CN111029301B

CN111029301B - Processing method of silicon carbide-based wafer

Info

Publication number: CN111029301B
Application number: CN201911202638.2A
Authority: CN
Inventors: 陈为彬; 林志东; 吴垚鑫; 程江涛
Original assignee: Xiamen Sanan Integrated Circuit Co Ltd
Current assignee: Hunan Sanan Semiconductor Co Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2022-10-28
Anticipated expiration: 2039-11-29
Also published as: CN111029301A

Abstract

The invention discloses a processing method of a silicon carbide-based wafer, which comprises the steps of firstly adopting first laser to irradiate the back metal layer of the wafer from the back of the wafer and move along a cutting track so as to cut off metal at the position corresponding to the cutting track, then adopting second laser to irradiate the inside of the wafer from the front of the wafer and move along the cutting track so as to form a modified layer inside the wafer, splitting the wafer according to the cutting track, dividing the wafer into a plurality of single core particles, and carrying out wafer expansion treatment on the wafer so as to separate the core particles from one another. The invention adopts a mode of increasing back laser cutting, ensures that the wafer is not influenced by back metal when being divided into single core particles, does not generate bicrystal, and improves the slicing efficiency and the yield. The method has the advantages of simple process, short time consumption, low cost, easy operation and control and suitability for practical production and application.

Description

Processing method of silicon carbide-based wafer

Technical Field

The invention relates to the technical field of semiconductor manufacturing, in particular to a processing method of a silicon carbide-based wafer.

Background

Traditional carborundum base wafer scribing mode includes diamond abrasive wheel cutting, but because abrasive wheel cutting is mechanical type, the blade has certain thickness, has certain consume to the material during the cutting, the demand broad cutting path. In order to achieve better performance in cutting on a narrow cutting channel, a laser invisible cutting technology is introduced, and the technology can effectively reduce the requirement on the width of the cutting channel to a certain extent.

In the existing laser invisible cutting technology, laser is used for modifying and processing the interior of a silicon carbide-based wafer which is finished with a device manufacturing process to form a modified layer, and then the silicon carbide-based wafer is split and expanded to be divided into a plurality of single chips. However, since the back metal of the wafer has strong ductility, the wafer part is separated into core grains after the wafer is split, and the back metal is not separated, which causes the problems of double crystals and the like, and affects the splitting efficiency and the yield. Therefore, a method for solving the problems that a cutting channel is formed on the metal on the back surface of the silicon carbide-based wafer through etching, but the method has complex steps, increases the difficulty of process control and material cost, is long in time consumption, and is easy to cause yield loss in midway and the like.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a method for processing a silicon carbide-based wafer.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

a processing method of a silicon carbide-based wafer, wherein the silicon carbide-based wafer is provided with a back metal layer, and the processing method comprises the following steps:

1) Determining a cutting track, and adopting first laser to enter the back metal layer from the back of the wafer and move along the cutting track so as to cut off the back metal at a position corresponding to the cutting track;

2) Adopting second laser to enter the wafer from the front side of the wafer and move along the cutting track so as to form a modified layer in the wafer;

3) Splitting the wafer according to the cutting track, and dividing the wafer into a plurality of single core particles;

4) And carrying out wafer expansion treatment on the wafer to separate the core particles from each other.

Preferably, the wavelength of the first laser light is 320nm to 400nm.

Preferably, the scanning speed of the first laser is 100mm/s to 2000mm/s.

Preferably, the wavelength of the second laser light is 780nm to 1100nm.

Preferably, the cutting track is a cutting track arranged on the front surface of the wafer.

Preferably, in step 1), a first protective film is attached to the front surface of the wafer, so that the wafer is made to have a good appearanceWith the front facing downwardsAdsorbed on a transparent platform, the transparent platform below is equipped with CCD, first laserAnd advancing along the cutting channel in a mode of aligning the cutting channel through a CCD (charge coupled device), and removing the first protection film after the cutting is finished.

Preferably, in the step 2), the wafer is turned over, a second protective film is attached to the back surface of the wafer, the back surface of the wafer is made to face downwards to be adsorbed on the transparent platform, and then the second laser is emitted into the wafer from the front surface of the wafer and travels along the cutting channel.

Preferably, step 1) further comprises the steps of coating splash-proof protection liquid on the surface of the back metal layer before cutting, and removing the splash-proof protection liquid after cutting.

Preferably, in the step 2), the incident depth of the second laser is changed, so that the second laser travels along the cutting track in a plurality of planes inside the wafer, and a plurality of modified layers are formed.

Preferably, in the step 3), the wafer is split from the back surface of the wafer by using a cleaver, and the pressing depth of the cleaver is 1/8-1/2 of the thickness of the wafer.

Preferably, the thickness of the back metal layer is 1 to 5 μm, and the power of the first laser is 1 to 5W.

The invention has the beneficial effects that:

the invention adoptsThe metal on the back of the silicon carbide-based wafer does not need to be additionally etched to form a cutting path, but the cutting path is formedThe mode of back laser cutting is increased, the back metal at the position corresponding to the cutting track is cut off by the first laser, and then the interior of the wafer is modified by the second laser, so that the wafer is not influenced by the back metal when being divided into single core particles, double crystals are not generated, and the slicing efficiency and the yield are improved. The method has the advantages of simple process, short time consumption, low cost, easy operation and control and suitability for practical production and application.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a schematic structural view (in cross-section) of a silicon carbide-based wafer;

FIG. 3 is a schematic structural view (top view) of a front surface of a wafer with a first protective film attached thereon;

FIG. 4 is a schematic structural view (in cross-section) of a backside metal layer cut using a first laser;

FIG. 5 is a schematic structural diagram of a wafer obtained by stealth dicing using a second laser (a cross-sectional view of a scribe line in one direction is shown, where metal on a back metal layer corresponding to the scribe line in the one direction is removed and a trench 111 is formed corresponding to the scribe line in the other direction);

FIG. 6 is a schematic view of the structure of the product obtained by the method of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. The drawings are only schematic and can be easily understood, and the specific proportion can be adjusted according to design requirements. The relative positions of elements in the figures described herein are understood by those skilled in the art to refer to relative positions of elements, and thus all elements may be reversed to represent the same, all falling within the scope of the disclosure. In addition, the number of the elements and the structure shown in the drawings is only an example, and the number is not limited thereto, and can be adjusted according to the design requirement.

The processing method is specifically described below with reference to the process flow of fig. 1. Referring to fig. 2, the sic wafer 1 has a front side a and a back side B, wherein the front side a at least partially completes fabrication of the functional region, and the back side B is provided with a back metal layer 11 for metal interconnection fabrication, etc.

1) First laser cuts back metal layer from back

Referring to fig. 3, a first protective film 2 is attached to the front surface a of the wafer 1, and the first protective film 2 is tightened by a hoop 3. The first protective film 2 is a thin film having a good light transmittance, for example, a UV film or a blue film. The shape of the hoop 3 is not limited, and may be, for example, circular or square, and the wafer 1 is preferably located in the central region of the hoop 3. The back surface B of the wafer 1 is coated with a splash-proof protective solution to prevent splash-out residues from contaminating the surface of the wafer during cutting, and the splash-proof protective solution may be, for example, monopropylene glycol methyl ether. Referring to fig. 4, the wafer 1 is placed on a transparent platform of a laser cutting machine with the back side B facing upward, the transparent platform is provided with a vacuum adsorption device (not shown) to adsorb the wafer 1, and a CCD 4 is disposed below the transparent platform. The first laser 5 is used to enter the back metal layer 11 from the back side B of the wafer 1 and travel along the dicing track to cut off the back metal at the position corresponding to the dicing track. In this embodiment, the dicing track is a dicing street 12 provided in advance on the front surface of the wafer 1, and in other embodiments, the dicing track may be a virtual track. The cutting means that the metal corresponding to the position of the cutting street 12 is melted and gasified by the laser, and is substantially removed, and referring to fig. 5, a groove 111 facing the cutting street 12 is formed. For example, the scribe lines 12 are grid lines arranged in the X direction and the Y direction perpendicular to each other, the formed core grains have a square structure, and the back metal layer 11 is cut into independent squares corresponding to the grid lines by cutting the back metal at positions corresponding to the scribe lines 12. In addition, the cutting lines 12 may be arranged in other ways according to the shape and structure of the core particles. Specifically, the first laser 5 and the CCD 4 are located on the same axis, and the first laser 5 advances along the scribe line 12 by means of aligning the CCD with the scribe line 12, and cuts off the metal at the position of the back metal layer 11 corresponding to the scribe line 12. The wavelength of the first laser 5 is 320 nm-400 nm, the scanning speed is 100 mm/s-2000 mm/s, and the cutting depth is equal to or exceeds the thickness of the back metal layer 11. The power of the first laser 5 can be adjusted according to the thickness of the back metal layer 11, for example, the thickness of the back metal layer 11 is 1 to 5 μm, and the power of the first laser is 1 to 5W. And after the cutting is finished, cleaning and removing the anti-splash protection liquid.

2) Turning film

The wafer 1 is turned upside down, the first protective film 2 on the front side is removed, and the second protective film 6 is attached to the back side of the wafer 1. In the case where the first protective film 2 is a UV film, UV light irradiation is required before the film is peeled. The film turning can be automatically turned by using machine equipment, the front-side film pasting is turned into the back-side film pasting, and the film turning can be carried out by using an industrial jig or manually without limitation. The second protective film 6 is made of a material and has a mounting structure similar to that of the first protective film 2.

3) Second laser recessively cuts the wafer from the front side

Referring to fig. 5, the back surface of the wafer 1 is downward and attached to the transparent platform, and the second laser 7 is incident into the wafer from the front surface a of the wafer and travels along the scribe lines to perform recessive cutting, so as to form a modified layer 13 inside the wafer, and generate microcracks near the modified layer 13. By changing the incident depth of the second laser 7, the second laser respectively travels along the scribe lines in a plurality of planes perpendicular to the thickness direction inside the wafer 1 to form a plurality of modified layers 13, and the multilayer cutting can improve the cutting quality. The wavelength of the second laser is 780 nm-1100 nm, and the power is 0.1-3W.

4) Splinting

The wafer 1 is placed on a receiving table, a cleaver is used for cleaving the wafer 1 from the back side along a cutting track, the pressing depth of the cleaver is 1/8-1/2 of the thickness of the wafer 1, the wafer 1 is separated along the hidden-cutting crack under the opposite action force of the receiving table and the cleaver, and the wafer 1 can be divided into a plurality of single core particles because the part of the back metal layer 11 corresponding to the cutting track is cut off and is not influenced by metal after being split.

5) Crystal expansion

And placing the wafer after the splitting on a wafer expanding machine for expanding, and enabling the second protective film to extend outwards under stress, so that the core particles are separated from each other.

As a specific example, the thickness of the wafer part of a silicon carbide-based wafer is 350 μm; the back metal layer is 2 μm thick and made of Ti/Ni/Ag. And (3) cutting the metal layer on the back by adopting ultraviolet light with the wavelength of 355nm, wherein the scanning speed is 1000mm/s, and the laser power is 1-2W, so that the metal at the position corresponding to the cutting track can be completely cut off. And performing front surface wafer recessing cutting by adopting laser with the wavelength of 1064nm, and cutting 6 layers, wherein the laser power is 0.2-1W. When the splitting is carried out, the depth of the cleaver is pressed down by about 60 mu m, and after the crystal is expanded, referring to a figure 6, core grains are thoroughly separated, the phenomenon of double crystals is effectively avoided, and the splitting efficiency and the splitting yield are improved.

The above embodiments are merely provided to further illustrate the method for processing a silicon carbide-based wafer according to the present invention, but the present invention is not limited to the embodiments, and any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention fall within the scope of the technical solution of the present invention.

Claims

1. A processing method of a silicon carbide-based wafer, wherein the silicon carbide-based wafer is provided with a back metal layer, it is characterized in that the processing method comprises the following steps:

1) There is a dicing line on the front of the wafer, and the first protective film is attached to the front of the wafer, so that the wafer is adsorbed on a transparent platform with the front facing down. A CCD is installed under the transparent platform, and the first laser is used to The back side of the wafer is incident on the back metal layer and travels along the dicing road through the CCD alignment dicing road to cut off the back metal at the position corresponding to the dicing road, and remove the first protective film after the cutting is completed. film; the wavelength of the first laser is 320nm~400nm; the thickness of the metal layer on the back is 1~5 µm, and the power of the first laser is 1~5W;

2) using a second laser to enter the wafer from the front of the wafer and travel along the dicing line to form a modified layer inside the wafer; the wavelength of the second laser is 780nm~1100nm;

3) Using a hacking knife to split the wafer from the back of the wafer according to the dicing line, the pressing depth of the hacking knife is 1/8~1/2 of the thickness of the wafer, and the wafer is divided into several Single core particle;

4) Expanding the wafer to separate the core particles from each other.

2. The processing method according to claim 1, characterized in that: the scanning speed of the first laser is 100mm/s~2000mm/s.

3. The processing method according to claim 1, characterized in that: in step 2), further comprising turning over the wafer, attaching a second protective film to the back of the wafer so that the back of the wafer faces downward adsorbed on the transparent platform, and then adopt the second laser to enter the inside of the wafer from the front of the wafer and travel along the dicing line.

4. The processing method according to claim 1, characterized in that: in step 1), it also includes coating the splash protection liquid on the surface of the back metal layer before cutting and removing the splash protection liquid after cutting step.

5. The processing method according to claim 1, characterized in that: in step 2), it also includes changing the incident depth of the second laser so that the second laser is in multiple planes inside the wafer and a step of forming a plurality of modified layers along the cutting lane.