CN120772693B - Processing method of edge high-stress hard and brittle semiconductor material - Google Patents

Abstract

This invention provides a method for processing hard and brittle semiconductor materials with high edge stress, belonging to the field of semiconductor material processing technology. The specific method involves first using a laser to perform a ring-shaped cut on the polycrystalline and slit regions of a silicon carbide ingot with polycrystalline and slit edges. It is important to note that the ring-shaped cut must be performed simultaneously along the symmetrical direction of the ingot to ensure that while introducing mechanical stress into the high-stress areas, stress is simultaneously released on both sides, reducing the risk of crystal cracking. After laser cutting, the remaining portion is removed using a single-line cutting method, with the single-line entry point being the center of the laser cut, thus completing the ingot removal process. Through this improved process, the ring-shaped cut of the polycrystalline and slit regions at the edges using laser cutting isolates the high edge stress from extending inwards, solving the cracking problem caused by the mechanical stress introduced during subsequent single-line removal, and achieving rapid, low-loss, and low-risk ingot processing.

Description

Processing method of edge high-stress hard and brittle semiconductor material

Technical Field

The invention relates to the technical field of semiconductor material processing, in particular to a processing method of a hard and brittle semiconductor material with high edge stress.

Background

At present, a rounding process is generally adopted to remove stress areas at the edge of an ingot, namely, the stress areas at the edge of the ingot are removed by adopting a diamond grinding wheel, the problem of ingot cracking easily occurs in the process of processing, meanwhile, the diamond grinding wheel required by rounding is consumable, and is high in price, so that the cost of the rounding process is overhigh, and the polished part in the rounding process is completely abandoned, so that the material waste is serious.

The formation of cracks in silicon carbide crystals is mainly related to two major factors:

Thermal stress-thermal stress is generated inside the crystal during the growth or annealing process due to the non-uniform distribution of temperature. When these thermal stresses exceed the tolerance threshold of the material, crack formation may occur.

Internal defects, such as inclusions, dislocations, etc., inside the crystal also become sources of stress concentration, which, to some extent, also lead to cracking of the crystal.

The occurrence of these cracks not only reduces the mechanical strength of the silicon carbide crystal, but may also affect the electrical properties of the crystal, limiting its use in high performance electronic devices. Therefore, controlling growth conditions, optimizing annealing processes, and employing advanced growth techniques to reduce internal stress and defects are key approaches to improving the quality of silicon carbide crystals.

SiC single crystals and substrates made therefrom exhibit high brittleness (or correspondingly low ductility). Bulk SiC crystals and the above-mentioned SiC substrates are subjected to large mechanical forces during their multi-stage machining. In particular, cracks or fissures can easily form along the preferred crystal cleavage plane (e.g., type and shape in the case of 4H-SiC) and result in damage or destruction of the SiC semi-finished cylinder and/or substrate. In particular, in mechanical processes where mechanical forces are applied radially (i.e., perpendicular to the outer diameter), an increased likelihood of cracking along the cleaved surface results in cracks in the crystal and substrate, resulting in undesirable yield loss.

DE102009048868 describes a thermal aftertreatment method for SiC crystals, which allows reducing the stress in the crystal and thus also reduces the susceptibility of SiC crystals to cracking.

CN110067020a describes a method of reducing the inherent stresses in crystals already present during production, which in turn should reduce the sensitivity of the crystals to cracking.

Patent CN118559900a provides a rounding method for processing a hard and brittle semiconductor material with high stress at the edge, and the rapid and low-loss cutting is realized by using a diamond single wire cutting machine and a diamond curve cutting machine to perform partial cutting and complete cutting. However, this method introduces mechanical stress in the direction of other cleaved surfaces of the ingot, and during practical experiments we have found that this embodiment does not reduce the cracking rate.

Patent CN113957532a provides a single crystal 4H-SiC substrate with improved robustness against cleaving machinery and a method of producing the same. The single crystal 4H-SiC substrate has improved mechanical robustness, enabling higher mechanical robustness of forces applied during production and machining of the outer surface of the 4H-SiC substrate, by distributing external mechanical forces over a plurality of equivalent parallel cleavage planes of force line segments L per unit length to reduce or even eliminate the occurrence of cracks, irrespective of the position around the entire periphery of the SiC semi-finished product to which such external mechanical forces are to be applied. The scheme is perfect in theory, and in the operation process, the complexity of the mechanical manufacturing equipment is increased, so that the low-cost batch processing is not facilitated.

Based on the principle of ingot cracking, the invention adopts a laser cutting mode to treat the edge high stress area, prevents the crack from extending from the high stress area into the ingot, and adopts a single wire integral treatment ingot edge after laser processing is finished, thereby realizing the processing results of high efficiency, high yield and low cost by adopting a laser processing and single wire cutting mode.

Disclosure of Invention

The invention aims to solve the technical problems of the prior art, and provides a processing method of a hard and brittle semiconductor material with high edge stress, which specifically comprises the following steps:

s1, preprocessing a silicon carbide ingot;

s2, releasing stress of laser annular cutting;

s3, forming a single-wire cutting rod.

Specifically, in the step S1, a silicon carbide ingot with a polycrystalline layer and a slit defect at the edge is provided, the distribution range of the polycrystalline region and the slit defect is determined through optical detection or X-ray diffraction, the symmetry axis of the ingot and the position of the edge of the defect are marked, and the ingot is required to be fixed on a processing platform with a multi-degree-of-freedom adjusting function, so that the cutting direction is ensured to be perpendicular to the c axis of the ingot.

Preferably, the step S2 specifically includes:

s2.1, planning a cutting path, namely setting annular cutting paths at the position 2-5 mm away from the defect edge along the circumferential direction of the ingot, wherein the two cutting paths are symmetrically distributed on two sides of the axis of the ingot;

S2.2, synchronously cutting along symmetrical paths by using double laser heads, wherein the cutting directions are opposite (one is forward and one is reverse);

s2.3, a stress release mechanism, namely, local thermal stresses generated by symmetrical cutting are mutually counteracted in the ingot, and crack propagation to the inside of the ingot is blocked.

Preferably, the technological parameters of the laser cutting are 355-1064nm wavelength, 0-50J/cm ² pulse energy, 1kHz-2MHz repetition frequency, 1-500fs pulse width, -3- +3 pulse stability, less than or equal to 3 space uniformity, 30-99 overlap, 10-2000mm/s scanning speed and environment control of argon/nitrogen.

And step S3, after the laser cutting is finished, the diamond single wire cutting machine is adopted to carry out the rod drawing processing of the rest part.

Preferably, the step S3 specifically includes:

s3.1, knife feeding positioning, namely cutting a single line from the midpoint of a symmetrical axis of a laser cutting area, wherein the knife feeding direction is perpendicular to a laser cutting surface, the initial feeding speed is 0.1-0.5mm/min, and the line tension is 5-50N;

s3.2, annular slitting, namely performing progressive slitting along an annular groove formed by laser pre-cutting, wherein the speed of a cutting line is 1-10m/s, and dynamically adjusting the tension and the feeding speed through a closed-loop control system to concentrate cutting stress on a pre-separation interface;

S3.3, finally forming, namely cutting to a target size, and obtaining the cylindrical silicon carbide ingot with the surface free of polycrystalline residue and slit defect stripping, wherein the cylindrical silicon carbide ingot can be directly used for a subsequent slicing process.

Compared with the prior art, the invention achieves the following technical effects:

According to the improved process, the edge polycrystal and the slit area are subjected to annular cutting by utilizing laser cutting, the edge high stress is isolated and extended inwards by the laser annular cutting, the cracking risk of mechanical stress introduced by a subsequent single-line rod is reduced, and the ingot is processed rapidly and with low loss and low risk.

Drawings

For ease of illustration, the invention is described in detail by the following detailed description and the accompanying drawings.

FIG. 1 is a schematic view of a silicon carbide ingot with polycrystalline and slits at the edge.

Fig. 2 is a schematic view of a laser cutting position.

Fig. 3 is a schematic view of a single line cutter direction.

FIG. 4 is a graph of the crystal without cracking after defect-free direct spheronization.

FIG. 5 is a graph of a crack at a defect site of a crystal after the edge defect of the ribbon of comparative example 1 is directly rounded.

FIG. 6 is a graph II of a crack at a defect site of a crystal after the edge defect of the band of comparative example 1 is directly rounded.

FIG. 7 is a graph showing the inward propagation of a single wire knife edge crack of comparative examples 2-3.

Detailed Description

The following are specific embodiments of the present invention and further description of the technical solutions of the present invention with reference to the accompanying drawings, but the present invention is not limited to these embodiments, and in the following description, specific details such as specific configurations are provided only for the purpose of helping to fully understand the embodiments of the present invention. It will therefore be apparent to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention.

In addition, the embodiments of the present invention and the features of the embodiments may be combined with each other without collision.

The principle of laser and single-wire cutting to reduce cracking is that after mechanical stress is directly introduced, a defective area at the edge is easily cracked towards a cleavage surface with slit/polycrystal, and cracks extend towards the inside of an ingot, the high-stress area is isolated from a wafer feeding area by laser cutting to prevent the cracks from extending inwards, and symmetrical orientation is adopted to synchronously carry out laser cutting processing, so that the cleavage surface in the symmetrical orientation uniformly releases stress, the cracking risk is reduced, and meanwhile, the single wire is cut from the laser cutting surface without an abnormal area, and then annular cutting is carried out to obtain the ingot with the wafer feeding size.

Example 1 laser drawing rod + Single wire feed machining 4H-SiC Crystal ingot (diameter 150 mm)

1-3, Step S1 (ingot pretreatment) provides a 4H-SiC ingot (diameter 150 mm) with polycrystalline layer and slip defects at the edge, determines the defect distribution range through X-ray diffraction, marks the symmetry axis of the ingot and the defect edge position, fixes the ingot on a six-degree-of-freedom processing platform, and adjusts the c-axis of the ingot to be perpendicular to the cutting direction.

Step S2 (laser ring cut stress relief):

s2.1, planning two symmetrical annular cutting paths (the distance is 6 mm) at the position 3 mm away from the defect edge, wherein the paths are symmetrically distributed on two sides of the axis of the ingot.

S2.2, adopting a double laser head (wavelength 1064 nm, pulse energy 30J/cm 2, frequency 500 kHz, scanning speed 500 mm/S and argon environment) to synchronously cut reversely.

S2.3, uniformly releasing stress field of the edge of the ingot after cutting, and limiting crack growth in a laser cutting area.

Step S3 (single line cutting bar forming):

S3.1, the diamond single wire is perpendicularly fed into the cutter from the center point of the axis of the laser cutting area (the feeding speed is 0.3 mm/min, and the wire tension is 20N).

S3.2, carrying out annular slitting along the laser precutting groove (linear speed is 5 m/S), dynamically adjusting the tension to 30N, and increasing the feeding speed to 0.5 mm/min.

S3.3 finally obtaining a defect-free cylindrical ingot with a diameter of 142 mm, completely peeling off the surface polycrystalline layer, and taking 5.5 hours (laser cutting 1h, single line undercut 4.5 h) in total, and 180 μm in material loss.

The ingot cracking rate is less than 5%, and the ingot can be directly used for slicing process.

Example 2 high stress 6H-SiC Crystal ingot processing (diameter 200 mm)

Step S1, ingot defect detection and fixing the same as in example 1, the platform was adjusted to accommodate an 8 inch ingot. Step S2, optimizing laser parameters to wavelength 355 nm (enhancing absorption of polycrystalline layers), pulse energy 40J/cm 2, frequency 1 MHz, scanning speed 300 mm/S and nitrogen environment.

And S3, carrying out single-wire initial feeding at a speed of 0.2 mm/min and a wire tension of 25: 25N, and finally cutting to obtain an ingot with a diameter of 190 mm.

The effect is that the total time is 6 hours (laser 1.2 h, single line 4.8 h), the material loss is 200 mu m, and the cracking rate is 4%.

Comparative example 1 direct spheronization with defects

The process is that a 150 mm ingot is directly processed by adopting a diamond grinding wheel to round, and as shown in figures 5-6, the crystal is directly rounded with edge defects, and the defect part is cracked.

As a result, the cracking rate is 30-50%, and the slip defect triggers radial cracks in the rolling process. It took 1.5 hours, but the material loss was 4 mm (all defective layers had to be removed).

Comparative example 2 Single wire cut+Rolling

The process is that the defect area is directly cut by a single wire and then rounded, as shown in figure 7, and the crack extends inwards.

As a result, mechanical stress causes 15-20% ingot cracking during single wire cutting. The total time is 4 hours, and the material loss is 380 μm.

Comparative example 3 Single wire cut defect + Single wire pulled ingot

The process is that the single line is cut step by step to form defect area, and then the bar is drawn out, as shown in figure 7, the crack is extended inwards.

As a result, the cracking rate at the time of single-wire cutting defect was 15-20%, and the total time was 9 hours (single-wire cutting 2.5 h, drawing bar 6.5. 6.5 h). The material loss was 80 μm but the efficiency was low and there was still a risk of cracking.

Table 1 comparative table of conventional processing and laser + single cut

Index (I)	Example 1	Example 2	Comparative example 1	Comparative example 2	Comparative example 3
						Cracking rate	<5%	<5%	30-50%	15-20%	15-20%
Time (six inches)	5-6 h	5-6 h	1.5-2 h	3-5 h	8-10 h
						Loss of material	150-200 μm	150-200 μm	3-5 mm	350-400 μm	20-100 μm

Those skilled in the art may make various modifications or additions to the described embodiments or substitutions in a similar manner without departing from the inventive concept or scope of the application as defined in the accompanying claims.

Claims (2)

1. The processing method of the edge high-stress hard and brittle semiconductor material is characterized by comprising the following steps of:

s1, preprocessing a silicon carbide ingot;

s2, releasing stress of laser annular cutting;

s3, forming a single-wire cutting rod;

Providing a silicon carbide ingot with a polycrystalline layer and a slit defect at the edge, determining the distribution range of the polycrystalline region and the slit defect through optical detection or X-ray diffraction, and marking the symmetry axis of the ingot and the position of the edge of the defect, wherein the ingot is required to be fixed on a processing platform with a multi-degree-of-freedom adjusting function, and ensuring the cutting direction to be perpendicular to the c axis of the ingot;

the step S2 specifically includes:

s2.1, planning a cutting path, namely setting annular cutting paths at the position 2-5 mm away from the defect edge along the circumferential direction of the ingot, wherein the two cutting paths are symmetrically distributed on two sides of the axis of the ingot;

s2.2, synchronously cutting along symmetrical paths by using double laser heads, wherein the cutting directions are opposite;

s2.3, a stress release mechanism, wherein local thermal stresses generated by symmetrical cutting are mutually counteracted in the ingot to block cracks from expanding to the ingot;

The laser cutting process has the parameters of 355-1064nm wavelength, pulse energy of 0-50J/cm ², repetition frequency of 1kHz-2MHz, pulse width of 1-500fs, pulse stability of-3- +3, spatial uniformity of less than or equal to 3%, overlap of 30-99%, scanning speed of 10-2000mm/s and environment control of argon or nitrogen;

and step S3, after the laser cutting is finished, the diamond single wire cutting machine is adopted to carry out the rod drawing processing of the rest part.

2. The method for processing the edge-high-stress brittle semiconductor material according to claim 1, wherein the step S3 specifically comprises:

s3.1, knife feeding positioning, namely cutting a single line from the midpoint of a symmetrical axis of a laser cutting area, wherein the knife feeding direction is perpendicular to a laser cutting surface, the initial feeding speed is 0.1-0.5mm/min, and the line tension is 5-50N;

s3.2, annular slitting, namely performing progressive slitting along an annular groove formed by laser pre-cutting, wherein the speed of a cutting line is 1-10m/s, and dynamically adjusting the tension and the feeding speed through a closed-loop control system to concentrate cutting stress on a pre-separation interface;

S3.3, finally forming, namely cutting to a target size, and obtaining the cylindrical silicon carbide ingot with the surface free of polycrystalline residue and slit defect stripping, wherein the cylindrical silicon carbide ingot can be directly used for a subsequent slicing process.