Chemical Boost For Diamond Wire Sawing

• DW PreTex from Schmid prepares diamond wire sawn multi c-Si wafers to be accepted by standard texturing process
• It's a simple one-step process and can be hooked to the end of the wafering line or placed at the beginning of the cell process sequence
• The process attains better uniform surface with reflection values below 23%
• Supporting a throughput range of 3,600 to 4,500 wafers per hour, the DW PreTex supports an OpEx of 1 euro cent per wafer
• A first system for industrial scale mass production with a capacity of 500 MW has already been ordered

Germany's equipment maker Schmid Group has developed an innovative method that enables diamond wire sawn multicrystalline wafers to be textured in the standard process flow. The technology is offered in the form of a production tool called DW PreTex in which wafers are pre-processed before subjecting typical acidic texturization. This way, Schmid's technology relieves a major bottleneck associated with adapting diamond wire sawing for producing multicrystalline wafers. Consequently the DW PreTex enjoys high demand, says Schmid, which has already found a first customer and expects several others to follow this lead.

Big promise of DW sawing
Diamond wire based sawing is dominating the technology development within the wafering segment. The process is faster than the slurry method and supports reducing kerf losses. The fixed abrasive principle using water as coolant not only avoids complex slurry management but opens up the opportunity for recycling of silicon kerf. All these factors collectively helps in reducing the manufacturing costs significantly – about 6 to 8 euro cents per wafer – compared to the slurry process.

Challenges for DW sawing of multi so far
However, so far the DW process is mainly accepted for producing monocrystalline wafers. In case of multicrystalline silicon, diamond wire based sawing leaves a smooth surface that poses a significant challenge to be textured with standard acidic texturing process. While technologies such as black silicon facilitate using diamond wire sawn wafers, the relevant production process is not completely mature or expensive.

How to solve the issue
The DW PreTex is a simple one step process implemented before the wafers are sent for texturization. The crux of the process is to roughen the relatively smooth wafer surface so that they can be textured in a standard HF/HNO3 chemical bath. According Schmid's PV business unit head Christian Buchner, the process results in a better surface uniformity compared to slurry-cut wafers after texturing. Wafers processed in this method have lower reflection of less than 23%. Adding to that, Schmid says its solution relies on materials that are commonly used in the PV industry. The process can be implemented either as a last step of wafer manufacturing or as a first step in cell lines.

The DW PreTex is a modular tool based on an inline platform that supports easy integration into existing production lines (cells or wafers) without any additional facility requirement. The system is available in two versions. A standalone single unit that feeds preprocessed wafers to the already installed texturing bath. Alternately, Schmid is also offering an integrated texturing solution. This inline tool is moving the wafers in 5 parallel tracks and has a rated throughput of 3,600 to 4,500 wafers per hour. According to Buchner, the DW PreTex has operating costs of 1 euro cent per wafer.

Schmid says a first system for industrial scale mass production with a capacity of 500 MW has already been ordered and the company expects to receive further orders worth of 5 GW by mid 2017. The first systems are expected to be shipped in Q2/2017.