Method for determining trace metals in silicon

Patent metadata

Field	Value
Publication number	US-12366567-B2
Application number	US-202017770633-A
Country	US
Kind code	B2
Filing date	Jul 21, 2020
Priority date	Jul 21, 2020
Publication date	Jul 22, 2025
Grant date	Jul 22, 2025

Abstract

A method for determining an amount of metallic impurities within silicon. The method includes the steps of (a) providing a rodlike silicon sample and a rodlike seed crystal in a zone melting apparatus, (b) zone melting to form a single silicon crystal having a conical end region with a droplike melt forming at the end of the single silicon crystal in a separation step, (c) cooling of the droplike melt to form a solidified silicon drop, (d) partial or complete dissolution of the silicon drop in an acid, and analyzing the solution obtained in step (d) by a trace analysis technique. Wherein the separation step further includes a remelting step for the silicon sample to reduce its diameter, forming a droplike melting zone, and separation of the seed crystal and the silicon sample by moving the seed crystal and the silicon sample apart from one another.

First claim

The invention claimed is:

1. A method for determining an amount of metallic impurities within silicon, comprising the steps of: a) providing a rodlike silicon sample and a rodlike seed crystal in a zone melting apparatus; b) zone melting to form a single silicon crystal having a conical end region, with a droplike melt forming at the end of the single silicon crystal in a separation step; c) cooling of the droplike melt to form a solidified silicon drop; d) partial or complete dissolution of the silicon drop in an acid; and e) analyzing the solution obtained within step d) by a trace analysis technique; wherein the separation step further comprises the steps of: (i) remelting of the silicon sample to reduce its diameter, where for a first time interval the direction of movement of the silicon sample and of the seed crystal is reversed relative to its previous direction of movement, to form the conical end region; (ii) forming a droplike melting zone, where for a second time interval the movement of the seed crystal is halted and the direction of movement of the silicon sample is reversed again; and (iii) wherein during separation of seed crystal and silicon sample where the direction of movement of the silicon sample is reversed, and wherein said separation step occurs for a duration of 5 to 20 s, and has a speed of movement of 150 to 400 mm/min.

2. The method of claim 1 , wherein after the remelting, the silicon sample in an end region of length l has a diameter which is less than or equal to the diameter of the single crystal at its contact face with the melt.

3. The method of claim 2 , wherein the diameter of the contact face of the single crystal with the melt is 3 to 8 mm, preferably 4 to 6 mm.

4. The method of claim 2 , wherein the diameter of the silicon sample in its end region of length l is 2 to 8 mm, preferably 3 to 6 mm.

5. The method of claim 2 , wherein the length l of the end region of the silicon sample corresponds to one to three times its diameter.

6. The method of claim 1 , wherein the silicon sample during remelting is moved at a higher speed of movement than the single crystal.

7. The method of claim 6 , wherein the speed of movement of the silicon sample is 5 to 15 mm/min, preferably 7 to 13 mm/min, more preferably 9 to 11 mm/min.

8. The method of claim 6 , wherein the speed of movement of the single crystal is 2 to 10 mm/min, preferably 3 to 8 mm/min, more preferably 4 to 6 mm/min.

9. The method of claim 1 , wherein the first time interval during remelting lasts 30 to 300 s, preferably 90 to 240 s, more preferably 60 to 120 s.

10. The method of claim 1 , wherein the formation of the droplike melting zone and a speed of movement of the silicon sample is 1 to 5 mm/min, preferably 2 to 4 mm/min.

11. The method of claim 1 , wherein the second time interval lasts 1 to 4 s, preferably 2 to 3 s.

12. The method of claim 1 , wherein the separation of seed crystal and silicon sample and a speed of movement of the silicon sample is 250 to 350 mm/min.

13. The method of claim 1 , wherein the cooling of the droplike melt, the movement of the silicon sample is halted and the seed crystal is removed in its original direction of movement with a speed of movement of 150 to 400 mm/min, preferably 250 to 350 mm/min, from the silicon sample.

14. The method of claim 1 , wherein the silicon drop is dissolved partially by immersion in the acid for a duration of 3 to 15 min, preferably 5 to 10 min.

15. The method of claim 14 , wherein the acid comprises a mixture of concentrated nitric acid and hydrofluoric acid in a ratio of 4:1 to 3:1, preferably 2:1 to 1:1.

Assignees

• Wacker Chemie Ag

Inventors

• Aschl Waltraud
• Kautnick Theresa
• Stadlmayr Manuel
• Steinkress Peter

Classifications

• G01N1/32

  Polishing; Etching · CPC title

• C30B29/06 Primary

  Silicon · CPC title

• C30B13/28

  Controlling or regulating · CPC title

• G01N33/2045 Primary

  Defects · CPC title

• C30B15/20

  Controlling or regulating (controlling or regulating in general G05) · CPC title