Electric heating – Metal heating – By arc
Reexamination Certificate
2000-10-23
2003-05-13
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121690
Reexamination Certificate
active
06563079
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for processing a work, by using laser, on a base such as a silicon substrate, and particularly relates to a perforating process for forming a hole such as a through-hole, or the like, or a grooving process.
BACKGROUND ART
A process such as a process of perforating a base such as a silicon substrate by laser light radiation has been performed heretofore. For example, a process of forming a through-hole by irradiation of a semiconductor wafer with a laser light has been performed. In the processing for formation of such a through-hole by laser light radiation, however, the quality of the processed hole was poor because distortion owing to heat generated at the time of laser machining remained in an inner wall surface of the processed hole or because a dissolved substance was deposited on the inner wall surface of the processed hole. Moreover, there was a problem that reliability was lowered because a scattered product (called “dross” or “debris”) was generated at the time of laser machining and deposited on the periphery of the base.
Moreover, when the hole width was to be enlarged by using a laser light alone, it was necessary to increase laser power or elongate the processing time. In addition, there was another problem that processing accuracy was worsened because a through-hole was bent and distorted when the through-hole was formed by use of a laser light. Further, there was a further problem that, when the through-hole was to be formed by etching alone, a through-hole with a high aspect ratio could not be formed because of the crystal orientation of silicon.
DISCLOSURE OF THE INVENTION
A work of the present invention is to provide a method for processing a work in which a processed hole with a high aspect ratio can be formed by laser machining.
Another work of the present invention is to provide a method for processing a work in which heat distortion remaining inside a processed hole or a dissolved substance deposited on the processed hole can be removed by laser machining.
A further work of the present invention is to provide a method for processing a work in which the processed hole obtained by laser machining can be enlarged easily.
A further work of the present invention is to provide a method for processing a work in which dross produced at the time of laser machining can be removed easily.
A further work of the present invention is to provide a method for processing a work in which processing accuracy can be improved without occurrence of any situation in which the through-hole produced by laser machining is bent and distorted.
(1) According to an aspect of the present invention, there is provided a method for processing a work, comprising the steps of: forming a prehole by irradiation with a laser light; and performing anisotropic etching to thereby enlarge the prehole. Wet etching (anisotropic etching) which greatly varies in etching speed depending on the crystal orientation of silicon is preferably used as the anisotropic etching when a silicon substrate is used as the base. Hence, the following effects are obtained in the present invention.
{circle around (1)} After a prehole is formed by laser light radiation, the prehole is enlarged by anisotropic etching. Hence, a hole or the like with a high aspect ratio can be obtained without any limitation that it is difficult to form a relatively narrow hole with respect to the thickness.
{circle around (2)} Further, when such a hole is to be processed by laser machining alone, either the processing time must be elongated or laser power must be increased. However, because the prehole is enlarged by anisotropic etching, a batch process can be performed. Hence, the processing time can be shortened. Moreover, the variations in diameter among the processed hole shapes are small, so that the holes are formed uniformly.
{circle around (3)} Moreover, enlargement of the hole diameter (hole width) of the hole shapes can be adjusted at option by adjustment of the time required for anisotropic etching.
{circle around (4)} Moreover, dross and processing dust remaining on the inner wall which are produced by laser light radiation can be removed automatically when anisotropic etching is performed.
{circle around (5)} Roughness of the inner wall surface owing to laser machining is removed by anisotropic etching. When the base is made of silicon, a smooth crystal surface of silicon is exposed. Hence, when, for example, a through-hole is formed to be used as a fluid channel for a fluid, the inner wall surface of the through-hole presents no obstacle to the fluid. On the other hand, when a through-hole is formed in a semiconductor wafer in order to electrically connect front and rear surfaces of the semiconductor wafer to each other, various thin films such as an electrically insulating film, an electrically conducting film, etc. must be formed on the inner wall surface. In this case, because a smooth inner wall surface can be obtained as described above, each of the various thin films can be also formed uniformly and thinly.
{circle around (6)} Because a place needing to be subjected to etching can be exposed by laser light radiation, a process of forming an opening in a protective film by photolithography may be omitted. Hence, production cost can be reduced.
(2) According to another aspect of the present invention, in the method for machining a work to be machined as stated in the above paragraph (1), a protective film is formed on the base and the base is irradiated with a laser light through the protective film. Dross is produced when machining is performed by laser light radiation. The dross is deposited on the base and the protective film but it can be removed easily by etching at the time of enlargement of the processed hole. Hence, high reliability is obtained.
(3) According to another aspect of the present invention, in the method for machining a work to be machined as stated in the above paragraph (2), an opening portion is formed in the protective film and a portion of the opening portion where the base is exposed is irradiated with a laser light.
(4) According to another aspect of the present invention, in the method for machining a work to be machined as stated in the above paragraph (2) or (3), the base is irradiated with a circularly polarized laser light. Because the base is irradiated with such a circularly polarized laser light, the processed hole can be formed straightly. Hence, the width of the hole after etching can be reduced more, and processing accuracy is improved.
(5) According to another aspect of the present invention, in the method for machining a work to be machined as stated in the above paragraph (2) or (3), the base is irradiated with a randomly polarized laser light. Because the base is irradiated with such a randomly polarized laser light, the processed hole can be formed straightly. Hence, the width of the hole after etching can be reduced more, and processing accuracy is improved.
(6) According to another aspect of the present invention, in the method for machining a work to be machined as stated in any one of the above paragraphs (1) through (5), the laser light is scanned to thereby form continuous preholes. The work to be machined can be machined into the form of a groove by the aforementioned process.
(7) According to another aspect of the present invention, in the method for machining a work to be machined as stated in any one of the above paragraphs (1) through (6), the prehole is enlarged by the anisotropic etching to thereby form a through-hole. Hence, the following effects can be obtained in the present invention.
{circle around (1)} After a prehole is formed by laser light radiation, the prehole is enlarged by anisotropic etching to thereby form a through-hole. Hence, a through-hole with a high aspect ratio can be obtained without any limitation that it is difficult to form a relatively narrow hole with respect to the thickness.
{circle around (2)} Further, when such a through-hole is to be formed by laser machining alone, either the
Amako Jun
Arakawa Katsuji
Umetsu Kazushige
Yotsuya Shinichi
Elve M. Alexandra
Johnson Jonathan
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