Abstract:
A method and apparatus for finding contamination occurrence and for preventing the propagation of the contamination is provided according to the present invention, which altogether constitutes a contamination prevention system. The present invention employs a computer for examining a process flow in order to find out whether a process step is contaminated by using a contaminated tool and therewith to show a proper representation on a process flow. Any process flow that passes the contamination prevention system of the present invention can be free of any contamination problem. Furthermore, The contamination prevention system according to the present invention gives a tag for each object. If an object is tagged “contaminated”, then the system forbids the next process step, that includes uncontaminated tools, to be executed. The present invention can be built to an automatic system to prevent the propagation of contamination from occurring.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a method and apparatus for preventing contamination during a process flow. 
     2. Description of the Related Art 
     For mass-production consideration, the sequence of equipment used in a process flow must be well kept in order to avoid cross-contamination. For example, in a process flow for semiconductor wafers, an etch equipment used for patterning a metal layer can not be used to pattern a polysilicon layer during the same process flow. It is because that metals, typically Al or Cu, can induce localized energy states in the forbidden energy gap of the gate oxide to increase the gate leakage and therefore degrade the device performance. If a wafer A having a metal layer and a wafer B not having a metal layer are both processed in the same equipment, it is possible for the wafer B to acquire some metal atoms undesirably from the wafer A. Since the wafer B may contribute the metal atoms directly to equipment during the subsequent steps of the process flow, other wafers not having the metal layers are also at the risk of being contaminated by the metal atoms. 
     Although the process flows in many semiconductor manufacturing factories today are performed and monitored by automatic computer-controlled systems, such as a manufacture executive system (MES), the typical methods employed to prevent wafer contamination are still manually performed. For example, when a well-trained operator receives a cassette containing a plurality of wafers, he (or she) has to check out whether or not a special mark or tag indicating the presence of metal is thereon attached to the cassette in order to process the cassette with a proper action. If by any chance the operator omits the step to check the mark or label on the surface of the cassette and process it directly, a disaster of a wide-spread contamination among the processed wafers may occur. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a method and apparatus for preventing contamination automatically during a process flow. 
     In accordance with one aspect of the present invention, a method is provided as follows for finding contamination occurrence in a process flow according to the present invention. First of all, a tool database in which a plurality of tools are defined of “tagged” by a set of contamination information of the tool database for being either a contaminated tool or an uncontaminated tool. Then a process database including the order of steps in the relevant process flow and a corresponding tool information for each step of the process is input to the computer. Said tool information includes at least one tool to be executed during the relevant step of the process flow without including the contamination information of each tool. Finally, the process database associated with the tool database is cross-examined in order to display a contamination warning message prior to the occurrence of contamination in one of the steps of a relevant process flow, which is in the danger of the process flow is already contaminated. 
     In accordance with another aspect of the present invention, an apparatus is provided for finding contamination occurrence in a process flow. Said apparatus comprises at least a memory device and a processor connected to the memory device, wherein a program is stored in the memory device for controlling the processor. Said processor operates according to the program of the memory device to input a tool database in which a plurality of tools are defined or “tagged” by a set of contamination information of the tool database for being either a contaminated tool or an uncontaminated tool. Then a process database including the order of steps in the relevant process flow and a corresponding tool information for each step of the process flow is input to the computer. Said tool information includes at least one tool to be executed during the relevant step of the process flow without including the contamination information of each tool. Finally, the process database associated with the tool database is cross-examined in order to display a contamination warning message prior to the occurrence of contamination in one of the steps of a relevant process flow, which is in the danger of being contaminated if any one of the preceding steps of the process flow is already contaminated. 
     The major advantage of the above-mentioned method and apparatus according to the present invention is that possible occurrence of contamination in a process flow can be detected and warned well before the actual implementation of the process flow by an automatic system. 
     In accordance with yet another aspect of the present invention, a contamination prevention system is provided for finding contamination occurrence in a process flow. Said system comprises at least a memory device and a processor. The memory device has a tool database in which a plurality of tools for manufacturing an object are defined. The memory device further includes a process database comprising a plurality of steps in a relevant process flow and a set of object specific information. In particular, the tool database includes a contamination information for each tool to determine whether the relevant tool is a contaminated tool or an uncontaminated tool. The process database comprises a set of tool information for each step of the process flow. The tool information includes at least one tool to be executed during the relevant step of the process flow. The object information includes a contamination tag to indicate whether the object is contaminated or uncontaminated. The processor communicates with the memory device and is configured to initiate a contamination tag to indicate that the object is uncontaminated before the object is sent to experience any process step. If, the object has experienced any process step whose tool information includes at least a contaminated tool, the contamination tag of the object would indicate that the object is contaminated. On the contrary, if the tool information of a succeeding process step indicates an uncontaminated tool and a contaminated object, the object is prohibited from being executed by said process step. 
     The major advantage of the above method is to prevent a widespread occurrence of contamination during a process of fabricating an object by an automatic system. 
    
    
     Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. 
     In the drawings, like reference numbers indicate identical or functionally similar elements. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram representing a first embodiment of the present invention; 
     FIG. 2 is a block diagram depicting the process flow of one embodiment of the program stored in the ROM shown in FIG. 1; 
     FIG. 3 is a schematic diagram representing a second embodiment of the present invention; 
     FIG. 4 is a block diagram depicting the process flow of one embodiment of the program stored when a “move-out” is initiated; and 
     FIG. 5 is a block diagram depicting the process flow of one embodiment of the program stored when a “move-in” is initiated. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a method and apparatus for finding contamination occurrence in a process flow before the process flow is set up in an automatic manufacturing system. According to a preferred embodiment of the present invention, the present invention is contrived to have its applications found in a semiconductor factory. 
     Referring to FIG. 1, FIG. 1 is a schematic diagram representing a first embodiment of the present invention. The apparatus  10  according to the present invention for finding contamination occurrence in a process flow comprises a memory device, such as the ROM  12 , and a processor, such as the CPU  14 , connected to the memory device. ROM  12  stores a program for controlling the CPU  14 . 
     On the other hand, a manufacture executive system (MES)  16  according to the present invention can handle each operation and relevant status of the tools, such as etch machine, furnace, stepper etc., used in a semiconductor factory. For example, MES  16  defines which tool is on working or on periodical maintenance, allowing wafers carried in a cassette to be processed by a tool, and decides the subsequent process that a cassette is subject to. MES  16  also stored a tool database  18  including a contamination information for each tool. Such a contamination information defining the pertaining tool is a post-metal (contaminated) tool, a pre-metal (uncontaminated) tool or a general (non-contamination-specific) tool. The process flows in a semiconductor factory can have process steps for forming such metal layers as Titanium layers, Copper layers, Alumni layers, etc. These metal layers are sources of contamination sources as well known in the art. The tools dedicated to process the wafers without metal layers, for instance, gate oxidation furnaces, are pre-metal tools, which should never be contaminated. Some other tools dedicated to process the wafers with metal layers, for instance, metal etchers, are post-metal tools where metal is allowed in these tools. Other tools not concerning the metal problem that never induce cross-contamination, such as photo steppers, are general tools. 
     Process integration engineers (PIE) or technology development engineers (TD) are usually the sources for providing a process database  22 , wherein the engineers design a process flow in the hope of building up the process flow in MES  16  to control the processes as required. The process database  22  represents a plurality of sequences of process steps associated with the process flow. The process database  22  also includes a set of tool information for each process step. Furthermore, a tool information includes at least one tool to execute the relevant process step and to exclude the contamination information of each tool. The process database also includes a recipe information for each process step. 
     Referring to FIG. 2, FIG. 2 is a block diagram depicting the process flow of one embodiment of the program stored in the ROM shown in FIG.  1 . CPU  14  operates according to the program in ROM  12 . At first, the process database  22  provided by the PIE/TD is input via a soft disk, a cable, a network, etc. and then stored in a data memory device  30 . The tool database  18  being stored in EMS  16  is input via a network and then stored in the data memory device  32 . IN addition, basic data formation of the process database is checked to find out if any unconscious errors  34 , such as an empty column, exist in the process database since the process flow is a draft from PIE/TD. Then, the process database is examined in associated with the tool database to find out the earliest process step N with a set of tool information that includes a post-metal tool and the last process step M with a set of tool information that includes a pre-metal tool  36 . If the process step N is executed prior to the process step M, a contamination warning message will be displayed to inform the PIE/TD that the process database contains the risk of being contaminated as soon as it is executed by the MES  40 . The PIE/TD must redraft the process database to reexperience the apparatus according to the invention. If the process step M is executed prior to the process step N, the tools listed in the process database can be free from contamination. However, if some unconscious errors have been found in the process database  42 , the PIE/TD should be able to correct these unconscious errors in order to prevent faulty process step from occurring during the process flow  44 . Each time the process database is modified by the PIE/TD, the modified process database is preferably implemented to the apparatus to prevent contamination from occurring. If there are neither contamination issue nor unconscious error existed in the process flow, the process flow then can be build in the MES  46 . 
     The major advantage of the first embodiment is providing a preventive contamination check before the process flow is actually set in the MES. If all wafers processed in a semiconductor factory are processed by process flows according to the present invention, contamination can be prevented before occurring. 
     The present invention further provides a method and system for preventing contamination from occurring during the manufacture of a semiconductor wafer since, after the process flow is set in the MES, engineers may occasionally change the process flow for various special reasons and may cause an unexpected contamination. Referring to FIG. 3, FIG. 3 is a schematic diagram representing a second embodiment of the present invention. According to this preferred embodiment, the present invention described hereinafter is applied to an MES  50  comprising a memory device  52  and a processor  54  for controlling process steps executable in order by a relevant tool. 
     The memory device stores a tool database, a process database, and wafer information. The tool database  52   a  represents the tools for manufacturing the wafer and includes a set of corresponding contamination information for each tool to indicate whether the pertaining tool is a contaminated tool or an uncontaminated tool. The process database  52   b  represents a plurality of process steps that includes a tool information for each process step. The tool information includes at least one tool to be executed in the relevant process step. The wafer information represents the relevant wafer that includes a contamination tag for indicating whether the wafer is contaminated or uncontaminated. 
     The processor  54  communicating with the memory device  52  is configured to have the following features. First of all, the processor  54  initiates a contamination tag to indicate whether the wafer is clean before the wafer experiences any process step. For example, as a wafer or a cassette is to be processed in a semiconductor factory, operator(s) must create a set of wafer information relevant to the wafer in the MES with the default of the contamination tag being clear. 
     Secondly, after the wafer experiences a process step in which the relevant tool information includes at least a contaminated tool, the processor forces the contamination tag of the wafer to indicate a status of contamination. For example, when a trained operator wants to begin a process for a wafer, the operator has to key “move-in” into the MES via an operator interface or an equipment application, moves the wafer with a certain tool handled by the operator, and starts the recipe shown by the MES. After the tool finished the process, the trained operator then has to key “move-out” into the MES via an operator interface or an equipment application. Referring to FIG. 4, FIG. 4 is a block diagram depicting the process flow of one embodiment of the program when “move-out” is initiated. At this moment, if the certain tool is a post-metal tool  60 , the MES according to the present invention forces the contamination tag of the wafer to indicate whether the wafer is contaminated as represented by step  62 . Otherwise, the contamination tag of the wafer is kept unchanged as represented by step  64 . 
     Thirdly, if the tool information of a next process step includes the status of an uncontaminated tool and a contaminated wafer, the processor forbids the wafer from being executed by the next process step. Referring to FIG. 5 FIG. 5 is a block diagram depicting the process flow of one embodiment of the program when “move-in” is initiated. For example, as soon as the trained operator keys “move-in” into the MES&lt;the MES according to the present invention begins to check the contamination tag of the wafer and the contamination information of the relevant tool. If the contamination tag of the wafer shows that the wafer is contaminated  70  and the contamination information of the relevant tool shows that the tool is a pre-metal tool  72 , it means that processing the wafer by the relevant tool will cause a contamination not allowed. MES will either show a message to the trained operator or step the relevant tool immediately in order to stop the processing as represented by the step  74 . Otherwise, the MES allows the proceeding of the process step to continue, and the operator can thereafter move the wafer to the next step  76 . 
     In contrast to the manual method for preventing contamination, the present invention provides a method and apparatus to find out possible occurrence of contamination in a process flow before the process flow is built in the MES. Furthermore, a system is provided to forbid the contaminated wafer from being processed in a pre-metal tool. All the activities of the present invention can be automatically executed by computer(s) with proper programming to keep those pre-metal tools away from unpredicable contaminated source(s). 
     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.