Etching and CVD cleaning for semiconductors

LIQUID CRYSTAL DISPLAYS, AND PHOTOVOLTAICS

TIER 1

The default emission factors for the Tier 1 method is presented in Table 6.2 below.

In using Tier 1, it is not good practice to modify, in any way, the set of the FCs or the values of the emission factors assumed in Table 6.2. Inventory compilers should not combine emissions estimated using Tier 1 method with emissions estimated using the Tier 2 or 3 methods. For example, inventory compilers may not use the Tier 1 factor for CF4 to estimate the emissions of CF4 from semiconductors and combine it with the results of other FC gases from a Tier 2 or Tier 3 method. It should be also noted that the Tier 1 FC emission factors presented in Table 6.2 should not be used for any purpose other than estimating annual FC-aggregate emissions from semiconductor, TFT-FPD or PV manufacturing for compilation of the national greenhouse gas inventory.

12 Sources and methods for developing emissions factors, if not explicitly provided in Chapter 6, can be found in Burton (2006).

Table 6.2

Tier 1 Gas-specific emission factors for FC emissions from electronics manufacturing

Electronics Industry Sector

Emission Factor (EF) (Mass per Unit Area of Substrate Processed)

cf4

C2F6

CHF3

C3F8

NF3

SF6

C6F14

Semiconductors, kg/m2

0.9

1.

0.04

0.05

0.04

0.2

NA

TFT-FPDs, g/m2

0.5

NA

NA

NA

0.9

4.

NA

PV-cellsa, g/m2

5

0.2

NA

NA

NA

NA

NA

Heat Transfer Fluidsb, kg/m2

NA

NA

NA

NA

NA

NA

0.3

a EFs adapted from unpublished work of Fthenakis, Alsema and Agostinelli. (Fthenakis ,2005) Note that factor is applicable only to silicon-specific technologies and is applied for abatement.

b EF assumes HTFs have the same GWP and C6Fi4 represents a suitable proxy. The origin of this factor is described in Burton, 2004, and is based in part on the work of Tuma and Tousignant (2001).

TIER 2

As discussed above, emissions factors based on simple electronics production variables are not adequate to account for all of the factors that influence emissions. Data for each of the following parameters are necessary to prepare a reliable estimate:

• The brand of process tool used;

• Emission reduction technology.

Default values have been developed for the parameters used in Tier 2a and 2b methods (See Figure 6.1) on the basis of direct measurements, literature, and expert judgement (see Tables 6.3, 6.4, and 6.5 Tier 2 Default Emission Factors for FCs Emissions from Semiconductor12, TFT-FPD13, and PV12 Manufacturing respectively). Given the difficulty in representing the diverse production conditions within the electronics industry, default emission parameters are inherently uncertain. While accuracy can be improved with larger sets of measured data and where factors are applied to similar processes using similar or identical chemical recipes, developing default factors necessarily involves some form of averaging across all of the data.

Electronics industry specialists expect that rapid technical innovation by chemical and equipment suppliers and electronics manufacturers will result in major emission reductions in the future (i.e., 2006 onwards). As a result, emission factors for these categories should evolve to reflect these changes. The semiconductor and TFT-FPD industries have established mechanisms through the World Semiconductor Council and the World LCD Industry Cooperation Committee, respectively, to evaluate global emission factors. The PV industry may be considering establishing a mechanism for tracking its PFC emissions during PV manufacture. (Fthenakis, 2006)

FC-use during PV manufacture may or may not increase. Existing evidence suggests that, should FC-use in this industry grow, efforts will be made to control their emissions (Agostinelli et al, 2004; Rentsch et al, 2005). Inventory compilers may wish to periodically consult with the industry to better understand global and national circumstances.

Tables 6.3 and 6.4 include two entries for NF3: Remote-NF3 and NF3. The first refers to a cleaning method in which the film cleaning-agents formed from NF3 (F-atoms) are produced in a plasma upstream (remote) from the chamber being cleaned. The last, denoted as simply NF3, refers to an in-situ NF3 cleaning process that is analogous to the process for other cleaning gases like C2F6 and C3F8.

The default value for the fraction of gas remaining in the shipping container (heel) is 0.10.

13 The emissions factors (EFs) for TFT-FPD manufacturing are simple (unweighted) averages developed from gas- and process-specific values published by Nishida et al. (2005).

Chapter 6: Electronics Industry Emissions

Table 6.3

Tier 2 Default emission factors for FC emissions from semiconductor manufacturing

Greenhouse Gases with TAR GWP

Greenhouse Gases without TAR GWP

Non-GHGs Producing FC By-products*

Process Gas (i)

cf4

c2f6

chfj

CH2F2

CjFs

Remote

nf3

sf6

c4f6

c5f8

c4f8o

f2

cof2

Tier 2a

1-Ui

0.9

0.6

0.4

0.1

0.4

0.1

0.02

0.2

0.2

0.1

0.1

0.1

NA

NA

Bcf4

NA

0.2

0.07

0.08

0.1

0.1

0.02t

0.09

NA

0.3

0.1

0.1

0.02t

0.02t

Bc2f6

NA

NA

NA

NA

NA

0.1

NA

NA

NA

0.2

0.04

NA

NA

NA

Bc3f8

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

0.04

NA

NA

Tier 2b

Etch 1-Ui

0.7*

0.4*

0.4*

0.06*

NA

0.2*

NA

0.2

0.2

0.1

0.2

NA

NA

NA

CVD 1-Ui

0.9

0.6

NA

NA

0.4

0.1

0.02

0.2

NA

NA

0.1

0.1

NA

NA

Etch BCF4

NA

0.4*

0.07*

0.08*

NA

0.2

NA

NA

NA

0.3*

0.2

NA

NA

NA

Etch BC2F6

NA

NA

NA

NA

NA

0.2

NA

NA

NA

0.2*

0.2

NA

NA

NA

CVD BCF4

NA

0.1

NA

NA

0.1

0.1

0.02f

o.it

NA

NA

0.1

0.1

0.02f

0.02f

CVD BC2F6

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

CVD BC3F8

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

0.04

NA

NA

Notes: NA denotes not applicable based on currently available information

' The default emission factors for F2 and COF2 may be applied to cleaning low-k CVD reactors with CIF3.

Estimate includes multi-gas etch processes t Estimate reflects presence of low-k, carbide and multi-gas etch processes that may contain a C-containing FC additive

Table 6.4

Tier 2 Default emission factors for FC emissions from LCD manufacturing

Greenhouse Gases with TAR GWP

Greenhouse Gases without TAR GWP

Non-GHGs Producing FC By-products

Process Gas (i)

CF4

c2f6

chf3

CH2F2

C3FS

Remote

nf3

sf6

c4f6

c5f8

c4f8o

f2

cof2

Tier 2a

1-Ui

0.6

NA

0.2

NA

NA

0.1

0.03

0.3

0.6

NA

NA

NA

NA

NA

bcf4

NA

NA

0.07

NA

NA

0.009

NA

NA

NA

NA

NA

NA

NA

NA

bchf3

NA

NA

NA

NA

NA

0.02

NA

NA

NA

NA

NA

NA

NA

NA

bc2f6

NA

NA

0.05

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

Bc3f8

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

Tier 2b

Etch 1-Ui

0.6

NA

0.2

NA

NA

0.1

NA

NA

0.3

NA

NA

NA

NA

NA

CVD 1-Ui

NA

NA

NA

NA

NA

NA

0.03

0.3

0.9

NA

NA

NA

NA

NA

Etch BCF4

NA

NA

0.07

NA

NA

0.009

NA

NA

NA

NA

NA

NA

NA

NA

Etch BCHf3

NA

NA

NA

NA

NA

0.02

NA

NA

NA

NA

NA

NA

NA

NA

Etch BC2F6

NA

NA

0.05

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

CVD BCF4

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

CVD BC2F6

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

CVD BC3F8

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

Notes: NA denotes not applicable based on currently available information

Chapter 6: Electronics Industry Emissions

Table 6.5

Tier 2 Default emission factors for FC emissions from PV manufacturing

Greenhouse Gases with TAR GWP

Greenhouse Gases without TAR GWP

Non-GHGs Producing FC By-products

Process Gas (i)

CF4

c2f6

chf3

CH2F2

C3F8

c-C4F8

Remote

nf3

sf6

c4f6

c5f8

c4f8o

f2

cof2

Tier 2a

1-Ui

0.7

0.6

0.4

NA

0.4

0.2

NA

0.2

0.4

NA

NA

NA

NA

NA

bcf4

NA

0.2

NA

NA

0.2

0.1

NA

0.05

NA

NA

NA

NA

NA

NA

bc2f6

NA

NA

NA

NA

NA

0.1

NA

NA

NA

NA

NA

NA

NA

NA

bc3f8

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

Tier 2b

Etch 1-Ui

0.7

0.4

0.4

NA

NA

0.2

NA

NA

0.4

NA

NA

NA

NA

NA

CVD 1-Ui

NA

0.6

NA

NA

0.1

0.1

NA

0.3

0.4

NA

NA

NA

NA

NA

Etch BCF4

NA

0.2

NA

NA

NA

0.1

NA

NA

NA

NA

NA

NA

NA

NA

Etch BC2F6

NA

NA

NA

NA

NA

0.1

NA

NA

NA

NA

NA

NA

NA

NA

CVD BCF4

NA

0.2

NA

NA

0.2

0.1

NA

NA

NA

NA

NA

NA

NA

NA

CVD BC2F6

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

CVD BC3F8

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

Notes: NA denotes not applicable based on currently available information

Table 6.6

Tier 2a & 2b Default efficiency parameters for electronics industry FC emission reduction

Table 6.6

Tier 2a & 2b Default efficiency parameters for electronics industry FC emission reduction

Emission Control Technology

cf4

C2F6

CHF3

C3F8

c-C4F8

NF3f

SF6

Destruction0

0.9

0.9

0.9

0.9

0.9

0.95

0.9

Capture/Recoveryd

0.75

0.9

0.9

NT

NT

NT

0.9

a Values are simple (unweighted) averages of destruction efficiencies for all abatement technologies. Emission factors do not apply to emission control technologies which cannot abate CF4 at destruction or removal efficiency (DRE) > 85 percent when CF4 is present as an input gas or by-product and all other FC gases at DRE > 90 percent. If manufacturers use any other type of emission control technology, its destruction efficiency is 0 percent when using the Tier 2 methods. b Tier 2 emission control technology factors are applicable only to electrically heated, fuelled-combustion, plasma, and catalytic devices that

• are specifically designed to abate FCs,

• are used within the manufacturer's specified process window and in accordance with specified maintenance schedules and

• have been measured and has been confirmed under actual process conditions, using a technically sound protocol, which accounts for known measurement errors including, for example, CF4 by-product formation during C2F6 as well as the effect of dilution, the use of oxygen or both in combustion abatement systems

c Average values for fuelled combustion, plasma, and catalytic abatement technologies. d Average values for cryogenic and membrane capture and recovery technologies.

e Vendor data verified by semiconductor manufacturers. Factors should only be used when an emission control technology is being utilised and maintained in accordance with abatement manufacturer specifications. f Use of NF3 in the etch process is typically small compared to CVD. The aggregate emissions of NF3 from etch and CVD under Tier 2b will usually not be greater than estimates made with Tier 2a or Tier 1 methods. NT = not tested.

Process tool emission factors

The procedures for calculating process tool emission factors for Tier 2a and Tier 2b methods are identical. Process tool emission factors are defined as the amount of greenhouse gas emitted divided by the amount of greenhouse gas used in the process. The emission factors correspond to the '(1 - U)' term in the Tier 2 formulas. For example, the emission factor of 0.9 for CF4 (see Table 6.3 above, Tier 2a value) means that 90 percent of the CF4 used in the process is emitted as CF4.

By-product emission factors were also calculated. The major by-product emission of significance is CF4. While it is generally held that the only gases that emit significant amounts of CF4 as a by-product are C2F6 and C3F8, the data provided by tool manufacturers and chemical suppliers showed that CF4 is also formed from mixtures of gases (e.g., that contain CHF3 or CH2F2) and c-C4F8. As a result of this discussion, CF4 by-product emission factors were calculated for CHF3, CH2F2, C2F6, C3F8, c-C4F8 and C4F8O. For example, a value of 0.1for C3F8 (taken from Table 6.3 above, Tier 2a value) means that 10 percent of the C3F8 used is converted into CF4. However, C2F6 may also be emitted from the decomposition of molecules such as C4F6. As described previously, CF4 may also be formed when etching or cleaning chambers where carbon-containing films are present.

In order to calculate the Tier 2b process tool emission factors, data were collected from process equipment and gas manufacturers. The data were collected according to process type (either Chemical Vapour Deposition (CVD) or etch) and also by type of gas (e.g. C2F6, CF4). The methods used to conduct the emissions testing were real time Quadrupole Mass Spectrometry (QMS) and Fourier Transform Infrared Spectroscopy (FTIR), the best known methods for measuring process tool emissions. Calibration standards (usually 1 percent mixtures with a balance of N2) were used to quantify the results. The measurement protocol and quality control requirements that were followed are outlined in the 'Guidelines for Environmental Characterisation of Semiconductor Equipment.' (Meyers et al, 2001)14 The emission factors for Tier 2b (see Tables 6.3 and 6.4 above) are the simple (unweighted) average of the data collected for each gas for etch and CVD, rounded to one significant figure.12, 16

In order to determine the Tier 2a process tool emission factors, knowledge of the amounts of gas used in typical semiconductor manufacturing processes is required. The Tier 2a emission factors were obtained using weights provided by industry experts for the proportion of each gas used in etching and cleaning processes. For example, the Tier 2b emission factors for C2F6 (Table 6.3) are 0.5 (etch) and 0.6 (CVD). The distribution of C2F6 usage between etching and CVD chamber cleaning processes during semiconductor manufacture is 20:80. Applying these weights to each of the emission factors gives 0.6 for the Tier 2a factor for C2F6 to one significant figure.

14 These guidelines have also been adopted by flat panel display manufacturers for measuring FC-emissions during flat panel device manufacture.

The corresponding distribution of SF6 usage in TFT-FPD manufacture is 50:50, which gives 0.6 for corresponding Tier 2a emission factor (Table 6.4).15

For Tier 3 emission factors, semiconductor manufacturers use company or plant-specific values rather than using default values as listed in Table 6.1 above. In order to assure the quality of emission factors, emission testing should be conducted in accordance with accredited methods.16 If a third-party supplier conducts the emissions testing, the semiconductor manufacturer should make sure that the third-party supplier is capable of meeting all of the requirements outlined in Revision 3.0 of the Equipment Environmental Characterisation Guidelines (SIA, 2000). Semiconductor manufacturers who use emission factors provided by the process tool equipment supplier should make sure that the emission factors are applicable to their specific manufacturing process. Manufacturing methods with process parameters (e.g., pressure, flow rate) that deviate from centreline conditions may have different emission factors than those provided by the tool manufacturer.

Emission control technology factors for Tier 2 methods

Emissions control technologies are developing at a rapid pace along with electronics manufacturing technology. Default control technology emission factors in Table 6.6 are based on tests of control devices that have been optimised for specific processes and tools. Results are expected to vary across tools and gas flow rates. Emission factors are not applicable to all tools or processes in semiconductor, liquid crystal display, or photovoltaic manufacturing facilities. The Tier 2 default destruction efficiency parameters presented in Table 6.6 are only applicable when the inventory compiler can demonstrate through communication with facility managers and subsequent documentation that emissions control technologies are operated and maintained in accordance with manufacturer specifications. If companies use any other type of abatement device, they should assume that its destruction efficiency is 0 percent under the Tier 2 a and b methods.

Assumptions for the emissions control technology emission factors for the Tier 2 (a & b) methods include:

(i) Specific emissions control technologies are not listed; emission factors for each chemical were established based on results achieved during testing of emissions control technologies in semiconductor manufacturing applications;

(ii) Emission factors should only be used when abatement is applied to emissions that fall within the operating range specified by the abatement manufacturer to meet or exceed the factors listed in Table 6.6;

(iii) Emission factors apply only to that portion of emissions that pass through a properly operating and maintained control device; emission factors should not be applied when control device is bypassed, not operating according to manufacturer specifications, or not maintained in accordance with specifications.

(iv) Emission factors do not apply to emission control technologies which cannot abate CF4 at a destruction removal efficiency (DRE) > 85 percent when CF4 is present as an input gas or by-product and all other FC gases at DRE > 90 percent. If manufacturers use any other type of emission control technology, its destruction efficiency is 0 percent when using the Tier 2 methods.

The default Tier 2 emission control factors in Table 6.6, Default Efficiency Parameters for Electronics Industry FC Emission Reduction Technologies were calculated from data received from equipment suppliers, abatement technology suppliers and electronic device manufacturers. It should be noted that only data from abatement devices that were specifically designed to abate FCs were used in the calculation. Data were received from combustion abatement devices (all of which used some type of fuel), plasma abatement devices, electrically heated abatement devices, and catalytic abatement devices.

The values presented in Table 6.6, Default Efficiency Parameters for Electronics Industry FC Emission Reduction Technologies, are the results of all of the data received for optimized technologies and for each input gas, rounded down to the next 5 percent (e.g., an average of 98 percent would be rounded down to 0.95). The averages were rounded down to reflect that (i) emissions control devices vary in their efficacy depending upon what gas they are optimised to destroy, and (ii) the efficacy of emission control devices depends on the type of tool they are installed on (150, 200 or 300mm wafers) and the amount of FC gas flown through that particular tool, and total exhaust flow through the emissions control device. An emission control device that can destroy 99 percent of a FC when it is optimised to destroy that FC on a certain tool may destroy less than 95 percent of that FC when it is optimised to destroy something else or when it is used on a tool for which it was not designed, or if the FC or total exhaust flow exceeds a certain limit. Electronics manufacturers and abatement tool manufacturers

15 The 50:50 SF6 usage rates represent an average for the leading TFT-FPD manufacturing regions of Japan, Republic of Korea and Taiwan. That proportion was provided by Nishida (2006) and Kim (2006).

16 One example of an internationally accredited testing method is Meyers et al. (2001).

should ensure that the abatement system installed is properly sized and maintained and that the emission control device can meet or exceed the default emission factor highlighted in Table 6.6.

Continue reading here: Choice of activity data

Was this article helpful?

0 0