CN115838966B - Molecular beam epitaxial growth process optimization method of pHEMT device - Google Patents
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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 rotating speed range of a rotating speed of a sample rack capable of being used for molecular beam epitaxial growth; selecting N rotational speeds R different from each other in rotational speed range i The method comprises the steps of carrying out a first treatment on the surface of the For pHEMT device and each rotating speed R i Calculating the value of the corresponding evaluation function; and determining the rotating speed corresponding to the smallest evaluation function value in the calculated evaluation function values, and taking the rotating speed as the rotating speed of the sample frame when the pHEMT device is grown by using molecular beam epitaxy. According to the epitaxial layer structure of the target device, an evaluation function aiming at the rotation speed of the sample frame is established, the evaluation function is related to the uniformity of the doping concentration of the channel layer, and the minimum value of the evaluation function is obtained by calculation aiming at the optional rotation speed, so that the rotation speed of the sample frame corresponding to the optimal doping uniformity of the channel layer can be rapidly selected, 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 typically carried simultaneously on one substrate carrier for mass molecular beam epitaxy, thereby improving production efficiency and reducing production costs. In this case, the in-chip uniformity of the epitaxial layer on the substrate sheet and the uniformity between sheets are a key index 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 typically employ molecular beam epitaxy to produce their epitaxial wafers, and the doping concentration of the channel layer of the pseudomorphic high electron mobility transistor 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 pseudo-high electron mobility transistor device, the doping uniformity of the planar doping layer and the thickness uniformity of the isolation layer can influence the doping concentration uniformity of the channel layer. Since the flow rates of the molecular beams ejected from the source furnace (e.g., si furnace) providing the dopant and the source furnace (e.g., ga furnace and Al furnace) providing the molecular beams required for the spacer layer are not uniformly distributed on the substrate carrier during the growth of the epitaxial layer in the molecular beam epitaxy apparatus, it is necessary to uniformly rotate the sample holder carrying the substrate carrier during the growth of the epitaxial layer in order to improve the uniformity of the epitaxial wafer, so that the equivalent beam flow rates of the various molecular beam sources actually reaching the substrate over a period of time are relatively uniform.
However, in the prior art, in order to improve the uniformity of epitaxial wafer growth, the rotation speed of the sample holder rotation can only be carried out by means of multiple fumbling tests, thereby greatly increasing the production test cost.
Disclosure of Invention
The invention aims to provide an optimization method of a molecular beam epitaxial growth process of a pHEMT device to solve the problem of optimization of the uniformity of the molecular beam epitaxial growth of the pHEMT device.
In order to achieve the above 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, which comprises a lower plane doped layer, a lower isolation layer, a channel layer, an upper isolation layer and an upper plane doped layer which are sequentially stacked from bottom to top, wherein the method comprises the following steps:
determining a rotating speed range of a rotating speed of a sample rack capable of being used for molecular beam epitaxial growth;
selecting N rotational speeds R different from each other in rotational speed range i ，R i In revolutions per minute, wherein i=1, 2,..n, and N is an integer greater than 5;
for each selected rotational speed R for pHEMT devices i Calculate the corresponding evaluation function F i Is used as a reference to the value of (a),
wherein ,T j representation ofS j The absolute value of the difference from its nearest neighbor integer,
，j=1, 2, 3, 4, 5，t 1 representing the time required for the epitaxial growth of the lower planar doped layer of the molecular beam,t 2 represents the time required for the isolation layer under the epitaxial growth of the molecular beam,t 3 Represents the time required for the epitaxial growth of the channel layer by the molecular beam,t 4 Representing the time required for molecular beam epitaxy to grow an upper spacert 5 Representing the time required for the epitaxial growth of the upper planar doped layer of the molecular beam,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；
And determining the rotating speed corresponding to the smallest evaluation function value in the calculated evaluation function values, and taking the rotating speed as the rotating speed of the sample frame when the pHEMT device is grown by using molecular beam epitaxy.
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 rotational speeds R different from each other i The number of each rotation speed is an integer.
Alternatively, n=21.
Optionally, after growing the pHEMT device using the determined sample holder rotational speed to obtain a pHEMT epitaxial wafer, selecting a plurality of sites on the pHEMT epitaxial wafer at which an epitaxial layer thickness test and a pinch-off voltage test are respectively performed, the epitaxial layer thickness test being used to obtain a thickness sum T of the lower and upper isolation layers at each of the plurality of sites n The pinch-off voltage test is used for obtaining the pinch-off voltage value at each of the plurality of pointsV p ；
Assuming that the current values of the weighting coefficients A and B are A 0 and B0 The weighting coefficients A and B are corrected according to the following specification to obtain corresponding correction value A 1 and B1 And the corrected weighting coefficient A is utilized in the next growth of pHEMT devices 1 And weighting coefficient B 1 To calculate the evaluation function F i ：
Calculating a correlation coefficient between the pinch-off voltage absolute value array, which is a pinch-off voltage value V obtained by measurement at the plurality of points, and the thickness and the array p An array of absolute values of thickness and array of thickness and T obtained from measurements at said plurality of points n An array is formed, if the correlation coefficient is smaller 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 representing the modified 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 0.6<a 2 <1；b 1 Representing the modified 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 0.6<b 2 <1。
Optionally, the correlation coefficient is a pearson correlation coefficient.
Optionally, the plurality of dots are distributed along a radial direction passing through a center of the pHEMT epitaxial wafer, and the radial direction is as follows: when the pHEMT epitaxial wafer is positioned on the molecular beam epitaxial growth substrate support plate, the direction is determined by the line connecting the center of the pHEMT epitaxial wafer and the center of the molecular beam epitaxial growth substrate support plate.
Optionally, the plurality of points comprises a plurality of points equally spaced in a radial direction.
Optionally, the number of the plurality of points is 5.
Optionally, the substrate for growing the pHEMT device is a GaAs substrate, the lower planar doped layer and the upper planar doped layer are both Si planar doped layers, the lower isolation layer and the upper isolation layer are both 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 rotating speed range of a rotating speed of a sample rack capable of being used for molecular beam epitaxial growth; selecting N rotational speeds R different from each other in rotational speed range i ，R i In revolutions per minute, wherein i=1, 2,..n, and N is an integer greater than 5; for each selected rotational speed R for pHEMT devices i Calculate the corresponding evaluation function F i Is used as a reference to the value of (a),
, wherein ,T j representation ofS j Absolute value of difference between the integer nearest to it, < ->
，j=1, 2, 3, 4, 5，t 1 Representing the time required for the epitaxial growth of the lower planar doped layer of the molecular beam,t 2 represents the time required for the isolation layer under the epitaxial growth of the molecular beam,t 3 Represents the time required for the epitaxial growth of the channel layer by the molecular beam,t 4 Representing the time required for molecular beam epitaxy to grow an upper spacert 5 Representing the time required for the epitaxial growth of the upper planar doped layer of the molecular beam,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, a step of; and determining the rotating speed corresponding to the smallest evaluation function value in the calculated evaluation function values, and taking the rotating speed as the rotating speed of the sample frame when the pHEMT device is grown by using molecular beam epitaxy. According to the specific epitaxial layer structure of the target device, an evaluation function aiming at the rotation speed of the sample frame is established, the evaluation function is related to the uniformity of the doping concentration of the channel layer, and the minimum value of the evaluation function is obtained by calculation aiming at the optional rotation speed, so that the rotation speed of the sample frame corresponding to the optimal uniformity of the doping concentration of the channel layer can be rapidly selected, repeated tests are not needed, and time cost and material cost are greatly saved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows a schematic flow chart of a molecular beam epitaxial growth process optimization method of a pHEMT device provided by an embodiment of the present invention;
fig. 2 shows a schematic structural 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 following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Compound semiconductor-based pseudomorphic high electron mobility transistor (pHEMT) devices typically employ molecular beam epitaxy to produce their epitaxial wafers, and the doping concentration of the channel layer of the pseudomorphic high electron mobility transistor 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 pseudo-high electron mobility transistor device, the doping uniformity of the planar doping layer and the thickness uniformity of the isolation layer can influence the doping concentration uniformity of the channel layer. Since the flow rates of the molecular beams ejected from the source furnace (e.g., si furnace) providing the dopant and the source furnace (e.g., ga furnace and Al furnace) providing the molecular beams required for the spacer layer are not uniformly distributed on the substrate carrier during the growth of the epitaxial layer in the molecular beam epitaxy apparatus, it is necessary to uniformly rotate the sample holder carrying the substrate carrier during the growth of the epitaxial layer in order to improve the uniformity of the epitaxial wafer, so that the equivalent beam flow rates of the various molecular beam sources actually reaching the substrate over a period of time are relatively uniform. However, in the prior art, in order to improve the uniformity of epitaxial wafer growth, the rotation speed of the sample holder rotation can only be carried out by means of multiple fumbling tests, thereby greatly increasing the production test cost. It is therefore desirable to propose a molecular beam epitaxial growth process optimization method for pHEMT devices to achieve a fast determination of the optimal rotation rate of the sample holder.
Fig. 1 shows a schematic flow chart of a molecular beam epitaxial growth process optimization method of a pHEMT device provided by an embodiment of the present invention; fig. 2 shows a schematic structural diagram of a pHEMT device provided by an embodiment of the present invention.
As shown in fig. 2, the structure of the pHEMT device provided by the embodiment of the present invention includes a lower planar doped layer 202, a lower isolation layer 203, a channel layer 204, an upper isolation layer 205, and an upper planar doped layer 206, which are sequentially stacked from bottom to top. It should be appreciated that the structure of the pHEMT device may also include: a substrate 200, a buffer layer 201 between the substrate 200 and a lower planar doped layer 202, a schottky layer 207 above an upper planar doped 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 capping 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 each be a Si planar doping layer (planar doping layer of silicon as a dopant), the lower isolation layer 203 and the upper isolation layer 205 may each be an AlGaAs isolation layer, 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 epitaxial growth process of a pHEMT device, including:
For a determined molecular beam epitaxy apparatus, a range of rotational speeds of the sample holder rotational speeds that can be used for molecular beam epitaxy can be empirically determined. The rotating speed of the sample rack is too small, so that the uniformity of the epitaxial wafer is difficult to improve; the excessive rotation speed of the sample rack easily causes the substrate slice to slide in the substrate supporting plate in the molecular beam epitaxial growth process, so that the surface quality of the epitaxial slice is degraded and even broken. Alternatively, for example, the rotational speed range 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 rotational speed may take on any integer rotational speed 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 rotational speeds R different from each other i The number of each rotation speed is an integer. For example, in the rotational speed range: in the case of 15 rpm or more and 35 rpm or less, N may be, for example, 21, and N rotational speeds R i The method comprises the following steps: 15 rpm, 16 rpm, 17 rpm18 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 (2) is as follows:
wherein ,T j representation ofS j The absolute value of the difference from its nearest neighbor integer,
，j=1, 2, 3, 4, 5，t 1 representing the time required for the epitaxial growth of the lower planar doped layer of the molecular beam,t 2 represents the time required for the isolation layer under the epitaxial growth of the molecular beam,t 3 Represents the time required for the epitaxial growth of the channel layer by the molecular beam,t 4 Representing the time required for molecular beam epitaxy to grow an upper spacert 5 Representing the time required for the epitaxial growth of the upper planar doped layer of the molecular beam,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-described evaluation function will be explained below.
Fig. 3 shows a schematic plan view of a growth chamber of a molecular beam epitaxy apparatus according to an embodiment of the present invention, in fig. 3, a substrate carrier 302 is carried by a sample holder in a chamber 301, and a source furnace 304 is located at a bottom circumference of the chamber 301, and 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 carry four substrates simultaneously, 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 rate is non-uniform at different locations on the substrate support plate, and when the substrate support plate is stationary, the beam current rate is greater at locations on the substrate support plate closer to the source furnace, thus, uniformity of deposition rates at different locations on the substrate support plate can be improved by rotating the substrate support plate. Taking a Ga source furnace as an example, ga beam deposition rates at different positions on a substrate supporting plate satisfy the following relation:
wherein VrRepresenting Ga beam deposition rate, alpha is a coefficient obtained by fitting based on the whole substrate support plate growth rate data, alpha is a fixed value and can be obtained by pre-testing for a fixed molecular beam epitaxy apparatus, and for different source furnaces of the same apparatus, the values of alpha can be considered to be equal, r represents distance from the center of the substrate support plate, θ represents azimuth angle, θ 1 Representing the phase shift based on the Ga source furnace position, θ in the case of Ga source furnace position determination 1 Is a fixed value that can be obtained in advance. R is R 0 Indicating the rotational speed of the substrate support (i.e., the rotational speed of the sample holder) in revolutions per minute; t represents time in minutes; vr (Vr) 0 Representing the center point O of the substrate pallet 1 Deposition rate at the location. Integrating the time t for the above relationship can obtain the deposition thickness profile at different locations on the substrate support plate over a predetermined period of time. For example, for slave time t 1 To time t 2 The time period between the two times is integrated by the relation, and the time t is obtained 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 trigonometric functions and the product of difference formula to the above can be modified as:
as can be seen from the above, when
When the value of (2) is equal to an integer, the above is further simplified to:
As can be seen from the above definition of the evaluation function,S j representing the number of rotations of the sample holder during growth of the corresponding layer, for j=1, 2, 3, 4, 5, ideally ifS j Just are integers, thenT j Are all equal to zero, at this time, the evaluation function F i Is the smallest and has a value of zero. Typically, for j=1, 2, 3, 4, 5,S j there is a value other than an integer, at this time corresponding to
The value of (2) is greater than zero, which in turn results in an evaluation function F i Is greater than zero. From the above analysis, the evaluation function F i The smaller the value of (c), the better the corresponding device uniformity. The weighting coefficient A and the weighting coefficient B are determined empirically, wherein the weighting coefficient A represents the influence of the upper and lower plane doping layers on the evaluation function value, and the weighting coefficient B represents the influence of the upper and lower isolation layers on the evaluation function value. For pHEMT devices of different structures, 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 isolation layer have the same influence on the evaluation function value; for example, a=0.5 and b=1.5 indicate that the influence of the isolation layer on the evaluation function value is greater 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 frame when the pHEMT device is grown by using molecular beam epitaxy.
For a specific pHEMT structure, and optionally a plurality of rotational speeds, an evaluation function for each rotational speed may be calculated, and the rotational speed corresponding to the smallest evaluation function value is selected from the calculated evaluation function values, with which the overall pHEMT device is grown with relatively better uniformity, as can be seen from the above analysis.
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 the minimum value of the evaluation function is obtained by calculation for the optional rotation speed, so that the rotation speed of the sample holder corresponding to the optimal uniformity of the doping concentration of the channel layer can be rapidly selected, multiple repeated tests are not required, and the time cost and the material cost are greatly saved.
Alternatively, the coefficients a and B may be further optimally corrected by the following method. After growing pHEMT devices using the determined sample holder rotational speed to obtain pHEMT epitaxial wafers, selecting a plurality of sites on the pHEMT epitaxial wafers at which an epitaxial layer thickness test and a pinch-off voltage test are respectively performed, the epitaxial layer thickness test being used to obtain thicknesses and T of the lower and upper isolation layers at each of the plurality of sites n Pinch-off voltage test for obtaining pinch-off voltage value V at each of the plurality of points p 。
Optionally, as shown in fig. 3, the plurality of dots are distributed along a radial direction passing through a center of the pHEMT epitaxial wafer, and the radial direction is as follows: when the pHEMT epitaxial wafer is positioned on the molecular beam epitaxial growth substrate supporting plate, the center O of the pHEMT epitaxial wafer 2 Center O of substrate carrier for epitaxial growth with molecular beam 1 The direction in which the lines are routed (as indicated by the dashed lines on the epitaxial wafer formed by the first substrate 331 in fig. 3). Optionally, the plurality of points comprises a plurality of points equally spaced in a radial direction. Optionally, the number of the plurality of points is 5.
Assuming that the current values of the weighting coefficients A and B are A 0 and B0 The weighting coefficients A and B are corrected according to the following specification to obtain corresponding correction value A 1 and B1 And the corrected weighting coefficient A is utilized in the next growth of pHEMT devices 1 And weighting coefficient B 1 To calculate the evaluation function F i ：
Calculating a correlation coefficient between an array of pinch-off voltage absolute values, and a thickness and array, optionally the correlation coefficient being a pearson correlation coefficient, the array of pinch-off voltage absolute values being pinch-off voltage values V obtained by measurements at the plurality of points p An array of absolute values of thickness and array of thickness and T obtained from measurements at said plurality of points n An array is formed, if the correlation coefficient is smaller 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 representing the modified 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 0.6<a 2 <1；b 1 Representing the modified 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 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 is that 0 =1，B 0 =1; if the correlation coefficient between the array of absolute values of pinch-off voltage obtained by the test and the thickness and array is less than-0.6, it is indicated that there is a correlation between the absolute values of pinch-off voltage and the sum of thickness and is a negative correlation, it is indicated that the absolute values of thickness and the pinch-off voltage are affected more greatly, and at this time the influence of the non-uniformity of the isolation layer on the pinch-off voltage is greater, and therefore, the influence of the isolation layer needs to be reduced, and therefore, the contribution of the isolation layer needs to be increased in the evaluation function, 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 the absolute value of the pinch-off voltage and the thickness and the array obtained by the test is larger than 0.6, the correlation between the absolute value of the pinch-off voltage and the thickness and the array is shown to exist, and the correlation is positive, and the influence of the non-uniformity of the isolation layer on the pinch-off voltage is shownThe effect of the planar doped layer on the pinch-off voltage is small and therefore needs to be reduced, and therefore the contribution of the planar doped 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 decreased. If the absolute value of the correlation coefficient is less than or equal to 0.6, it is indicated that there is no correlation between the absolute value of the pinch-off voltage and the sum of thicknesses, at this time, the value of the weighting coefficient a can be finely tuned while the weighting coefficient B is kept unchanged, further observation of the subsequent test results is performed, and further optimization of the weighting coefficient a and the weighting coefficient B is performed according to the subsequent test results.
The above further optimization of the weighting coefficient a and the weighting coefficient B does not require an additional separate test process, but can realize the optimization correction of the weighting coefficient a and the weighting coefficient B only by the test data result in the normal mass production process. Therefore, through the correction process, further optimization of the process is realized without adding extra cost.
The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, but not limit the scope of the present invention, and all equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of the present invention.
Claims (8)
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 planar doping layer, a lower isolation layer, a channel layer, an upper isolation layer and an upper planar doping layer which are sequentially stacked from bottom to top, and the method comprises the following steps:
determining a rotating speed range of a rotating speed of a sample rack capable of being used for molecular beam epitaxial growth;
selecting N rotational speeds R different from each other within the rotational speed range i ，R i In revolutions per minute, wherein i=1, 2,..n, and N is an integer greater than 5;
for the pHEMT device and each selected rotational speed R i Calculate the correspondenceIs a function of the evaluation F of (2) i Is used as a reference to the value of (a),
wherein ,T j representation ofS j The absolute value of the difference from its nearest neighbor integer,
，j=1, 2, 3, 4, 5，t 1 representing the time required for the molecular beam epitaxy to grow the lower planar doped layer,t 2 represents the time required for molecular beam epitaxy to grow the lower isolation layer,t 3 Represents the time required for the molecular beam epitaxy of the channel layer,t 4 Representing the time required for molecular beam epitaxy to grow the upper spacert 5 Representing the time required for the molecular beam epitaxy to grow the upper planar doped 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；
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 a sample frame when the pHEMT device is epitaxially grown by using a molecular beam;
after growing the pHEMT device using the determined sample holder rotational speed to obtain a pHEMT epitaxial wafer, selecting a plurality of sites on the pHEMT epitaxial wafer at which an epitaxial layer thickness test and a pinch-off voltage test are respectively performed, the epitaxial layer thickness test being used to obtain thicknesses and T of a lower isolation layer and an upper isolation layer at each of the plurality of sites n The pinch-off voltage test is used for obtaining the pinch-off voltage value V at each of the plurality of points p ；
Assuming that the current values of the weighting coefficients A and B are A 0 and B0 The weighting coefficients A and B are corrected according to the following specification to obtain corresponding correction value A 1 and B1 And the corrected weighting factor A is used in the next growth of the pHEMT device 1 And weighting coefficient B 1 To calculate the evaluation function F i ：
Calculating a correlation coefficient between an array of pinch-off voltage absolute values, which is a pinch-off voltage value V obtained by measurement at the plurality of points, and a thickness and array p An array of absolute values of the thickness and the array is a thickness sum T obtained by measurement at the plurality of points n An array of components, 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 representing the modified 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 0.6<a 2 <1；b 1 Representing the modified 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 0.6<b 2 <1；
The correlation coefficient is a pearson correlation coefficient.
2. The method for optimizing a molecular beam epitaxial growth process of a pHEMT device according to claim 1, wherein the rotational speed range is: greater than or equal to 15 revolutions per minute and less than or equal to 35 revolutions per minute.
3. The method for optimizing molecular beam epitaxy growth process of pHEMT device according to claim 2, wherein said N rotational speeds R are different from each other i The number of each rotation speed is an integer.
4. A method of optimizing a molecular beam epitaxial growth process of a pHEMT device according to claim 3, characterised in that n=21.
5. The method of optimizing a molecular beam epitaxial growth process of a pHEMT device according to claim 1, wherein the plurality of spots are distributed along a radial direction passing through a center of the pHEMT epitaxial wafer, the radial direction being a direction of: and when the pHEMT epitaxial wafer is positioned on the molecular beam epitaxial growth substrate supporting plate, determining the direction by connecting the center of the pHEMT epitaxial wafer with the center of the molecular beam epitaxial growth substrate supporting plate.
6. The method of optimizing a molecular beam epitaxy growth process of a pHEMT device according to claim 5, wherein said plurality of spots includes a plurality of spots equally spaced along said radial direction.
7. The method of optimizing a molecular beam epitaxy growth process of a pHEMT device according to claim 6, wherein a number of said plurality of sites is 5.
8. The optimization method of molecular beam epitaxial growth process of pHEMT device according to claim 1, wherein the substrate on which said pHEMT device is grown is a GaAs substrate, said lower planar doped layer and said upper planar doped layer are Si planar doped layers, said lower isolation layer and said upper isolation layer are AlGaAs isolation layers, and said channel layer is an InGaAs channel layer.
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