Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-04-29
2004-01-27
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S110000
Reexamination Certificate
active
06684124
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method of controlling a process appliance for the sequential processing of a number of semiconductor wafers, using at least one micro measuring instrument to determine the quality of the process carried out in the process appliance.
During the production of semiconductor products with a widely branched chain of individual production steps, one main focus of attention in relation to cost efficiency lies in the optimal utilization of the existing process appliances, with a simultaneously high quality of the products.
In this case, the optimal utilization in a fabrication shop is normally ensured by an internal factory planning system (CIM, Computer Integrated Manufacturing), while the quality is normally monitored by the measuring instruments following the respective process in conjunction with various methods of evaluation.
Silicon wafers count as a typical example of semiconductor products. As a rule, there are large numbers of wafers to be processed in the same way. “In the same way” here means identical chemical and physical characteristics—in particular of the surface, for example structure sizes or layout compositions. Because of identical process conditions, the wafers to be processed in the same way are combined into groups and are processed one after another, that is to say sequentially, or in parallel chambers in process appliances for the respective fabrication step. Wafers passing jointly through the individual fabrication steps—normally combined into wafer carriers, as they are known—are referred to as a batch which, for example, can consist of 25 wafers. If such a batch passes to the input of a process appliance, then the wafers contained briefly form a batch queue, also referred to merely as a “batch” below, because of the processing, which is often possible only sequentially.
The finally processed, for example 25 wafers, are normally combined again and are fed to one or more measuring instruments to measure the quality of the process just carried out. For this purpose, a number of different types of microscope measuring instruments are used in the semiconductor industry. Designated by this term in this document are optical microscope measuring instruments, and those operating in the ultraviolet, for measuring the positional accuracy or structure sizes etc., but also microscopes in the wider sense, such as a scanning electron microscope (SEM), or AFM (Atomic Force Microscope), or else measuring instruments operating with interference, such as layer thickness measuring instruments, particle counters etc., or in general terms defect inspection instruments. This corresponds to the English language designation “metrology tools” which is usual in the semiconductor industry.
Various process-relevant parameters are measured during such an inspection, the methods of statistical process control (SPC) normally being applied nowadays for the selection. Because not every batch or each product batch is inspected, but instead randomly selected entities are measured in accordance with statistical methods, on the one hand additional capacity of the abovementioned microscope measuring instrument can advantageously be released. If problems occur for example measured values lying close to specification limits—the statistical samples can be adapted dynamically.
On the other hand, measured value histories can also be monitored, in order to be able to establish characteristic system trends of the process appliance, such as systematic parameter displacements and violations of limiting values which may possibly result from these and manifest themselves. Likewise, by averaging as a function of the time, systematic measured value jumps can be determined from the history, which are then compared with results from the process appliance history.
Using the findings obtained from this, the process parameter adjustments of the process appliance considered can be readjusted or optimized.
In this case, it is a disadvantage that these optimizations can take effect only on the next batch brought up to the process appliance or, respectively, the wafers belonging to said batch. For the batch which has just been processed it is true, firstly, that in the event of system errors occurring in the process appliance, all contained are affected as a whole and therefore have to be sent to rework, that is to say reprocessing. For this reason, additional costs arise and the yield can decrease disadvantageously.
On the other hand, effects that act only on individual wafers can be overlooked by the manner of statistical sampling. Furthermore, it is not ensured that the assumption that the process optimizations consequent on the batch currently being processed are subject to the same conditions as for the following batch is justified.
Another method constitutes that from a preceding wafer. Before the actual production batch of wafers is started, a precursor, normally functioning as a test wafer, is processed and is then transferred as quickly as possible to the metrology tool, after which the process parameters of the process appliance can then be adjusted for the following. This method has the particular disadvantage that not only is it necessary for the wafers of the batch to wait for the measurement of the precursor and as a result be processed later, but also an unproductive time has to be kept free for the process appliance itself.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to increase the proportion of useful time of process appliances for semiconductor fabrication, to reduce the production time of semiconductor products and to improve the yield in the process appliances.
The object is achieved by a method of controlling a process appliance for the sequential processing of a number of semiconductor wafers, using at least one microscope measuring instrument for determining the quality of the process carried out in the process appliance, target and limiting values for structure parameters on the wafer being predefined, comprising the steps of: processing a first wafer in the process appliance, transferring the wafer to the microscope measuring instrument, measuring structure parameters of structures formed or modified on the wafer in the process, processing a second wafer during the measurement of the first wafer, comparing the measured values of the structure parameters with the predefined target and limiting values, generating a result signal as a function of the comparison result, and transmitting the signal to the process appliance.
According to the present method, a first leading wafer is processed in a process appliance and then transferred to a microscope measuring instrument to measure the structure parameters. Process appliance includes all the appliances which are normally used in semiconductor production and which perform chemical or physical changes in or on the wafer or the substrate. These therefore include in particular all appliances in the lithography sequence, etching chambers, developers, CMP appliances, ovens, implanters, deposition tools (CVD, PVD, PECVD, etc.) and more of the like. Designated microscope measuring appliances are—as mentioned at the beginning—all optical or ultraviolet illuminating microscope types, adjustment measuring instruments, scanning electron microscopes, AFM and also instruments operating interferometrically or acoustically for measurements of position, layer thickness, inclination angle or structure widths.
The present invention permits the processing of a second wafer from the batch, during sequential processing, directly after the conclusion of the process for the first wafer. The time during which the first wafer processed would have to wait for the fabrication of the second wafer is advantageously used for the inspection or measurement of the metrology parameters which necessarily have to be measured for the quality of the process respectively carried out.
The advantage accordingly resides in the fact that the preceding wafer neither has to
Fischer Thomas
Hommen Heiko
Otto Ralf
Schedel Thorsten
Schmidt Sebastian
Greenberg Laurence A.
Infineon - Technologies AG
Jarrett Ryan
Mayback Gregory L.
Picard Leo
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