JP2005235889A - Method for protecting surface of wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for protecting the surface of a wafer by which, when a radiation curing type adhesive tape is adhered to the wafer applied with etching it, paste exposed around the wafer can be prevented from contaminating the rear face of the wafer accompanied by the elution of the paste into an etchant, and the invasion of the etchant into a pattern section on the surface of the wafer can be blocked. <P>SOLUTION: Radiation is applied only to a predetermined area around the entire circumference of the wafer to which the tape is adhered, and an adhesive layer in the area is cured. Then, the wafer is subjected to etching. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface protection tape for non-etched portions used for surface protection during back surface grinding and back surface chemical etching of a semiconductor wafer, or when etching various metal materials.

Silicon, gallium arsenide, and the like are generally well known as wafers used in the manufacture of semiconductors, and silicon is often used. This silicon wafer is processed by various methods to form a large number of integrated circuit patterns on the wafer. Next, the wafer on which this circuit pattern is formed is thinned by subjecting the back surface thereof to grinding processing or chemical etching processing (hereinafter referred to as etching), depending on the intended use.
In this backside grinding process of the semiconductor wafer, the wafer circuit pattern surface is fixed by vacuum suction and the backside of the wafer is ground, for example, a 500 μm-thick one is thinned to 300 to 200 μm and processed to a uniform thickness. . Thereafter, for the purpose of removing processing distortion caused by heat during grinding or the like, or for the purpose of further reducing the thickness of the wafer, for example, an etching process of immersing in an etching solution is performed.

Therefore, in these wafer back surface processing steps, it is necessary to apply a resist ink or the like excellent in etching resistance for the purpose of protecting the pattern surface. However, in order to remove the resist ink after etching, it is necessary to perform cleaning with an organic solvent. Therefore, there are problems such as work environment pollution or solvent regulations, and countermeasures are required. Therefore, a new surface protection method that does not use resist ink has been desired.
On the other hand, for the purpose of protecting the wafer surface at the time of etching, attempts have been made to use a low-adhesion surface protection tape, but the etching resistance is poor and the protective tape is better than the adherend wafer during the etching process. There is often a problem that the pattern on the wafer is corroded and corroded. Although attempts have been made to increase the adhesive strength of the tape in order to prevent the tape from peeling off, the adhesive strength is still insufficient when the tape is peeled off the adherend wafer after the etching process as well as insufficient etching resistance. There was also a problem that the wafer was damaged due to its strength.

In order to solve these problems, a support that transmits radiation, for example, light such as ultraviolet rays or ionizing radiation such as an electron beam, and has etching resistance, and radiation applied to the support are used. A radiation-curable pressure-sensitive adhesive tape comprising a pressure-sensitive adhesive layer having a curing property has been developed. This is because the adhesive strength before radiation curing is made strong adhesive strength to reduce the intrusion of the etching liquid when the tape is bonded to the adherend and etched, and the tape itself has etching resistance. Yes, it is easy to peel off the adherend by making the tape have low adhesive strength by irradiation with radiation after etching.
However, since the adhesive itself of this radiation curable adhesive tape is inferior in etching resistance, the portion where the adhesive itself is exposed in the etching solution is eroded by the etching solution, causing the adhesive residue. The glue residue itself is only on the periphery of the wafer and does not reach the pattern surface, but since this glue contains an etching solution, corrosive gas is volatilized due to heat at the time of radiation irradiation and adversely affects the aluminum terminal part. There were problems such as being easy to affect.

Further, there is a problem that the exposed portion of the adhesive during etching is eluted into the etching solution to contaminate the etching solution, and the eluted material adheres to the back surface of the wafer and is contaminated.
As a method for solving such a problem, there has been proposed a method in which a radiation-curable adhesive tape is attached to the wafer surface, and then an etching process is performed in a state where the pressure-sensitive adhesive layer is cured by irradiation with radiation in advance. In order to prevent the tape from peeling and floating due to the intrusion of the etching solution, it is possible to carry out an appropriate curing process that leaves a certain level of adhesive force, improving the etching resistance, and remaining glue and peeling due to heat generated during the etching process. This is to prevent defects.
However, in this method, the adhesive force decreases, so that the etchant can easily enter from the interface between the tape and the wafer, and in some cases, the pattern may be reached and the pattern may be partially destroyed. In addition, there is a problem that peeling is difficult in the case of finishing a thin film wafer having a thickness of 200 μm or less, for example, because a certain degree of adhesive strength remains after radiation curing.

JP 5-195255

The present invention provides a surface protection method that prevents contamination of the wafer back surface due to elution of the glue exposed in the peripheral portion of the wafer into the etching solution and prevents the etching solution from entering the pattern portion of the wafer surface. Objective.

  The inventors of the present invention have made various studies in order to overcome the drawbacks of the surface protection method during etching using the conventional radiation curable adhesive tape. By exposing to a predetermined area along the entire circumference of the film, the adhesive layer in that part is cured to form a three-dimensional network structure, and then etched to expose it to the peripheral part of the wafer. Elution of the glue in the etchant and the resulting contamination of the backside of the wafer can be prevented, and the main part other than the periphery of the wafer is uncured and maintains sufficient adhesive strength to prevent the etchant from entering. Based on this finding, the present inventors have made the present invention.

That is, the present invention is a method for protecting a surface during chemical etching of a wafer, wherein a radiation-curable adhesive tape is attached to the back surface of the surface on which the wafer is subjected to etching, and the entire surface of the wafer is covered with the adhesive tape. A method for protecting the surface of a wafer is provided, in which a predetermined region is cured by irradiation and then subjected to an etching treatment, and the entire adhesive tape is further cured by radiation and peeled off.

In the surface protection method of the present invention, a radiation curable adhesive tape is bonded to the adherend wafer, and etching is performed after curing by irradiation only in a predetermined area along the entire circumference of the tape wafer. As a result, it is possible to prevent adhesive residue on the periphery of the wafer and to prevent the exposed portion of the adhesive from eluting into the etching solution and contaminating the backside of the wafer. It is possible to prevent deterioration of the material. Furthermore, the tape can be easily peeled off by irradiating the entire wafer with radiation after the etching process and curing the remaining part.

Specific embodiments of the present invention will be described with reference to the accompanying drawings.
The radiation curable pressure-sensitive adhesive tape used in the surface protection method of the present invention is formed by coating a radiation curable pressure-sensitive adhesive on a radiation transmissive film-like support made of a material having etching resistance. The etching solution for chemical etching includes a chemical etching solution containing at least one of hydrogen fluoride, hydrogen chloride, sulfuric acid, nitric acid, acetic acid, hydrogen peroxide, and phosphoric acid.

Examples of the film-like support include homopolymers of α-olefins such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, isotactic polypropylene, and poly-4-methylpentene-1. The fluorine-containing resin is preferably a fluorine polymer such as polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene copolymer, tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, and the polyester resin is preferably polyethylene terephthalate. Used.
Among these resins, it is more preferable to use high-density polyethylene, isotactic polypropylene, or polyethylene terephthalate. Also required on the film-like support (1) Relieves and absorbs external impact force applied to the wafer during back grinding of a semiconductor wafer, prevents damage to the wafer itself such as microcracks, and provides cushioning to the tape itself And (2) other than the resin layer having etching resistance in order to satisfy the function of (2) providing the flexibility to adhere well to the wafer pattern surface having complicated irregularities and to prevent the occurrence of floating or peeling. It can also be set as the film-form support body which laminated | stacked these resin. However, in this case, it is necessary to set a combination of resins so as not to impair the etching resistance of the film-like support.
Examples of the resin laminated on the resin having etching resistance include, for example, ethylene-vinyl acetate copolymer, polybutene-1,1,2-polybutadiene, polyurethane, ethylene-ethyl acrylate copolymer, ethylene-acrylic. Examples include α-olefin homopolymers or copolymers such as acid methyl copolymers, ethylene-acrylic acid copolymers, and ionomers, or mixtures thereof, which are arbitrarily selected according to the required characteristics of the film-like support. be able to.
As a method for producing these film-like supports, conventionally known extrusion methods can be used, but in the case of film-like supports obtained by laminating various resins, a co-extrusion method, a laminating method or the like is used. In this case, an adhesive layer may be provided between the resins as is usually done in the production of a normal laminate film. The thickness of such a film-like support is usually suitably from 30 to 300 μm from the viewpoint of strength / elongation characteristics and radiation transparency.

The radiation-curable pressure-sensitive adhesive provided on the film-like support is not particularly limited as long as the desired radiation-curing property is exhibited. For example, the radiation-curable pressure-sensitive adhesive has a carbon-carbon double bond with respect to 100 parts by mass of the acrylic pressure-sensitive adhesive. Containing 5 to 300 parts by mass of at least one compound selected from the group of cyanurate compounds and isocyanurate compounds, photoinitiators and polymerization accelerators, other well-known tackifiers, softeners, antioxidants, pigments And the like can be mentioned. In addition, a polyester or polyol urethane acrylate compound having two or more carbon-carbon double bonds may be added to the above compound in order to impart flexibility or the like to the pressure-sensitive adhesive after irradiation.
The acrylic pressure-sensitive adhesive used in the present invention is a homopolymer mainly composed of an ester of acrylic acid or methacrylic acid, or acrylic acid, methacrylic acid, an ester thereof, an acid amide thereof, or other copolymerizable substances. Copolymers with comonomers or mixtures of these polymers. Examples of the monomers and comonomers thereof include alkyl esters of acrylic acid or methacrylic acid, such as methyl ester, ethyl ester, butyl ester, 2-ethylhexyl ester, octyl ester, glycidyl ester, hydroxymethyl ester, 2-hydroxyethyl ester, hydroxypropyl ester And amides of acrylic acid or methacrylic acid and N-substituted amides such as N-hydroxymethylacrylic acid amide or methacrylic acid amide. If necessary, a compound containing a crosslinking agent such as a polyisocyanate compound or an alkyl etherified melamine compound can be used.

Further, the cyanurate or isocyanurate compound is a compound having a triazine ring or an isotriazine ring in the molecule and further having at least two radiation-polymerizable carbon-carbon double bonds, and is a monomer, oligomer or a mixture thereof. It doesn't matter. A compound having a triazine ring or an isotriazine ring can generally be synthesized by a conventional cyclization reaction using a halocyan compound, dianiline compound, diisocyanate compound or the like as a raw material. Furthermore, a compound used in the present invention can be obtained by introducing a functional group containing a radiation-polymerizable carbon-carbon double bond-containing group such as a vinyl group, an acryloxy group or a methacryloxy group into the compound synthesized in this way. .
In the present invention, except for the above points, the cyanurate or isocyanurate compound is not particularly limited, but the carbon-carbon double bond-containing group introduced into the triazine ring or the isotriazine ring is a so-called rigid molecular structure such as an aromatic ring. Those not containing a nodal ring group are desirable. The reason is that the pressure-sensitive adhesive of the present invention becomes excessively brittle due to radiation curing if it imparts excessive rigidity to the radiation-polymerizable compound. Therefore, it is preferable that the bonding group between the carbon-carbon double bond and the triazine ring or the isotriazine ring includes a group rich in free rotation of atoms. Examples of these groups include aliphatic groups such as alkylene groups and alkylidene groups, and these groups may have —O—, —OCO—, —COO—, —NHCO—, —NHCOO— bonds, and the like. Good. When this linking group is bonded to the triazine ring via —O—, at least one of the three alkylene groups, alkylidene groups, etc. bonded to this —O— should have 2 or more carbon atoms.
Specific examples of these cyanurate or isocyanurate compounds include 2-propenyl di-3-butenyl cyanurate, 2-hydroxyethylbis (2-acryloxyethyl) isocyanurate, tris (acryloxyethyl) isocyanurate, tris ( Methacryloxyethyl) isocyanurate, bis (2-acryloxyethyl) 2- (5-acryloxy) hexyloxyethyl isocyanurate, tris (1,3-diacryloxyisopropyl-oxycarbonyl-n-hexyl) isocyanurate, tris (1-acryloxy-3-methacryloxyisopropyl-oxycarbonylamino-n-hexyl) isocyanurate and the like.
The number of radiation-polymerizable carbon-carbon double bonds per repeating unit of the cyanurate compound or isocyanurate compound monomer or oligomer used in the present invention should usually be at least 2, more preferably 2-6. Good. If the number of double bonds is less than 2, a sufficient degree of crosslinking cannot be obtained to reduce the adhesive strength by irradiation, and if it exceeds 6, the brittleness of the adhesive after radiation curing becomes excessive. Sometimes.
The compounding quantity of the cyanurate compound or isocyanurate compound in the radiation-curable adhesive of the present invention is usually 5 to 300 parts by mass with respect to 100 parts by mass of the acrylic adhesive. If this amount is too small, the radiation curable adhesive may be insufficiently cured by irradiation (three-dimensional reticulation), and the exposed portion of the adhesive will be eluted into the etching solution during etching. Not only can contamination of the liquid and the backside of the wafer easily occur, but even if the entire tape is irradiated with radiation after the etching process, sufficient curing of the adhesive cannot be obtained, making it difficult to remove the tape. There is sex. Conversely, if the amount is too large, the pressure-sensitive adhesive after radiation curing becomes too hard and may become brittle.

The urethane acrylate compound that can be added to the above compound to give flexibility in the physical properties of the pressure-sensitive adhesive after irradiation has two or more radiation-polymerizable carbon-carbon double bonds, and the physical properties after radiation curing. And a urethane acrylate compound such as polyester or polyol having a linear aliphatic structure and a urethane bond in the molecule, and may be a monomer or an oligomer.
Examples of such compounds include methacrylic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylamino. Ethyl acrylate, diethylaminoethyl methacrylate, polyethylene glycol acrylate and the like and polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylene diisocyanate, Diphenylmethane-4,4′-diisocyanate or the like can be synthesized as a raw material.

When the radiation curable adhesive tape of the present invention is cured by ultraviolet irradiation, a photopolymerization initiator such as isopropyl benzoin ether, isobutyl benzoin ether, benzophenone, Michler's ketone, chlorothioxanthone, dodecylthioxanthone, dimethylthioxanthone, diethylthioxanthone, benzyl Dimethyl ketal, α-hydroxycyclohexyl phenyl ketone, 2-hydroxymethylphenylpropane and the like can be used in combination. By adding one or more of these to the pressure-sensitive adhesive layer, the curing reaction can be efficiently advanced even if the curing reaction time or the amount of UV irradiation is small, and the adherend fixing adhesive force can be reduced. .
The thickness of the radiation curable pressure-sensitive adhesive layer provided on the film support is usually 10 to 50 μm in order to improve the adhesion to the pattern surface. Here, the radiation means light rays such as ultraviolet rays or ionizing radiations such as electron beams.

In the present invention, first, the radiation curable pressure-sensitive adhesive tape is attached to a protective surface of a material to be subjected to an etching process. Next, the adhesive layer in that portion is cured by irradiating only the peripheral portion of the wafer of the tape with radiation. After the wafer is etched in this state, a cleaning process or the like is performed as necessary, and the entire adhesive layer is cured by irradiating the entire tape with radiation.
However, such partial irradiation still has the problem that the adhesive that has not been irradiated changes in quality due to the heat generated in the etching process, and the adhesive strength is less likely to decrease after the irradiation after the etching process. Has been. However, many of recent etching processing apparatuses are equipped with a cooling mechanism that can control the temperature of the etching solution while suppressing the temperature rise of the etching solution, and the influence of such heat can be substantially ignored.

The irradiation area when irradiating only the peripheral portion of the wafer of the tape before the etching process is desirably an area of 0.1 mm to 3 mm, preferably 0.3 mm to 1 mm from the periphery. If the irradiated area is 0.1 mm or less from the periphery of the wafer, the cured part of the adhesive is too narrow and the etching solution is insufficiently resistant and may be eluted, and if it is 3 mm or more from the periphery of the wafer, the wafer surface There is a high possibility that an integrated circuit pattern is formed, and if the adhesive is irradiated to that portion, there is a possibility that the integrated circuit pattern is destroyed due to penetration of the etching solution.
As a method of irradiating only the peripheral portion of the wafer, it is possible to irradiate a desired region by irradiating a portion other than the irradiation region with a material such as a metal plate that does not transmit radiation.
Curing in the present invention means that the adhesive strength is reduced to such an extent that a sufficient three-dimensional network structure is formed so that the pressure-sensitive adhesive does not elute into the etching solution during the etching process. This curing treatment can be arbitrarily adjusted by appropriately setting the irradiation time. The degree of curing can be set using the adhesive force as an index. Irradiation conditions for the partial irradiation before the etching treatment and the entire irradiation after the etching may be the same, but different conditions may be set as necessary. In any case, it is desirable that the adhesive strength after radiation curing measured based on JIS Z0237 is 2 N / 25 mm or less, for example, as a stainless steel plate obtained by polishing an adherend of radiation curable adhesive tape with water-resistant abrasive paper No. 280. . If it is 2 N / 25 mm or more, resistance to the etching solution may be insufficient, or peeling may be difficult.

EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.
(Example 1)
100 parts by mass of an acrylic pressure-sensitive adhesive (copolymer of 2-ethylhexyl acrylate and n-butyl acrylate) is 3 parts by mass of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Co., Ltd.), and the number of functional groups is 6. A radiation-curable pressure-sensitive adhesive was prepared by adding and mixing 150 parts by mass of an isocyanurate compound and 1 part by mass of α-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator. This radiation-curable pressure-sensitive adhesive is subjected to corona treatment on a film-like support made of a high-density polyethylene resin having a thickness of 100 μm, and applied to the surface so that the thickness after drying becomes 20 μm. An adhesive tape was prepared.
This radiation curable adhesive tape was cut to a width of 25 mm, and a stainless steel plate polished with water-resistant abrasive paper No. 280 was bonded as an adherend, and the adhesive strength before and after UV irradiation was measured based on JIS Z0237 (90 ° peeling, peeling (The speed is 50 mm / min, the ultraviolet irradiation condition is a high-pressure mercury lamp of 80 w / cm as the ultraviolet lamp, the irradiation time is 10 seconds, and the integrated light quantity is 1000 mJ / cm 2. The following examples and comparative examples are based on this method.) .
Also, this radiation curable adhesive tape was bonded as a substrate with a 5 inch diameter silicon wafer on which a circuit pattern was formed from the circumference to a maximum position of 3 mm. With the central portion shielded by an aluminum disc, only the portion from the wafer circumference to 1 mm was irradiated with ultraviolet rays, and the radiation-curable pressure-sensitive adhesive layer in that portion was completely cured. The conditions for this ultraviolet irradiation were the same as described above. Etching solution consisting of a mixture of nitric acid (conc. 61%) and hydrogen fluoride water (conc. 46%) in a tank equipped with a temperature controller so that the heat generated by etching does not rise above 50 ° C. (Mixing ratio is nitric acid: hydrogen fluoride water = 10: 1 by volume ratio) After etching for 5 minutes, the tape state is observed, peeling or floating of adhesive tape, alteration, etc. evaluated.
Next, the wafer was thoroughly washed with water to remove the etching solution, and then the entire wafer was irradiated with ultraviolet rays to completely cure the entire adhesive. The conditions for this ultraviolet irradiation were the same as described above. Thereafter, the adhesive tape was peeled off from the wafer, and the circuit pattern near the wafer was observed with a microscope, and the back surface was also visually observed. These results are shown in Table 1.

(Example 2)
As a radiation curable pressure-sensitive adhesive, 100 parts by mass of an acrylic pressure-sensitive adhesive (copolymer of 2-ethylhexyl acrylate and n-butyl acrylate) and 3 parts by mass of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Co., Ltd.) Radiation curing prepared by adding 80 parts by mass of an isocyanurate compound having 6 functional groups, 20 parts by mass of a urethane acrylate compound having 2 functional groups, and 1 part by mass of α-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator A radiation-curable pressure-sensitive adhesive tape was prepared in exactly the same manner as in Example 1 except that the adhesive was used.
Next, the adhesive force of this radiation curable adhesive tape was measured in the same manner as in Example 1, and the surface of the silicon wafer with a circuit pattern of the same type as in Example 1 was used to protect the surface. Only the 1 mm portion from the periphery of the wafer was irradiated with ultraviolet rays, and then an etching process was performed. Thereafter, the entire wafer was irradiated with ultraviolet rays to perform tape peeling. The observation and evaluation results during that time are shown in Table 1.

(Comparative Example 1)
The radiation curable adhesive tape prepared in Example 1 was bonded to the same silicon wafer with a circuit pattern as in Example 1, and only the part from the wafer circumference to 5 mm was irradiated with ultraviolet rays in the same manner as in Example 1. After that, an etching process was performed, and then the entire wafer was irradiated with ultraviolet rays to peel off the tape. The observation and evaluation results during that time are shown in Table 1.

(Comparative Example 2)
Except that the radiation curable adhesive tape prepared in Example 1 was used, etching was performed without irradiating the wafer with ultraviolet rays, and then the entire wafer was irradiated with ultraviolet rays to remove the tape. It was done. The observation and evaluation results during that time are shown in Table 1.

As is apparent from the results in Table 1, according to the present invention, adhesive residue at the wafer peripheral portion can be prevented, the circuit pattern portion is not altered, and the back surface of the wafer is not contaminated by the dissolution of the adhesive. .

The surface protection method of the present invention provides a method for preventing adhesive residue of the protective tape and alteration of the semiconductor wafer due to an etching solution when a surface protection tape is bonded to a semiconductor wafer, and grinding and etching are performed.

Claims (1)

A method for protecting a surface during chemical etching of a wafer, wherein a radiation curable adhesive tape is attached to the back surface of the wafer to be etched, and a predetermined area is formed along the entire circumference of the wafer of the adhesive tape. A method for protecting a surface of a wafer, comprising: curing the film by radiation irradiation, performing an etching process, and further curing the entire adhesive tape by radiation curing.