APC and Chamber Management Application for PECVD TEOS Deposition

摘要

An advanced process control (APC) system forrnPECVD TEOS chambers has been developedrnincorporating run-to-run control, chamberrnmanagement, and improved process diagnostics. Thisrnsystem is designed to improve tool efficiency andrncapability in a high-volume manufacturingrnenvironment.rnPrior to the development of this system, qualificationrntests were run based on wafer counts through a givenrnchamber. A single test wafer was run for eachrnthickness recipe (up to 13 different TEOS thicknessrnrecipes). Recipe adjustments were made only whenrnone of the SPC rules was violated. The practice ofrnusing a single test wafer for each thickness eliminatesrncontrol system sensitivity to wafer-to-wafer thicknessrnvariation. The new control system is capable of usingrnresults from six test wafers to calculate depositionrntimes for all 13 recipes. These deposition times arerncalculated using an experimentally derived algorithmrnand fed back into the production recipes via thernequipment interface. The ability to update depositionrntimes in production recipes, combined with therndeposition rate algorithm based on qualification testrndata, allows for run-to-run control based on feedforwardrnof production lot measurements.rnAnother aspect of the control system that was builtrninto the equipment interface is the ability to selectrnchambers to send production lots through. Prior to thernimplementation of this system, the productionrnsequences included all chambers on the tool. Thisrnsituation reduced overall equipment effectivenessrn(OEE) by preventing manufacturing fromrnsimultaneously running production and qualifyingrnchambers after maintenance work. The new systemrnallows the interface to select one of 195 sequences (13rnrecipes X 15 permutations per recipe) stored on anrnexternal server. Chambers are included only whenrnthey meet all three of the following conditions at therntime when the lot is tracked in:rn1- Chamber must be ONLINE in the tool softwarern2- Chamber status in manufacturing executionrnsystem (MES) must be in a condition wherernproduction material is allowed to run (AVAIL orrnPAVAIL).rn3- MES capability flag on the chamber must bernTRUE for the deposition recipe to be run. When a lot is tracked in, if a chamber does not meetrnall three above criteria, the sequence selected wouldrnnot include that chamber. Qualification tests may bernrun manually for such a chamber without worryingrnabout production material running in an unqualifiedrnchamber.rnOne of the characteristics of PECVD TEOS chambersrnis a deposition rate degradation in between chamberrnwet cleans. Since an SPC-based control system treatsrnall variation as random in nature, no correction isrncalled for until a SPC rule is violated. The new controlrnsystem centers the process automatically after eachrnqualification test (quasi run-to-run control). Afterrnimplementing the new control system, tool capabilityrnindices (Cpk) improved ～ 20% (Fig. 1,2). The newrnqualification test uses fewer wafers and takes lessrntime, on both the deposition tool and the measurementrnequipment.rnThe new qualification test also provides betterrninformation about the health of the process. Inrnaddition to thickness average and percent standardrndeviation, other indicators are tracked to speed therndiagnosis of process issues. Information regardingrnwafer-to-wafer variation, deposition rate, and withinrnwafer uniformity characteristics are used to determinernif any mechanical or process adjustments are in order.rnA wafer-to-wafer thickness variation issue was caughtrnusing the new control system; after extensive testing,rnit was observed that spacing had a dramatic effect.rnAfter a wet clean and spacing calibration, the chamberrnbehavior returned to normal (Fig. 3). In anotherrnexample, monitoring the ratio of the outer ringrnthickness / inner thickness revealed a uniformity issuernthat was resolved with a spacing adjustment (Fig. 4).rnUsing range of the outer ring thickness as a metric,rnmechanical handoff issues have been identifiedrn(Fig 5).