Flat femtosecond laser supersaturated doping device and method and preparation method of detector

Abstract

The invention provides a flat femtosecond laser supersaturated doping device and method and a preparation method of a detector, and belongs to the technical field of photoelectricity, the flat femtosecond laser supersaturated doping device comprises a femtosecond laser, an electro-optical shutter, a second half-wave plate, a second Glan-Taylor prism, a focusing lens and a closed processing cavity which are arranged in sequence, and a sulfur film is plated on the silicon surface through a thermal evaporation method to serve as a doping agent. And the electro-optical shutter is used for accurately controlling the number of machining pulses, machining of any number of pulses is achieved, and uncontrollable random influences caused by surface energy localization, the incubation effect and the like are restrained. The prepared flat supersaturated doped silicon material surface is compatible with the modern semiconductor industrial technology, development of silicon-based series photoelectric devices is facilitated, and development of focal plane devices such as a CCD (charge coupled device) and a CMOS (complementary metal oxide semiconductor) is promoted. In addition, the light responsivity of the flat supersaturated doped silicon detector prepared by the invention in the wave band of 350-1200nm exceeds 1A / W, and ultraviolet enhancement and sub-band gap infrared detection are realized at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic technology, and in particular relates to a flat femtosecond laser supersaturation doping device, method and detector preparation method. Background Art

[0002] Semiconductor doping is an essential step in the preparation of semiconductor functional devices, and increasing the doping concentration to above the physical equilibrium limit is called supersaturated doping. Supersaturated doping can change the optoelectronic properties of materials and facilitate the development of new optoelectronic devices. For example, doping sulfur in silicon to supersaturation can expand the absorption spectrum of the material to ultraviolet and infrared, and prepare silicon-based wide-spectrum photodetectors.

[0003] Conventional supersaturation doping methods include ion implantation and femtosecond laser doping. Ion implantation can precisely control the doping concentration and depth, but the doping atoms are mostly in invalid interstitial positions, rather than effective substitution or quasi-substitution positions, that is, the doping activation rate is low, and the ion implantation cost is very high. In comparison, femtosecond laser doping is a new supersaturation doping technology with good prospects.

[0004] In a specific environment (doped atomic atmosphere, surface coating, etc.), supersaturated doping of the corresponding elements can be achieved by irradiating the material with a femtosecond laser. 6 The use of femtosecond laser focused scanning of silicon materials in atmosphere has become a standard technical solution for preparing supersaturated sulfur-doped silicon. Compared with other doping methods, femtosecond laser supersaturated doping has low cost and high doping activation rate.

[0005] However, femtosecond laser ablation doping will induce micro-conical light-trapping structures on the surface of the material, and obtain a doping concentration on the surface of the material that far exceeds the solid solubility limit. Since the modified area is black, supersaturated doped silicon is also called "black silicon". Since the doping process and the formation process of the surface micro-nanostructure are easily disturbed by environmental factors and random defects of the material itself, the disadvantage of femtosecond laser supersaturated doping is that there are concave and convex microstructures randomly distributed on the surface, and the doping concentration, depth, and especially uniformity are difficult to control, resulting in high dark current and poor uniformity of the black silicon detector prepared by femtosecond laser. In addition, the fluctuations of the surface microstructure also make the silicon material supersaturated doped by femtosecond laser difficult to be compatible with modern semiconductor industry technology, especially for the production of focal plane devices such as CCD and CMOS. Summary of the invention

[0006] The problem to be solved by the present invention is to provide a flat femtosecond laser supersaturation doping device, method and detector preparation method.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a flat femtosecond laser supersaturation doping device, comprising a femtosecond laser, an electro-optical shutter, a second half-wave plate, a second Glan Taylor prism, a focusing lens and a closed processing chamber arranged in sequence, a sample holder is installed in the closed processing chamber, and the sample holder is installed on a three-dimensional translation device.

[0008] Furthermore, the electro-optical shutter includes a first half-wave plate, a Pockels cell and a first Glan Taylor prism, and the Pockels cell includes an electro-optical crystal and a driving power supply.

[0009] Furthermore, a mechanical shutter is provided between the femtosecond laser and the closed processing chamber.

[0010] Furthermore, the mechanical shutter is located between the femtosecond laser and the electro-optical shutter.

[0011] The present invention also provides a planar femtosecond laser supersaturation doping method, comprising the following steps:

[0012] S1. Fix the sample to be doped on a sample holder in a closed processing chamber;

[0013] S2, the femtosecond laser emits laser pulses, and the number of pulses is controlled by the mechanical shutter and the electro-optical shutter in turn; because the mechanical shutter has a response time of the order of ten milliseconds, it cannot realize single pulse control of high-frequency (>100Hz) femtosecond lasers, and the electro-optical shutter is required to accurately control the number of pulses to realize arbitrary pulse number processing;

[0014] S3. After the number of pulses is controlled, the laser pulses sequentially pass through the second half-wave plate and the second Glan Taylor prism. The second half-wave plate is used to rotate the pulse polarization disk. The second Glan Taylor prism only transmits the projection with a fixed polarization direction. The combination of the second half-wave plate and the second Glan Taylor prism can realize continuous control of laser polarization and energy flow.

[0015] S4, focusing the femtosecond laser pulse shaped in step S3 onto the sample surface through a focusing lens, and scanning and processing the sample surface by a three-dimensional translation device in conjunction with a mechanical shutter and an electro-optical shutter to achieve sample modification.

[0016] Further, in step S2, the first half-wave plate in the electro-optical shutter is used to change the polarization of the original pulse of the femtosecond laser to match the angle of the electro-optical crystal; the electro-optical crystal is modulated by the driving power supply, and the driving power supply can output a specific square wave, and the level, frequency and width of the square wave are adjustable. When the level changes, the corresponding laser pulse polarization rotation changes, the level is set so that the polarization rotation is exactly 90°, and the first Glan Taylor prism angle is rotated accordingly, and the high and low levels of the square wave correspond to the opening and closing of the electro-optical shutter.

[0017] Further, in step S4, the femtosecond laser scanning processing method is: electro-optical shutter, mechanical shutter and three-dimensional translation device cooperate for processing, the moving speed of the three-dimensional translation device is 1mm / s, the opening time of the electro-optical shutter corresponds to the laser pulse period, the frequency is set to 10Hz, and the laser energy flux density is 2.2kJ / m 2 , ensuring that each point of the sample is irradiated by two pulses on average.

[0018] The present invention also provides a method for preparing a flat femtosecond laser supersaturated doping detector, comprising the following steps:

[0019] S101, achieving sample modification by flattening femtosecond laser supersaturation doping method;

[0020] S102, annealing the supersaturated doped modified sample;

[0021] The annealing temperature is controlled at 500-1000 K, and the annealing time is controlled at 1-30 min.

[0022] S103, preparing metal electrodes on the light absorbing surface of the sample surface (black silicon surface in this embodiment) and the sample base material respectively to obtain a photodetector;

[0023] Further, in step S101, the sample is provided with a coating layer, and the coating method is thermal evaporation, magnetron sputtering, or ion beam deposition.

[0024] Furthermore, in step S101, the sample preparation method is: first, use the RCA standard cleaning method to clean the metal and organic pollutants on the surface of the silicon wafer (it can also be Ge, etc.) to obtain a pure silicon wafer, and then use a thermal evaporation method to coat a 200nm thick sulfur film (it can also be Se, Te, Au, Ag, Cu, etc.) on the surface of the silicon wafer to obtain a sample to be doped.

[0025] Furthermore, in step S103, aluminum or other metal electrodes are plated by thermal evaporation, magnetron sputtering or the like.

[0026] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0027] The present invention innovatively uses thermal evaporation to deposit a sulfur film on the silicon surface as a dopant, and uses an electro-optical shutter to precisely control the number of processing pulses, thereby achieving processing with any number of pulses and suppressing uncontrollable random influences such as surface energy localization and incubation effect (on the one hand, the incubation effect refers to the fact that after multiple pulses act, the defects accumulated inside the sample make subsequent pulses more easily absorbed, that is, the ablation threshold becomes lower and lower as the number of pulses increases; on the other hand, it refers to the fact that after a pulse ablates the sample, the surface morphology of the sample affects the action of subsequent pulses, and the ablation morphology gradually evolves as the number of pulses increases. In general, incubation refers to a series of evolutionary processes in which multiple pulses act on the sample).

[0028] It can be seen that the present invention prepares a flat supersaturated doped material by coating and processing with any pulse number. On the one hand, the surface sulfur coating is used to replace SF 6 Doping under atmosphere avoids unnecessary over-doping of fluorine, and the doping concentration is relatively easier to control. Due to the significant size difference between fluorine atoms and silicon atoms, fluorine is more likely to occupy interstitial positions in the silicon lattice, which will lead to the formation of deep energy level recombination centers, thereby reducing the performance of the subsequently prepared photodetectors. On the other hand, this method also reduces the etching effect of fluorine on the silicon surface during femtosecond laser irradiation. By precisely controlling the processing conditions, a uniform, smooth, and microstructure-free femtosecond laser supersaturated sulfur-doped silicon is finally prepared. Although there is no microstructure that traps light on the surface, the wide spectrum absorption of the material and the performance of the prepared detector are still at a very high level, with excellent comprehensive performance such as a wide spectrum range, ultra-low dark current, and high responsiveness.

[0029] Based on the above method, the present invention prepares a wide spectrum supersaturated doped silicon photodetector from ultraviolet to near infrared. Specifically, the flat supersaturated doped silicon detector prepared by the present invention has a photoresponsivity of more than 1A / W in the 350-1200nm band, and simultaneously achieves ultraviolet enhancement and sub-bandgap infrared detection, and the dark current is at a very low level of 100 nanoamperes. With the support of high responsivity, the specific detection rate at room temperature reaches a maximum of 1.27×10 14 Jones@840nm, far exceeding commercial standards.

[0030] In addition, the flat supersaturated doped silicon material surface prepared by the present invention is compatible with modern semiconductor industry technology, is conducive to the development of silicon-based series optoelectronic devices, and is expected to promote the development of focal plane devices such as CCD and CMOS. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be described in detail below with reference to the accompanying drawings and in combination with examples, and the advantages and implementation methods of the present invention will become more obvious. The contents shown in the accompanying drawings are only used to explain the present invention and do not constitute any limitation to the present invention in any sense. In the accompanying drawings:

[0032] Figure 1 It is a schematic structural diagram of the flat femtosecond laser supersaturation doping device of the present invention.

[0033] Figure 2 This is a schematic diagram of the femtosecond laser scanning processing method of the present invention.

[0034] Figure 3 It is a schematic diagram of the planar femtosecond laser supersaturation doping method of the present invention.

[0035] Figure 4 Schematic diagram for comparing the planarized black silicon of the present invention with conventional black silicon.

[0036] Figure 5 This is a SIMS test chart of sulfur element concentration of the flat black silicon of the present invention.

[0037] Figure 6 This is a performance indicator diagram of the flat black silicon detector of the present invention.

[0038] In the figure:

[0039] 1. Femtosecond laser; 2. Mechanical shutter; 3. First half-wave plate; 4. Electro-optical crystal; 5. First Glan-Taylor prism; 6. Second half-wave plate; 7. Second Glan-Taylor prism; 8. Focusing lens; 9. Sealed processing chamber; 10. Three-dimensional translation device; 11. Sample holder; 12. Driving power supply. DETAILED DESCRIPTION

[0040] like Figure 1 As shown, a flat femtosecond laser supersaturation doping device of the present invention comprises a femtosecond laser 1, a mechanical shutter 2, an electro-optical shutter, a second half-wave plate 6, a second Glan Taylor prism 7, a focusing lens 8 and a closed processing chamber 9 which are arranged in sequence, wherein a sample holder 11 is installed in the closed processing chamber 9, and the sample holder 11 is installed on a three-dimensional translation device 10.

[0041] The electro-optical shutter includes a first half-wave plate 3 , a Pockels cell and a first Glan-Taylor prism 5 , and the Pockels cell includes an electro-optical crystal 4 and a driving power supply 12 .

[0042] The electro-optical crystal 4 is connected to a driving power source 12 .

[0043] like Figure 1 and Figure 2 As shown, the present invention also provides a planar femtosecond laser supersaturation doping method, comprising the following steps:

[0044] S1. Fix the sample to be doped on the sample holder 11 in the closed processing chamber 9. When the sample is coated as a dopant, it needs to be processed in a vacuum environment.

[0045] S2, femtosecond laser 1 emits laser pulses, and the number of pulses is controlled by mechanical shutter 2 and electro-optical shutter in turn; because the mechanical shutter 2 has a response time of the order of ten milliseconds, it cannot realize single pulse control of high-frequency (>100Hz) femtosecond laser 1, and electro-optical shutter is required to accurately control the number of pulses to realize less pulse processing;

[0046] In step S2, the first half-wave plate 3 in the electro-optical shutter is used to change the polarization of the original pulse of the femtosecond laser 1 so that it matches the angle of the electro-optical crystal 4; the electro-optical crystal 4 is modulated by the driving power supply 12, and the driving power supply 12 can output a specific square wave, and the level, frequency and width of the square wave are adjustable. When the level changes, the corresponding laser pulse polarization rotation changes, and the level is set so that the polarization rotation is exactly 90°, and the first Glan Taylor prism 5 is rotated accordingly. The high and low levels of the square wave correspond to the opening and closing of the electro-optical shutter.

[0047] S3, the laser pulses after controlling the number of pulses pass through the second half-wave plate 6 and the second Glan Taylor prism 7 in sequence. The second half-wave plate 6 is used to rotate the pulse polarization disk. The second Glan Taylor prism 7 only transmits the projection with a fixed polarization direction. The combination of the second half-wave plate 6 and the second Glan Taylor prism 7 can realize continuous control of laser polarization and energy flow.

[0048] S4, focusing the femtosecond laser pulse shaped in step S3 onto the sample surface through the focusing lens 8, and scanning and processing the sample surface by the three-dimensional translation device 10 in cooperation with the mechanical shutter 2 and the electro-optical shutter to achieve sample modification.

[0049] In step S4, the femtosecond laser scanning processing method is: the electro-optical shutter, the mechanical shutter 2 and the three-dimensional translation device 10 cooperate for processing, the moving speed of the three-dimensional translation device 10 is 1 mm / s, the opening time of the electro-optical shutter corresponds to the laser pulse period, the frequency is set to 10 Hz, and the laser energy flux density is 2.2 kJ / m 2 , ensuring that each point of the sample is irradiated by two pulses on average.

[0050] like Figure 3 As shown, the present invention also provides a method for preparing a flat femtosecond laser supersaturated doping detector, comprising the following steps:

[0051] S101, achieving sample modification by flattening femtosecond laser supersaturation doping method;

[0052] The sample is provided with a coating layer, and the coating method is thermal evaporation, magnetron sputtering, or ion beam deposition.

[0053] Among them, the sample preparation method is: first use the RCA standard cleaning method to clean the metal and organic pollutants on the surface of the silicon wafer (it can also be Ge, etc.) to obtain a pure silicon wafer, and then use the thermal evaporation method to coat a 200nm thick sulfur film (it can also be Se, Te, Au, Ag, Cu, etc.) on the surface of the silicon wafer to obtain the sample to be doped.

[0054] S102, annealing the supersaturated doped modified sample;

[0055] The annealing temperature is controlled at 500-1000 K, and the annealing time is controlled at 1-30 min.

[0056] S103, preparing metal electrodes on the light absorbing surface of the sample surface (black silicon surface in this embodiment) and the sample base material respectively to obtain a photodetector;

[0057] Among them, aluminum or other metal electrodes are plated using thermal evaporation, magnetron sputtering and other methods.

[0058] like Figure 4 As shown, Figure 4 The flat black silicon on the left is produced by using a titanium sapphire femtosecond laser, with a pulse center wavelength of 800nm, a pulse width of 120fs, and a frequency of 1KHz. The silicon is an N-type 100 crystal phase, with a resistivity of 3-5KΩ·cm and a thickness of 420μm. A 0.2μm sulfur film is coated on the silicon surface. The scanning energy flow, speed, and pulse number are the same as above. It can be seen that the flat black silicon surface prepared by the present invention is smooth and flat, and the surface fluctuation of the AFM test is less than 1nm. Figure 4 The one on the right shows the morphology of conventional black silicon, with micrometer-scale cone-shaped undulations on the surface. The two figures share the same scale.

[0059] like Figure 5 As shown, the sulfur doping concentration of the flat black silicon of the present invention was tested by SIMS, and the results showed that the surface doping concentration could reach 10 18 cm -3 , exceeding the solid solubility limit by two orders of magnitude, that is, black silicon with a flat surface also achieves supersaturated doping.

[0060] The black silicon material prepared above was subjected to thermal annealing at 600° C. for 600 s, and aluminum electrodes were plated on the front and back surfaces to obtain the following photodetector.

[0061] like Figure 6 As shown, Figure 6(a) Comparing the 100% EQE, Thorlabs DET100A commercial silicon-based detector, Thorlabs DET50B commercial germanium detector and the flat black silicon detector of the present invention, the commercial silicon-based detector can only work within 1100nm, while the flat black silicon detector has a response wavelength covering near ultraviolet to near infrared, and achieves stable detection in the 350nm to 1300nm band. Under -5V bias, the light responsivity in the ultra-wide band from 350nm to 1200nm exceeds 1A / W, and can reach up to 120.07AW -1 @840nm, which is much higher than the standards of two commercial detectors (EQE is the external quantum efficiency, the ratio of the number of electrons emitted by the detector to the number of photons received. When the two are equal, it is 100%. When they are greater than 100%, it means that the device has gain and one photon can generate multiple electrons). Figure 6 (b) shows the dark current and specific detection rate of the flat black silicon detector of the present invention. Specific detection rate is an important parameter for evaluating the performance of photodetectors, which is used to describe the ability of photodetectors to detect light signals in a noisy environment. It is a standardized parameter used to compare the performance of different detectors, usually in cm Hz 1 / 2 W -1 The specific detection rate is proportional to the responsivity and inversely proportional to the dark current noise. Therefore, the lower the dark current, the stronger the detection capability of the photodetector. Under a bias voltage of -5V, the dark current of the flat black silicon detector of the present invention is at a very low level of 100 nanoamperes. With the support of high responsivity, the specific detection rate at room temperature reaches a maximum of 1.27×10 14 Jones@840nm, far exceeding commercial standards.

[0062] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A flat femtosecond laser supersaturation doping device, characterized in that: The invention comprises a femtosecond laser, an electro-optical shutter, a second half-wave plate, a second Glan Taylor prism, a focusing lens and a closed processing chamber which are arranged in sequence. A sample rack is installed in the closed processing chamber, and the sample rack is installed on a three-dimensional translation device.

2. The flat femtosecond laser supersaturation doping device according to claim 1, characterized in that: The electro-optical shutter comprises a first half-wave plate, a Pockels cell and a first Glan-Taylor prism, and the Pockels cell comprises an electro-optical crystal and a driving power supply.

3. The flat femtosecond laser supersaturation doping device according to claim 1, characterized in that: A mechanical shutter is arranged between the femtosecond laser and the closed processing chamber.

4. The flat femtosecond laser supersaturation doping device according to claim 3, characterized in that: The mechanical shutter is located between the femtosecond laser and the electro-optical shutter.

5. A planar femtosecond laser supersaturation doping method, which is implemented by using the planar femtosecond laser supersaturation doping device according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Fix the sample to be doped on a sample holder in a closed processing chamber; S2, femtosecond laser emits laser pulses, and the number of pulses is controlled by mechanical shutter and electro-optical shutter to achieve processing with any number of pulses; S3, the laser pulse after the pulse number is controlled passes through the second half-wave plate and the second Glan-Taylor prism, and the second half-wave plate and the second Glan-Taylor prism are combined to realize continuous control of laser polarization and energy flow; S4, focusing the femtosecond laser pulse shaped in step S3 onto the sample surface through a focusing lens, and scanning and processing the sample surface by a three-dimensional translation device in conjunction with a mechanical shutter and an electro-optical shutter to achieve sample modification.

6. The planar femtosecond laser supersaturation doping method according to claim 5, characterized in that: In step S4, the femtosecond laser scanning processing method is: electro-optical shutter, mechanical shutter and three-dimensional translation device cooperate for processing, the moving speed of the three-dimensional translation device is 1mm / s, the opening time of the electro-optical shutter corresponds to the laser pulse period, the frequency is set to 10Hz, and the laser energy flux density is 2.2kJ / m 2 , ensuring that each point of the sample is irradiated by two pulses on average.

7. A method for preparing a flat femtosecond laser supersaturated doping detector, which is achieved by the flat femtosecond laser supersaturated doping method of claim 5, characterized in that: The following steps are involved: S101, achieving sample modification by flattening femtosecond laser supersaturation doping method; S102, annealing the sample after supersaturated doping modification; S103. Prepare metal electrodes on the light-absorbing surface of the sample surface and on the sample base material respectively to obtain a photodetector.

8. The method for preparing a flat femtosecond laser supersaturated doping detector according to claim 7, characterized in that: In step S101 , a sample is provided with a coating layer.

9. The method for preparing a flat femtosecond laser supersaturated doping detector according to claim 8, characterized in that: In step S101, the sample preparation method is: first use the RCA standard cleaning method to clean the metal and organic pollutants on the surface of the silicon wafer to obtain a pure silicon wafer, and then use a thermal evaporation method to coat a sulfur film on the surface of the silicon wafer to obtain a sample to be doped.

10. The method for preparing a flat femtosecond laser supersaturated doping detector according to claim 7, characterized in that: In step S102, the annealing temperature is controlled at 500-1000 K, and the annealing time is controlled at 1-30 min. In step S103, the metal electrode is plated by thermal evaporation or magnetron sputtering.

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