Research On The Control Of Single-armed Cluster Tools With Mixed-processing Of Multi-variety Wafers

Semiconductor chip manufacturing is the pilot and fundamental industry for modern society.Among the five stages of chip manufacturing,wafer fabrication is the most complicated link that occupys the biggest investment.With wafer size increasing,traditional batch processing technology becomes difficult to meet the stricter requirements.Since the unique single-wafer processing technology cluster tools possess can cope with technical bottlenecks effectively,they have been widely used in large-size wafer processing.Although cluster tools provide an efficient,highly flexible and reconfigurable environment,they are still difficult to be controlled availably.Currently,wafer fabrication tends to be the pattern of multi-varieties and small-batch for the increasing of wafer size and the demand changes.However,mainly existing scheduling methods are focussed on the control of cluster tools with single-variety wafers.In such case,scheduling has to be altered continually,which results in a substantial increase on commissioning work and manufacturing cost.Consequently,it's great of importance on the theory and practical to study on the scheduling of cluster tools with multi-type wafers.To improve the production efficiency of cluster tools,the scheduling and control of single-armed cluster tools with mixed-processing of multi-variety wafers are addressed.A resource-oriented Petri net(ROPN)model is developed to describe the wafer fabrication processes.Workloads among the processing steps are balanced via virtual process modules.Analytic expressions for testing schedulability are derived based on the ROPN model and backward scheduling strategy.Finally,a scheduling algorithm for the steady state is presented.Meanwhile,illustrative examples are given to verify the validity of the scheduling algorithm proposed.This thesis acquires some results as follows.(1)The ROPN model of single-armed cluster tools with mixed-processing of multi-variety wafers is developed.Controlled transitions are introduced into models to avoid deadlock,and time is associated with places and transitions to model activity times.The wafer fabrication process can be described accurately by the ROPN models for their simple and generalized structures.(2)Schedulability test conditions for single-armed cluster tools with mixed-processing of multi-variety wafers are derived.Calculation methods for the cycle time of wafer and robot are obtained by ROPN,and their coupling characteristics are also revealed.Furthmore,the interactions between processing parameter distribution and schedulability are presented.(3)The steady state scheduling algorithms for single-armed cluster tools with mixed-processing of multi-type wafers are proposed.All constraints expressed formally deciding schedulability are presented based on theoretical analysis.The proposed scheduling algorithms,the above works show,are both effective and valuable for the practical application.