Power semiconductor chip cutting protection liquid and preparation method and application thereof

Abstract

The invention relates to a water-based cutting protection liquid for laser cutting of a power semiconductor chip, a preparation method and application of the water-based cutting protection liquid, and a laser cutting protection method for the power semiconductor chip by using the water-based cutting protection liquid. The water-based cutting protection liquid comprises 10-30 parts of a main polymer, 1-5 parts of an improving agent, 0.1-10 parts of a light absorbing agent, 30-70 parts of a hydrophilic solvent and 30-50 parts of ultrapure water, and through selection and use of a plurality of specific components, the water-based cutting protection liquid has excellent film forming performance, laser cutting protection performance and easy-to-clean performance; the method has good application value in the field of power semiconductor chip processing and packaging.

Description

Technical Field

[0001] The present invention relates to a composition used in semiconductor processing, a preparation method, its use and a chip laser cutting protection method using the same, and more specifically to a chip laser cutting protection liquid capable of preventing metal slag and silicon vapor contamination, a preparation method, application and a semiconductor power chip laser cutting protection method using the same, and other technical solutions, belonging to the field of semiconductor processing technology. Background Art

[0002] Power semiconductor devices, also known as power electronic devices, are the core devices for power electronic devices to achieve power conversion and circuit control. The main functions of power semiconductor devices include frequency conversion, rectification, voltage conversion, power amplification and power control, energy saving, etc. For example, vertical double diffused metal oxide semiconductor field effect transistors (VDMOS) and fast recovery diodes (FRD) are widely used in power electronic systems such as switching power supplies and motor drives.

[0003] In order to reduce the conduction loss of this type of chip, the parasitic resistance on the back of the chip needs to be as small as possible. To achieve this goal, in the later stage of the chip manufacturing process, the wafer is thinned from the back and a metal layer is deposited on the back. The currently commonly used back metal layer structure is usually a titanium / nickel / silver combination. The back metal layer plays the role of adhering to the silicon layer, blocking diffusion and conducting electricity.

[0004] The last step in the chip manufacturing process is to cut the wafer into individual chips, which is usually done by using a knife wheel to cut and separate them. If a wafer with a metal layer deposited on the back is diced using a conventional knife wheel, it will cause problems such as chip edge collapse and electrical degradation on the back of the chip. In addition, as the power demand of today's power systems is getting higher and higher, the thickness of the metal layer on the back of the chip has a trend of gradually thickening. The method of using a single knife wheel to scribing is gradually no longer suitable for wafer cutting. In order to overcome this defect, the combination of knife wheel cutting and laser cutting of metal layers is becoming more and more important. The process of this combined cutting is as follows: First, use a knife wheel to scribing the upper silicon layer to form a groove (usually 28-60μm wide and 10-100μm deep) on the cutting path. Figure 1As shown). Laser cutting is then performed along the groove to cut the bottom metal layer (i.e., the back metal layer), and finally form independent chips. Although this process is becoming more and more mainstream, it still has some defects: during the laser cutting process, the heated vaporized silicon vapor and molten metal will splash upward and adhere to the side walls and surface of the chip, which will cause the subsequent patch to be weak and then cause electrical abnormalities. Although there are some protective liquids that are simply used for conventional laser grooving processes, they are mainly used to protect the surface of wafers with small differences in plane or concave-convex structures, and cannot quickly penetrate into cutting grooves with high aspect ratios to form an effective protective film, which means that they are not suitable for the processing of power semiconductors at all.

[0005] Therefore, it is necessary to develop a laser cutting protective liquid for the combined cutting process of wheel cutting and laser cutting in the power semiconductor processing process, so as to prevent the silicon vapor and molten metal generated by the cutting from adhering to the side walls and front of the chip, which is one of the difficulties in the current type of chip cutting. This has very important industrial significance for improving cutting efficiency, reducing production costs, and improving product yield. Summary of the invention

[0006] In order to prevent silicon vapor and silicon slag generated during laser cutting of power semiconductor chips with a back metal layer from adhering to the side walls of the cutting grooves, and conventional protective liquids from being difficult to effectively protect and difficult to clean and remove thoroughly, the inventors conducted in-depth exploration and research, thereby completing the present invention and successfully solving the above-mentioned many defects.

[0007] More specifically, the present invention aims to provide a water-based cutting protection liquid for laser cutting of power semiconductor chips and its related technical solutions (including its preparation method, cutting protection method using it, cutting protection use, etc.), wherein the cutting protection liquid can form a fully covered and uniform water-soluble protective film during the laser cutting process, thereby isolating silicon slag and molten metal from adhering to the sidewall surface of the cutting groove, and is easy to clean and cleans thoroughly. With these remarkable excellent effects, the processing qualification rate of precision semiconductor components can be significantly improved, the processing efficiency can be greatly improved, and the production cost can be greatly reduced.

[0008] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising" and similar meanings, and closed-ended "consisting of..." and similar meanings.

[0009] The present invention mainly relates to the following specific technical solutions.

[0010] [The first technical solution]

[0011] The first technical solution, an object of the present invention is to provide a water-based cutting protection liquid for laser cutting of power semiconductor chips (hereinafter sometimes also referred to as "water-based cutting protection liquid" or "cutting protection liquid" or "protective liquid" or "chip cutting protection liquid" or "water-based protective liquid", all of which have the same meaning).

[0012] The water-based cutting protection liquid comprises a main polymer, an improving agent, a light absorber, a hydrophilic solvent and ultrapure water.

[0013] More specifically, the water-based cutting protection liquid comprises the following components in parts by mass:

[0014]

[0015] In the water-based cutting protection liquid of the present invention, the mass fraction of the main polymer is 10-30 parts, for example, 15-25 parts, and more for example, 10 parts, 15 parts, 20 parts, 25 parts or 30 parts.

[0016] Among them, the main polymer is preferably a copolymer having both an ester group and a carbonyl group, such as a vinyl acetate-ethylene copolymer or a vinyl acetate-vinyl pyrrolidone copolymer; the most preferred is a vinyl acetate-vinyl pyrrolidone copolymer having both an ester group, a carbonyl group and a pyrrolidone group.

[0017] More preferably, the vinyl acetate-vinyl pyrrolidone copolymer is a copolymer of vinyl acetate and vinyl pyrrolidone in a molar ratio of 1:0.5-2.5. The copolymers in different molar ratios are well-known copolymers, and various specifications of polymers in different molar ratios of vinyl acetate and vinyl pyrrolidone can be purchased through various commercial channels, which will not be described in detail here.

[0018] In the water-based cutting protection fluid of the present invention, the mass fraction of the improving agent is 1-5 parts, for example, 2-4 parts, and more for example, 1 part, 2 parts, 3 parts, 4 parts or 5 parts.

[0019] Wherein, the improving agent is sodium p-styrene sulfonate.

[0020] In the water-based cutting protection liquid of the present invention, the mass fraction of the light absorber is 0.1-10 parts, for example, it can be 0.1 parts, 0.2 parts, 0.5 parts, 1 parts, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts.

[0021] The light absorber includes any one or a mixture of any two or more of benzophenone compounds, benzophenone sulfonic acid compounds and salts thereof, salicylate compounds, benzotriazole compounds, triazine compounds and cinnamic acid compounds.

[0022] Furthermore, the light absorber may be, for example, any one of methyl salicylate, benzotriazole, 2-hydroxy-4-methoxy-5-sulfonic acid benzophenone or its sodium salt, or a mixture of any two or more thereof.

[0023] In the water-based cutting protection liquid of the present invention, the mass fraction of the hydrophilic solvent is 30-70 parts, for example, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts or 70 parts.

[0024] Wherein, the hydrophilic solvent is C 1-8 Alcohol compounds, alcohol ether compounds or C 1-8 The mixture of alcohol compounds and alcohol ether compounds can be, for example, any one of ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethanol, methanol, n-propanol, n-butanol, n-pentanol, n-hexanol, etc., or a mixture of any one of the alcohol ether compounds and any one of the alcohol compounds.

[0025] Most preferably, the hydrophilic solvent is a mixture of propylene glycol monomethyl ether and ethanol, wherein the molar ratio of propylene glycol monomethyl ether to ethanol is 3:0.5-1, for example, 3:0.5, 3:0.6, 3:0.7, 3:0.8, 3:0.9 or 3:1.

[0026] In the water-based cutting protection liquid of the present invention, the mass fraction of the ultrapure water is 30-50 parts, for example, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts.

[0027] Wherein, the ultrapure water is deionized water with a resistance ≥ 18 MΩ.

[0028] As described above, the present invention provides a water-based cutting protection liquid for laser cutting of power semiconductor chips. The inventors have found that in the water-based cutting protection liquid of the present invention, by selecting a specific main polymer, a specific improver and a specific hydrophilic additive, the best technical effect can be achieved (see the subsequent performance test section for details), such as excellent film-forming performance, cutting protection performance, easy cleaning performance and many other advantages, which overcomes the many defects existing in the cutting process of power semiconductors in the current prior art, can significantly improve and increase the processing qualification rate and yield rate of power semiconductor chips, and solves the above-mentioned technical defects.

[0029] [Second technical solution]

[0030] The second technical solution, an object of the present invention is to provide a method for preparing the above-mentioned water-based cutting protection liquid.

[0031] The preparation method comprises the following steps:

[0032] Step 1: Weigh the required mass of each component;

[0033] Step 2: adding the main polymer to the hydrophilic solvent, controlling the stirring rate between 100-500 rpm and the temperature between 30-60° C., until the main polymer is completely dissolved, which is recorded as liquid A;

[0034] Step 3: Add the improving agent to the ultrapure water, control the stirring rate between 200-500 rpm, and control the temperature between 20-30° C., and stir and mix thoroughly until the mixture is uniform and transparent, which is recorded as liquid B;

[0035] Step 4: Add the light absorber to the liquid B, and continue stirring and mixing until uniform, which is recorded as liquid C;

[0036] Step 5: Add the liquid C into the liquid A, control the stirring rate between 250-500 rpm, and control the temperature between 20-30° C. until the materials are evenly mixed, thereby obtaining the water-based cutting protection liquid.

[0037] In the preparation method of the present invention, the stirring speed in step 2 is 100-500rpm, and further for example, 100rpm, 200rpm, 300rpm, 400rpm or 500rpm. Those skilled in the art can make appropriate selections and determinations, which will not be described in detail here.

[0038] In the preparation method of the present invention, the stirring temperature in step 2 is 30-60°C, for example, 30°C, 40°C, 50°C or 60°C.

[0039] In the preparation method of the present invention, the stirring speed in step 3 is 200-500rpm, and further for example, 200rpm, 300rpm, 400rpm or 500rpm. Those skilled in the art can make appropriate selections and determinations, which will not be described in detail here.

[0040] In the preparation method of the present invention, the stirring temperature in step 3 is 20-30°C, for example, 20°C, 25°C or 30°C.

[0041] In the preparation method of the present invention, the stirring speed in step 4 is 200-500 rpm, and further for example, 200 rpm, 300 rpm, 400 rpm or 500 rpm. Those skilled in the art can make appropriate selections and determinations, which will not be described in detail here.

[0042] In the preparation method of the present invention, the stirring temperature in step 4 is 20-30°C, for example, 20°C, 25°C or 30°C.

[0043] In the preparation method of the present invention, the stirring speed in step 5 is 250-500rpm, and further for example, is 250rpm, 300rpm, 350rpm, 400rpm, 450rpm or 500rpm. Those skilled in the art can make appropriate selections and determinations, which will not be described in detail here.

[0044] In the preparation method of the present invention, the stirring temperature in step 5 is 20-30°C, for example, 20°C, 25°C or 30°C.

[0045] [The third technical solution]

[0046] The third technical solution, an object of the present invention is to provide the use of the above-mentioned cutting protection liquid in laser cutting protection of power semiconductor chips.

[0047] As described above, the water-based cutting protection liquid of the present invention can achieve the best technical effect (details can be seen in the subsequent performance test section) by selecting a specific main polymer, a specific improver and a specific hydrophilic solvent, such as excellent film-forming performance, cutting protection performance, easy cleaning performance and many other advantages. It overcomes the many defects existing in the cutting process of power semiconductors in the current prior art, can significantly improve and increase the processing qualification rate and yield rate of power semiconductor chips, and solves the above-mentioned technical defects.

[0048] [The fourth technical solution]

[0049] A fourth technical solution, an object of the present invention is to provide a power semiconductor chip laser cutting protection method using the above-mentioned water-based cutting protection liquid, the cutting protection method comprising the following steps:

[0050] Step A: firstly perform cutting with a knife wheel on the wafer to obtain a pre-cut wafer with grooves formed therein;

[0051] Step B: cleaning the pre-cut wafer with ultrapure water to remove dust particles on the surface, thereby obtaining a pre-cleaned wafer;

[0052] Step C: When the wafer is rotating at a low speed, ultrapure water is sprayed onto the surface of the wafer, thereby forming a uniform water film on the surface of the wafer;

[0053] Step D: uniformly dripping the water-based cutting protection liquid from the center to the periphery of the wafer while the wafer is rotating at a low speed, and spin coating to form a complete protection liquid film;

[0054] Step E: After the dropwise addition is completed, the water-based cutting protection liquid is dried to form a film;

[0055] Step F: Perform laser cutting to cut the back metal layer to form a single chip;

[0056] Step G: The protective film is removed by washing with deionized water to obtain a single chip, thereby completing the cutting protection process.

[0057] In the cutting protection method of the present invention, the wafer in step A can be, for example, an 8-12 inch wafer. For a semiconductor power chip, the width of the groove formed by cutting is usually 28-60 μm, the depth can be 10-100 μm, the aspect ratio can be, for example, 1:0.2-4, and the depth is usually 2-5 times the width. The overall shape can be seen, for example, in the attached Figure 1 .

[0058] In the cutting protection method of the present invention, in step B, the ultrapure water is deionized water with a resistance ≥ 18MΩ, and the cleaning time is not strictly limited, as long as the dust particles on the surface of the wafer can be completely cleaned, for example, it can be 1-3 minutes, and more preferably 1 minute, 2 minutes or 3 minutes. Those skilled in the art can make appropriate selections and determinations based on actual conditions, and will not be described in detail here.

[0059] In the cutting protection method of the present invention, in step C, the ultrapure water is deionized water with a resistance ≥ 18 MΩ.

[0060] In the cutting protection method of the present invention, in step C, the water spraying time is 1-2 minutes, for example, 1 minute, 1.5 minutes or 2 minutes; the amount of water sprayed is not strictly limited, as long as a uniform water film can be formed on the wafer surface (of course, including the groove surface formed by cutting, the same below), and its thickness can generally be 20-150μm, for example, 40-130μm, 60-110μm or 70-90μm. Those skilled in the art can make appropriate determinations based on actual conditions (such as wafer size, rotation speed, etc.), and will not be described in detail here.

[0061] In the cutting protection method of the present invention, in step C, the low-speed rotation speed of the wafer is 10-100rpm, for example, it can be 10rpm, 20rpm, 30rpm, 40rpm, 50rpm, 60rpm, 70rpm, 80rpm, 90rpm or 100rpm. A uniform water film can be formed by low-speed rotation and the formed water film can be prevented from rupturing.

[0062] In the cutting protection method of the present invention, in step D, the time of the low-speed rotation is not strictly limited, for example, it can be 30-90s, for example, 30s, 40s, 50s, 60s, 70s, 80s or 90s.

[0063] In the cutting protection method of the present invention, in step D, the rotation speed of the low-speed rotation is not strictly limited, as long as a complete protective liquid film can be formed, for example, it can be 30-70rpm, and further for example, it can be 30rpm, 40rpm, 50rpm, 60rpm or 70rpm. Those skilled in the art can make appropriate selections and determinations according to actual conditions, and will not be described in detail here.

[0064] In the cutting protection method of the present invention, in step D, an appropriate amount of water-based cutting protection liquid can be added according to the size of the wafer. This is a conventional choice in the field of chip processing. For example, relative to a 12-inch wafer, 30-80 ml of water-based cutting protection liquid can be added, for example, 30 ml, 40 ml, 50 ml, 55 ml, 60 ml, 70 ml or 80 ml.

[0065] In the cutting protection method of the present invention, the drying film forming and laser cutting of steps EF are both well-known operating methods, and those skilled in the art can make appropriate selections and determinations according to actual conditions. For example, the laser cutting power of step F is 0.5-10W, and further examples include 0.5W, 1W, 2W, 5W, 6W, 7W or 10W. The specific operations will not be described in detail here.

[0066] In the cutting protection method of the present invention, in step G, the deionized water is preferably deionized water with a resistance ≥ 18 MΩ.

[0067] As described above, the present invention provides a protective liquid for laser cutting of a power semiconductor chip, a preparation method and use thereof, and a power semiconductor chip laser cutting protection method using the same. The water-based cutting protective liquid for a power semiconductor chip has the following advantages:

[0068] 1. The composition of the protective liquid is novel in the field of power semiconductor chip processing. The protective liquid uses ultrapure water as a medium, and utilizes the compatibility of a specific hydrophilic solvent with water and the permeability of the overall composition in a cutting groove with a large aspect ratio, so that when the groove width is narrow and the groove depth is deep, it can penetrate to the bottom of the groove and simultaneously form a protective film layer on the side wall of the chip (see attached Figure 2 Schematic diagram of forming a protective film layer).

[0069] 2. The protective liquid increases its adhesion by using a copolymer containing ester groups, carbonyl groups and pyrrolidine groups with high adhesion, so that it can penetrate downward on the side walls and surface of the chip under a groove structure with a high aspect ratio and form an effective protective barrier film to isolate the metal slag and silicon vapor generated by laser cutting from adhering.

[0070] 3. By using sodium p-styrene sulfonate as an improving agent, the cleaning performance after laser cutting can be significantly improved. The silicon slag and various dirt formed during the laser cutting process can be completely removed, and it has excellent cleanability.

[0071] 4. By forming a water film before film formation, the final cleaning and removal effect can be significantly improved, simplifying and shortening the process flow, which is of great significance in the field of semiconductor technology. In addition, there is no need for subsequent more complicated organic solvent cleaning, which can significantly improve production efficiency, reduce process costs, increase product yield, and significantly reduce the generation of waste liquid.

[0072] Therefore, the water-based cutting protection liquid of the present invention has very good application prospects and large-scale industrial promotion potential in the field of laser cutting protection of power semiconductor chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Attached Figure 1 This is a schematic diagram of the structure of a wafer with a back metal layer after being cut by a knife wheel and before being cut by laser.

[0074] Attached Figure 2 It is a schematic diagram of forming a protective film after the cutter wheel cutting and before the laser cutting of the back metal layer wafer using the water-based cutting protection liquid of the present invention.

[0075] Attached Figure 3 This is a microscope image magnified 200 times of the side wall of the wafer trench after the water-based cutting protection liquid S1 of Example 1 was dried and formed into a film.

[0076] Attached Figure 4 This is a microscope image magnified 200 times of the side wall of the wafer groove after the water-based cutting protection liquid D1 of Comparative Example 1 was dried and formed into a film.

[0077] Attached Figure 5 This is a microscope image magnified 200 times of the side wall of the wafer groove after the water-based cutting protection liquid D15 of Comparative Example 15 was dried and formed into a film.

[0078] Attached Figure 6 This is a microscope image magnified 200 times of the side wall of the wafer groove after the water-based cutting protection liquid D17 of Comparative Example 17 was dried and formed into a film.

[0079] Attached Figure 7 This is a microscope image of the original groove side wall magnified 200 times using the water-based cutting protection liquid S1 of Example 1 for film protection and after laser cutting.

[0080] Attached Figure 8 This is a microscope image magnified 200 times of the original groove side wall after laser cutting using the water-based cutting protection liquid D1 of comparative example 1 for film protection.

[0081] Attached Fig. 9This is a microscope image of the original groove side wall magnified 200 times using the water-based cutting protection liquid D4 of comparative example 4 for film protection and laser cutting.

[0082] Attached Fig.10 This is a microscope image magnified 200 times of the original groove side wall after laser cutting using the water-based cutting protection liquid D15 of comparative example 15 for film protection.

[0083] Attached Fig.11 This is a microscope image of the original groove sidewall after laser cutting, magnified 200 times, using the water-based cutting protection liquid S1 of Example 1, omitting the film forming protection in step C. DETAILED DESCRIPTION

[0084] The present invention is described in detail below through specific examples, but the use and purpose of these exemplary implementation modes are only used to illustrate the present invention, and do not constitute any form of limitation on the actual protection scope of the present invention, nor limit the protection scope of the present invention to them.

[0085] Unless otherwise specified, the ultrapure water involved in any step used in the following preparation examples, embodiments and / or performance tests is deionized water with a resistance ≥ 18 MΩ, so it is not listed one by one.

[0086] Among them, each component used below can be purchased through commercial channels and will not be described in detail here.

[0087] Example 1: Preparation of water-based cutting protection fluid

[0088] Step 1: Weigh 20 parts by weight of a main polymer vinyl acetate-vinyl pyrrolidone copolymer (a copolymer of vinyl acetate and vinyl pyrrolidone in a molar ratio of 1:1.5), 3 parts by weight of an improver sodium p-styrene sulfonate, 5 parts by weight of a light absorber 2-hydroxy-4-methoxy-5-sulfonic acid dibenzophenone, 50 parts by weight of a hydrophilic solvent mixture of propylene glycol monomethyl ether and ethanol (wherein the molar ratio of propylene glycol monomethyl ether to ethanol is 3:0.75), and 40 parts by weight of ultrapure water;

[0089] Step 2: adding the main polymer to the hydrophilic solvent, controlling the stirring rate to 300 rpm and the temperature to 45° C., until the main polymer is completely dissolved, which is recorded as liquid A;

[0090] Step 3: Add the improving agent into the ultrapure water, control the stirring rate to 350 rpm, and control the temperature to 25° C., and stir and mix thoroughly until the mixture is uniform and transparent, which is recorded as liquid B;

[0091] Step 4: Add the light absorber to the liquid B, continue stirring and mixing until uniform, the stirring rate is 350 rpm, and the temperature is controlled at 25° C., recorded as liquid C;

[0092] Step 5: Add the liquid C into the liquid A, control the stirring rate to 350 rpm, and control the temperature to 25° C. until the materials are evenly mixed, thereby obtaining a water-based cutting protection liquid, which is named S1.

[0093] Example 2: Preparation of water-based cutting protection fluid

[0094] Step 1: Weigh 30 parts by weight of a main polymer vinyl acetate-vinyl pyrrolidone copolymer (a copolymer of vinyl acetate and vinyl pyrrolidone in a molar ratio of 1:0.5), 1 part by weight of an improver sodium p-styrene sulfonate, 10 parts by weight of a light absorber benzotriazole, 30 parts by weight of a hydrophilic solvent mixture of propylene glycol monomethyl ether and ethanol (wherein the molar ratio of propylene glycol monomethyl ether to ethanol is 3:1), and 50 parts by weight of ultrapure water;

[0095] Step 2: adding the main polymer to the hydrophilic solvent, controlling the stirring rate to 500 rpm and the temperature to 30° C., until the main polymer is completely dissolved, which is recorded as liquid A;

[0096] Step 3: Add the improving agent into the ultrapure water, control the stirring rate to 200 rpm, and control the temperature to 30° C., and stir and mix thoroughly until the mixture is uniform and transparent, which is recorded as liquid B;

[0097] Step 4: Add the light absorber to the liquid B, continue stirring and mixing until uniform, the stirring rate is 200 rpm, and the temperature is controlled at 30° C., which is recorded as liquid C;

[0098] Step 5: Add the liquid C into the liquid A, control the stirring rate to 500 rpm, and control the temperature to 30° C. until the materials are evenly mixed to obtain a water-based cutting protection liquid, which is named S2.

[0099] Example 3: Preparation of water-based cutting protection fluid

[0100] Step 1: Weigh 10 parts by mass of a main polymer vinyl acetate-vinyl pyrrolidone copolymer (a copolymer of vinyl acetate and vinyl pyrrolidone in a molar ratio of 1:2.5), 5 parts by mass of an improver sodium p-styrene sulfonate, 0.1 parts by mass of a light absorber methyl salicylate, 70 parts by mass of a hydrophilic solvent mixture of propylene glycol monomethyl ether and ethanol (wherein the molar ratio of propylene glycol monomethyl ether to ethanol is 3:0.5), and 30 parts by mass of ultrapure water;

[0101] Step 2: adding the main polymer to the hydrophilic solvent, controlling the stirring rate to 100 rpm and the temperature to 60° C., until the main polymer is completely dissolved, which is recorded as liquid A;

[0102] Step 3: Add the improving agent into the ultrapure water, control the stirring rate to 500 rpm, and control the temperature to 20° C., and stir and mix thoroughly until the mixture becomes uniform and transparent, which is recorded as liquid B;

[0103] Step 4: Add the light absorber to the liquid B, continue stirring and mixing until uniform, the stirring rate is 500 rpm, and the temperature is controlled at 20° C., recorded as liquid C;

[0104] Step 5: Add the liquid C into the liquid A, control the stirring rate to 250 rpm, and control the temperature to 20° C. until the materials are evenly mixed to obtain a water-based cutting protection liquid, which is named S3.

[0105] Comparative Example 1-3: Preparation of water-based cutting protection liquid

[0106] Except that the main polymers in Examples 1-3 were replaced by vinyl acetate-vinyl pyrrolidone with vinyl acetate-ethylene copolymers polymerized in equal parts by mass and at the same molar ratio, other operations remained unchanged, and the obtained water-based cutting protection liquids were named D1, D2 and D3 in sequence.

[0107] Comparative Examples 4-6: Preparation of water-based cutting protection fluid

[0108] Except for deleting the improving agent sodium p-styrene sulfonate in Examples 1-3, other operations remained unchanged, and the obtained water-based cutting protection liquids were named D4, D5 and D6 in sequence.

[0109] Comparative Example 7-21: Preparation of water-based cutting protection liquid

[0110] Comparative Examples 7-16: Except that the hydrophilic solvents in Examples 1-3 are replaced by the same mass parts of ethylene glycol (Example 1), propylene glycol (Example 2), ethylene glycol monomethyl ether (Example 3), methanol (Example 1), n-propanol (Example 2), n-butanol (Example 3), n-pentanol (Example 1), n-hexanol (Example 2), propylene glycol monomethyl ether (Example 3) and ethanol (Example 1), respectively, other operations remain unchanged, and the obtained water-based cutting protection liquids are named D7-D16 in sequence.

[0111] Among them, the corresponding replaced embodiments are in brackets, for example, "ethylene glycol (Example 1)" means that the hydrophilic solvent in Example 1 is replaced by ethylene glycol of the same mass, and other brackets have such corresponding meanings, so they are not listed in detail one by one.

[0112] Comparative Examples 17-21: Except for replacing the hydrophilic solvents in Examples 1-3 with two-component solvents of the same mass and the same molar ratio as "propylene glycol monomethyl ether + methanol" (Example 1), "propylene glycol monomethyl ether + n-propanol" (Example 2), "ethylene glycol monomethyl ether + methanol" (Example 3), "ethylene glycol monomethyl ether + ethanol" (Example 1), and "ethylene glycol monomethyl ether + n-propanol" (Example 2), other operations remain unchanged, and the obtained water-based cutting protection liquids are named D17-D21 in sequence.

[0113] The corresponding meanings of the brackets are as described above, so they will not be listed in detail one by one.

[0114] After obtaining the above-mentioned multiple water-based cutting protection liquids, the following performance tests were respectively carried out, as shown in detail below.

[0115] Film forming performance test

[0116] After the above-mentioned water-based cutting protection liquids are prepared, a film forming test of laser cutting protection of power semiconductor chips is performed. The specific operation and steps are as follows (i.e., steps AE of the cutting protection method in the above-mentioned [fourth technical solution]):

[0117] Step A: Firstly, the 12-inch wafer is cut by a cutter wheel to obtain a pre-cut wafer with grooves formed therein;

[0118] Step B: Cleaning the pre-cut wafer with ultrapure water for 2 minutes to fully remove dust particles on the surface to obtain a pre-cleaned wafer;

[0119] Step C: When the wafer is rotating at a low speed (rotation speed is 50 rpm), ultrapure water is sprayed on the surface of the wafer for 90 seconds, thereby forming a uniform water film on the surface of the wafer, and the amount of water sprayed is controlled so that the thickness of the obtained water film is between 70-90 μm;

[0120] Step D: When the wafer is rotating at a low speed (rotation speed is 50 rpm), a water-based cutting protection liquid is dripped from the center to the periphery, with a total amount of 55 ml, and the spin coating is performed for 60 seconds, thereby forming a complete protection liquid film;

[0121] Step E: After the dropwise addition is completed, the water-based cutting protection liquid is dried to form a film.

[0122] Through the operation and processing of the above steps AE, protective films of various water-based cutting protection liquids are formed on the surface of the front side of the wafer and the side walls of the cut grooves. Among them, it is very easy to form a protective film with comprehensive coverage and uniform thickness on the front surface of the wafer. The protection of the groove side walls is examined below.

[0123] After the above steps AE are implemented, the film-forming protection performance of each water-based cutting protection liquid on the groove sidewall is shown in the following figures, specifically as follows:

[0124] 1. Attachment Figure 3 This is a microscope image magnified 200 times of the side wall of the wafer trench after the water-based cutting protection liquid S1 of Example 1 was dried and formed into a film.

[0125] Among them, the longitudinal groove on the left side (the bottom of which is the back metal layer) is the intersection of the transverse cutting groove of the transverse side wall extending left and right and the longitudinal cutting groove extending front and back (that is, the intersection of two mutually perpendicular cutting grooves). The same position reference meaning is used in the following multiple drawings, so it will not be described one by one.

[0126] It can be seen that the groove sidewalls of the pre-cut wafer are fully covered with a protective film layer with uniform thickness, which is flat and smooth as a whole and has an excellent protective effect on the groove sidewalls.

[0127] The microscope image of the side wall of the wafer groove after drying and film formation using the water-based cutting protection liquids S2-S3 and D4-D6 of Examples 2-3 and Comparative Examples 4-6 is exactly the same as the attached image. Figure 3 Similarly, a protective film layer with full coverage and uniform thickness is formed on the groove sidewalls of the pre-cut wafer, which is flat and smooth as a whole and has an excellent protective effect on the groove sidewalls, so they are no longer listed one by one.

[0128] 2. Attachment Figure 4 This is a microscope image magnified 200 times of the side wall of the wafer groove after the water-based cutting protection liquid D1 of Comparative Example 1 was dried and formed into a film.

[0129] It can be seen that a large area of ​​the protective film layer is missing on the sidewall of the groove of the pre-cut wafer (as shown in the three white ovals), and the white substrate surface is exposed.

[0130] The microscopic image of the side wall of the wafer groove after drying and film formation using the water-based cutting protection liquid D2-D3 of Comparative Examples 2-3 is highly similar to the attached Figure 4 Similarly, a large area of ​​the protective film layer is missing on the groove sidewalls of the pre-cut wafer, exposing the substrate surface, so they are not listed one by one.

[0131] The inventors believe that this is because when vinyl acetate-vinyl pyrrolidone copolymer is used as the main polymer, it has both ester and carbonyl groups, which can provide good adhesion, and the presence of pyrrolidone can maintain its good water solubility and film-forming properties, thereby forming a uniform and completely covered protective film layer with a smooth surface. When the vinyl acetate-vinyl pyrrolidone copolymer is replaced with a similar vinyl acetate-ethylene copolymer, although the ester and carbonyl groups are still present at the same time, the absence of pyrrolidone causes a significant decrease in its water solubility and film-forming properties, resulting in a large area of ​​exposed substrate, which affects the smooth progress of subsequent processes.

[0132] Therefore, it is not obvious that vinyl acetate-vinyl pyrrolidone copolymer is most preferred as the host polymer.

[0133] 3. Attachment Figure 5 This is a microscope image of the side wall of the wafer groove magnified 200 times after the water-based cutting protection liquid D15 of Comparative Example 15 (that is, using a single component "propylene glycol monomethyl ether" as a hydrophilic solvent) is dried and formed into a film.

[0134] It can be seen that the thickness of the protective film layer on the groove sidewall of the pre-cut wafer is uneven, and there is a significantly thinned area (as shown in the two white ovals). Figure 4 , but significantly inferior to the complete coverage and uniform thickness of the attached Figure 3 .

[0135] The microscopic image of the wafer trench sidewall after drying and film formation using the water-based cutting protection liquid D7-D14 and D16 of Comparative Examples 7-14 and 16 is highly similar to the attached Figure 5 Similarly, there are some obvious thinning areas on the groove sidewalls of the pre-cut wafer, and their total area is similar to that of the attached Figure 5 , so I won’t list them one by one.

[0136] 4. Attachment Figure 6 This is a microscope image of the side wall of the wafer groove magnified 200 times after the water-based cutting protection liquid D17 of Comparative Example 17 (that is, using two-component "propylene glycol monomethyl ether + methanol" as the hydrophilic solvent) was dried and formed into a film.

[0137] It can be seen that the thickness of the protective film layer on the groove sidewall of the pre-cut wafer is uneven, and there are many areas where it is obviously thinned (as shown in the three white ovals). Figure 4 However, it is still significantly inferior to the attached Figure 3 , and the thinning area is larger than the attached Figure 5 .

[0138] The microscopic image of the side wall of the wafer groove after drying and film formation using the water-based cutting protection liquid D18-D21 of Comparative Examples 18-21 is highly similar to the attached Figure 6 Similarly, there are some obvious thinning areas on the groove sidewalls of the pre-cut wafer, and their total area is similar to that of the attached Figure 6 , and is larger than the attached Figure 5 , so I won’t list them one by one.

[0139] By the above attachment Figure 5-6 It can be seen that when the composition of the hydrophilic solvent is changed, the film-forming protection performance will be weakened / reduced to a certain extent. Even if the most preferred "propylene glycol monomethyl ether + ethanol" is modified to "propylene glycol monomethyl ether + methanol (or other alcohols)" or changed to any single component, the film-forming performance will be reduced.

[0140] The inventor believes that the principle is as follows: after being cut by a knife wheel, a groove (i.e., a groove) with a certain depth is formed on the wafer, and the side walls of the groove are silicon newly exposed to the atmosphere. After the wafer is pre-cleaned and a water film is formed, the silicon surface has polar OH bonds, making its surface hydrophilic. When a mixture of ethanol and propylene glycol monomethyl ether is used as a hydrophilic solvent, the following composite effects can be produced: 1. Ethanol and propylene glycol monomethyl ether can improve the leveling performance of the water-based cutting protection liquid. Both can reduce the surface tension of the liquid to achieve an excellent paving effect, and the hydrophilicity of both can also enhance the adhesion of the film layer at the same time; 2. Ethanol and propylene glycol monomethyl ether are both strong solvents for the main polymer, so that the main polymer has good compatibility with water, so that good spreading and coverage of the hydrophilic silicon surface can be achieved, and ethanol with the most appropriate carbon chain length can make the main polymer have the best stability in the pre-formed water film; 3. Ethanol, as a small molecule alcohol solvent, has a large solubility in water, has the most appropriate hydrogen bonding parameters in the system, and has the best adaptability and synergistic effect with propylene glycol monomethyl ether.

[0141] However, when any single component is used or the type of alcohol or ether in the optimal two-component is changed (even if the alcohol is replaced by the closest adjacent methanol or n-propanol, or propylene glycol monomethyl ether is replaced by the highly similar ethylene glycol monomethyl ether), the film-forming protection effect will be reduced.

[0142] In summary, the inventors found that when ethanol and propylene glycol monomethyl ether are used as hydrophilic solvents, the two interact and promote each other to achieve the best film-forming protection effect, which is unexpected.

[0143] Laser cutting protection performance test

[0144] After the above-mentioned water-based cutting protection liquids are prepared, a laser cutting protection test of a power semiconductor chip is performed. The specific operation and steps are as follows (i.e., steps AG of the cutting protection method in the above-mentioned [fourth technical solution]):

[0145] Step A: Firstly, the 12-inch wafer is cut by a cutter wheel to obtain a pre-cut wafer with grooves formed therein;

[0146] Step B: Cleaning the pre-cut wafer with ultrapure water for 2 minutes to fully remove dust particles on the surface to obtain a pre-cleaned wafer;

[0147] Step C: When the wafer is rotating at a low speed (rotation speed is 70 rpm), ultrapure water is sprayed onto the surface of the wafer for 100 seconds, thereby forming a uniform water film on the surface of the wafer. The amount of water sprayed is controlled so that the thickness of the obtained water film is between 70-90 μm.

[0148] Step D: When the wafer is rotating at a low speed (rotation speed is 60 rpm), a water-based cutting protection liquid is dripped from the center to the periphery, the total amount of dripping is 60 ml, and the spin coating is performed for 55 seconds, thereby forming a complete protection liquid film;

[0149] Step E: After the dropwise addition is completed, the water-based cutting protection liquid is dried to form a film;

[0150] Step F: performing laser cutting (laser cutting power is 6W) to cut the back metal layer to form a single chip;

[0151] Step G: Use deionized water with a resistance of ≥18MΩ to remove the protective film and obtain a single chip, thereby completing the cutting protection process.

[0152] After step G, the silicon slag and dirt on the sidewalls of the chip after laser cutting, i.e., the sidewalls of the original grooves, are inspected as follows:

[0153] 1. Attachment Figure 7 This is a microscope image of the original groove side wall magnified 200 times using the water-based cutting protection liquid S1 of Example 1 for film protection and after laser cutting.

[0154] It can be seen that through the protective film formation of S1, after laser cutting, the cleanliness of the original groove sidewall is very high, without any silicon slag and dirt.

[0155] The microscope image of the original groove side wall after laser cutting magnified 200 times using the water-based cutting protection liquid S2-S3 of Example 2-3 for film protection is exactly the same as the attached Figure 7 Similarly, the cleanliness of the groove sidewalls is very high, without any silicon slag and dirt, so they are not listed one by one.

[0156] 2. Attachment Figure 8This is a microscope image magnified 200 times of the original groove side wall after laser cutting using the water-based cutting protection liquid D1 of comparative example 1 for film protection.

[0157] It can be seen that after laser cutting, the water-based cutting protection liquid D1 has more silicon slag and dirt on the sidewalls of the original groove, and the cleanliness is reduced.

[0158] The microscope image of the original groove side wall magnified 200 times after laser cutting using the water-based cutting protection liquid D2-D3 of comparative examples 2-3 is highly similar to the attached Figure 8 Similarly, there is a lot of silicon slag and dirt on the side walls of the groove, which reduces the cleanliness, so they are not listed one by one.

[0159] 3. Attachment Fig. 9 This is a microscope image of the original groove side wall magnified 200 times using the water-based cutting protection liquid D4 of comparative example 4 for film protection and laser cutting.

[0160] It can be seen that after laser cutting, the original groove sidewalls have more silicon slag and dirt, but it is better than the attached Figure 8 .

[0161] The microscope image of the original groove side wall magnified 200 times after laser cutting using the water-based cutting protection liquid D5-D6 of comparative examples 5-6 is highly similar to the attached Fig. 9 Similarly, there is a lot of silicon slag and dirt on the side walls of the groove, which reduces the cleanliness, so they are not listed one by one.

[0162] It can be seen that when sodium p-styrene sulfonate is not present, the cleaning effect is significantly reduced. The inventor believes that when sodium p-styrene sulfonate is present, on the one hand, due to its high thermal decomposition temperature (greater than 300°C), its presence improves the temperature resistance of the film layer as a whole, and can maintain chemical stability at the higher temperature generated by laser cutting, so that the protective film can still maintain integrity during laser cutting, achieving excellent protection. More importantly, sodium p-styrene sulfonate has the function of acting as an electrolyte in the protective film layer. When it is washed with ultrapure water after cutting, the film layer is in contact with water, which can generate osmotic pressure, thereby accelerating the penetration of water outside the film layer into the inside, making it easier to quickly remove the film layer with slag inside the groove, thereby improving the cleanliness of the groove sidewall area.

[0163] 4. Attachment Fig.10 This is a microscope image magnified 200 times of the original groove side wall after laser cutting using the water-based cutting protection liquid D15 of comparative example 15 for film protection.

[0164] It can be seen that after laser cutting, the water-based cutting protection liquid D15 has intermittent long silicon slag / dirt on the side wall of the original groove (see attached Fig.10The upper part of the side wall in the Figure 8-9 , but relative to the attached Figure 7 There is a significant reduction in cleanliness.

[0165] The microscope images of the original groove sidewalls magnified 200 times after laser cutting using the water-based cutting protection liquids D11-D21 of comparative examples 11-21 are highly similar to those in the attached figure. Fig.10 Similarly, there are intermittent long strips of silicon slag / dirt on the sidewalls of the grooves, which reduces the cleanliness, so they are not listed one by one.

[0166] Impact test of step C

[0167] The inventors found that step C in the cutting protection method of the present invention is very critical. Its presence or absence directly and significantly affects the final protection performance. Therefore, this test specifically uses water-based cutting protection liquid S1-S3 to test step C, as follows:

[0168] 1. Use water-based cutting protection liquid S1 and perform the test according to the method in the above-mentioned "film forming performance test". The only difference is that step C is omitted, that is, step D is directly performed after step B is implemented.

[0169] The results show that the trench sidewalls of the pre-cut wafers are fully covered with a protective film layer with uniform thickness, which is flat and smooth as a whole and has an excellent protective effect on the trench sidewalls. Figure 3 They are exactly the same, so they are not listed again.

[0170] When the same test is performed using the water-based cutting protection liquid S2-S3 of Examples 2-3, the microscope image of the wafer trench sidewall after drying and film formation at 200 times magnification is exactly the same as the attached Figure 3 , and they are not listed one by one.

[0171] It can be seen that when step C is omitted, comprehensive and uniform excellent protection of the groove sidewalls can still be achieved.

[0172] 2. Use water-based cutting protection fluid S1 and perform the test according to the method in the above “Laser Cutting Protection Performance Test”. The only difference is that step C is omitted, that is, step D is performed directly after step B. The results are as follows:

[0173] Attached Fig.11 This is a microscope image of the original groove sidewall after laser cutting, magnified 200 times, using the water-based cutting protection liquid S1 of Example 1, omitting the film forming protection in step C.

[0174] It can be seen that after laser cutting, the water-based cutting protection liquid S1 has a little strip or filamentary silicon slag / dirt on the side wall of the original groove, which is significantly better than the attached Figure 8-9 , but relative to the attached Figure 7 There is a decrease in cleanliness.

[0175] The microscope image of the original groove sidewall magnified 200 times after laser cutting using the water-based cutting protection liquid S2-S3 of Example 2-3 is highly similar to the attached Fig.11 Similarly, there are a few strip-shaped or filament-shaped silicon slag / dirt on the sidewalls of the groove, which reduces the cleanliness, so they are not listed one by one.

[0176] Based on the above 1-2, it can be seen that although the omission of step C does not affect the film-forming performance of the protective liquid on the side wall surface, it has a significant negative impact in the subsequent cleaning, resulting in the presence of some silicon slag / dirt, and the cleaning effect is significantly inferior to that of the attached Figure 7 , so the existence of step C is necessary and essential.

[0177] The inventor believes that when step C is present, a uniform water film is formed, which can achieve good miscibility with the water-based cutting protection liquid, without affecting the excellent film-forming performance of the cutting protection liquid, and in the subsequent cleaning, it is easier to completely remove it by simply cleaning with ultrapure water. When this step is omitted, the adhesion between the formed protection film and the silicon substrate is too strong, and it is difficult to remove it by simply cleaning with ultrapure water.

[0178] Therefore, the existence of step C can significantly improve the cleaning effect and simplify and shorten the process flow, which is of great significance in the field of semiconductor technology. In addition, there is no need for subsequent more complicated organic solvent cleaning, which can significantly improve production efficiency, reduce process costs, increase product yield, and significantly reduce the generation of waste liquid.

[0179] In summary, the present invention provides a method for preparing a water-based cutting protection liquid for power semiconductors, its uses, a semiconductor laser cutting protection method using the protection liquid and other technical solutions. The water-based cutting protection liquid can achieve the best technical effect (see the subsequent performance test section for details) by selecting a specific main polymer, a specific improver and a specific hydrophilic additive, such as excellent cutting protection performance, cleaning performance and many other advantages. It overcomes the many defects existing in the cutting process of power semiconductors in the current prior art, can significantly improve and increase the processing qualification rate and yield rate of power semiconductor chips, and solves the above-mentioned technical defects.

[0180] It should be understood that the purpose of these embodiments is only to illustrate the present invention and is not intended to limit the protection scope of the present invention. In addition, it should also be understood that after reading the technical content of the present invention, those skilled in the art can make various changes, modifications and / or variations to the present invention, and all of these equivalent forms also fall within the protection scope defined by the appended claims of this application.

Claims

1. A water-based cutting protection liquid for laser cutting of power semiconductor chips, the water-based cutting protection liquid comprising the following components in parts by mass:

2. The water-based cutting protection liquid according to claim 1, Features: The mass fraction of the main polymer is 15-25 parts.

3. The water-based cutting protection liquid according to claim 1 or 2, Features: The mass fraction of the improving agent is 2-4 parts.

4. The water-based cutting protection liquid according to any one of claims 1 to 3, Features: The light absorber is any one of methyl salicylate, benzotriazole, 2-hydroxy-4-methoxy-5-sulfonic acid benzophenone or its sodium salt, or a mixture of any two or more thereof.

5. The water-based cutting protection liquid according to any one of claims 1 to 4, Features: The ultrapure water is deionized water with a resistance of ≥18 MΩ.

6. A method for preparing the water-based cutting protection liquid according to any one of claims 1 to 5, Features: The preparation method comprises the following steps: Step 1: Weigh the required mass of each component; Step 2: adding the main polymer to the hydrophilic solvent, controlling the stirring rate between 100-500 rpm and the temperature between 30-60° C., until the main polymer is completely dissolved, which is recorded as liquid A; Step 3: Add the improving agent to the ultrapure water, control the stirring rate between 200-500 rpm, and control the temperature between 20-30° C., and stir and mix thoroughly until the mixture is uniform and transparent, which is recorded as liquid B; Step 4: Add the light absorber to the liquid B, and continue stirring and mixing until uniform, which is recorded as liquid C; Step 5: Add the liquid C into the liquid A, control the stirring rate between 250-500 rpm, and control the temperature between 20-30° C. until the materials are evenly mixed, thereby obtaining the water-based cutting protection liquid.

7. The preparation method according to claim 6, Features: The stirring speed in step 4 is 200-500 rpm, and the stirring temperature is 20-30°C.

8. Use of the water-based cutting protection liquid according to any one of claims 1 to 5 in laser cutting protection of power semiconductor chips.

9. A method for protecting power semiconductor chips from laser cutting using the water-based cutting protection liquid according to any one of claims 1 to 5, the method comprising the following steps: Step A: firstly perform cutting with a knife wheel on the wafer to obtain a pre-cut wafer with grooves formed therein; Step B: cleaning the pre-cut wafer with ultrapure water to remove dust particles on the surface, thereby obtaining a pre-cleaned wafer; Step C: When the wafer is rotating at a low speed, ultrapure water is sprayed onto the surface of the wafer, thereby forming a uniform water film on the surface of the wafer; Step D: uniformly dripping the water-based cutting protection liquid from the center to the periphery of the wafer while the wafer is rotating at a low speed, and spin coating to form a complete protection liquid film; Step E: After the dropwise addition is completed, the water-based cutting protection liquid is dried to form a film; Step F: Perform laser cutting to cut the back metal layer to form a single chip; Step G: Use deionized water to wash and remove the protective film to obtain a single chip, thereby completing the cutting protection process.

10. The cutting protection method according to claim 9, Features: In step F, the laser cutting power is 0.5-10W.

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