ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Plasma Etching Chamber

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Plasma Etching Chamber Prepared by: Zhuo Li Dept. of Electrical and Computer Engineering Utah State University 3/16/2012

2. Outline • Statement • Reference list • To probe further • Major applications • Introduction • Working principle • Influencing Factors • Advantages & Disadvantages • Equipment and on-shelf products ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Statement • Actuator The broad definition of actuator is:  the mechanism by which an agent acts upon an environment. The agent can be either an artificial intelligence agent or any other autonomous being. In engineering, actuators are a subdivision of transducers. [Wikipedia.org] Thus, actuator is not limited to the types of electric, hydraulic fluid pressure or pneumatic pressure powered devices. Since the plasma etch chamber is the equipment used to etching/shaping the surface of a sample material, it can be categorized as a actuator. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. Reference List • [1]. Shane Lynn, Virtual Metrology for Plasma Etch Processes, PhD thesis, Electronic Engineering Department, National Univ. of Ireland. • [2]. Lynn Fuller, Plasma Etching, lecture slides, Microelectronic Engineering, Rochester Institute of Technology. • [3]. Lab modules, webpage, [online], http://matec.org/ps/library3/secure/modules/047/, [Mar.16.2012] • [4]. Henri Janseny, Han Gardeniers, Meint de Boer, Miko Elwenspoek and Jan Fluitman, A survey on the reactive ion etching of silicon in micro-technology, J. Micromech. Microeng. 6 (1996), 14–28. • [5]. Brian E. Goodlin, Multivariate Endpoint Detection of Plasma Etching Processes, PhD thesis, Dept. of Chemical Engineering, MIT. • [6]. Tao Ding, Fei Wang, Kai Song, Guoqiang Yang, and Chen-Ho Tung, Oxygen Plasma Etching-Induced Crystalline Lattice Transformation of Colloidal Photonic Crystals, J. Am. Chem. Soc., 2010, 132 (49), pp 17340–17342. • [7]. Hess, Dennis W., Levitin, Galit, Myneni, Satya, Removal of Photoresist and Post-Plasma Etch Sidewall Films Using Supercritical and Subcritical CO2 with Additives, EPA project annual report, 2002 Progress Report. • [8]. J. Tian, S. Sosin, J. Iannacci, R. Gaddi, M. Bartek, RF–MEMS wafer-level packaging using through-wafer interconnect, Sensors and Actuators A: Physical, Vol. 142, Issue 1, 10 March 2008, Pages 442–451. • [9]. K Denpoh, Locally enhanced discharges at gas hole outlets of a showerhead in a plasma etching reactor, J. Phys. D: Appl. Phys. 42 (2009). ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. To Explore Further • [i] Plasma Etch Inc., http://www.plasmaetch.com/Corporate_Information.html • [ii] Oxford Instruments., http://www.oxford-instruments.com/Pages/home.aspx • [iii] MEMSnet®, https://www.memsnet.org/mems/beginner/etch.html • [iv] Stanford Nanofabrication Facility (SNF) lab community, Labmembers Wiki, https://snf.stanford.edu/SNF • [v] KLA-Tencor Corporation, http://www.kla-tencor.com/high-brightness-led-manufacturing.html • [vi] SNTEK, Crystec Tech. Trading GMbH, http://www.crystec.com/trietche.htm • [vii] Daniel M. Dobkin, Plasmas for CVD, http://www.enigmatic-consulting.com/semiconductor_processing/CVD_Fundamentals/plasmas/plasmaTOC.html • [viii] CLARYCON Plasma Tech, For Advanced Devices, Plasma etch fundamentals, http://www.clarycon.com/plasmaetchfundam.html • [ix] Georgia Tech Microelectronics Research Center, CMOS as a Research Platform, http://cmos.mirc.gatech.edu/documents/ ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Major Applications • Micro/Nano-scale industries • Semiconductor manufacturing • Silicon wafers • Integrated circuits • Solar panels • LEDs • MEMS • Etch/deposit films • Medical • Remove organic/inorganic contamination Fig1. Structures made by deep reactive ion etching or surface machining technology. [iii] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Introduction • Wet etch • Wet etching removes the surface material on a wafer through a chemical reaction. It is by nature highly selective with respect to mask and substrate. • Wet etch processing had been till recently predominate type of etch process used in the manufacturing of integrated circuits. In today's fabrication processes wet etches are still performed to remove contamination from the wafer surface prior to the next fabrication process step. [2] • Dry etch • Arose from the need to define circuit features smaller than 3000 nm. Etchant used in dry etch are usually reactive ions or a vapor phase etchant. [ii] • Comparison • In wet etch, the wafer is immersed in a tank of chemical liquid etchant.  Isotropic • In dry etch, the wafer is exposed to the etchant in a gaseous state suspended in an RF energized plasma under vacuum [2]. Anisotropic • Dry etch provide more control of the etching parameters, anisotropic profiles, etc. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Introduction • Plasma etching A form of plasma processing used to fabricate integrated circuits, which involves a high-speed stream of glow discharge (plasma) of an appropriate gas mixture being shot (in pulses) at a sample. The plasma source, known as etch species, can be either charged (ions) or neutral (atoms and radicals). [Wikipedia.org] • Chemical etching (Spontaneous surface etching) • Physical etching (Sputter/mechanical etching) • Reactive ion etching (RIE) An etching technology that uses chemically reactive plasma to remove material deposited on wafers. • Inductive coupled plasma etching (ICP) • Electron cyclotron resonance (ECR) ICP ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Introduction • Etching outcome and profile • Isotropic (non-directional removal of material from a substrate) • Anisotropic (directional) Ideal etch Poor etch Fig3. One-run multi-step RIE process. Top left: after anisotropic etching the top Si of an SOI wafer. Top right: after etching the insulator and sidewall passivation. Middle left: during isotropic etching of the base Si. Middle right: after isotropic etching the base Si. Bottom: typical finished MEMS products. [4] Fig2. No process is ideal, some anisotropic plasma etches are close. [2] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Introduction • Etching outcome and profile • Isotropic (non-directional removal of material from a substrate) • Anisotropic (directional) Fig4-1. Different etching outcomes [5] Fig4-2. Etching profiles. [viii] Fig5. Isotropic and anisotropic (directional) etch profiles. [1] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. The big picture Fig6: Typical parallel-plate RIE system. [iii] Fig7. RIE Process Chamber. [3] Fig9. Physical etch process chamber. [3] Fig8: Typical RF sputtering system. [iii] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Working Principle • In short The etching is achieved by using the plasma etchant to bombard or react with the materials on the sample surface (e.g. SiO2) The surface is charged by the electrodes to attract the “right” plasma particles to etch the “right” profile; or etching occurs spontaneously by choosing selective etch species. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Working Principle • Key words • Glow discharge, Collisions, Ion, Bombard. • A typical plasma etching process system consists of: • Plasma generator (RF) • Chamber • Electrodes (parallel-plate) • Plasma Plasma, or “radiant matter” as it was first dubbed, was discovered by Sir William Crookes in 1879 in a Crooke's tube [1]. Plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Plasma contains charged particles: positive ions and negative electrons or ions. [Wikipedia.org] Overall the plasma remains electrically neutral. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Working Principle • Plasma generation • DC discharge • RF discharge (13.56 MHz) • Electrodes (parallel-plate) RFdischarge   DCdischarge Fig10. from [1] [5] Fig11: Typical parallel-plate electrodes in RIE chambers. [1]  ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Working Principle • Plasma composition • Neutral Molecules at a density of 1016/cm3 • Radicals 1014/cm3 • Electrons 108/cm3 • Positive ions 108/cm3 • There are a million times more radicals than ions or electrons. • Ions don’t etch, radicals do. • Ions affect the process by energetic (physical) bombarding of the surface. • Radicals are responsible for the dry etching process. They are chemically active and react with the surfaces to produce volatile products [2] Fig12. Cartoon of etching. [6] Fig13. adapted from [3] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Working Principle • Plasma bombardment Fig15. from [6] Fig14. from [7] Fig16. from http://www.helsinki.fi/research/news/2011/week20.html Fig17. from [vii] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Working Principle • Plasma etching Steps [3] • Loading wafers • Create a vacuum chamber and vacuum pump system • Generating a plasma • Producing a clean etch profile Fig18: Plasma etching work flow. [iii] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Working Principle Fig19. Schematic of Etch Process. Reactive etchant species are created in the plasma which react with the wafer surface to form volatile etch products. A continuous gas flow is maintained to replenish the supply of etchant species. [1] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Working Principle Fig20. Plasma etch mechanisms. [viii] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Working Principle • An plasma etching example [2] CF4 is inert gas add electron impact to produce fluorine radicals: CF4 + e => CF3+ + F + 2 e (Dissociative Ionization) CF4 + e => CF3 + F + e (impact dissociation) Then chemically form volatile SiF4: Si + 4F => SiF4 (gas) • More examples are available in [4]. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Influencing Factors • Factors influencing dry etch [3] • Etch Rate.  The etch rate during a plasma etch is determined by system design, pressure and chemical etchant density. • Pressure. Pressure levels also can influence the etch profile. • Temperature. Increasing temperature increases the etch rate. • Micro-loading. Micro-loading is a problem that can affect selectivity during the dry etch process. “RIE lag”, “loading effect” • Post-etch corrosion.  Post-etch corrosion occurs when residue from the etchant is left on the wafer surface after the etch. Fig20-1. left: resist residueafter etching; right: effectiveness of ACT 935 solvent strip process. [3] Fig20-2. SEM cross-sectional photograph illustrating significant dependency of the DRIE plasma etch rate on the trench width. [8] Fig20-3. “RIE lag”, “loading effect”. [9] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. Advantages & Disadvantages • Advantages [3] • No photoresist adhesion problems • Anisotropic etch profile is possible • Chemical consumption is small • Disposal of reaction products less costly • Suitable for automation, single wafer, cassette to cassette • Disadvantages • The etching chamber in operation is like a “black box”, which mak it difficult to measure the etching variables. [1] • Complex equipment • Residues left on wafer, polymers, heavy metals • Particulate formation • Stringers, profile effects ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

23. Plasma Etch Equipment • The major types of dry etching equipment are [3] • Barrel.  in a Barrel reactor, the wafers do not rest on one of the electrodes. • Reactive Ion Beam. Pressure levels also can influence the etch profile. • Plasma (High Pressure) and Reactive Ion (Low Pressure) reactors. Micro-loading is a problem that can affect selectivity during the dry etch process. Fig21-2. Cross-sectional micrographs of two gas holes of a showerhead used for some plasma processes in an actual etching reactor. (b) is sealed at the back side of the showerhead to prevent gas flow in it. One can easily see the barrelerosion in the hole for the case with gas flowing (a). Barrel erosion is completely absent for the case when gas is not flowing (b) Note that the facet at the edge of the outlet is formed due to ion impact sputtering. [9] Fig21-1. Cross-section milling of AMD CPU in focused ion beam system ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

24. On-shelf Products • LAM Research, CA, USA • LAM 9400 TCP Poly Etcher A single wafer, low pressure, high density plasma etcher for poly-silicon processing. • LAM 4600 Aluminum Etcher • LAM 490 Plasma Etcher Fig24-2. LAM 9400 TCP Poly Etcher. [iv] Fig24-1. LAM 4600 Aluminum Etcher. [3] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

25. On-shelf Products • Oxford Instruments [ii] • Plasmalab 800Plus • PlasmaPro NGP 1000 Table1. Production Tools List. Complete table available in [ii]. Fig25. from [ii] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

26. On-shelf Products • Stanford Nanofabrication Facility Lab community [iv] Table2. Dry Etch Product List. Complete table available in [iv]. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

27. On-shelf Products • DRYTEK QUAD Etch Recipe For CC AND VIA [2] Fig26. DRYTECH QUAD RIE. [2] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators