Plasma etching Plasma etching K - JIST K - JIST Materials Science & Engineering Nanophotonic semiconductor Materials Lab. 1 Bibliography 1. B. Chapman, “Glow discharge processes”, (Wiley, New York, 1980). - Classical plasma processing of etching and sputtering 2. D. M. Manos and D. L. Flamm, “Plasma etching; An introduction”, (Academic, Boston, 1989). - Most helpful textbook for the researcher majoring the dry etching. 3. M. Sugawara, “Plasma etching; Fundamentals and applications”, (Oxford Univ. Press, New York, 1998). - Mostly dedicated to the high density plasma sources such as ICP and ECR 4. W. N. G. Hitchon, “Plasma processes for semiconductor fabrication”, (Cambridge Univ. Press, Cambridge, 1999) - Theoretical approach to the plasma etching and plasma deposition process 5. R. J. Shul and S. J. Pearton, “Handbook of advanced plasma processing techniques”, (Springer, Heidelberg, 2000). - Helpful textbook for the researcher in the field of compound semiconductor process 6. http://newton.hanyang.ac.kr/plasma/ - Dedicated to the plasma physics for graduate student in physics
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Bibliography1. B. Chapman, “Glow discharge processes”, (Wiley, New York, 1980).
- Classical plasma processing of etching and sputtering2. D. M. Manos and D. L. Flamm, “Plasma etching; An introduction”,
(Academic, Boston, 1989).- Most helpful textbook for the researcher majoring the dry etching.
3. M. Sugawara, “Plasma etching; Fundamentals and applications”, (Oxford Univ. Press, New York, 1998).- Mostly dedicated to the high density plasma sources such as ICP and ECR
4. W. N. G. Hitchon, “Plasma processes for semiconductor fabrication”, (Cambridge Univ. Press, Cambridge, 1999)- Theoretical approach to the plasma etching and plasma deposition process
5. R. J. Shul and S. J. Pearton, “Handbook of advanced plasma processing techniques”, (Springer, Heidelberg, 2000).- Helpful textbook for the researcher in the field of compound semiconductor process
6. http://newton.hanyang.ac.kr/plasma/- Dedicated to the plasma physics for graduate student in physics
1. Introduction2. What is plasma??3. Reaction processes in plasma4. Mechanism of plasma etching5. Dry etch reactor6. Process requirement of dry etching7. In-situ diagnostic method of plasma etch8. Device damage from plasma9. Case study
9.1 Silicon etch9.2 Metal etch9.3 GaAs and InP etch9.4 GaN and related material etch
Etching can be anisotropicLess consumption of chemicals; cost, environment impactClean process (vacuum)Compatible with automationPrecise pattern transfer
The fast-moving electrons hit the wall before the ions do and some stick to the wall.
The wall charges up negatively and this negative charge pushes other electrons away at the same time as attracting positive ions.
The field near the wall holds the electrons away from the wall and accelerates the positive ions toward the wall.
High energy ion bombardment
cf) Generally, the voltage drop couldn’t be measured. In practice process engineers usually monitor the dc potential (relative to ground) of the electrode instead, which is called “dc-bias”.
(a) Physical sputtering - purely physical process by energetic ion bombardment
(b) Chemical etching - purely chemical process by forming volatile by-product through chemical reaction between substrate and active radicals in plasma
(c) Accelerated ion-enhanced etching -chemical etching + physical etching: removal of volatile product is accelerated by energetic ion bombardment
(d) Sidewall-protected (inhibitor driven) ion-enhanced etching – deposition of etch-resistant layer with ion bombardment isotropic etching
Radicals are generated through dissociation and ionizationex) e + O2 O+ + O* + 2e,
e + CF4 CF3+ + F* + 2e
Radicals are much more abundant than ions in plasma because;(1) They are generated at a higher rate due to;
- lower threshold energy and ionization is often dissociative(2) Radicals survive longer than ions
Although the concentration of radicals is much larger than that of positive ions, the reactive fluxes incident on the surfaces can be comparable, since ions are moving faster because they have large energy obtained from the electric field in the sheath.
Volatility of etch-products is a key distinction between plasma etching and sputtering.In general, desorption is a rate-limiting steps in the plasma etching Highly volatile by-product formation is important.Evaporation rate of material (a) of molecular weight Ma is proportional to its vapor pressure, pa, (refer to Chap. II)
The evaporation rate is increased with increasing temperature. However, plasma etching generally done at room temperature.
formation of volatile product at RT is most important.
Ga2H6 -63 Gas at RTGaCl3 201.3GaCl2 535GaF3 ~ 1000GaBr3 279GaI3 < 345
(CH3)3Ga 55.7(C2H5)3In -32 Gas at RT(CH3)3In 88
InCl3 418 SublimationInBr3 371 SublimationAsH3 -54.8 Gas at RTAsF5 -52.9 Gas at RTAsF3 63AsCl3 130.4AsBr3 221PF3 -101 Gas at RTPH3 -88 Gas at RTPF5 -75 Gas at RTPCl5 62NCl3 < 71NF3 -129 Gas at RTNI3 - ExplodeNH3 -33 Gas at RTN2 -196 Gas at RT
Examples that show extremely low etch rate.Etch Al in fluorine-based gas : AlF3 is not volatileEtch Ni in chlorine-based gas : NiCl2 is not volatileEtch Al2O3 in Cl2 plasma:Al2O3 + Cl2 AlCl3 + O2
(Uphill thermodynamically, but etched with UV laser irradiation)Etch SiO2 in Cl2 plasma: Uphill thermodynamically, but etched with energetic ion bombardment.
7.5.1. Dry etch methodPlasma method(a) Plasma etching (PE)(b) Reactivel ion etching (RIE) (c) High density plasma etching: Electron cyclotron resonance
etching (ECR) and inductively coupled plasma etching (ICP)
Ion beam method(a) Ion beam etching (IBE)(b) Reactive ion beam etching (RIBE)(c) Chemically-assisted ion beam etching (CAIBE)
Plasma etching (PE)Same reactor geometry as PECVD systemLow ion bombardment energy due to the low sheath voltage drop sample was loaded on the grounded electrode (anode)Mainly chemical reactions and negligible physical etchingIsotropic etch profileAt relatively high pressure: 0.1 ~ 10 Torr
Reactive ion etch (RIE)Combination of chemical activity of reactive radicals with physical effects due to high sheath drop sample was loaded on the powered electrode (cathode)Ion bombardment strongly enhances the chemical processAnisotropic etch profile due to ion bombardmentLower operation pressure of 0.01 ~ 0.1 Torr
Reduce the plasma loss on the chamber wall using magnetic field by electromagnet bucketElectron collisional efficiency increase by interaction of E and B fieldSubstrate rotation for uniformity increase
ECR: Plasma generation by combining microwave(2.45 GHz) and the magnetic field by additional magnet.Plasma generation mechanism
Microwave (2.45 GHz) is introduced into reaction chamber through quartz windowMagnetic field is generated in the reaction chamber by magnet (permanent or electro magnetic)Electrons rotate around the magnetic line of force with the electron cyclotron angular frequency of ωc:
When the electric field E of microwave is perpendicular to the magnetic field and the circular wave of magnetic field satisfies ω = ωc, electrons are continuously accelerated by the electric filed of the microwave, obtaining high energy, and then ionizing the gas molecules by collisions.If microwave of 2.45 GHz are used, the ECR takes place at the magnetic field flux density of 875 G.
IBE – inert gas ion (Ar+) formation in external RF ion source and extracted to the reaction chamber by acceleration electrode (grid).RIBE – reactive gas besides inert gas ions are extracted from the external source to the reaction chamber. Etch rate is increased by the additional chemical reactionCAIBE – inert gas ion (Ar+) are extracted from the external source and the reactive gas are independently supplied to the wafer surface through shower-ring just above the wafer.