A method for determining the equivalent pressure of arsenic beam in molecular beam epitaxy system

Abstract

The present invention provides a method for determining the equivalent pressure of an arsenic beam in a molecular beam epitaxy system, and relates to the field of semiconductor manufacturing technology. The method comprises: at a first time, for the transition between the first and second reconstruction states of the surface reconstruction of the sample surface, obtaining a first boundary straight line relationship in which the logarithm of the beam equivalent pressure changes with the inverse of the sample temperature; at a second time, obtaining the second boundary straight line relationship of the change; calculating and obtaining the conversion relationship between the first and second boundary straight line relationships; for the preset beam equivalent pressure at the first time, using the conversion relationship, calculating and obtaining the corresponding beam equivalent pressure at the second time. The method obtains boundary straight line relationships at different times, and then calculates the conversion relationship. For the beam equivalent pressure at the first time, the corresponding beam equivalent pressure at the second time can be calculated using the conversion relationship, thereby realizing accurate determination of the arsenic beam equivalent pressure and saving costs.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a method for determining the equivalent pressure of an arsenic beam in a molecular beam epitaxy system. Background Art

[0002] In the production of molecular beam epitaxy (MBE), the molecular beam size of the Group V elements (for example, arsenic or phosphorus) is a key parameter affecting the quality of epitaxial materials. In the molecular beam epitaxy system, the beam current (also called beam equivalent pressure) corresponding to the valve opening of the Group V molecular beam source at different openings is measured by a beam current meter (also known as an ion gauge). During epitaxial growth, the system provides the desired beam current value by controlling the valve opening.

[0003] The beam meter is located in the growth chamber of the molecular beam epitaxy system. With the long-term growth and use of the epitaxy system, a small amount of molecular beam source may be deposited on the beam meter, causing the detection capability of the beam meter itself to change, thereby causing the beam meter's measurement value of the beam to drift. In this way, for different periods of the molecular beam epitaxy system, the same measurement value of the beam meter corresponds to different molecular beam currents. However, in order to ensure the quality of epitaxial products, the actual value of the molecular beam current needs to be relatively stable in production. Therefore, a method needs to be proposed to determine the beam meter measurement value of the equivalent pressure of the arsenic beam required for growth at different times. Summary of the invention

[0004] The purpose of the present invention is to provide a method for determining the equivalent pressure of the arsenic beam in a molecular beam epitaxy system in view of the above-mentioned deficiencies in the prior art, so as to solve the problem of determining the equivalent pressure of the arsenic beam in the molecular beam epitaxy system at different periods.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a method for determining the equivalent pressure of an arsenic beam in a molecular beam epitaxy system, the method comprising:

[0007] Step a, at a first time, for the transition of the surface reconstruction of the GaAs sample surface between the first reconstruction state and the second reconstruction state, obtaining a first transition boundary straight line relationship between the logarithm of the As beam equivalent pressure and the inverse of the sample temperature;

[0008] Step b, obtaining a second transition boundary straight line relationship of the change at a second time;

[0009] Step c, calculating and obtaining a conversion relationship between the first transition boundary straight line relationship and the second transition boundary straight line relationship;

[0010] Step d: for the preset As beam equivalent pressure at the first time, using the conversion relationship, calculate and obtain the corresponding As beam equivalent pressure at the second time.

[0011] Optionally, the transition between the first reconstructed state and the second reconstructed state is one of the following transitions: a transition between c(4×4) and (2×4), a transition between (2×4) and (3×1), or a transition between (3×1) and (4×2).

[0012] Optionally, the first transition boundary straight line relationship is ln(BEP As1 )=a 1 ×1 / T+b 1 , BEP As1 represents the equivalent pressure of the As beam at the first time, T represents the sample temperature, a 1 and b 1 are coefficients obtained by linear fitting.

[0013] Optionally, the second transition boundary straight line relationship is ln(BEP As2 )=a 2 ×1 / T+b 2 , BEP As2 represents the equivalent pressure of the As beam at the second time, a 2 and b 2 are coefficients obtained by linear fitting.

[0014] Optionally, step c includes: using ln(BEP As1 )=a 1 ×1 / T+b 1 and ln(BEP As2 )=a 2 ×1 / T+b 2 , calculate and obtain BEP As2 With BEP As1 The relationship between them is ln(BEP As2 )=a 2 / a 1 ×ln(BEP As1 )-a 2 / a 1 ×b 1 +b 2 , and take this relation as the conversion relation.

[0015] The beneficial effects of the present invention include:

[0016] The method for determining the arsenic beam equivalent pressure of a molecular beam epitaxy system provided by the present invention comprises: step a, at a first time, for the transition of the surface reconstruction of the GaAs sample surface between the first reconstruction state and the second reconstruction state, obtaining a first transition boundary straight line relationship of the logarithm of the As beam equivalent pressure changing with the inverse of the sample temperature; step b, at a second time, obtaining the second transition boundary straight line relationship of the change; step c, calculating and obtaining the conversion relationship between the first transition boundary straight line relationship and the second transition boundary straight line relationship; step d, for the preset As beam equivalent pressure at the first time, using the conversion relationship, calculating and obtaining the corresponding As beam equivalent pressure at the second time. The method obtains the transition boundary straight line relationship associated with the As beam equivalent pressure at different times, and then calculates the conversion relationship between the obtained straight line relationships. For any preset beam equivalent pressure at the first time, the corresponding beam equivalent pressure at the second time can be calculated using the conversion relationship, thereby realizing the accurate determination of the arsenic beam equivalent pressure, avoiding verification tests, and saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A flow chart showing a method for determining an equivalent pressure of an arsenic beam in a molecular beam epitaxy system provided by an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of the state transition of the GaAs (001) surface reconstruction in the molecular beam epitaxy system provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] In the molecular beam epitaxy system, the beam meter is located in the growth chamber of the molecular beam epitaxy system. As the epitaxy system grows over a long period of time, a small amount of molecular beam sources may be deposited on the beam meter, causing the detection capability of the beam meter to change, thereby causing the beam meter's measured value of the beam to drift. In this way, for different periods of the molecular beam epitaxy system, the same measured value of the beam meter actually corresponds to different molecular beam currents. For example, at the first time, the As beam equivalent pressure measured by the beam meter is 1×10 -5 torr is the optimal beam current value required for epitaxial growth. As the beam current meter's detection capability weakens during long-term use, at the second time, when the As beam current equivalent pressure measured by the beam current meter is 1×10 -5 torr, the As molecular beam current actually reaching the substrate surface must be greater than the required optimal beam current value.

[0022] In order to ensure the quality of epitaxial products, the actual value of the molecular beam needs to be relatively stable during production. Therefore, a method needs to be proposed to determine the beam meter measurement value of the equivalent pressure of the arsenic beam required for growth at different times.

[0023] Figure 1 FIG. 4 is a flow chart showing a method for determining the equivalent pressure of an arsenic beam in a molecular beam epitaxy system according to an embodiment of the present invention. Figure 1 As shown, the method for determining the equivalent pressure of the arsenic beam in the molecular beam epitaxy system provided by the present invention includes:

[0024] Step a: at a first time, for the transition of the surface reconstruction of the GaAs sample surface between a first reconstruction state and a second reconstruction state, obtain a first transition boundary straight line relationship of the logarithm of the As beam equivalent pressure changing with the inverse of the sample temperature.

[0025] In the present application, the first time means that during this period, the beam meter has been experimentally calibrated and the beam meter measurement value corresponding to the actual arsenic molecular beam required for epitaxial growth (that is, the As beam equivalent pressure) is known.

[0026] The sample surface can be, for example, a GaAs (001) surface. For the surface reconstruction of the GaAs sample surface, the As beam equivalent pressure corresponding to the transition of the surface reconstruction state is different with the different sample temperatures. The reconstruction states of the GaAs sample surface include c (4×4), (2×4), (3×1) and (4×2). For the transition boundary between two adjacent reconstruction states, take the logarithm of the As beam equivalent pressure and the inverse of the sample temperature to draw the transition boundary curve, such as Figure 2 As shown in Figure 2, the transition boundary curve is linear. Figure 2In the figure, the black dots represent the measured values ​​of the As beam equivalent pressure corresponding to the reconstruction state transition at different sample temperatures, and the dotted line represents the transition boundary line obtained by linear fitting. The unit of As beam equivalent pressure is torr, and the unit of temperature is Kelvin. The transition between the first reconstruction state and the second reconstruction state is one of the following transitions: the transition between c(4×4) and (2×4), the transition between (2×4) and (3×1), or the transition between (3×1) and (4×2). Therefore, the first transition boundary line relationship can be Figure 2 One of the first straight line relationship 21, the second straight line relationship 22 or the third straight line relationship 23 in the first reconstruction state. For example, if the first reconstruction state is c(4×4) and the second reconstruction state is (2×4), the corresponding first transition boundary straight line relationship is the third straight line relationship 23; if the first reconstruction state is (2×4) and the second reconstruction state is (3×1), the corresponding first transition boundary straight line relationship is the second straight line relationship 22, and so on.

[0027] The first transition boundary straight line relationship can be expressed as ln(BEP As1 )=a 1 ×1 / T+b 1 , BEP As1 represents the As beam equivalent pressure measured by the beam meter at the first time, ln(BEP As1 ) indicates to BEP As1 Take the logarithm, T represents the sample temperature, a 1 and b 1 are all coefficients obtained through linear fitting. It should be noted that the first transition boundary straight line relationship here is the numerical fitting relationship between the As beam equivalent pressure and the sample temperature obtained through experimental measurement. Specifically, the first transition boundary straight line relationship can be obtained in the following way: at a first time, at a plurality of different GaAs sample temperatures, use a beam current meter to measure the As beam equivalent pressure corresponding to the transition of the surface reconstruction of the sample surface between the first reconstruction state and the second reconstruction state, and then use linear fitting to obtain ln(BEP As1 ) linear relationship with 1 / T ln(BEP As1 )=a 1 ×1 / T+b 1 .

[0028] Step b, obtaining the second transition boundary straight line relationship of the change at the second time. That is, at the second time, for the transition of the surface reconstruction of the GaAs sample surface between the first reconstruction state and the second reconstruction state, obtaining the second transition boundary straight line relationship of the logarithm of the As beam equivalent pressure changing with the inverse of the sample temperature.

[0029] In the present application, the second time is a time different from the first time. It should be understood that the present application discusses the measurement values ​​of the same beam meter of the same molecular beam epitaxy system at different times. Generally speaking, the second time and the first time can be separated by several weeks, months or longer. At the second time, the beam meter has not been calibrated, that is, at this time, the beam meter measurement value corresponding to the actual arsenic molecular beam required for epitaxial growth (that is, the As beam equivalent pressure) is unknown. After a long period of epitaxial growth, the detection capability of the beam meter may have changed at the second time. In order to determine the beam meter measurement value corresponding to the actual arsenic molecular beam required for epitaxial growth at the second time, the second transition boundary straight line relationship of the logarithm of the As beam equivalent pressure changing with the inverse of the sample temperature can be obtained for the transition between the first reconstruction state and the second reconstruction state of the surface reconstruction of the GaAs sample surface at the second time. Although the time is different, for GaAs samples, the actual As beam required for the corresponding transition at a specific temperature is specific and unchanged. For the reconstruction state transition, the relationship between the logarithm of the As beam equivalent pressure and the inverse of the sample temperature is still linear, but due to the change in the detection capability of the beam meter, the linear relationship at this time is different from the first transition boundary linear relationship obtained at the first time.

[0030] The second transition boundary straight line relationship is ln(BEP As2 )=a 2 ×1 / T+b 2 , BEP As2 represents the equivalent pressure of the As beam measured by the beam meter at the second time, a 2 and b 2 are all coefficients obtained through linear fitting. It should be noted that the straight line relationship of the second transition boundary here is the numerical fitting relationship between the As beam equivalent pressure and the sample temperature obtained through experimental measurement.

[0031] Specifically, the second transition boundary straight line relationship can be obtained as follows: at the second time, at a plurality of different GaAs sample temperatures, the As beam equivalent pressure corresponding to the transition of the surface reconstruction of the sample surface between the first reconstruction state and the second reconstruction state is measured using a beam current meter, and ln(BEP As2 ) linear relationship with 1 / T ln(BEP As2 )=a 2 ×1 / T+b 2 .

[0032] Optionally, in the process of obtaining the first transition boundary straight line relationship and the second transition boundary straight line relationship, the plurality of different GaAs sample temperatures include 5 to 10 temperature values, and a difference of 10 Kelvin is observed between two adjacent temperatures.

[0033] It should be understood that if the first transition boundary straight line relationship corresponds to the transition between c(4×4) and (2×4), then the second transition boundary straight line relationship also corresponds to the transition between c(4×4) and (2×4), and so on.

[0034] Step c: Calculate and obtain the conversion relationship between the first transition boundary straight line relationship and the second transition boundary straight line relationship.

[0035] Specifically, step c includes: using ln(BEP As1 )=a 1 ×1 / T+b 1 and ln(BEP As2 )=a 2 ×1 / T+b 2 , calculate and obtain BEP As2 With BEP As1 The relationship between them is ln(BEP As2 )=a 2 / a 1 ×ln(BEP As1 )-a 2 / a 1 ×b 1 +b 2 , and take this relation as the conversion relation.

[0036] In step a and step b, by adjusting the As beam current during the heating process of the GaAs sample and observing the changes in the RHEED graph, multiple transition point temperatures and beam equivalent pressure data can be obtained. According to the requirements of step a and step b, linear fitting can be performed to obtain a 1 、a 2 、b 1 、b 2 Four fitting coefficients, so through mathematical calculation, eliminating 1 / T, the conversion relationship ln(BEP As2 )=a 2 / a 1 ×ln(BEP As1 )-a 2 / a 1 ×b 1 +b 2 .

[0037] Step d: for the preset As beam equivalent pressure at the first time, using the conversion relationship, calculate and obtain the corresponding As beam equivalent pressure at the second time.

[0038] As described above, since the beam current meter measurement value corresponding to the actual arsenic molecular beam required for epitaxial growth at the first time (that is, the As beam equivalent pressure) is known, the preset As beam equivalent pressure BEP at the first time is As1 , the conversion relationship can be used to calculate the corresponding As beam equivalent pressure BEP at the second time As2 That is, at the second time, the beam current meter measures the As beam equivalent pressure equal to BEP As2 The actual As beam current provided at this time is consistent with the BEP measured by the beam current meter at the first time. As1 The actual As beam current provided is consistent.

[0039] The method obtains the transition boundary linear relationship associated with the As beam equivalent pressure at different times, and then calculates the conversion relationship between the obtained linear relationships. For any preset beam equivalent pressure at the first time, the corresponding beam equivalent pressure at the second time can be calculated using the conversion relationship, thereby achieving accurate determination of the arsenic beam equivalent pressure, avoiding verification tests, and saving costs.

[0040] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the equivalent pressure of an arsenic beam in a molecular beam epitaxy system, characterized in that: The method comprises: Step a, at a first time, for the transition of the surface reconstruction of the GaAs sample surface between the first reconstruction state and the second reconstruction state, obtaining a first transition boundary straight line relationship between the logarithm of the As beam equivalent pressure and the inverse of the sample temperature; Step b, obtaining a second transition boundary straight line relationship of the change at a second time; Step c, calculating and obtaining a conversion relationship between the first transition boundary straight line relationship and the second transition boundary straight line relationship; Step d: for the preset As beam equivalent pressure at the first time, using the conversion relationship, calculate and obtain the corresponding As beam equivalent pressure at the second time.

2. The method for determining the equivalent pressure of arsenic beam in a molecular beam epitaxy system according to claim 1, characterized in that: The transition between the first reconstructed state and the second reconstructed state is one of the following transitions: a transition between c(4×4) and (2×4), a transition between (2×4) and (3×1), or a transition between (3×1) and (4×2).

3. The method for determining the equivalent pressure of arsenic beam in a molecular beam epitaxy system according to claim 2, characterized in that: The first transition boundary straight line relationship is ln(BEP As1 )=a1×1 / T+b1, BEP As1 represents the As beam equivalent pressure at the first time, T represents the sample temperature, and a1 and b1 are coefficients obtained by linear fitting.

4. The method for determining the equivalent pressure of arsenic beam in a molecular beam epitaxy system according to claim 3, characterized in that: The second transition boundary straight line relationship is ln(BEP As2 )=a2×1 / T+b2, BEP As2 represents the equivalent pressure of the As beam at the second time, and a2 and b2 are coefficients obtained by linear fitting.

5. The method for determining the equivalent pressure of arsenic beam in a molecular beam epitaxy system according to claim 4, characterized in that: Step c includes: using ln(BEP As1 )=a1×1 / T+b1and ln(BEP As2 )=a2×1 / T+b2, calculate and obtain BEP As2 With BEP As1 The relationship between them is ln(BEP As2 )=a2 / a1×ln(BEP As1 )-a2 / a1×b1+b2, and use this relationship as the conversion relationship.

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