Real-time beam measurement system based on dielectric spectrum light source and self-calibration method thereof

Abstract

The invention belongs to the field of molecular beam epitaxy of compound materials, and particularly relates to a real-time beam measurement system based on a dielectric spectrum light source and a self-calibration method thereof, a continuous dielectric spectrum light source with the spectral width ranging from 10 nanometers to dozens of nanometers is used as a light source for real-time online beam measurement, the system has a self-calibration function, namely, a single measurement light path is adopted, and the beam measurement accuracy is improved. The method comprises the following steps: acquiring specific spectral data after the action of a light source beam and a molecular beam by using a spectrograph, calculating three or more data points in the specific spectral data to directly obtain real-time absorption intensity data of a corresponding molecular beam after reference, and thus obtaining relative beam intensity; the system and the self-calibration method thereof are not only suitable for real-time on-line measurement of a single type of beams, but also can be used for real-time on-line measurement of various beams through light source light path switching, and can also be used for real-time on-line separate or simultaneous measurement of various beams through light source beam synthesis or customization of a multi-wavelength multi-chip single-beam packaging device. The method is a universal scheme.

Description

Technical Field

[0001] The invention belongs to the field of molecular beam epitaxy of compound materials, and in particular relates to a real-time beam current measurement system based on a mesospectral 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 wavelengths. For semiconductor optoelectronic devices and electronic devices, epitaxial growth is the main means of making device structures, among which molecular beam epitaxy is favored by people due to its precision and high controllability.

[0003] The measurement and monitoring of molecular beam current in molecular beam epitaxy is a necessary condition for growing high-performance materials, and precise, reliable and convenient online real-time monitoring is what people expect. The traditional beam monitoring method is based on the use of a vacuum gauge to measure the thermal electron emission current related to the beam intensity. Although it is an online measurement, it cannot achieve real-time measurement during the growth process, that is, measurement and growth cannot be carried out at the same time; the optical method that emerged later is based on the "old" atomic absorption spectroscopy technology in principle, and has developed measuring instruments that can perform online real-time measurements, but it has a series of problems and has not yet been widely used. At present, the main problems of the optical method are the light source and the calibration reference method, and the two are closely related to each other.

[0004] At present, the light sources used in optical methods can be divided into two categories: wide spectrum and narrow spectrum. Wide spectrum light sources are often thermal light sources, such as xenon lamps, halogen tungsten lamps, etc., whose power can be large enough but the spectrum utilization efficiency is extremely low. This is because the measurement of atomic absorption generally only needs to be carried out within a very narrow spectral range, such as ten to tens of nanometers, while the spectral range of thermal light sources at least covers several microns, that is, its spectrum 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 heat generation and cause a series of problems. In addition, the stability of thermal light sources is poor and the lifespan is also very short, generally only a few hundred hours; narrow spectrum light sources are often hollow cathode lamps or semiconductor lasers. Although the emission spectrum of the hollow cathode lamp can be well matched with the measured beam source, its output power is very low, and its life span is short, only a few hundred hours. It decays seriously during its life cycle, and the stability of the gas discharge itself is poor, which increases the difficulty of signal measurement. Although the power of the semiconductor laser is sufficient, the optional wavelength is very limited and relatively fixed, and it is difficult to obtain a suitable device that matches the measured beam source. The universality is poor, and the wavelength of the semiconductor laser is inevitably affected by the ambient temperature, and the stability is difficult to meet the requirements. For these two types of light sources, due to their stability and other factors, it is necessary to make a reference in the measurement. Generally, a reference optical path is set up separately. On the one hand, this makes the system complicated and the overall stability worse. On the other hand, although setting up an external optical path for reference can compensate for the influence of light source stability, it is difficult to compensate for the signal fluctuations of the internal optical path, especially the more serious effects caused by the light scattering of the molecular beam itself. These limitations are essential. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a universal online real-time beam current measurement system based on a mesoscopic light source and a corresponding self-calibration method, aiming to fundamentally solve the problems existing in the light source and reference in the previous methods. Figure 1 Please explain in detail.

[0006] The molecular beam epitaxial growth of the material is carried out in a molecular beam epitaxial vacuum chamber 7 which can reach an ultra-high vacuum state; it includes a beam source furnace crucible and a beam source material 8 as a growth source. According to the specific growth requirements, the beam source often needs to have multiple paths, and the attached Figure 1 Only one of the paths is shown as a schematic diagram; the growth source in the beam source furnace is heated to form the required molecular beam 9; which acts on the epitaxial substrate 10 to perform epitaxial growth; these parts are conventional configurations of the molecular beam epitaxy system.

[0007] The online real-time beam measurement system based on the mesospectrum light source of the present invention introduces the light input window 5 and its flange and the light output window 6 and its flange on the molecular beam epitaxy vacuum chamber 7. The optical window and the flange are integrated components suitable for vacuum system installation, located at the relative position of the radial center of the system and orthogonal to the molecular beam 9, ensuring that the light beam and the molecular beam form the maximum action area. The two windows can use the central position of the molecular beam epitaxy system. The ready-made flange port that penetrates and is unobstructed; the collimated light beam generated by the mesospectrum light source 1 system including the light source switching / synthesis / collimation optical path 2 is input from the light input window 5 and its flange and acts on the molecular beam. The light beam after acting on the molecular beam is output through the light output window 6 and its flange, and is input to the spectrometer 3 through the output focusing optical path 4 for spectral signal detection to obtain specific spectral data.

[0008] The present invention uses a medium spectrum light source with a spectrum width (i.e., light intensity half-width) of several nanometers to tens of nanometers as a measurement light source, and tens of nanometers can be 30 to 50 nanometers. In view of the fact that the atomic absorption line width of the molecular beam is much smaller than 1 nanometer and the wavelength position is fixed, it is only necessary to basically align the central wavelength of the medium spectrum light source with the selected atomic absorption line wavelength so that the spectrum width of the medium spectrum light source can cover the atomic absorption line wavelength, and there is no strict requirement. For multiple molecular beam measurements, the multiple measurement wavelengths selected by the medium spectrum light source should match the respective atomic absorption lines and avoid overlapping. In addition, the wavelength used by the medium spectrum light source should also be compatible with the spectral measurement range of the spectrometer.

[0009] The present invention adopts a single optical path reference scheme, which is self-calibration. The spectral intensity distribution of the mesoscopic light source generally conforms to the central wavelength of , the half-width is Gaussian distribution or other similar symmetric distribution, let its distribution be , Indicates wavelength. The wavelength of the absorption spectrum of the atom to be measured in the molecular beam source is According to the above principles, the mesospectral light source only needs to meet Falling on Otherwise, it cannot be measured. are two reference wavelength measurement points. The data of the absorption line wavelength measurement point are directly calibrated. About 1 to 2 nanometers can avoid the broadening of atomic absorption lines and the influence of the resolution of conventional spectrometers, and make the two reference wavelengths still fall within the half-width wavelength of the intermediate spectrum light source. It can be expressed as:

[0010] ,

[0011] The data contained in this formula are all measurable data of the spectrometer, that is, only three wavelength points, namely, the wavelength of the atomic absorption line to be measured and its two closest reference wavelengths, are needed. , , The intensity data on the beam can be used to directly calculate the absorbance data related to the molecular beam intensity, and this absorbance data is independent of the fine spectral distribution of the mesospectral light source.

[0012] When there are various fluctuations in the measurement system, including possible fluctuations in the intensity of the medium spectrum light source, fluctuations in the geometry of the optical path, the switching of the molecular beam source, the addition or withdrawal of different molecular beam sources, the fluctuations in the scattering intensity caused by the change in beam intensity, and the fluctuations in the measurement of the spectrometer itself, these fluctuations are independent of the wavelength itself within a smaller wavelength range. A fluctuation factor is introduced for these fluctuations. The absorbance measured at this time is It is expressed as:

[0013] ,

[0014] Right now ,

[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 pointed out that the attenuation of the signal may cause the measurement signal-to-noise ratio to decrease, that is, the influence of the measurement system noise may increase, but it will not have a significant impact on the measurement results in a larger range. For the medium-spectrum light source, another possible fluctuation is the temperature drift of the central wavelength. For example, for LEDs (light-emitting diodes) in the ultraviolet band, the wavelength temperature coefficient is about 0.2-0.4nm / K, that is, the central wavelength will drift by about 2 to 4 nanometers when the temperature fluctuates by 10°C. However, since this reference method uses two reference wavelength points on the left and right sides for averaging, as long as the central wavelength is selected appropriately, a small range of central wavelength drift will not affect the reference correction effect. Similarly, more wavelength reference points can be selected for reference, but it cannot significantly improve the reference correction effect.

[0016] It should be noted that the absorbance After that, 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 according to the real-time absorption intensity are all common knowledge in the art and will not be elaborated herein.

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

[0018] In view of the fundamental problems existing in the two major types of light sources, broad spectrum and narrow spectrum, the present invention proposes a solution of using an intermediate spectrum light source, which can fundamentally solve the main problems of both light source and reference. Here, an intermediate spectrum light source is defined as another type of light source whose spectral range is between broad spectrum and narrow spectrum, and its spectral range can be between a few nanometers and tens of nanometers, and tens of nanometers can be 30 to 50 nanometers. On the one hand, the use of intermediate spectrum light sources can solve the above-mentioned key problems such as spectral utilization, coverage, light source stability and life, and measurement signal-to-noise ratio. On the other hand, the single optical path reference solution of the present invention can compensate for the influence of a series of fluctuations including light source and optical path and molecular beam scattering, and can be used for real-time online measurement of multiple beams by switching the light source optical path. It can also perform real-time online simultaneous measurement of multiple beams by light source beam synthesis or customized multi-wavelength multi-chip single beam packaging devices, so it is a universal solution.

[0019] As described above, the online real-time beam measurement system based on the medium spectrum light source and the self-calibration method thereof provided by the present invention have the advantages of simple method, less equipment required, low cost, good reference correction effect, strong robustness and convenient operation. It can be applied to real-time online measurement of a single type of beam, and can also be used for real-time online measurement of multiple beams through light source optical path switching. It can also perform real-time online separate or simultaneous measurement of multiple beams through light source beam synthesis or customized 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 briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without creative work. In the drawings:

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

[0022] Among them, 1: medium 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; 10: epitaxial substrate. DETAILED DESCRIPTION

[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 accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein, which are instead provided for a more thorough and complete understanding of 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 uses the optical online real-time beam current measurement system and its self-calibration method required for 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, as long as the corresponding adjustments are made. The specific concepts and steps are as follows:

[0025] The III-V compound semiconductor molecular beam epitaxy growth involves mainly Al (aluminum), Ga (gallium) and In (indium), and the V-group growth sources are mainly P (phosphorus), As (arsenic) and Sb (antimony). The doping source generally does not require real-time monitoring because the required beam intensity is low and relatively stable. The wavelengths of the atomic absorption spectra of the above III- and V-group sources are mainly concentrated in the near-ultraviolet band. For the medium-spectrum light source, the LED device in the ultraviolet band is preferred, and its spectrum width is generally between ten and tens of nanometers and is a continuous spectrum, CW (continuous wave) operation, which just meets the use requirements. The central wavelength of LED devices in the ultraviolet band cannot be selected arbitrarily due to the limitations of the material system used, but there are quite a few central wavelengths to choose from, such as 405 nanometers, 395 nanometers, 390 nanometers, 385 nanometers, 365 nanometers, 310 nanometers, 285 nanometers and 254 nanometers, etc., and each central wavelength itself generally has a variation range of several nanometers to choose from. New central wavelength devices are constantly emerging, so the measurement requirements of molecular beam epitaxial growth of III-V materials can be basically met. For example, a device with a central wavelength of 395 nanometers can be used to measure the strong absorption line of the Al beam at 396.15 nanometers. A device with a 254 nanometer wavelength can be used to measure the strong absorption line of the P beam at 253.56 nanometers or the Sb beam at 252.85. Since the wavelengths of the strong absorption lines of these two elements are close but still within the resolution capability of the spectrometer, if these two molecular beams exist in the system at the same time and need to be measured simultaneously, the corresponding reference wavelength can be selected as Nano and Nanometers, and other situations can be deduced accordingly. Correspondingly, the measurement range of the spectrometer used in the measurement system is set at 200 to 400 nanometers. A fiber-optic input micro-grating spectrometer is selected, and its resolution is better than about 0.1 nanometers to meet the needs. Linear detectors are used for detection, so there are no moving parts, and a computer interface is provided to facilitate data collection and subsequent processing, which can meet the use requirements. The output focusing optical path uses an integrated 90° angle parabolic mirror to efficiently introduce the parallel light beam into the ultraviolet optical fiber and then input it into the spectrometer.

[0026] The basic configuration of the media spectrum 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 to measure a single type of molecular beam. The light input and light output windows on the molecular beam epitaxy device can be equipped with corresponding mechanical shutter baffles, so that the shutter can block the inside of the window when not measuring to avoid beam deposition. In addition, a heating component can also be configured on the window flange to reduce beam deposition during measurement. The improved configuration of the media spectrum light source can include a mechanically switched multi-wavelength light source, a beam combining light source of multiple wavelength devices, a multi-chip multi-wavelength single-beam packaged device light source, etc., and a corresponding driving power supply, which can be used for simultaneous or separate measurement of multiple elements.

[0027] The data collected by the spectrometer is sent to the computer and processed using the self-developed special software. This software can set the wavelength of one or several absorption lines of the absorption data. and the wavelength offset of its reference data The data can be used to obtain the absorbance of one or more corresponding absorption lines of the elements through simple reference calculation as described above, and self-calibration can be completed in real time. This absorbance data can be directly applied to online real-time beam current monitoring in molecular beam epitaxy growth.

[0028] It should be noted that the term "including" and its variations used in the embodiments of the present invention are open inclusions, that is, "including but not limited to". The term "based on" means "based at least in part on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other 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 and not restrictive. Those skilled in the art should understand that unless the context clearly indicates otherwise, 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 used for analysis, stored data, displayed data, etc.) involved in the embodiments of the present invention are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with the relevant laws, regulations and standards of relevant countries and regions, and provide corresponding operation entrances for users to choose to authorize or refuse.

[0030] The various steps described in the method implementation methods provided by the embodiments of the present invention may be performed in different orders and / or in parallel. In addition, the method implementation methods may include additional steps and / or omit the steps shown. The scope of protection of the present invention is not limited in this respect.

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

[0032] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of protection. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the attached 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 spectral width ranging from ten to tens of nanometers as the light source for real-time online beam current measurement.

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.

Images