Focused scanning pulsed laser thin film deposition device and deposition method

Abstract

The present invention relates to a focused scanning pulse laser thin film deposition device and deposition method, which uses a converging lens to converge the collimated laser to the order of 0.01 mm, and the focus falls on the target material, reaching 10 6 W / cm 2 The average power density above 10 9 W / cm 2 Peak power densities above this level vaporize the atoms on the surface of the solid target, enabling thin film deposition on the sample. The device uses galvanometers in the X and Y directions to scan the light spot across the target surface; real-time adjustment in the Z direction ensures that the light spot on the target surface is always in focus. A variety of materials can be placed on the target, and multi-component thin film deposition can be achieved by controlling the laser's on / off switching, output power, two sets of galvanometers, and the Z-direction adjustment mechanism. The laser does not use toxic or hazardous gases, and the deposition process has excellent temporal uniformity. The chemical composition of the deposited sample can be freely adjusted without changing the target, improving the controllability and convenience of thin film deposition.

Description

Technical Field

[0001] The present invention relates to a thin film material preparation technology, and in particular to a focused scanning pulse laser thin film deposition device based on an optical fiber laser and a deposition method. Background Art

[0002] A fiber laser uses rare-earth-doped glass fiber as its gain medium. Developed based on fiber amplifiers, a fiber laser utilizes pump light to generate high power density within the working fiber, causing a population inversion of the laser energy level in the working medium. By incorporating a positive feedback loop to form a resonant cavity, laser oscillation output is achieved.

[0003] Fiber lasers are divided into two categories: continuous fiber lasers and pulsed fiber lasers. Pulsed fiber lasers can be further divided into Q-switched fiber lasers (pulse widths in the nanosecond range) and mode-locked fiber lasers (pulse widths in the picosecond or femtosecond range) based on their pulse formation principles. Pulsed fiber lasers have higher peak power than continuous fiber lasers of the same power, with common pulse generation frequencies in the range of 20-60kHz.

[0004] Traditional pulsed laser deposition (PLD) equipment usually uses excimer lasers. This type of laser uses gases such as krypton fluoride (KrF, 248nm), xenon chloride (XeCl, 308nm), and argon fluoride (ArF, 193nm) as laser media. The pulse generation frequency of this type of laser used for thin film deposition is generally lower than 100Hz, the pulse width is about 10-20ns, and the spot size at the sample is on the order of millimeters. In order to reach the volatilization threshold of the target material, the energy required for a single pulse is generally above 100mJ. The main advantage of this type of laser is that it can easily excite wide-bandgap (above 3eV) targets; but for metal and narrow-bandgap targets, it has no outstanding advantages compared to fiber lasers. Its disadvantages are complex structure, the use of high-cost and highly toxic gases, and the need for regular replenishment. Due to the low frequency and short pulses, the duty cycle is less than 2×10 -6 This means that a large amount of target material falls onto the sample substrate in a very short period of time, followed by a long window of inactivity; therefore, the deposition process is extremely uneven in time. Furthermore, in traditional pulsed laser deposition, sample composition is primarily adjusted by replacing the target material and adjusting the chamber pressure. However, for samples that are not subject to atmosphere control (such as metal samples) or have a large number of constituent elements, it is difficult to easily and freely combine and continuously adjust the composition. Summary of the Invention

[0005] In response to the problems of current pulsed laser deposition (PLD) equipment based on excimer lasers, such as complex structure, the need to regularly replenish toxic and harmful working gases, poor temporal uniformity of the deposition process, and limited freedom in controlling the film composition, a focused scanning pulsed laser thin film deposition device and deposition method are proposed. The device improves the safety and maintainability of the laser, improves the temporal uniformity of the deposition process, increases the freedom in controlling the film composition, and realizes free and continuous control of the film sample composition without changing the target.

[0006] The technical solution of the present invention is: a focused scanning pulse laser thin film deposition device, comprising a pulse fiber laser, a collimator, an X-direction galvanometer, a Y-direction galvanometer, a converging lens, a window, a target material, a Z-direction adjustment mechanism, a controller and a vacuum chamber; laser light emitted by the pulse fiber laser passes through the collimator to output collimated light, which is incident on the X-direction galvanometer, reflected by the X-direction galvanometer into the Y-direction galvanometer, and then reflected by the Y-direction galvanometer to the converging lens, and becomes a convergent light beam after passing through the converging lens. The convergent light beam is introduced into the vacuum chamber through the window on the vacuum chamber, and the relative position of the target material and the converging lens in the optical axis direction is adjusted by the Z-direction adjustment mechanism. When the thin film deposition sample is facing the target material surface, the controller communicates with the pulse fiber laser and outputs a control signal to the X-direction galvanometer, the Y-direction galvanometer and the Z-direction adjustment mechanism, so that the focus of the convergent light beam just falls on the surface of the target material, and the peak power density of the light spot at the focus exceeds the vaporization threshold of the target material, thereby volatilizing the target material on the target material and performing thin film deposition on the sample.

[0007] The target material and the sample are both located in a vacuum chamber, and the target material and the converging light beam are placed at an angle, that is, the converging light beam is incident obliquely on the surface of the target material.

[0008] The deposition method of the focused scanning pulsed laser thin film deposition device specifically includes the following steps:

[0009] 1) Building the focused scanning pulsed laser thin film deposition device, wherein the controller calculates the output power and output frequency of the pulsed fiber laser according to the composition characteristics of the deposited target material;

[0010] 2) The controller calculates the optical path according to the position and optical parameters of each device in the focused scanning pulsed laser thin film deposition apparatus constructed in step 1), outputs the rotation angles of the X-direction galvanometer and the Y-direction galvanometer, and the displacement of the Z-direction adjustment mechanism to the X-direction galvanometer, the Y-direction galvanometer, and the Z-direction adjustment mechanism, turns on the pulsed fiber laser, detects the size of the focused spot on the target material, and sends the detected value to the controller. The controller records the error value and adjusts the rotation angles of the X-direction galvanometer and the Y-direction galvanometer and the Z-direction adjustment mechanism respectively, and records and calculates the optical path error of each segment from the pulsed fiber laser to the X-direction galvanometer, from the X-direction galvanometer to the Y-direction galvanometer, and from the Y-direction galvanometer to the Z-direction adjustment mechanism;

[0011] 3) After adjusting the error, the focused spot size on the target reaches a diameter of the order of 0.01 mm. Turn off the pulsed fiber laser and place the sample to be deposited directly opposite the target surface.

[0012] 4) Inputting target material area information on the target material into the controller, the controller formulates a scanning plan based on the output power and output frequency of the pulsed fiber laser, the target material evaporation rate, and the target material area; the controller controls the X-direction galvanometer, the Y-direction galvanometer rotation angle, and the Z-direction adjustment mechanism to the initial position according to the scanning plan, turns on the pulsed fiber laser, and completes the focused scanning thin film deposition of the sample under the control of the controller.

[0013] The pulsed laser output from the pulsed fiber laser passes through a collimating lens and is output as parallel light with a diameter of 5-20 mm. The diameter of the light spot of the parallel laser and the focused light spot of the working point on the target surface are on the order of 0.01 mm.

[0014] Several different target materials are installed on the target material at intervals. The controller formulates a scanning plan and controls the volatilization rate of each target material through the linkage of the pulse fiber laser opening and closing, the output power of the pulse fiber laser, the X-direction galvanometer, the Y-direction galvanometer and the Z-direction adjustment mechanism to achieve uniform deposition of multi-component thin films.

[0015] The beneficial effects of the present invention are as follows: compared with existing pulsed laser deposition (PLD) equipment that uses excimer lasers (which require expensive and toxic working gases) as energy sources, the focused scanning pulsed laser thin film deposition device of the present invention uses pulsed fiber lasers as energy sources. The lasers are lighter and more environmentally friendly, while reducing purchase and use costs. Compared with the maximum output frequency of the excimer laser of less than 100 Hz, the typical output frequency of the pulsed fiber laser is 20-60 kHz, thereby significantly improving the temporal uniformity of the deposition process and allowing rapid switching between multiple target materials, making it more suitable for the uniform deposition of multi-component thin films. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic structural diagram of an embodiment of a focused scanning pulsed laser thin film deposition device according to the present invention;

[0017] Figure 2 This is a measured image of the target material (plume) volatilized by the target material under focused laser irradiation in an embodiment of the present invention;

[0018] Figure 3 Schematic diagram of the optical path of the light spot after defocusing in the Z direction (optical axis direction) in an embodiment of the present invention;

[0019] Figure 4 Schematic diagram of the change in the diameter of the light spot after the light spot is defocused by 1 mm in the Z direction (optical axis direction) in an embodiment of the present invention;

[0020] Figure 5 Schematic diagram of the scanning path of the focused light spot on the target surface in an embodiment of the present invention;

[0021] Figure 6 Schematic diagram of the control strategy for scanning the target surface in three directions (X, Y, and Z) using a focused light spot in an embodiment of the present invention;

[0022] Figure 7 Schematic diagram of the target scanning path of the multi-element target in an embodiment of the present invention;

[0023] Figure 8 Schematic diagram of the control strategy for laser switching, power control, and linkage in the XYZ directions during the scanning process of a multi-target material in an embodiment of the present invention.

[0024] Figure numerals: 1. Pulsed fiber laser; 2. Collimating mirror; 3. Collimated laser beam; 4. Electrically controlled rotatable reflector (galvanometer) in the X direction; 5. Electrically controlled rotatable reflector (galvanometer) in the Y direction; 6. Converging lens (field lens); 7. Window; 8. Target material; 9. Sample; 10. Z-direction (optical axis direction) adjustment mechanism; 11. Vacuum chamber; 12. Volatilized target material (feather). DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0026] like Figure 1 The schematic diagram of the structure of an embodiment of a focused scanning pulsed laser thin film deposition device is shown. The device includes a pulsed fiber laser 1, a collimator 2, an X-direction electrically controlled rotatable reflector (galvanometer) 4, a Y-direction electrically controlled rotatable reflector (galvanometer) 5, a converging lens (field lens) 6, a viewing window 7, a target 8, a sample 9, a Z-direction (optical axis) adjustment mechanism 10, a controller, and a vacuum chamber 11. The laser light emitted by the pulsed fiber laser 1 passes through the collimator 2 and outputs collimated light 3. The collimated light 3 is incident on the X-direction electrically controlled rotatable reflector (galvanometer) 4, reflected by the X-direction galvanometer 4 into the Y-direction galvanometer 5, and then reflected by the Y-direction galvanometer 5 into the converging lens (field lens) 6. After passing through the converging lens (field lens) 6, it becomes a converged light beam. The converged light beam is introduced into the vacuum chamber 11 through the viewing window 7 on the vacuum chamber 11. Inside the vacuum chamber 11, the distance between the target 8 and the converging lens (field lens) 6 is adjusted by the Z-direction (optical axis) adjustment mechanism 10 so that the focus falls exactly on the surface of the target 8. The peak power density of the light spot at the focus exceeds the vaporization threshold of the target material 8 , thereby causing the target material to volatilize, and a deposited thin film is obtained at the sample 9 facing the target material 8 .

[0027] like Figure 2 The measured image of the target material (plume) volatilized from the target under focused laser irradiation shows that the target material 12 mainly escapes from the direction perpendicular to the surface of the target 8. Therefore, in actual operation, the target 8 is placed at an angle to the laser to reduce deposition on the window.

[0028] like Figure 3 The diagram shows the optical path of the light spot after it is defocused in the Z direction (optical axis direction). When the converged laser is scanning on the inclined target surface 8, if there is no optical path for Z direction compensation, due to the existence of the inclination angle, when the light spot falls on the upper and lower sides of the target material 8, it is in a defocused state due to the different distances from the converging lens 6, resulting in a large change in the energy density of the light spot and the inability to uniformly utilize the target material.

[0029] like Figure 4 The illustrated embodiment shows a schematic diagram of the change in spot diameter after a 1mm defocus in the Z direction (optical axis). In this embodiment, the focal length of the converging lens (field lens) 6 is 80mm, and the focused spot diameter is 0.01mm. It can be estimated that after a 1mm defocus in the Z direction (optical axis), the cross-sectional diameter of the spot perpendicular to the optical axis decreases to 0.1mm, the spot area increases 100 times, and the peak power density drops to 1% of the original value. Since target materials are typically on the order of centimeters, without Z-direction (optical axis) compensation, there will be centimeters of defocus during the X and Y scanning process, preventing the target material from escaping. This calculation result clearly demonstrates the necessity of the Z-direction (optical axis) adjustment mechanism 10.

[0030] like Figure 5 The schematic diagram of the scanning path of the focused light spot on the target surface shows that at a 45° inclination angle, the target 8 is scanned from the upper left corner along the marked serpentine trajectory. The synchronous control strategy of the X-direction galvanometer 4, the Y-direction galvanometer 5, and the Z-direction (optical axis direction) adjustment mechanism 10 is as follows: Figure 6 As shown, the X-mirror 4 scans back and forth in the X direction, with a scanning path length slightly smaller than the target width and a linear speed of 10-2000 mm / s. The Y-mirror 5 steps in the -Y direction at the moment it scans both sides in the X direction, with a step length on the order of the spot size (~0.01 mm). The Z-direction (optical axis) adjustment mechanism 10 drives the target 8 in the +Z direction at the moment the X-mirror scans both sides, with a step length equal to that in the Y direction (at 45°). The cumulative movement in the Y and Z directions is slightly less than ~0.7 (Sin 45°) times the target length. In this way, through the real-time linkage of the X and Y galvanometers and the Z-direction (optical axis) adjustment mechanism, full-target scanning is achieved in a focused state. Target material 12 escaping from target 8 is deposited onto the facing sample 9 in a vacuum, thereby achieving thin film deposition.

[0031] like Figure 7The schematic diagram of the target scanning laser control of the multi-target material is shown in the figure. Four different materials (A, B, C, D) are installed on the target material 8. The laser spot is scanned in a serpentine shape along the arrow in the figure. The thickness of the arrow represents different laser powers. The dotted line part is the laser off area. The controller is as follows Figure 8 The control strategy shown here controls the volatilization rate of each material by interlocking the laser on / off, output power, two sets of XY galvanometers, and the Z-axis (optical axis) adjustment mechanism. Therefore, by editing the real-time output power of the laser spot as it passes through each material, the composition and ratio of the deposited film can be freely adjusted.

[0032] A pulsed fiber laser is used as the energy source for target volatilization. This type of laser utilizes an all-solid-state structure and does not use reactive gases. The average output power of the laser does not exceed 50W, the output frequency is 1-60kHz, and the pulse width is 10-1000ns.

[0033] The pulsed laser output from the laser passes through a collimating mirror and is output as a collimated beam with a diameter of 5-20 mm. Compared with the focused spot (diameter of the order of 0.01 mm) at the working point on the target surface, the power density of the collimated laser spot is reduced by at least 5 orders of magnitude, thereby avoiding ablation of subsequent X, Y galvanometer mirrors, focusing mirrors (field mirrors) and vacuum windows.

[0034] The collimated laser is modulated by electrically controlled rotatable mirrors (galvanometers) in the X and Y directions. These two sets of galvanometers, under the control of the controller, rotate via motors to alter the optical path deflection angle, thereby achieving two-dimensional scanning of the target surface. When operating within the permitted scanning range, the laser light deflected by the X-direction galvanometer still falls completely within the mirror area of ​​the Y-direction galvanometer, and the laser light deflected by both the X and Y galvanometers still passes completely through the subsequent converging lens (field lens).

[0035] Parallel laser light modulated by two sets of galvanometer mirrors is focused by a converging lens (field lens). The focal point is located on the target surface within the vacuum chamber, and the spot diameter at the focal point is on the order of 0.01mm.

[0036] The target and sample are both located in a vacuum chamber. The target is tilted relative to the laser optical axis. The sample faces the target. A vacuum must be maintained in the chamber during operation.

[0037] The Z-direction (optical axis) adjustment mechanism allows the distance between the target and the converging lens (field lens) to be adjusted in real time, thus keeping the light spot on the target surface in a focused state. Because there is an inclination angle between the laser optical axis and the target, the distance in the Z-direction (optical axis) needs to be adjusted in real time according to the light spot position during the target scanning process to keep the working point in a focused state.

[0038] The Z-direction (optical axis) adjustment mechanism can be achieved in two ways: by moving the converging lens in the Z direction or by moving the target in the Z direction. This adjustment mechanism must be linked to the X and Y galvanometer mirrors and the laser output. The ultimate goal is to ensure that the laser spot on the target surface is always in focus when scanning the tilted target.

[0039] The laser's on / off and output power can be controlled by a program, linked to the X and Y galvanometers and the Z (optical axis) adjustment mechanism. This feature allows for the installation of multiple materials at the target location. By editing the program to select the scanning area (target type) and the corresponding laser power (evaporation rate), multi-target scanning can be achieved, thereby quantitatively controlling the composition ratio of the thin film.

[0040] The foregoing description is merely an example of the present invention and the principles of its application. The present invention is not limited to the specific embodiments described herein, and those skilled in the art will readily appreciate that various modifications, readjustments, and substitutions may be made without departing from the scope of the present invention. Therefore, while the present invention has been described using the foregoing examples, the present invention is not limited thereto and, without departing from the spirit of the present invention, may include other equivalent embodiments, not limited to the embodiments described herein.

Claims

1. A focused scanning pulsed laser thin film deposition device, characterized in that: The invention comprises a pulse fiber laser (1), a collimating mirror (2), an X-direction galvanometer (4), a Y-direction galvanometer (5), a converging lens (6), a window (7), a target material (8), a Z-direction adjustment mechanism (10), a controller and a vacuum chamber (11); the laser light emitted by the pulse fiber laser (1) passes through the collimating mirror (2) to output collimated light, the collimated light is incident on the X-direction galvanometer (4), is reflected by the X-direction galvanometer (4) into the Y-direction galvanometer (5), and is then reflected by the Y-direction galvanometer (5) to the converging lens (6), and becomes a converging light beam after passing through the converging lens (6). The converging light beam passes through the vacuum chamber (11) The window (7) is introduced into the vacuum chamber (11), and the relative position of the target material (8) and the converging lens (6) in the optical axis direction is adjusted by the Z-direction adjustment mechanism (10). When the thin film deposition sample (9) is facing the surface of the target material (8), the controller communicates with the pulse fiber laser (1), and the controller outputs a control signal to the X-direction galvanometer (4), the Y-direction galvanometer (5) and the Z-direction adjustment mechanism (10), so that the focus of the converging light beam just falls on the surface of the target material (8), and the peak power density of the light spot at the focus exceeds the vaporization threshold of the target material (8), thereby volatilizing the target material on the target material (8) and performing thin film deposition on the sample (9); Several different target materials are installed at intervals on the target material (8), and a controller formulates a scanning plan. The volatilization rate of each target material is controlled by the linkage of the opening and closing of the pulse fiber laser (1), the output power of the pulse fiber laser (1), the X-direction galvanometer (4), the Y-direction galvanometer (5) and the Z-direction adjustment mechanism (10), thereby achieving uniform deposition of a multi-component thin film.

2. The focused scanning pulse laser thin film deposition device according to claim 1, characterized in that: The target material (8) and the sample (9) are both located in a vacuum cavity (11), and the target material (8) is placed at an angle to the convergent light beam, that is, the convergent light beam is incident obliquely on the surface of the target material (8).

3. The deposition method of the focused scanning pulse laser thin film deposition device according to claim 2, characterized in that: The specific steps include: 1) Build the focused scanning pulsed laser thin film deposition device, and the controller calculates the output power and output frequency of the pulsed fiber laser according to the composition characteristics of the deposited target material; 2) The controller calculates the optical path according to the position and optical parameters of each device in the focused scanning pulse laser thin film deposition device built in step 1), outputs the rotation angle of the X-direction galvanometer (4) and the Y-direction galvanometer (5) and the displacement of the Z-direction adjustment mechanism (10) to the X-direction galvanometer (4), the Y-direction galvanometer (5) and the Z-direction adjustment mechanism (10), turns on the pulse fiber laser, detects the size of the focused spot on the target material (8) and sends it to the controller, the controller records the error value and adjusts the rotation angle of the X-direction galvanometer (4), the Y-direction galvanometer (5) and the Z-direction adjustment mechanism (10), and records and calculates the optical path error of each section from the pulse fiber laser (1) to the X-direction galvanometer (4), the X-direction galvanometer (4) to the Y-direction galvanometer (5), and the Y-direction galvanometer (5) to the Z-direction adjustment mechanism (10); 3) After adjusting the error, the focused spot size on the target (8) reaches a diameter of the order of 0.01 mm, the pulsed fiber laser is turned off, and the sample (9) to be deposited is placed directly opposite the surface of the target (8); 4) Input the target material area information on the target material into the controller, and the controller formulates a scanning plan according to the output power and output frequency of the pulse fiber laser, the evaporation rate of the target material, and the target material area; the controller controls the rotation angle of the X-direction galvanometer (4), the Y-direction galvanometer (5) and the Z-direction adjustment mechanism (10) to the initial position according to the scanning plan, and then turns on the pulse fiber laser to complete the focused scanning thin film deposition of the sample under the control of the controller.

4. The deposition method of the focused scanning pulsed laser thin film deposition device according to claim 3, characterized in that: The pulsed laser output from the pulsed fiber laser (1) passes through the collimating mirror (2) and is collimated and output as a parallel laser with a diameter of 5-20 mm; the diameter of the light spot of the parallel laser and the focused light spot of the working point on the surface of the target material (8) are on the order of 0.01 mm.

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