Wafer processing base

Abstract

Provided is a substrate for processing a wafer. The present invention can provide a substrate having excellent heat resistance and dimensional stability. The present invention can provide a substrate that has excellent stress relaxation properties, and therefore can prevent a wafer from being destroyed due to residual stress. Also, the present invention can provide a substrate that can prevent a wafer from being damaged or fried off due to a non-uniformly applied pressure during the wafer processing process, and that exhibits excellent cuttability. For these reasons, the substrate can be useful as a sheet for processing a wafer in various wafer preparation processes such as dicing, back-grinding, and picking-up.

Claims

1. A pressure-sensitive adhesive sheet for processing a wafer, comprising: a heat resistant substrate that is a photo-cured product of a photo-curable composition, and a pressure-sensitive adhesive layer formed on one or both sides of the substrate and coming in contact with the substrate, wherein the photo-curable composition comprises a high-molecular weight acrylic polymer and a monomer component, wherein the substrate has a glass transition temperature of 20 C. to 45 C. and a toughness of 10 kg.Math.mm to 250 kg.Math.mm at 23 C., wherein the high-molecular weight acrylic polymer comprises a partially polymerized product of a monomer mixture including: (a) an alkyl(meth)acrylate having an alkyl group having 1 to 14 carbon atoms; (b) at least one selected from the group consisting of a (meth)acrylate having an alkoxy group; a (meth)acrylate having a alicyclic group; a (meth)acrylate having an aromatic group; and a (meth)acrylate having a heterocyclic moiety; and (c) a monomer having a hydroxyl group, carboxyl group, nitrogen-containing group or glycidyl group, and wherein the monomer mixture does not include urethane acrylate.

2. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the substrate has a glass transition temperature of 10 C. to 40 C.

3. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the substrate has a toughness of 10 kg.Math.mm to 200 kg.Math.mm at 23 C.

4. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the substrate has a toughness of 10 kg.Math.mm to 250 kg.Math.mm at 20 C. to 25 C.

5. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the high-molecular weight acrylic polymer has an average molecular weight of 500 to 1,000,000.

6. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the photo-curable composition further comprises multi-functional acrylate.

7. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the photo-curable composition further comprises a photoinitiator.

8. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the substrate has a thickness of 5 m to 400 m.

9. The pressure-sensitive adhesive sheet for processing a wafer according to claim 1, wherein the pressure-sensitive adhesive layer comprising an acrylic polymer that is cross-linked by a multi-functional cross-linking agent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:

(2) FIGS. 1 and 2 are cross-sectional views of an exemplary pressure-sensitive adhesive sheet for processing a wafer according to the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(3) Hereinafter, exemplary embodiments of the present invention will be described in detail.

Preparation Example 1. Preparation of Partially Polymerized Product (A1)

(4) A monomer mixture of 60 parts by weight of 2-ethylhexyl acrylate (2-EHA), 35 parts by weight of isobornyl acrylate (IBOA) and 5 parts by weight of acrylic acid (AA) was input into a 1 L reactor containing refluxed nitrogen gas and a cooling apparatus for easy control of the temperature. The nitrogen gas was then purged in order to remove oxygen. Afterwards, the mixture was homogenized while maintaining the temperature at 60 C., and the reaction was initiated by adding 0.015 parts by weight of diethylhexyl peroxydicarbonate as an initiator and 0.08 parts by weight of n-dodecyl mercaptan (n-DDM) as a chain transfer agent so as to prepare a partially-polymerized acrylic syrup having a solid content of 25 wt %, a weight average molecular weight of 400,000 and a glass transition temperature of 21 C. In the above, the weight average molecular weight of the syrup was the weight average molecular weight of the polymer included in the syrup.

Preparation Example 2. Preparation of Partially Polymerized Product (A2)

(5) A monomer mixture of 70 parts by weight of 2-ethylhexyl acrylate (2-EHA), 27 parts by weight of isobornyl acrylate (IBOA) and 3 parts by weight of hydroxyethyl acrylate (HEA) was input into a 1 L reactor containing refluxed nitrogen gas and a cooling apparatus for easy control of the temperature. The nitrogen gas was then purged in order to remove oxygen. Afterwards, the mixture was homogenized while maintaining the temperature at 60 C., and the reaction was initiated by adding 0.015 parts by weight of diethylhexyl peroxydicarbonate as an initiator and 0.04 parts by weight of n-dodecyl mercaptan (n-DDM) as a chain transfer agent so as to prepare a partially-polymerized acrylic syrup having a solid content of 35 wt %, a weight average molecular weight of 800,000 and a glass transition temperature of 36 C. In the above, the weight average molecular weight of the syrup was the weight average molecular weight of the polymer included in the syrup.

Example 1

(6) A photo-curable composition was prepared by mixing 30 parts by weight of isobornyl acrylate (IBOA) with 70 parts by weight of the partially polymerized product (A1), adding 1.0 part by weight of 1,6-hexanediol diacrylate as a multi-functional acrylate and 1.0 part by weight of 1-hydroxycyclohexyl phenyl ketone (Igacure 184) as a photoinitiator thereto, and mixing and defoaming the resultant mixture. Afterwards, the resultant composition was coated on a polyester releasing film using a bar coater to a thickness of about 140 m. Subsequently, to prevent the coated layer from being in contact with oxygen, another polyester releasing film was laminated on the coated layer while UV-A irradiation was performed using a metal halide lamp at a light intensity of 800 mJ/cm.sup.2, thereby preparing a photo-cured product (substrate).

Examples 2 to 7 and Comparative Examples 1 to 3

(7) Photo-cured products were prepared by the same method as in Example 1, except that the composition of the photo-curable composition was changed as summarized in Table 1.

(8) TABLE-US-00001 TABLE 1 Comparative Example Example 1 2 3 4 5 6 7 1 2 3 High- Partially 70 Molecular- Polymerized Weight product(A1) Polymer Partially 50 70 Polymerized product(A2) Oligomer(A3) 50 40 Oligomer(A4) 30 40 40 Oligomer(A5) 45 50 Monomer IBOA 30 43 40 25 40 10 10 50 30 Component t-BA 38 EHA 10 15 45 20 20 EOEOEA 15 PHEA 45 AA 7 7 10 HEA 5 MFA 1.0 1.0 1.0 Photoinitiator 1.0 0.7 0.5 0.5 0.5 0.5 1.0 1.0 0.5 1.0 OligomerA3: Urethane Acrylate(T.sub.g: 20 C., M.sub.w: 8,000) OligomerA4: Urethane Acrylate(T.sub.g: 10 C., M.sub.w: 20,000) OligomerA5: Epoxy Acrylate(T.sub.g: 54 C., M.sub.w: 3,000) IBOA: Isobornyl Acrylate(T.sub.g: 94 C.) t-BA: t-Butyl Acrylate(T.sub.g: 43 C.) EHA: 2-Ethylhexyl Acrylate(T.sub.g: 65 C.) EOEOEA: 2-(2-Ethoxyethoxy)ethyl Acrylate(T.sub.g: 70 C.) PHEA: Phenoxyethyl Acrylate(T.sub.g: 22 C.) AA: Acrylic Acid(T.sub.g: 106 C.) HEA: 2-Hydroxyethyl Acrylate(T.sub.g: 15 C.) MFA: 1, 6-Hexanediol Diacrylate Photoinitiator: Igacure 184 Content Unit: Part by Weight

Comparative Example 4

(9) A polypropylene film (melting point (T.sub.m): 80 C.) having a thickness of 140 m was used as a substrate of Comparative Example 4 in order to compare properties.

(10) The properties of the substrates of the Examples and Comparative Examples were evaluated by the method described below, and the results are summarized in Table 2.

(11) <Measurement of Glass Transition Temperature (T.sub.g)>

(12) The glass transition temperature was measured by using a differential scanning calorimeter (TA Instruments, Inc.) at a heating rate of 10 C./min. When at least two glass transition temperatures were detected, an average value calculated by considering the weight ratio of each component in the composition was determined as the glass transition temperature.

(13) <Measurement of Toughness Value>

(14) Samples were prepared by cutting the substrates of the Examples and Comparative Examples to a size of 15 mm35 mm (widthlength). Afterwards, the samples were taped on the top and bottom sides of the sample in the length direction with lengths of 10 mm each. Subsequently, the taped top and bottom sides of the sample were fixed to a measuring apparatus (XP Plus, TA, Inc.) in a perpendicular direction with respect to the apparatus. Then, the sample was elongated at a rate of 200 mm/min and at a temperature of 23 C., and a graph of force (Y axis) measured according to distance (X axis) until the sample was cut was plotted. The distance-versus-force curve was integrated to estimate toughness.

(15) <Evaluation of Formability of Substrate>

(16) Formability of the substrate was evaluated according to the following criteria.

(17) <Criteria for Evaluating Formability of Substrate>

(18) O: The case in which the cured product having a supporting force and a shape enough to function as the substrate was formed.

(19) X: The case in which the cured product was too viscous, did not have a supporting force enough to function as the substrate or did not have the shape as the substrate.

(20) <Evaluation of Cuttability>

(21) Preparation of Pressure-Sensitive Adhesive Sheet

(22) A pressure-sensitive adhesive layer having a thickness of 30 m was formed on each of the substrates of the Examples and Comparative Examples by using the product obtained by reacting an acrylic polymer consisting of 90 parts by weight of 2-ethylhexyl acrylate (2-EHA) and 10 parts by weight of 2-hydroxy ethyl acrylate (HEA) in polymerized form with methacryloyloxyethyl isocyanate (MOI), thereby preparing a pressure-sensitive adhesive sheet.

(23) Evaluation of Cut Property

(24) An 8-inch silicon (Si) wafer was attached to the pressure-sensitive sheet using a wafer mounter, and the sheet was cut along the shape of the wafer using an expender (HS-1810, Hugle electronics, Inc.). Subsequently, the height of the stage was set to 3 to observe the cutting plane of the sheet. In detail, the starting and intermediate portions of the cutting plane were observed using an optical microscope, and cuttability was measured by evaluating burr generation and torn degree in the cutting plane according to the following criteria:

(25) : The case in which an area rate of a torn part with respect to the total area of the film is 3% or less when the starting portion of the cutting of the sheet was observed at a magnification of 50 and a resolution of 640480.

(26) : The case in which an area rate of a torn part with respect to the total area of the film is 4% to 7% when the starting portion of the cutting of the sheet was observed at a magnification of 50 and a resolution of 640480.

(27) x: The case in which an area rate of a torn part with respect to the total area of the film is 8% or more when the starting portion of the cutting of the sheet was observed at a magnification of 50 and a resolution of 640480.

(28) <Evaluation of Adhesion Strength>

(29) An 8-inch silicon (Si) wafer was attached to the same pressure-sensitive adhesive sheet as used when measuring the cuttability using a wafer mounter (DS Precision, Inc. DYWMDS-8), and a surface of the attached wafer was observed to count lamination bubbles to evaluate the adhesion strength according to the following criteria.

(30) <Criteria for Evaluating Adhesion>

(31) : 3 or less bubbles are generated.

(32) : 4 to 7 bubbles are generated.

(33) x: 8 or more bubbles are generated.

(34) <Evaluation of Grindability of Wafer>

(35) An 8-inch silicon (Si) wafer was attached to the same pressure-sensitive adhesive sheet as used when measuring the cuttability using a wafer mounter (DS Precision, Inc. DYWMDS-8), and the film was cut along the shape of the wafer using an expender. Subsequently, the wafer was grinded using a wafer back-grinder (SVG-502MKII8), and the grindability of the wafer was evaluated based on the frequencies of warpage, damage and cracking of the wafer according to the following criteria:

(36) : The wafer suffered no warpage, damage or cracking.

(37) : The wafer suffered warpage of about 1 to 5 mm, or weak damage and/or cracking.

(38) x: The wafer suffered warpage greater than 5 mm, or large damage and cracking.

(39) The observation results are summarized in Table 2.

(40) TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 4 5 6 7 1 2 3 4 Glass Transition 5 16 32 15 4 9 0 34 61 35 Temperature( C.) Toughness(Kg .Math. mm) 60 40 110 120 190 130 30 5 8 500 Substrate X Formability Cuttability X X X Adhesion strength X Wafer Grindability X X

(41) As seen in Table 2, the Examples according to the present invention showed excellent substrate formability, and also excellent cuttability, adhesion strength and grindability required to be a sheet for processing a wafer.

(42) On the other hand, as in Comparative Example 1, due to the excessively low glass transition temperature, the toughness could not be measured, and due to the difficulty in forming the substrate, the cuttability, adhesion strength and grindability were also difficult to measure.

(43) Comparative Example 2 had a high glass transition temperature and low toughness, resulting in poor cuttability, adhesion strength and grindability.

(44) Comparative Example 3 exhibited poor cuttability and grindability due to low toughness. In addition, Comparative Example 4 having no glass transition temperature and high toughness also exhibited very poor cuttability and grindability.

(45) Consequently, the present invention can provide a substrate having excellent heat resistance and dimensional stability. The present invention can provide a substrate that has excellent stress relaxation properties and therefore can prevent a wafer from being destroyed due to residual stress. Also, the present invention can provide a substrate that can prevent a wafer from being damaged or flied off due to a non-uniformly applied pressure during the wafer processing process, and that exhibits an excellent cuttability. For these reasons, the substrate can be useful as a sheet for processing a wafer in various wafer preparation processes such as dicing, back-grinding, and picking-up.

(46) While the invention has been shown and described in reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.