Bio-Microsystems 고려대학교 Center for MNB Sensor Technology Nam Ki Min

Microfabrication 민 남 기민 남 기 Chapter 2

What is Microfabrication ?

고려대학교 Center for MNB Sensor Technology 4 What is Microfabrication? Historically the earliest micromanufacturing was used for semiconductor devices in integrated circuit fabrication and these processes have been covered by the term "semiconductor device fabrication," "semiconductor manufacturing," etc. Practical advances in MEMS and other nanotechnology, where the technologies from IC fabrication are being re-used, adapted or extended have led to the extension of the scope and techniques of microfabrication. Microfabrication (or micromanufacturing) is the design and creation of devices whose size can be measured in micrometers(10 -6 meters) or microns. Microfabrication typically uses methods and techniques developed by the semiconductor industry for creating IC, as well as new processes developed specifically for MEMS.

고려대학교 MNB Sensor Lab 5 What is Microfabrication? IC MESM

고려대학교 MNB Sensor Lab 6 Basic Microfabrication Steps

What are Semiconductors ?

Korea University MNB Sensor Lab 8 What are Semiconductors ? A group of materials having conductivities between those of metals and insulators. InsulatorConductor Semiconductor Very sensitive to temperature and light. Extremely minute traces of impurity atoms (routinely less than one atom per 10 9 Si atoms) can have a drastic effect on the electrical properties of semiconductors.  Semiconductor Properties

Korea University MNB Sensor Lab What are Semiconductors ?  General classifications of semiconductors Elemental semiconductors - Si(Silicon), Ge(Germanium) Compound semiconductors - IV-IV : SiC - III-V : GaAs(Gallium arsenide), GaN(Gallium nitride) - II-VI : ZnO(Zinc Oxide) - IV-VI : PbS(Lead sulfide), PbSe(Lead selenide) Alloys - Binary : Si 1-x Ge x - Ternary : Al x Ga 1-x As

Korea University MNB Sensor Lab 10  Atomic structure +14 Atomic core Valence electrons Silicon

Korea University MNB Sensor Lab 11  Covalent bond Si Shared electrons Silicon

Korea University MNB Sensor Lab 12  Silicon crystal Si Silicon

Korea University MNB Sensor Lab 13  Energy Levels : Hydrogen  Energy band EnEn eV eV eV 0 eV n=1 n=2 n=o o n=3 +1 n=1 n=2 n=3 Silicon

Korea University MNB Sensor Lab 14 (a)The splitting of the energy levels when two atoms are brought together. (b) The splitting when six atoms are brought together.  Energy band formation Silicon

Korea University MNB Sensor Lab 15 (c) If we consider the total number of atoms (N=10 23 atoms/cm 3 ), we find a very large number of levels (determined by N) spaced within the width ΔE, so the levels may be regard as a continuous band of energy levels. Silicon

Korea University MNB Sensor Lab 16  Energy band formation Silicon

Korea University MNB Sensor Lab 17  Silicon energy band Band Model Si Conduction band (Empty of electrons at T=0 K) Electron energy Valence band (Full of electrons at T=0 K) Band Model Bonding Model Silicon

Korea University MNB Sensor Lab 18 Carrier Generation in Semiconductors At T>0K, a few valence band electrons may gain enough thermal energy to break the covalent bond. Free electron Hole Conduction band Valence band Si Band Model Bond Model

Korea University MNB Sensor Lab 19 Electrical Conduction in Semiconductors Both electrons and holes contribute electric current in a semiconductor.

Korea University MNB Sensor Lab 20 Electrical Conduction in Semiconductors Current density and Conductivity semiconductor metal

Korea University MNB Sensor Lab 21 The techniques of adding controlled amounts of impurity atoms to a semiconductor material in order to change its conductivity. -Pentavalent impurity (5 valence electron) : P, As, Sb -Trivalent impurity (3 valence electron ) : B, Ga, Al Extrinsic (Impurity) Semiconductors  Doping of Semiconductor

Korea University MNB Sensor Lab 22 The addition of pentavalent impurity contributes free electrons, greatly increasing the conductivity of the intrinsic semiconductor. Extrinsic (Impurity) Semiconductors  N-type Semiconductor Si free electron P Si

Korea University MNB Sensor Lab 23 This type of impurity atom donates an electron to the conduction band and so is called a donor impurity atom. The resulting material is referred to as an n-type semiconductor. P Si Free electron generated by donor ionization Donor ions Free electrons Donor level Extrinsic (Impurity) Semiconductors

Korea University MNB Sensor Lab 24 The addition of trivalent impurity to an intrinsic semiconductor creates deficiencies of valence electrons, called "holes".  P-type Semiconductor Extrinsic (Impurity) Semiconductors Si hole B Si

Korea University MNB Sensor Lab 25 The group III atom accepts an electron from the valence band and so is referred to as an acceptor impurity atom. This type of semiconductor material is referred to as a p-type material. What are Semiconductors? B Si hole generated by acceptor ionization Acceptor ions Acceptor level

Korea University MNB Sensor Lab 26 Intrinsic n-type p-type n : electron p: hole n i =intrinsic carrier concentration n : majority carrier : p p : minority carrier : n  Summary n = p n >>p n <<p What are Semiconductors?