Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2001-11-07
2004-07-27
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298230, C204S298350, C118S719000, C118S729000, C156S345310, C156S345540
Reexamination Certificate
active
06767439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for high throughput thin film deposition upon and substrate handling of optical disk substrates. In particular, multi-layer thin films are deposited on substrates which are subsequently finished for use in optical disk applications such as DVD (digital versatile disk). To obtain increased processing efficiencies, the deposition apparatus includes a moving web which holds substrates in position as they are carried from one processing location to another.
2. Brief Description of Background Art
Throughput or processing rate (number of substrates processed per hour) directly impacts on the cost of manufacturing the optical disks. Due to the nature of the process steps used to produce an optical disk, and particularly thin film deposition where vacuum maintenance requirements and cleanliness (avoidance of substrate contamination by particulates) is critical in ensuring film quality, the optical disk industry has struggled with system-related throughput problems.
One of the more popular methods of optical disk production used to improve throughput is the cluster tool. The cluster tool is a multi-chamber tool sharing a common substrate handler. From a cost perspective, multiple chambers running the same process in parallel and sharing a common substrate handler can provide throughput which is superior to an equivalent number of stand-alone single substrate tools or to an in-line system (which will be described subsequently herein). A multi-chamber tool uses floor space and processing time more efficiently than a number of stand-alone single substrate tools. The substrate handler also has much less idle time than if it were only servicing one chamber. While one chamber is busy, the handler can still transfer wafers to or from other pods of the multi-chamber system.
Additional economic benefits accrue when a series of processes that could be performed separately are linked in one tool. The reduced substrate handling and decreased numbers of pump-and-vent cycles decrease foreign material, especially in vacuum-equipped clusters used for plasma processing. Eliminating substrate transfer from tool to tool reduces the substrate processing time through the cluster and decreases the cycle time and lot turn-around time. When substrates are processed in a continuous manner, delay times between sequential steps can be more tightly controlled. Clusters that keep substrates under vacuum during diverse sequential process steps allow new processing options since surface interactions with atmosphere and moisture are avoided. Multiple repetitive steps are also more attractive. Despite these advantages, the types and capabilities of the component process modules/chambers and substrate transfer capabilities limit the flexibility of the cluster tools on the market. One of the most significant detractors to cluster processing is mean time-to-failure (MTTF); this must be addressed with high priority, especially since an entire cluster is incapacitated when a single module fails.
The overall control of the multi-layer processing may be the most difficult aspect of the cluster system. Due to an intrinsic nature of substrate routing sequence in a cluster tool system, the presently available software limits the maximum throughput. The most popular cluster tool's throughput is limited to about 72 substrates per hour for a single-layer deposition. When three different layers must be processes, the presently available throughput is 36 to 40 substrates per hour in a 3-chamber/module system.
The production system most commonly used in the industry employs an in-line batch system for the thin film deposition process. In in-line batch systems, the substrates are loaded onto a substrate holder or pallet. In a batch sputter-down system, the substrates may only be placed on a holder. Under this configuration, there are defects generated from the sputter target and shield areas, which affect on film quality and consequently product yield. Use of pallets also increases the particle occurrence and overall cost of ownership (COO) from maintenance and spare stocks.
An in-line batch system may be able to handle up to about 100 substrates per hour for a single layer film deposition; however, because of batch-nature of the substrate loading, there is a penalty for throughput loss from engineering reliability such as loading and unloading steps. In addition, there is a build up of particulates on the moving carrier used to move the substrates through the deposition processing area. For example, a moving belt which repeatedly circles within the process area, handling a series of substrates, accumulates particulates and requires a cleaning process for particulate removal, leading to high maintenance downtime. In addition to maintenance downtime, particulates which accumulate on the belt may contaminate substrates which contact the belt. Belt hardening occurs over time, requiring belt replacement. When a more complicated product is produced, such as one which requires a three layer film deposition, the slowest deposition process dictates the overall throughput rate for the system, since such systems are not equipped with flexible hardware of the kind which will be described with reference to applicant's invention. In addition, presently known in-line batch systems frequently experience cross-contamination when more than one film material is deposited, due to lack of proper isolation shields between material deposition areas.
Web deposition systems have long been used in the preparation of coated substrates such as metallized films. As its name implies, web deposition or coating involves the vacuum deposition of thin films onto flexible substrates such as films which act as moving webs. The substrate is unrolled from a feed reel at the beginning of the web, the deposition is made on the substrate surface, and then the substrate is rolled back up again on a take up reel. The deposition rate and the film thickness required limit the speed at which the substrate travels past a deposition station. Web coaters often contain several deposition stations that coat the substrate sequentially as it moves past them.
Vacuum web coating is the expansion of vacuum coating to large-surface, web-shaped substrates. The substrate is coated in a partial vacuum as the substrate passes by the deposition source along the path between the feed reel and the take up reel. An interesting history of web coating is provided in an article by E. O. Dietrich et al., entitled “Vacuum Web Coating—An Old Technology With A High Potential For The Future”, Society of Vacuum Coaters, 40th Annual Technical Conference Proceedings, pp. 354-364 (1997). These systems involve the application of coatings to a substrate which is moved past the coating source in the form of a continuous web which is unwound from one roll and rewound upon another roll.
In addition to sputter or evaporated coatings, plasma assisted chemical vapor deposition films have been deposited upon moving web substrates. Web coaters may contain several deposition stations that coat the substrate sequentially as it moves past them. Some of the more significant problem areas include the release of water vapor from the substrate during web coating; buckling or tensioning along the longitudinal edges of the web; transverse warping of the web of substrate material; and the presence of particulate contaminants. Transverse warping of the web is caused by the force of gravity acting upon the web, the elongated path of travel which the web of substrate material follows, stresses from external sources developed upon the web of substrate material, the high deposition temperatures to which the web of substrate material is continuously subjected, and the forces created by the highly stressed semiconductor alloy material deposited upon the web of substrate material. U.S. Pat. No. 4,664,951 to Joachim Doehler, issued May 12, 1987 describes a method of providing for corrective lateral movement of a web of
Church Shirley L.
McDonald Rodney G.
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