JP2008260113A - Self-organizing process of polyimide thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide thin film self-organizing technology of a polyimide base capable of reducing costs and simplifying and miniaturizing a manufacturing process. <P>SOLUTION: Self-organization of a microstructure is completed by (1) evaporating a consumable layer 20 and a low stress microstructure layer 30 on a silicone substrate 10, (2) furnishing a stationary part and a movable part of the microstructure by patterning and etching the low stress microstructure layer, (3) covering it with a photosensitive polyimide thin film as an elastic connecting part 41 of the microstructure layer and demarcating the shape by using photo lithography technology, (4) removing the consumable layer below the movable part of the microstructure layer by wet etching and (5) contracting the elastically connected part by proceeding a reflowing process of polyimide, rotating the movable part and lifting it at last. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a self-assembly process for polyimide thin films. The process solves the problems of conventional self-organization techniques using an integrated miniaturized planar technique with simple, fast and economical characteristics.

  The development and application of miniaturization technology is a major trend in modern science. In particular, self-organization technology has recently become a fundamental method of the micro world.

  In the micro rotating fan manufactured by the micro electro mechanical system (MEMS) technology, as shown in Appendix 1, the portion between the scratch drive actuator (SDA) of the micro rotating fan and the micro blade structure is a self-organizing technology and multi-rotating fan. Formed by user MEMS processes (MUMPs).

  So-called self-assembly techniques are those that cause the microstructure to self-align after completion of the final release process. As shown in Appendix 2, there are the following three types of conventional self-organization techniques.

  Type 1 uses the residual stress in the manufacturing process to cause deformation as shown in FIG. 1 of Appendix 2, resulting in microstructural displacement. FIG. 1 shows a three-dimensional micro-optical switch developed by Lucent Technology.

  In Type 2, as shown in FIG. 2 of Appendix 2, the microstructure is moved to a preset position by vibration using surface acoustic waves generated by ultrasonic waves.

Type 3 uses a solder ball, photoresist or other polymer to form an elastic joint on the micro hinge. The elastic joint is melted by a high temperature reflow process, which produces a surface tension that pulls up the microstructure, as shown in FIG.
Ryan. J. Linderman, Paul. E. Kladitis, Victor. M. Bright, “Development of a micro-rotating fan”, Sensors and Actuators A, 95, 2002, pages 135-142

  However, Type 1 and Type 2 with conventional self-organization technology are applicable only for static applications or fixed microstructures, and are suitable for dynamic or rotating microstructures such as microfan applications. Absent.

  For the type 3 self-organization technology, many materials suitable for the production of elastic joints are used. Each of these materials has drawbacks. A solder ball will be described below as an example.

  Lead contamination: Solder balls are made of tin and lead (63Sn / 37Pb). During the reflow process, equipment and the environment are contaminated with lead.

  High cost: Most of the micro-machined microstructures are usually made of polycrystalline silicon (Poly-Si), where the gold pad layer interconnects the solder balls and Poly-Si It is formed as a film. This additional process inevitably makes production difficult and increases costs.

  Low accuracy: In order to calculate the launch angle or displacement of the microstructure, the dimensions of the solder balls must be precisely controlled. However, the conventional solder balls have a volume variation as high as 25%, and the start-up angle and displacement accuracy become uncontrollable.

  Manual processing: At present, the solder balls are still mounted on the gold pads by manual centering.

  Miniaturization impossible: At present, the minimum size of the solder ball is 100 μm or more, and there is a limit to the minimum size of the device using solder.

  The elastic bond formed by the photoresist will be described with reference to another example.

  The manufacturing process of the elastic bond formed by the photoresist is not as complicated and low-cost as the process using solder balls. However, a dry or wet etching process is required to release the microstructure.

  In dry etching, the fine structure is released using liquid carbon dioxide, and water molecules are replaced to prevent the adsorption effect of the fine structure. However, the supercritical CO2 dry removal apparatus used in this method is very expensive. Therefore, the cost of this process is relatively high.

  Wet etching does not require an extra manufacturing apparatus and does not cost. However, after the sacrificial layer is etched using a dilute hydrofluoric acid (HF) solution or buffered oxide etching (BOE), isopropyl alcohol (IPA) is further applied to rapidly vaporize water molecules. Since IPA has the property of dissolving the photoresist, it damages the initially made photoresist-based elastic joint.

  In other words, in consideration of production cost, process integration, and miniaturization performance, a completely new manufacturing process is urgently required to solve various problems arising from elastic bonding formed by solder balls and photoresists.

  In view of the above circumstances, the present invention provides a polyimide-based thin film self-assembly technique, which consists of the following five processing steps. (1) depositing a sacrificial layer and a low-stress microstructure on the silicon substrate; (2) patterning and etching the low-stress microstructure layer to form a stationary part and a movable part of the microstructure; (3) A photosensitive polyimide thin film is coated as an elastic coupling part of the fine structure layer, and the shape of the thin film is limited by photolithography technology. (4) The sacrificial layer below the movable part of the fine structure is removed by wet etching. (5) Finally, the polyimide reflow process is advanced to contract the elastic joint, and when the self-organization of the microstructure is completed, the movable part can be further rotated and lifted. Since the present invention can be widely applied to many miniaturization industries, the problems of the prior art can be solved, and the requirements of low cost, simplification of manufacturing process and miniaturization can be satisfied.

The polyimide thin film self-assembly process of the present invention has the following characteristics.
a. Depositing a sacrificial layer on the silicon substrate and depositing a low stress microstructure layer on the sacrificial layer;
b. Patterning and etching the microstructure formed on the sacrificial layer;
c. Coating a polyimide thin film on the microstructure layer;
d. Patterning and etching the elastic coupling part formed on the polyimide thin film; and
e. Performing a wet etching process to etch and remove pre-defined contours of the sacrificial layer;
f. Performing a polyimide reflow process to shrink the elastic joint, and further rotating and lifting the predefined portion of the microstructured layer.
The low-stress sacrificial layer is made of phosphate silicate glass (PSG).
The microstructure layer is made of polycrystalline silicon (Poly-Si).

  The polyimide thin film self-assembly process of the present invention includes self-organization of a micro-rotating fan, self-organization of a microworm-like chip, self-organization of a scratch drive actuator, self-organization of a micro-optical bench chip, and self-assembly of a micro-optical switch. It can be applied to organization and self-organization of micro passive devices. The micro passive element is a micro derivative or a micro capacitor.

  The present invention relates to a polyimide thin film self-assembly process using a photosensitive polyimide thin film as an elastic bonding material. During the reflow process, the polyimide-based elastic bond is melted at high temperatures (380 ° C. to 405 ° C.), which generates surface tension and lifts the microstructure.

  As shown in FIG. 1, the manufacturing process of the present invention includes the following processes.

  Process 1: Phosphate silicate glass (PSG) is deposited on the silicon substrate 10 as a sacrificial layer 20 by a plasma enhanced chemical vapor deposition (PECVD) method, and further, a low stress poly- as a microstructure layer 30 is deposited by a low pressure chemical vapor deposition (LPCVD) method. Si is deposited on the sacrificial layer 20.

  Process 2: A first photolithographic process is performed and the microstructure layer 30 is etched using an inductively coupled plasma (ICP) etching method to define the overall contour.

  Process 3: A photosensitive polyimide thin film 40 is deposited on the microstructure layer 30 using a spin coater.

  Process 4: A second photolithography process is performed to define the shape contour of the polyimide elastic joint 41.

  Process 5: Immerse the wafer in BOE, wet etch a predefined portion of the sacrificial layer 20, and then release the microstructured layer.

  Process 6: The elastic coupling part 41 is melted at a high temperature of 380 ° C. to 405 ° C. by performing a reflow process of the polyimide thin film using a high temperature furnace. As shown in Appendix 3, the heated polyimide elastic bonding portion 41 shrinks and deforms, rotating and lifting a predefined portion of the Poly-Si microstructure layer 30.

  First, the advantages and disadvantages of the polyimide elastic joint and the solder ball formed according to the present invention are compared as follows.

  In the present invention, lead contamination does not occur.

  The present invention does not require the addition of a gold pad that covers the connection interface, and can provide a simple and inexpensive manufacturing process.

  In the present invention, alignment can be performed with considerably high accuracy by photolithography technology, and better accuracy can be provided.

  The present invention can perform an integrated miniaturized planar self-organization process.

  There is no limit to the miniaturized dimensions of the present invention.

  Further, the advantages and disadvantages of the polyimide elastic joint formed by the present invention and the polyimide elastic joint formed using the photoresist are compared as follows.

  Although both photosensitive polyimide and photoresist are classified as polymer materials, polyimide has a higher surface tension and can be launched at a larger angle if it has the same microstructure layer. As a result, according to the present invention, there is no fear that the elastic coupling portion is damaged by dissolution by IPA.

  The photosensitive polyimide thin film has sufficient organic solution resistance and can be formed by an inexpensive wet etching process. Therefore, the manufacturing cost of the present invention is low and can be kept relatively low.

  In summary, the present invention simplifies the manufacturing process, lowers costs, and completely solves the problems arising from elastic joints formed by solder balls and photoresists.

  Furthermore, as shown in FIG. 2, the time and temperature directly affect the rising angle of a predetermined rising portion of the Poly-Si microstructure layer 30. As a result, by controlling the polyimide time and the reflow temperature, the rising angle of the rising portion defined in advance of the microstructure layer 30 can be accurately controlled.

  The actual result based on the experiment of the photosensitive polyimide thin film having a thickness of 20 μm is shown below.

  The patterned microstructure layer 30 cannot be lifted if the temperature of the reflow process is below 330 ° C.

  The rising phenomenon gradually appears after the polyimide reflow temperature reaches 380 ° C. or higher.

  According to the experimental results, the rise angle at the reflow temperature of 450 ° C. is larger than the rise angle at 380 ° C., but the yield at 450 ° C. is less than half of the yield at 380 ° C. This is based on the fact that the photosensitive polyimide thin film shrinks excessively at 405 ° C. (or higher) and the width of the polyimide is smaller than the gap between the movable part and the stationary part of the Poly-Si microstructure layer 30. There is a malfunction of the polyimide elastic coupling portion 41.

  In our experience, the optimum reflow temperature for a polyimide-based elastic bond is 380 ° C.

  By the above manufacturing process, the present invention completely solves many problems resulting from the elastic bonding of solder balls or photoresists, and the self-organization technology can be widely applied to various miniaturization industries. Thus, the present invention is not only new and progressive, but also has industrial applicability.

FIG. 1 is a schematic view showing the manufacturing process of the present invention. FIG. 2 is a graph showing the relationship between the reflow temperature of the polyimide of the present invention and the rising angle of the microstructure layer.

Claims (11)

a. Depositing a sacrificial layer on the silicon substrate and depositing a low stress microstructure layer on the sacrificial layer;
b. Patterning and etching the microstructure formed on the sacrificial layer;
c. Coating a polyimide thin film on the microstructure layer;
d. Patterning and etching the elastic coupling part formed on the polyimide thin film; and
e. Performing a wet etching process to etch and remove pre-defined contours of the sacrificial layer;
f. Performing a polyimide reflow process to shrink the elastic bond and further rotating and lifting the predefined portion of the microstructured layer.   The polyimide thin film self-assembly process according to claim 1, wherein the low-stress sacrificial layer is made of phosphate silicate glass (PSG).   The polyimide thin film self-assembly process according to claim 1, wherein the microstructure layer is made of polycrystalline silicon (Poly-Si).   2. The polyimide thin film self-assembly process according to claim 1, wherein the process is applied to self-assembly of a micro-rotating fan.   2. The polyimide thin film self-assembly process according to claim 1, wherein the process is applied to the self-assembly of a microworm-like chip.   2. The polyimide thin film self-assembly process according to claim 1, which is applied to self-assembly of a scratch drive actuator.   2. The polyimide thin film self-assembly process according to claim 1, wherein the process is applied to self-assembly of a micro optical bench chip.   2. The polyimide thin film self-assembly process according to claim 1, wherein the process is applied to self-assembly of a micro optical switch.   The polyimide thin film self-assembly process according to claim 1, which is applied to self-assembly of a micro passive device.   The polyimide thin film self-assembly process according to claim 9, wherein the micro passive element is a micro derivative.   The polyimide thin film self-assembly process according to claim 9, wherein the micro passive element is a micro capacitor.

Images