A negative thick film photoresist for advanced packaging

Abstract

The invention discloses a negative thick film photoresist for advanced packaging, the formula of which includes: 40-60 parts by mass of solvent, 30-50 parts by mass of acrylic resin, 3-10 parts by mass of initiator, 10-30 parts by mass of cross-linking agent and 500-1500ppm of additives; the viscosity of the photoresist is 3000-5000mPa.s; the molecular weight of the acrylic resin is 6000-15000, preferably 8500-12000. The invention increases the coating thickness of the photoresist and improves the uniformity of the coating; at a thickness of 110um, exposure and development are performed, followed by electroplating of copper, nickel, and selenium silver, the photoresist surface is intact and not cracked, the photoresist is easy to remove after electroplating, and the angle of the electroplated copper column is steep.

Description

[Technical field]

[0001] The invention relates to the technical field of advanced packaging electroplating process, and in particular to a negative thick film photoresist used for advanced packaging. [Background technology]

[0002] The surge in demand for the semiconductor IC packaging industry has led to a surge in orders from packaging and testing manufacturers. At present, the average factory utilization rate of packaging and testing manufacturers is above 80%, and of course many types of packaging and testing capacity are running at full capacity. The tight capacity is manifested in several aspects. Among them, the biggest bottleneck is a mature manufacturing process called wafer bumping, especially on 200mm wafers. Currently, companies such as Amkor, ASE, STATS ChipPAC, etc. all provide wafer bumping services. As part of the turnkey service, wafer bumping is performed directly on 200mm or 300mm wafers. Bumping itself is not a type of packaging, it is a manufacturing process that forms tiny solder balls or copper pillars on the wafer.

[0003] Photoresist is a transition material for a mask. It is composed of resin, photosensitive compounds, solvents, additives, etc. After ultraviolet irradiation, it undergoes cross-linking and decomposition. Due to different solubility properties in the developer, the required pattern is formed. Due to different fields of use, the types of photoresist used are different. Photoresist is divided into positive photoresist and negative photoresist. The positive photoresist is mainly composed of phenolic resin as the main frame. It is characterized by high resolution and fast development speed. However, due to the limitation of molecular weight, the coating film thickness can only reach 30um. In addition, phenolic resin is rigid enough. After long-term electroplating at high temperature, it is easy to cause cracking and infiltration of the glue surface. Negative photoresist of acrylic system has a large molecular weight and a viscosity ranging from thousands to tens of thousands of centipoise. The coating thickness can reach more than 100um. Because acrylic resin has a high Tg value and good toughness, it has good electroplating resistance. The electroplating copper pillar process used in the advanced packaging industry requires a film thickness of more than 100um, a steep graphic morphology, and easy debonding after electroplating. The steepness of the electroplated copper pillar is close to 90°.

[0004] In the prior art, patent publication number CN112650024A discloses a high-thickness negative photoresist used in chip packaging technology. The patent independently developed an acrylic resin structure containing a molecular weight of 5,000 to 50,000, which greatly increased the solid content of the photoresist and reduced the viscosity, thereby increasing the thickness of the photoresist coating and improving the coating uniformity. However, after the thickness of the negative photoresist is increased, its toughness is insufficient and cracks are easily generated. At the same time, its electroplating resistance is poor, especially the electroplating temperature resistance is low, which can only reach room temperature or about 35°C, and it is easy to corrode.

[0005] Therefore, it is necessary to provide a new negative thick film photoresist for advanced packaging to solve the above technical problems. [Summary of the invention]

[0006] The main purpose of the present invention is to provide a negative thick film photoresist for advanced packaging, which can effectively improve the coating thickness, electroplating resistance and toughness of the photoresist and is not prone to cracks.

[0007] The present invention achieves the above-mentioned purpose through the following technical scheme: a negative thick film photoresist for advanced packaging, the formula of which includes: 40 to 60 parts by mass of a solvent, 30 to 50 parts by mass of an acrylic resin, 3 to 10 parts by mass of an initiator, 10 to 30 parts by mass of a cross-linking agent and 500 to 1500 ppm of an additive; the viscosity of the photoresist is 3000 to 5000 mPa.s; the molecular weight of the acrylic resin is 6000 to 15000, preferably 8500 to 12000, and the structural formula is:

[0008]

[0009] Furthermore, the preparation of the acrylic resin includes: adding 10 parts of styrene, 6.9 parts of isoprene, 9 parts of methacrylic acid, 21 parts of isobornyl acrylate, 13 parts of hydroxyethyl methacrylate, 75 parts of xylene, and 0.8 parts of tert-butyl perbenzoate into a reaction flask, heating to 70°C under nitrogen protection, reacting for 3 hours, cooling to room temperature after reaction, pouring into a methanol solvent, precipitating a white solid, filtering, placing in a nitrogen oven at 80°C, and baking to constant weight to obtain the acrylic resin.

[0010] The main component of the photoresist in the present invention is formed by the polymerization of several monomers, and its main cross-linking property is completed by the double bonds of styrene and isoprene therein. Methacrylic acid provides a certain acidity, which can promote the resin to dissolve in an alkaline developer. Isobornyl acrylate and hydroxyethyl methacrylate provide the toughness of the resin. At the same time, due to the esterified groups in the structure, it can be dissolved in propylene glycol methyl ether acetate used in the photoresist. At the same time, due to its hydrophobic property, it can effectively resist the dissolution property and electroplating resistance of the photoresist in the developer, thereby making the prepared photoresist have excellent electroplating resistance and toughness.

[0011] If the molecular weight of the acrylic resin is too large or too low, the thickness and photosensitivity of the photoresist coating will be affected; after the initiator absorbs the light source, it will cross-link with the double bond groups of the acrylic resin and the cross-linking agent. The larger the molecular weight, the greater the cross-linking density and the stronger the electroplating resistance, but at the same time, it will cause the viscosity of the photoresist to be high, the coating film thickness is high, and the uniformity is poor. Therefore, by synthesizing a resin with a specific molecular weight, a balance can be achieved in terms of electroplating, cross-linking density, viscosity, film thickness, and uniformity to meet various characteristic requirements.

[0012] Furthermore, the general structural formula of the cross-linking agent is:

[0013] (CH2=CHCOOCH2)3-C-CH2-OR,

[0014] Wherein, R is one of H or COCH=CH2.

[0015] Furthermore, the structural formula of the initiator is:

[0016]

[0017] Furthermore, the initiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP for short).

[0018] Too high or too low a ratio of the crosslinking agent will affect the photoresist morphology and electroplating characteristics; and too much or too little ratio of the initiator will also affect the photoresist morphology and exposure. The acrylic resin itself has a certain solubility. The present invention uses a crosslinking agent that conforms to the above structural formula, which helps to increase the dissolution rate of the unexposed area of ​​the photoresist; after exposure, the initiator absorbs the light source and crosslinks with the double bond groups of the acrylic resin and the crosslinking agent to form an insoluble and dense network structure. The crosslinking agent is embedded in the acrylic resin system to form a new structure without alkali solubility. In this way, in the developer, the unexposed area is alkali-soluble, and the exposed area is not alkali-soluble. The thicker the film thickness, the higher the graphic contrast and the steeper the angle formed.

[0019] Furthermore, the additive is a leveling agent, specifically polyether polyester modified organosiloxane, with a molecular weight of 1200. The additive is a leveling agent, which mainly improves the uniformity of the film thickness of the photoresist during coating. Too much or too little will affect the uniformity of the spin coating of the photoresist.

[0020] Furthermore, the solvent is selected from propylene glycol methyl ether acetate, propylene glycol methyl ether, or a mixture of the two.

[0021] The present invention adds isobornyl acrylate and hydroxyethyl methacrylate structures to the structure, which effectively improves the toughness of the resin, improves the toughness and Tg value of the resin, and can effectively improve the electroplating resistance of the photoresist surface and the compressive performance of the resin in the electroplating fixture without generating cracks. At the same time, since the Tg value of the resin is improved, the temperature of the photoresist electroplating is significantly improved; the resin structure synthesized by the present invention is an esterified structure, which has better resistance to electroplating resistance, and is combined with initiators and crosslinkers of different structures, so that the electroplating resistance of the photoresist is significantly improved, especially the resistance to the temperature of the electroplating solution is significantly improved, which can reach 60°C.

[0022] Compared with the prior art, the invention has the beneficial effects of a negative thick film photoresist for advanced packaging: by synthesizing acrylic resin with a specific molecular weight as the main component, the coating thickness of the photoresist is improved by combining the viscosity control of the photoresist, and by controlling the molecular weight and content of the resin, the viscosity and coating of the photoresist are guaranteed, and a single coating can reach 60um, and a double coating can reach 110um; while the viscosity of the traditional positive phenolic series photoresist reaches 600cp, and the coating thickness is only 20um for a single coating, and only 40um for a double coating; at the same time, the initiator and the cross-linking agent are combined to play an exposure cross-linking role, so that the properties of the film-forming resin are changed, and the film-forming resin has the characteristics of toughness, electroplating resistance and the like; the photoresist is used in the electroplating process of the advanced packaging industry, and at a thickness of 110um, exposure and development are carried out, followed by electroplating of copper, nickel, and selenium silver, the resin surface is intact and not cracked, the photoresist is easy to remove after electroplating, and the angle of the electroplated copper column is steep.

Brief Description of the Drawings

[0023] Figure 1 Schematic diagram of the morphology of the photoresist after electroplating and stripping in an embodiment of the present invention. [Specific implementation method]

[0024] Example:

[0025] The present embodiment is a negative thick film photoresist for advanced packaging, and its formula includes: 40-60 parts by mass of solvent, 30-50 parts by mass of acrylic resin, 3-10 parts by mass of initiator, 10-30 parts by mass of cross-linking agent and 500-1500 ppm of additives; the viscosity of the photoresist is 3000-5000 mPa.s; the molecular weight of the acrylic resin is 6000-15000, preferably 8500-12000, and its structural formula is:

[0026]

[0027] The preparation of the acrylic resin comprises: adding 10 g of styrene, 6.9 g of isoprene, 9 g of methacrylic acid, 21 g of isobornyl acrylate, 13 g of hydroxyethyl methacrylate, 75 g of xylene, and 0.8 g of tert-butyl perbenzoate into a reaction flask, heating to 70° C. under nitrogen protection, reacting for 3 hours, cooling to room temperature after reaction, pouring into a methanol solvent, precipitating a white solid, filtering, placing in a nitrogen oven at 80° C., and baking to constant weight to obtain the acrylic resin.

[0028] The general structural formula of the cross-linking agent is:

[0029] (CH2=CHCOOCH2)3-C-CH2-OR,

[0030] Wherein, R is one of H or COCH=CH2.

[0031] The structural formula of the initiator is:

[0032]

[0033] The additive is polyether polyester modified organic siloxane.

[0034] The solvent is selected from propylene glycol methyl ether acetate, propylene glycol methyl ether, or a mixture of the two.

[0035] The present invention is further described in detail below with reference to specific embodiments.

[0036] Acrylic resin, initiator, crosslinking agent, additive, and solvent were prepared into multiple embodiments according to the formula in Table 1. The components of each embodiment were added into a feeding kettle and stirred for 10 hours. After dissolution, the mixture was filtered and coated on a 6-inch copper sheet with a thickness of 110 um. After coating, the electroplating resistance and the angle after electroplating were tested. The results are shown in Table 2. The photoresist prepared by the present scheme was coated on a 6-inch silicon wafer by spin coating with a coating thickness of 110 um. After coating, the desired pattern was obtained by baking, hardening, exposure, and development. After electroplating, the photoresist was removed to obtain the desired electroplated pattern, as shown in Table 2. Figure 1 shown.

[0037] Table 1

[0038] Material Name Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Acrylic resin A 50 48 30 40 - - 30 40 Acrylic resin B - - - - 50 - - - Acrylic resin C - - - - - 48 - - Initiator A 6 7 3 10 6 7 - 10 Initiator B - - - - - - 3 - Crosslinker A 27 25 10 30 27 25 10 - Crosslinker B - - - - - - - 30 additive 800 500 1000 1500 800 500 1000 1500 Solvents 50 55 40 60 50 55 40 60

[0039] Remark:

[0040] In Table 1, acrylic resin A, initiator A and cross-linking agent A are the acrylic resin, initiator and cross-linking agent described in this embodiment; the unit of acrylic resin, initiator, cross-linking agent and solvent is phr, and the unit of additive is ppm;

[0041] Acrylic resin B is an acrylic resin of Hitachi Chemical Co., Ltd. with publication number TW 201546554A;

[0042] Acrylic resin C is an acrylic resin produced by Asahi Glass Co., Ltd. with publication number 201530263A;

[0043] Initiator B is 369 initiator;

[0044] Crosslinking agent B is trimethylolpropane propoxylate triacrylate.

[0045] Table 2

[0046] Angle after electroplating° Electroplating characteristics Glue removal performance Comprehensive Assessment Example 1 89 OK OK OK Example 2 89 OK OK OK Example 3 88 OK OK OK Example 4 88 OK OK OK Comparative Example 1 83 Plating OK NG Comparative Example 2 84 Plating OK NG Comparative Example 3 82 OK NG NG Comparative Example 4 79 OK NG NG Target ≥87 Normal graphics, no seepage Clean glue removal

[0047] It can be seen from the test results shown in Table 2 that the photoresist prepared by this scheme is coated with a thickness of 110um, and the electroplating resistance, post-electroplating angle and debonding performance tested after coating all meet the requirements.

[0048] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A negative thick film photoresist for advanced packaging, characterized in that: The formula includes: 40-60 parts by mass of solvent, 30-50 parts by mass of acrylic resin, 3-10 parts by mass of initiator, 10-30 parts by mass of cross-linking agent and 500-1500 ppm of additives; the viscosity of the photoresist is 3000-5000 mPa.s; the molecular weight of the acrylic resin is 6000-15000, and the structural formula is: ； The preparation of the acrylic resin comprises: adding 10 parts of styrene, 6.9 parts of isoprene, 9 parts of methacrylic acid, 21 parts of isobornyl acrylate, 13 parts of hydroxyethyl methacrylate, 75 parts of xylene, and 0.8 parts of tert-butyl perbenzoate into a reaction flask, heating to 70° C. under nitrogen protection, reacting for 3 hours, cooling to room temperature after reaction, pouring into a methanol solvent, precipitating a white solid, filtering, placing in a nitrogen oven at 80° C., and baking to constant weight to obtain the acrylic resin; The general structural formula of the cross-linking agent is: ， Wherein, R is one of H or COCH=CH2; The structural formula of the initiator is: 。 2. The negative thick film photoresist for advanced packaging as claimed in claim 1, characterized in that: The additive is epoxy polyether silicone with a molecular weight of 1200.

3. The negative thick film photoresist for advanced packaging as claimed in claim 1, characterized in that: The solvent is selected from propylene glycol methyl ether acetate, propylene glycol methyl ether, or a mixture of the two.

4. The negative thick film photoresist for advanced packaging as claimed in claim 1, characterized in that: The molecular weight of the acrylic resin is 8500-12000.

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