7/31/2019 Chemical Mechanical Planarization

1/4

VMIC 2007 1

Unique SmartPadTM for CMP End-point Applications

Lily Yao, Randy Treur, Alice Dalrymple,Bryan Sennett, Mike Kirkpatrick and Bill Kalenian

Strasbaugh, 825 Buckley Rd. San Luis Obispo, CA, 93401

rtreur@strasbaugh.comlyao@strasbaugh.com

Abstract

Efficient end-point detection (EPD) inchemical mechanical planarization (CMP) isvery critical to monitor and control theprocess. Strasbaughs new nVision EPDsystem with SmartPad technology hasprovided advanced operations from user-

friendly software to process accuracy.Working closely with customers has enabledStrasbaugh to significantly improve thesystem for use in oxide, tungsten, and MRHAlTiC applications.

Introduction

Chemical mechanical planarization (CMP)requires and highly relies on advanced in-line monitoring and control during theprocess. Engineers like to call End-pointdetection (EPD) precise engineering eyesthat closely monitors the wafer surfaceduring the polishing process. When thetargeted layer or feature is exposed thesystem can detect changes and stop theprocess or move forward to the next step.When combined with an optimized processincluding consumables and advanced wafercarrier technology, EPD can be used toachieve polish targets with consistent wafer-to-wafer results.

There are many techniques and methods theindustry has researched, developed andemployed in EPD for wafer fabricationprocesses. Most notably fraction sensing,electrical methods such as motor current andeddy current, optical signal, thermal

detection and chemical spike, etc. [1-5]. Eachtechnique utilizes its own unique solutionfor targeted applications. It is acomprehensive factor of sensitivity,resolution, accuracy, reliability, processconsistency, CoO and friendly usage.

System Overview

Strasbaugh uses the nVision system as anEPD control. The nVision EPD systemcombines multiple techniques of opticalreflectance, table/spindle motor current andtable temperature for process control. Figure1 illustrates the end point signals collectedfrom one of the process applications.

Figure 1. nVision End Point signals

The optical technique relies on an opticalsensor embedded completely within thepolishing pad (SmartPad), as shown inFigure 2b. During the applications theinterferometry and reflectance signals fromSmartPad are used to monitor film removal

7/31/2019 Chemical Mechanical Planarization

2/4

VMIC 2007 2

in real time and to pinpoint the precisemoment of transition from one layer toanother, respectively. With this technology,it is convenient to choose the wavelength oflight that provides the optimum results for a

particular film.

(a)

(b)

Figure 2. Strasbaugh nVision EPD system withthe SmartPad technology (a) EPD system (b)SmartPad.

Software

Well designed new nVision EPD systemsoftware provides a user-friendly graphicaluse interface (GUI) with access to allfeatures of recipe setup, signal setup,operations and data review. Figure 3 shows

a few snap shots of nVision softwarescreens.

The recipe set up is using event dictationmethod. Each channel can be associatedwith an event type and an action to beperformed when that event type is seen bythe EDS system.

Figure 3. nVision GUI (a) Main Screen (b)Setup screen (c)Recipe setup (d) Signal setup

The Signal Setup module can modify and

interpret the raw signal into a deterministicand robust signal traces. All signalscollected from the process through thesoftware can adjusted for signal drift. Noisein the raw data can be efficiently filtered outby defining scale and filter orders.Additionally, there is digital and analoginput/output viewing and control.

Figure 4. nVision process monitor.

The Figure 4 shows the real time datacollected from processing. Signal values aredisplayed in numeric format as well asgraphed on the chart.

(a) (b)

(c) (d)

7/31/2019 Chemical Mechanical Planarization

3/4

VMIC 2007 3

Because the original signal data from eachrun is captured to a log file, it makes laterreview and analysis possible. The post runanalysis of the previous wafer runs can be

performed under a multitude of signalfiltering and adjustment scenarios.Analyzing these stored log files decreasesthe number of wafers necessary to create afilter and/or recipe. Stored data can also bedownloaded to an ASCII file for offlineanalysis.

Process Applications

Working closely with customers, thenVision system has been successfully testedwith blanket oxide, blanket tungsten, patterntungsten and MRH AlTiC applications.

Oxide Blanket Wafer

The blanket thermal oxide wafers wereemployed to test the systems capabilitiesfor thin film endpointing as shown in Figure5.

1stmaxima1stminima

2ndmaxima&Automatic

Endpoint

3500 Oxide Removal2 Maxima + 1 Minima

1stmaxima1stminima

2ndmaxima&Automatic

Endpoint

3500 Oxide Removal2 Maxima + 1 Minima

1stmaxima1stminima

2ndmaxima&Automatic

Endpoint

3500 Oxide Removal2 Maxima + 1 Minima

Figure 5. Blanket oxide Endpoint signals

Interferometry is used to establish theamount of film removed in real time. Usinginfrared diodes and thermal oxide wafers,each maxima-to-maxima relates toapproximately 3300- removal. Within a

given wavelength of light and a given thinfilm material, the amount of materialremoval per sine wave is constant. With thisinformation and known incoming waferthickness, an endpoint recipe can be created

to target a desired endpoint thickness.Shown is an endpoint recipe targeting 3500- thermal oxide film removed.

Tungsten Blanket Wafer

Blanket tungsten wafers were employed totest the systems capabilities for endpointingat a transition from one film to another (Fig.6). The optical signal shows an increase inreflectance when tungsten film transitions tothe Ti/TiN adhesion layer followed by adecrease of the reflectance when Ti/TiNtransitions to the underlying thermal oxide.

Figure 6. Blanket tungsten Endpoint signals

Tungsten Pattern WaferCurrent SEMITECH tungsten test patternwafers were employed to test the systemcapabilities for endpointing with pattern

wafers (Fig. 7). Planarization of thetungsten can be seen as a momentarydecrease of the rising slope in the optical,pad temperature and table motor currentsignals. Endpoint occurs at the transitionfrom tungsten to oxide. The adhesion layerused on the pattern wafers is much thinnerthan the blanket wafers tested and no

7/31/2019 Chemical Mechanical Planarization

4/4

VMIC 2007 4

increase in the optical signal is seen whenthe adhesion layer is polished.

Polishing Tungsten Wto barrierto oxide

Automatic Endpoint atBreakthrough to OxideTungsten

Planarization

Figure 7. Tungsten test pattern Endpoint signals

Pattern MRH AlTiC wafernVision EPD system shows success usingendpoint for MRH AlTiC applications.Several test wafers from MRH AlTiCapplications were employed to further testthe system capabilities for endpointing withpattern wafers. One such application isalumina thin film transition to alumina withlow pattern density NiFe.

Alumina

Low Density NiFe toAlTiC Transition

Alumina to Low Density

NiFe transition

Figure 8. AiTiC lower density pattern Endpointsignals

Figure 8 shows wafer polished through toAlTiC substrate. The optical signal shows anincrease in reflectance when alumina filmtransitions to the alumina with low patterndensity NiFe followed by a decrease of the

reflectance when alumina with low patterndensity NiFe transitions to the underlyingAlTiC substrate.

Conclusion

The Strasbaugh nVision optical endpointsystem with SmartPadTM technology, polishpad embedded optics, measures opticalreflectance signal, table/spindle motorcurrent and table temperature. The systemprovides precise control for both filmtransitions (i.e. tungsten to oxide) and thinfilm removal (i.e. real-time oxide removalcontrol). The well designed new nVisionEPD system software provides a user-

friendly graphical use interface (GUI) givinga high degree of system functionality.

Reference:

1. H. Hocheng & Y. L Huang: Comprehensivereview of endpoint detection in chemicalmechanical planarization of rdeep submicronintegrated curcuits manufacturing InternationalJournal of Materials and Product Technology,

2003 Vol18 No4/5/6 pp 469-486;2. H. Jeong et al: Multi-sensormonitoringsystem in chemical mechanical planarization forcorrelations with process issues Annals of theCIRP Vol 55, 2006

3. C.Yu: Chemical mechanical polishing ofcopper for advanced semiconductor devicefabrication Future Fab Intl Volume 10, 2001;

4. T.Bibby & K. Holland: Endpoint detection

for CMP Journal of Electronic Materials. Oct1998;

5. Sang Yong Kim et al: In-situ end point of theSTI CMP process using a high selectivityslurry Microelectronic Engineering, Vol 66,Issue 1-4, 2003.