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Solar wafer texturing with 3M Trizact Diamond Tile

IP.com Disclosure Number: IPCOM000245806D
Publication Date: 2016-Apr-11
Document File: 4 page(s) / 149K

Publishing Venue

The IP.com Prior Art Database

Abstract

The method describes an abrasive mechanical process as a means of providing texture for the wafer surface for solar cell application. Among all the abrasive products listed, the Trizact Diamond Tile abrasive (available commercially from 3M) provided suitable texture for the solar wafers while achieving a surface morphology which is the most similar to a slurry-sawn wafer. Moreover, it is also able to meet the reflectance specification.

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       Solar wafer texturing with 3M Trizact Diamond Tile
1) Introduction:

In the basic process of solar wafer manufacturing, high purity silicon is use to go through a process of growing and casting it into ingot. The ingot will then be cut into blocks, and each individual block will be sliced into wafers (Diagram 1.1).

Diagram 1.1: Solar wafer manufacturing

For bare solar wafers, there is a requirement to achieve a specific reflectance specification after wire-saw from the ingot. The reflectance specification can be achieved by using slurry wire-saw as shown in (Diagram
1.2) instead of the conventional wire-saw. It can also be achieved by ion etch process, whereby conventional wire-sawn wafers are placed in a vacuum chamber and ions are used to etch the surface of the wafers, a basic diagram of ion etch process is shown in (Diagram 1.3).

Diagram 1.2: Slurry wire-saw Diagram 1.3: Ion etch process

Ion etch process could be the best method for manufacturing as the etching machine can handle high volume in a short process time. However, high investment cost is required in setting up ion etch process facility in the manufacturing environment. Thus, an alternative method is evaluated and tests were done on wire-sawn solar wafers with different method of texturing the wafer surface.

Different types of abrasives were tested for this application, and mechanical method is used to texture the wafer surface. Among all the abrasive products tested, the Trizact Diamond Tile abrasive (available commercially from 3M) provided suitable texture the wafers while achieving a surface morphology which is the most similar to a slurry-sawn wafer. Moreover, it is also able to meet the reflectance specification.


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2) Experimental Method:

3M Trizact Diamond Tile is an engineered composite fixed abrasive that is made of cross-linked polymer and vitrified bonded diamond abrasive. The diamond minerals are mixed with agglomerates and patterned into tile form with a micro-replicated pattern. It is designed to provide a uniform cut rate throughout the life of the product. It has channels that seem to allow coolant flow during process.

The dimension of the solar wafer is approximately 15cm by 15cm, it is attached onto a holder such that one side of the wafer is facing the 3M abrasive. During the texturing process, a down force is applied on the wafer while both the holder with wafer and the abrasive are rotating. A coolant is flown during the process so as to maintain the temperature and improves the finishing of the wafer surface at the same time. (Diagram 2.1) shows a basic schematic diagram of how the wafer is attached on the holder, and also how the process is run.

Diagram 2.1: Texturing process of the wafer


3) Experimental results:


3.1 Scanning Electron Microscope (SEM) analysis:

After the texturing process, the wafer is inspected under the scanning electron microscope (SEM) at 500x, 1000x,...