the lower planar doping layer,t 2 when it is necessary to form an isolation layer by molecular beam epitaxial growthA chamber,t 3 The time required for the molecular beam epitaxial growth of the channel layer,t 4 Represents the time required for the molecular beam epitaxial growth of the upper spacer layer, andt 5 represents the time required for the molecular beam epitaxial growth of the upper planar doping layer,t j in minutes, a and B are empirically determined weighting coefficients, a and B satisfying the following conditions: 0.3<A<3，0.3<B<3。
The meaning of the above evaluation function will be explained below.
Fig. 3 is a schematic plan view of a molecular beam epitaxy apparatus growth chamber provided by an embodiment of the present invention, in fig. 3, a substrate pallet 302 is carried by a sample holder in a chamber 301, and a source furnace 304 is located at the bottom circumference of the chamber 301, it should be understood that other source furnaces may be included at the bottom circumference of the chamber 301. For example, as shown in fig. 3, the substrate carrier 302 may simultaneously carry four substrates, e.g., a first substrate 331, a second substrate 332, a third substrate 333, a fourth substrate 334, it being understood that the substrate carrier 302 may also be a substrate carrier carrying other numbers and/or sizes of substrates.
For any source furnace, the beam current velocity is not uniform at different positions on the substrate support plate, and when the substrate support plate is static and does not rotate, the beam current velocity is larger at the position on the substrate support plate closer to the source furnace, so that the uniformity of the deposition rate at different positions on the substrate support plate can be improved by rotating the substrate support plate. Taking the Ga source furnace as an example, the deposition rates of Ga beams at different positions on the substrate supporting plate satisfy the following relation:
wherein VrRepresenting the Ga beam deposition rate, wherein alpha is a coefficient obtained by fitting growth rate data based on the whole substrate supporting plate, alpha is a fixed value and can be obtained by testing in advance for fixed molecular beam epitaxy equipment, the values of alpha can be considered to be equal for different source furnaces of the same equipment, r represents the distance from the center of the substrate supporting plate, theta represents an azimuth angle, and theta represents the distance from the center of the substrate supporting plate 1 Is based on Ga phase shift of the position of the source furnace, theta in the case of a fixed Ga source furnace position 1 Is a fixed value that can be obtained in advance. R is 0 Represents the rotation speed of the substrate pallet (i.e. the rotation speed of the sample holder) in revolutions per minute; t represents time in minutes; vr 0 Showing the center point O of the substrate supporting plate 1 The deposition rate at the location. By integrating the time t of the above relation, the deposition thickness distribution at different positions on the substrate support plate over a predetermined period of time can be obtained. For example, for the slave time t 1 To time t 2 The integral of the above relation is obtained from the time t 1 To time t 2 The deposition thickness of the Ga source furnace at different positions on the substrate supporting plate is as follows:
applying the trigonometric function and the product of difference formula to the above equation can be modified as:
as can be seen from the above formula, when
When the numerical value of (b) is equal to an integer, the above formula is further simplified to:
As can be seen from the above definition of the merit function,S j representing the number of sample holder rotations during growth of the corresponding layer, for j =1, 2, 3, 4, 5, ideally ifS j Exactly all are integers, thenT j Are all equal to zero, when the evaluation function F i Is the smallest and has a value of zero. In general, for j =1, 2, 3, 4, 5,S j in (a) there is a value which is not an integer, in which case it corresponds to
Is greater than zero, resulting in an evaluation function F i Is greater than zero. From the above analysis process, the evaluation function F i The smaller the value of (a), the better the corresponding device uniformity. The weighting coefficient a and the weighting coefficient B are empirically determined, the weighting coefficient a representing the influence of the upper and lower planar doping layers on the evaluation function value, and the weighting coefficient B representing the influence of the upper and lower isolation layers on the evaluation function value. For pHEMT devices of different configurations, the weighting coefficients a and B may be adjusted within the range of weighting coefficients a and B. For example, a = B =1, indicating that the planar doping layer and the spacer layer have the same effect on the evaluation function value; for example, a =0.5, b =1.5, indicating that the influence of the spacer layer on the evaluation function value is larger than the influence of the planar doping layer on the evaluation function value.
And 104, determining the rotating speed corresponding to the minimum evaluation function value in the calculated evaluation function values, and taking the rotating speed as the rotating speed of the sample holder when the pHEMT device is epitaxially grown by using the molecular beam.
For a particular pHEMT configuration, and optionally a plurality of rotation speeds, an evaluation function for each rotation speed may be calculated, and the rotation speed corresponding to the smallest evaluation function value is selected from the calculated evaluation function values, which, from the above analysis, results in a relatively better uniformity for the entire pHEMT device grown using this rotation speed.
In summary, according to the specific epitaxial layer structure of the target device, an evaluation function for the rotation speed of the sample holder is established, the evaluation function is associated with the uniformity of the doping concentration of the channel layer, and for the selectable rotation speed, the minimum value of the evaluation function is obtained through calculation, so that the corresponding rotation speed of the sample holder can be quickly selected when the uniformity of the doping concentration of the channel layer is optimal, repeated tests are not required, and the time cost and the material cost are greatly saved.
Alternatively, the coefficient a and the coefficient B may be further optimally modified by the following method. After a pHEMT device grows by using the determined rotation speed of the sample frame to obtain a pHEMT epitaxial wafer, selecting a plurality of point positions on the pHEMT epitaxial wafer, and respectively performing epitaxial layer thickness test and pinch-off voltage test on the plurality of point positions, wherein the epitaxial layer thickness test is used for obtaining the thickness of a lower isolation layer and an upper isolation layer at each point position in the plurality of point positions and the thickness of the T isolation layer n The pinch-off voltage test is used for obtaining the pinch-off voltage value V of each point position in the plurality of point positions p 。
Alternatively, as shown in fig. 3, said plurality of points are distributed along a radial direction passing through the center of said pHEMT epitaxial wafer, the radial direction being as follows: when the pHEMT epitaxial wafer is positioned on the molecular beam epitaxial growth substrate supporting plate, the central O of the pHEMT epitaxial wafer is arranged 2 With the center O of the molecular beam epitaxial growth substrate supporting plate 1 The direction determined by the lines (as indicated by the dashed lines on the epitaxial wafer formed by the first substrate 331 in fig. 3). Optionally, the plurality of point locations comprise radial squaresA plurality of points distributed at equal intervals. Optionally, the number of the plurality of point locations is 5.
Assume that the current values of the weighting factor A and the weighting factor B are A 0 and B0 The weighting coefficient A and the weighting coefficient B are corrected according to the following specifications to obtain a corresponding correction value A 1 and B1 And using the corrected weighting coefficient A when growing the pHEMT device next time 1 And a weighting factor B 1 To calculate an evaluation function F i ：
Calculating a correlation coefficient between the pinch-off voltage absolute value array and the thickness and array, optionally the correlation coefficient being a pearson correlation coefficient, the pinch-off voltage absolute value array being pinch-off voltage values V obtained from measurements at the plurality of points p Is an array of absolute values of, the thickness sum array being the thickness sum T obtained from the measurements at the plurality of points n Formed into an array, if the correlation coefficient is less than-0.6
，/>
If the correlation coefficient is greater than 0.6, then->
，
If the absolute value of the correlation coefficient is less than or equal to 0.6, then->
，/>
, wherein ,a 1 represents a correction magnification of the weighting factor A, and 1<a 1 <1.5；a 2 Represents a modified reduction factor of the weighting factor A, and is 0.6<a 2 <1；b 1 Represents the correction magnification of the weighting factor B, and 1<b 1 <1.5；b 2 Represents a modified reduction factor of the weighting factor B, and is 0.6<b 2 <1. Specifically, for example, the current values of the weighting coefficient a and the weighting coefficient B may be set to: a. The 0 =1，B 0 =1; if the correlation coefficient between the array of absolute values of pinch-off voltage and the array of thickness and pinch-off voltage obtained by the test is smaller than-0.6, the correlation between the absolute value of pinch-off voltage and the sum of thickness is shown and is negative correlation, the absolute value of pinch-off voltage is shown to be greatly influenced by the thickness and the absolute value of pinch-off voltage, and the influence of the nonuniformity of the isolation layer on the pinch-off voltage is larger at the moment, so that the influence of the isolation layer needs to be reduced, the contribution of the isolation layer in the evaluation function needs to be improved, and therefore, the value of the weighting coefficient A needs to be reduced and the value of the weighting coefficient B needs to be increased. If the correlation coefficient between the array of absolute values of pinch-off voltage and the array of thickness and pinch-off voltage obtained by the test is greater than 0.6, it indicates that the correlation exists between the absolute value of pinch-off voltage and the array of thickness and is a positive correlation, and at this time, it indicates that the influence of the nonuniformity of the isolation layer on the pinch-off voltage is small and the influence of the planar doping layer on the pinch-off voltage is large, so that the influence of the planar doping layer needs to be reduced, and therefore, the contribution of the planar doping layer in the evaluation function needs to be increased, and therefore, the value of the weighting coefficient a needs to be increased and the value of the weighting coefficient B needs to be reduced. If the absolute value of the correlation coefficient is less than or equal to 0.6, the absolute value of the pinch-off voltage and the thickness sum do not have correlation, the value of the weighting coefficient A can be subjected to fine adjustment at the moment, the weighting coefficient B is kept unchanged, the subsequent test result is further observed, and the weighting coefficient A and the weighting coefficient B are further optimized according to the subsequent test result.
The further optimization of the weighting coefficient A and the weighting coefficient B does not need an additional separate test process, and the optimization and correction of the weighting coefficient A and the weighting coefficient B can be realized only through the test data result in the normal batch production process. Therefore, through the correction process, the process is further optimized on the premise of not increasing extra cost.
The above-mentioned embodiments are only for illustrating the technical idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention, and all equivalent changes or modifications made according to the spirit of the present invention should be covered in the protection scope of the present invention.
Claims (10)
1. The molecular beam epitaxial growth process optimization method of the pHEMT device is characterized in that the structure of the pHEMT device comprises a lower plane doping layer, a lower isolation layer, a channel layer, an upper isolation layer and an upper plane doping layer which are sequentially stacked from bottom to top, and the method comprises the following steps:
determining a rotation speed range of a sample frame rotation speed capable of being used for molecular beam epitaxial growth;
selecting N rotation speeds R different from each other in the rotation speed range i ，R i In revolutions per minute, where i =1, 2, ·, N, and N is an integer greater than 5;
for the pHEMT device and each selected rotation speed R i Calculating a corresponding evaluation function F i The value of (a) is,
wherein ,T j to representS j The absolute value of the difference between the integer and its nearest neighbor,
，j=1, 2, 3, 4, 5，t 1 represents the time required for molecular beam epitaxial growth of the lower planar doping layer,t 2 represents the time required for the molecular beam epitaxial growth of the lower isolation layer,t 3 Represents the time required for the molecular beam epitaxial growth of the channel layer,t 4 Represents the time required for the molecular beam epitaxial growth of the upper isolation layer, andt 5 represents the time required for molecular beam epitaxial growth of the upper planar doping layer,t j in minutes, a and B are empirically determined weighting coefficients, a and B satisfying the following condition: 0.3<A<3，0.3<B<3；
And determining the rotating speed corresponding to the minimum evaluation function value in the calculated evaluation function values, and taking the rotating speed as the rotating speed of the sample holder when the pHEMT device is epitaxially grown by using the molecular beam.
2. The method for optimizing molecular beam epitaxial growth process of pHEMT device according to claim 1, wherein the rotation speed range is: greater than or equal to 15 revolutions per minute and less than or equal to 35 revolutions per minute.
3. Method for optimizing a molecular beam epitaxial growth process of a pHEMT device according to claim 2, characterized in that said N rotation speeds R, which are different from each other, are different from each other i The numerical value of each of the rotational speeds is an integer.
4. The method for optimizing a molecular beam epitaxial growth process of a pHEMT device according to claim 3, wherein N =21.
5. The method for optimizing a molecular beam epitaxy growth process of a pHEMT device according to claim 1, wherein after the pHEMT device is grown using the determined rotation speed of the sample holder to obtain a pHEMT epitaxial wafer, a plurality of point sites are selected on the pHEMT epitaxial wafer, and at the plurality of point sites, an epitaxial layer thickness test for obtaining the thickness of the lower isolation layer and the upper isolation layer and the thickness T of the upper isolation layer at each of the plurality of point sites and a pinch-off voltage test are performed, respectively n The pinch-off voltage test is used for acquiring a pinch-off voltage value V of each point location in the plurality of point locations p ；
Assume that the current values of the weighting factor A and the weighting factor B are A 0 and B0 The weighting coefficient A and the weighting coefficient B are corrected according to the following specifications to obtain a corresponding correction value A 1 and B1 And using the modified weighting coefficient A when growing the pHEMT device next time 1 And a weighting factor B 1 To calculate an evaluation function F i ：
Calculating a correlation coefficient between a pinch-off voltage absolute value array and a thickness and array, the pinch-off voltage absolute value array being pinch-off voltage values V obtained by measurement at the plurality of points p Is an array of absolute values of, the thickness sum array being a thickness sum T obtained from measurements at the plurality of point locations n Formed array, if the correlation coefficient is less than-0.6
，
If the correlation coefficient is greater than 0.6, then
，
If the absolute value of the correlation coefficient is less than or equal to 0.6, then
，
, wherein ,a 1 represents the correction magnification of the weighting factor A, and 1<a 1 <1.5；a 2 Represents a modified reduction factor of the weighting factor A, and is 0.6<a 2 <1；b 1 Represents the correction magnification of the weighting factor B, and 1<b 1 <1.5；b 2 Represents a modified reduction factor of the weighting factor B, and is 0.6<b 2 <1。
6. The method for optimizing a molecular beam epitaxial growth process of a pHEMT device according to claim 5, wherein the correlation coefficient is a pearson correlation coefficient.
7. The method for optimizing a molecular beam epitaxial growth process for pHEMT devices according to claim 5, wherein the plurality of spots are distributed along a radial direction passing through the center of the pHEMT epitaxial wafer, the radial direction being the following direction: and when the pHEMT epitaxial wafer is positioned on the molecular beam epitaxial growth substrate supporting plate, determining the direction determined by a connecting line of the center of the pHEMT epitaxial wafer and the center of the molecular beam epitaxial growth substrate supporting plate.
8. The method for optimizing a molecular beam epitaxial growth process for a pHEMT device according to claim 7, wherein the plurality of dots comprises a plurality of dots that are equally spaced along the radial direction.
9. The method for optimizing a molecular beam epitaxy process for a pHEMT device according to claim 8, wherein the number of sites of the plurality of sites is 5.
10. The optimized molecular beam epitaxy process of pHEMT device according to claim 1, wherein the substrate on which the pHEMT device is grown is a GaAs substrate, the lower planar doping layer and the upper planar doping layer are both Si planar doping layers, the lower isolation layer and the upper isolation layer are both AlGaAs isolation layers, and the channel layer is an InGaAs channel layer.
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