A real-time beam measurement system based on a dielectric spectrum light source and its self-calibration method

Abstract

The present invention belongs to the field of molecular beam epitaxy of compound materials, and specifically relates to a real-time beam current measurement system based on a dielectric spectrum light source and its self-calibration method. A continuous dielectric spectrum light source with a spectral width in the range of ten to dozens of nanometers is used as the light source for real-time online beam current measurement, and it has a self-calibration function. That is, a single measurement optical path is adopted, and a spectrometer is used to collect specific spectral data after the interaction between the light source beam and the molecular beam current. By calculating three or more data points in the specific spectral data, the real-time absorption intensity data of the corresponding molecular beam current after reference is directly obtained, and the relative beam current intensity is obtained accordingly. This system and its self-calibration method are suitable for real-time online measurement of a single type of beam current, and can also be used for real-time online measurement of multiple beam currents by switching the light source optical path. It can also be used for real-time online separate or simultaneous measurement of multiple beam currents by synthesizing the light source beam or customizing a multi-wavelength multi-chip single-beam packaging device. It is a universal solution.

Description

Technical Field

[0001] The present invention belongs to the field of molecular beam epitaxy of compound materials, and particularly relates to a real-time beam current measurement system based on a dielectric spectrum light source and a self-calibration method thereof. Background Art

[0002] Compound semiconductor materials are a class of materials with extremely wide applications in the fields of electronics and optoelectronics. Various devices based on compound semiconductor materials can cover a wide range of wavelength bands. For semiconductor optoelectronic devices and electronic devices, epitaxial growth is the main means for fabricating device structures. Among them, the molecular beam epitaxy method is favored by people due to a series of advantages such as its precision and high controllability.

[0003] In the molecular beam epitaxy method, the measurement and monitoring of the molecular beam current are necessary conditions for growing high-performance materials, and precise, reliable and convenient on-line real-time monitoring is what people expect. The traditional beam current monitoring method is based on measuring the thermionic emission current related to the beam current intensity with a vacuum gauge. Although it is an on-line measurement, it cannot achieve real-time measurement during the growth process, that is, measurement and growth cannot be carried out simultaneously. Subsequently, the optical method is based on the "old" atomic absorption spectroscopy technology in principle, and measurement instruments have been developed, which can perform on-line real-time measurement, but it has a series of problems and has not been widely used. The main problems existing in the current optical method are in the light source and the calibration reference method, and the two are closely related to each other.

[0004] At present, the light sources adopted by optical methods can be divided into two categories: broad-spectrum and narrow-spectrum. Broad-spectrum light sources are often thermal light sources, such as xenon lamps and tungsten halogen lamps. Their power can be large enough, but the spectral utilization efficiency is extremely low. This is because measuring atomic absorption generally only needs to be carried out within a very narrow spectral range, such as ten to dozens of nanometers, while the spectral range of thermal light sources covers at least several micrometers, that is, their spectral utilization efficiency is less than one percent. In this way, when the light source power is small, the measurement signal-to-noise ratio will be very poor. Increasing the light source power will cause serious heating and a series of problems, and the stability of thermal light sources is poor and the lifespan is very short, generally only several hundred hours; Narrow-spectrum light sources are often hollow cathode lamps or semiconductor lasers, etc. Although the emission spectrum of the hollow cathode lamp can fit well with the measured beam source, its output power is very low and the lifespan is short, only several hundred hours, and it decays severely during the lifespan cycle. Moreover, the gas discharge itself has poor stability, which increases the difficulty of signal measurement; Although the power of semiconductor lasers is sufficient, the selectable wavelengths are very limited and relatively fixed. It is very difficult to obtain a suitable device that matches the beam source to be measured, and the universality is poor. Moreover, the wavelength of semiconductor lasers is necessarily affected by the ambient temperature, and the stability cannot meet the requirements. For these two categories of light sources, due to limitations such as their stability, it is necessary to carry out reference in the measurement. Generally, a reference optical path is set separately. On the one hand, this makes the system complicated and the overall stability worse. On the other hand, although setting an external optical path for reference can compensate for the influence of the light source stability, it is very difficult to compensate for the signal fluctuations in the internal optical path, especially the more serious influence caused by the light scattering of the molecular beam itself. These limitations are fundamental. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a universal on-line real-time beam measurement system based on a mesoscopic light source and its corresponding self-calibration method, aiming to fundamentally solve the problems existing in the light source and reference in the past methods. The summary of the invention will be specifically described in conjunction with the attached Figure 1 illustrations.

[0006] Molecular beam epitaxy of materials is carried out in a molecular beam epitaxy vacuum chamber 7 that can reach an ultra-high vacuum state; it includes a beam source furnace crucible and beam source materials 8 as the growth source. According to specific growth requirements, there are often multiple paths for the beam source. Only one path is shown as a schematic illustration in the attached Figure 1 figures; the growth source in the beam source furnace is heated to form the required molecular beam current 9; it acts on the epitaxial substrate 10 for epitaxial growth; these parts are all conventional configurations of the molecular beam epitaxy system.

[0007] The on-line real-time beam measurement system based on an inter-spectral light source according to the present invention introduces a light input window 5 and its flange, and a light output window 6 and its flange into the molecular beam epitaxy vacuum chamber 7. The optical window and the flange are an integrated component, suitable for installation in a vacuum system, located at opposite positions in the radial center of the system and orthogonal to the molecular beam 9, ensuring that the light beam and the molecular beam form a maximum interaction area. These two windows can utilize the ready-made through-hole and unobstructed flange openings at the center position on the molecular beam epitaxy system; the collimated light beam generated by the inter-spectral light source 1 system including the light source switching / synthesizing / collimating optical path 2 is input through the light input window 5 and its flange and interacts with the molecular beam. The light beam after interacting with the molecular beam is output through the light output window 6 and its flange, and is input into the spectrometer 3 through the output focusing optical path 4 for spectral signal detection to obtain specific spectral data.

[0008] The present invention uses an inter-spectral light source with a spectral width (i.e., the full width at half maximum of the light intensity) of several nanometers to dozens of nanometers as the measurement light source, and dozens of nanometers can be 30 to 50 nanometers. Given that the atomic absorption spectral line width of the molecular beam is much less than 1 nanometer and the wavelength position is fixed, therefore, it is only necessary that the central wavelength of the inter-spectral light source is basically aligned with the wavelength of the selected atomic absorption spectral line, so that the spectral width of the inter-spectral light source can cover the wavelength of the atomic absorption spectral line, and there are no strict requirements. For measuring multiple molecular beams, the multiple measurement wavelengths selected by the inter-spectral light source should match the respective atomic absorption spectral lines and avoid overlapping with each other. In addition, the wavelengths used by the inter-spectral light source should also be adapted to the spectral measurement range of the spectrometer.

[0009] The present invention adopts a single optical path reference scheme, which belongs to self-calibration. The spectral intensity distribution of the inter-spectral light source generally conforms to a Gaussian distribution or other similar symmetric distributions with a central wavelength of , and a full width at half maximum of . Let its distribution be , represents the wavelength. The wavelength of the absorption spectral line of the atom to be measured in the molecular beam source is . According to the foregoing principle, the inter-spectral light source only needs to satisfy that falls within , otherwise it cannot be measured. This reference scheme sets as two reference wavelength measurement points, and directly calibrates the data of this absorption spectral line wavelength measurement point. Given that the atomic absorption line spectral width is extremely narrow, selecting to be about 1 to 2 nanometers can avoid the influence of atomic absorption spectral line broadening and the resolution of a conventional spectrometer, and make the two reference wavelengths still fall within the full width at half maximum wavelength of the inter-spectral light source. At this time, the absorbance of the atom to be measured in the molecular beam source can be expressed as:

[0010] ,

[0011] All the data included in this formula are measurable by the spectrometer, that is, only three wavelength points, namely the wavelength of the atomic absorption line to be measured and the two reference wavelengths closest to it, need to be obtained. , , and the intensity data at these wavelengths, the absorbance data related to the molecular beam intensity can be directly calculated by reference, and this absorbance data is independent of the fine spectral distribution form of the dielectric spectral light source.

[0012] When there are various fluctuations in the measurement system, including possible fluctuations in the intensity of the dielectric spectral light source, fluctuations in the optical path geometry, and fluctuations in the scattering intensity caused by the switching of the molecular beam source, the addition or removal of different molecular beam sources, and the change in the beam intensity, as well as the fluctuations in the measurement of the spectrometer itself, etc., these fluctuations are independent of the wavelength itself within a small wavelength range. A fluctuation factor is introduced to describe these fluctuations. At this time, the measured absorbance is expressed as:

[0013] ,

[0014] That is ,

[0015] It can be seen that the measured absorbance is not affected by these fluctuation factors, that is, this reference method has a natural anti-fluctuation characteristic. It should be noted that the attenuation of the signal may cause a decrease in the measurement signal-to-noise ratio, that is, the influence of the measurement system noise may increase, but it will not have a significant impact on the measurement result within a large range. For the dielectric spectral light source, another possible fluctuation is the temperature drift of the central wavelength. For example, for an LED (light-emitting diode) in the ultraviolet band, its wavelength temperature coefficient is about 0.2 - 0.4 nm / K, that is, when the temperature fluctuates by 10 °C, the central wavelength will drift by about 2 to 4 nanometers. However, since two reference wavelength points on the left and right are used for averaging in this reference method, as long as the central wavelength is selected appropriately, the small-range drift of the central wavelength will not affect the reference correction effect. Similarly, more wavelength reference points can be selected for reference, but the reference correction effect cannot be significantly improved.

[0016] It should be noted that regarding how to perform subsequent calculations, obtain the real-time absorption intensity data of the corresponding molecular beam after reference, and obtain the relative beam intensity based on the real-time absorption intensity after obtaining the absorbance , all belong to the common knowledge of those skilled in the art and will not be elaborated here.

[0017] The above technical solutions of the present invention have the following beneficial effects compared with the prior art:

[0018] In view of the fundamental problems existing in two major categories of light sources, namely broadband and narrowband light sources, the present invention proposes a solution using an intermediate-spectrum light source, which can fundamentally solve the main problems in both the light source and the reference aspects. Here, the intermediate-spectrum light source is defined as another type of light source whose spectral range lies between those of broadband and narrowband light sources, and its spectral range can be between several nanometers and dozens of nanometers, and dozens of nanometers can be from 30 to 50 nanometers. On the one hand, using the intermediate-spectrum light source can solve key problems such as the above-mentioned spectral utilization rate, coverage range, light source stability and lifespan, and measurement signal-to-noise ratio. On the other hand, by adopting the single-light-path reference scheme of the present invention, it is possible to compensate for the influence of a series of fluctuations including the light source, the light path, and molecular beam scattering, and it can be used for real-time online measurement of multiple beam currents through light source light path switching. Moreover, it can also perform real-time online simultaneous measurement of multiple beam currents through light source beam synthesis or customizing multi-wavelength multi-chip single-beam packaging devices. Therefore, it is a universal solution.

[0019] As described above, an online real-time beam current measurement system based on an intermediate-spectrum light source and its self-calibration method provided by the present invention have the advantages of simple method, few required devices, low cost, good reference correction effect, strong robustness, and convenient operation. It can be applied to the real-time online measurement of a single type of beam current, and can also be used for the real-time online measurement of multiple beam currents through light source light path switching. Moreover, it can perform real-time online separate or simultaneous measurement of multiple beam currents through light source beam synthesis or customizing multi-chip multi-wavelength single-beam packaging devices, and has good versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other embodiments based on these drawings without creative efforts. In the drawings:

[0021] Figure 1 is a schematic diagram of an online real-time beam current measurement system based on an intermediate-spectrum light source and its self-calibration method provided by the present invention.

[0022] Wherein, 1: intermediate-spectrum light source; 2: light source switching / synthesis / collimation light path; 3: spectrometer; 4: output focusing light path; 5: light input window; 6: light output window; 7: molecular beam epitaxy vacuum chamber; 8: beam source furnace crucible and beam source material; 9: molecular beam current; 10: epitaxial substrate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0024] The following takes the optical on-line real-time beam current measurement system and its self-calibration method required in the molecular beam epitaxial growth of III-V compound semiconductors as an example to illustrate the relevant specific concepts and steps. These methods and steps can obviously be directly extended to the molecular beam epitaxial growth of other types of materials and electron beam evaporation, etc., as long as corresponding adjustments are made. The specific concepts and steps are as follows:

[0025] The group-III growth sources involved in the molecular beam epitaxial growth of III-V compound semiconductors are mainly Al (aluminum), Ga (gallium), and In (indium), and the group-V growth sources are mainly P (phosphorus), As (arsenic), and Sb (antimony). Doping sources generally do not require real-time monitoring because of the low and relatively stable required beam current intensity. The atomic absorption spectral line wavelengths of the above group-III and group-V sources mainly concentrate in the near-ultraviolet band. For the spectral light source, an LED device in the ultraviolet band is preferably used. Its spectral width is generally in the range of ten to dozens of nanometers and is a continuous spectrum, working in CW (continuous wave), which can just meet the use requirements. The central wavelength of the LED device in the ultraviolet band is restricted by the material system used and cannot be arbitrarily selected, but there are already quite a number of central wavelengths available for selection, such as 405 nm, 395 nm, 390 nm, 385 nm, 365 nm, 310 nm, 285 nm, and 254 nm, etc. And for each central wavelength, there is generally a variation range of several nanometers available for selection, and new central wavelength devices are constantly emerging. Therefore, it can basically meet the measurement requirements for the molecular beam epitaxial growth of III-V materials. For example, a device with a central wavelength of 395 nm can be used for the measurement of the strong absorption line of the Al beam current at 396.15 nm. A device with a central wavelength of 254 nm can be used for the measurement of the strong absorption line of the P beam current at 253.56 nm or the Sb beam current at 252.85 nm. Since the strong absorption line wavelengths of these two elements are relatively close but still within the resolution ability of the spectrometer, if these two molecular beam currents coexist in the system and need to be measured simultaneously, the corresponding reference wavelengths can be selected as nm and Nanometers, and the same can be inferred in other cases. Correspondingly, the measurement range of the spectrometer used in the measurement system is set to 200 to 400 nanometers. A fiber-optic input type micro-grating spectrometer is selected, and its resolution better than about 0.1 nanometer can meet the requirements. A linear array detector is used for detection, so there are no moving parts, and it is equipped with a computer interface for convenient data acquisition and subsequent processing, which can meet the usage requirements. The output focusing optical path uses an integrated 90° turning parabolic mirror to efficiently introduce parallel light beams into the ultraviolet fiber and then input them into the spectrometer.

[0026] The basic configuration of the dielectric spectroscopy light source is a single-wavelength LED light source and its driving power supply. Its circular light beam can be output to the light input window after being collimated by a simple lens, and is used for the measurement of a single type of molecular beam. Mechanical shutter baffles can be configured on the light input and output windows of the molecular beam epitaxy equipment, so that the shutter can block the inside of the window when not measuring to avoid beam deposition. In addition, heating components can also be configured on the window flange to reduce beam deposition during measurement. The improved configuration of the dielectric spectroscopy light source can include a mechanically switched multi-wavelength light source, a multi-wavelength device beam combining light source, a multi-chip multi-wavelength single-beam packaged device light source, etc., and corresponding driving power supplies are configured for the simultaneous or separate measurement of multiple elements.

[0027] The data collected by the spectrometer is sent to the computer and processed with self-developed special software. This software can separately set the absorption spectral line wavelengths of one to several absorption data and the wavelength offset of its reference data . Through simple reference calculations as described above, the absorbance of one to several elements' corresponding absorption lines can be obtained, and self-calibration is completed in real time. This absorbance data can be directly applied to the on-line real-time beam monitoring in molecular beam epitaxy growth.

[0028] It should be noted that the term "including" and its variants used in the embodiments of the present invention are open-ended, that is, "including but not limited to". The term "based on" is "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "multiple" mentioned in the embodiments of the present invention are illustrative rather than restrictive. Those skilled in the art should understand that unless clearly indicated otherwise in the context, it should be understood as "one or more".

[0029] The user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the embodiments of the present invention are all information and data that have been authorized by the user or fully authorized by all parties. Moreover, the collection, use, and processing of relevant data need to comply with relevant laws, regulations, and standards of relevant countries and regions, and corresponding operation entrances are provided for users to choose to authorize or refuse.

[0030] In the method implementation manners provided by the embodiments of the present invention, the steps recorded can be executed in different orders and / or executed in parallel. In addition, the method implementation manners may include additional steps and / or omit the steps shown. The protection scope of the present invention is not limited in this regard.

[0031] The term "embodiment" in this specification means that the specific features, structures, or characteristics described in combination with the embodiment may be included in at least one embodiment of the present invention. The phrase appears in various positions in the specification does not necessarily mean the same embodiment, nor does it mean being independent or alternative to other embodiments and mutually exclusive. The embodiments in this specification are all described in a related manner, and the same or similar parts among the embodiments are referred to each other. In particular, for device, equipment, and system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiments.

[0032] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the protection scope. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A real-time beam measurement system based on a medium-spectrum light source, characterized in that: This system uses a continuous medium spectrum light source with a spectrum width ranging from ten to tens of nanometers as the light source for real-time online beam current measurement; wherein the measured beam current is a molecular beam current.

2. A self-calibration method for a real-time beam current measurement system based on a meso-spectrum light source, applied to the real-time beam current measurement system based on a meso-spectrum light source as claimed in claim 1, characterized in that: This system has a self-calibration function, and the specific implementation steps are as follows: A single measuring optical path is used to collect specific spectral data using a spectrometer; By calculating three or more data points in specific spectral data, the real-time absorption intensity data of the corresponding molecular beam after reference can be directly obtained; The relative beam intensity is obtained based on the real-time absorption intensity data.

3. The self-calibration method of the real-time beam measurement system based on the meso-spectrum light source according to claim 2 is characterized in that: The self-calibration function is used for real-time online measurement of a single type of beam, or for real-time online separate measurement of multiple beams by switching the optical path of the light source, or for real-time online simultaneous or separate measurement of multiple beams by beam synthesis of the light source or customized multi-wavelength multi-chip single beam packaging devices.

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