Multi-wavelength semiconductor light source device for ellipsometer, control method and ellipsometer

Abstract

The invention discloses a multi-wavelength semiconductor light source device for an ellipsometer, a control method and the ellipsometer, and the device comprises a light source module which is provided with a plurality of semiconductor light-emitting units which are installed in parallel and have different wavelengths and a focusing coupling unit and is used for generating multi-wavelength light beams; the optical fiber transmission module transmits the light beam to an emergent end; the beam splitting element is used for splitting emergent light into a main light path entering the ellipsometer and a monitoring light path entering the light intensity monitoring module; the light intensity monitoring module detects light intensity and feeds back the light intensity to the light power closed-loop control module so as to adjust the output power of the light source; the temperature closed-loop control module and the thermoelectric refrigerating unit are used for stabilizing the temperature of the driving circuit board; through light intensity and temperature double-closed-loop control, efficient coupling, stable output and rapid switching of multi-wavelength light beams are achieved, a high-stability and compact multi-wavelength light source solution is provided for the ellipsometer, and the measurement precision and reliability are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical measurement technology, in particular to a multi-wavelength semiconductor light source device for an ellipsometer, a control method and the ellipsometer. BACKGROUND

[0002] The ellipsometer is a precision instrument for measuring the optical constants and film thickness of micro-nano thin films, based on the ellipsometric principle, by measuring the change of polarization state before and after reflection of the sample surface, the film thickness and optical constants of the sample are analyzed. The light source is one of the core components of the ellipsometer, and the performance of the light source directly determines the precision, speed and stability of the ellipsometric measurement.

[0003] The commonly used light source scheme of the ellipsometer: using a wide-spectrum halogen lamp and a deuterium lamp as the measurement light source, and performing wavelength spectrometer scanning through a grating monochromator. This light source scheme has many shortcomings: (1) The scanning spectrometer measurement speed is slow, and instantaneous multi-wavelength measurement cannot be realized; (2) Poor light source stability, the light intensity and spectrum of the wide-spectrum lamp are easy to drift with power fluctuations, environmental temperature and working time, and need to be calibrated frequently, which is easy to introduce measurement errors; (3) Short service life and high maintenance cost, the service life of the deuterium lamp and the halogen lamp is usually only 1000-2000 hours, and frequent replacement is required, and the deuterium lamp is expensive; (4) A complex optical system (monochromator) is needed for spectrometer, and the optical path adjustment is complex, and the system is large in size. SUMMARY

[0004] Technical purpose: in view of the shortcomings of the existing ellipsometer light source, the present application discloses a multi-wavelength semiconductor light source device for an ellipsometer, a control method and the ellipsometer.

[0005] Technical scheme: in order to achieve the above technical purpose, the present application adopts the following technical scheme: The present application provides a multi-wavelength semiconductor light source device for an ellipsometer, which comprises a light source module, a fiber transmission module, a beam splitting element and a light intensity monitoring module.

[0006] The light source module is used for providing a multi-wavelength light beam, which comprises a plurality of semiconductor light emitting units with different center wavelengths, and a focusing coupling unit for coupling the light beams emitted by different semiconductor light emitting units into the fiber transmission module.

[0007] The optical fiber transmission module is used for transmitting light beams to the ellipsometer optical path. The exit end is provided with the beam splitting element, and the exiting light is split into two perpendicular optical paths by the beam splitting element: one enters the ellipsometer, and the other enters the light intensity monitoring module. The light intensity data monitored by the light intensity monitoring module can be used to adjust the output power of the light source module, thereby realizing light intensity stabilization.

[0008] Further, the focusing coupling unit includes a coupling lens and a multi-in-one optical fiber coupling device arranged in sequence along the light path direction at the light exit end of the semiconductor light emitting unit. The multi-in-one optical fiber coupling device is connected with a multi-mode optical fiber. The semiconductor light emitting units are fixedly installed in parallel to each other on the driving circuit board in the light source module, the exiting light is kept parallel to each other, and the light beams are focused to the end face of the multi-mode optical fiber through the coupling lens.

[0009] Further, the coupling lens is a non-spherical achromatic lens group formed by combining cemented non-spherical lenses, which is used to correct chromatic aberration and spherical aberration of the semiconductor light emitting unit, thereby improving the coupling efficiency.

[0010] Further, the multi-mode optical fiber is an ultraviolet quartz multi-mode optical fiber with a core diameter of 400 μm, which is used to cover the wide light beam band of the semiconductor light emitting unit in the light source module, especially the ultraviolet to visible light range.

[0011] Further, the light intensity monitoring module includes a focusing lens and a wide electro-optical photodetector arranged on the beam splitting light path of the beam splitting element. The wide electro-optical photodetector is connected with a light power closed-loop control module, which is electrically connected with the driving circuit board in the light source module, and adjusts the output power of the semiconductor light emitting unit according to the light intensity data detected by the photodetector.

[0012] Further, the light splitting element includes a collimating lens and a beam splitter arranged along the light path direction. The collimating lens collimates the divergent light beams exiting from the optical fiber transmission module, and then transmits them to the beam splitter for light splitting.

[0013] Further, the beam splitter is a beam splitter, and the light splitting film thereof is a wide-band multi-layer dielectric film system. The wide electro-optical photodetector is a wide-band ultraviolet extended silicon photodetector, and its response band covers 200-1100 nm.

[0014] Further, the light source device is also provided with a temperature closed-loop control module and a thermoelectric cooler for temperature control of the driving circuit board. The thermoelectric cooler is arranged on the back of the driving circuit board. The driving circuit board is embedded with a temperature sensor. The temperature closed-loop control module controls the thermoelectric cooler according to the temperature detected by the sensor, so as to stabilize the working temperature and wavelength of the semiconductor light emitting unit.

[0015] The application provides a control method based on the light source device; a target light intensity value is set for each semiconductor light emitting unit in light intensity closed loop control. One of the split beams is detected by a wide electro-optical detector to obtain an actual light intensity value. A light power closed loop control module compares the actual value with the target value to generate an adjustment signal to the driving circuit board to change the driving current, thereby stabilizing the output light intensity.

[0016] In temperature closed loop control, a target temperature of the driving circuit board is set, and the current temperature is monitored by an embedded temperature sensor. A PID controller in the temperature closed loop control module adjusts the control signal of the thermoelectric cooler according to the temperature error to heat or cool the driving circuit board, thereby keeping the temperature constant.

[0017] The application provides an ellipsometer using the light source device, which is used for measuring the optical constants and film thickness of the micro-nanometer film of a sample.

[0018] Beneficial effects: the multi-wavelength semiconductor light source device for the ellipsometer, the control method and the ellipsometer have the following beneficial effects: 1. A plurality of parallel semiconductor light emitting units are used in cooperation with a dedicated focusing coupling unit and a multi-in-one fiber coupler to realize efficient and compact integration and transmission of multi-wavelength light beams, different wavelength light beams can be quickly provided according to requirements, the measurement speed is faster, the wavelength switching is electronic, there is no scanning type spectrometer, and microsecond-level switching can be realized.

[0019] 2. The light source output power is monitored and adjusted in real time through beam splitting sampling and light intensity closed loop feedback control, the light intensity incident to the ellipsometer is highly stable, the measurement signal-to-noise ratio and repeatability are improved, the temperature of the driving circuit board is detected by a temperature sensor to perform temperature closed loop control, and temperature and light intensity are double closed loop controlled, the problems of temperature drift and power drift of the semiconductor light source are solved, and the long-term stability is much better than that of a traditional wide spectrum lamp.

[0020] 3. The light source device has the advantages of long service life and low maintenance cost, the service life of the semiconductor light emitting unit is usually more than 20,000 hours, which is more than 10 times of that of a deuterium lamp, and the operation cost and downtime are greatly reduced.

[0021] 4. The integration degree is higher, the module volume is small, and the module can be easily integrated into various ellipsometers through a single optical fiber output. DETAILED DESCRIPTION

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description.

[0023] Figure 1 A schematic view of the multi-wavelength semiconductor light source device of the application; Figure 2 Fig. 1 is a schematic diagram of the optical power closed-loop control principle of the present application; Figure 3 Fig. 2 is a schematic diagram of the temperature closed-loop control principle of the present application; Fig. 1 is a schematic diagram of the optical power closed-loop control principle of the present application; DETAILED DESCRIPTION

[0024] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are set forth herein below. Each example and embodiment is provided by way of explanation of the present disclosure, not limitation. Contrarily, the following description provides a convenient illustration for implementing exemplary embodiments of the present disclosure. In fact, those skilled in the art will be apparent that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the present disclosure.

[0025] As shown in Fig. 1, the present application discloses a multi-wavelength semiconductor light source device for ellipsometer, which comprises a light source module for providing a multi-wavelength light beam, and a fiber transmission module for transmitting the light beam to the light path of the ellipsometer, the light source module comprises several semiconductor light emitting units 1 with different central wavelengths, and the light source module and the fiber transmission module are provided with a focusing coupling unit for coupling the light beams emitted by the different semiconductor light emitting units into the light transmission module. Figure 1

[0026] ​The focusing coupling unit comprises a coupling lens 2 and a multi-in-one optical fiber coupling device 3 arranged in sequence along the light path direction at the light exit end of the semiconductor light emitting unit, the multi-in-one optical fiber coupling device 3 is a multi-dimension optical fiber coupling adjusting frame, which can precisely adjust the optical fiber in multiple dimensions, and can fix and lock the optical fiber after adjustment, thereby ensuring stable and efficient coupling of the optical fiber; the multi-in-one optical fiber coupling device 3 is connected with a multi-mode optical fiber 4 for light beam transmission, the semiconductor light emitting unit 1 comprises light emitting diodes and / or laser diodes, the center wavelengths of these light emitting units cover from ultraviolet to near-infrared wave bands, for example, 265nm LED, 405nm LD, 532nm LD, 635nm LD, 785nm LD, 850nm LD, 1064nm LD, which are selected and soldered on a driving circuit board 5 in a linear array or matrix form, so as to keep the exit light of the semiconductor light emitting unit 5 parallel to each other, and the light beams are focused to the end face of the multi-mode optical fiber 4 through the coupling lens 2; in order to ensure the focusing effect, an aspheric collimating lens 13 is arranged on the light path of each semiconductor light emitting unit 1, and the light emitted by the corresponding semiconductor light emitting unit 1 is collimated as parallel light after collimation adjustment. The coupling lens 2 adopts an aspheric lens combination to form an aspheric achromatic lens group, which corrects the chromatic aberration and spherical aberration of the semiconductor light emitting unit 1. The multi-mode optical fiber 4 adopts an ultraviolet quartz multi-mode optical fiber with a core diameter of 400μm, which covers the light beam bands of the semiconductor light emitting units 1 in the light source module.

[0027] The exit end of the optical fiber transmission module is provided with a beam splitting element, the exiting light is split into two perpendicular light paths by the beam splitting element, one enters an ellipsometer, and the other enters a light intensity monitoring module, the output power of the light source module is adjusted through the light intensity data monitored by the light intensity monitoring module; the beam splitting element comprises a collimating lens 9 and a light beam splitter 10 arranged along the light path direction, the light beam exiting from the optical fiber transmission module is collimated and then transmitted to the light beam splitter 10 through the collimating lens 9, the collimating lens 9 is an aspheric achromatic lens group, which is combined by aspheric lenses and can correct chromatic aberration and spherical aberration at the same time, and collimates the light with different center wavelengths exiting from the optical fiber as parallel light, and the light beam is split into the ellipsometer and the light intensity monitoring module through the light beam splitter 10. The light beam splitter 10 adopts a beam splitter, and the beam splitting film of the light beam splitter 10 is a wide-band multi-layer dielectric film system, which can reflect about 5% of the light into the light intensity monitoring light path, and the remaining most of the light enters the ellipsometer light path after passing through the light beam splitter 10.

[0028] In order to reduce the influence of light source output light intensity precision on ellipsometer measurement, automatically compensate the light power attenuation caused by light source aging, temperature fluctuation and other factors, and maintain stable light intensity output, the application adopts light intensity monitoring module to proceed with closed loop control of light intensity; the light intensity monitoring module comprises focusing lens 6 and wide electro-optical photodetector 7 arranged on the beam splitting light path of the beam splitting element; the wide electro-optical photodetector 7 is a wide band ultraviolet extended silicon photodetector, and the response band covers 200-1100nm. The wide electro-optical photodetector 7 is connected with light power closed loop control module 8, the light power closed loop control module 8 is electrically connected with the drive circuit board 5 in the light source module for controlling the semiconductor light emitting unit 1, the output power of the semiconductor light emitting unit 1 is adjusted according to the light intensity data detected by the wide electro-optical photodetector 7, and the wide electro-optical photodetector is a wide band ultraviolet extended silicon photodetector, and the response band can cover 200-1100nm.

[0029] The light source device is also provided with temperature closed loop control module 11 and thermoelectric cooler 12 for temperature control of the drive circuit board, the thermoelectric cooler 12 is arranged on the side of the drive circuit board away from the semiconductor light emitting unit, the temperature of the drive circuit board 5 is controlled, the temperature sensor for detecting the temperature of the heating area is embedded in the drive circuit board 5, the temperature closed loop control module 11 is electrically connected with the thermoelectric cooler 12 and the temperature sensor, and the operation of the thermoelectric cooler 12 is controlled according to the temperature detected by the temperature sensor; the operation of each control module is controlled by computer 15.

[0030] The drive circuit board 3 is an aluminum nitride ceramic substrate, the temperature sensor is embedded in the substrate, the refrigeration surface of the thermoelectric cooler 2 is close to the multi-channel drive circuit board, the heat generated by the plurality of semiconductor light emitting units is conducted to the heat dissipation plate 14 on the other side through the thermoelectric cooler, the heat exchange efficiency is accelerated through the heat dissipation plate 14, as an optimization, the heat dissipation plate is made of copper or aluminum material, preferably red copper material, has high thermal conductivity, and the heat dissipation plate is connected with the light source module metal shell with heat dissipation fins, and the heat is conducted to the metal shell and dissipated through the heat dissipation fins.

[0031] As Figure 2 and Figure 3As shown, the application discloses a control method based on the light source device, when the light intensity closed loop control is carried out, a target light intensity value is set for each semiconductor light emitting unit in the light source module; the emitted light is split by a beam splitting element, one way of light is focused by a focusing lens and then incident to a wide electro-optical detector, the wide electro-optical detector converts the light signal into an electric signal, measures the actual light intensity, and returns the actual measured light intensity value to the comparator of the light power closed loop control module; the difference between the actual light intensity value and the preset target light intensity value is calculated by the comparator, the light power control circuit of the light power closed loop control module generates an adjusting signal according to the difference, and sends the adjusting signal to the multi-channel programmable constant current source matched with the driving circuit board, so that the driving current is changed, and the light emitting intensity of the semiconductor light emitting unit is changed, thereby providing stable detection light beams for the ellipsometer. When the temperature closed loop control is carried out, the target temperature of the driving circuit board is set, and the current temperature is monitored in real time by the embedded temperature sensor; the PID controller in the temperature closed loop control module receives the current temperature, calculates the temperature error with the target temperature, and adjusts the direction and size of the current of the TEC driver of the thermoelectric cooler according to the temperature error, so that the driving circuit board is heated or cooled.

[0032] The application also discloses an ellipsometer using the light source device, which inherits all the advantages of the light source device, and can quickly and accurately measure the optical constants and film thickness of the micro-nanometer film of the sample under test at multiple stable wavelengths.

[0033] When the ellipsometer is used for measurement, the substrate temperature of the driving circuit board to be controlled, the light emitting intensity of each semiconductor light emitting unit 1, the lighting sequence and the lighting time are set by the ellipsometer control software, the control circuit on the driving circuit board lights each wavelength of the semiconductor light emitting unit in turn according to the preset value quickly (up to microseconds), the light emitted by each unit is coupled into the same optical fiber after collimation, and is transmitted to the optical path of the ellipsometer as quasi-monochromatic light. According to the need, each wavelength of the semiconductor light emitting unit can also be lit at the same time, and is transmitted to the optical path of the ellipsometer as mixed light. The average service life of the semiconductor light source can reach at least 20,000 hours under good heat dissipation, which is much longer than the service life of the deuterium lamp and the halogen lamp. Since the switching is electrically controlled and there is no mechanical movement, the switching speed can reach microseconds, which greatly improves the speed of the ellipsometer measurement. At the same time, the temperature control and light power feedback system ensures that the light intensity and wavelength of each light beam are highly stable, so that the ellipsometric measurement data is more stable and reliable. Since the monochromator is not needed for scanning and light splitting, the whole system is greatly simplified, the module integration is higher, and the output is realized through a single optical fiber, so that the system can be integrated into various ellipsometers.

[0034] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A multi-wavelength semiconductor light source device for an ellipsometer, characterized in that, It includes a light source module for providing multi-wavelength beams and an optical fiber transmission module for transmitting the beams to the optical path of an ellipsometer. The output end of the optical fiber transmission module is provided with a beam splitting element, which splits the emitted light beams into two mutually perpendicular optical paths. One path enters the ellipsometer, and the other path enters a light intensity monitoring module. The output power of the light source module is adjusted based on the light intensity data monitored by the light intensity monitoring module. The light source module includes several semiconductor light-emitting units (1) with different center wavelengths. The light source module and the optical fiber transmission module are provided with a focusing coupling unit for coupling the beams emitted by different semiconductor light-emitting units into the light transmission module.

2. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 1, characterized in that, The focusing coupling unit includes a coupling lens (2) and a multi-fiber coupling device (3) arranged sequentially along the optical path at the light emission end of the semiconductor light-emitting unit. The multi-fiber coupling device (3) is connected to a multimode fiber (4) for beam transmission. The semiconductor light-emitting units (1) are fixedly mounted on the driving circuit board (5) in parallel within the light source module to keep the emitted light from the semiconductor light-emitting units (5) parallel to each other. The beam is focused onto the end face of the multimode fiber (4) through the coupling lens (2).

3. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 2, characterized in that, The coupling lens (2) is formed by combining cemented aspherical lenses to form an aspherical achromatic lens group, which corrects the chromatic aberration and spherical aberration of the semiconductor light-emitting unit (1).

4. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 2, characterized in that, The multimode fiber (4) is an ultraviolet quartz multimode fiber with a core diameter of 400μm, covering the beam band of the semiconductor light-emitting unit (1) in the light source module.

5. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 1, characterized in that, The light intensity monitoring module includes a focusing lens (6) and a wide electric photodetector (7) disposed on the beam splitting optical path of the beam splitting element. The wide electric photodetector (7) is connected to a light power closed-loop control module (8). The light power closed-loop control module (8) is electrically connected to the driving circuit board (5) in the light source module for controlling the semiconductor light-emitting unit (1). The output power of the semiconductor light-emitting unit (1) is adjusted according to the light intensity data detected by the wide electric photodetector (7).

6. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 1, characterized in that, The beam splitting element includes a collimating lens (9) and a beam splitter (10) arranged along the optical path direction. The collimating lens (9) collimates the beam emitted from the optical fiber transmission module and transmits it to the beam splitter (10). The beam splitter (10) splits the beam into corresponding beams to the ellipsometer and the light intensity monitoring module.

7. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 1, characterized in that, The beam splitter (10) is a beam splitter, and the beam splitting film of the beam splitter (10) is a wide-band multilayer dielectric film system; the wide-band photodetector (7) is a wide-band ultraviolet extended silicon photodetector with a response band covering 200-1100nm.

8. The multi-wavelength semiconductor light source device for an ellipsometer according to claim 1, characterized in that, The light source device is also provided with a temperature closed-loop control module (11) and a thermoelectric cooler (12) for temperature control of the drive circuit board. The thermoelectric cooler (12) is located on the side of the drive circuit board away from the semiconductor light-emitting unit and performs temperature control on the drive circuit board (5). The drive circuit board (5) is embedded with a temperature sensor for detecting the temperature of the heating area. The temperature closed-loop control module (11) is electrically connected to the thermoelectric cooler (12) and the temperature sensor and controls the operation of the thermoelectric cooler (12) according to the temperature detected by the temperature sensor.

9. A control method for a light source device according to any one of claims 1-8, characterized in that, During the light intensity closed-loop control, a target light intensity value is set for each semiconductor light-emitting unit in the light source module. The emitted light is split by a beam splitter, and one beam is focused by a focusing lens and incident on a wide-band photodetector. The wide-band photodetector converts the light signal into an electrical signal, measures the actual light intensity, and returns the measured light intensity value to the comparator of the light power closed-loop control module. The comparator calculates the difference between the actual light intensity value and the preset target light intensity value. The light power closed-loop control module generates an adjustment signal based on this difference and sends it to the drive circuit board to change the drive current, thereby changing the luminous intensity of the semiconductor light-emitting unit and providing a stable detection beam for the ellipsometer. When performing temperature closed-loop control, the target temperature of the drive circuit board is set, and the current temperature is monitored in real time by the embedded temperature sensor. The PID controller in the temperature closed-loop control module receives the current temperature, calculates the temperature error with the target temperature, and controls the thermoelectric cooler based on the temperature error. Adjust the direction and magnitude of the current to heat or cool the drive circuit board.

10. An ellipsometer, characterized in that, The optical constants and film thickness of the micro / nano thin film of the sample under test are measured using the light source device described in any one of claims 1-8.

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