Tsutomu Miura

High-Vacuum Planar Magnetron Sputtering

High-vacuum planar magnetron sputtering is performed in a wide pressure range of 10-1 Pa to 10-3 Pa. The measured sputter-deposition rates of Al are 0.2 µm/min at a pressure of 0.12 Pa (discharge current 0.2 A) to 8.3 A/min at 0.0025 Pa (1 mA). The deposition rate is proportional to the discharge current, and increases rapidly with the discharge voltage and the magnetic flux density. It is found that the optimum distance between the substrate (anode) and target surface gives the maximum deposition rate.

Filling of Sub-μm Through-holes by Self-sputter Deposition

Filling of sub-µ m holes with a high aspect ratio by self-sputter deposition of copper is investigated. Good bottom coverages of 100% by means of thinner thin-film deposition and 50% by thicker thin-film deposition are attained. It is found that the bottom coverage decreases sharply when the ratio of the distance between the target and the substrate, D st, to the diameter of the erosion center ring is less than 1, and although the bottom coverage by the self-sputter deposition at lower pressures saturates at longer D st, that by the conventional sputter deposition at higher pressures decreases with D st. The bottom coverage also decreases with increases of the pressure, the thin film thickness deposited, and the radial distance of the substrate position from the target center toward the erosion center.

High‐vacuum planar magnetron discharge

The present article demonstrates the possibility of developing a high‐vacuum planar magnetron discharge. Until recently, developed cathodes applying a high electric field and a high magnetic field which cross each other in a discharge space enable the discharge to be sustained at 0.1 Pa. Experimental results of this article show that even at pressures lower than 10−3 Pa the discharge can be sustained. The discharge intensity I/P is proportional to the discharge voltage and depends strongly on the magnetic flux density. It is found that the high‐vacuum planar magnetron discharge requires a magnetic flux density higher than 0.1 T and a discharge voltage higher than 2 kV, for its effective sustenance. Sputtering of aluminum by this discharge is performed and the deposition rate 0.2 μm/min is obtained.

Copper Filling of Deep Sub-µm Through-Holes by High-Vacuum Planar Magnetron Sputtering Using Argon Gas with Added Nitrogen: Optimum Quantity of Nitrogen in Argon Gas

We investigated the effectiveness of using argon gas with added nitrogen when filling deep sub-µm through-holes with copper by high-vacuum planar magnetron sputtering, and we examined the optimum amount of added nitrogen. This is done by varying the amount of added nitrogen between 0.5, 1.0, 3.0, 10, and 20 at. % in copper filling experiments conducted at a substrate temperature of 280°C and a gas pressure of p=9.0×10-2 Pa with 80-nm-diameter holes having an aspect ratio of 5.6. The results show that the optimal amount of added nitrogen for copper filling is 1.0 at. %, and that the proportion of conformal filling is 1/5. The reasons for this are discussed in terms of the energy relationship between copper atoms adsorbed physically or chemically by nitrogen, sputtered atoms, and recoil atoms or molecules.

Axial Structure of High-Vacuum Planar Magnetron Discharge Space

The spatial structure of high-vacuum planar magnetron discharge is theoretically investigated taking into account the electron confinement. The boundary xes of the electron confinement region depends on BA with Ea/BA as the parameter (BA: the magnetic flux density at the anode, Ea: the average electric field strength). The location at which the frequency of ionization events takes the maximum is expressed as CnNxiep (CnN: a factor related to the electron density distribution, xiep: the distance of the location from the cathode at which the ionization is most efficient). With increasing Ea and BA at a fixed Ea/BA, the density of the confined energetic electrons increases. With increasing Ea, the region where ionization is efficient shifts to the cathode side to give a high efficiency of the magnet. The boundary xes as determined by the probe method agreed with the theoretical prediction.

A theory on planar magnetron discharge

A new theory on planar magnetron discharge is developed by taking into account relevant parameters: the kinetic energy of electrons, the potential distribution, the magnetic flux density distribution, the collision frequency and the ionization probability. The discharge current is expressed as a function of the average electric field strength and the magnetic flux density. Experimental results show good agreement with the theory.

Theory on high-vacuum planar magnetron discharge

A theory on high-vacuum planar magnetron discharge for the wide range of E a/B A>2.0×106/n V/(mT) has been developed (E a: magnitude of the average electric field strength; B A: magnetic flux density at the anode; n: power index of the potential distribution). The relevant parameters on the ionizing collisions and the geometrical factors from the cross section of erosion are incorporated in the theory. The discharge current I becomes a function of E a/B A with the parameter of B A. With E a/B A fixed, I∝B A is shown. The optimum E a/B A ratio gives the local maximum of I. This ratio depends on n and the power index of magnetic flux density distribution N. In the range of E a/B A2.3×107/n V/(mT), function I becomes the simple form I∝E aMB A1-M, where M=N/(n-1+N). Experimental work has also been carried out.

Theory on High-Vacuum Planar Magnetron Discharge Incorporating the Effect of Escaping Electrons

A theory, which includes the case where BA (magnetic flux density at the anode) is insufficient to confine the energetic electrons in the discharge space, has been developed. At a fixed Ea/BA (Ea≡VA/d0, VA: anode voltage and d0: distance between the electrodes), I∝BAβ (I: discharge current and β: const. 1). With increasing BA, so that most of the energetic electrons are confined, β becomes 1. For d0=42 mm, in Ea/BA2.3×107/n V/(mT) when BA>5 mT and Ea>1.2×105/n V/m when BA 2.0×106/n V/(mT) when BA>10 mT and Ea>2.0×104/n V/m when BA<10 mT for d0=42 mm and Ea<(G0/n)BA2 (G0: const.). With decreasing d0, the above conditions are modified by a corresponding increment in BA. Experimental works have been carried out.

Development of high-vacuum planar magnetron sputtering using an advanced magnetic field geometry

A permanent magnet in a new magnetic field geometry (namely, with the magnetization in the radial direction) was fabricated and used for high-vacuum planar magnetron sputtering using Penning discharge. Because of the development of this magnet, the discharge current and deposition rate were increased two to three times in comparison with the values attainable with a magnet in the conventional geometry. This improvement was because the available space for effective discharge of the energetic electrons for the ionization increased because the magnetic field distribution increased in both the axial and radial directions of discharge.

A Hot Cathode Magnetron Gauge using a Divergence-Type Magnetic Field for Electric Field Control

A new sensitive type of magnetron gauge has been developed in order to obtain a linear response of ion current, Ii, to pressure, P, with a high sensitivity over a wide range. The gauge is equipped with two ion collectors. The ratio of the ion currents of the two ion collectors is measured and kept constant by controlling the filament voltage, in order to keep the electric field constant within the anode over a wide range of pressure measurement. When a divergent-magnetic field is applied to this hot-cathode magnetron gauge, the slope of the plot of the filament voltage vs the ratio of the ion current of the two separate two ion collectors is improved from -0.28 to +1.1–+3.9 (V-1). When the diameters of the ion collectors were investigated, it was found that the current ratio η=1 was attained when the outer diameters of the ion collectors were identical, and their inner diameters were 2 and 8 mm respectively. With this configuration, ion current was directly proportional to pressure in the range of 1×10-8–1×10-4 Pa.