Directional Snow Clean Process
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-19
Snow cleaning is a process where an intense CO2 stream is directed towards the wafer. The gas/particle stream is capable of removing poorly adhesive material. A commercially available tool exists . This tool allows choosing between two different nozzles with different pressures (non aggressive snow clean and aggressive snow clean). The wafer is rotated during process so that the stream hits the wafer from different directions. In this publication, an advancement of the snow clean process is disclosed, called directional snow clean. Directional snow clean means that the wafer is oriented in a well defined angle to the direction of the CO2 stream. This requires an automatic wafer aligning system in combination with an adjustable or controllable angle of incidence for the snow stream. In contrast to standard snow clean process, directional snow clean process allows removing selective particles. Furthermore, damages can be circumvented which are caused by a stream hitting the broadside of fine structures. Multi-step ion mill processes including different angles of ion incidence are state of the art in production of magnetic read write heads. One typical example is the shaping of the pole tip of the write head. Extremely critical dimensions are realized by means of trimming and notching of the pole zone. However, as a side effect, redeposited material can occur (see Fig.1). These structures are useless. They not only create cavities, which might trap moisture or contaminants, but also will affect adversely the growth of the alumina overcoat. Both effects can lead to reliability problems. It is possible to remove these unwanted structures by means of the snow clean process. This is demonstrated in Fig.1 where a head is shown before and after snow cleaning. The redeposited material has been cut mechanically by the intense CO2 stream. 1 Fig. 1 Redeposited material is observed left and right of the yoke (left). After snow cleaning the redeposition structures are vanished (right).