The experiments have shown that microwave preliminary ionization of the plasma-forming gas increases the rate of the reactive ion etching of monocrystalline silicon (mono-Si) by four and more times in comparison with the etching process without it. It is established that the mode of plasma activation (the power of microwave discharge) and the value of plasma-forming gas pressure significantly affect the characteristics of mono-Si surface micro-roughness obtained in the result of etching.mixtures are mainly in the boiling point and the GWP

Bordusau, S.

Kovalchuk, N.

Lushakova, M.

Madveika, S.

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

doi:10.14311/ppt.2017.1.13Plasma Physics and Technology 4(1):13–16, 2017 © Department of Physics, FEE CTU in Prague, 2017THE INFLUENCE OF MICROWAVE CF4 PLASMA ACTIVATION ON THECHARACTERISTICS OF REACTIVE ION ETCHING OF MONO-SIS. Bordusau∗, S. Madveika, M. Lushakova, N. KovalchukBelarusian State University of Informatics and Radioelectronics, P.Brovki 6, 220013 Minsk, Belarus∗ bordusov@bsuir.byAbstract. The experiments have shown that microwave preliminary ionization of the plasma-forminggas increases the rate of the reactive ion etching of monocrystalline silicon (mono-Si) by four and moretimes in comparison with the etching process without it. It is established that the mode of plasmaactivation (the power of microwave discharge) and the value of plasma-forming gas pressure significantlyaffect the characteristics of mono-Si surface micro-roughness obtained in the result of etching.Keywords: microwave discharge, activation, etching, roughness, surface.1. IntroductionOne of the main characteristics of material’s plasmaetching is the processing rate [1]. This parameterbecomes of utmost importance during plasma etchingof microelectromechanical systems [2], deep etchingof integrated circuits elements [3], making sensors us-ing planar technologies methods [4], etc. Note, thenecessity of plasma etching process acceleration isconnected not only with the requirement to improvethe efficiency of technological equipment but with theneed to reduce the duration of plasma component in-fluence (primarily of charged particles) on the surfacelayers of the material and the elements of integratedcircuits structures [5]. Direct increase of power ap-plied to the electric discharge plasma is reasonablewithin certain values. The exceeding of this level canlead to such negative effects as discharge instability,significant heating of technological discharge systemsconstruction elements, uncontrolled heating of treatedmaterials’ surface, etc.Because of this, the investigation and developmentof such method of non-thermal intensification of thematerials’ etching process as preliminary etching gasactivation in the off-site plasma source becomes inter-esting. Microwave plasmatron has been chosen as suchsource. It is determined by the fact that microwavedischarge plasma has a number of specific peculiari-ties that make it rather attractive for the purpose ofmaterials plasma treatment [6],[7].2. Experimental partFigure 1 shows schematically the construction of avacuum gas discharge technological system used forinvestigation of the reactive ion etching of monocrys-talline silicon (mono-Si) wafers.The preliminary plasma activation of etching gas(CF4) was performed in a microwave plasmatron 1. Itis developed on the base of the rectangular waveguide6 bent into a ring with holes on the internal surfacefor microwave energy 7 feed into the internal region 5.Quartz discharge chamber 2 was placed along thewaveguide’s axis in which microwave discharge 4 hadbeen excited in vacuum. From one side, the quartzchamber is closed with vacuum-tight cover 3 in theplane of the microwave applicator 5 end face, andfrom the other side it enters technological chamber 8.Mono-Si wafer 11 under treatment was placed invacuum chamber 8 out of the microwave plasma-formation region on the wafer-holder electrode 12.Between grounded electrode 9 and potential electrode12 of the planar discharge E-type system a glowinglow-frequency discharge 10 was excited in which thereactive ion etching process was performed.The experiments were carried out with the wafersof 76mm in diameter. The level of microwave power(at 2.45GHz frequency) was within the range ofPMW = 250–650W. CF4 was used as working gas.The value of mono-Si etching rate was defined bymeasuring the depth of the etched hole, dividing it bythe time of the wafers’ treatment. The local etchingof the holes on the surface of wafers was providedwith the masking coating which was removed afterthe treatment. The measuring of the etched holesdepth was performed according to the interferometricmethod by the MII-4 interferometer.The analysis of mono-Si morphology and surface mi-crorelief after the reactive ion etching was performedby the atomic-force microscopy method. The surfaceroughness parameter Rz (ten-point mean roughness)was measured using the standard method.The experimental data were obtained at fixed lowfrequency generator output power.The pressure value of CF4 and output microwavemagnetron power served as operation parameters ofthe treatment process.3. The results and discussionIt has been experimentally established that microwaveplasma activation of the gas used for reactive ionetching allows to accelerate the etching process by13S. Bordusau, S. Madveika, M. Lushakova, N. Kovalchuk Plasma Physics and TechnologyFigure 1. Diagram of the experimental plasmadischarge system:1—microwave plasmatron; 2—cylindrical quartzchamber; 3—vacuum-tight flange cover; 4—microwave discharge zone; 5— internal region;6—rectangular waveguide bent into a ring; 7—connection holes; 8—vacuum chamber; 9—groundedelectrode; 10—glow discharge region; 11—wafer;12—wafer-holder electrode; 13— low frequencygeneratorfour and more times in comparison with the etchingprocess in E-type discharge without activation.Fig. 2 shows the dependence of reactive ion etchingrate of mono-Si in CF4 on the value of pressure inthe vacuum chamber at various microwave power ofworking gas plasma activation. Within the range of10–133Pa pressure these dependencies have extremecharacter. Maximum rate of mono-Si wafers etchingin CF4 is reached at the pressure of 40–50Pa in thevacuum chamber.Fig. 3 shows the dependence of hole bottom surfaceroughness values Rz after reactive ion etching of mono-Si in CF4 on the value of pressure in the vacuumchamber. It has an extreme form similar to the dataof Fig.2.Fig. 4 shows the dependence of the rate values ofreactive ion etching of mono-Si in CF4 on the value ofmicrowave plasma activation power of the etching gas.The presented data show that the maximum effect ofmicrowave plasma activation is observed at the gaspressure of p = 46Pa, at which the rate of mono-Sireactive ion etching is maximum.For other pressure values in the chamber(23 and 80Pa) the influence of gas plasma activationmicrowave power on the etching rate is lower.Fig. 5 shows the results of investigation of thehole bottom surface morphology after the process ofreactive ion etching of mono-Si in CF4 in the regionof microwave discharge plasma afterglow at variouspressure values. The roughness value of the treatedsamples in the range of the investigated pressure values(20–80Pa) varies from Rz = 7.75 nm to Rz = 31.5 nmand correlates with the value of etching rate.The experiments have shown that in the area oflower pressure values the surface relief uniformity ishigher than at 40–50Pa (Fig. 5) but the rate valuesFigure 2. Dependence of the rate values of reactive ionetching of mono-Si in CF4 on the values of pressurein the vacuum chamber at various microwave powerof etching gas plasma activation:—PMW = 250W ; —PMW = 500W ;N—PMW = 650WFigure 3. Dependence of hole bottom surface roughnessvalues Rz after reactive ion etching of mono-Si in CF4on the values of pressure in the vacuum chamber atPMW = 250W microwave discharge powerof mono-Si etching are lower. In the area of higherpressure values, the wafer surface morphology has amore ordered structure in comparison with the areaof lower pressure values (Fig. 5c). The mono-Si wafersurface microrelief at p = 46Pa pressure in the vacuumchamber has a more disordered character (Fig. 5b).Analysing the character of mono-Si surface microre-lief after reactive ion etching in CF4 at various pres-sure values it is possible to assume that 40–50Papressure provides better plasma-formation conditionsand the silicon wafer surface is bombarded by ionsmost intensively.The analysis of experimental data also shows thatin case of CF4 microwave plasma activation presencethe etched surface of mono-Si holes bottom has a more14vol. 4 no. 1/2017 The influence of microwave CF4 plasma activationFigure 4. Dependence of the rate values of mono-Sireactive ion etching in CF4 on the values of microwavegas plasma activation power:— p = 23Pa; — p = 46Pa; N— p = 80Padeveloped periodic structure, the roughness is moreeven and regular in form than in case of reactive ionetching without it.4. ConclusionsThe results of the performed experiments show thesignificant effect of preliminary microwave plasmaactivation of CF4 on the rate of reactive ion etch-ing process of mono-Si as well as on the characterof treated surface microrelief. Choosing the modeof pre-ionisation (the value of microwave dischargepower) and the value of plasma-forming gas pressure,it is possible to control the character of surface pro-file during the process of the reactive ion etching ofmono-Si. Note, the character of the surface pro-file roughness after the reactive ion etching with mi-crowave pre-ionisation may be more ordered and uni-form than without it.AcknowledgementsThis research has been supported by the Belarusian StateProgram of Scientific Research "Science of physical mate-rials, new materials and technologies", assignment 3.5.02.References[1] Nojiri Kazuo. Dry Etching Technology forSemiconductors. Springer International Publishing, 2015.[2] Bliznetsov V., Lin Hua Mao, Zhang Yue Jia, andJohnson D. Deep SiO2 etching with Al and AlN masksfor MEMS devices. Journal of Micromechanics andMicroengineering, 25(8):087002, 2015.doi:10.1088/0960-1317/25/8/087002.[3] Porter D. and Berfield T. Die separation and rupturestrength for deep reactive ion etched silicon wafers.Journal of Micromechanics and Microengineering,23(8):085020, 2013.doi:10.1088/0960-1317/23/8/085020.Figure 5. Hole bottom surface microrelief after reactiveion etching of mono-Si in CF4 in the conditions ofgas microwave plasma activation at various values ofpressure in the vacuum chamber:a— p = 23Pa; Rz = 15.32 nm; max height 32.4 nm;b— p = 46Pa; Rz = 31.48 nm; max height 62.8 nm;c— p = 80Pa; Rz = 7.75 nm; max height 15.8 nm;[4] Narducci M., Yu-Chia L., Fang W., and Tsai J. CMOSMEMS capacitive absolute pressure sensor. Journal ofMicromechanics and Microengineering, 23(5):055007,2013. doi:10.1088/0960-1317/23/5/055007.[5] Fonash S. Plasma processing damage in etching anddeposition. IBM J.RES. DEVELOP., 43(12):103–106,1999.[6] Bordusov S. Microwave plasma technologies in theproduction of electronic devices. Minsk: Bestprint, 2002.[7] Lebedev Yu. Microwave discharges at low pressuresand peculiarities of the processes in stronglynon-uniform plasma. Plasma Sources Science andTechnology, 24(5):053001, 2015.doi:10.1088/0963-0252/24/5/053001.15

The Influence of Microwave CF4 Plasma Activation on the Characteristics of Reactive Ion Etching of Mono-Si

The experiments have shown that microwave preliminary ionization of the plasma-forming gas increases the rate of the reactive ion etching of monocrystalline silicon (mono-Si) by four and more times in comparison with the etching process without it. It is established that the mode of plasma activation (the power of microwave discharge) and the value of plasma-forming gas pressure significantly affect the characteristics of mono-Si surface micro-roughness obtained in the result of etching

Bordusov, S. V.

Belarusian State University of Informatics and Radioelectronics Repository

The influence of microwave CF4 plasma activation on the characteristics of reactive ion etching of mono-Si

https://ojs.cvut.cz/ojs/index.php/PPT/article/download/5903/5210

The Influence of Microwave CF4 Plasma Activation on the Characteristics of Reactive Ion Etching of Mono-Si

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