A semiconductor device is ordinarily produced by a method in which high purity silicon monocrystal or the like is sliced to produce a wafer and, then, an integrated circuit is embedded in the thus-produced wafer by ion implantation, etching or the like and, thereafter, the wafer thus embedded with the integrated circuit is subjected to back side grinding processing in which a side of the wafer is mechanically ground by means of grinding, lapping, polishing or the like to allow it to be thin and, subsequently, the thus-ground wafer is subject to dicing processing to produce a chip. Ordinarily, in order to avoid breakage or contamination of the wafer in a step of grinding the back side of the wafer among these steps as described above, a surface protecting adhesive film for a semiconductor wafer has been used.
Specifically, a surface protecting adhesive film for a semiconductor wafer is adhered to a surface of a semiconductor wafer via an adhesive layer thereof to protect the wafer surface and, then, a back side of the wafer is mechanically ground. After such grinding, a chemical treatment step may subsequently be carried out on the back side of the wafer as required. After these steps of processing the back side are completed, the adhesive film is peeled away from the wafer surface.
As one of performances required for such a surface protecting adhesive film for a semiconductor wafer as described above, there can be mentioned prevention of penetration of cooling water (hereinafter referred to also as grinding water) used in grinding a back side of a semiconductor wafer. There has been a case in which an unevenness hollowed in a shape of groove from the outermost portion of a wafer derived from a coating layer made of polyimide or the like, a vapor deposited layer such as a silicon oxide layer, a silicon nitride layer or the like, a scribe line (dicing street) or the like is present on a wafer surface. Ordinarily, the depth of the unevenness hollowed in a shape of groove is about from 2 μm to 20 μm. In grinding a back side of a semiconductor wafer in which the unevenness present on the wafer surface reaches to the outermost portion of the wafer, if an adhesiveness to the unevenness of an adhesive layer is not sufficient, grinding water might be entered through the unevenness in some cases. In case grinding water is entered between the wafer surface and an adhesive film through the unevenness, the adhesive film begins to be peeled away from the wafer surface by the thus-entered grinding water and such penetration of grinding water becomes accelerated between the wafer surface and the adhesive layer so that it tends to contaminate a whole surface of the integrated circuit by a grinding dust entered along with grinding water. At worst cases, a surface protecting adhesive film is totally delaminated during the grinding processing on the back side under the influence of the penetrated grinding water, thereby resulting in wafer breakage in some cases.
In order to prevent such a problem, a device to enhance adhesiveness between the unevenness of the wafer surface and the adhesive layer by heightening a thickness of the adhesive layer of the adhesive film has been required. However, in using this device, as an adhesive force to the wafer surface of an adhesive film was increased more than strength of the wafer, the peeling trouble happened in an automatic detaping machine when the adhesive film was peeled away from the wafer surface after back grinding depending on various conditions such as the thickness of the wafer and shape of the surface and the like; therefore, workability became deteriorated or the semiconductor wafer was completely broken in some cases. Further, there were cases where the depth of the unevenness was exceeding 20 μm depending on the wafer types. In order to handle such wafers, when the adhesive layer was made thicker, productivity of the adhesive film was worsened thereby increasing a production cost, which made it difficult to provide an inexpensive adhesive film. Therefore, this has not been a practical solution.
As a device to solve a problem of penetration of grinding water in grinding on the back side as described above, JP60-189938A discloses a protecting method for a semiconductor wafer in which a pressure-sensitive adhesive film is adhered to the wafer surface in grinding on the back side of a semiconductor wafer and after the wafer back side is ground, the adhesive film is peeled, wherein the pressure-sensitive adhesive film is made of a light transmitting supporting body and a pressure-sensitive adhesive layer having a property capable of curing by light irradiation formed on the light-transmitting supporting body to form a three-dimensional network and light irradiation is carried out to the adhesive film before peeling the adhesive film after grinding.
The protecting method of a semiconductor wafer disclosed in the above-mentioned invention might reduce an adhesive force to the wafer surface of an adhesive film by means of a light irradiation before peeling, and an adhesion to the wafer surface can be greatly heightened during grinding without considering workability at the time of peeling and the breakage of the wafer so that a problem in penetration of grinding water and grinding dust between the above-described wafer surface and the adhesive layer can be solved.
However, the adhesive film comprises low molecular weight compounds such as light initiator, photo-curable oligomer and the like in the adhesive layer in order to give a property to cure by light irradiation and to form a three-dimensional network to the pressure-sensitive adhesive layer. The adhesive layer may not be sufficiently cured depending on various conditions such as the shape of a wafer surface, strength or time of light irradiation, or the like in some cases. An adhesive residue problem may occur due to these low molecular weight compounds remained unreacted on the wafer surface after peeling in some cases. In order to prevent this problem, it is required to fill a light-irradiating device with inert gas such as nitrogen or the like, thereby causing problems of increasing a production cost, and at the same time making process large and complicated.
Further, in a publication of JP05-335288A is disclosed a protective member for a semiconductor wafer characterized in that a pressure-sensitive adhesive layer is provided on the supporting sheet and gel fraction of the pressure-sensitive adhesive layer is 40% or more, and a water-soluble polymer is included. The protective member (adhesive film) for the semiconductor wafer disclosed in this invention comprises a water soluble polymer on a pressure-sensitive adhesive layer, which enables a rinsing treatment in a sufficiently clear and clean manner by directly rinsing with water without pre-rinsing with an organic solvent after peeling the protective member away from a circuit pattern-formed surface or the like. Therefore, the above rinsing with an organic solvent can be omitted. Further, protective functions such as prevention of penetration of water into the adhesive interface, contamination of a circuit pattern-formed surface due to an adhesive residue, breakage of the wafer by the peeling at the time of grinding processing on the wafer back side and the like are disclosed. Also is disclosed that the easiness of peeling is satisfactory to prevent breakage of a grinding wafer at the time of peeling and a water soluble polymer attached on the semiconductor wafer by bleed can be easily cleaned with a water rinsing as well.
However, when this protective member was used for protecting the wafer surface in grinding the back side of a semiconductor wafer, a cohesive force of the adhesive layer was deteriorated due to a bled water soluble polymer and an adhesive residue was generated due to breakage of cohesion in peeling the protective member from the wafer depending on various conditions such as shape of the wafer surface, back grinding conditions, peeling conditions and the like, thereby contaminating the wafer surface in some cases. Such an adhesive residue resulting from breakage of cohesion might not be completely removed even by water rinsing, thereby causing problems of packaging failure or the like in post-processing in some cases.
In recent year, thinning of semiconductor integrated circuit chips for hand-held information terminal, IC cards and the like has been in high demand. The thickness of the semiconductor wafer used for the above-described purposes has been generally thinned less than 200 μm by the back grinding processing and the wafer has been ground until it has been thinned as low as about 50 μm in some cases. The thinner the thickness is after grinding, it takes more time for grinding, which means the time to expose to cooling water in grinding. Accordingly, contamination or breakage of the wafer becomes much higher due to penetration of water during the foregoing grinding under the grinding conditions to thin the wafer until the thickness becomes 200 μm or less. Further, the shape of the integrated circuit surface tends to be complicated according to high performance of the chip and technical innovation of the semiconductor production process and even the unevenness of a wafer surface having a depth of more than 20 μm appears. Some might reach to about 50 μm.
In addition, in a publication of JP05-335411A is disclosed a method of producing a semiconductor chip in which the wafer is ground from the back side after grooves having predetermined depth are formed from the surface of the wafer. Depth of grooves formed on the wafer used for such a method of producing a semiconductor chip is various depending on the thickness of the chips. Depth ranges from about 30 μm for a thin groove to 200 μm or more for a deep groove. A protecting adhesive film for a semiconductor wafer has been needed, which can be used free from a possibility of contamination or breakage of the wafer due to penetration of water during the grinding processing even in a wafer where grooves having a predetermined depth from the surface used for such a method of producing of a semiconductor chip are formed.
Under these circumstances, on a surface protecting adhesive film for a semiconductor wafer, as an unevenness formed on the wafer surface is deep, grinding water is easily penetrated into the wafer through the unevenness or the thickness becomes thin after grinding and the wafer is exposed to grinding water for a long time, it has been required that an invention satisfies a performance of preventing penetration of water, which enables to effectively prevent penetration of water from the circuit surface at a higher level under grinding conditions that might highly be subject to penetration of water.
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