ECE 541/ME 541 Microelectronic Fabrication Techniques

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1 ECE 541/ME 541 Microelectronic Fabrication Techniques MW 4:00-5:15 pm Metrology and Characterization Zheng Yang ERF 3017, ECE541/ME541 Microelectronic Fabrication Techniques Page 1

2 Ellipsometry Ohmic contacts I-V, C-V, Hall effect measurements Material Characterization PL, Raman, XRD, XPS, SIMS, EDX, etc ECE541/ME541 Microelectronic Fabrication Techniques Page 2

3 Ellipsometry Ohmic contacts I-V, C-V, Hall effect measurements Material Characterization PL, Raman, XRD, XPS, SIMS, EDX, etc ECE541/ME541 Microelectronic Fabrication Techniques Page 3

4 Ellipsometry ECE541/ME541 Microelectronic Fabrication Techniques Page 4

5 What is ellipsometry? Ellipsometry is an optical technique used for analysis and metrology Non contact, non destructive method It determines the change in polarization state of light reflected from a sample. Typically used for characterizing thin films (thickness, optical constants complex refractive index). It is a model-based technique ECE541/ME541 Microelectronic Fabrication Techniques Page 5

6 What is ellipsometry? Transparent films from a sub-nanometre up to several microns can be measured using ellipsometry. The surface upon which the film is measured can be a semiconductor, dielectric or metal. The film can be transparent or absorbing on a transparent or opaque substrate (need contrast) The measuring polarized light can range from the ultra violet to the infra-red. ECE541/ME541 Microelectronic Fabrication Techniques Page 6

7 By convention, the polarization of light is described by specifying the orientation of the wave's electric field at a point in space over one period of the oscillation. When light travels in free space, in most cases it propagates as a transverse wave the polarization is perpendicular to the wave's direction of travel. In this case, the electric field may be oriented in a single direction (linear polarization), or it may rotate as the wave travels (circular or elliptical polarization). ECE541/ME541 Microelectronic Fabrication Techniques Page 7

8 Polarized and un-polarized light Most sources of electromagnetic radiation contain a large number of atoms or molecules that emit light. The orientation of the electric fields produced by these emitters may not be correlated, in which case the light is said to be unpolarized. If there is partial correlation between the emitters, the light is partially polarized. If the polarization is consistent across the spectrum of the source, partially polarized light can be described as a superposition of a completely unpolarized component, and a completely polarized one. One may then describe the light in terms of the degree of polarization, and the parameters of the polarization ellipse ECE541/ME541 Microelectronic Fabrication Techniques Page 8

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10 Crossed Polarizers ECE541/ME541 Microelectronic Fabrication Techniques Page 10

11 Crystal polarizers (II) [birefringence] isotropic crystal (sodium chloride) The 2 output beams are polarized (orthogonally). anisotropic crystal (calcite) most stable polymorph of calcium carbonate (CaCO3) ECE541/ME541 Microelectronic Fabrication Techniques Page 11

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15 Ellipsometry Ohmic contacts I-V, C-V, Hall effect measurements Material Characterization PL, Raman, XRD, XPS, SIMS, EDX, etc ECE541/ME541 Microelectronic Fabrication Techniques Page 15

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29 Ellipsometry Ohmic contacts I-V, C-V, Hall effect measurements Material Characterization PL, Raman, XRD, XPS, SIMS, EDX, etc ECE541/ME541 Microelectronic Fabrication Techniques Page 29

30 Semiconductor device measurements setup 30 ECE541/ME541 Microelectronic Fabrication Techniques Page 30

31 I-V test setup Probe station Large working distance microscope Movable stage and platform Movable optics Movable electrical contacts Semiconductor Device Analyzer (SDA) 31 ECE541/ME541 Microelectronic Fabrication Techniques Page 31

32 Probe Station parts 32 ECE541/ME541 Microelectronic Fabrication Techniques Page 32

33 Micropositioners 33 ECE541/ME541 Microelectronic Fabrication Techniques Page 33

34 Probes 34 ECE541/ME541 Microelectronic Fabrication Techniques Page 34

35 Tips Metals used: Tungsten, Steel, Palladium, Osmium. 35 ECE541/ME541 Microelectronic Fabrication Techniques Page 35

36 Complete setup 36 ECE541/ME541 Microelectronic Fabrication Techniques Page 36

37 Semiconductor device analyzer 37 ECE541/ME541 Microelectronic Fabrication Techniques Page 37

38 I-V characteristic curve of Diode ECE541/ME541 Microelectronic Fabrication Techniques Page 38

39 What is Four Point Probing Four Point Probing is a method for measuring the resistivity of a substance. ECE541/ME541 Microelectronic Fabrication Techniques Page 39

40 How the system works In order to measure the resistivity of a substance, four points of contact must be made with the probe and the substance. Current goes through the two outer probes, and the difference in voltage is measured between the two inner probes. Through this process the resistance can be calculated. ECE541/ME541 Microelectronic Fabrication Techniques Page 40

41 Surface Resistivity In a regular three-dimensional conductor, the resistance can be written as where ρ is the resistivity, A is the cross-sectional area and L is the length. The cross-sectional area can be split into the width W and the sheet thickness t. By grouping the resistivity with the thickness, the resistance can then be written as: R s is then the sheet resistance. ECE541/ME541 Microelectronic Fabrication Techniques Page 41

42 High-accuracy capacitance measurements An AC signal of known frequency is applied through an internal low value resistor and the capacitor under test in a series configuration. The AC current flowing into the capacitor must also flow through the resistor, creating an AC voltage across the resistor. The magnitude and phase of this voltage can be measured and compared to the original AC signal, and the capacitance can be computed. Techniques such as this frequency domain measurement can be very accurate. LCR meter (Inductance (L), Capacitance (C), and Resistance (R)) ECE541/ME541 Microelectronic Fabrication Techniques Page 42

43 Tools for measurement Probe Station ECE541/ME541 Microelectronic Fabrication Techniques Page 43

44 Agilent Semiconductor Parameter Analyzer ECE541/ME541 Microelectronic Fabrication Techniques Page 44

45 Capacitance Voltage Measurements capacitance voltage (C-V) testing is to determine semiconductor parameters, particularly in MOSCAP and MOSFET structures. C-V measurements are also widely used to characterize other types of semiconductor devices and technologies, including bipolar junction transistors, JFETs, III-V compound devices, photovoltaic cells, MEMS devices, organic thin film transistor (TFT) displays, photodiodes, and carbon nanotubes (CNTs). Metal Oxide Silicon (MOS) capacitor ECE541/ME541 Microelectronic Fabrication Techniques Page 45

46 Capacitance Voltage Measurements C V measurements can reveal oxide thickness, oxide charges, contamination from mobile ions, and interface trap density in wafer processes. A deep depletion C V curves for an SiO2/Si MOS capacitor. NA = 1017 cm 3, t ox = 10 nm, A = cm 2. The capacitance is determined by superimposing a small amplitude ac voltage v on the dc voltage V. The ac voltage frequency is typically 10 khz to 1 MHz with 10 to 20 mv amplitude. ECE541/ME541 Microelectronic Fabrication Techniques Page 46

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48 I Basic Physical Phenomena of Hall Effect When an electron moves in a direction perpendicular to an applied magnetic field, it experiences a force (Lorentz force) acting normal to both directions and moves in response to this force (see below for an n- type semiconductor) Constant current I (flows References: 2, 3. v e Lorentz Force F= ev x B F V V H B B V=0 Coordinate System d z y x along x axis) in the presence of magnetic field B (z axis) causes Lorentz force F (y axis) Causes electron paths to bend towards negative y axis Charge builds up on the surface of the side of sample, and the potential drop across the two sides of the sample is known as the Hall voltage (V H ) ECE541/ME541 Microelectronic Fabrication Techniques Page 48

49 When electrons flow without magnetic field... t semiconductor slice + _ I I d ECE541/ME541 Microelectronic Fabrication Techniques Page 49

50 When the magnetic field is turned on... I qbv B-field ECE541/ME541 Microelectronic Fabrication Techniques Page 50

51 As time goes by... high potential qe I qbv = qe low potential ECE541/ME541 Microelectronic Fabrication Techniques Page 51

52 Finally... V H I B-field ECE541/ME541 Microelectronic Fabrication Techniques Page 52

53 Basic Hall effect measurement system 53 ECE541/ME541 Microelectronic Fabrication Techniques Page 53

54 Ellipsometry Ohmic contacts I-V, C-V, Hall effect measurements Material Characterization PL, Raman, XRD, XPS, SIMS, EDX, etc (please also refer to Lecture 16, 17, and 25 for more details) ECE541/ME541 Microelectronic Fabrication Techniques Page 54

55 Photoluminescence Spectroscopy Continuum states Electronic bound state Laser energy E CB k h excitation h emission VB PL Intensity A laser excites electrons from the valence band into the conduction band, creating electron-hole pairs These electrons and holes recombine (annihilate) and emit a photon. The number of emitted photons (intensity) as a function of energy, which is photoluminescence (PL). ECE541/ME541 Microelectronic Fabrication Techniques Page 55

56 Discovery of Raman Spectroscopy In 1928, Raman discovered that the spectrum of scattered lines of CCl 4 liquid not only consisted of the Rayleigh lines but a pattern of lines of shifted frequency the Raman spectrum. Mr. Raman won the Nobel Prize of Physics in 1930, for his work on the scattering of light and for the discovery of the effect named after him. C.V. Raman ( ) ECE541/ME541 Microelectronic Fabrication Techniques Page 56

57 Stokes S Anti-Stokes S L q S L q S S L q ECE541/ME541 Microelectronic Fabrication Techniques Page 57 S L q