《微机电系统》PPT课件

The key to building semiconductor devices and integrated circuits lies in the ability to control the local doping and hence the local electronic properties of a semiconductor crystal.
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of
air. 100class, 10class
3. X-Ray lithography
A type of light lithography techniques using short wavelength X-Rays Pros • Fast process • High aspect ratio • Solves depth of focus problem • High resolutions of ~ .5 µm • Reduction in diffraction,
4. Electron Beam Lithography
As scanning electron microscopes, an
electron beam scans across the substrate surface and exposes electron
sensitive coating.
2) Commonly used MEMS materials
Category
Material
Property or application
Metal
Au,Al,Cu,Ni,Cr
Conductor
Silicon
Structure, semiconductor
Poly-crystalline silicon Semicondu
CHAPTER 2. Micro fabrication technology
1. Semi-conductor industry and MEMS materials.
1) Introduction to modern Semiconductor industry
Semiconductor industry is playing more and more important role in modern society. We can say, no semiconductor industry, no modern civilization!
2) Photoresist Spin Coating
3) Clean-Rooms, Wafer Cleaning
-- A very clean environment is needed for micro fabrication to prevent dirt or other particles from contamination the micro devices.
The most commonly used IC devices are:
1) PN Diodes
2) Bipolar Junction Transistors
3) MOS Transistors
2. Introduction to the Lithography Process
1) Positive and Negative Resist
7) Semiconductor Devices
Understanding of how the basic devices used ICs operate is useful, because it provides some understanding of the objectives we have for IC technology.
ctor
Single-crystalline silicon
GaAs
e, semiconductor
Structure, Anisotropic etch properties
Structure, optical properties
Quartz
Crystalline SiO2
Substrate, structures
HF
KOH、Acetone、TMAH
☼ Basic step of lithography:
1）The maximum resolution of a device:
where λis the wave length of light used to make
image transfer. e.g. UV λ=500nm
--Air purification: humidity(45%), temperature(70°F)
--If we need to maintain a “clean” environment, we need to pay a lot of cost.
Definition of clean-room class: number of
substrate limit resolution
5. Diffusion and Implantation of Dopants
6.Thin film addition
• PR Spin on • Thermal oxidation • Thermal evaporation • E-beam evaporation • Sputtering process • CVD (LPCVD,PECVD) • Electroplating
2
A
A2
Where t: time; A、B: constant; when t<<
4B
d≈ B t/A
A and B can be obtained from ‘handbook’
2) Deposition (no chemical reaction on surface)
--Vacuum chambers are needed + thin film deposition
4)CVD (Chemical Vapor Deposition)
6) Why do we choose silicon as a MEMS structural material?
Semiconductors are a class of materials which have the unique property that their electrical conductivity can be controlled over a very wide range by the introduction of dopants. While this property can easily be observed in crystalline, polycrystalline, or amorphous semiconductor materials, crystalline materials provide the most reproducible properties and the highest performance
① Geometric representation of crystal Si Definition:
“( )” specific plane equivalent plane
“{ }”
“[ ]” specific direction “< >” equivalent direction
② Wafers are classified as how they are doped (n-type, p-type), and how the Si crystals are oriented as seen from the top of the shape of the wafers are cut differently.
in integrated circuits.
Dopants are atoms that generally contain either one more or one fewer electrons in their outermost shell than the host semiconductor. They provide one extra electron or one missing electron (a "hole") compared to the host atoms. These excess electrons and holes are the carriers, which carry current in semiconductor devices.
--Al, Au, Cr
3) Sputtering --A momentum-exchange process (not heating) --Low temperature process --We can sputter anything onto substrate
theoretically
reflection, and scattering effects • Not affected by organic defects in mask
Cons
– Shadow printing – Lateral magnification error – Brighter x-ray sources needed – More sensitive resists needed – Difficult fabrication of x-ray mask
features for very accurate registrar
Cons
– Swelling occurs when developing negative electron beam resists, limiting resolution
– Expensive as compared to light lithography systems – Slower as compared to light lithography systems – Forward scattering in the resist and back scattering in the
1) Thermal oxidation
--growingSiO 2
on Si
Dry oxidation:Si O2 SiO 2
Wet (o1x1i5d0a°tiCo,n:S4hir)2H2O（g） SiO 2 2H2
( 800°C~1200°C ) d
o.44d Si
d 1 A 1 4Bt 1
2）Steps: substrate preparation→ thin film addition →cast PR →pre-designed mask →expose in UV light →develop PR in developing solution →Etch the thin film covered with PR in a solution that will attack the thin film but not the PR →remove PR
Polymer Non-metals
Parylene-C Nafion
Diamond(C)
Polymeric materials structure
3) Crystal structure of Silicon 4) Crystal planes 5) Types of silicon wafer
Pros
• Computer-controlled beam • No mask is needed • Can produce sub-1 µm features • Diffraction effects are minimized • Electron beam can detect surface