As the electronic and electric appliances are reduced in size recently, component parts are also reduced in size and advanced in definition, and high definition and high precision are demanded in machining of parts at machining precision of +/−50 μm or less. In the conventional press processing or blanking process, the precision is about +/−100 μm at most, and such demand cannot be satisfied. Drilling of materials is also demanded to conform to high definition and high precision, and drilling by using conventional drill or die cannot meet the needs.
To solve the problems, lately, machining of materials by using laser beam is attracting wide attention. In particular, the machining method by ultraviolet absorption ablation of laser beam of small heat damage and high definition is noticed as precise outline processing method or fine drilling method.
By using laser beam, however, carbon deposits and other decomposition matter generated from the work, pressure-sensitive adhesive tape or absorption plate during laser processing may stick to the surface of the work. It hence requires an aftertreatment called desmearing to remove the decomposition products. For example, in the case of wet desmearing by using aqueous solution of potassium permanganate, the environmental pollution is increased due to treatment of the waste liquid.
Sticking strength of decomposition products increases in proportion to the laser beam power. Accordingly, in the case of laser processing at high laser power, it is hard to remove decomposition products in aftertreatment.
On the other hand, if a specified region of the work is cut off at once, the work (cut piece) drops off immediately after processing, and handling is difficult. To avoid this, part of the specified region is left over without being processed.
As a specific example of laser processing, a dicing method of semiconductor wafer is disclosed, for example, Japanese Laid-open Patent No. 2002-343747. In this method, the work is supported and fixed on a dicing sheet, and the work is diced by laser beam. As described in this patent reference 1, the dicing sheet comprises a base material including a support sheet, and a pressure-sensitive adhesive layer disposed on one side of the base material. Further, the pressure-sensitive adhesive layer can be cut off by laser beam, while the support sheet cannot be cut off by laser beam.
When using the dicing sheet disclosed in this publication, the pressure-sensitive adhesive layer is thermally cut off by fundamental wave (wavelength 1064 nm) of YAG laser being used, or laser beam of ruby laser (wavelength 694 nm). Accordingly, a decomposition product of the pressure-sensitive adhesive layer may invade into the interface of the dicing sheet and the work, and may stick firmly to the interface area. As a result, it becomes difficult to peel off the dicing sheet from the work after application of laser processing. It is hence hard to remove the deposit completely by aftertreatment. Further, since the process includes a thermal process, edge portions are exposed to thermal damages. As a result, the processing precision is lowered and the reliability also declines.
A laser processing method combining fundamental wave of YAG laser and water microjet has been also proposed (Japanese Laid-open Patent No. 2003-34780). As disclosed in this publication, the pressure-sensitive adhesive tape for laser dicing has a non-radiation curing type pressure-sensitive adhesive layer and a radiation curing type pressure-sensitive adhesive formed on one side of the base material, and the base material can pass jet water stream of water jet, and the non-radiation curing type pressure-sensitive adhesive layer is provided between the base material and the radiation curing type pressure-sensitive adhesive layer.
When this pressure-sensitive adhesive tape is combined with the water microjet and laser, and used in a dicing method of semiconductor wafer, thermal damage of pressure-sensitive adhesive tape is lessened by the cooling effect of the water jet. Accordingly, it is expected to suppress melting or decomposition of pressure-sensitive adhesive layer or base material by heat of laser irradiation. However, when the pressure-sensitive adhesive tape is used in the dicing method of semiconductor by using only the laser, the pressure-sensitive adhesive layer or base material may be melted by the heat of laser irradiation, and the decomposition products of pressure-sensitive adhesive layer or base material may invade into the interface of the pressure-sensitive adhesive sheet and semiconductor wafer, and may stick firmly to the interface area, and similar problems as mentioned above may occur. When using water microjet, there is a limit in reducing the cutting width in dicing. This is because the cutting width is limited by the diameter of the water jet. Hence, the manufacturing efficiency of semiconductor chips is lowered.