SiO2 and SiN etching by Low Global Warming Potential Gas
Since the 1997 Kyoto Protocol (COP3), many people have been attempting to stop global warming. Scientists whoconduct research using the dry etching and deposition processes are no- exception to the requirement to reducegreenhouse gas (GHG) exhausts . Since 1995 (before COP3), we at Samco have been researching systems that captureand disintegrate perﬂuorocarbon compounds (PFCs).

This article introduces Samcoʼ s recent research on dry etching with carbonyl diﬂuoride (COF 2), which has lower globalwarming potential (GWP) than tetraﬂuoromethane (CF4) and triﬂuoromethane (CHF3).

Introduction(CH). COF 2 and CF 4 showed close selectivity, and CHF 3 showed

CF 4 and CH 3 gases are commonly used in dry etching ofsilicon dioxide (SiO2) and silicon nitride (SiN) ﬁlms. However, use

the lowest selectivity among the three gases. We observed nosigniﬁcant diﬀerence in surface smoothness and etch proﬁle likeof these gases is to be reduced in accordance with COP3

the previous experiment on the SiO2 ﬁlms.

Samco has studied the feasibility of COF 2 as an alternative toConclusion

guidelines, because their GWP is high, as shown in Table 1.
CF4 and CH3.

COF2 was developed in New Energy and Industrial

Technology Development Organization (NEDO) project as analternative to PFC. Some researchers reported that COF 2 wasused to clean the chambers after Chemical Vapor Deposition(CVD), but COF2ʼ s use in etching has not been reported yet. We

discovered that COF 2 can etch SiO 2 ﬁlm, as it can function as ac l e a n i n g g a s f o l l o w i n g C V D . A d d i t i o n a l l y, S a m c o h a s

determined that COF 2 could be broken down into carbon

monoxide (CO) and Flourine (F2 ) easily, and that F 2 could serveas the precursor (preliminary, original) gas that, like CF 4, can beconverted into CF 3 , CF 2 , 2F, etc. On the other hand, we shouldcarefully observe the CO within the COF 2 , as CO may lower theselectivity.

global warming gases, and has concluded that COF 2 is notnecessarily inferior to CF 4 and CHF 3 as an etching gas for SiO 2and SiN. We learned that the selectivity in SiO2 and SiN etchingby COF2 can be improved by adding hydrogen (H2) andmethane (CH 4 ) to the experiment of SiO 2 etching by CHF 3 , andbelieve that COF 2 works well as an etching gas for SiO 2 etching
and SiN etching. However, we should pay attention to thecharacteristics that result when COF 2 reacts with some metals

and water.
Table 1.

GWP（Global Warming Potential）data sheet [1]Gas

Experiment Results
We compared the etching performance of COF 2 , CF 4 , andCHF 3 , both on SiO 2 ﬁlms and SiN ﬁlms. Samcoʼ s ICP Etching

System, the RIE-200iP, was used in this experiment. The etchingrate, selectivity, and surface smoothness were evaluated and areshown in Tables 2 and 3.

CF 4 showed the highest etch rate on the SiO 2 ﬁlm, and theetch rates of COF 2 and CHF 3 on SiO 2 ﬁlm were close. On theother hand, CHF 3 showed the best selectivity, as it will break

down into carbon hydride) CH components, while COF2 showed
the worst result because it contained oxygen. Surfaces weresmooth and no diﬀerence among the three gas processes wasobserved. Etch proﬁles cannot be evaluated quantitatively, but

a selectivity of 1:1 or better suggests that all gases work well intransferring the mask shape onto SiO2.

We achieved similar results to SiO 2 ﬁlm etching experiments

in SiN ﬁlm etching, except that CHF 3 attained a signiﬁcantly
lower etch rate. The possible causes were disruption byhydrogen atoms and deposition by carbon hydride molecules

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Samco has executed experiments to see whether or not
COF 2 can serve as an alternative to CF 4 and CHF 3 , which are

CO2CH4N2O
SF6NF3
CF4C2F6C3F8
CHF3
CH2F2

GWP 100yr（PFC-14）（PFC-116）（PFC-218）（HFC-23）（HFC-32）

1 [2]

COF2

Table 2.

SiO2 Etching Results

Gas

Etch Rate（nm/min）

COF2
CF4CHF3

Table 3.

125
298
22,80017,2007,390
12,2008,830
14,800675

Selectivity（SiO2/PR）

Surface

130.4

1.23

Good165.2

1.69

Good

130.0

2.96

Good

SiN Etching Results

Gas

Etch Rate（nm/min）

Selectivity（SiN/PR）

Surface

COF2

127.0

1.11

Good

CF4

153.0

1.23

Good

CHF3

87.0

1.09

Good

References[1] IPCC Fourth Assessment Report（AR4）[2] Energy and Industrial Technology Development Organization（NEDO）

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