Comparison of 100 torr and 200 torr bpsg layer deposited using sub atmospheric chemical vapour deposition (sacvd) process
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Comparison of 100 torr and 200 torr bpsg layer deposited using sub atmospheric chemical vapour deposition (sacvd) process

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Comparison of 100 torr and 200 torr bpsg layer deposited using sub atmospheric chemical vapour deposition (sacvd) process Document Transcript

  • 1. International Journal of Advanced in Engineering and Technology (IJARET)International Journal of Advanced Research Research in EngineeringISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEMEand Technology (IJARET), ISSN 0976 – 6480(Print)ISSN 0976 – 6499(Online) Volume 1 IJARETNumber 1, May - June (2010), pp. 96-104 © IAEME© IAEME, http://www.iaeme.com/ijaret.html COMPARISON OF 100 TORR AND 200 TORR BPSG LAYER DEPOSITED USING SUB ATMOSPHERIC CHEMICAL VAPOUR DEPOSITION (SACVD) PROCESS. Jagadeesha T Department of Mechanical Engineering National Institute of Technology,Calicut E-Mail: Jagdishsg@nitc.ac.in Louis Kim Thin Film Division Chartered Semiconductor Manufacturing Woodlands, Singpaore Thammaiah Gowda Department of Industrial & Production Engineering AIT,ChikmagalurABSTRACT: Borophosphosilicate glass (BPSG) is most commonly used as poly-metalinterlevel dielectric film. BPSG layer is obtained by doping silicon dioxide withphosphorous and boron. Phosphorous can trap mobile ions. Silicon dioxide with higherphosphorus concentration will facilitate the reflow smoothing but is detrimental to themetallization, because of aluminium corrosion. Adding boron can reduce the reflowtemperature further. Present work focuses on a new low pressure BPSG process that canbe used for Flash memory and Logic devices. It is shown that films with phosphorus andboron concentrations in the range of 1.85-9.15 elemental wt% are deposited with filmthickness 6000 Å/14000 Å BPSG and 100 Torr process has been found to achieve morestable film thickness. Decreasing the deposition pressure from 200 to 100 Torr results ina 50% increase in the deposition rate of twin-wafer SACVD BPSG and has zero effect onfilm properties. Throughput has been improved by 20% on SACVD PMD BPSGapplication. 96
  • 2. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEMEKeywords: BPSG, PSG, Low pressure BPSG, SACVD1. INTRODUCTION Advances in integrated circuit fabrication technology over the past two decadeshave resulted in integrated circuits with smaller device dimensions, larger area andcomplexity. Many integrated circuits now have features, such as traces or trenches thatare significantly less than a micron across. While the reduction in feature size hasallowed higher device density, more complex circuits, lower operating powerconsumption and lower cost, the smaller geometries have also given rise to newproblems, or have resurrected problems that were once solved for larger geometries(Haruhisa Kinoshita et al., 2004). One example of a manufacturing challenge presented by submicron devices is theability to completely fill a narrow trench in a void-free manner while keeping the thermalbudget of the trench-filling process at a minimum. For example, in order to meet themanufacturing requirements of 0.18 micron geometry devices and below, a BPSG layermay be required to fill 0.1 micron wide and narrower gaps having an aspect ratio of up to6:1. At the same time, these manufacturing requirements demands minimum thermalbudget (Arbinda Das et al., 2008). Borophosphosilicate glass (BPSG) is used in the semiconductor industry asseparation layers between the polysilicon gate/interconnect layer and the first metal layerof MOS transistors. Such a separation layer is often referred to as pre-metal dielectric(PMD) layer because it is deposited before metal layers. PMD is used to electricallyisolate portions of the first deposited metal layer from the semiconductor substrate. It isimportant for PMD layers to have good planarization and gap-fill characteristics (ChiWen Liu et al., 1995). BPSG deposition methods have been developed to meet thesecharacteristics and often include planarizing of the layer by heating it above its reflowtemperature so that it flows as a liquid. The reflow process enables the BPSG to filltrenches of small width with high-aspect ratio (Werner K et al., 1991). Osorio et al.(1993) have demonstrated that the heating necessary to reflow a BPSG layer can beachieved using either the rapid thermal pulse (RTP) method or a conventional furnace ineither a dry (e.g., N2 or O2) or wet (e.g., steam H2 /O2) ambient. Standard BPSG films 97
  • 3. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEMEare formed by introducing a phosphorus-containing source and a boron-containing sourceinto a processing chamber along with silicon-and oxygen-containing sources.Triethylphosphate (TEPO), triethylphosphite (TEPi), trimethylphosphate (TMOP),trimethylphosphite (TMPi), and similar compounds contain phosphorus as dopantconstituent. Similarly, Trietbylborate (TEB), trimethylborate (TMB), and similarcompounds contain boron as dopant constituent. Figure 1 shows the device application ofBPSG layer. Figure 1 Device application of BPSG layer In general, doped oxides used for the reflow process contain 6 to 9 wt %phosphorus (Adam et al., 1981). Silicon dioxide with higher phosphorous concentrationwill facilitate the reflow smoothing but is detrimental to the metallization, because ofaluminium corrosion. After the doped silicon oxide is deposited, a subsequent heating isnecessary until the oxide softens and flows. In addition to the phosphorous concentration,the reflow morphology of the doped silicon dioxide can also be determined by heatingtemperature, heating time, heating rate, and heating ambient. Sometimes, boron dopantsare added to the phosphorous –doped silicon dioxide to further reduce the softeningtemperature by decreasing the glass viscosity (Levy and Nassau, 1981). 98
  • 4. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEME2. EXPERIMENTAL DETAILS Experimental work has been conducted using commercially available SACVDsystem known as ProducerTM. Figure 2 shows the Producer platform that combines theproductivity benefits of twin wafer handling with the advantages of single waferprocessing. Twin process chambers permit simultaneous processing of two wafers side byside in separate environments, resulting in ultra high productivity. Up to three twinchambers can be mounted on the platform, allowing for simultaneous processing of sixwafers. The gas inlets, chamber pressure and pumping capability are shared within a twinchamber, providing reliability, ease of maintenance and reduced capital expenses.However; spacing, RF power and processing time can be optimized for the two chambersseparately. Producer also utilizes remote plasma clean technology to addressenvironmental concerns reduces wear on the process kit and also minimizes theprocessing time. Figure 2 Producer Tool used for deposition process This work provides a new and improved process for filling small-width, high-aspect ratio gaps with a BPSG layer. The present invention deposits a low pressure BPSGlayer over a small-width, high-aspect ratio gap that requires filling with a dielectricmaterial and reflows the layer in a rapid thermal pulse (RTP) furnace. It is shown that bychanging the process pressure from standard 200 Torr to 100 Torr, deposition rate can beincreased. The relation between the pressure versus deposition rate was first established 99
  • 5. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEMEusing the producer tool equipped with PLIS (Precision Liquid Injection System).Theeffect of the other parameters were also studied and found that pressure had greaterinfluence on the deposition rate and Figure 3 shows the other parameters considered andFigure 4 shows the effect of varying the pressure of process. Figure 3 Process parameters studied to optimize the BPSG parameters 5000 Dep Rate (A/min) Deposition Rate (A/min) 4000 3000 2000 1000 0 50 70 100 150 200 250 300 Pressure (Torr) Figure 4 Effect of pressure on deposition rate in BPSG process.3. RESULTS AND DISCUSSION3.1 Deposition rate In order to improve device characteristics and to use the deposited dielectric andpolysilicon films in various applications, the properties of these films are important.Deposition rate is a critical parameter which affects the throughput of wafers and is agood indicator of wafer fabrication unit’s performance.Other parameters such asrefractive index, film stress, dielectric strength, and leakage current , all significantly 100
  • 6. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEMEdetermine the film properties and even the applications of these deposited oxidefilms.The stress in silicon dioxide can change the film quality. Tensile stress in silicondioxide may induce crack in the films. Stress in silcion dioxide depends on the depositionrate, deposition temperature , post annealing cycle, dopant concentration, film porosity,and water content. Hence, the processing of silicon dioxide should be carefullycontrolled. Table 1 shows the comparison between 100 Torr and 200 Torr processes.Process parameters indicated in the Table 1 are the average values of measurement takenover 240 wafers and for various technology nodes ranging from 0.13 micron to 0.1micron devices. It is clear from the experimental results that 100 Torr gives lowestprocessing time. Range difference up to 500 Å is observed between chamber 1 andchamber 2. This difference is due to heater and other hardware settings. The range can befurther reduced by fine tuning of hardware. Process parameter Unit 100 Torr 200 Torr Chamber Chamber Chamber 1 Chamber 1 2 2Thickness (A) 14494 14538 14561 14523Deposition rate (A/min) 3370 3391 2342 2336Deposition time (s) 258 386Range (A) 164 535 297 825Uniformity (%) 0.80 0.65 1.29 0.96Refractive Index - 1.4849 1.4852 1.4888 1.4689Stress – as deposited MPa 46.8 43.9 42.1 39.1Stress – after RTA MPa -18 -19 -16 -19.6B dopant Concentration (wt %) 1.83 1.84 1.87 1.86B dopant Concentration (wt %) 0.04 0.07 0.06 0.05rangeP dopant Concentration (wt %) 9.113 9.117 9.129 9.134P dopant Concentration (wt %) 0.081 0.24 0.066 0.05rangeParticle adder @0.2 - <50 <50 <50 <50micron for 6000 AthicknessThroughput WPM 7875 6550TEOS consumption mgm 850 850TEPO consumption mgm 110 151CMP removal rate (A/min) 3092 3109 3083 3113WEER - 19.35 19.13 19.78 19.75 Table 1 Comparison of 100 Torr and 200 Torr BPSG Processes 101
  • 7. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEME3.2 Thicknes Range Improvement and TEPO usage reduction The step coverage of deposited oxides can be improved by planarization. Lowerthickness range is better for planarization operation like Chemical mechanical polishing.Summary of four important performance parameters are indicated in Table 2. Rangemprovement of 54.2 % is seen for 100 Torr process compared to 200 Torr process. Waferoutput from one twin chamber of Producer system for 100 Torr process is 7875 WPM(wafers per month) whereas, it is only 6550 WPM for 200 Torr process. In other words,cost per wafer using 100 Torr process is less compared to 200 Torr process. In addition,100 Torr process gives 37.2% saving in TEPO usage. Process parameter Unit 100 Torr 200 Torr Saving/Improvement Deposition time (s) 258 386 49.6% Thickness Range (A) 535 825 54.2% TEPO usage mgm 110 151 37.2% Wafer output WPM 7875 6550 20.1% Table 2 Comparison of 100 Torr and 200 Torr processes in terms of performance parameters.3.3 Yield results For use in ULSI devices the reliability of silicon dioxide is important. Hence , thetime for failure and charge to breakdown under constant voltage or constant current stressare analysed to determine the oxide quality. The stress in silicon dioxide can change thefilm quality. Table 3 and Table 4 shows the yield results of the 100 Torr and 200 Torrprocesses. Experiments were conducted on different devices using different technologynodes. Yield results are quite comparable and the 100 Torr processes give better yield ,which is desirable from the productivity point of view.It can also be observed that the 100Torr processes are technology node and device independent. Lot ID Technology Node Device CP1(%) CP2(%) S1 1 D1 87 87.6 S2 1 D2 87.6 84.3 S3 1 D3 86.6 85.5 S4 1 D4 75.5 75.6 S5 2 D5 84.3 83.3 S6 2 D6 80.32 78.91 S7 2 D7 80.67 77.25Table 3 Yield results obtained using 100 Torr for different technology nodes and devices 102
  • 8. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEME Lot ID Technology Node Device CP1 (%) CP2(%) S1 1 D1 84.0 85.3 S2 1 D2 61.8 60 S3 1 D3 87.2 86.2 S4 1 D4 74.8 74.7 S5 2 D5 81.8 78.8 S6 2 D6 75.4 72.9 S7 2 D7 82.9 80.3Table 4 Yield results obtained using 200 Torr for different technology nodes and devices3.4 Gap filling capability Figure 5 shows step coverage for 100 Torr BPSG and 200 Torr BPSG processes.Both processes give completely uniform or conformed step coverage. The film thicknessalong the walls and at the bottom of step are constant. As the reactants or reactiveintermediates adsorb on the surface and then rapidly migrate along the surface beforereaction, the resulting films will have a uniform surface concentration on the substrateand constant thickness. It is important to avoid cusp formation, it will be unfavorable forsubsequent metal deposition. Figure 5 Gap filling capability of 100 Torr BPSG layer and 200 Torr BPSG layers4. CONCLUSIONS In this paper, a new and improved process for filling small-width, high-aspectratio gaps with a Borophosphosilicate glass (BPSG) layer has been presented. Thepresent invention deposits low pressure BPSG layer over a small-width, high-aspect ratiogap that requires filling with a dielectric material and reflows the layer in a rapid thermal 103
  • 9. International Journal of Advanced Research in Engineering and Technology (IJARET)ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 1, Number 1, May - June (2010), © IAEMEpulse (RTP) furnace. It is shown that by changing the process pressure from standard 200Torr to 100 Torr, deposition rate can be increased. Range improvement of 54.2 % is seenfor 100 Torr process compared to 200 Torr process. Cost per wafer using 100 Torrprocess is less compared to 200 Torr process due to high deposition rate and low TEPOusage.100 Torr process gives 37.2% saving in TEPO usage. Yield results and gap fillingcapabilities of both processes are comparable. The feasibility of the new fabricationprocess has been demonstrated with production wafers and found to be technology nodeand device independent.REFERENCES 1. Adams A.C., et al., 1981. Planarization of Phosphorous –doped silicon dioxide. J. Electrochemical Society. 128, 423-429 2. Arbinda Das, et al., 2008. Phosphorous doped as a pre-metal-dielectric for sub 50 nm technology nodes. J. of Microelectronic Engineering. 85, 2085-2088 3. Chi Wen Liu, et al., 1995. Chemical mechanical polishing of PSG and BPSG dielectric films: The effect of phosphorous and boron concentration, Journal of Thin Solid Films. Volume 270, 1995, Pages 607-611. 4. Haruhisa Kinoshita, et al., 2004. Chemical vapour deposition of SiO2 films by TEOS/O2 supermagnetron plasma, J. of Surface Engineering, Surface Instrumentation and Vacuum Technology. 76, 19-22. 5. Levy, R.A., et al., 1986. Reflow mechanism of contact bias in VLSI processing. J. Electrochemical Society. 133, 1417-1428 6. Osorio, S. P. A., et al., 1993. Effect of annealing on the composition of PECVD borosilicate and borophosphosilicate glasses, J. of applied surface science. 70, 772-776. 7. Voulgaris, et al., 2005. RF power effect on TEOS/O2 PECVD of silicon oxide thin films, J. of Surface coating and technology. 200, 351-354. 8. Werner K., et al., 1991. Simultaneous deposition and fusion flow planarization of borophosphosilicate glass in a new chemical vapour deposition reactor, J. of Thin Solid Films. 206, 64-69. 104