Technical Report

SiNx PECVD Technology
without Using Explosive SiH4 Gas■Samco R&D Dept.

Introduction

Although SiH4 (silane) gas is widely used in
the semiconductor manufacturing industry todeposit thin films, its potential to detonate
poses significant health and safety hazards.
In fact, just 0.45 kg of SiH4 gas has the same
explosive power as 2.7 kg of TNT. 1)

the PD-220NL. For comparison, the resultsfor SiH4/SiNx deposition are also shown.

For a safer, easier-to-handle alternative to
SiH4 gas, Samco developed a proprietary
CVD method that instead utilizes a liquid
precursor, also known as Liquid Source
Plasma CVD (LS-CVD).
Although TEOS is well-known as a liquidsource for SiO2, liquid sources for SiNx
plasma deposition are not common. In thistechnical report, we introduce a newly-developed liquid source called SN-2 (named bySamco), and review its basic properties
within two types of plasma-enhanced CVD
applications, namely anode type and cathodetype.

< System body >Figure 1 PD-220NL Exterior

About SN-2

SN-2 is a liquid source with a vapor pressureof 420hPa at 25°C. Although it is flammable,
SN-2 differs from SiH4 gas because it is notpyrophoric and will therefore not spontaneously combust. For gas abatement, a dryabsorption scrubber can be used. SN-2 andN2 are the only gasses needed for basic SiNx
deposition; however, adding NH3 can lead toeasier refractive index adjustments andimproved refractive index uniformity.

SiH4
SN-2

Intensity (a.u.)■< SN-2 supply unit >

4400

3400

2400

Wavenumber (cm2)

1400

400

SN-2 Based SiNx Deposition withAnode Coupled PECVD (Model: PD-220NL)

Figure 2 FTIR evaluation of each SiNx ﬁlm

Figure 1 illustrates the PD-220NL's exterior.
An external unit that supplies SN-2 is to thesystem’s side. Figure 2 shows an FTIR spectrum of SN-2/SiNx deposition performed by

In SN-2/SiNx film, peaks originating fromhydrogen such as N-H wagging mode(~1200cm-1),
Si-H
stretchingmode(2160cm-1) and N-H stretching mode■

Technical Report(3350cm-1) are more clearly observed than in
SiH4/SiNx film. This indicates that the chemical composition of SN-2/SiNx has a higher
amount of hydrogen than SiH4/SiNx film.

these favorable results.
200Tensile

100

Stress (MPa)Figure 3 and Table 1 respectively show across-section SEM of deposition performed
over Al wires and evaluation results for stepcoverage. We defined step coverage as theSiNx film thickness divided by the film thickness at the top surface.

0-100-200-300

Compressive
0100200300

N2 (sccm)
Figure 4 SN-2/SiNx ﬁlm stress controllability based on
N2 gas ﬂow
SN-2/SiNx
308nm ②611nm ①Al252nm ③■364nm ④SiO2

Figure 3 SN-2/SiNx ﬁlm deposition over Al wire

Evaluated Area

Step Coverage (%)

① Top

100

② Upper side50

③ Lower side41

④ Bottom60

Table 1 Step coverage

The deposition over the Al wires had a favorable step coverage of more than 40%. Figure
4 shows the film stress control as a function ofN2 flow rate of the PD-220NL using SN-2, NH3
and N2 gases. The film stress changed
almost linearly from compressive to tensile
based on the N2 flow rate.
This trend of SN-2/SiNx film stress controllability is similar to that of SiH4/SiNx film. Currently, Samco is evaluating device samplesfor passivation and insulator properties, with

SN-2 Based SiNx Deposition with Cathode
Coupled PECVD

We are now developing SN-2/SiNx for anotherdeposition method, namely cathode coupledplasma CVD. This method actively utilizes
ion bombardment for film deposition, whichmakes it easier to deposit dense film. Depending on the process requirements for thesamples’ temperature stability, deposition ispossible at temperatures ranging from room
temperature to 400°C, with film stress control
ranging from almost zero to more than 1 GPa.
■Conclusion

SN-2/SiNx deposition using anode coupledplasma CVD clearly produces film that contains a higher amount of hydrogen than thatof SiH4/SiNx deposition. A step coverage of
40% and a wide range of stress controllability
from -300MPa (compressive) to +100MPa(tensile) are also confirmed.
The application of SN-2 to cathode coupledplasma is currently under investigation.
With those processes, we are in the processof uncovering new applications, such as optical waveguides, MEMS and organic device
passivation films. Going forward, we will continue to develop new applications and provide
systems for our customers.References and Contact Information■Reference1) Fischman, Michael L. "Semiconductor Manufacturing Hazards."
Clinical Environmental
Health and Toxic Exposures. By Gary R. Krieger and John Burke. Sullivan. Philadelphia, Pa.:
Lippincott Williams & Wilkins, 2001. N. pag. Print.
Contact Information

Email: info@samco.co.jp
Phone: +81(0)75-621-7841(Headquarters)

Visit www.samcointl.com