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LPCVD Pecvd

This document provides an overview of low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) thin film deposition techniques. LPCVD involves depositing films at low pressures between 10-1000 Pa to achieve high purity films and uniform thickness due to reduced gas phase reactions. PECVD enhances CVD by using a plasma to excite reactive gases, allowing for film deposition at lower temperatures than thermal CVD but providing higher film density and step coverage. Both techniques have advantages for depositing various thin films but LPCVD provides better uniformity and purity while PECVD enables lower temperature deposition.

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Goran Wnis
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458 views15 pages

LPCVD Pecvd

This document provides an overview of low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) thin film deposition techniques. LPCVD involves depositing films at low pressures between 10-1000 Pa to achieve high purity films and uniform thickness due to reduced gas phase reactions. PECVD enhances CVD by using a plasma to excite reactive gases, allowing for film deposition at lower temperatures than thermal CVD but providing higher film density and step coverage. Both techniques have advantages for depositing various thin films but LPCVD provides better uniformity and purity while PECVD enables lower temperature deposition.

Uploaded by

Goran Wnis
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Low-pressure CVD and PlasmaEnhanced CVD

Ronald Curley, Thomas


McCormack, and Matthew Phipps

CVD overview
Chemical Vapor Deposition
Thin films on substrate
Chemical oven + insert gas = deposited film

CVD overview
Four steps[1]:
1.
2.
3.
4.

Transport gas species to surface


Gas species absorption into surface
Reaction deposits products
Remove unwanted products and leftover
reactant

CVD overview
Velocity ratio (molecules/s, not meters/s!):
Mass transport velocity
Depends on pressure

Surface reaction velocity


Does not depend on pressure

Low ratio -> pure; well-controlled thickness


High ratio -> contaminants; poorly-controlled
thickness

CVD overview
Atmospheric-pressure CVD (APCVD) velocity
ratio too high: ~1:1
Mass transport velocity proportional to
1/pressure[2]
1 atm ~= 100 kPa

LPCVD

LPCVD typical pressure: 10-1000 Pa


Ratio 1:1001:10,000!
Reduced film variation
Increased purity

LPCVD
Substrate inserted
Tube evacuated to 0.1 Pa
Process gas (working gas)
added at 10-1000 Pa
Reaction performed
Substrate removed

Source: [3]

LPCVD
Best for polysilicon, using
SiH4
Oxides, PSG as well
Nitride encapsulation

Source: [4]

LPCVD
Advantages:

Disadvantages:

Excellent uniformity of
thickness & purity
Simple
Reliable/reproducible
Homogenous layer

Slows down deposition rate


Requires high temperatures,
<600C

PECVD
Plasma added with reactive gases
RF voltage excites plasma
Only electrons are hot, not ions: low
temperatures possible

PECVD

Picture: http://timedomaincvd.com/CVD_Fundamentals/plasmas/capacitive_plasma.html

Film

Reactive Gas

Silicon Nitride
Silicon dioxide

SIH4 or S1H2C12 &


NH3
SiH4 & O2

Amorphous silicon

SiH441

Thermal Deposition
CVD (Celsius)
750

Plasma Enhanced CVD


(Celsius)
200-500

350-550

200-400

550-650

200-400

Table: http://www.eng.auburn.edu/~tzengy/ELEC7730/ELEC%207730%20Fall%202003/Fall%202003%20Presentation%201/Park%20%20PECVD.ppt

PECVD
Conformal step coverage of PECVD SixNy

http://www.hitech-projects.com/dts/docs/pecvd.htm

PECVD
Advantages

Disadvantages

Equipment is expensive
Plasma bombardment is
stressful
Small batch sizes: 1-4 wafers,
one side
Compare to LPCVD: at least 25
wafers, both sides[5]

Low temperature
Higher film density
Higher dielectric constant
Good step coverage
Chamber easy to clean

Questions?

References:
[1] A Stoffel, A Kovcs, W Kronast and B Mller, LPCVD against PECVD for micromechanical applications
J. Micromech. Microeng., Vol. 6 No. 1 pp. 20-33, Mar. 1996
[2] Ivanda, Mile, Implementation and Development of the LPCVD Process, [Online], Available:
http://www.irb.hr/en/str/zfm/labs/lmf/Previous_projects/LPCVD/ [Accessed: 24 Nov. 2011]
[3] Dow Corning, Chemical Vapor Deposition, [Online], Available:
http://www.dowcorning.com/content/etronics/etronicschem/etronics_newcvd_tutorial3.asp?DCWS=El
ectronics&DCWSS=Chemical%20Vapor%20Deposition [Accessed: 25 Nov. 2011]
[4] Doolittle, Alan, Thin Film Deposition and Epitaxy, [Online], Available FTP:
http://users.ece.gatech.edu/~alan/ECE6450/Lectures/ECE6450L13and14-CVD%20and%20Epitaxy.pdf
[Accessed: 23 Nov. 2011]
[5] MEMSnet, MEMS Thin Film Deposition Processes, [Online], Available:
http://www.memsnet.org/mems/processes/deposition.html [Accessed: 23 Nov. 2011]
[6] Plasma-Enhanced CVD. Hitech-Projects. 2011. 28 Nov. 2011 <http://www.hitechprojects.com/dts/docs/pecvd.htm>.
[7] Mahalik, Nitaigour. Introduction to Microelectromechanical Systems (MEMS). New Delhi, India. Tata
McGraw-Hill, 2007.
[8] Plasma (Physics). Wikipedia. 29 Nov. 2011. 29 Nov 2011.
<http://en.wikipedia.org/wiki/Plasma_%28physics%29>.
[9] Fundamentals of Chemical Vapor Deposition Plasmas for CVD. TimeDomain CVD, Inc. 2002. 29
Nov. 2011.<http://timedomaincvd.com/CVD_Fundamentals/plasmas/plasma_deposition.html>.

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