JP4923254B2 - Exposure method - Google Patents

Description

  The present invention relates to an exposure method in photolithography of a three-dimensional shape such as a catheter / endoscope.

  Minimally invasive treatment has been widely performed in which a thin and small medical tool is inserted without making a large incision in the human body, and an effect comparable to that of surgery. Medical tools such as catheters and endoscopes are used for these procedures. In addition, capsule endoscopes that are placed in the body for examination while reducing the burden on the patient, and implantable drug delivery systems that realize optimal medication according to the situation are attracting attention. These tools should be as thin, small and highly functional as possible.

  The shape of catheters and endoscopes and their lumens are circular, and the lumen of the needle that pierces the body when some tools are inserted into the body is also circular. desirable. In addition, by securing the lumen, it can be used for insertion of another tool and injection of drug solution in catheters and endoscopes, and as a storage place for drug solution tanks and batteries in capsule endoscopes and drug delivery systems. It is desirable to secure a cavity (see FIG. 1).

  One way to satisfy these requirements is to mount the functions by microfabrication and assembly on a cylindrical surface. However, there is a limit to the microfabrication and assembly performed on the conventional flat surface, and it is difficult to perform microfabrication on the tube outer peripheral curved surface. To date, micro-fabrication on the outer peripheral curved surface of a tube such as device mounting on a catheter using laser processing technology (Non-Patent Document 1) and cylindrical surface patterning using a flexible mask (Non-Patent Document 2) to achieve high functionality And assembly is being attempted.

For pattern formation on a cylindrical surface, a flexible mask method (Non-Patent Document 2) in which a flexible mask provided with a metal thin film pattern is wound around the cylindrical surface, and the cylinder is rolled onto a flat surface on a silicone rubber mold on which the pattern is formed. Micro contact printing method to form a pattern (Non-patent Document 3), Rolling exposure method to synchronize the rotation of a cylinder and the parallel movement of a photomask (Non-Patent Documents 4 and 5), Control the beam without using a mask Then, there is a maskless exposure method that performs direct drawing.
Hiroshi Misawa, Satoshi Nakagawa, Hitoshi Komine, Noriko Itana, Susumu Tanabe: Microcatheter Microfabrication Technology, The FirstInternational Micromachine Symposium, 123-126 (1995) WJ Li, John D. Mai, Chih-Ming Ho, Sensors and actuators on non-planar substrates, Sensors and Actuators 73, 80-88 (1999) RJ Jackman, JL Wilbur, and GM Whitesides, Fabrication of Submicrometer Features on CurvedSubstrates by Microcontact Printing, Science, 269, No. 4, 664 (1995) Hane Kazuhiro, Sasaki Minoru, Sugawara Takashi, Nogawa Shinichiro: Development of Cylindrical Rolling Lithography Equipment, IEEJ Sensor Micromachine Division PS-98-10, 47-51 (1998) Takashi Hamada, Yoichi Haga, Masayoshi Esashi: Actuator creation from shape memory alloy pipe by non-planar photofabrication, IEEJ Transactions E, 123, No.5, 2003

The conventional exposure method for photolithography to a three-dimensional shape has the following problems, and a sufficiently satisfactory exposure cannot be achieved.
(A) It is difficult to form a resist with a uniform film thickness in a three-dimensional shape.
(B) It is difficult to align the resist-coated sample and the photomask.
(C) The exposure dose changes due to a large change in the resist thickness and the exposure incident angle on the resist film, and accurate photolithography cannot be performed.
Accordingly, an object of the present invention is to solve the above-described conventional problems and realize an optimum exposure distribution condition in photolithography to a three-dimensional shape.

Means for solving the problems are as follows.
(1) In photolithography to a three-dimensional shape having a curved surface , the resist height position and film thickness distribution are divided into a two-dimensional matrix, and the focus height is adjusted to the exposure height for each matrix without using a photomask. An exposure method characterized by performing exposure using an exposure dose that matches the resist thickness.
(2) Estimating in advance the interaction between adjacent two-dimensional matrices based on the height position of the resist and the film thickness distribution, taking into account irregular reflection of light inside the resist and reflection at the interface between the resist and its lower layer. (1) The exposure method according to (1), wherein optimal exposure reflecting a latent image in the resist film is performed.
(3) The exposure method according to (1) or (2), wherein the resist height position and film thickness distribution are measured, and the measurement result is divided into a two-dimensional matrix and reflected in exposure.
(4) The resist height position and film thickness distribution are measured using at least one of a laser displacement meter, optical coherence tomography, Gaussian lens law, and Fizeau interferometer (3 ) Exposure method.
(5) A three-dimensional structure of a resist is produced on a three-dimensional shape having a curved surface by using gray scale exposure that changes the height of the developed resist by changing the exposure dose (1) Or the exposure method according to (2).
(6) The exposure height is optimized by using at least one of vertical movement of the focus by the optical system, vertical movement of the substrate, and movement other than vertical movement according to the substrate shape (1). The exposure method according to any one of (4) to (4).
(7) The exposure method according to (5), wherein the substrate having a slope shape is subjected to either an oblique movement of the substrate corresponding to the inclination of the slope or an inclination of the substrate.
(8) The exposure method according to any one of (1) to (7), wherein a single exposure beam that performs point irradiation is used.
(9) The exposure method according to any one of (1) to (8), wherein one-dimensional or two-dimensional collective irradiation is performed using an optical deflection device such as an optical scanner or DMD.
(10) For a substrate having a curved outer shape such as a column or cylinder, a columnar convex portion or a concave portion on the substrate, rotation about a circular central axis, and a long axis direction synchronized with the rotation The exposure method according to (8), wherein the linear pattern exposure is performed.
(11) For a substrate having a curved outer diameter such as a column or cylinder, a columnar convex portion or a concave portion on the substrate, linear movement in the major axis direction and rotation about a circular central axis; The exposure method according to (9), wherein point irradiation is performed in synchronization with each movement.
(12) The exposure according to any one of (1) to (11), wherein the three-dimensional shape having the curved surface is a support layer covering the substrate tube and the periphery thereof, and the substrate tube is removed after the exposure. Method.

  According to the exposure method of the present invention, since an optimal exposure distribution condition is realized in photolithography to a three-dimensional shape, an accurate pattern can be formed on a three-dimensional shape such as a cylindrical surface.

FIG. 2 shows a conceptual diagram of matrix division exposure according to the exposure method of the present invention.
As can be seen from FIG. 2, in photolithography to a three-dimensional shape (convex surface and concave surface of the substrate), the resist height position (A, B, C) and film thickness distribution are divided into a two-dimensional matrix, and a photomask is formed. The exposure is performed using the focus height matched to the exposure height (A ′, B ′, C ′) for each matrix and the exposure dose matched to the resist thickness.
Furthermore, taking into account irregular reflection of light inside the resist and reflection at the interface between the resist and its lower layer, the resist is estimated by estimating the interaction between adjacent two-dimensional matrices in advance based on the height position of the resist and the film thickness distribution. Optimal exposure reflecting the latent image in the film can be performed to realize more accurate and fine lithography.

Next, the exposure method of the present invention will be described in detail by exemplifying the production process of the multilayer solenoid coil shown in FIG.
(A): A Cu / Ti seed layer is formed on the outer surface of a glass cylinder by sputtering.
(B): A negative resist (Tokyo Ohka Kogyo Co., Ltd., OMR83) is dip coated or spray coated, and then exposed in the following procedure.
Measure the resist height position and film thickness distribution as necessary, divide the resist height position and film thickness distribution into a two-dimensional matrix, and adjust the focus height and resist thickness according to the exposure height for each matrix. The resist is exposed by using an exposure dose that matches the thickness.

Here, the height position and film thickness distribution of the resist are measured using at least one of a laser displacement meter, optical coherence tomography, Gauss's lens law, and Fizeau interferometer.
The exposure height is optimized by using at least one of vertical movement of the focal point by the optical system, vertical movement of the substrate, and movement other than vertical movement according to the substrate shape.
Next, development is performed to form a resist pattern.

(C): A Cu layer is grown using electroplating.
(D): The resist is removed and an unnecessary seed layer is etched.
(E): A SiO ₂ insulating layer is formed by PECVD (plasma assisted chemical vapor deposition).
(F): A positive resist (Tokyo Ohka Kogyo Co., Ltd., OFPR800) is dip coated or spray coated, and similarly exposed and developed to form a resist pattern.
(G): The SiO ₂ is etched and the resist is removed.
(H): The above processes (a) to (g) are repeated again.

Based on the above process, a single-layer pattern was prepared using a stage-controlled point irradiation apparatus (see FIGS. 4A and 5) and an exposure apparatus using DMD (see FIGS. 4B and 6). .
In the stage control type point irradiation apparatus, a test pattern, an electrode wiring pattern, and a solenoid coil were made of copper on a glass cylinder having a diameter of 2 mm using a third harmonic (355 nm) of a YAG laser. In an exposure apparatus using a DMD (digital micromirror device), a test pattern and a solenoid coil were made of chromium on a glass cylinder having a diameter of 3 mm.
In addition, in the exposure apparatus using DMD, a thick film resist (PMER P-LA900, Tokyo Ohka Kogyo Co., Ltd.) is used, and the slope of the resist is applied in the axial direction and circumferential direction of a glass cylinder having a diameter of 3 mm using gray scale exposure. A structure (width 500 μm, length 500, 1000, 1500 μm) was prepared.

FIG. 7 shows a copper pattern on a glass tube (diameter 2 mm) produced using a stage-controlled point irradiation apparatus.
FIG. 8 shows a pattern produced by a chromium pattern exposure apparatus on a glass tube (diameter 3 mm) produced using a line irradiation exposure apparatus utilizing DMD.
For the solenoid coil, the prober and impedance analyzer were used to measure resistance and inductance, respectively, and the measurement results close to the theoretical values were obtained.

FIG. 9 shows a slope structure produced by gray scale exposure on a glass tube (diameter 3 mm). In gray scale exposure, by changing the exposure dose, the height of the resist to be developed is changed, and a three-dimensional structure pattern of the resist is formed on a three-dimensional shape such as a cylindrical surface.
In the production of the slope structure by gray scale exposure, a smooth slope having a maximum height of about 20 μm was obtained as shown in FIG.

  In the case of a tube-shaped device, thinning is to secure a wide lumen (working channel for passing drugs, contrast agents, and micro tools) while maintaining the thinness of catheters and small diameter endoscopic tools. (See FIG. 10). Fabrication is performed by first forming an insulating film on a glass or metal substrate to form a thinned support layer for the device, and forming a sandwich structure by providing a similar film as a protective layer on the outermost layer. Specifically, parylene, polyimide, or the like is suitable as the material, but any material that can form a thin film and has high chemical resistance (can withstand an etching solution) may be used. In the case of a tube, the etching solution does not reach the lumen as the diameter is reduced, making it impossible to perform etching efficiently. However, the substrate can be efficiently and easily flowed (circulated) through the tube by applying a little pressure. Etching is possible.

  In the exposure method of the present invention, the interaction between adjacent two-dimensional matrices is estimated in advance based on the measurement result of the height position of the resist and the film thickness distribution, taking into account irregular reflection of light inside the resist. Optimal exposure reflecting the latent image in the resist film can be performed.

  This method can realize unprecedented high integration and high functionality for medical tools, and is an important technology for the development of next-generation medical devices such as intravascular MRI probes and integrated ultrasound endoscopes. Expected to get.

  That is, in the former, both conventional excitation magnetic resonance imaging (MRI) and excitation coil are located outside the body, but both the excitation coil and the detection coil, or only the detection coil, are exposed by the exposure method according to the present invention. By miniaturizing it and mounting it at the tip of a catheter and bringing it into the body, high resolution imaging of intravascular lesions (stenosis and plaque) and detection of substances useful for diagnosis become possible. It is also possible to create a matching circuit by using the present exposure method.

  In the latter case, a signal amplification circuit and an electrical impedance matching circuit are integrated in the vicinity of the ultrasonic transducer in the ultrasonic endoscope, so that a small diameter is ensured while securing a through hole for passing a guide wire or angiographic contrast agent at the center. In addition, a high-performance intravascular imaging probe can be realized (see FIG. 11).

The conceptual diagram of cylindrical surface microfabrication. The conceptual diagram of matrix division | segmentation exposure. Multi-layer solenoid coil manufacturing process. The conceptual diagram of the maskless exposure method. Stage control type point irradiation device using laser beam. Line irradiation device using DMD. A copper pattern on a glass tube (diameter 2 mm) produced using a stage-controlled point irradiation device. A chromium pattern on a glass tube (3 mm in diameter) produced using a line irradiation exposure apparatus using DMD. A slope structure of a resist on a glass tube (diameter 3 mm) produced using an exposure apparatus utilizing DMD. Fabrication of multilayer thin film tubes by etching away substrate tubes. The conceptual diagram of an integrated ultrasonic endoscope.

Claims (12)

In photolithography to a three-dimensional shape with a curved surface , the resist height position and film thickness distribution are divided into a two-dimensional matrix, and the focus height and resist thickness are adjusted to the exposure height for each matrix without using a photomask. An exposure method characterized by performing exposure using an exposure dose in accordance with the thickness.   By taking into account irregular reflection of light inside the resist and reflection at the interface between the resist and its lower layer, the resist film can be estimated in advance by estimating the interaction between adjacent two-dimensional matrices based on the height position of the resist and the film thickness distribution. 2. The exposure method according to claim 1, wherein optimum exposure reflecting a latent image is performed.   3. The exposure method according to claim 1, wherein the height position and film thickness distribution of the resist are measured, and the measurement result is divided into a two-dimensional matrix and reflected in exposure.   4. The resist height position and film thickness distribution are measured using at least one of a laser displacement meter, optical coherence tomography, Gaussian lens law, and Fizeau interferometer. Exposure method. 3. The three-dimensional structure of the resist is formed on a three-dimensional shape having a curved surface by using gray scale exposure that changes the height of the resist to be developed by changing the exposure dose. An exposure method according to 1.   5. The exposure height is optimized by using at least one of vertical movement of the focal point by the optical system, vertical movement of the substrate, and movement other than vertical movement according to the substrate shape. The exposure method according to any one of the above.   6. The exposure method according to claim 5, wherein either an oblique movement of the substrate or an inclination of the substrate corresponding to the inclination of the slope is performed on the substrate having a slope shape.   The exposure method according to claim 1, wherein a single exposure beam that performs point irradiation is used.   9. The exposure method according to claim 1, wherein one-dimensional or two-dimensional collective irradiation is performed using an optical deflecting device such as an optical scanner or DMD.   For a substrate having a curved outer shape such as a cylinder or a cylinder, a columnar convex portion or a concave portion on the substrate, rotation about a circular central axis, and a long axis direction line synchronized with the rotation The exposure method according to claim 8, wherein pattern exposure is performed.   For a substrate having a curved outer diameter such as a cylinder or a cylinder, a columnar convex portion or a concave portion on the substrate, a linear movement in the major axis direction and a rotation around a circular central axis, The exposure method according to claim 9, wherein point irradiation is performed in synchronization with movement. The exposure method according to any one of claims 1 to 11, wherein the three-dimensional shape having the curved surface is a support layer covering the substrate tube and the periphery thereof, and the substrate tube is removed after the exposure.