What is the etching process and packaging process of the MEMS pressure sensor?
MEMS, Micro-Electro-Mechanical System, is the first concept proposed by Richard Feynman in December 1959. It combines micro-simulated mechanical components, micro-sensors, micro-actuators, signal processing and control circuits, up to interface, signal transmission and power supply. Complicated micro-devices or systems including such devices that can be manufactured in batches that are integrated into one body. Its development began in the 1960s and entered a stage of rapid development in the 1980s. It has broad development prospects in various fields. In recent years, the manufacture and sales of MEMS devices have shown rapid growth.
MEMS pressure sensors are currently an important application field of MEMS devices. They can be roughly divided into capacitive, piezoresistive, piezoelectric, metal strain, and optical fiber types. The performance of MEMS pressure sensors improves with the progress of materials and manufacturing processes. Several orders of magnitude, and through the use of design technology and manufacturing processes similar to integrated circuits, high-precision, low-cost mass production has been achieved, and it has a wide range of industrial applications and good development prospects in the future.
The technical composition of MEMS pressure sensor mainly includes the following branches.
MEMS pressure sensor substrate material
The base material is the basis for the manufacture of MEMS pressure sensors. The choice of different base materials not only affects the performance of the MEMS pressure sensor, but also determines the process selection in the device preparation process. The current base materials for MEMS pressure sensor processing are mainly divided into silicon-based Materials and non-silicon-based materials, among which the processing technology of silicon-based devices is currently widely used due to its compatibility with the existing integrated circuit processing technology.
The types of silicon-based materials are mainly divided into silicon materials including polycrystalline silicon, single crystal silicon, and amorphous silicon, silicon-on-insulator including SOI and SOG, and emerging silicon carbide semiconductor materials.
Early MEMS pressure sensors were manufactured based on copper as the base material for conventional pressure devices. After the 1990s, conventional silicon materials such as amorphous silicon, monocrystalline silicon, polycrystalline silicon, etc. were used as base materials for MEMS device manufacturing due to silicon integration. The basis of circuit processing has become the mainstream process for MEMS device processing and industrialization, but MEMS devices have higher requirements for device performance and size compared to integrated circuits. In order to improve the structure and performance of conventional silicon substrate materials in the manufacture of different types and applications of MEMS devices, based on the improvement of conventional silicon-based substrate materials, Siemens proposed to use SOI substrates to manufacture MEMS pressure sensors. Stanford University proposed that Use monolithic silicon carbide as a substrate to manufacture MEMS pressure sensors.
Since then, due to the need for the integrated industrialization of MEMS devices prepared from silicon-based materials, a complete MEMS sensor structure and supporting ASIC system based on the substrate material are required to achieve a complete integrated pressure sensing system. The Netherlands NX company proposed to use SOI substrate to make MEMS sensors As for the integrated system of circuit structure, MEMS-VISION company proposed to use silicon carbide substrate to make MEMS sensor and circuit structure integrated system.
In addition, with the continuous promotion of pressure sensor research and application fields, based on different device types, other materials with specific properties such as electro-shrinkable materials, magnetic materials, piezoelectric ceramics, memory alloys, polymer materials, etc. Device manufacturing.
MEMS pressure sensor etching process
The etching process is a key process for constructing device patterns and structures based on MEMS substrate materials. The choice of different etching processes has an important impact on the accuracy of the device pattern and the performance of the device. The current etching process includes a wet method using alkaline/organic solutions. Etching process and dry etching process, the main dry etching process currently used includes plasma etching process (PE), reactive ion etching process (RIE) and inductively coupled plasma etching process (ICP).
Since the manufacturing technology of MEMS sensors is based on the more mature integrated circuit manufacturing process, the dry and wet etching processes of semiconductor device manufacturing in the integrated circuit process based on conventional silicon substrate materials have been experienced for a long time before the emergence of MEMS devices. The development and evolution of time.
The dry and wet etching processes related to the isotropic and anisotropy of conventional silicon materials to obtain specific device patterns have been developed relatively mature, while dry etching has high resolution compared with wet etching processes, and each It has strong anisotropic corrosion ability and is not easy to produce device structure adhesion. It has obvious advantages in the size control of the device preparation process.
Among them, after the Bosch process of obtaining high aspect ratio silicon patterns by ion reactive etching, the dry etching process has gradually become the main method of device etching due to the ability to control the etching rate to produce high aspect ratio device pattern structures, which promotes MEMS The manufacturing process of pressure sensors is developing in the direction of higher resolution.
MEMS pressure sensor packaging process
The packaging process is a key process to realize the industrialization of MEMS pressure sensors, accounting for 60% to 80% of the total manufacturing cost of MEMS pressure sensors.
The MEMS pressure sensor needs to be bonded during the packaging process to support and protect the device structure and to realize the electrical connection between the device structure and the external circuit. Although it is not a technology for directly processing the MEMS pressure sensor device structure, it is important for realizing the device structure. The application and function of the system play a decisive role.
Relying on the semiconductor processing technology, there are many ways to realize the component bonding of MEMS devices, including the bonding process through adhesive bonding, the bonding process through solder welding, and the bonding process through the fusion connection of intermediate materials. Thermal bonding process, silicon-glass electrostatic bonding through the principle of charge accumulation, and metal eutectic bonding process through the formation of eutectic by the reaction between metal and silicon or metal. However, because MEMS devices have a variety of three-dimensional structures and different composition material layers, the vacuum degree of the working environment of the components in the device is high, and the bonding process using adhesives for packaging cannot meet the processing requirements of the device.
At present, the bonding process used in the packaging process of MEMS devices does not use any adhesives, and only uses chemical bonds and physical effects to achieve tight bonding between device structures. The main methods are direct silicon-silicon bonding, silicon-glass electrostatic bonding and co-bonding. Three kinds of crystal bonding. The bonding process has been relatively mature with the advancement of silicon semiconductor technology before the emergence of MEMS pressure devices. In the device manufacturing process, different bonding processes are selected to achieve the assembly and assembly of the device based on the different materials and the requirements of the device connection performance. Connection has always been a conventional method in the process of device processing, but due to the particularity of MEMS pressure sensor devices in terms of size, structure and working principle, the bonding process of MEMS devices has a certain improvement in the technology of conventional semiconductor bonding processes.
In terms of silicon-to-silicon direct bonding and electrostatic bonding technology, because it needs to use a high temperature close to 1000 ℃ in the bonding process, it will cause stress in the device and cause warpage deformation. Therefore, the bonding process of MEMS pressure sensor The bonding area is optimized and improved to reduce temperature unevenness and device structure deformation during the bonding process; in terms of eutectic bonding technology, as the need for integrated connection between MEMS pressure sensors and ASIC systems, eutectic bonding The advantages of forming electrical connections have become the main bonding method in the integrated manufacturing of MEMS devices. In the future, with the development of the size and performance of MEMS pressure sensors, the requirements for achieving electrical interconnection during the bonding process with other chips in the system will also Will continue to improve, the future eutectic bonding will be the main method of MEMS pressure sensor bonding process.
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