1 Micro-fabrication Process. 2 Clean Room 3 Clean room classifications and applications.

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Micro-fabrication Process

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Clean Room

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Clean room classifications and applications

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Clear room classification

Class 1000: fewer than 1,000 particles (>0.5μm) in 1 cubic foot of air

Class 100: fewer than 1,00 particles (>0.5μm) in 1 cubic foot of air

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Micromachining Materials

Substrates:

• Silicon

• GaAs

• Other elemental or compound semiconductors

• Metals (bulk and foils)

• Glasses

• Quartz

• Sapphire

• Ceramics

• Plastics, polymers and other organics

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Micromachining Materials

Additive Materials:

• Silicon (amorphous, polycrystalline, epitaxial)

• Silicon compounds (oxides, nitrides, carbides, …)

• Metals and metal compounds

• Glass

• Ceramics

• Polymers and other organics

• Biomaterials

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Silicon Crystallography

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Cubic Lattices

• Simplest arrangements of atoms in three dimension in which the unit cell is a cubic volume

• Simple Cubic (sc) structure has an atom located at each corner of the unit cell

•Body Centered Cubic (bcc) has an additional atom at the center of the cube

• Face Centered Cubic (fcc) unit cell has atoms at the eight corners and on the six faces.

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Cubic Lattices

sc bcc fcc

• How is the arrangement of atoms in Silicon?

• Silicon has fcc + (1/4x, 1/4y, 1/4z) fcc structure

a is lattice constant

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Si crystal structure

Si crystal= fcc +1/4(x,y,z)fcc

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Planes and directions

Lattice vector R= r*a+ s*b+ t*c, r, s & t are integers

We can define a plane in a crystal lattice with three integer, called Miller indices

1. Find the intercepts of the plane in terms of integral multiples of the basis vectors

[Fig2, 4, 1]

2. Take the reciprocal of the integers and reduce to smallest set of integers h, k, l, in this case 2,1,4

3. Label the plan (214) & direction is <214>

a

b

c(214) plane

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Planes and directions

a

b

c

a

b

c

a

b

cBlue is (100) plane, yellow arrow is <100> dirn

Blue is (010) plane, yellow arrow is <010> dirn

Blue is (110) plane, yellow arrow is

<110> dirn

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晶圓製作流程

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Czochralski Method

For growing single-crystalline ingot

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CZ 晶體提拉過程

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Floating Zone Method(FZ)

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懸浮帶區法 (FZ 法 )

因CZ法缺點，乃因坩鍋內的氧原子會滲入單晶錠長晶過程中。 FZ 法可以生產含氧量非常低的單晶錠。 先以模子鑄出含摻雜物多晶矽棒。 種晶被熔融並接合於棒的下端。 射頻 (RF)加熱線圈沿軸向上移動，多晶棒熔融，原子排成種

晶方向。 缺點 –無法生成大直徑晶錠。 –差排 (dislocation) 密度較高。 生成的晶錠以製造 –功率晶體 (thyristor) 。 –大功率整流元件 (rectifier) 等為主要目的。

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比較柴氏和浮動區長晶法

兩法之比較 柴氏法 (Czochralski) – 較普遍、便宜。 – 較大晶圓尺寸 (300 mm in production) 。 – 原料可再度使用。 懸浮帶區法 (FZ 法 ) – 純矽晶 ( 無坩堝 ) 。 – 較昂貴，晶圓尺寸較小 (150 mm) 。 – 主要用來製造分離式功率元件所需晶圓。

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比較柴氏和浮動區長晶法

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晶圓的備製

去除末端：用鋸將晶錠的兩端 ( 頸及尾 ) 切除。 研磨直徑尺寸：用無心研磨機 (centerless grinder) 。 檢測結晶方向、導電形式，以及阻抗性結晶方向檢測方法 -X 光繞射 (diffraction) 、平行 (collimated) 光束折射。

晶錠刻意偏移主方向 (off-orientation) 幾度：離子植入。

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晶塊修整 “裁切”錐形的晶塊與錐體末端。 驗證程序控制以控制小塊金屬或雜質。

晶塊本體研磨至所需直徑，並加上平的或槽口記號。

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Silicon Wafer Cuts

Miller indices indicated by ground edges called “flats”. “n”-type and “p”-type refer to “doping”. N means “negative” (phosphorous) and P means “positive” (boron).

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Photolithography

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Lithography devices

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Lithography process

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Lithography process-cont.

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Positive/negative resist

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Positive/negative resist-cont.

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Positive/negative resist-cont.

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Masking and Exposure

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Mask fabrication process

M ASK 10um〈 〉

PATTERNTRANSFER

4000dpiPL OTTER

M ASK 2um〈 〉

DEVEL OPEPATTERN

L ASERWRITER

M ASK 1um〈 〉

DEVEL OPEPATTERN

E-BEAMWRITER

Auto-CADL -edit, etc.

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Lithographic masks

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Lithographic light source

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Exposure Light Source (UV)

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Development

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Developing the pattern (C)

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Oven Baking

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Lithographic processing: Repeat process

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Etching

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Etching Mechanism

Etching type

Wet etching

Dry etching Etching steps

Oxidation

Reaction

Remove products

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Factors in Wet Etching

• Limited• Reaction limited• Diffusion limited

• Factors• Concentration• Temperature• Stirring

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Anisotropic Wetting Etching

HNA system

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Anisotropic Etch

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Anisotropic Etchants

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Wet anisotropic etching

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Etch the material

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Dry Etching

Ion bombardment Plasma reactor

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Bulk machining using dry etch

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Lithographic processing: Final release

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Micro device integration: Packaging

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Commercial micro devices: sensors and actuators