Laser processing apparatus and laser processing method

Abstract

The invention provides a laser processing device and method, and the device comprises a laser device which is used for emitting laser; the optical system comprises a collimating lens, a shaping lens and a focusing lens, the laser is collimated and amplified by the collimating lens and then enters the shaping lens, the incident laser is converted into a flat-topped light spot from a Gaussian light spot by the shaping lens, and the flat-topped light spot is positioned on a bonding interface by moving the position of the focusing lens; the displacement table system comprises a longitudinal displacement table and a horizontal displacement table, and the longitudinal displacement table is used for driving the focus lens to move synchronously, so that the flat-topped light spot is located on a bonding interface; the horizontal displacement table is used for driving the heterogeneous bonding material to move synchronously so as to realize that the flat-topped light spot scans the whole bonding interface; the in-situ observation system is used for obtaining light spot images of the surface and the bonding interface at at least one height measurement point; and the processing control system is used for obtaining the moving distance of the focus lens according to the light spot image of the height measurement point so as to adjust the position of the focus lens. According to the method, the bonding interface can be optimized.

Description

Technical Field

[0001] This application relates to the field of laser processing technology, and in particular to a laser processing apparatus and a laser processing method. Background Technology

[0002] Bonding technology can bond two heterogeneous materials together, but this technology still suffers from problems such as low bond strength, high thermal resistance, and the introduction of interface states. In current technologies, to achieve sufficient bond strength, the bonded structure is typically heated to extremely high temperatures via annealing after bonding. However, traditional thermal annealing heat-treats the entire wafer, which can easily damage the already fabricated heterogeneous device structure or metal layer. Therefore, it is necessary to propose a new method for optimizing the heterogeneous bonding interface to improve the bond strength and reduce thermal resistance and interface states. Summary of the Invention

[0003] In view of this, this application provides a laser processing apparatus and a laser processing method, which uses a flat-top laser spot to scan the bonding interface to achieve bonding interface optimization.

[0004] In a first aspect, this application provides a laser processing apparatus for optimizing the bonding interface of heterogeneous bonding materials, comprising: A laser for emitting laser light that can penetrate one layer of a heterobonded material; An optical system includes a collimating lens, a shaping lens, and a focusing lens. The laser emitted by the laser is collimated and amplified by the collimating lens and then incident on the shaping lens. The shaping lens transforms the incident laser from a Gaussian spot into a flat-top spot. By moving the position of the focusing lens, the flat-top spot is positioned at the bonding interface. The displacement stage system includes a longitudinal displacement stage and a horizontal displacement stage. The longitudinal displacement stage is fixedly connected to the focusing lens and is used to move in a direction perpendicular to the surface of the heterogeneous bonding material after each loading, thereby driving the focusing lens to move synchronously and positioning the flat-top light spot at the bonding interface. The horizontal displacement stage is used to place the heterogeneous bonding material and moves in the horizontal direction, thereby driving the heterogeneous bonding material to move synchronously, so as to enable the flat-top light spot to scan the entire bonding interface. An in-situ observation system for obtaining spot images of the surface and bonding interface at at least one elevation measurement point; The machining control system is used to calculate the surface height and bonding interface height of the measuring point based on the spot image obtained from the measuring point, further calculate the moving distance of the focusing lens based on the surface height and bonding interface height, and control the movement of the longitudinal displacement stage based on the moving distance of the focusing lens.

[0005] Optionally, the moving distance of the focusing lens satisfies the expression: ΔZ = WD - [n·(Z0–Z1) + Z1], where ΔZ is the moving distance of the focusing lens, WD is the working distance of the focusing lens, n is the refractive index of the layer of material through which the laser emitted by the laser passes, Z0 is the bonding interface height of the measuring point, Z1 is the surface height of the measuring point, a positive ΔZ represents movement away from the surface, and a negative ΔZ represents movement towards the surface.

[0006] Optionally, the machining control system is further configured to set the scanning path and scanning speed, and control the movement of the horizontal displacement stage according to the set scanning path and scanning speed.

[0007] Optionally, the scanning path is one of the following: a straight scanning path, a staggered superimposed scanning path, or a circular / spiral scanning path.

[0008] Optionally, the processing control system is further configured to set the laser energy and laser repetition frequency, and adjust the laser according to the set laser energy and laser repetition frequency.

[0009] Optionally, the in-situ observation system includes a white light source and an imaging device. Part of the white light emitted by the white light source is reflected at the surface of the heterogeneous bonding material and received by the imaging device to obtain a first spot image; part of the white light passes through one layer of the heterogeneous bonding material, is reflected at the bonding interface, and is received by the imaging device to obtain a second spot image. The processing control system is used to calculate the surface height based on the first spot image; and is also used to calculate the bonding interface height based on the second spot image.

[0010] Optionally, the shaping mirror is one of a diffractive optical element (DOE), a liquid crystal spatial light modulator (LCoS), a metasurface, and a microlens array.

[0011] Optionally, the laser is a short-pulse laser, and the emitted laser wavelength can pass through at least one of the heterobonded materials.

[0012] Secondly, this application provides a laser processing method applied to the laser processing apparatus as described in the first aspect, the method comprising: The in-situ observation system obtains spot images of the surface and bonding interface of the heterogeneous bonding material at at least one elevation measurement point, and uploads the spot images to the processing control system so that the processing control system can determine the moving distance of the focusing lens; The laser emits a laser beam, which is collimated and amplified by a collimating lens, and then shaped by the shaping lens to transform the Gaussian spot into a flat-top spot. The longitudinal displacement stage moves the focusing lens so that the flat-top spot is located at the bonding interface. The horizontal displacement stage moves in the horizontal direction, causing the heterogeneous bonding material to move synchronously, so as to achieve scanning of the entire bonding interface by the flat-top light spot.

[0013] Optionally, the moving distance of the focusing lens satisfies the expression: ΔZ = WD - [n·(Z0–Z1) + Z1], where ΔZ is the moving distance of the focusing lens, WD is the working distance of the focusing lens, n is the refractive index of the layer of material through which the laser emitted by the laser passes, Z0 is the bonding interface height of the measuring point, Z1 is the surface height of the measuring point, a positive ΔZ represents movement away from the surface, and a negative ΔZ represents movement towards the surface.

[0014] The laser processing apparatus and method provided in this application obtain laser spot images at various height measurement points through an in-situ observation system. The processing control system obtains accurate surface height and bonding interface height based on the laser spot images and determines the moving distance of the focusing lens. Combined with a shaping lens, the laser is transformed from a Gaussian spot to a flat-top spot. The position of the focusing lens is adjusted by a longitudinal displacement stage so that the flat-top spot is located at the bonding interface. A horizontal displacement stage is used to drive the heterogeneous bonding material to move synchronously, so that the flat-top spot can scan the entire bonding interface, thereby achieving interface optimization. Attached Figure Description

[0015] Figure 1 This is a schematic system block diagram of the laser processing apparatus in the embodiments of this application; Figure 2 This is a schematic diagram of the optical system in an embodiment of this application; Figure 3 This is a schematic diagram illustrating the focusing lens position control principle in an embodiment of this application; Figure 4 This is a schematic diagram of the in-situ observation system in the embodiments of this application; Figure 5 This is a schematic diagram of several optional scanning paths in the embodiments of this application; Figure 6 This is a schematic flowchart of the laser processing method in the embodiments of this application. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of this disclosure.

[0017] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0018] This application provides a laser processing apparatus for optimizing the bonding interface of heterogeneous bonding materials, such as... Figure 1 As shown, the laser processing device includes: Laser 101 is used to emit laser light, which can penetrate one layer of the heterogeneous bonding material to reach the bonding interface, forming a laser source required for bonding interface optimization. The optical system 102 includes a collimating lens, a shaping lens, and a focusing lens. The laser emitted by the laser 101 is collimated and amplified by the collimating lens and then incident on the shaping lens. The shaping lens transforms the incident laser from a Gaussian spot into a flat-top spot. By moving the position of the focusing lens, the flat-top spot is positioned at the bonding interface of the heterogeneous bonding materials. The displacement stage system 103 includes a longitudinal displacement stage and a horizontal displacement stage. The longitudinal displacement stage is fixedly connected to the focusing lens in the optical system 102 and is used to move in a direction perpendicular to the surface of the heterogeneous bonding material after each loading, driving the focusing lens to move synchronously so that the flat-top light spot is located at the bonding interface. The horizontal displacement stage is used to place the heterogeneous bonding material and moves in the horizontal direction, driving the heterogeneous bonding material to move synchronously, so that the flat-top light spot can scan the entire bonding interface. In-situ observation system 104 is used to obtain spot images of the surface and bonding interface at at least one elevation measurement point; The machining control system 105 is used to calculate the surface height and bonding interface height of the measuring point based on the spot image obtained from the measuring point, and further calculate the moving distance of the focusing lens based on the surface height and bonding interface height, and control the movement of the longitudinal displacement stage based on the moving distance of the focusing lens.

[0019] Furthermore, the machining control system 105 is also used to set the scanning path and scanning speed, and to control the movement of the horizontal displacement stage according to the set scanning path and scanning speed.

[0020] Figure 2 This is a schematic diagram of the optical system in an embodiment of this application. After being processed by the optical system, the laser forms a flat-topped spot at the bonding interface. For example... Figure 2 As shown in (a), the optical system collimates and amplifies the laser output from the laser through a collimating lens, and then directs it onto a shaping lens and a focusing lens. If the laser propagates in the air, a flat-topped spot is formed at the working distance (WD) of the focusing lens. Figure 2As shown in (b) in this embodiment, the laser needs to pass through a layer of heterogeneous bonding material to reach the bonding interface. By moving the position of the focusing lens, the optical path from the focusing lens to the bonding interface is equal to Z0, where Z0 is the height of the bonding interface, thus ensuring that the flat-top spot is located at the bonding interface.

[0021] For ease of understanding, in the embodiments of this application, the heterogeneous bonding material is illustrated by a stack of diamond and GaN, with diamond on the upper layer and GaN on the lower layer.

[0022] The following explanation concerns the movement distance of the longitudinal displacement stage and the focusing lens: For each heterogeneous bonding material to be processed, the thicknesses of diamond and GaN will differ due to process variations. To ensure the flat-top laser spot remains at the bonding interface of the heterogeneous bonding material, the position of the longitudinal displacement stage must be adjusted after each loading (i.e., fixing the heterogeneous bonding material to be processed), and the position of the focusing lens must be adjusted synchronously. If the surface of the heterogeneous bonding material is flat, only one measurement point needs to be set. However, considering the surface unevenness during processing, one measurement point is insufficient, and multiple measurement points are required. The in-situ observation system 104 obtains laser spot images of the surface and bonding interface at multiple measurement points at a set sampling interval and uploads them to the processing control system 105. The processing control system 105 calculates the surface height and bonding interface height at each measurement point in real time, and further calculates the movement distance of the focusing lens based on the surface height and bonding interface height, adjusting the position of the focusing lens in real time.

[0023] refer to Figure 3 For any given elevation point, the distance the focusing lens moves satisfies the expression: ΔZ = WD - [n·(Z0–Z1) + Z1], where ΔZ is the moving distance of the focusing lens, WD is the working distance of the focusing lens in the air, n is the refractive index of the layer of material through which the laser emitted by the laser passes, Z0 is the bonding interface height of the current height measurement point, Z1 is the surface height of the current height measurement point, a positive ΔZ represents movement away from the surface, and a negative ΔZ represents movement towards the surface.

[0024] In the above expression, WD and n are constants, while Z0 and Z1 are variables, depending on the location of the altimeter. At each altimeter, there is a corresponding distance the focusing lens moves.

[0025] In one embodiment, a displacement table can be generated in advance, recording the coordinates of each elevation point and the corresponding focusing lens movement distance. The machining control system obtains the focusing lens movement distance corresponding to the current coordinates by querying the displacement table, and then controls the focusing lens movement.

[0026] Specifically, before processing begins, the in-situ observation system measures the elevation at a set sampling interval (e.g., 5 ms) at the elevation measurement point (X). i Y i The laser spot image of the surface and bonding interface is obtained at the location, and the laser spot image is uploaded to the machining control system. The machining control system calculates the focusing lens movement distance ΔZ. i Based on the coordinates of the elevation point (X i Y i ) and ΔZ i Generate a displacement table.

[0027] During the processing, the processing control system uses the coordinate position as a reference, obtains the focusing lens movement distance at the current coordinate position by querying the displacement table, and adjusts the focusing lens movement to precisely control the flat-top spot to be located at the bonding interface position.

[0028] The surface height Z1 and bonding interface height Z0 are calculated by the machining control system 105 based on the spot images of the surface and bonding interface uploaded by the in-situ observation system 104. The in-situ observation system 104 is explained as follows: Figure 4 A schematic diagram of an in-situ observation system, such as Figure 4 As shown, the in-situ observation system 104 includes a white light source and an imaging device. The white light emitted from the white light source can pass through one layer of the heterogeneous bonding material, such as diamond. Diamond is transparent. Part of the white light emitted from the white light source is reflected on the diamond surface and received by the imaging device to obtain a first light spot image. Another part of the white light passes through the diamond, is reflected at the bonding interface, and is then received by the imaging device to obtain a second light spot image. The processing control system 105 calculates the surface height Z1 based on the first light spot image; it is also used to calculate the bonding interface height Z0 based on the second light spot image. Specific calculation methods include, but are not limited to, trigonometric methods, interferometry, etc., and this application does not impose any limitations.

[0029] Figure 4 The bonding interfaces and surfaces of the heterogeneous bonding materials shown are flat. In some embodiments, to address the issue of uneven surface texture of the heterogeneous materials, multiple light spot images of elevation points are obtained using a white light source and an imaging device at set sampling intervals. Based on the light spot images of the multiple elevation points, the processing control system obtains the surface height and bonding interface height of the multiple elevation points, and moves the position of the focusing lens in real time to compensate for the height differences on the surface.

[0030] Figure 5 This is a schematic diagram of several optional scan paths. Figure 5 (a) is a schematic diagram of a straight scanning path, (b) is a schematic diagram of a staggered superimposed scanning path, and (c) is a schematic diagram of a circular / spiral scanning path.

[0031] In one embodiment, the processing control system 105 is also used to set the laser energy and laser repetition frequency, and adjust the laser 101 according to the set laser energy and laser repetition frequency.

[0032] In one embodiment, the shaping mirror includes one of a diffractive optical element (DOE), a liquid crystal spatial light modulator (LCoS), a metasurface, and a microlens array, which can be pre-designed to form a flat-top light spot at the WD position.

[0033] Flat-top light spots exhibit better energy uniformity, and this application embodiment uses flat-top light spots to optimize the bonding interface. The shape of the flat-top light spot can be circular, rectangular, square, straight, elliptical, or a custom shape.

[0034] In one embodiment, the laser 101 is a short-pulse laser, and the emitted laser wavelength can pass through at least one of the heterobonded materials, i.e., λ>1240 / Eg, where Eg is a value with a larger band gap in the heterobonded material. The bonding interface temperature is controlled by selectively absorbing low-energy laser light through the heterobonded material.

[0035] The laser processing apparatus provided in this application obtains spot images at various height measurement points through an in-situ observation system. The processing control system obtains accurate surface height and bonding interface height based on the spot images and determines the moving distance of the focusing lens. Combined with a shaping lens, the laser is transformed from a Gaussian spot to a flat-top spot. The position of the focusing lens is adjusted by a longitudinal displacement stage so that the flat-top spot is located at the bonding interface. A horizontal displacement stage is used to drive the heterogeneous bonding material to move synchronously, so that the flat-top spot can scan the entire bonding interface, thereby achieving interface optimization. This is mainly reflected in: reducing the amorphous layer and changing the crystalline state of the interface, improving the interface bonding strength, reducing thermal resistance, and reducing interface damage and interface state.

[0036] On the other hand, embodiments of this application provide a laser processing method, implemented using the laser processing apparatus provided in the above embodiments, such as... Figure 6 As shown, laser processing methods include: S61, the in-situ observation system obtains a spot image of the surface and bonding interface of the heterogeneous bonding material at at least one height measurement point, and uploads the spot image to the processing control system so that the processing control system can determine the moving distance of the focusing lens; S62, the laser emits a laser beam, which is collimated and amplified by a collimating lens, and then shaped by a shaping lens, transforming the Gaussian spot into a flat-top spot. The longitudinal displacement stage moves the focusing lens to position the flat-top spot at the bonding interface. S63, the horizontal displacement stage moves in the horizontal direction, driving the heterogeneous bonding materials to move synchronously, so as to realize the scanning of the entire bonding interface by the flat-top spot.

[0037] In one embodiment, the moving distance of the focusing lens satisfies the expression: ΔZ = WD - [n·(Z0–Z1) + Z1], where ΔZ is the moving distance of the focusing lens, WD is the working distance of the focusing lens, n is the refractive index of the layer of material through which the laser emitted by the laser passes, Z0 is the bonding interface height of the measuring point, Z1 is the surface height of the measuring point, and a positive ΔZ represents movement away from the surface, while a negative ΔZ represents movement closer to the surface.

[0038] In one embodiment, the scanning path is one of the following: a straight scanning path, a staggered superimposed scanning path, or a circular / spiral scanning path.

[0039] Additionally, the processing control system can also set parameters such as laser energy, laser repetition frequency, scanning path, and scanning speed. Through the combined design of laser energy, laser repetition frequency, scanning path, and scanning speed, a uniform and optimized bonding interface effect can be achieved.

[0040] The laser processing method provided in this application obtains spot images at various height measurement points through an in-situ observation system. The processing control system obtains accurate surface height and bonding interface height based on the spot images and determines the moving distance of the focusing lens. Combined with a shaping lens, the laser spot is transformed from a Gaussian spot to a flat-top spot. The position of the focusing lens is adjusted by a longitudinal displacement stage so that the flat-top spot is located at the bonding interface. A horizontal displacement stage is used to drive the heterogeneous bonding material to move synchronously, so that the flat-top spot can scan the entire bonding interface, thereby achieving interface optimization. This is mainly reflected in: reducing the amorphous layer and changing the crystalline state of the interface, improving the interface bonding strength, reducing thermal resistance, and reducing interface damage and interface state.

[0041] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A laser processing apparatus characterized by comprising: The laser processing device is used for optimizing the bonding interface of a heterogeneous bonding material, and comprises: a laser for emitting laser light which can penetrate one of the layers of the heterogeneous bonding material; an optical system comprising a collimating mirror, a shaping mirror and a focusing mirror, the laser light emitted by the laser is collimated and enlarged by the collimating mirror, and then is incident on the shaping mirror, the shaping mirror converts the incident laser light from a Gaussian spot into a flat-top spot, and the flat-top spot is located on the bonding interface by moving the position of the focusing mirror; a displacement table system comprising a longitudinal displacement table and a horizontal displacement table, the longitudinal displacement table is fixedly connected with the focusing mirror, and is used for moving in a direction perpendicular to the surface of the heterogeneous bonding material after each feeding to drive the focusing mirror to move synchronously so that the flat-top spot is located on the bonding interface; the horizontal displacement table is used for placing the heterogeneous bonding material and moving in a horizontal direction to drive the heterogeneous bonding material to move synchronously so as to realize scanning of the flat-top spot on the entire bonding interface; an in-situ observation system for obtaining spot images of the surface and the bonding interface at at least one height measuring point; a processing control system for calculating the surface height and the bonding interface height at the height measuring point according to the spot images obtained at the height measuring point, and further calculating the moving distance of the focusing mirror according to the surface height and the bonding interface height, and controlling the movement of the longitudinal displacement table according to the moving distance of the focusing mirror.

2. The laser processing apparatus according to claim 1, characterized by The moving distance of the focusing mirror satisfies the expression: ΔZ = WD - [n·(Z0 - Z1) + Z1], wherein ΔZ is the moving distance of the focusing mirror, WD is the working distance of the focusing mirror, n is the refractive index of the material penetrated by the laser light emitted by the laser, Z0 is the bonding interface height of the height measuring point, Z1 is the surface height of the height measuring point, and ΔZ is a positive number representing the moving direction away from the surface, and ΔZ is a negative number representing the moving direction close to the surface.

3. The laser processing apparatus according to claim 1, characterized by The processing control system is further used for setting a scanning path and a scanning speed, and controlling the movement of the horizontal displacement table according to the set scanning path and scanning speed.

4. The laser processing apparatus according to claim 3, characterized by The set scanning path is one of a straight line scanning path, a staggered and superimposed scanning path, a circular / helical scanning path.

5. The laser processing apparatus according to claim 1, characterized by The processing control system is further used for setting a laser energy and a laser repetition frequency, and adjusting the laser according to the set laser energy and laser repetition frequency.

6. The laser processing apparatus according to claim 1, characterized by The in-situ observation system comprises a white light source and an imaging device, a part of the white light emitted by the white light source is reflected at the surface of the heterogeneous bonding material, and a first spot image is obtained after being received by the imaging device; another part of the white light penetrates one of the layers of the heterogeneous bonding material, is reflected at the bonding interface, and a second spot image is obtained after being received by the imaging device. The processing control system is used for calculating the surface height according to the first spot image, and is further used for calculating the bonding interface height according to the second spot image.

7. The laser processing apparatus according to claim 1, wherein The shaping mirror is one of a diffractive optical element, a liquid crystal spatial light modulator, a metasurface and a microlens array.

8. The laser processing apparatus according to claim 1, characterized by The laser is a short pulse laser, and the wavelength of the emitted laser can penetrate at least one of the materials of the heterogeneous bonding material.

9. A laser processing method characterized by, The method is applied to the laser processing device as claimed in claim 1, and the method comprises: The in-situ observation system obtains a light spot image of a surface of a hetero-junction material and a bonding interface at at least one height measuring point, and uploads the light spot image to a processing control system, so that the processing control system determines a moving distance of a focusing mirror; The laser emits laser light, the emitted laser light is collimated and enlarged by a collimating mirror, and then is shaped by the shaping mirror, so that the laser light is converted from a Gaussian light spot into a flat-top light spot; a longitudinal displacement table drives the focusing mirror to move, so that the flat-top light spot is located at the bonding interface; A horizontal displacement table moves in a horizontal direction, and drives the hetero-junction material to move synchronously, so that the flat-top light spot scans the entire bonding interface.

10. The method of claim 9, wherein, The moving distance of the focusing mirror satisfies an expression: ΔZ=WD-[n·(Z0–Z1)+ Z1], wherein ΔZ is the moving distance of the focusing mirror, WD is a working distance of the focusing mirror, n is a refractive index of a material layer through which the laser emitted by the laser is transmitted, Z0 is a height of the bonding interface of the height measuring point, Z1 is a surface height of the height measuring point, ΔZ is a positive number representing a moving direction away from the surface, and ΔZ is a negative number representing a moving direction close to the surface.

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