Planarization of femtosecond laser over-doped devices, methods and methods of making probes

Abstract

The application provides a preparation method of a flat femtosecond laser oversaturated doping device, a method and a detector, and belongs to the technical field of photoelectricity, comprising a femtosecond laser, an electro-optic shutter, a second half-wave plate, a second Gartai Taylor prism, a focusing lens and a closed processing cavity arranged in sequence, sulfur film is plated on the surface of silicon as a dopant by using a thermal evaporation method, and the number of processing pulses is accurately controlled by using the electro-optic shutter, so that arbitrary pulse number processing is realized, and uncontrollable random influences caused by surface energy localization and hatching effect are inhibited. The surface of the flat oversaturated doping silicon material prepared by the application is compatible with modern semiconductor industrial technology, is beneficial to the development of silicon-based series photoelectric devices and promotes the development of CCD and CMOS focus plane devices. In addition, the light responsivity of the flat oversaturated doping silicon detector prepared by the application exceeds 1A / W in the 350-1200nm wave band, and ultraviolet enhancement and sub-bandgap infrared detection are simultaneously realized.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology, and in particular relates to a planar femtosecond laser oversaturated doping device, method, and detector fabrication method. Background Technology

[0002] Semiconductor doping is an essential step in the fabrication of functional semiconductor devices. Increasing the doping concentration above the physical equilibrium limit, known as supersaturation doping, can transform the photoelectric properties of materials, facilitating the development of novel optoelectronic devices. For example, doping silicon with sulfur to supersaturation can extend the absorption spectrum of the material into the ultraviolet and infrared regions, enabling the fabrication of silicon-based broadband photodetectors.

[0003] Conventional supersaturated doping methods include ion implantation and femtosecond laser doping. Ion implantation can precisely control the doping concentration and depth, but the doped atoms are mostly located in ineffective interstitial sites rather than effective substitution or quasi-substitution sites, resulting in low doping activation rate and high cost. In contrast, femtosecond laser doping is a promising new supersaturated doping technology.

[0004] In specific environments (doped atomic atmosphere, surface coating, etc.), femtosecond laser irradiation of materials can achieve supersaturated doping of corresponding elements. For example, focusing a femtosecond laser on silicon materials in an SF6 atmosphere has become a standard technique for preparing supersaturated sulfur-doped silicon. Compared with other doping methods, femtosecond laser supersaturated doping is low in cost and has a high doping activation rate.

[0005] However, femtosecond laser ablation doping induces microconical light-trapping structures on the material surface, achieving doping concentrations far exceeding the solid solubility limit. Because the modified areas turn black, supersaturated doped silicon is also known as "black silicon." Since the doping process and the formation of surface micro / nano structures are easily disturbed by environmental factors and random defects in the material itself, the disadvantages of femtosecond laser supersaturation doping include randomly distributed uneven microstructures on the surface, and difficulty in controlling the doping concentration, depth, and especially uniformity. This results in high dark current and poor uniformity in black silicon detectors fabricated by femtosecond lasers. Furthermore, the unevenness of the surface microstructure makes femtosecond laser supersaturated doped silicon materials incompatible with modern semiconductor technology, particularly for fabricating focal plane array devices such as CCDs and CMOS sensors. Summary of the Invention

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

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a flat femtosecond laser oversaturation doping device, comprising a femtosecond laser, an electro-optic shutter, a second half-wave plate, a second Glan Taylor prism, a focusing lens and a sealed processing cavity arranged in sequence, wherein a sample holder is installed in the sealed processing cavity and the sample holder is mounted on a three-dimensional translation device.

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

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

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

[0011] This invention also provides a method for supersaturated doping of a flat femtosecond laser, comprising the following steps:

[0012] S1. Fix the sample to be doped on the sample holder inside the sealed processing chamber;

[0013] S2. The femtosecond laser emits laser pulses, and the number of pulses is controlled sequentially by a mechanical shutter and an electro-optical shutter. Because the mechanical shutter has a response time on the order of tens of milliseconds, it cannot achieve single-pulse control of high-frequency (>100Hz) femtosecond lasers. An electro-optical shutter is needed to precisely control the number of pulses and achieve processing with any number of pulses.

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

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

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

[0017] Furthermore, in step S4, the femtosecond laser scanning processing method is as follows: processing is carried out in conjunction with an electro-optical shutter, a mechanical shutter, and a three-dimensional translation device. The moving speed of the three-dimensional translation device 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 / m². 2 This ensures that each point on the sample receives an average of two pulses of irradiation.

[0018] This invention also provides a method for fabricating a flat femtosecond laser oversaturated doped detector, comprising the following steps:

[0019] S101. Sample modification is achieved through a flat femtosecond laser supersaturation doping method;

[0020] S102. Anneal the supersaturated doped sample.

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

[0022] S103. Metal electrodes are fabricated on the light-absorbing surface of the sample (black silicon surface in this embodiment) and on the sample substrate material to obtain a photodetector;

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

[0024] Further, in step S101, the sample preparation method is as follows: First, the RCA standard cleaning method is used to clean the metal and organic contaminants on the surface of the silicon wafer (or Ge, etc.) to obtain a pure silicon wafer. Then, a 200nm thick sulfur film (or Se, Te, Au, Ag, Cu, etc.) is deposited on the surface of the silicon wafer using a thermal evaporation method to obtain the sample to be doped.

[0025] Furthermore, in step S103, aluminum or other metal electrodes are deposited using methods such as thermal evaporation or magnetron sputtering.

[0026] By adopting the above technical solution, the present invention has the following beneficial effects:

[0027] This invention innovatively uses thermal evaporation to deposit a sulfur film as a dopant on the silicon surface and employs an electro-optical shutter to precisely control the number of processing pulses, enabling processing with any number of pulses. This suppresses uncontrollable random effects such as surface energy localization and the hatching effect (the hatching effect refers to two aspects: firstly, after multiple pulses, the accumulated defects inside the sample make subsequent pulses more easily absorbed, i.e., the ablation threshold decreases with increasing pulse number; secondly, after pulse ablation of the sample, the surface morphology of the sample affects subsequent pulses, and the ablation morphology gradually evolves with increasing pulse number. In general, hatching refers to a series of evolutionary processes on the sample caused by multiple pulses).

[0028] As can be seen, this invention prepares a flat, supersaturated doped material through coating and processing with arbitrary pulse counts. On the one hand, using a sulfur coating on the surface instead of doping under an SF6 atmosphere avoids unnecessary overdoping 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 leads to the formation of deep-level recombination centers, thereby reducing the performance of the subsequently fabricated photodetector. On the other hand, this method also mitigates the etching effect of fluorine on the silicon surface during femtosecond laser irradiation. By precisely controlling the processing conditions, a uniform, flat, and microstructure-free femtosecond laser-supersaturated sulfur-doped silicon is finally prepared. Although there are no microstructures that trap light on the surface, the material's broad-spectrum absorption and the performance of the fabricated detector are still at a very high level, exhibiting excellent comprehensive performance such as a wide spectral range, ultra-low dark current, and high responsivity.

[0029] Based on the above method, this invention fabricates a broadband supersaturated doped silicon photodetector from ultraviolet to near-infrared. Specifically, the planar supersaturated doped silicon photodetector fabricated in this invention exhibits a photoresponsivity exceeding 1 A / W in the 350–1200 nm wavelength range, simultaneously achieving ultraviolet enhancement and sub-bandgap infrared detection, with a very low dark current in the order of hundreds of nanoamperes. With the support of high responsivity, the specific detectivity reaches a maximum of 1.27 × 10⁻⁶ at room temperature. 14 Jones@840nm, far exceeding commercial standards.

[0030] Furthermore, the flat, supersaturated doped silicon material surface prepared by this invention is compatible with modern semiconductor industry technology, which is conducive to the development of silicon-based optoelectronic devices and is expected to promote the development of focal plane devices such as CCD and CMOS. Attached Figure Description

[0031] The present invention will be described in detail below with reference to the accompanying drawings and examples. The advantages and implementation methods of the present invention will become more apparent from this description. The accompanying drawings are for illustrative purposes only and do not constitute any limitation on the present invention. In the accompanying drawings:

[0032] Figure 1This is a schematic diagram of the structure of the flat femtosecond laser supersaturated 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 This is a schematic diagram of the planar femtosecond laser supersaturation doping method of the present invention.

[0035] Figure 4 This is a schematic diagram comparing the flat black silicon of the present invention with conventional black silicon.

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

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

[0038] In the picture:

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

[0040] like Figure 1 As shown, the present invention provides a flat femtosecond laser oversaturation doping device, comprising a femtosecond laser 1, a mechanical shutter 2, an electro-optic shutter, a second half-wave plate 6, a second Glan Taylor prism 7, a focusing lens 8, and a sealed processing cavity 9 arranged in sequence. A sample holder 11 is installed in the sealed processing cavity 9, and the sample holder 11 is mounted on a three-dimensional translation device 10.

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

[0042] Among them, the electro-optic crystal 4 is connected to the driving power supply 12.

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

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

[0045] S2. The femtosecond laser 1 emits laser pulses, and the number of pulses is controlled sequentially by the mechanical shutter 2 and the electro-optic shutter. Because the mechanical shutter 2 has a response time on the order of tens of milliseconds, it cannot achieve single-pulse control of the high-frequency (>100Hz) femtosecond laser 1. The electro-optic shutter is required to precisely control the number of pulses to achieve low-pulse processing.

[0046] In step S2, the first half-wave plate 3 in the electro-optic shutter is used to change the polarization of the original pulse of the femtosecond laser 1 so that it matches the angle with the electro-optic crystal 4. The electro-optic crystal 4 is modulated by the driving power supply 12, which can output a specific square wave. The level, frequency, and width of the square wave are adjustable. When the level changes, the polarization of the laser pulse changes accordingly. The level is set so that the polarization rotation is exactly 90°, and the angle of 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-optic shutter.

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

[0048] S4. The femtosecond laser pulse shaped in step S3 is focused onto the sample surface through the focusing lens 8. The three-dimensional translation device 10, in conjunction with the mechanical shutter 2 and the electro-optic shutter, scans and processes the sample surface to achieve sample modification.

[0049] In step S4, the femtosecond laser scanning processing method is as follows: the electro-optic shutter, the mechanical shutter 2, and the three-dimensional translation device 10 work together. The moving speed of the three-dimensional translation device 10 is 1 mm / s, the opening time of the electro-optic shutter corresponds to the laser pulse period, the frequency is set to 10 Hz, and the laser energy flux density is 2.2 kJ / m². 2 This ensures that each point on the sample receives an average of two pulses of irradiation.

[0050] like Figure 3 As shown, the present invention also provides a method for fabricating a planar femtosecond laser oversaturated doped detector, comprising the following steps:

[0051] S101. Sample modification is achieved through a flat femtosecond laser supersaturation doping method;

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

[0053] The sample preparation method is as follows: First, the RCA standard cleaning method is used to clean the metal and organic contaminants on the surface of the silicon wafer (or Ge, etc.) to obtain a pure silicon wafer. Then, a 200nm thick sulfur film (or Se, Te, Au, Ag, Cu, etc.) is deposited on the surface of the silicon wafer using a thermal evaporation method to obtain the sample to be doped.

[0054] S102. Anneal the supersaturated doped sample.

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

[0056] S103. Metal electrodes are fabricated on the light-absorbing surface of the sample (black silicon surface in this embodiment) and on the sample substrate material to obtain a photodetector;

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

[0058] like Figure 4 As shown, Figure 4 The smooth black silicon on the left was prepared using a Ti:sapphire femtosecond laser with a pulse center wavelength of 800 nm, a pulse width of 120 fs, and a frequency of 1 kHz. The silicon was in the N-type 100 crystal phase with a resistivity of 3–5 KΩ·cm and a thickness of 420 μm. A 0.2 μm sulfur film was deposited on the silicon surface. The scanning energy flow, velocity, and pulse number were obtained as above. As can be seen, the smooth black silicon prepared by this invention has a smooth and flat surface, and the surface undulation in the AFM test is less than 1 nm. Figure 4 The image on the right shows the morphology of conventional black silicon, with micron-sized conical undulations on the surface. Both images share the same scale.

[0059] like Figure 5 As shown, the sulfur doping concentration of the planar black silicon of the present invention was tested by SIMS. The results showed that the surface doping concentration could reach 10. 18 cm -3 This exceeds the solid solubility limit by two orders of magnitude, meaning that even black silicon with a smooth surface has achieved supersaturated doping.

[0060] The black silicon material prepared above was subjected to thermal annealing at 600°C for 600 seconds, and aluminum electrodes were deposited 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 with the Thorlabs DET50B commercial germanium detector and the planar black silicon detector of this invention, the commercial silicon-based detector can only operate within 1100nm, while the planar black silicon detector's response wavelength covers the near-ultraviolet to near-infrared range, achieving stable detection in the 350nm–1300nm band. At a -5V bias, the photoresponsivity in the ultra-wide band from 350nm to 1200nm exceeds 1A / W, reaching a maximum of 120.07AW. -1 @840nm, far exceeding the standards of two commercial detectors (EQE, or external quantum efficiency, is the ratio of the number of electrons emitted by a detector to the number of photons received; when the two are equal, it is 100%; when it is greater than 100%, it indicates that the device has gain, meaning that one photon can generate multiple electrons). Figure 6 (b) The dark current and specific detectivity of the planar black silicon detector of the present invention are given. Specific detectivity is an important parameter for evaluating the performance of a photodetector, used to describe the ability of a photodetector to detect optical signals in noisy environments. It is a standardized parameter used to compare the performance of different detectors, typically expressed in cm Hz. 1 / 2 W -1 The unit is (Jones). Specific detectivity is directly proportional to responsivity and inversely proportional to dark current noise; therefore, the lower the dark current, the stronger the detection capability of the photodetector. At a -5V bias, the dark current of the flat black silicon detector of this invention is in the very low range of hundreds of nanoamperes. With the support of high responsivity, the specific detectivity reaches a maximum of 1.27 × 10⁻⁶ at room temperature. 14 Jones@840nm, far exceeding commercial standards.

[0062] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope 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 femtosecond laser over-doping method, characterized by: The femtosecond laser supersaturation doping device is realized, and the femtosecond laser supersaturation doping device comprises a femtosecond laser, an electro-optic shutter, a second half-wave plate, a second Gartai prism, a focusing lens and a closed processing cavity arranged in sequence, a sample holder is installed in the closed processing cavity, and the sample holder is installed on a three-dimensional translation device; the electro-optic shutter comprises a first half-wave plate, a Puker box and a first Gartai prism, the Puker box comprises an electro-optic crystal and a driving power supply; a mechanical shutter is arranged between the femtosecond laser and the closed processing cavity; the mechanical shutter is located between the femtosecond laser and the electro-optic shutter; The femtosecond laser supersaturation doping method comprises the following steps: S1, fixing the sample to be doped on the sample holder in the closed processing cavity, and the sample is provided with a plated film layer; S2, the femtosecond laser emits laser pulses, the pulse number is controlled through the mechanical shutter and the electro-optic shutter, and arbitrary pulse number processing is realized; S3, the laser pulse after pulse number control passes through the second half-wave plate and the second Gartai prism, and the second half-wave plate and the second Gartai prism are combined to realize continuous control of laser polarization and energy flow; S4, the femtosecond laser pulse after shaping in step S3 is focused on the sample surface through the focusing lens, and the sample surface is scanned and processed by the three-dimensional translation device in cooperation with the mechanical shutter and the electro-optic shutter, so that the sample is modified; In step S4, the femtosecond laser scanning processing mode is: the cooperation processing of the electro-optic shutter, the mechanical shutter and the three-dimensional translation device, the moving speed of the three-dimensional translation device is 1 mm / s, the opening time of the electro-optic shutter corresponds to the laser pulse period, the frequency is set to 10 Hz, and the laser energy flow density is 2.2 kJ / m 2 , so that each point of the sample is averagely irradiated by two pulses.

2. A method for preparing a femtosecond laser oversaturated doped detector, which is achieved by the femtosecond laser oversaturated doping method of claim 1, characterized in that: Comprising the following steps: S101, realizing sample modification by the femtosecond laser supersaturation doping method; S102, annealing the sample modified by supersaturation doping; S103, preparing a metal electrode on the light-absorbing surface of the sample surface layer and the sample base material respectively to obtain a photoelectric detector; In step S101, the preparation method of the sample is as follows: first, using the RCA standard cleaning method to clean the metal and organic contaminants on the surface of the silicon wafer to obtain a pure silicon wafer, and then using a thermal evaporation method to evaporate a sulfur film on the surface of the silicon wafer to obtain a sample to be doped; In step S102, the annealing temperature is controlled at 500-1000K, and the annealing time is controlled at 1-30min; in step S103, the metal electrode is plated by using a thermal evaporation or a magnetron sputtering method. In step S101, the preparation method of the sample is as follows: first, using the RCA standard cleaning method to clean the metal and organic contaminants on the surface of the silicon wafer to obtain a pure silicon wafer, and then using a thermal evaporation method to evaporate a sulfur film on the surface of the silicon wafer to obtain a sample to be doped;

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