Roland A. - PVD for microelectronics (779636), страница 22
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1979 is shown).Introduced in mid- 1980, the 3180 coater from Varian Associates was thefirst of these production-oriented PVD systems and offered fully automated, cassette-to-cassette, single-wafer PVD processing (Fig. 5.7). An inline architecture was used in which individual wafers were moved sequentially from one vacuum process station to the next and which anticipatedthe coming of truly modular PVD cluster tools in the 1985-1990 timeframe.
Vacuum loadlocks and cryopumped PVD process chambers replaced the manual loading and diffusion pumping of earlier generationtools, with the result that base pressure was now in the low 10 -7 Tortrange. The 3180 coater was also significant in that it utilized backside-gasassisted heat transfer that allowed one to rapidly change and/or controlwafer temperature while retaining the mTorr-level vacuum ambient neededfor PVD. In addition, the method produced improved temperature uniformity, which was of particular interest since the industry was now facing thetransition from 4-inch-diameter substrates to 6-inch ones. It is interestingto note that this backside-gas-assisted method of wafer temperature controlhas become pervasive in the equipment industry and is still used 20 yearslater in today's most advanced PVD cluster tools (see Section 5.3.4).110R.
POWELL AND S. M. ROSSNAGELFIG. 5.7 The Varian model 3180 coater illustrates the move toward automated, cassette-to-cassettesingle-wafer PVD processing in the 1980-1985 time frame.5.1.4 1985-1989: PVD CLUSTERTOOLSu IThis period saw the development of single-wafer, multichamber standalone sputtering systems and the introduction of PVD-specific cluster toolsin which modular, vacuum-isolated, and independently operated processchambers were interfaced to a central robotic wafer-handling platform.The cluster tool concept provided a vacuum-integrated processing capability that allowed complex process flows for selected applications such asbarrier/liner (e.g., degas + preclean + PVD Ti + PVD TiN) and slab AIinterconnect (e.g., degas + preclean + PVD Ti/TiN+ PVD AI-Cu + PVDTiN ARC layer).
The control of film properties, particles, and interfacequality needed to carry out such process sequences in a production environment could not have been accomplished without the process isolationand vacuum integrity of these PVD tools. In addition, it was believed thatSPUTTERING TOOLS111a flexible, cluster-tool approach to semiconductor processing would allowso-called best-of-breed modules to be integrated by the primary equipmentsupplier onto their tool u e.g., addition of a third party's rapid thermal annealing module.
This direction was encouraged in 1990 by the Semiconductor Equipment and Materials Institute (SEMI) through the formation of a Modular Equipment Standards Committee (MESC) to establish"MESC standards" for such things as the mechanical and electrical interface between process module and cluster tool backbone.In other developments, the planaf magnetron was beginning to replacethe conical magnetron in high-end applications where uniformity of stepcoverage over 8-inch wafers was a concern, and the need to reduce yieldkilling fine particles was forcing suppliers to pay increased attention tosuch hardware details as materials of construction; sputter shield design;wafer clamping; and gas delivery, pumping, and venting.Representative tools from this period include the ClusterLine TM modelfrom Balzers (Fig.
5.8a), the Sigma TM model from Electrotech (Fig. 5.8b),the Eclipse TM model from MRC (Fig. 5.8c), the Loadlok TM model fromCVC (Fig. 5.8d), and the M2000 TM model from Varian (Fig. 5.8e). TheM2000 was introduced in 1987 as the first open-architecture PVD clustertool with totally independent and interchangeable process modules.5.1.5 1990-1997: PVD CLUSTERTOOLSm IISince much of the tool design strategy and PVD technology embodied inthese more recent PVD tools will be discussed in the remaining sections ofthis chapter, only a few comments will be made here. Probably the mostsignificant change in design philosophy was the recognition that technology and productivity (i.e., cost-of-ownership [COO]) had now becomeequally important in an advanced semiconductor fabrication tool and thatthe tool provider (equipment supplier) and the tool user (IC manufacturer)must work together in the spirit of the quality improvement process (QIP)to develop and improve such hardware.
This view, quantified and promoted by organizations such as SEMATECH, meant that mean-time-tofailure (MTTF) and mean-time-to-repair (MTTR) considerations were nowbeing given equal attention to film uniformity and step coverage. Also,much more attention was being given to the reduction of process-addedparticles, which generally have a dominant impact on CoO calculations. Inaddition, it began to be recognized that PVD was far from a mature technology and that the technology could be extended to deal with advanceddevices through improved directional PVD source concepts and process112R. POWELL AND S.
M. ROSSNAGELFIG. 5.8 PVD systems of the 1985-1990 period were strongly influenced by the move toward vacuum-integrated cluster tools for semiconductor processing.SPUTTERING TOOLS113recipes enabled by high-vacuum compatible cluster tools m e.g., A1 reflow-type planarization, collimated barriers and liners, long-throw directional sputtering, and ionized metal plasma PVD. Cluster tools capable oftrue ultrahigh vacuum (UHV) base pressure in the process chamber( < 10 -9 Torr) were also of interest based on data that this level of vacuumquality would result in A1 alloy interconnect films with improved electromigration resistance.
On the other hand, whether or not UHV base pressureis actually required to obtain a given film property, UHV-compatible practices (e.g., polished chamber surfaces with low outgassing rates) are desired to meet the stringent requirements of ULSI device fabrication.
Astrong motivation to extend PVD also stemmed from the enormous installed base of sputter metallization tools. Finally, since sputtering usesinert gases and nontoxic targets, a PVD push was provided by environmental awareness and increasingly stringent legislation regarding the handling, use, and disposal of hazardous materials.Addressing the above noted customer needs for lower C o 0 and highervacuum technology, Applied Materials introduced its first PVD tool inmid-1990 ~ the Endura TM 5500 system. The Endura system was designedto be a robust, high-throughput ultrahigh vacuum PVD system [5.8] directed to such high-volume applications as slab-Al interconnect (Fig. 5.9).Other new and/or improved PVD systems introduced during 1990-1997included the CVC Connexion TM model and Sputtered Films Endeavor TMmodel for general purpose, integrated processing; the MRC Solarus TMmodel for advanced AI applications; and the applications-specific Varianmb2 TM model for barriers and liners.
In 1997, Novellus Systems bought theThin Film Systems business from Varian Associates and introduced theINOVA TM PVD cluster tool shown in Fig. 5.10.5.1.6 1998-2001 : PVD CLUSTERTOOLS m IIIBased on the established success of the cluster tool concept, changes inPVD tools in the 1998-2001 are expected to be evolutionary and drivenprimarily by the need to further reduce cost-of-ownership while meetingthe process and thin film requirements of 0.18-k~m (1 Gb DRAM) deviceson the MLM Interconnect Roadmap. For maximum productivity, any overhead time associated with wafer transfer will need to be minimized m e.g.,by use of rapid acceleration-deceleration robotic handling with dual armsfor extremely high mechanical throughput ( > 60 wafers per hour).Software on PVD tools will be accessed via operator-friendly, highly intuitive graphical user interfaces (GUI), and factory automation of the wafer114FIG.
5.9R. POWELL AND S. M. ROSSNAGELEndura T M PVD cluster tool (courtesy of Applied Materials, Inc., Santa Clara, CA).fab line will require PVD tools to provide direct loadlock access for wafercarrying robots (such as the automated guided vehicle [AGV] or less automated rail guided vehicle [RGV]) and cassette containers or "pods" havingan environmentally controlled or vacuum ambient (e.g., the standard mechanical interface [SMIF] box). Dealing with the transition to 300-mmwafer fabrication in the most advanced fabs (see Section 5.4) will probably result in scaling up proven 200-mm PVD cluster tool designs and usingcorrespondingly larger process modules capable of uniformly degassing,precleaning, and coating 300-mm substrates.With regard to process modules, just as collimation was used to improvethe directionality of PVD in the 1990-1997 time frame, even more directional PVD methods based on ionized metal plasmas are expected to beused for barrier/liner and even fill applications after 1998.
Also, it is likelythat PVD tool architecture will permit a mix-and-match approach to PVDand CVD in which both methods can be used to advantage on a commonbackbone (see Section 9.9). For example, a vacuum-integrated PVD TiSPUTTERING TOOLSFIG. 5.10115INOVA TM PVD cluster tool (courtesy of Novellus Systems, Inc., San Jose, CA).wetting layer + CVD A1 + PVD Al sequence might be used to fill a highaspect ratio structure. Low-damage, in-situ cleaning of such steep featuresprior to PVD will probably require the use of reactive gas chemistry, andwe can expect future PVD tools to incorporate modules for reactive plasmaprecleaning similar to the technology used on high-density plasma etchingtools.Finally, the transition from A1 alloys to Cu interconnects m at least atthe higher levels of metallization m will require PVD tools to deposit suitable barriers such as Ta and TaN and to interface with potentially exoticwet deposition methods such as electroless plating or electroplating.
Forexample, a PVD tool might provide a vacuum-integrated stack of PVDTa + CVD Cu or PVD Ta + PVD Cu on which to plate Cu.5.2 Generic PVD Cluster ToolAll PVD equipment for advanced microelectronic device metallization iscurrently based on the single-wafer, vacuum-integrated cluster tool design.There are as many ways of implementing the basic design concept as there116R. POWELL AND S.
M. ROSSNAGELare suppliers, and Fig. 5.11 shows schematically how several have configured their tools. As shown, both the maximum number of process chambers and their placement around and/or within the central vacuum handlersvary greatly from tool to tool. Also, the flexible design allows one to usefewer process modules than the maximum number (e.g., removing a module for preventive maintenance without taking the entire tool off-line) andto double up on modules for optimum throughput (e.g., devoting two modules to the same low-deposition-rate process).The basic architecture of an application-flexible PVD cluster tool is illustrated in Fig. 5.12 (based on an Applied Materials design).
This sort oftool might be used to perform a multistep integrated process sequence suchas Al-slab deposition (e.g., preclean/Ti/TiN/Al-Cu/TiN). Application-FIG. 5.11 PVD cluster tools can be configured in a variety of ways, including both the number ofmodules and their positioning on the wafer handling backbone (tools are not drawn to scale).SPU'ITERING TOOLS117FIG.
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