The method and principles of the construction and placement of the MEMS nano- electric and mechanical system

Department of systems (nano and microelectric and mechanical  MEMS )  

The method and principles of the construction and placement of the MEMS nano-  electric and mechanical system

Researcher  and author:  Dr. (   Afshin Rashid)

Note: MEMS are integrated in mobile microstructures (with electromechanical components), sensors, actuators, radiant energy devices and microelectronics. These MEMS can be made for use in various microfabrication technologies such as micromachines. 

Basic technology in making MEMS, CMOS  and biCOMS (for making ICs) and  micromachines (for producing movement and radiation and  energy radiation to micron-scale devices and structures  ). One of the main goals is to combine  microelectronics with devices and structures of  mechanical electromechanical micromachines to produce integrated MEMS with high efficiency . To ensure high performance, workability, reliability and manufacturability,  CMOS-based bulk fabrication processes are well developed and need to be  refined and enhanced.

Bulk body micromachining in MEMS components

Micromachining of the surface and body (BULK), as well as high-aspect ratio  (LIGA-like) or (high-aspect ratio) techniques are the most developed manufacturing methods. Silicon  is the material under the first layer that   is used in the microelectronics industry. A crystal mold (  a solid cylinder of 300 mm diameter and 100 mm length)  is crystallized from silicon with a very high purity percentage and is cut to the desired thickness, and then  it is polished by means of mechanical and chemical polishing technologies  . The properties of electromagnetic and  mechanical tablets are based on the direction and place of crystallization of the crystal and  its expected impurities. Depending on the  silicon substrate, CMOS and biCMOS processes They are used for the production of ICs, and micromachining (micromachining) surface and body (BULK), (in addition to high-aspect ratio techniques  , (LIGA-like and LIGA) or high-aspect ratio)  are the most developed manufacturing methods. Silicon  is the material under the first layer that  is used in the microelectronics industry. A crystal mold (  a solid cylinder of 300 mm diameter and 100 mm length)  is crystallized from silicon with a very high purity percentage and is cut to the desired thickness, and then  it is polished by means of mechanical and chemical polishing technologies  . The properties of electromagnetic and  mechanical tablets are based on the direction and place of crystallization of the crystal and  its expected impurities. Depending on the following Silicon layer, CMOS and biCMOS processes  are used to produce ICs and the processes  are classified as: well-n (n), well-p (well-p), or well-twin. The main steps  are : Diffusion, oxidation, polysilicon gate arrangement, optical photolithography, gate formations,  masking, etching, metallization, wire bonding  , etc. In the following,  we list the main and basic processes and stages of MEMS manufacturing.

 Classified processes  such as:    

N well-n source, (p source)  (well-p) (or well-twin source)  (the main steps  are: diffusion, (oxidation)

oxidation, polysilicon gate arrangement,  photolithography, gate formations

Masking, etching, metallization, wire  bonding, etc. In the following,  we list the major and basic processes and stages of MEMS manufacturing.

 Stage 1 (Crystallization of silicon dioxide  (grow silicon dioxide): 

(Silicon dioxide  is crystallized by a thermal method on a silicon base. For example, crystallization can be done in  a space full of water vapor at a temperature of 1000 degrees  Celsius and for one hour.  Silicon surfaces with a layer with a diameter of 5 0 to 1 micron  are covered by silicon dioxide (the  thermal oxide thickness is limited to a few microns as a result of the diffusion of water vapor along the  silicon oxide). Silicon dioxide can  be deposited without changing the surface of the layer, but this process is so slow. which  minimizes the pressure of the thin membrane.Silicon nitride  may also be deposited and  its thickness is limited to 4 to 5 micrometers. 

Step 2: (photoresistor)

(photoresist): a light-sensitive material (photoresist) is used on the surface of silicon dioxide. This process can be done by rotating the photoresist coating suspended  in a solvent. The result after rotating and  removing the solvent  is a photoresist with a thickness of 0.2 to 2 microns. The photoresist  is completely cooked and soft to remove the solvents from it  .

Step 3 (in exposing the photolithography and its development  :  (photolithography Exposure, and Development)

The photoresist  is exposed to ultraviolet light like a light engraving mask (optical mask). This optical mask blocks the light path and  defines a pattern to ensure optimal surface mapping . Optical masks are usually made using fused silica  and optical transparency that are subjected to effective wavelength, width and thermal expansion. A cloudy layer is placed on a glass or (quartz) surface  as a sample. ( Usually a chrome layer with a thickness of hundreds of angstroms). An  optical mask is produced based on the required shape of polysilicon shell  . The mapping of the surface  is determined by the mask. Photoresist  is then created. In a positive photoresistor, light, It reduces the molecular weight of the optical resistance and selectively  removes the  material with the lowest molecular weight that causes the optical resistance  .

Step 4 (Etch silicon dioxide :

Silicon dioxide is applied . The remaining photoresist is used as a  hard mask that protects the silicon dioxide part. Photoresist is removed by wet etching ( hydrofluoric acid, sulfuric acid and  hydrogen peroxide) or dry etching (using  oxygen plasma). The result  is a thin film of silicon dioxide on a silicon base. 

Step 5 (Polysilicon  Deposit:

(A thin film of polysilicon  is deposited on silicon dioxide. For example, polysilicon  can be  deposited in an LPCVD system at 600 degrees Celsius in a confined space of silane (SiH4)  . The deposition rate under normal conditions is 65 to  80 angstroms . per minute (Almin) which  minimizes the internal pressure and prevents bending and folding . (The thin polysilicon curtain must be without pressure or have a tensile internal pressure). The thickness of the thin curtain is more than (4) ) is micron.

Conclusion in the method of manufacturing and reproduction of MEMS system

With the works done in the field of NEMS, MEMS  today, the industry has moved more towards the science of micro and  nano electronics. Therefore, research works in this  field seem to be mandatory, the result of which is the achievement  of the best science and technology of the century. Among the  future works that should be done in this field is the  optimal design of MEMS and obtaining its modified types  for work in other sciences.

Researcher  and author: Dr.   (   Afshin Rashid)

Specialized doctorate in nano-microelectronics