Hard and brittle wafer lossless thinning method based on internal and external cooperative laser modification and electrochemical stripping

Abstract

The invention discloses a hard and brittle wafer lossless thinning method based on internal and external cooperative laser modification and electrochemical stripping, and belongs to the technical field of semiconductor manufacturing. The method comprises the following steps: (1) scanning in a predetermined depth in a wafer by adopting a first beam of ultrafast laser to form a continuous internal modified layer so as to define the final stripping thickness; (2) scanning and ablating the back surface of the wafer by adopting a second beam of laser to form a micro-channel array which is directly communicated with the internal modification layer; (3) placing the wafer as an anode in an electrochemical device, and performing selective electrochemical anode dissolution on the internal modified layer by using the micro-channel array as a channel for efficiently permeating electrolyte and rapidly discharging reaction products, so that the main body layer of the wafer with the preset thickness is nondestructively stripped from the matrix; and (4) carrying out ultra-precision polishing on the new surface of the stripped wafer main body. Through internal and external synergistic modification, an efficient mass transfer channel is constructed, and the problems of efficiency and uniformity in large-area internal stripping are innovatively solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser-assisted processing, and particularly relates to a hard and brittle wafer non-destructive thinning method based on internal and external collaborative laser modification and electrochemical stripping. BACKGROUND

[0002] With the wide application of the third-generation semiconductor materials (such as silicon carbide SiC, gallium nitride GaN and diamond) in high-power electronic devices, radio frequency devices and new energy vehicle power modules, the demand for processing and thinning of large-size and high-quality wafers is rapidly increasing. Wafer thinning is a key link in the semiconductor manufacturing process, and its purpose is to reduce thermal resistance, improve heat dissipation performance and realize lightweight devices. However, due to the characteristics of high hardness, high brittleness and high chemical inertness of such materials, the traditional mechanical grinding and chemical mechanical polishing (CMP) methods are prone to introduce micro-cracks, residual stress and warping deformation in the processing process, which seriously affects the surface integrity of the wafer and the subsequent device performance.

[0003] At present, the common thinning and stripping technologies mainly include mechanical thinning method, chemical etching method and laser stripping method. However, the existing laser stripping process usually has problems such as uneven stress of the modified layer, uncontrollable crack extension and rough residual interface, especially in SiC or diamond high-thermal-conductivity high-bandgap crystals, the energy deposition and transfer of the laser-induced modified region are limited, which makes it difficult to accurately control the depth and continuity of the modified layer.

[0004] In addition, the buried layer formed by laser modification often needs to be assisted by mechanical stripping or strong acid chemical etching in subsequent separation, which may still cause structural damage or surface contamination; while the pure electrochemical stripping method has been applied in silicon-based materials, but in hard and brittle crystals, due to low electrical conductivity, interface closure and other problems, it is difficult to achieve uniform penetration of the reaction interface, and the stripping efficiency is low and local over-etching is easy to occur.

[0005] In summary, the existing technology still lacks a hard and brittle wafer non-destructive thinning method with high selective modification, effective mass transfer channel and controllable delamination stripping capability. Especially for silicon carbide or diamond wafers, how to realize efficient and low-stress thinning and stripping while ensuring the structural integrity is still a key technical problem faced by the current industry. SUMMARY

[0006] (I) Invention purpose

[0007] In view of the deficiencies of the prior art, the present application aims to provide a hard and brittle wafer non-destructive thinning method based on internal and external collaborative laser modification and electrochemical stripping, which aims to improve the mass transfer bottleneck problem of internal stripping of large-size wafers by creatively introducing a micro-channel network on the back surface of the wafer and directly communicating it with the internal modification layer, thereby constructing a three-dimensional and efficient fluid exchange system.

[0008] (II) Technical scheme

[0009] The present application is implemented by the following technical scheme.

[0010] (1) A first beam of ultrafast laser beam with a first set of laser parameters is used to focus on the inside of the conductive semiconductor wafer and scan at a predetermined depth from the front surface (device surface) of the wafer, thereby forming a continuous internal modification layer with different electrochemical activity or structural damage in the inside of the wafer, which divides the wafer into a front wafer body to be retained and a back sacrificial layer to be removed;

[0011] (2) A second beam of laser beam with a second set of laser parameters is used to scan and ablate the back surface of the wafer, and a high-density micro-channel array is processed in the back sacrificial layer, the micro-channels extending from the back surface to and communicating with the internal modification layer;

[0012] (3) The wafer processed in step (2) is installed as an anode in an electrochemical device, and the back surface with the micro-channel array is in contact with the electrolyte;

[0013] (4) An electric field is applied between the anode and the cathode in the electrochemical device, the micro-channel array is used to guide the electric field distribution and as a high-speed ion migration channel for the electrolyte, and the internal modification layer is subjected to electrochemical anodic etching; by utilizing the electrochemical activity difference between the conductive wafer substrate and the modification layer, the internal modification layer is selectively removed by corrosion until the back sacrificial layer is completely separated from the front wafer body;

[0014] (5) The separation surface of the front wafer body separated in step (4) is cleaned and subjected to ultra-precision polishing treatment to obtain an atomically smooth surface.

[0015] Further, the semiconductor wafer in step (1) is conductive silicon carbide (SiC) or doped conductive diamond;

[0016] Further, in step (2), the hole spacing of the micro-channel array is 10-500 μm, and the hole diameter is 1-50 μm;

[0017] Further, the first set of laser parameters in step (1) is set as follows: pulse width 100fs-50ps, wavelength 355nm-1064nm, single pulse energy 1μJ-20μJ, repetition frequency 100KHz-5MHz, and scanning speed 100mm / s-5000mm / s.

[0018] Further, the second set of laser parameters in step (2) is set as follows: pulse width 100fs-200ns, wavelength 266nm-1064nm, single pulse energy 5μJ-100μJ, and repetition frequency 10KHz-1MHz;

[0019] Furthermore, in step (4), while applying an electric field, ultraviolet light is applied to the wafer to increase the carrier concentration inside the semiconductor through the photovoltaic effect, thereby assisting the electrochemical reaction.

[0020] Furthermore, during the electrochemical stripping process in step (4), ultrasonic vibration is applied simultaneously to remove bubbles generated within the microchannels and enhance mass transfer.

[0021] Furthermore, the ultra-precision polishing process in step (5) is chemical mechanical polishing (CMP) or plasma-assisted polishing (PAP).

[0022] (III) Beneficial Effects

[0023] The above-described technical solution of the present invention has the following beneficial technical effects:

[0024] (1) Effectively improves peeling efficiency and uniformity: The microchannel array effectively shortens the mass transfer path, which greatly improves the efficiency of electrolyte exchange and product discharge, thereby realizing rapid and uniform peeling of large-size wafers.

[0025] (2) Enhanced process reliability and yield: effectively avoided peeling failure caused by reaction stagnation in the central area, and significantly improved the success rate and yield of large-size and thick peeling processes.

[0026] (3) It retains the core advantage of internal stripping: Although microchannels are processed on the back side, the final separated wafer surface is still a low-damage native crystal surface, maintaining a high surface quality. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0028] Figure 2 The image is the AFM image obtained after processing in Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention.

[0030] Example 1: This example describes the thinning of a conductive 4H-SiC wafer with an initial thickness of 350 μm, with the goal of obtaining an ultrathin wafer with a thickness of 100 μm.

[0031] (1) Laser Internal Modification: The wafer is fixed with the front side (device side) facing down. An ultrafast laser with a wavelength of 1030 nm and a pulse width of 5 ps is incident from the back side of the wafer, and the focal point is focused at a depth of 100 μm from the front side (i.e., 250 μm from the back side). An amorphization modification layer is formed by scanning. At this point, the wafer is divided into two parts in terms of thickness: a 100 μm thick front wafer body and a 250 μm thick back sacrificial layer.

[0032] (2) Microchannel construction (ion channels): The back surface was scanned using a nanosecond ultraviolet laser with a wavelength of 355 nm. A high-density grid-like microchannel array with a spacing of 200 μm was fabricated. Each channel has a diameter of 15 μm and penetrates the entire 250 μm thick back sacrificial layer until it connects to the internal modified layer.

[0033] (3) Electrochemical stripping: The wafer is placed as the anode in a bath containing an electrolyte of HF:Ethanol (volume ratio 1:1). A 10V DC voltage is applied, supplemented by full-range irradiation with 365nm ultraviolet light and ultrasonic vibration. The electric field acts directly on the internal modified layer through the microchannel, eliminating the resistive shielding caused by the thickness. Under high current density, the amorphous SiC in the modified layer is rapidly oxidized and dissolved.

[0034] (4) Separation and polishing: After a period of time, the current drops sharply, indicating that the modified layer has been completely consumed and the back sacrificial layer (along with the microchannels on it) has fallen off as a whole. The remaining front wafer body with a thickness of about 100 μm is removed, cleaned and then CMP polished to remove the residual reaction layer on the surface, and finally a high-flatness ultrathin SiC wafer is obtained.

Claims

1. A non-destructive thinning method for hard and brittle wafers based on internal and external synergistic laser modification and electrochemical exfoliation, characterized in that... Includes the following steps: (1) A first ultrafast laser beam with a first set of laser parameters is used to focus the beam inside the conductive semiconductor wafer and scan it at a predetermined depth from the front side (device side) of the wafer, thereby forming a continuous internal modification layer with different electrochemical activities or structural damage inside the wafer. The modification layer defines the wafer as the front wafer body to be retained and the back sacrificial layer to be removed. (2) A second laser beam with a second set of laser parameters is used to scan and ablate the back surface of the wafer to process a high-density microchannel array in the back sacrificial layer. The microchannels extend from the back surface to and connect with the internal modified layer. (3) The wafer processed in step (2) is installed as the anode in the electrochemical device, and the back side with the microchannel array is in contact with the electrolyte. (4) An electric field is applied between the anode and the cathode in the electrochemical device, and the electric field distribution is guided by the microchannel array and used as a high-speed ion migration channel for the electrolyte to perform electrochemical anodic etching on the internal modified layer; By utilizing the difference in electrochemical activity between the conductive wafer substrate and the modified layer, the internal modified layer is selectively etched away until the back sacrificial layer is completely peeled off from the front wafer body. (5) The stripped surface of the front wafer body after separation in step (4) is cleaned and ultra-precision polished to obtain an atomically flat surface.

2. The method according to claim 1, characterized in that, The semiconductor wafer in step (1) is conductive silicon carbide (SiC) or doped conductive diamond.

3. The method according to claim 1, characterized in that, In step (2), the spacing between the microchannels is 10μm-500μm and the aperture is 1μm-50μm.

4. The method according to claim 1, characterized in that, The first set of laser parameters in step (1) is set as follows: pulse width 100fs-50ps, wavelength 355nm-1064nm, single pulse energy 1μJ-20μJ, repetition frequency 100KHz-5MHz, and scanning speed 100mm / s-5000mm / s.

5. The method according to claim 1, characterized in that, The second set of laser parameters in step (2) is set as follows: pulse width 100fs-200ns, wavelength 266nm-1064nm, single pulse energy 5μJ-100μJ, and repetition frequency 10KHz-1MHz.

6. The method according to claim 1, characterized in that, In step (4), while applying an electric field, ultraviolet light is applied to the wafer to increase the carrier concentration inside the semiconductor through the photovoltaic effect, thereby assisting the electrochemical reaction.

7. The method according to claim 1, characterized in that, During the electrochemical stripping process in step (4), ultrasonic vibration is applied simultaneously to remove bubbles generated in the microchannel and enhance mass transfer.

8. The method according to claim 1, characterized in that, The ultra-precision polishing process in step (5) is chemical mechanical polishing (CMP) or plasma-assisted polishing (PAP).

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