A method for optimizing a molecular beam epitaxy variable composition epitaxy process

Abstract

The application provides a molecular beam epitaxy variable composition epitaxy process optimization method, and relates to the technical field of semiconductor manufacturing. The method comprises the following steps: stabilizing the temperature of an indium source furnace to a first temperature and stabilizing the temperature of a gallium source furnace to a second temperature; lowering the temperature of the gallium source furnace to a third temperature in a step mode and synchronously starting to grow an epitaxial layer; testing and obtaining the actual thickness and actual surface composition of the epitaxial layer, calculating and determining a fourth temperature of the indium source furnace, linearly changing the temperature of the indium source furnace from the first temperature to the fourth temperature in the next growth, correcting the actual thickness h0 to h1, and then optimizing the growth time and the length of the interruption time according to the difference between h1 and a preset thickness h. The application optimizes the temperature of the indium source furnace by testing the surface In composition, corrects the thickness of the epitaxial layer obtained by testing, adjusts and optimizes the growth time and the interruption time, adjusts the actual growth thickness, and realizes accurate control of the composition and thickness of the variable composition epitaxial layer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically to an optimization method for molecular beam epitaxy variable composition epitaxy process. Background Technology

[0002] For InP-based high-speed HBT devices, to reduce specific contact resistance and improve high-frequency performance, the surface of the HBT device typically employs an InGaAs ohmic contact layer with an In composition greater than 0.7. However, the In composition of InGaAs, which matches the InP lattice, is 0.53. When the In composition exceeds 0.7, severe lattice mismatch occurs. A thin contact layer with a thickness of less than 30 nm can be used, utilizing strain relaxation to suppress dislocation propagation into the base region. Stress can be released by designing the thin contact layer with the In composition increasing from 0.53 to 0.7.

[0003] When growing thin contact layers with increasing composition using molecular beam epitaxy, the In composition can be increased by simultaneously growing the InGaAs layer while lowering the temperature of the gallium source furnace (i.e., reducing the gallium beam current rate). However, it is difficult to precisely control the thickness of the InGaAs layer grown during temperature variation using only the gallium beam current rate calibrated under conventional fixed temperature conditions. This is because when there is a large amount of material in the gallium source furnace, the actual cooling rate of the gallium material is slow under zero heating power, resulting in a thicker InGaAs layer; conversely, when there is a small amount of material in the gallium source furnace, the actual cooling rate is fast under zero heating power, resulting in a thinner InGaAs layer. In molecular beam epitaxy (MBE) equipment, the gallium raw material in the gallium source furnace decreases slowly over the long term as it is used and consumed. Therefore, at different times of the equipment (difference of several weeks or months), when the gallium source furnace is lowered to the same temperature at zero heating power, the thickness of the variable composition InGaAs layer grown for the same time is usually different, and the In composition on the surface of the variable composition InGaAs layer may also be different.

[0004] To ensure that the thickness of the variable composition InGaAs thin layer and the In composition on the upper surface are equal to or approximately equal to the preset values, the growth process of the variable composition InGaAs epitaxial layer needs to be optimized. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by providing an optimization method for the variable composition epitaxy process of molecular beam epitaxy, so as to solve the problem of precise control of the growth thickness and the In composition of the upper surface of variable composition InGaAs thin films.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides an optimization method for molecular beam epitaxy variable composition epitaxy processes, which is used to optimize In x Ga 1-x As the growth process of the epitaxial layer, In x Ga 1-x The thickness of the As epitaxial layer is a preset thickness h, where h ≤ 20 nm, and the composition x is derived from In. x Ga 1-x The composition of the As epitaxial layer increases from 0.53 on the lower surface to x on the upper surface. h x h >0.7, the method includes: The temperature of the indium source furnace is stabilized at a first temperature, and the temperature of the gallium source furnace is stabilized at a second temperature. The first and second temperatures correspond to the composition x equal to 0.53. The temperature of the gallium source furnace is gradually reduced to a preset third temperature. Simultaneously with the cooling of the gallium source furnace, In metal growth begins. x Ga 1-x As the epitaxial layer, the first and third temperatures are equal to the composition x. h Correspondingly, in the growth In x Ga 1- x The process of creating the As epitaxial layer includes multiple alternating growth and interruption times; Test to obtain the grown In x Ga 1-x As the actual thickness h0 and actual surface composition x of the epitaxial layer h0 According to x h0 The calculation determined that the surface composition reached x. h The fourth temperature required for the indium source furnace, and during the next growth, in In x Ga 1- x Throughout the growth process of the epitaxial layer, the temperature of the indium source furnace linearly changes from a first temperature to a fourth temperature. Based on the impact of the indium source furnace temperature change on the epitaxial layer thickness, the actual thickness h0 is corrected to h1. Then, based on the difference between h1 and the preset thickness h, the growth time and interruption time for the next growth cycle are adjusted. During this adjustment, the growth of In... x Ga 1-x The total time for the process of creating the epitaxial layer remains constant.

[0007] Optionally, the indium beam current rate V corresponding to the first temperature In1 The value range is 0.2 micrometers / hour ≤ V In1 ≤0.5 micrometers / hour.

[0008] Optionally, based on the effect of the temperature change of the indium source furnace on the epitaxial layer thickness, the actual thickness h0 is corrected to h1, specifically including: calculating the average beam current rate V. In =(V In1 +V In4 ) / 2, V In4 This represents the beam rate of indium at the fourth temperature, where [(0.53+x h0 ) / (0.53+x h )×V In / V In1 ]×h0 is used as h1.

[0009] Optionally, the preset thickness h ranges from 10 nm to 15 nm.

[0010] Optionally, x h The range is 0.7 <x h <0.9.

[0011] Optionally, the multiple alternating growth times and interruption times specifically include the following stages in sequence: the first growth time, the first interruption time, the second growth time, the second interruption time, ..., the m-th growth time, the m-th interruption time, and the (m+1)-th growth time, where m is an integer greater than or equal to 3, and the i-th growth time t i t is obtained by calculation as follows: i =b / V i V i =V In1 / x i x i =0.53+(x h -0.53) / (m+1)×(i-1), b=h / (m+1), i=1, 2, …, m+1, the j-th interruption time s j =a×t j , j=1, 2, …, m, a is an empirical coefficient.

[0012] Optionally, m is less than or equal to 7.

[0013] Optionally, the growth time and interruption time for the next growth cycle are adjusted based on the difference between h1 and the preset thickness h. Specifically, this includes adjusting the i-th growth time t. i =h / h1×t i According to t i 'and t i The interruption time adjacent to the i-th growth time is adjusted accordingly to ensure that growth In x Ga 1-x The total time for the process of creating the epitaxial layer remains constant.

[0014] Optionally, if the adjusted first growth time or the adjusted (m+1)th growth time changes compared to before the adjustment, the total time is kept constant by adjusting the corresponding adjacent first or mth interruption time; if the adjusted kth growth time changes compared to before the adjustment, the increase is assumed to be Δt. k If k = 2, 3, …, m, then the (k-1)th interrupt time and the kth interrupt time are reduced by Δt respectively. k / 2, so that the total time remains unchanged.

[0015] The beneficial effects of this invention include: The molecular beam epitaxy variable composition epitaxy process optimization method provided by this invention is used to optimize In x Ga 1-x As the growth process of the epitaxial layer, In x Ga 1-x The thickness of the As epitaxial layer is a preset thickness h, where h ≤ 20 nm, and the composition x is derived from In. x Ga 1-x The composition of the As epitaxial layer increases from 0.53 on the lower surface to x on the upper surface. h x h >0.7, the method includes: stabilizing the temperature of the indium source furnace to a first temperature, stabilizing the temperature of the gallium source furnace to a second temperature, the first and second temperatures corresponding to a composition x equal to 0.53; decreasing the temperature of the gallium source furnace to a preset third temperature in a stepwise manner, and simultaneously starting In growth while the gallium source furnace begins to decrease in temperature. x Ga 1-x As the epitaxial layer, the first and third temperatures are equal to the composition x. h Correspondingly, in the growth In x Ga 1-x The process of creating the As epitaxial layer includes multiple alternating growth and interruption times; the grown In is tested and obtained. x Ga 1-x As the actual thickness h0 and actual surface composition x of the epitaxial layer h0 According to x h0 The calculation determined that the surface composition reached x. h The fourth temperature required for the indium source furnace, and during the next growth, in In x Ga 1-x Throughout the growth process of the epitaxial layer, the temperature of the indium source furnace linearly changes from a first temperature to a fourth temperature. Based on the impact of the indium source furnace temperature change on the epitaxial layer thickness, the actual thickness h0 is corrected to h1. Then, based on the difference between h1 and the preset thickness h, the growth time and interruption time for the next growth cycle are adjusted. During this adjustment, the growth of In... x Ga 1-xThe total time for the As epitaxial layer process remains constant. This application optimizes the temperature of the indium source furnace based on the In composition of the InGaAs epitaxial layer surface obtained from testing, then corrects the epitaxial layer thickness obtained from testing based on the optimized indium source furnace temperature, and further adjusts the growth time and interruption time according to the corrected thickness to adjust the actual growth thickness, thereby achieving precise control of the composition and thickness of the variable composition epitaxial layer. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating the optimization method for molecular beam epitaxy variable composition epitaxy provided in an embodiment of the present invention is shown. Figure 2 A schematic diagram of a variable component epitaxial structure provided in an embodiment of the present invention is shown; Figure 3 This diagram illustrates the change of gallium molecular beam rate over time according to an embodiment of the present invention. Figure 4 This diagram illustrates the change in the switching state of the source furnace baffle over time, as provided in an embodiment of the present invention. Figure 5 A schematic diagram of the composition variation curve of the variable composition epitaxial layer provided in an embodiment of the present invention is shown. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] To ensure that the thickness and In composition of the variable-component InGaAs thin layer are equal to or approximately equal to preset values, the growth process of the variable-component InGaAs epitaxial layer needs to be optimized. This application provides an optimization method for the variable-component molecular beam epitaxy process to solve the problem of precise control over the growth thickness and In composition of the variable-component InGaAs thin layer.

[0020] Figure 1 A schematic flowchart of the method for optimizing the variable composition epitaxy process in molecular beam epitaxy provided in an embodiment of the present invention is shown. Figure 1 As shown, this invention provides an optimization method for molecular beam epitaxy variable composition epitaxy processes, which is used to optimize In x Ga 1-x As the growth process of the epitaxial layer, In x Ga 1-x The thickness of the As epitaxial layer is a preset thickness h, where h ≤ 20 nm, and the composition x is derived from In. x Ga 1-x The composition of the As epitaxial layer increases from 0.53 on the lower surface to x on the upper surface. h x h >0.7.

[0021] Optionally, the preset thickness h ranges from 10 nm to 15 nm.

[0022] Figure 2 This diagram illustrates a variable-component epitaxial structure provided in an embodiment of the present invention. On an InP substrate 20, the uppermost epitaxial layer is InP. x Ga 1-x As epitaxial layer 22, on InP substrate 20 and In x Ga 1-x As, other device layers 21 exist between the epitaxial layers 22; however, this application does not limit the other device layers 21. x Ga 1-x In at the lower surface 221 of As epitaxial layer 22 x Ga 1-x The In content in the As material is 0.53. At this point, In x Ga 1-x The As epitaxial layer is lattice-matched with the InP substrate. x Ga 1-x In at the upper surface 222 of As epitaxial layer 22 x Ga 1-x The In component in As material is x h In other words, for In with variable components x Ga 1-x As epitaxial layer 22, wherein the In composition varies from 0.53 at the lower surface 221 to x at the upper surface 222. h Optionally, x h The range is 0.7 <x h <0.9.

[0023] It should be noted that the increase of component x from the lower surface 221 to the upper surface 222 only means that the value of component x increases from the lower surface 221 to the upper surface 222, and does not limit whether x increases continuously or discontinuously. x Ga 1-xThe preset thickness h of the epitaxial layer 22 and the composition x of the upper surface. h These are all design values ​​predetermined based on the device's functional and manufacturing requirements.

[0024] like Figure 1 As shown, the method for optimizing the molecular beam epitaxy variable composition epitaxy process provided by the present invention includes: Step 101: Stabilize the temperature of the indium source furnace to the first temperature, and stabilize the temperature of the gallium source furnace to the second temperature.

[0025] The first and second temperatures correspond to a composition x of 0.53. Specifically, the purpose here is solely to determine the first and second temperatures so that the In composition in the obtained InGaAs is 0.53. The core is to determine the relative ratio between the indium beam rate and the gallium beam rate. The temperature of the indium source furnace corresponds one-to-one with the indium beam rate; the higher the indium source furnace temperature, the higher the beam rate, and the same applies to the gallium source furnace. For example, any commonly used indium beam rate can be selected, such as 0.2 μm / h. Based on the empirical relationship between the indium source furnace temperature and the indium beam rate, the corresponding indium source furnace temperature at this beam rate can be determined, and this indium source furnace temperature is taken as the first temperature. With an indium beam rate of 0.2 μm / h, to achieve a composition x of 0.53, the corresponding gallium beam rate can be calculated to be 0.2 / 0.53 - 0.2 = 0.177 μm / h. Similarly, based on the empirical relationship between the gallium source furnace temperature and the gallium beam rate, the corresponding gallium source furnace temperature at this beam rate can be determined, and this temperature is taken as the second temperature. It should be understood that the specific values ​​of the beam current rates mentioned above are merely examples. In practical applications, other commonly used indium beam current rates can be selected, and then the corresponding gallium beam current rate can be calculated based on the composition. The corresponding source furnace temperature can then be determined based on the empirical relationship between the source furnace temperature and the beam current rate. Optionally, the indium beam current rate V corresponding to the first temperature... In1 The value range is 0.2 micrometers / hour (μm / h) ≤ V In1 ≤0.5 μm / h. For indium and gallium source furnaces, the beam rate under stable temperature conditions can be determined using conventional calibration structure growth measurements or empirical data curves. Therefore, suitable indium and gallium source furnace temperatures can be selected to ensure that the In obtained at these temperatures yields optimal beam rates. x Ga 1-x The composition x of the As epitaxial layer is equal to 0.53. It should be noted that all temperatures mentioned in this application are thermocouple temperatures obtained from thermocouple measurements. To stabilize the beam rate, in actual operation, the stabilization time after the indium source furnace reaches the first temperature is greater than or equal to 2 minutes, and the stabilization time after the gallium source furnace reaches the second temperature is greater than or equal to 2 minutes. During the stabilization time, the corresponding baffle of the source furnace is in the closed state, and epitaxial growth does not occur.

[0026] Step 102: The temperature of the gallium source furnace is gradually reduced to the preset third temperature. Simultaneously with the cooling of the gallium source furnace, In growth begins. x Ga 1-x As epitaxial layer.

[0027] The first and third temperatures are equal to the component x. h Correspondingly, in the growth In x Ga 1-x The process of creating the As epitaxial layer includes multiple alternating growth and interruption times. After stabilizing the temperature of the indium source furnace to a first temperature in step 101, the indium source furnace provides a stable indium beam rate. In step 102, the indium source furnace temperature remains constant at the first temperature; that is, the indium beam rate remains stable (corresponding to the first temperature). In step 102, only the temperature of the gallium source furnace is adjusted. The first temperature and the third temperature are equal to x in the composition. h Correspondingly, this indicates that while maintaining the same indium beam current rate as in step 101, through component x h A third temperature for the gallium source furnace is determined such that the composition of InGaAs grown by the indium source furnace at the first temperature and the gallium source furnace at the third temperature is equal to x. h Specifically, for example, as described above regarding step 101, the indium source furnace temperature corresponding to an indium beam current rate of 0.2 μm / h is taken as the first temperature (and remains unchanged in step 102), in order to obtain composition x equal to x h For example, x h =0.8, the corresponding gallium beam rate is calculated to be 0.2 / 0.8-0.2=0.05 μm / h. Based on the empirical relationship between gallium source furnace temperature and gallium beam rate, the gallium source furnace temperature corresponding to a beam rate of 0.05 μm / h can be determined, and this temperature is taken as the third temperature.

[0028] It should be noted that the growth of In described in this application x Ga 1-x The process of As epitaxial layer includes the initial deposition and growth of In x Ga 1-x Starting from the epitaxial layer (As) and continuing to In... x Ga 1-x The entire process from the complete growth of the Ga epitaxial layer to its final stage includes the deposition process when the source furnace baffle is open and the interruption process when the baffle is closed (the interruption process is used to provide cooling time for the Ga source furnace, and the baffle is subsequently opened again for deposition and growth).

[0029] In molecular beam epitaxy (MBE) systems, source furnace cooling typically employs two methods: step-type and linear-type. The linear method refers to the source furnace temperature changing linearly with time under PID control. The step-type method, as described here, refers to the "step" mode in MBE systems. Specifically, the target temperature for the gallium source furnace is set lower than the current temperature (e.g., 50°C lower), and then the actual temperature of the gallium source furnace is reduced to the target value as quickly as possible using the maximum achievable cooling rate of the epitaxy system. Typically, in step-type cooling, the source furnace operates at zero heating power to achieve the fastest possible cooling. As the actual temperature of the source furnace approaches the target value, the heating power is slowly increased under PID control to bring the actual temperature close to and reach the target value.

[0030] During the process of the gallium source furnace being cooled to the preset third temperature in a stepwise manner, such as Figure 3 As shown, the gallium molecule beam rate provided by the gallium source furnace decreases over time. Figure 3 In the graph, the horizontal axis represents time, and the vertical axis represents the gallium molecule beam velocity. At time 0, the temperature of the gallium source furnace is the second temperature, and the corresponding gallium molecule beam velocity is V. Ga0 And in V In1 and V Ga0 In obtained by growing at beam rate x Ga 1-x The In composition x of As is 0.53. Then, as time progresses, the gallium source furnace begins to cool down, and the gallium molecule beam rate decreases over time, resulting in the growth of In. x Ga 1-x As the epitaxial layer at time S m+1,0 End of point, time S m+1,0 The corresponding gallium molecule beam velocity is V. Ga1 The target temperature for cooling the gallium source furnace is a preset third temperature. The first and third temperatures are equal to the component x. h Correspondingly, under steady-state temperature conditions, the first and third temperatures are equal to component x. h Correspondingly, under the conditions that the indium source furnace is stabilized at the first temperature and the gallium source furnace is stabilized at the third temperature, the In obtained by growth... x Ga 1-x The In component x of As is x h However, when the temperature of the gallium source furnace decreases in a stepwise manner, the gallium source furnace at time S... m+1,0 The actual instantaneous beam rate V at the location Ga1 Not necessarily related to component x h Correspondence. Assuming in V In1 and V Ga2 In obtained by growing at beam rate x Ga 1-x The In component x of As is x hIn actual operation, time S m+1,0 For the setpoint in growth control, for example, when S m+1,0 When the size is small, the gallium source furnace at time S m+1,0 The actual temperature at that location has not yet dropped to the third temperature, V Ga1 V greater than expected Ga2 When S m+1,0 When the value is large, although it can ensure that the gallium source furnace is at time S m+1,0 The actual temperature at that point is equal to the third temperature, and V Ga1 Equal to the expected V Ga2 However, due to the excessively long growth period, In x Ga 1-x The total thickness of As is greater than the preset thickness h. Typically, since h ≤ 20 nm, In... x Ga 1-x The total growth time required for the As epitaxial layer is relatively short; although the temperature of the gallium source furnace decreases in a stepwise manner, when x h When the temperature is >0.7, the actual temperature required for the gallium source furnace to drop to the third temperature is relatively long. Therefore, if in In x Ga 1-x During As epitaxial layer growth, the baffles of both the gallium and indium source furnaces remain open, resulting in either a thickness exceeding expectations or a composition lower than anticipated. Therefore, during In growth... x Ga 1-x The process of creating an As epitaxial layer can include multiple alternating growth and interruption times. During the growth time, the baffles of both the gallium source furnace and the indium source furnace are open, corresponding to the beam deposition onto the substrate, performing In deposition. x Ga 1-x As epitaxial layer growth and deposition; during the interruption period, the baffles of both the gallium source furnace and the indium source furnace are in the closed state, and the beam is blocked by the baffles. During the interruption period, the actual temperature of the gallium source furnace will continue to decrease, but during this period, no In... x Ga 1-x As epitaxial layer growth and deposition. By setting multiple alternating growth times and interruption times, the cooling time of the gallium source furnace is extended, which is beneficial for achieving an upper surface composition equal to x. h This also reduced In x Ga 1-x The deposition time of the As epitaxial layer is beneficial for achieving In x Ga 1-x The actual thickness of the epitaxial layer is equal to the preset thickness h, to avoid it being too thick.

[0031] like Figure 4 As shown, the multiple alternating growth times and interruption times specifically include the following stages in sequence: the first growth time (corresponding to time 0 to time S) 10The time between), the first interruption time (corresponding to time S) 10 up to time S 11 The time between), the second growth time (corresponding to time S) 11 up to time S 20 The time between), the second interruption time (corresponding to time S) 20 up to time S 21 The time between), the third growth time (corresponding to time S) 21 up to time S 30 The time between (…), the m-th growth time (corresponding to time S) m-1,1 up to time S m,0 The time between), the m-th interrupt time (corresponding to time S) m,0 up to time S m,1 The time between (m+1)th growth time (corresponding to time S) m,1 up to time S m+1,0 The time interval (m is an integer greater than or equal to 3) is used. As mentioned earlier, during the i-th growth time interval, an epitaxial layer is deposited; during the i-th interruption time interval, no epitaxial layer is deposited, but the gallium source furnace continues to cool down. Figure 4 As shown, the growth of In described in this application x Ga 1-x The process of the epitaxial layer as A includes the time from time 0 to time S. m+1,0 The overall process during this period. Using this alternating growth and interruption method, the desired variable component In is... x Ga 1-x As the compositional changes of the epitaxial layer are as follows Figure 5 As shown, Figure 5 The horizontal axis represents the epitaxial layer thickness, and the vertical axis represents the In composition. When the thickness is 0, it corresponds to In... x Ga 1-x The lower surface of the As epitaxial layer has an In composition of 0.53. At a thickness of h, the corresponding In composition is... x Ga 1-x As is the upper surface of the epitaxial layer, and the corresponding In composition is x. h Because of the interruption in growth time, the component change curve showed... Figure 5 The discontinuity shown is illustrated. Figure 5 Each curve segment in the graph corresponds to a growth period.

[0032] The i-th growth time t i (that is, time S) i-1,1 up to time S i,0 The time between, moment S 0,1 That is, time 0 is obtained by calculating t as follows: i =b / Vi V i =V In1 / x i x i =0.53+(x h -0.53) / (m+1)×(i-1), b=h / (m+1), i=1, 2, …, m+1, the j-th interruption time s j =a×t j j=1, 2, …, m, where a is an empirical coefficient, for example, 0.5≤a≤3. The value of a is usually related to the epitaxial system itself and the beam rate of the selected indium and gallium source furnaces.

[0033] Optionally, m is less than or equal to 7. In the above calculation, In x Ga 1-x As, the total thickness h of the epitaxial layer is divided into m+1 equal parts (corresponding to m+1 growth times), and b represents the average thickness of the m+1 parts, approximated by x. i This represents the In component of the i-th portion out of the m+1 portions, thus allowing the calculation of the total beam rate V of the i-th In and Ga components. i And thus through b / V i To determine the growth time t of the i-th part i It should be understood that the above process uses approximate calculations, and the calculated growth time t is used. i The final thickness of the epitaxial layer is approximately the preset thickness h. Then, the source furnace temperature and / or growth time are corrected and adjusted through subsequent steps 103 to finally obtain the desired growth process parameters.

[0034] Step 103: Test and obtain the grown In x Ga 1-x As the actual thickness h0 and actual surface composition x of the epitaxial layer h0 According to x h0 The calculation determined that the surface composition reached x. h The fourth temperature required for the indium source furnace, and during the next growth, in In x Ga 1-x Throughout the growth process of the epitaxial layer, the temperature of the indium source furnace linearly changes from a first temperature to a fourth temperature. Based on the impact of the indium source furnace temperature change on the epitaxial layer thickness, the actual thickness h0 is corrected to h1. Then, based on the difference between h1 and the preset thickness h, the growth time and interruption time for the next growth cycle are adjusted. During this adjustment, the growth of In... x Ga 1-x The total time for the process of creating the epitaxial layer remains constant.

[0035] After growth In x Ga1-x After the As epitaxial layer is formed, X-ray diffraction can be used for testing, and the grown In can be obtained through simulation calculations. x Ga 1-x As the actual thickness h0 and actual surface composition x of the epitaxial layer h0 If the actual surface composition x h0 equals x h If the temperature of the indium source furnace is not adjusted further, then the fourth temperature is equal to the first temperature. If, within the total cooling time (i.e., the total time of the multiple alternating growth times and interruptions), the temperature of the gallium source furnace does not decrease to the desired third temperature, resulting in an actual surface composition x... h0 Less than x h Then, a fourth temperature higher than the first temperature is obtained through calculation, and the surface composition is achieved by increasing the temperature of the indium source furnace. h When calculating the fourth temperature, the beam current rate of indium corresponding to the first temperature and the actual surface composition x can be used. h0 The beam rate M of gallium at the upper surface of the growth chamber (i.e., after the gallium source furnace has undergone the total cooling time) is calculated. Ga If the gallium source furnace undergoes the same cooling time next time (the beam rate is stable in the short term), the gallium beam rate is assumed to remain at M. Ga Therefore, based on x h The required indium beam rate and corresponding fourth temperature were calculated at this point. In In x Ga 1-x Throughout the growth process of the As epitaxial layer, the temperature of the indium source furnace changes linearly from a first temperature to a fourth temperature. Because the average temperature of the indium source furnace increases throughout the epitaxial growth process, the expected epitaxial layer thickness will increase accordingly. Therefore, the actual thickness h0 can be corrected to h1 based on the effect of the indium source furnace temperature change on the epitaxial layer thickness. Specifically, this includes calculating the average beam rate V. In =(V In1 +V In4 ) / 2, V In4 This represents the beam rate of indium at the fourth temperature, where [(0.53+x h0 ) / (0.53+x h )×V In / V In1 ]×h0 is used as h1. Similarly, an approximate calculation is also used here.

[0036] After correcting the actual thickness h0 to h1, the growth time and interruption time for the next growth cycle can be adjusted based on the difference between h1 and the preset thickness h. During this adjustment, the growth In... x Ga 1-xThe total time of the epitaxial layer process remains constant (that is, the total time of the multiple alternating growth times and interruption times remains constant, i.e.) Figure 3 and Figure 4 S in m+1,0 (The value remains unchanged). When adjusting the duration of growth time and interruption time, only the proportion of growth time in the total time is adjusted. That is, if h1 is greater than h, the growth time is reduced and the interruption time is increased to reduce the expected growth thickness; if h1 is less than h, the growth time is increased and the interruption time is decreased to increase the expected growth thickness. Optionally, the duration of growth time and interruption time for the next growth is further adjusted based on the difference between h1 and the preset thickness h, specifically including: the adjusted i-th growth time t i =h / h1×t i According to t i 'and t i The interruption time adjacent to the i-th growth time is adjusted accordingly to ensure that growth In x Ga 1-x The total time for the process of creating the epitaxial layer remains constant.

[0037] If the adjusted first growth time or the adjusted (m+1)th growth time changes compared to before the adjustment, then the total time is kept constant by adjusting the corresponding adjacent first or mth interrupt time; if the adjusted kth growth time changes compared to before the adjustment, the increase is assumed to be Δt. k If k = 2, 3, …, m, then the (k-1)th interrupt time and the kth interrupt time are reduced by Δt respectively. k / 2, so that the total time remains unchanged. Specifically, refer to Figure 4 For example, if time 0 to time S 10 If the time interval changes, then adjust time S. 10 up to time S 11 The time interval between these intervals makes the total time constant, if time S m,1 up to time S m+1,0 If the time interval changes, then adjust time S. m,0 up to time S m,1 The time interval between these intervals makes the total time constant; if time S 11 up to time S 20 If the time interval changes, then adjust time S simultaneously. 10 up to time S 11 The time and moment S between 20 up to time S 21 By using the time between the two to keep the total time constant, the error caused by approximate calculation can be minimized.

[0038] After adjusting the temperature, growth time, and interruption time of the indium source furnace using the method in step 103, the adjusted temperature and time are used as the process conditions for the next growth cycle. After the next growth cycle is completed and test data is obtained, the new test data can be used as the actual thickness h0 and actual surface composition x in step 103. h0 This allows for further optimization and adjustment based on step 103. In large-scale mass production, the method described above can achieve continuous optimization and adjustment, ensuring that the measured parameters of the mass-produced epitaxial wafers are strictly controlled within the preset specification range.

[0039] The specific operation process will be illustrated below with an example. This is to grow a variable composition In substrate with a total thickness of 15 nm and a composition x increasing from 0.53 to 0.8. x Ga 1-x As the epitaxial layer, firstly, for example, the indium source furnace temperature corresponding to an In beam rate of 0.2 μm / h is selected as the first temperature. The Ga beam rate corresponding to a composition of 0.53 is calculated to be 0.177 μm / h. Based on empirical data, the Ga source furnace temperature corresponding to 0.177 μm / h is determined as the second temperature. The Ga beam rate corresponding to a composition x of 0.8 is calculated to be 0.05 μm / h. Based on empirical data, the Ga source furnace temperature corresponding to 0.05 μm / h is determined as the third temperature. The In layer will then be grown. x Ga 1-x The As epitaxial layer process is divided into 5 growth times and 4 interrupt times. The expected thickness of the growth layer in each growth time is 3 nm. The corresponding growth time t is calculated using the following formula. i =b / V i V i =V In1 / x i x i =0.53+(x h -0.53) / (m+1)×(i-1), b=h / (m+1), i=1, 2, …, m+1, the j-th interruption time s j =a×t j j=1, 2, …, m, a is an empirical coefficient, here m+1=5, h=15nm, V In1=0.2 μm / h. Regarding the value of 'a', if the gallium source furnace has a large amount of raw material remaining (in the initial stage of use after the epitaxial system is fully loaded), the value of 'a' can be large, for example, a=3; if it reaches the middle stage of system use, for example, a can be equal to 1.5; in the later stage of system use, when the gallium source furnace has less raw material remaining, a can be equal to 0.8 or smaller. The calculation is as follows: x1=0.53, x2=0.584, x3=0.638, x4=0.692, x5=0.746, the five growth times are: t1=28.6 seconds, t2=31.5 seconds, t3=34.5 seconds, t4=37.4 seconds, t5=40.3 seconds. With a=1, the four interruption times are s1=28.6 seconds, s2=31.5 seconds, s3=34.5 seconds, s4=37.4 seconds, and the total time is 304.3 seconds. The measured surface composition of the variable composition epitaxial layer obtained under these conditions is 0.791, and the measured thickness is 15.9 nm. For a composition of 0.791, the corresponding Ga beam current rate can be calculated to be 0.2 / 0.791-0.2=0.0528 μm / h. If the total time for growing the variable composition InGaAs layer remains unchanged (i.e., the cooling time of the Ga source furnace remains unchanged) during the next growth (within a few days), the beam current rate of the Ga source furnace during the growth of the upper InGaAs layer can be considered constant, equal to 0.0528 μm / h. To achieve the desired composition of 0.8 on the upper surface, the adjusted beam current rate of In at the upper surface can be calculated using the following formula: 0.0528 / (1-0.8)-0.0528=0.211 μm / h. Based on the empirical relationship between indium beam current rate and temperature, the indium source furnace temperature corresponding to 0.211 μm / h is determined as the fourth temperature. Average beam current rate V In =0.2055 μm / h. Due to the increased average indium rate, the actual thickness h0 = 15.9 nm is corrected to h1 = 16.2 nm, according to the following formula t i =h / h1×t i The adjusted growth times for the five intervals are t1' = 26.5 seconds, t2' = 29.2 seconds, t3' = 31.9 seconds, t4' = 34.6 seconds, and t5' = 37.3 seconds. The adjusted interruption times for the four intervals are s1' = 31.8 seconds, s2' = 34 seconds, s3' = 37.2 seconds, and s4' = 41.8 seconds. The total time is 304.3 seconds, consistent with the original total time. During the new growth cycle, in In... x Ga 1-xThroughout the growth process of the As epitaxial layer, the temperature of the indium source furnace changes linearly from the first temperature to the fourth temperature. The growth time and interruption time are adjusted as described above. The surface composition of the obtained variable composition epitaxial layer is 0.8004, and the measured thickness is 15.2 nm, which is very close to the design value. This accuracy can meet the requirements and confirms the effectiveness of the method provided in this application.

[0040] In summary, this application optimizes the temperature of the indium source furnace based on the In composition of the InGaAs epitaxial layer surface obtained from testing, then corrects the epitaxial layer thickness obtained from testing based on the optimized indium source furnace temperature, and further adjusts the growth time and interruption time according to the corrected thickness to adjust the actual growth thickness, thereby achieving precise control of the composition and thickness of the variable composition epitaxial layer.

[0041] 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 it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An optimization method for molecular beam epitaxy variable composition epitaxy process, characterized in that, The method is used to optimize In x Ga 1- x As the growth process of the epitaxial layer, In x Ga 1-x The thickness of the As epitaxial layer is a preset thickness h, where h ≤ 25 nm, and the composition x is derived from In. x Ga 1-x The composition of the As epitaxial layer increases from 0.53 on the lower surface to x on the upper surface. h x h >0.7, the method includes: The temperature of the indium source furnace is stabilized at a first temperature, and the temperature of the gallium source furnace is stabilized at a second temperature. The first and second temperatures correspond to the composition x equal to 0.

53. The temperature of the gallium source furnace is gradually reduced to a preset third temperature. Simultaneously with the cooling of the gallium source furnace, In metal growth begins. x Ga 1-x As the epitaxial layer, the first and third temperatures are equal to the composition x. h Correspondingly, in the growth In x Ga 1-x The process of creating the As epitaxial layer includes multiple alternating growth and interruption times; Test to obtain the grown In x Ga 1-x As the actual thickness h0 and actual surface composition x of the epitaxial layer h0 According to x h0 The calculation determined that the surface composition reached x. h The fourth temperature required for the indium source furnace, and during the next growth, in In x Ga 1-x Throughout the growth process of the epitaxial layer, the temperature of the indium source furnace changes linearly from a first temperature to a fourth temperature. Based on the impact of the indium source furnace temperature change on the epitaxial layer thickness, the actual thickness h0 is corrected to h1. Then, based on the difference between h1 and the preset thickness h, the growth time and interruption time for the next growth cycle are adjusted. During this adjustment, the growth of In... x Ga 1- x As the total time for the epitaxial layer process remains constant. The indium beam rate V corresponding to the first temperature In1 The value range is 0.2 micrometers / hour ≤ V In1 ≤0.5 micrometers / hour; Based on the effect of indium source furnace temperature changes on epitaxial layer thickness, the actual thickness h0 is corrected to h1, specifically including: calculating the average beam rate V. In =(V In1 +V In4 ) / 2, V In4 This represents the beam rate of indium at the fourth temperature, where [(0.53+x h0 ) / (0.53+x h )×V In / V In1 ]×h0 as h1; The multiple alternating growth times and interruption times specifically include the following stages in sequence: the first growth time, the first interruption time, the second growth time, the second interruption time, ..., the m-th growth time, the m-th interruption time, and the (m+1)-th growth time, where m is an integer greater than or equal to 3, and the i-th growth time t i t is obtained by calculation as follows: i =b / V i V i =V In1 / x i x i =0.53+(x h -0.53) / (m+1)×(i-1), b=h / (m+1), i=1, 2, …, m+1, the j-th interruption time s j =a×t j j=1, 2, …,m, where a is an empirical coefficient; Then, based on the difference between h1 and the preset thickness h, the growth time and interruption time for the next growth are adjusted, specifically including: the adjusted i-th growth time t i =h / h1×t i According to t i 'and t i The interruption time adjacent to the i-th growth time is adjusted accordingly to ensure that growth In x Ga 1-x The total time for the process of creating the epitaxial layer remains constant.

2. The method for optimizing the molecular beam epitaxy variable composition epitaxy process according to claim 1, characterized in that, The preset thickness h ranges from 10nm to 15nm.

3. The method for optimizing the molecular beam epitaxy variable composition epitaxy process according to claim 1, characterized in that, x h The range is 0.7 <x h <0.

9.

4. The method for optimizing the molecular beam epitaxy variable composition epitaxy process according to claim 1, characterized in that, m is less than or equal to 7.

5. The method for optimizing the molecular beam epitaxy variable composition epitaxy process according to claim 1, characterized in that, If the adjusted first growth time or the adjusted (m+1)th growth time changes compared to before the adjustment, then the total time is kept constant by adjusting the corresponding adjacent first or mth interrupt time; if the adjusted kth growth time changes compared to before the adjustment, the increase is assumed to be Δt. k If k = 2, 3, …, m, then the (k-1)th interrupt time and the kth interrupt time are reduced by Δt respectively. k / 2, so that the total time remains unchanged.

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