Wafer Manufacturing with Modern Multi Wire Saws

© Fraunhofer CSP

Purification of the Si ingot after the grinding procedure.

The Fraunhofer CSP provides a wafering line compatible to industrial application which covers the entire value chain from the slicing of ingots , the wafer manufacturing and the cleaning all the way to wafer characterization. To this end, full manufacturing can be run as well as smaller pilot trials to test consumables, new process parameters, new cleaning processes, or to pursue research purposes.

Services

  • Squaring the ingots into blocks
  • Grinding and cropping of the blocks
  • IR inspection of the Si blocks
  • Resistance mapping on Si blocks
  • Determination of wire performance, benchmarking wafering technologies (slurry based process: straight and structured wire, water based process: diamond wire)
  • Process monitoring (for grinding process and wafer manufacture)
  • Cleaning of wafers
  • Wafer inspection and wafer classification

Examples

© Fraunhofer CSP

Load profile of a silicon brick sliced in wafers from the diamond wire sawing process over the entire sawing time.

Process Monitoring

An optimization of the wafering process can be done in many ways. Both empirical sawing tests and individual concept trials are possible. The multi-wire saws (Meyer Burger DS264 & DS265) available at the Fraunhofer CSP were equipped with load sensors, especially to explore the influence of processing parameters and consumables with as few sawing experiments as possible. This enables us to determine the interactions between wire and workpiece in order to obtain a maximum of process understanding. The figure shows the load profile of a silicon brick sliced in wafers over the entire sawing time of the diamond wire sawing process. Based on the results obtained, we can draw conclusions on wire and cooling lubricant performance and on the optimal processing parameters.         

© Fraunhofer CSP

By testing special dimensions and new materials, we are working on the continuous optimization of the sawing process.

Sawing for Special Applications

An increase of the yield of wafers can be achieved by means of thinner wafers and wires: more wafers can be produced from the same amount of silicon material. This changes both process control and the following cutting result. Testing new processing windows, new consumables (e.g. saw wires) and new materials such as molybdenum or marble belong to the range of Fraunhofer CSP services.     

© Fraunhofer CSP

Wafer thickness profile of all sawed wafers of a sawing cycle.

Wafer Thickness Profile

The investigation of the geometry of the wafer is an essential component of process evaluation as the various influences of the process are reflected by the quality of the wafer. The analyses are carried out conventionally, by defining the specifications for the wafers and applying tolerance limits. In innovative approaches we determine the wafer thickness profiles of all wafers sawed in one sawing step (see figure) which can be correlated with the wear of the wire and the load data in order to identify critical process windows.

Wire Performance Determination

The improvement of each single process step is the major focus of all photovoltaic companies in order to decrease costs and provide high quality products. A new wafering process analysis based on big data sets from machine and wafer characterization is established at the Fraunhofer CSP. A correlation between the multi wire wafering technology and the resulting wafer geometry is determined. New parameters are defined which are indicating directly process variations and the impact of different wire types to the wafer quality and wire performance. Thus, the analysis of wafer thickness distribution was improved to create a multi wire process benchmark to address process issues and wire performance.