Background Statement for SEMI Draft Document 4806 New Standard: GUIDE TO DEFECTS FOUND ON MONOCRYSTALLINE SILICON CARBIDE SUBSTRATES

Transcription

1 Background Statement for SEMI Draft Document 4806 New Standard: GUIDE TO DEFECTS FOUND ON MONOCRYSTALLINE SILICON CARBIDE SUBSTRATES NOTICE: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this document. NOTICE: Recipients of this document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, patented technology is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided. This document is intended to give users of silicon carbide substrate material a guideline for the nomenclature of defects commonly found on this kind of material. Many defects are specific to SiC and experience and naming conventions of traditional Si material (e.g. in SEMI M1 and related documents) is not always appropriate. It is separated into three sections: bulk defects, surface defects and features observed after etching in molten KOH salt. Test methods are not listed, as SEMI M55 and its sub-standards list the appropriate test methods and redundancy should be avoided. For several defects as micropipes no standard test methods are currently existing. Review and Adjudication Information Task Force Review Committee Adjudication Group: SiC TF Defect Catalog Group EU CS Materials Committee Date: TBD March 21, 2011 (tentative) Time & Timezone: TBD TBD Location: TBD TBD City, State/Country: TBD Frankfurt, Germany Leader(s): Arnd Weber (SiCrystal) Arnd Weber (SiCrystal) Roland Bindemann (FCM) Standards Staff: Ian McLeod (SEMI NA) imcleod@semi.org OR James Amano (SEMI HQ) jamano@semi.org Ian McLeod (SEMI NA) imcleod@semi.org OR James Amano (SEMI HQ) jamano@semi.org This meeting s details are subject to change, and additional review sessions may be scheduled if necessary. Contact the task force leaders or Standards staff for confirmation. Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will not be able to attend these meetings in person but would like to participate by telephone/web, please contact Standards staff. i

2 SEMI Draft Document 4806 New Standard: GUIDE TO DEFECTS FOUND ON MONOCRYSTALLINE SILICON CARBIDE SUBSTRATES 1 Purpose 1.1 The purpose of this guide is to list, illustrate and provide reference for various characteristic features and defects that are seen on silicon carbide wafers. Recommended practices for observation are referenced as far as available standards. The artifacts described in this guide are intended to support the development of test methods and to support the content of SEMI M55. 2 Scope 2.1 Observed defects on monocrystalline SiC substrates, which are of potential relevance for industrial application are identified and described on the basis of examples, mainly by photos, pictures and other relevant data for these defects. 2.2 The defect terminology is reviewed and adapted where necessary. 2.3 This document does not cover epitaxial layers grown on SiC substrates. NOTICE: This standard does not purport to address safety issues, if any, associated with its use. It is the responsibility of the users of this standard to establish appropriate safety and health practices and determine the applicability of regulatory or other limitations prior to use. 3 Limitations 3.1 Defects, structures, features or artifacts revealed or enhanced by the referenced methods and exhibited in this guide must be carefully interpreted. Unless utmost care is exercised, the identification of the structure may be ambiguous. 4 Referenced Standards and Documents 4.1 SEMI Standards SEMI M55 Specification for Polished Monocrystalline Silicon Carbide Wafers 4.2 ASTM Standards ASTM F (2007) Test Method for Crystallographic Perfection of Gallium Arsenide by Molten Potassium Hydroxide (KOH) Etch Technique NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions. Page 1

3 5 Terminology List of defects Table 1 List of defects Defect / Keyword Remark Figure micropipe bulk defect, no special preparation 1, 3, 6 planar defect bulk defect, no special preparation 2, 3 crystallite, crystallite defect bulk defect, no special preparation 6 polytypes, polytype defect bulk defect, no special preparation 4, 5 crossed polarizers method 5, 6 edge chip surface feature 7 indent surface feature 7 pit surface feature 8 scratch, microscopic scratch surface feature 9 crack surface feature 10 large hexagonal etch pit KOH etched surface, see also ASTM F , 12 basal plane dislocation (BPD) KOH etched surface, see also ASTM F , 15 threading dislocation (TSD, TED) KOH etched surface, see also ASTM F , 15 screw dislocation (SD) KOH etched surface, see also ASTM F , 14 edge dislocation (ED) KOH etched surface, see also ASTM F Bulk features (no special preparation) Figure 1 Micropipes, optical microscope, transmission mode, focus in bulk. Material: 4H, 4deg off, Si-face. Page 2

4 0.5 mm Figure 2 Planar Defect (void or negative crystal in bulk), optical microscope, transmission mode, focus in bulk. Material: 4H, 4 deg off, Si face. Figure 3 Planar Defect with micropipe attached on top left (optical microscope, transmission mode, different depth of focus in the material). Material: 4H, 4deg off, Si-face, n-type. Page 3

5 20 mm Figure 4 Polytypes (foreign polytypes, polytype defect): deviating yellowish colour due to 15R or 21R or similar modification on n-type material. The affected area may be much smaller in the order of 0.1 mm 2. Material: 6H, n-type Figure 5 Left: crossed polarizer image showing weak structural imperfections visible due to contrast patterns. (example area marked by red circle). Also present is a polytype defect on the left wafer side with deviating color. (arrow, compare also Fig. 4) Right: same wafer in transmission mode, only polytpe defect is visible. Material: 4H, n-type. Page 4

6 Figure 6 Crossed Polarizer Image showing crystallite defect (red circle). The darker region results from facetted growth and exhibits higher doping concentrations. Also visible are micropipes due to cross-like contrast patterns in the upper half of the wafer. Material: 4H wafer, 50.8mm, 8 deg off, n-type. 7 Surface Features (no special preparation required, wafer as received) 0.5 mm Figure 7 Edge chip and indent Page 5

7 Figure 8 Pits (optical microscope, DIC-mode). Material: 4H. 0.5 mm Figure 9 Microscopic Scratch. Material: 4H, Si-face. 0.5 mm Figure 10 Crack Page 6

8 8 Features revealed by molten KOH etching 8.1 Preparation The material is exposed to molten KOH at approx 540 C for several minutes thereby revealing characteristic etch pits on the polished Si-face. As a guideline ASTM F1404 should be used. Special attention has to be paid to possible artifacts in the etch pattern due to preparation conditions, as e.g. those caused by scratches. 8.2 Interpretation of etch pits in general depends on polytype, conductivity type and doping level 100 um Figure 11 Large hexagonal etch pit (etched micropipe, super-screw dislocation, large defect), the appearance depends on the etching and inspection conditions. Material: 4H, 4 deg off, Si-face, n-type Figure 12 Large hexagonal etch pits in various configurations: (1) with white center, (2) with black center, (3) multiple overlaying non-hexagonal pits, (4) multiple overlaying hexagonal pits. Many threading dislocations and basalplane dislocations (small etch pits) are also present (see also figure 14 and 15 below). Material: 4H, 4 deg off, Si-face, n-type. Page 7

9 100 um Figure 13 Basal plane dislocation. Material: 4H, 4 deg off, Si face, n-type. 100 um Figure 14 Threading dislocations (edge or screw depending on doping level). Material: 4H, 4 deg off, Si face, n-type. Page 8

10 Figure 15 Threading dislocations (appearing dark, marked with arrow) and basal plane dislocations (appearing bright, marked with circles). Material: 4H, nominally on-axis, Si-face, semi-insulating. NOTICE: SEMI makes no warranties or representations as to the suitability of the standard(s) set forth herein for any particular application. The determination of the suitability of the standard(s) is solely the responsibility of the user. Users are cautioned to refer to manufacturer s instructions, product labels, product data sheets, and other relevant literature respecting any materials or equipment mentioned herein. These standards are subject to change without notice. By publication of this standard, Semiconductor Equipment and Materials International (SEMI) takes no position respecting the validity of any patent rights or copyrights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of any such patent rights or copyrights, and the risk of infringement of such rights are entirely their own responsibility. Page 9