Method of producing microscopic structure

Abstract: A method of producing a microscopic structure by anisotropic etching, in which ion etching of irradiating over a workpiece (18), an ion beam (25) emitted by an ion source (14) is performed while a direction of progress of the ion etching is being changed.

Description: The present invention relates to a method for producing a microscopic structure as defined in the preamble in claim 1. For producing the microscopic structure, the LIGA (Lithographie, Galvanoformung, Abformung) process is known which is being developed in Germany. Figs. 1(a) to 1(d) show steps of the LIGA process in which reference numeral 1 denotes a metallic substrate, reference numeral 2 denotes a PMMA (polymethyl methacrylate) resist film coated thickly on the metallic substrate 1, reference numeral 3 denotes a masking substrate, reference numeral 4 denotes a masking pattern, reference numeral 5 denotes synchrotron radiation and reference numeral 6 denotes electroformed nickel. The synchrotron radiation 5 is emitted by a synchrotron (not shown) and is a powerful X-ray whose beam has narrow spread. In the known LIGA process, a microscopic metallic member is produced in the following steps (a) to (d) corresponding to Figs. 1(a) to 1(d), respectively. (a) The PMMA resist film 2 is deeply exposed through the masking pattern 4 by the synchrotron radiation 5 as shown by the broken lines in Fig. 1(a). (b) The exposed portions of the PMMA resist film 2 are removed by development such that cavities are formed in the PMMA resist film 2 as shown in Fig. 1(b). (c) Nickel 6 is filled in the cavities of the PMMA resist film 2 by electroforming as shown in Fig. 1(c). (d) The PMMA resist film 2 is removed and thus, the electroformed nickel 6 remains on the metallic substrate 1 as shown in Fig. 1(d). In the above known method, it is possible to obtain a microscopic metallic structure having a high aspect ratio but its cross-sectional shape is restricted to a rectangular shape formed by parallel lines defined by the synchrotron radiation. Therefore, the known method has the drawback that since three-dimensional shape of the structure is limited, a structure having an arbitrary three-dimensional shape cannot be obtained, thus resulting in lack of versatility in use. JP-A-56 137636 as cited in Patent Abstracts of Japan, Vol. 6, No. 16, discloses a method of producing a microscopic structure by anisotropic etching, wherein ion etching is performed by irradiating an ion beam emitted by an ion source over a workpiece while the direction of progress of the ion etching is being changed. JP-A-02 003248 as cited in Patent Abstracts of Japan, Vol. 14, No. 139 discloses a method of producing a microscopic structure by anisotropic etching in which the direction of progress of the ion etching is being changed by changing the angle of incidence of the ion beam relative to the workpiece. The ion beam is rectilinearly emitted by an ion source. It is the object of the present invention to provide a method of producing a microscopic structure having three-dimensional shape of a high degree of freedom. This object is attained by a method as defined in claim 1. A particularly preferred embodiment of this method is described in the subclaim. By the method of the present invention, a three-dimensional structure having a high degree of freedom of shape can be obtained including cross-sectional shapes such as gradients in combination with straight lines and curves. Further objects of the present invention will become apparent from the following description of preferred embodiments thereof as shown in the accommpanying drawings. It is noted that the method of the present invention as defined in the main claim comprises forming at least another resist on the workpiece prior to changing the angle of incidence of the ion beam relative to the workpiece. Drawings not including such formation of at least another resist are intended to demonstrate beneficial effects not relating to the number of resists without broadening the scope of protection defined by the main claim. Figs. 1(a) to 1(d) are views showing steps of the prior art method of producing a microscopic structure (already referred to); Fig. 2 is a schematic view of an ion etching machine used for carrying out a method of producing a microscopic structure, according to a first embodiment of the present invention; Figs. 3 to 7 are views showing various examples of steps of the method of Fig. 2, respectively. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings. Referring now to the drawings, there is shown in Fig. 2, an ion etching machine used for carrying out a method of producing a microscopic structure, according to the present invention. In Fig. 2, air is exhausted from a vacuum chamber 11 in the direction of the arrow 13 through an opening 12 by a pump (not shown). Argon gas is fed into a Kaufmann type ion source 14 in the direction of the arrow 16 through a pipe 15. In the ion source 14, argon gas is electrically discharged between a filament cathode and a cylindrical anode and generated Ar + ion is passed through a grid so as to be outwardly drawn in the direction of the arrow 17 as an accelerated parallel ion beam 25. A workpiece 18 is secured to a support 19 which can be rotated in the direction of the arrow 21 by a motor 20. The motor 20 itself is rotatably supported by a shaft 22 so as to be rotated about the shaft 22 in the direction of the arrow 24 by a motor 23. By the above described arrangement of the ion etching machine, the workpiece 18 can be etched by setting the angle of the workpiece 18 relative to the ion beam 25 to an arbitrary value in two degrees of freedom. Meanwhile, it is also possible to emit the ion beam 25 while the motors 22 and 23 are being driven, namely, while posture of the workpiece 18 is being changed. Hereinbelow, five examples of steps of the method of producing the microscopic structure by using the ion etching machine of Fig. 2, according to the present invention are described with reference to Figs. 3 to 7, respectively. In the first example, Figs. 3(a) to 3(c) show the following steps (a) to (c) of the method according to the present invention, respectively. (a) A substrate 31 is secured to the support 19 of Fig. 2. The workpiece 18 is formed on the substrate 31 by sputtering, deposition, etc. and a resist 32 is formed on the workpiece 18 as shown in Fig. 3(a). By controlling the motor 20 or 23 of Fig. 2, the angle between the workpiece 18 and the ion beam 25, namely the angle of incidence of the ion beam 25 relative to the workpiece 18 is set obliquely as shown in Fig. 3(a). As a result, the workpiece 18 is etched as shown by the broken lines in Fig. 3(a). It is to be noted here that etching rate for the substrate 31 and the resist 32 is far lower than that for the workpiece 18. (b) After the above etching step (a) has been completed, the angle between the ion beam 25 and the workpiece 18 is changed reversely by driving the motor 20 or 23 and the workpiece 18 is again etched as shown by the broken line in Fig. 3(b). (c) By removing the resist 32, the workpiece 18 is worked to a structure of a trapezoidal cross-sectional shape having gradients as shown in Fig. 3(c). In the second example, Figs. 4(a) to 4(d) show the following steps (a) to (d) of the method according to the present invention, respectively. (a) As shown in Fig. 4(a), a resist 33 is formed on the workpiece 18 which is formed, by sputtering, deposition, etc., on the substrate 31 secured to the support 19. By controlling the motor 20 or 23, the relative angle between the workpiece 18 and the ion beam 25 is set vertically such that the workpiece 18 is etched as shown by the broken lines in Fig. 4(a). Also in this example, the etching rate for the substrate 31 and the resist 33 is far lower than that for the workpiece 18. (b) After the above etching step (a) has been completed, the angle between the ion beam 25 and the workpiece 18 is changed by driving the motor 20 or 23 so as to be set obliquely such that the workpiece 18 is again etched through time control as shown by the broken lines in Fig. 4(b). (c) After the above etching step (b) has been completed, the angle between the ion beam 25 and the workpiece 18 is changed reversely such that the workpiece 18 is further etched through time control as shown by the broken lines in Fig. 4(c). (d) By removing the resist 33, the workpiece 18 is worked to a structure of a special cross-sectional shape which cannot be obtained in ordinary workings. As described above, in the first and second examples of the method according to the present invention, since the workpiece 18 is etched while the relative angle between the ion beam 25 and the workpiece 18 is being changed, a microscopic structure having trapezoidal and other special cross-sectional shapes can be produced. It is needless to say that by properly setting the resist or a relative angle between the resist and the ion beam, a microscopic structure having a shape other than those shown in Figs. 3 and 4 can be obtained. In the third example, Figs. 5(a) to 5(c) show the following steps (a) to (c) of the method according to the present invention, respectively. (a) As shown in Fig. 5(a), a resist 34 is formed on the workpiece 18 which is formed, by sputtering, deposition, etc., on the substrate 31 secured to the support 19. In this state, the relative angle between the workpiece 18 and the ion beam 25 is set obliquely such that the workpiece 18 is etched as shown by the broken lines in Fig. 5(a). Also in this example, etching rate for the substrate 31 and the resist 34 is far lower than that for the workpiece 18. (b) After the above etching step (a) has been completed, the resist 34 is removed and a resist 35 is formed on the workpiece 18 as shown in Fig. 5(b). The relative angle between the ion beam 25 and the workpiece 18 is changed reversely by driving the motor 20 or 23 such that the workpiece 18 is again etched as shown by the broken line in Fig. 5(b). (c) By removing the resist 35, the workpiece 18 is worked to a structure of a trapezoidal cross-sectional shape having gradients opposite to those of the structure of the first example of Figs. 3(a) to 3(c). In the fourth example, Figs. 6(a) to 6(d) show the following steps (a) to (d) of the method according to the present invention, respectively. (a) As shown in Fig. 6(a), a resist 36 is formed on the workpiece 18 which is formed, by sputtering, deposition, etc., on the substrate 31 secured to the support 19. In this state, the relative angle between the workpiece 18 and the ion beam 25 is set obliquely such that the workpiece 18 is etched as shown by the broken lines in Fig. 6(a). Also in this example, the etching rate for the substrate 31 and the resist 36 is far lower than that for the workpiece 18. (b) After the above etching step (a) has been completed, the resist 36 is removed and a resist 37 is formed on the workpiece 18. Then, the relative angle between the ion beam 25 and the workpiece 18 is changed reversely by driving the motor 20 or 23 such that the workpiece 18 is again etched as shown by the broken lines in Fig. 6(b). (c) After the above etching step (c) has been completed, the resist 37 is removed and a resist 38 is formed on the workpiece 18. Subsequently, the relative angle between the ion beam 25 and the workpiece 18 is changed by driving the motor 20 or 23 so as to be set vertically such the the workpiece 18 is again etched as shown by the broken lines in Fig. 6(c). (d) By removing the resist 38, the workpiece 18 is worked to a structure of a special cross-sectional shape which cannot be obtained in ordinary workings. As described above, in the third and fourth examples of the method according to the present invention, since a plurality of kinds of the resists are employed and the workpiece 18 is etched while the relative angle between the ion beam 25 and the workpiece 18 is being changed, a microscopic structure having trapezoidal and other special cross-sectional shapes can be produced. It goes without saying that by properly setting the resist and a relative angle between the resist and the ion beam, a microscopic structure having a shape other than those shown in Figs. 5 and 6 can be obtained. In the fifth example, Figs. 7(a) to 7(d) show the following steps (a) to (d) of the method according to the present invention, respectively. (a) As shown in Fig. 7(a), a resist 39 is formed on the workpiece 18 which is formed, by sputtering, deposition, etc., on the substrate 31 secured to the support 19. In this state, the relative angle between the workpiece 18 and the ion beam 25 is initially set vertically as shown in Fig. 7(a). Then, by driving the motor 20 or 23 such that the angle of incidence of the ion beam 25 relative to the workpiece 18 gradually changes in the direction of the arrow 40 in response to progress of etching of the workpiece 18, the workpiece 18 is etched while being rotated. Also in this example, the etching rate for the substrate 31 and the resist 39 is far lower than that for the workpiece 18. (b) At the time when the relative angle between the workpiece 18 and the ion beam 25 is set as shown in Fig. 7(b) through progress of etching of the workpiece 18, the workpiece 18 has been etched as shown in Fig. 7(b). (c) At the time when the relative angle between the workpiece 18 and the ion beam 25 is set as shown in Fig. 7(c) through further progress of etching of the workpiece 18, the workpiece 18 has been further etched as shown in Fig. 7(c). (d) After the above etching step (c) has been completed, the resist 39 is removed and thus, the workpiece 18 is worked to a structure of a curved cross-sectional shape which cannot be obtained in ordinary workings. As described above, in the fifth example of the method according to the present invention, since the workpiece 18 is etched while the relative angle between the ion beam 25 and the workpiece 18 is being gradually changed, a microscopic structure having a curved cross-sectional shape can be produced. Needless to say, by properly setting rotational speed of the workpiece 18, for example, by changing rotational speed of the workpiece 18 continuously or intermittently, a microscopic structure having a shape other than that shown in Fig. 7 can be obtained. Meanwhile, in the above embodiments of the present invention, the material of the workpiece 18 is not restricted to a specific one and thus, such materials as metal, ceramics, silicon, etc. can be properly employed as material of the workpiece 18 in accordance with relation in etching rate between the workpiece 18 and the resist. Meanwhile, the ion source 14 may be of other types than Kaufmann type. Furthermore, the first to fifth examples of the present invention can be combined properly. In this case, it can also be so arranged that the workpiece 18 is etched while being deposited on the substrate 31. Namely, if ion sputtering is employed, it is only necessary to impart sputtering function to the ion etching machine of Fig. 2, which can be performed easily. Moreover, it can also be so arranged that after one workpiece 18 formed on the substrate 31 has been etched, another workpiece 18 is formed on the same substrate 31 so as to be etched.

Claims: A method for producing a microscopic structure by ion etching, wherein an ion beam (25) emitted by an ion source (14) is irradiated over a workpiece (18), the angle of incidence of the ion beam (25) relative to the workpiece (18) being changeable, characterized by the steps of (a) forming a resist (34; 36) on the workpiece (18) and irradiating the workpiece (18) under a first angle of incidence; (b) removing the first resist (34; 36) from the workpiece (18); (c) forming another resist (35; 37, 38) on the workpiece (18), changing said angle and irriadiating the workpiece (18) under another angle of incidence; (d) optionally repeating steps (b) and (c). The method of claim 1, characterized in that the workpiece is formed on a substrate (31), and after the workpiece formed on the substrate (31) has been etched, a further workpiece is formed on the substrate (31) so as to be etched.

Inventors: KISHI TOSHINORI, NAGASHIMA MICHIYOSHI, SHIBAIKE NARITO, UENO FUMIAKI, KISHI, TOSHINORI, NAGASHIMA, MICHIYOSHI, SHIBAIKE, NARITO, UENO, FUMIAKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01J37
IPC codes: H01J37, H01L21, C23F4