bullet MEMS Pressure Sensors: Fabrication and Process Optimization


  Title: MEMS Pressure Sensors: Fabrication and Process Optimization

  Author: Parvej Ahmad Alvi

  Publisher: International Frequency Sensor Association (IFSA) Publishing

  Formats: print (hardcover) and pdf (Acrobat),176 pages

  Pubdate: 12 December 2012

  Price:  109.99 EUR (e-book in pdf format) and 139.99 EUR (print hardcover book). Taxes and shipping costs (mail) are included

  Delivery time for print book: 7-17 days dependent on country of destination. Please contact us for priority (5-9 days), ground (3-8 days) and express (3-5 days) delivery options by e-mail

  BN: 20121212-XX

  ISBN: 978-84-616-2207-8

  e-ISBN: 978-84-616-2438-6



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MEMS Pressure Sensors: Fabrication and Process Optimization book's cover

Book Description


So far, no book has described the step by step fabrication process sequence along with flow chart for fabrication of micro pressure sensors, and therefore, the book has been written taking into account various aspects of fabrication and designing of the pressure sensors as well as fabrication process optimization. A complete experimental detail before and after each step of fabrication of the sensor has also been discussed. This leads to the uniqueness of the book.



  • A complete detail of designing and fabrication of MEMS based pressure sensor

  • Step by step fabrication and process optimization sequence along with flow chart, which is not discussed in other books

  • Description of novel technique (lateral front side etching technique) in terms of chip size reduction and fabrication cost reduction, and comparative study on both the techniques (i.e. Front Side Normal Etching Technology and Front Side Lateral Etching Technology) for the fabrication of thin membrane

  • Discussion on issues of sealing of conical tiny cavity; because the range of pressure applied (i.e. greater or less than atmospheric pressure) can be decided by methodology of sealing of tiny cavity

  • A complete theoretical detail regarding aspects of designing and fabrication, and experimental results before and after each step of fabrication

MEMS Pressure Sensors: Fabrication and Process Optimization will greatly benefit undergraduate and postgraduate students of MEMS and NEMS course, process engineers and technologists in the microelectronics industry as well as MEMS-based sensors manufacturers.





For the great progress of MEMS (Micro-Electro-Mechanical Systems) in recent years, there are at least four kinds of processing methods including silicon bulk micro-machining, silicon surface micro-machining, LIGA and CMOS (complementary metal-oxide-semiconductor) process to fabricate the micro-sensors at present. Among these technologies, CMOS process for micro-sensors has the advantages of the maturity in IC (integrated circuit) foundry, the sub-micrometer spatial resolution of device fabrication and the functionality of on-chip circuitry. CMOS layers have been successfully used as the mechanical structures or the sensing elements of accelerometers, thermal sensors, magnetic sensors and pressure sensors. A group of Scientist has also designed a magnetic Hall sensor by the standard SPDM (single-polysilicon-double-metal) CMOS foundry service provided by the Chip Implementation Center (CIC), Taiwan, without post-processing. However, it caused some difficulties in achieving the design and the fabrication of the CMOS mechanical sensors due to the violations of some electric rules provided by the CMOS foundry line and the uncertainty of post-processing used to form the special geometry of sensor chip. However, recently a novel technique (Lateral front side etching technique) has been utilized to fabricate MEMS based micro pressure sensors. Front side etching technique is the most advanced and recently developed MEMS technology. It takes the advantages of both the bulk and surface micromachining technologies. Micro-electro-mechanical systems (MEMS) are Freescale's enabling technology for acceleration and pressure sensors. MEMS based sensor products provide an interface that can sense, process and/or control the surrounding environment.

Freescale's MEMS-based sensors are a class of devices that builds very small electrical and mechanical components on a single chip. MEMS-based sensors are a crucial component in automotive electronics, medical equipment, hard disk drives, computer peripherals, wireless devices and smart portable electronics such as cell phones. These sensors began in the automotive industry especially for crash detection in airbag systems. Throughout the 1990s to today, the airbag sensor market has proved to be a huge success using MEMS technology. MEMS-based sensors are now becoming pervasive in everything from inkjet cartridges to cell phones. Every major market has now embraced the technology.

Fabrication of thin membranes has been an important aspect in common micromechanical devices owing to its numerous industrial applications. The pressure sensing technology that provides a multiple-measurement and multiple-range capability is also based on a thin diaphragm or membrane fabrication process. This book describes the experimental details of the fabrication of a thin membrane over a conical V-shaped cavity using front side lateral etching technology and the results obtained are discussed.

In the reported work, front side lateral etching technology has been studied. This study proposes a novel front side lateral etching fabrication process for silicon based piezoresistive pressure sensor. As far as the fabrication process is concerned, this technique successfully accomplished a front side etching process laterally to replace the conventional back-side bulk micromachining. This novel structure pressure sensor can achieve the distinguishing features of the chip size reduction and fabrication costs degradation.


About the Authors


Dr. Parvej Ahmad Alvi is an Assistant Professor in the Department of Physics, School of Physical Sciences, Banasthali University, India. He has got a PhD in Applied Physics (2009) from Department of Applied Physics, Faculty of Engineering & Technology, Aligarh Muslim University, Aligarh, India. His research area is MEMS, NEMS technologies, Opto-electronics, and Material Science. He has active collaboration with CEERI (CSIR) Pilani (India), Elettra Synchrotron (Italy), Aligarh Muslim University, Aligarh (India), and Royal University of Phnom-Penh (Cambodia). Dr. Ahmad Alvi has published many international research papers and articles in his field and four books. He is an editorial board member of International Journal of Optoelectronics Engineering (Scientific Academic Publishing, USA), Nanoscience and Nanotechnology (Scientific Academic Publishing, USA) and lifetime member of International Union of Crystallography.






About the Autor

1. Introduction

1.1. MEMS Technology
      1.1.1. Bulk Micro-machining
      1.1.2. Surface Micro-machining
      1.1.3. High Aspect Ratio Micro-machining LIGA Other Techniques
1.2. Transduction Mechanism
      1.2.1. Piezoresistance
      1.2.2. Piezoelectricity
      1.2.3. Bimorphs
      1.2.4. Capacitance
      1.2.5. Electrostatics
1.3. Micro-machined Pressure Sensors
      1.3.1. Macro- and Micro-scale Devices
      1.3.2. Piezoresistive Pressure Sensors
      1.3.3. Capacitive Pressure Sensors
      1.3.4. Piezoelectric Pressure Sensors
      1.3.5. Optical Sensors


2. Micro-fabrication Technologies

2.1. Micro-fabrication Techniques
2.2. Silicon Wafers
2.3. Wafers Cleaning
      2.3.1. Degreasing
      2.3.2. RCA 1
      2.3.3. RCA 2
      2.3.4. Piranha Treatment
2.4 Thermal Oxidation
2.5. CVD Techniques
      2.5.1. LPCVD (Low pressure Chemical Vapor Deposition)
      2.5.2. PECVD (Plasma Enhanced Chemical Vapor Deposition)
      2.5.3. APCVD (Atmospheric Pressure Chemical Vapor Deposition)
2.6. Photolithography
      2.6.1. Wafer Alignment and Wafer Exposure
      2.6.2. Photoresist
      2.6.3. Etching Dry Etching Wet Etching
2.7. Metallization
2.8. Device Processing


3. Thin Film Materials

3.1. Silicon Dioxide (SiO2)
3.2. Silicon Nitride (Si3N4)
3.3. Polycrystalline Silicon (Polysilicon)
      3.3.1. Properties of Polysilicon Film Residual Stress Young’s Modulus Roughness Electrical Properties
      3.3.2. Polysilicon as a Sacrificial Layer
      3.3.3. Effect of Doping Temperature on Polysilicon Grains
      3.3.4. Advantages and Disadvantages of Polysilicon Film
      3.3.5. Applications of Polysilicon


4. Anisotrpic Etching

4.1. Introduction
4.2. Wet Etching Fundamentals
      4.2.1. Isotropic Etching
      4.2.2. Anisotropic Etching
      4.2.3. Wet Anisotropic Etching Using Aqueous KOH Solution
4.3. Experimental Methodology
4.4. Surface Roughness due to KOH Etching
4.5. Physical Models for KOH Etching
4.6. Results and Inferences


5. Fundamental Theory and Design of Pressure Sensor

5.1. Stress Analysis for Thin Diaphragm
5.2. Wheatstone Bridge
5.3. Piezoresistors


6. Fabrication of Micro Pressure Sensor (using Fron-side Lateral Etching Technology)

6.1. Front-Side-Etching Technology
      6.1.1. Front Side Normal Etching Technology
      6.1.2. Front Side Lateral Etching Technology
6.2. Fabrication Process Sequence Optimization
      6.2.1. Fabrication Process Sequence (I)
      6.2.2. Fabrication Process Sequence (II)
6.3. Fabrication Process Detail
      6.3.1. Detail of Process Sequence (I) Thermal Growth of SiO2 LPCVD of Si3N4 Photolithography-1 (PLG-1) RIE of Si3N4 (0.15 Microns) Wet etching of SiO2 (0.5 Microns) Stripping Off of Photoresist LPCVD of Polysilicon (Thickness 1.0 μm) Etching of Polysilicon PECVD of (Si3N4 + SiO2 + Si3N4) PECVD of Si3N4 for Thickness 0.2 Microns PECVD of SiO2 for Thickness 0.5 Microns Boron Doping of Polysilicon for Piezoresistors Boron Diffusion Conditions Metallization for Contact Lines and Contact Pads Photolithography (PLG-4) for Defining Metal Contact Lines and Contact Pads Aluminium Etching Sintering Details of the PLG-5 KOH Etching
      6.3.2. Detail of Process Sequence (II) Membrane and Cavity Formation Sealing of the Cavity and Deposition of Resistors


7. In-Process Observations

7.1. Photographs for Process Sequence (I)
      7.1.1. Photograph after PLG-1, SiO2 and Si3N4 Etching
      7.1.2. Photograph after PLG-2 and Poly Etch (with Photoresist)
      7.1.3. Photograph after PLG-2 and Poly Etch (without Photoresist)
      7.1.4. Photograph after PECVD (Si3N4 + SiO2 + Si3N4)
      7.1.5. Photograph after (LPCVD of Polysilicon + Boron Doping + + PLG-3 + RIE of Polysilicon) Defining of Boron Doped Polysilicon Resistors
      7.1.6. Photograph after (Al metallization + PLG-4 + Wet Etching of Al) Defining Metal Contact Pads and Contact Lines
      7.1.7. Photographs after KOH Etching for Cavity Formation
7.2. Photographs for Process Sequence (II)
      7.2.1. Photograph after LPCVD (Si3N4 + SiO2 + Si3N4)
      7.2.2. Photographs after PLG-3 and RIE of LPCVD (Si3N4 + SiO2 + Si3N4)
      7.2.3. Photographs after KOH Operation
      7.2.4. Photographs after Defining Resistors and Metallic Lines

8. Summary

Future Scope of the Work




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