Wet Bulk Micromachining湿体微加工

Wet Bulk Micromachining –
a STIMESI II tutorial 23.02.2019
Per Ohlckers, Vestfold University College
hive.noPer.Ohlckershive.no
Daniel Lapadatu, SensoNor Technologies
denominator (in this case 6):
3, 6 and 2.
2
► The Miller indices of the plane are:
y
(362).
1
1
O
x
1
2
3
Slide 13
Crystallographic Planes and Directions
(abc) denotes a plane. {abc} denotes a family of
Secondary flat Primary flat
Slide 15
Standard 100 mm Wafers
The position of the flat(s) indicates the surface orientation and the type of doping.
The primary flat on (100) and (110) wafers is along the [110] direction.
multimemsdaniel.lapadatusensonor.no
Outline
1. Background and Motivation 2. The Silicon Crystal 3. Isotropic Wet Etching 4. Anisotropic Wet Etching 5. Selective Etching 6. Convex Corners
Slide 3
Manufacturing Processes
Serial (e.g. Focused Ion Milling - FIB) vs. batch (e.g. bulk Si micromachining) vs. continuous (e.g. doctor’s blade).
z
along the crystallographic axes, e.g. 4
2, 1 and 3.
► The reciprocal of the three integers
are taken:
1/2, 1/1 and 1/3.
3
► Multiply by the smallest common
Slide 11
Miller Indices
Miller indices are a notation system in crystallography for planes and directions in crystal lattices.
A lattice plane is determined by three inteLeabharlann Baiduers h, k and l, the Miller indices, written (hkl). The indices are reduced to the smallest possible integers with the same ratio.
Micromachining
Bulk Micromachining is a process that produces structures inside the substrate by selective etching.
Surface Micromachining is a process that creates structures on top of the substrate by film deposition and selective etching.
Bulk Micromachining
Surface Micromachining
Slide 5
Classification of Bulk Silicon Etching
Bulk Micromachining is a process that produces structures inside the substrate by selective etching.
Additive (e.g. evaporation) or subtractive (e.g. dry etching).
Projection (almost all lithography techniques) vs. truly 3D.
Mold vs. final product.
R S
B
Slide 7
Bulk Silicon Etching: Examples
Deep cavity by wet, anisotropic etching
Release etch by RIE
Recess etch by RIE
Slide 8
Wet Silicon Etching: Examples
equivalent planes. [abc] denotes the direction
perpendicular on (abc) plane. <abc> denotes a family of
equivalent directions. {100}, {110} and {111}
F-based plasmas
Slide 6
Etching Features
Etch rate:
► Rate of removal of material/film. ► Varies with concentration, agitation and temperature of etchant,
Slide 2
Outline
1. Background and Motivation 2. The Silicon Crystal 3. Isotropic Wet Etching 4. Anisotropic Wet Etching 5. Selective Etching 6. Convex Corners
One atom is located in position with xyz coordinates (0, 0, 0), the other in position (a/4, a/4, a/4), a being the basic unit cell length.
Lattice constant a = 5.43 Å.
Isotropic etching with HNA (HF : Nitric Acid : Acetic Acid)
Anisotropic etching with KOH
(110)
(100)
Slide 9
Outline
1. Background and Motivation 2. The Silicon Crystal 3. Isotropic Wet Etching 4. Anisotropic Wet Etching 5. Selective Etching 6. Convex Corners
Slide 10
Structure of Single Crystal Silicon
Face-centred cubic (fcc) structure (diamond structure) with two atoms associated with each lattice point of the unit cell.
Wet Etching
Dry Etching
Crystal orientation dependent
Process dependent
Isotropic Anisotropic
Isotropic Anisotropic
Acidic Etchants
Alkaline Etchants
BrF3 XeF2
Orientation of flats for 100 mm wafers
p-(111)
n-(111)
Primary flat
p-(100)
n-(100)
Secondary flat
Slide 16
Wafers Used in MultiMEMS
P-type, 150 mm Si wafer.
Determining the Miller indices for planes by using the intercepts with the axes of the basic cell.
Slide 12
Determining Miller Indices
Example:
► Take the intercepts of the plane
are the most important families of crystal planes for the silicon crystal.
Slide 14
Single Crystal Silicon Wafers
Primary and secondary flats indicate the dopant type and surface orientation.
There are many different techniques that are being used.
However, in general, batch processing is the most powerful technique and used mostly.
FIB
Slide 4
porosity and density of etched film.
Etch selectivity:
U
► Relative etch rate of mask, film and substrate.
Etch geometry:
► Etching depth (R); ► Mask undercut (U); ► Slope of lateral walls (S); ► Bow of floor (B); ► Anisotropy.
The arrangement of the silicon atoms in a unit cell, with the numbers indicating the height of the atom above the base of the cube as a fraction of the cell dimension.
(100) ± 0.5ºSurface.
[110] ± 0.5ºPrimary Flat.
z {1 0 0 }
(1 0 0 ) S u rfa c e
Si Wafer
< 1 1 0 > D ire c tio n s
[1 1 0 ]
O
y
x
W a fe r's P rim a ry F la t
Slide 17
Outline
1. Background and Motivation 2. The Silicon Crystal 3. Isotropic Wet Etching 4. Anisotropic Wet Etching 5. Selective Etching 6. Convex Corners
Wafer diameter in current fab standards: from 100 to 300 mm.
Wafer thickness in current fab standards: from 250 to 600 µm.
Surface orientation:
► (100) for MOS and MEMS; ► (110) for MEMS; ► (111) for bipolar.
Slide 18
Isotropic Wet Etching of Silicon
All crystallographic directions are etched at the same rate.
Features: Si ► Etchants are usually acids;