Langmuir probe, optical emission spectroscopy, and biased quartz crystal microbalance measurements were used to investigate an argon and copper plasma used for ionized physical vapor deposition of copper. Copper vapor generated by a magnetron sputter discharge is ionized upon passing through an argon discharge excited by an internal rf induction antenna. Argon plasma characteristics such as electron temperatures T e , plasma densities n e , and plasma and floating potentials V p and V f , were studied as a function of argon pressure and rf power. An increase of plasma density versus rf discharge power and argon pressure was observed. The radial profile of plasma density measured by a Langmuir probe reveals a peak ion density at the center of the rf antenna and an increase in the radial ion concentration gradient with argon pressure. The ratios of optical emission intensities from Cu ϩ ion and Cu neutral lines increase with rf discharge power and argon pressure. The biased quartz crystal microbalance measurements show an increase of both Cu ϩ ion flux and the ratio of Cu ϩ ion to Cu neutral fluxes with rf power and argon pressure; however, they also show a decrease of total Cu flux with increasing argon pressure.
Ionized physical vapor deposition is a technique for sputtering metal into small trenches, by ionizing sputtered metal atoms so that their trajectories can be controlled by electric fields. To this date no one has quantified exactly what fraction of the metal vapor is ionized, although the trends of how ionization varies with input parameters is known. This article describes and demonstrates a new quartz crystal microbalance design, which can be used to measure the ionized metal flux fraction arriving at the substrate location. Instead of using grids to repel ions as similar devices do, this analyzer works by applying a voltage bias to the front surface of the crystal in order to repel ions. A magnetic field adjacent to the face limits electron current to the microbalance, minimizing its perturbation of the plasma. The measurement tool described in this article does not suffer from complications caused by placing grids in front of the monitor and is an attractive method for characterizing ionized physical vapor deposition systems. Ion and neutral metal fluxes as a function of ionizer power are presented for an argon/copper discharge.
Ionized physical vapour deposition (IPVD) is of current interest to the semiconductor industry for the deposition of thin metal films as diffusion barriers and seed layers in high aspect ratio features. One of the aims of IPVD is to collimate depositing particle fluxes by ionizing a significant fraction of the incident metal vapour and applying an electric potential bias to the substrate. A system consisting of a dc-powered, 15 cm diameter copper sputter source and a RF induction plasma powered by a single-turn, 36 cm diameter, loop antenna internal to the vacuum chamber has been examined. Measurements made with a biased quartz crystal microbalance in an argon background of 10-90 mTorr demonstrate that, at low magnetron sputtering levels of 100 W, ionized metal flux fractions (IMFFs) as high as 90% can be observed. However, further measurements of the IMFFs and plasma density indicate rarefaction of the background argon gas as the metal flux to the plasma increases. Results are presented from an experimental investigation of methods to reduce the gas rarefaction. These include the modulation of the metal flux on the timescale of the process gas residence time and increasing the target-to-substrate height.
The electron energy distribution function (EEDF) has been measured under a variety of conditions in an Ar/Cu plasma for ionized physical vapor deposition. The EEDF is directly measured in a system including a direct-current magnetron sputter source for copper and a radio frequency (rf) induction plasma, using a Langmuir probe with a modulated bias voltage in combination with a lock-in amplifier. The experimental data indicate that at fixed rf ionization power, the electron population in the tail of the EEDF is depleted by the introduction of copper vapor, and the electron average energy decreases slightly. Observed changes in the EEDF are attributed to inelastic collisions with copper atoms, which have lower threshold energies for excitation and ionization as well as larger cross sections as compared to argon, and the resulting reduction in the measured plasma potential.
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