SEMI International Standards
SEMI New Activity Report Form (SNARF)

Activity Number: 4675
SNARF for: New Standard: Test Method for the Measurement of Elemental Impurity Concentrations in Silicon Feedstock by Bulk Digestion, Inductively-Coupled-Plasma Mass Spectrometry

Originating Global Technical Committee: Photovoltaic (PV) - Materials
Originating Technical Committee Region: North America
Task Force in which work is to be carried out: International PV Analytical Test Methods Task Force

1. Rationale: The manufacturers of crystalline and micro-crystalline silicon to be used in silicon solar cells, purchase or manufacture for internal use, silicon that is used as feedstock. This Si Feedstock can take many physical forms, including, for example, granules, powders, polysilicon chunks, wafers, reclaimed silicon, and top and tail cuts from silicon boules.

The purity level of PV Si Feedstock can affect solar cell efficiency, as well as the productivity of some processes used to transform the PV Si Feedstock into solar cells.

SEMI has many test methods that can be used to determine the purity level of PV Si Feedstock, depending upon its physical form and the elements of interest: SEMI MF 397-02 for measuring net resistivity, SEMI 1389-00 for measuring dopants by photoluminescence, SEMI MF 1724-01 for measuring surface metal contamination on granules, chunks or powders by acid extraction followed by atomic absorption spectroscopy, SEMI1188-1105 for measuring interstitial oxygen by Fourier Transform Infrared Spectroscopy, SEMI MF1391-0704 for measuring substitutional carbon by Fourier Transform Infrared Spectroscopy, and SEMI MF1630-0704 for measuring dopants by low temperature Fourier Transform Infrared Spectroscopy. SEMI MF28-0707 can be used to indirectly measure the purity level using photoconductive decay. SEMI PV1-0309 can be used to measure a broad range of elemental impurities in 6N silicon feedstock by GDMS.

However, the existing SEMI test methods do not provide for the direct measurement of a broad range of elemental impurities in all grades in silicon feedstock including 7N-8N silicon feedstock. SEMI MF1724 states that the acid extraction of surface metal impurities on polysilicon can be extended to bulk digestion for the impurity collection and to inductively-coupled-plasma mass spectrometry (ICP-MS) for the analysis, but SEMI MF1724 does not provide a test method for those extensions. In addition SEMI MF 1724 is designed for alkali metals and first series transition elements using GF-AAS, not for a broader range of elements including dopants.

While the bulk digestion ICP-MS measurement of impurities in Si Feedstock is used commercially today, it is not possible to quantify the impact on the ROI if this standard is implemented.

Rate the Estimated Effect on the Industry
2: Major effect on an industry sector - identify the relevant sector

Rate the Estimated Technical Difficulty of the Activity
II: Some Difficulty - Disagreements on known requirements exist but developing consensus is possible

2. Scope:
a: Define the areas to be covered or addressed by this activity or document:
This document will provide a standard test method for the measurement of elemental impurity concentrations in Si Feedstock by bulk digestion Inductively-Coupled-Plasma Mass Spectrometry.

b: Expected result of activity
New Standard

3. Projected Timetable for Completion:
a: General Milestones
a. Activity Start: 10/16/2008b. 1st Draft by: 01/01/2009
c. Preballot by: d. Technical Ballot by: 01/01/2009
e. Committee Approval By:04/01/2009

Safety Considerations:
The resulting document is expected NOT to be a Safety Guideline

Intellectual Property Considerations:
a. In complying with the standard or safety guideline to be developed, the use of patented technology or a copyrighted item(s) is NOT required
b. The body of the standard and any appendices or related information sections will NOT include copyrighted material

Comments, Special Circumstances: None.

Approval: Activity approved by Committee/GCS on October 15, 2008