Radiant energy – Inspection of solids or liquids by charged particles – Methods
Reexamination Certificate
2000-09-01
2003-04-08
Anderson, Bruce (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Methods
C250S397000, C250S492200
Reexamination Certificate
active
06545274
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to microlithography of a pattern, defined by a reticle, to a sensitive substrate using a charged particle beam such as an electron beam or ion beam. Microlithography is a key technology used in the manufacture of microelectronic devices such as integrated circuits and displays. More specifically, the invention pertains, in the context of charged-particle-beam (CPB) microlithography, to methods and devices for accurately determining proper times (e.g., prescribed intervals) for performing scheduled maintenance (e.g., cleaning or replacement) of certain components of the apparatus.
BACKGROUND OF THE INVENTION
In recent years, as the critical dimensions of electronic devices in integrated circuits have become progressively smaller, the resolution limitations of optical microlithography have become increasingly apparent. Hence, much attention has been focused on the development of alternative microlithography technologies offering better resolution than optical microlithography. For example, microlithography using a charged particle beam (e.g., electron beam or ion beam) has been the subject of considerable development effort.
Although current charged-particle-beam (CPB) microlithography apparatus offer prospects of high resolution and exposure accuracy, the throughput obtainable with currently available equipment is disappointingly low. Various approaches are being investigated to improve throughput without adversely affecting image quality or imaging accuracy.
In one approach, the pattern to be transferred (by CPB microlithography) to a substrate is divided, or segmented, on the reticle into a large number of subfields or analogous exposure units that are exposed individually. This approach is termed “divided-reticle” projection exposure.
Various components used in a CPB microlithography apparatus are subject to accumulation of contaminants, which can cause degradation or drift in performance of the apparatus. For example, irradiation of the resist layer on the substrate can cause outgassing of organic compounds from the resist. Also, CPB-optical systems (including reticle and substrate) must be evacuated during use. Components located adjacent to evacuation ports can become contaminated by deposits of oil from the vacuum pumps used to evacuate the CPB-optical system.
Hence, in any of various CPB microlithography approaches, in order to form accurate patterns consistently over time, cleaning of various components (e.g., electrodes, apertures, and the like) in the CPB-optical system must be performed. Conventionally, such cleaning is performed on a predetermined periodic basis, such as every six months or year. However, an optimal cleaning interval depends upon the conditions (e.g., beam current or frequency of rough pump-down) of use and how often or how much the CPB microlithography apparatus is used. Hence, attention currently is being given to establishing scheduled cleaning intervals based on experience, with appropriate margins applied.
However, whenever a problem such as significant beam instability arises (which can degrade pattern accuracy), cleaning of the CPB-optical system is indicated regardless of whether a scheduled cleaning is due. Contamination of the CPB-optical system usually is manifest as deposits of hydrocarbons (from outgassing of resist and residual vapor of pump oil) that adhere especially to components situated around the trajectory of the charged particle beam. The longer the apparatus is operated, the greater the volume of contaminant deposits. Deposits of contaminant hydrocarbons are usually electrically insulative. Deposits of insulative contaminants on an aperture or on the reticle entrap charged particles and thus experience localized “charge-up,” which creates random electric fields in the vicinity of the deposits. The random electric fields perturb beam trajectory, with an attendant loss of transfer accuracy and resolution due to beam blur. The severity of charge-up varies with beam current and the actual amount of contaminant(s) in the respective deposits.
Whenever cleaning intervals are based on experience, certain systems may in fact go too long without being cleaned, or time may be wasted by cleaning certain components or systems more often than necessary. Failure to clean a system promptly when cleaning is necessary can degrade pattern-transfer resolution and increase distortions caused by beam deflections. These problems can be avoided by constantly monitoring and measuring of resolution and beam deflection. Unfortunately, such monitoring and measurements require large amounts of time and fail to identify individual components requiring cleaning.
SUMMARY OF THE INVENTION
In view of the shortcomings of conventional methods and apparatus as summarized above, an object of the present invention is to provide charged-particle-beam (CPB) microlithography methods and apparatus that provide accurate and timely information of the proper time (prescribed interval) for performing scheduled cleaning of the apparatus. Thus, the present invention solves problems such as degraded resolution and increased beam-deflection distortions caused by insufficient or inadequate cleaning. Another object is to provide semiconductor-device-manufacturing methods employing such microlithography methods and apparatus.
To such ends, and according to a first aspect of the invention, methods are provided (in the context of CPB microlithography methods) for detecting a time for a maintenance activity performed on a component in the column of a CPB microlithography apparatus. According to a representative embodiment of such a method, the component is subjected to a condition tending to cause release of molecules of a contaminant from the component to an atmosphere in the column. The atmosphere within the column is analyzed (e.g., by mass analysis) to detect an amount of a contaminant released from the component. From data produced during the analysis, a time for performing the maintenance activity of the component is determined according to the results of the detection. The condition to which the component is subjected can be, for example, irradiation of the component with the charged particle beam. The steps of irradiating the component and analyzing the atmosphere inside the column can be performed simultaneously and can be performed on multiple components in the column at the same time. The resulting data from the determinations can include times for performing the maintenance activity as determined individually for each component. The analysis can be performed at any of various times such as during startup of the column.
The method can include the step of determining a variance in beam positioning arising as a result of accumulation of the contaminant on the component. In this regard, the method can further include the step of determining a correlation between accumulation of the contaminant on the component and the variance in beam positioning. Data concerning the correlation can be stored in a memory for subsequent recall. Hence, the method can further include the step of recalling the data from the memory and determining the time for performing the maintenance activity of the component according to the recalled data.
Another aspect of the invention is directed to CPB microlithography apparatus that comprise a CPB-optical column. The apparatus includes a device for detecting an amount of a contaminant on a component of the CPB-optical column. According to a representative embodiment, such a device comprises a deflector situated and configured to direct a charged particle beam, propagating through the column, to impinge on the component and thus cause release of molecules of the contaminant. A sensor is situated and configured to detect the released molecules of the contaminant. The device also includes an analyzer (e.g., mass analyzer) connected to the sensor. The analyzer is configured to receive data from the sensor and to determine, from the data, a type and amount of the contaminant on the component. The apparatus can
Anderson Bruce
Klarquist & Sparkman, LLP
Nikon Corporation
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