Electrochemical fine processing apparatus

Abstract: An electrochemical fine processing apparatus for electrochemically performing an adding processing and a removing processing of a substance such as a metal or a polymer in a solution in order to produce a structure necessitating a high aspect ratio. Removing electrodes (3) for applying an electric potential opposite to that of an addition electrode (2) are disposed around the addition electrode, thereby an excess portion of metal or polymer film pattern can be scraped electrochemically. In addition, alternate electric potentials are applied successively for each pulse to the addition electrode and next to removing electrodes. It becomes possible to form on the sample a structure with sharp pattern end portion and high aspect ratio.

Description: BACKGROUND OF THE INVENTION The present invention relates to an electrochemical fine processing apparatus for electrochemically performing the removing processing and the adding processing of metal or polymer in a solution in order to produce a structure necessitating a high aspect ratio. It is especially used in a field in which the structure is manufactured using the micromachining technique. Electrochemical processing apparatusses and corresponding methods for treating one side only of a substrate are for example known from GB - 1 258 809, which discloses a method of electrolytically treating one side only of a metal article maintained at earth potential, as well as from US-3 989 604, which discloses a method for producing galvanized metal sheet or strip material having a zinc coating on one side only. One example of a conventional fine processing method is shown in Figs. 3A - 3D. This fine processing method uses photolithography represented by the semiconductor process (subtractive method). At first, a desired thin film 11 is formed on a substrate 10 such as silicon or the like using the sputtering method or the CVD method (Fig. 3A). Next, a resist 12 is formed by spin coating or the like, the shape of a structure is exposed onto the resist 12 using a mask or an electron beam, and the development is performed (Fig. 3B). Further, an extra thin film is removed using an etching liquid (Fig. 3C), and the resist 12 is removed to form the structure 13(Fig. 3D). In addition, in a fine processing method called the LIGA process, a photo-resist for X-ray thickly coated on a substrate is exposed by X-ray having strong linearity and strength generated from synchrotron radiation light, thereby the resist can be formed deeply with a good pattern accuracy. Metal is formed between this pattern by means of electrocasting, and the resist is removed, thereby a structure having a high aspect can be obtained. However, in the conventional fine processing method, although the resolution in an order of sub-micrometres of the pattern can be achieved, it is difficult to perform film formation in the height direction, and it has been difficult to obtain a high aspect ratio. In addition, in the LIGA process, the equipment of a synchrotron is necessary, which cannot be used easily, resulting in a problem of increase in cost. Thus, there is also such a method by an electrochemical reaction in which a sample is allowed to approach a counter electrode with close distance, the sample being used as an acting electrode, and an addition electrode being used as a counter electrode, an electric current is allowed to flow between the addition electrode and the sample, thereby an electrochemical reaction is caused on the sample close to the addition electrode, so that metal or polymer is deposited on the sample, however, in such a method by the electrochemical reaction, as shown in Fig. 4, a high aspect ratio can be obtained, but a deposited substance 5 (metal and polymer) exhibits a film thickness distribution having no sharpness as shown in the figure. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrochemical fine processing apparatus for forming a metal or polymer film pattern having a high aspect ratio and a clear pattern edge by an electrochemical reaction. In order to achieve the above-mentioned object, there is added a removing electrode for applying an electric potential opposite to that of an addition electrode around the addition electrode, thereby an excess portion of metal or polymer film pattern can be scraped electrochemically. In addition, an electric potential is applied successively for each pulse to the addition electrode and next to removing electrodes around the addition electrode, thereby with respect to the deposition of the metal or polymer film pattern and around the deposition portion, an electric potential opposite to that of the addition electrode is applied, thereby the metal or polymer film pattern can be scraped electrochemically. The counter electrode, which consists of the addition electrode and the removing electrode, is allowed to approach the sample. The electric current is flown between the addition electrode and the sample. Deposition of the metal or polymer is made by the electrochemical reaction. In addition, the removing electrodes exist around the addition electrode, to which the electric potential opposite to that of the addition electrode is applied, thereby the metal or the polymer film pattern is scraped. By scanning the counter electrode above the sample, an optional pattern can be formed on the sample. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross-sectional view of the counter electrode used for the fine processing apparatus of the present invention; Fig. 2 is a lateral cross-sectional view of the counter electrode used for the fine processing apparatus of the present invention; Figs. 3A - 3D are explanatory views showing the conventional fine processing method by the photolithography. Fig. 4 is an explanatory view of the conventional film formation using the addition electrode only; Fig. 5 is an illustrative view of the fine processing apparatus of the present invention; and Figs. 6A - 6C are explanatory views showing the pattern formation method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An example of this invention will be explained hereinafter on the basis of drawings. Fig. 1 shows a cross-sectional view of a structure of a counter electrode 1 constituted by an addition electrode 2 and removing electrodes 3. The counter electrode 1 consists of the addition electrode 2 for performing film formation, the removing electrodes 3 for making the edge of a pattern to be sharp, and an insulation tube 4 for supporting the addition electrode 2 and the removing electrodes 3. For the addition electrode 2 and the removing electrodes 3, a metal such as tungsten, platinum or the like is used. The addition electrode 2 and the removing electrodes 3 have the structure to be supported by passing through the insulation tube 4. The addition electrode 2 and the removing electrodes 3 have the structure to be covered by an insulator as thoroughly as possible. Around the addition electrode 2, the removing electrodes 3 for applying an electric potential of opposite polarity to that of the addition electrode 2 are supported by the insulation tube separated with a gap of 10 µm with respect to the addition electrode 2. The diameter of the addition electrode 2, which may be changed depending on a width of film formation, has been performed at 500 µm in this case. The structure of the addition electrode 2 and the removing electrodes 3 and the method of the film formation will be explained using Fig. 2. The structure is such that the removing electrodes 3a - 3d are provided around the addition electrode 2. Four removing electrodes 3a - 3d are provided so as to surround the addition electrode 2. The method of film formation is performed by controlling the counter electrode 1 in accordance with scanning directions. For example, in the case of driving in the X direction, an electric current is allowed to pass through the addition electrode to perform film formation, and then an electric current of opposite direction is allowed to pass through the removing electrodes 3b and 3d, so as to scrape the film under the removing electrodes 3b and 3d. During this period, no electric current is allowed to pass through the other removing electrodes 3a and 3c. By scanning in the X direction while performing the film formation, thereby the both sides of the pattern are clearly formed. When the film formation is performed in a diagonal direction, for example, an electric current is allowed to pass through the addition electrode 2 to perform film formation, thereafter an electric current of opposite direction is allowed to pass through the removing electrodes 3c and 3d, and the film under the removing electrodes 3c and 3d is scraped. In the case of scanning in the diagonal direction, the control of the width of the pattern is determined by the number of the circumferential electrodes, so that it is necessary to determine the number of the removing electrodes 3a - 3d and the control method suitable for pattern accuracy. In addition, by providing the removing electrodes 3a - 3d with a rotation mechanism, it is also possible to make them move to a portion desired to be removed and perform removal processing. Fig. 5 shows an illustrative view of a fine processing apparatus according to this invention. An electrochemical cell is constituted in a container 20 by a sample 14, a reference electrode 30, and the counter electrode 1 consisting of the addition electrode 2 and the removing electrodes 3. Further, the sample 14, the reference electrode 30, and the counter electrode 1 consisting of the addition electrode 2 and the removing electrodes 3 are electrically connected to a potentiostat 21. The sample 14 may be either an electrically conductive substance or an insulator in which being coated with an electrically conductive substance. The reference electrode 30 is an electrode for generating an electric potential to serve as a standard for the case of controlling electric potential of the counter electrode in the electrochemical reaction, for which the saturated calomel electrode (SCE) or the silver - silver chloride electrode is generally used. For the electrodes for constituting the additon electrode 2 and the removing electrodes 3, tungsten or platinum is used. The electrochemical cell of the present invention is installed on a vibration-removing stand 15 in order to suppress the distance fluctuation between the sample 14 and the addition electrode 2 and the removing electrodes 3. The movement of the counter electrode 1 includes the X, Y movement and the Z movement. The X, Y movement is performed by a coarse movement mechanism not shown in the figure (for example, a magnet mechanism). The Z axis movement has been performed using a coarse mechanism (not shown in the figure, for example, a ball nut screw) and a fine movement mechanism (not shown in the figure, for example, a piezoelectric element). By using a piezoelectric element for the fine movement mechanism, the movement control in an order of several micrometres is performed by controlling the voltage applied to the piezoelectric element, and those larger than the above are performed by the coarse movement mechanism. By controlling the Z axis as described above, a structure having a high aspect ratio can be obtained. With respect to the movement of the counter electrode 1, it becomes possible to move along the X, Y and Z axes direction. A chromium film formation method will be explained using the apparatus of the present invention. A mixed solution of chromic acid and sulfuric acid is poured into the container 20, in which the sample 14, the reference electrode 30 and the counter electrode 1 are immersed, so as to constitute an electrochemical cell. Further, the sample 14, the reference electrode 30 and the counter electrode 1 are connected to the potentiostat 21. The tip of the counter electrode is moved to a position at which the processing of the sample is intended to be performed by means of the X-Y movement mechanism. At the processing portion, using the Z axis movement mechanism, the counter electrode 1 is allowed to approach the sample (see Fig. 6A). Next, using the potentiostat 21, the electric potential of the addition electrode 2 is set to an electric potential at which the substance is deposited from the solution onto the sample 14. By doing so, the electrochemical reaction occurs in the vicinity of the tip of the addition electrode 2, and a thin film of chromium is formed on the sample surface. Next, an opposite electric potential is applied to the removing electrodes 3, thereby the formed thin film is removed. When such operation is effected to the addition electrode 2 and the removing electrodes 3 successively for each pulse, the addition processing and the removing processing can be performed, and a pattern with sharp pattern end portion is obtained. When a desired pattern is formed, using the Z axis movement mechanism (not shown in the figure), the counter electrode 1 is allowed to approach the sample as shown in Fig. 6A, subsequently an electric potential is applied to the addition electrode 2 to deposit metal or polymer film, and the opposite electric potential is applied by the removing electrodes 3 so as to scrape the pattern end portion. And the counter electrode 1 is scanned by the X-Y movement mechanism (not shown in the figure), thereby the desired pattern can be formed (see Fig. 6B and 6C). In this invention, as explained above, in the electrochemical cell in which the sample 14, the counter electrode 1 and the reference electrode 30 are installed in the solution, the sample 14 is allowed to approach the addition electrode 2 of the counter electrode 1 in a close distance, and the electric current is allowed to flow between the sample 14 and the addition electrode 2, thereby the electrochemical reaction is performed to deposit the metal or polymer film pattern on the sample 14, there are added the removing electrodes 3 for applying the electric potential opposite to that of the addition electrode 2 around the addition electrode 2, thereby the metal or polymer film can be scraped, so that there is such an effect that a structure which has sharp pattern end portion with high aspect ratio due to electrochemical reaction can be obtained.

Claims: An electrochemical fine processing apparatus for forming a fine pattern having a high aspect ratio and a clear pattern edge on a sample (14) to be processed, said apparatus comprising: an electrolytic solution filled in a container (20) for soaking the sample (14) to be provided in the container (20); an addition electrode (2) disposed to be dipped in said electrolytic solution in close proximity to the sample for effecting deposition of a substance from said electrolytic solution on the sample (14) by electrochemical reaction when a first potential is applied to said addition electrode (2); a removing electrode (3) disposed adjacent to said addition electrode (2) to be dipped in close proximity to the sample (14) for scraping a part of the deposited substance on the sample (14) by electrochemical reaction when a second potential is applied to said removing electrode (3), wherein the second electric potential is of opposite polarity to the first electric potential; and potential supplying means electrically connected to said addition electrode (2) and said removing electrode (3) for applying the first electric potential to said addition electrode (2) and the second electric potential to said removing electrode (3), respectively. An apparatus according to claim 1, wherein a plurality of said removing electrodes (3) are disposed around said addition electrode (2). A method for electrochemical fine processing of a sample by use of an apparatus according to claim 1 or 2, wherein said potential supplying means alternately applies the first electric potential to said addition electrode (2) for depositing the substance and the second electric potential to said removing electrode (3) for scraping a part of the deposited substance, and wherein said addition electrode (2) and said removing electrode (3) are moved above the sample to form a predetermined pattern of the structure. A method according to claim 3, wherein the substance deposited on the sample (14) is a metal. A method according to claim 3, wherein the substance deposited on the sample (14) is a polymer.

Inventors: IWASAKI FUMIHARU, SAKUHARA TOSHIHIKO, SHINOGI MASATAKA, SUDA MASAYUKI, IWASAKI, FUMIHARU, SAKUHARA, TOSHIHIKO, SHINOGI, MASATAKA, SUDA, MASAYUKI, IWASAKI, FUMIHARU, C/O SEIKO INSTRUMENTS INC., SAKUHARA, TOSHIHIKO, C/O SEIKO INSTRUMENTS INC., Shinogi, Masataka, c/o Seiko Instruments Inc., Suda, Masayuki, c/o Seiko Instruments Inc.
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1993
Main classification: C25F3
IPC codes: C25D7, B23H7, C25D5, C25F3, C25F7, C25D17, C23F4, B81C99