Magnetic-field-enhanced rf argon plasma for ionized sputtering of copper

Abstract

A multipole magnetic field was used to increase the ion density of an inductively coupled rf ͑13.5 MHZ͒ argon plasma for ionized magnetron sputtering of copper ͑Cu͒. Langmuir probe measurements showed an increase of plasma density over a factor of 2 with the application of the magnetic field. At an argon pressure of 15 mTorr and a rf power of 600 W, an ion density of 1.2 ϫ10 12 ions/cm 3 was achieved. When this plasma was applied to ionize the magnetron sputtered Cu vapor, a high emission intensity ratio from the Cu ϩ ion line to the Cu neutral line was observed from the optical emission spectroscopy, suggesting a high ionization fraction for the sputtered Cu vapor. © 1997 American Institute of Physics. ͓S0003-6951͑97͒05038-9͔One of the challenges for the continuous reduction of semiconductor devices to subquarter micron regimes is to uniformly deposit metals ͑Al, Cu͒ films into deep trenches with a high aspect ratio for contact and interconnect applications. 1,2 Conventional sputtering becomes insufficient because of its broad angular distribution of the sputtered atom flux, which leads to pinch-off near the opening of the trench and void formation in the films during the trench filling.Recently, ionized sputtering was proposed to solve the aforementioned issues. [3][4][5][6][7] In ionized sputtering, a highdensity argon plasma is generated between the sputtering target and substrates, and the sputtered metal vapor atoms become ionized when they traverse the high-density argon plasma region. When a negative dc bias is applied to the substrate, the positive metal ions are attracted toward the substrate and deposit on the bottom of the trenches with a good directionality. At the same time, resputtering by the metal or argon ions can help to minimize the pinch-off at the top of the trench.In this letter, we report results of a study using a multipole magnetic field to enhance an inductively coupled rf argon plasma for ionized magnetron sputtering of copper, including Langmuir probe and optical emission spectroscopy measurements of plasma density and Cu vapor ionization.The experimental apparatus is shown in Fig. 1. An aluminum chamber of 48 cm diam and 54 cm height was used. The chamber has a base pressure of 8ϫ10 Ϫ7 Torr. A dcmagnetron sputtering source was installed from the top of the chamber. The Cu vapor was produced by sputtering of a Cu target of 5 cm diam. A rf antenna was installed from the top of the chamber and located approximately 5 cm below the sputtering source. The antenna, consisting of one and onehalf turns of aluminum tubing ͑outside diameter 6 mm͒, has a diameter of approximately 15 cm.A multipole magnetic field was produced by a set of alternating rows of north and south pole permanent ceramic magnets placed around the circumference of an aluminum ring ͑25 cm diam͒ inside the vacuum chamber. Each row is composed of four permanent magnets ͑diameter and length of 2.5 cm, and 1 kG at the surface͒. A total of 12 rows were used. The alternating rows of magnets generate a line cusp magnetic configur...

Ionized physical vapor deposition (IPVD): A review of technology and applications

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An rf sustained argon and copper plasma for ionized physical vapor deposition of copper

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