In this chapter, we describe the knowledge requirements of knowledge support for problem-solving, including the concepts of the problem-solving process, the knowledge requirements for problem-solving, and the context-based knowledge requirements for problem-solving. A wafer manufacturing process in a semiconductor foundry is used to illustrate the proposed approach. The process comprises the following steps: crystal growing, wafer cutting, edge rounding, lapping, etching, polishing, cleaning, final inspection, pack-aging and shipping. The wafer cleaning step mainly uses DI (de-ionized; ultra-pure) water to remove debris left over from the mounting wax and/or polishing agent. A stable water sup-ply system to deliver ultra-pure water for wafer cleaning is therefore vital in semiconductor manufacturing.
3.1. The problem-solving process
In business enterprises, especially the manufacturing industry, various problem situa-tions may occur during the production process; for example, poor production performance, system overload, and low machine utilization. A situation denotes an evaluation point to determine the status (i.e., desirable or undesirable) of a production process. A problem may occur if there is a discrepancy between the actual situation and the desired one. For example, when the current production output is below the desired level, the production line may have some problems. Thus, a problem-solving process is often initiated to achieve the desired situation. In the process, workers take several problem-solving steps to determine what ac-tion needs to be taken to resolve the situaac-tion. Such acac-tion involves both human wisdom and enterprise knowledge. Workers may observe a problem situation, collect relevant informa-tion from the enterprise knowledge repository, explore possible causes, and identify opera-tional conditions in order to decide appropriate action. Moreover, a problem-solving process generally consists of levels of progressive sub-problem solving, which form different stages of the process. Such stage-wise problem-solving reduces the complexity of a problem and solves it more effectively. The stages of problem-solving in a production process are usually pre-determined by experienced workers or experts according to the characteristics of the process and their experience in solving previous problems.
3.2. Knowledge requirements for problem-solving
Situation and action relevant knowledge. In a specific stage of problem-solving, a worker can access relevant documents associated with the problem situation to find the causes. For example, for the situation “crash of the water supply system”, the diagnostic documents contain information about the temperature, pressure, and electric power, which may provide clues to possible causes. The expert-reports indicate that the temperature and pressure fea-tures could be the key reasons for the system’s failure. The experiment-reports show that high pressure may cause an increase in temperature, which would make the system unstable and result in a crash. The know-how hidden in relevant documents can help workers dis-cover the causes of problem situations. These relevant documents are defined as situation relevant knowledge.
After determining the cause of a problem situation, workers must decide what action to take. They do this by accessing documents related to the cause in order to identify the normal operational-conditions of the production system, and choose an appropriate course of action.
Continuing with the example of the water system crash, if the cause is an anomalous tem-perature level, a safe temtem-perature range is required to stabilize the system. The system’s operational manual defines the normal pressure and temperature ranges. For example, when the system’s output pressure is one degree of atmospheric pressure, its temperature range is 30 to 32 °C. In addition, the standard operating procedures specify the system’s tuning rules:
the system temperature increases 4 °C per degree of atmospheric pressure. The experi-ment-reports indicate a reasonable temperature range of a stable system, where, for example, 55°C is the upper limit of the range. Such relevant operational know-how is hidden in en-terprise documents that must be discovered to help workers take appropriate action, i.e., tune the output pressure and temperature to keep the system stable. These documents are defined as action relevant knowledge.
Decision-making and dependency knowledge. Knowing what action to take to solve problem situations is defined as decision-making knowledge, which can be discovered from previous problem-solving logs. Decision-making knowledge is expressed as association rules that represent the association of frequently adopted actions for handling specific situations. These knowledge rules are generated as knowledge support to help workers take appropriate action in handling situations. Moreover, in stage-wise problem-solving, a
three stages of problem-solving on a production line, namely, engineering improvement, quality improvement, and maintenance management.
Engineering Improvement Stage
Quality Improvemenmt Stage Maintain Management Stage System
Fig. 1: A problem-solving process for a production line
In the first stage, tuning the system’s temperature and shutting down the system are two appropriate ways to resolve a system crash. The shutting down action may trigger a system control situation, which requires rebooting action in the maintenance management stage.
Moreover, the tuning action may cause the situation of unstable quality in the quality im-provement stage. Such cause-effect relationships (chain reactions) across different stages are called dependency knowledge, which helps workers make appropriate action plans across problem-solving stages. Note that decision-making knowledge represents the in-tra-relationships between the situations and actions within a stage, while dependency knowledge denotes the inter-relationships between the situations and actions across different stages.
3.3. Context-based knowledge requirements for problem-solving
Context-based inference. For a given problem, a situation may occur with various features according to the context at that time. Because situation features collected by system are usually partial or incomplete, a worker can not easily identify current situation. Accordingly, inferring more situation features according to the context characteristics is important in situation identification. For example, the water supply system in a production line provides pure water for wafer cleaning. When the system gets the situation feature “Produc-tion-quality low”, the causes may be so many that a worker can not easily identify the situation. Situation feature “Parameters of water supply quantity service incorrect” is in-ferred from the situation feature “Production quality low” and context characteristic
“Pressure of water unstable”. The context characteristic “Pressure of water unstable” and inferred situation features “Parameters of water supply quantity service incorrect” provide CBR with more clues to identify current situation as “Water supply abnormal issue”.
Context-based situation profile. For specific situation, Information Retrieval (Automatic Indexing) techniques are used to extract key terms from situation relevant documents. The extracted key terms form a profile to represent the information needs of workers for handling the situation. Moreover, the profile can be generated according to the context of the situation and is regarded as a context-based situation profile. According to certain context, the key terms recorded in a context-based situation profile are used to locate the relevant documents.
The relevant documents are recommended as knowledge support to help workers take ap-propriate action for handling the situation in certain context.
Context-based decision-making and dependency knowledge. Knowing what action to take according to problem situation features is defined as context-based decision-making knowledge, which can be discovered from the problem-solving logs. The context-based decision-making knowledge patterns indicate the inferred associations of actions and situa-tion features in certain context of the problem-solving process. These context-based knowledge patterns are generated as knowledge support to help workers take appropriate action in handling situations. Moreover, in stage-wise problem-solving, a situation/action may trigger/affect a situation/action in a later stage. Context-based dependency knowledge indicates the inferred relationships between situation/action features in current stage and situations/actions across different stages of the whole problem-solving process context.
Context-based dependency knowledge helps workers make appropriate action plans across problem-solving stages.