High density plasma process chamber

#The present invention relates to a plasma process chamber for processing semiconductor substrates.

#A plasma process chamber is used in semiconductor fabrication processes, for plasma enhanced chemical vapor deposition (CVD), reactive ion-etching (RIE), and ion implantation. FIG. 1 shows a conventional process chamber 20 having a gas distributor 22 that provides process gas to the chamber. A coil power supply 24 powers an inductor coil 26 adjacent to the chamber that inductively couples RF energy to the process gas to form a plasma. Process electrodes that are used to couple RF power to the plasma typically include a cathode 28 below the substrate and an anode 32 surrounding the cathode. The cathode 28 is electrically insulated from the anode 32 by one or more quartz or silicon dioxide insulator shields 34 that extend below and around the cathode. The power supply 36 applies an impedance matching RF bias power to the cathode and the anode is formed by electrically grounded sidewalls and top walls in the chamber 20. The cathode 28 is capacitively coupled to the anode 32 via the electrostatic chuck 38 that rests on the cathode, the substrate 30, and the plasma sheath that forms at the boundary of the cathode. The capacitively coupled electric field energizes and accelerates the plasma ions toward the substrate 30.

#Conventional chambers 20 often have low plasma ion densities and plasma ion energy distributions which are spread out over a wide range of energy levels with multiple energy level peaks. The plasma ion density and energy levels depend upon the electron density or energy distribution in the plasma sheath, the power and frequency of the capacitively-coupled RF power applied to the electrodes 28, 32, the process gas composition and pressure, and the components inside the chamber. The plasma sheath is an electron deficient region that arises due to the difference in mobility between electrons and positive ions in the plasma, and has an associated voltage waveform that is effected by the resonance, impedance load, and other electrical characteristics of the chamber. This voltage waveform is perturbed from normal by the harmonic content of the plasma sheath. The RF bias and impedance matching circuit, power transmission lines, structure of the electrodes 28, 32, and the components inside the chamber 20, all effect the development of harmonics at the plasma sheath, which in turn disturb the sheath voltage waveform over time giving rise to perturbed waveforms. The perturbed waveform can give rise to a "dual predominant" multimodal plasma energy distributions in which the plasma ion energy distribution curve has two or more peaks. Such multi-peak energy distributions are undesirable because a large spread of plasma ion energies provides lower average plasma ion energy levels that result in poor plasma performance, for example, etch stopping in processes for etching high aspect ratio trenches.

#These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings which illustrate examples of preferred embodiments of the invention, where:

#FIG. 1 (prior art) is a partial sectional schematic view of a prior art process chamber showing insulator shields around the cathode and capacitance couples formed in the chamber;

#FIG. 2 is a sectional schematic view of a process chamber according to the present invention illustrating an exemplary arrangement of inductor coils, primary bias electrode, power electrode, and secondary bias electrode;

#The present invention is directed to a plasma processing apparatus 50 used to process substrates 30 in a high density, highly directional, plasma formed in a process chamber 55. A high density plasma is a plasma having an ion energy density in excess of 10.sup.11 ions/cm.sup.3 in contrast to conventional plasmas that have lower ion densities on the order of 10.sup.10 ions/cm.sup.3. By highly directional it is meant that the charged plasma ions and species are energized by electric field vector components 60 within the plasma zone 65 to accelerate in the direction substantially perpendicular to the plane of the substrate 30. The high density and highly directional plasma provides a large number of reactive plasma species that energetically impinge on the substrate 30 to efficiently chemically react with or transfer energy to the substrate. The highly directional plasma can be used to etch, implant, or deposit material on a substrate 30.

#An exemplary plasma processing apparatus 50 of the present invention, is schematically illustrated in FIG. 2, and is provided only to illustrate an example of the present invention and should not be used to limit the scope of the invention. The apparatus 50 generally comprises an enclosed chamber 55 having sidewalls 70 and a bottom wall 75 fabricated from any one of a variety of materials including metals, ceramics, glasses, polymers and composite materials. Metals commonly used to fabricate the process chamber 55 include aluminum, anodized aluminum, "HAYNES 242," "A1-6061," "SS 304," "SS 316," and INCONEL, of which anodized aluminum is preferred. Process gas is introduced into the chamber 55 through a gas distribution system 80 that distributes the gas in the chamber, and includes a process gas supply 85 and a gas flow control system 90 that operates gas flow meters 95. Preferably, the gas distributor comprises a silicon ring 100, that surrounds the substrate 30. As shown in FIG. 3a, the silicon ring 100 comprises a circular passageway 105 for holding process gas and an array of gas injection holes 110 to distribute the process gas around the periphery of the substrate 30. Preferably, the silicon ring 100 is temperature controlled to an accuracy of .+-.5.degree. C. in a temperature range of about 250 to about 600.degree. C., using an optical pyrometer for temperature feedback, an array of lamps 115 below the ring for radiant heating of the ring, and cooling by conduction to the bottom wall 75. The temperature controlled silicon ring 100 also provides a controlled source of silicon for scavenging free fluorine ions and radicals from the process environment. An exhaust system 120, comprising one or more exhaust pumps 125 (typically including a 1000 liter/sec roughing pump) and throttle valves 130 is used to exhaust spent process gas and control the pressure of process gas in the chamber 55. Preferably, an asymmetric pumping channel 132 is used to pump gases out of the chamber 55 to provide a uniform distribution of gaseous species around the surface of the substrate 30.

#In the embodiment shown in FIG. 2, the chamber 55 comprises an inductor antenna 135 adjacent to the chamber that generates an induction coupled field in the chamber to form a high density inductive plasma therein. The inductor antenna 135 preferably comprises multiple coils positioned adjacent to the chamber ceiling 140 for inductively coupling RF power into the chamber 55. A plurality of process electrodes are electrically biased relatively to one another and capacitively couple through the plasma sheath and dielectric layers separating the electrodes to energize the plasma ions. A primary bias electrode 145 comprises a first conducting surface 150 exposed to the plasma zone 65. A unitary monolithic dielectric member 155 positioned directly below the primary bias electrode 145 has a receiving surface 160 for receiving a substrate 30 thereon. A power electrode 165 is embedded in the dielectric member 155 so that dielectric material completely surrounds the power electrode. The chamber 55 further comprises a secondary bias electrode 170 positioned directly below the dielectric member 155 and preferably having a second conducting surface 175 exposed to the plasma zone 65. An electrode voltage supply 180 is provided for maintaining the power electrode 165, and the primary and secondary bias electrodes 145, 170 at different electrical potentials relative to one another. The combination of three or more electrodes, which are vertically aligned to form a stacked cylindrical arrangement of electrodes, provides an energetic plasma having highly directional plasma ions within the chamber 55.