A review of microelectronic film deposition using direct and remote electron-beam-generated plasmas

Abstract

Abstract-Soft-vacuum-generated electron beams employed to create a large area plasma for assisting chemical vapor deposition (CVD) of thin films are reviewed. The electron beam plasma is used both directly, where electron impact dissociation of feedstock gases plays a dominant role, and indirectly in a downstream afterglow, where electron impact dissociation of feedstock reactants plays no role. Rather, photodissociation and metastable atom-molecule reactions dominate in the downstream afterglow. To better understand electron-beam-created plasmas using a slotted ring cathode, the transmitted beam spatial intensity profiles have been quantified from initial generation at a slotted line-shaped cold cathode through acceleration in the cathode sheath and propagation in the ambient gas. To better understand the role of photodissociation in downstream plasma-assisted CVD, the VUV output spectrum and VUV generation efficiency from electron-beam-excited plasmas have been measured. The properties of films deposited via both direct electron-beam-generated plasma-assisted CVD and downstream afterglow CVD are reviewed and compared to conventional plasma assisted CVD films. I. SOFT-VACUUM ELECTRON BEAM GENERAnONA. Thermionic Sources T HE conventional means of producing electron beams uses thermionic cathode sources to emit electrons, which are accelerated in an ambient pressure typically below 10-4 torr. Thermionic emitters have limited application because of the low required operating pressure and the likelihood of poisoning from ambients other than inert gases. Wide area ( > 10 em") electron beams are usually not generated from thermionic cathodes, further precluding the use of this type of source in many practical applications. B. Glow Discharge SourcesA glow discharge environment provides a simple means to produce wide-area electron beams without the need of Manuscript received April 3, 1989; revised May 30, 1990 either thermionic sources or acceleration in high vacuum. In general, there are two groups of electrons that emerge from the cathode sheath created in a gas discharge plasma. One group contains the electrons that have undergone many inelastic collisions with gas atoms and are less energetic and isotropic in direction. Another group is comprised of energetic and highly directed electrons that have been produced at the cold cathode and accelerated perpendicular to the cathode surface. These electrons are often called beam electrons. Five established methods to create soft-vacuum electron beams from a plasma are outlined next. 1) Cold Cathodes:Electrons are emitted from a cold cathode following bombardment of the cathode by energetic species (ions, metastables, and photons) whose energy exceeds the threshold for cold electron emission, which is roughly equal to the work function of the surface for pure metal cathodes. Ion-induced secondary emission usually dominates in a discharge, and the secondary emission coefficient varies with ion species, the work function, and the Fermi energy of the cathode [I]. Cold-cathod...

A hierarchy of diffusion models for partially ionized plasmas

“…We now look for the limit ε → 0 of this macroscopic system (46) -(47). To this aim, we have to perform the limit ε → 0 in the microscopic system (43)-(45), with collision terms given by (21). We first replace in (21) the elastic (and inelastic for neutrals) inter species collision operators by their expansions in terms of ε (according to Lemma A.1, A.2 and A.5).…”

“…We also remark that, at this level, the electrons have not necessarely reached their local thermodynamical equilibrium: the order zero term f 0 e is only for the moment an isotropic function. Moreover, on account of the assumption (20) (and the resulting scaling (21) for the collision terms), it will not be possible to go further (i.e. to obtain a Maxwellian distribution) if we suppose for example δ i = ε 2 , which corresponds to the two last cases under consideration here.…”

“…External electromagnetic fields are thus often used for accelerating them, narrowing their thermal velocity distribution, also for deflecting, focussing, or keeping parallel the beam in order to transport and utilize it effectively. Charged particle beams were first used for atomic and nuclear physics, and are now also applied to plasma diagnostics, space propulsion applications, film deposition [21] and ion implantation for microelectronics, to perform precision electron beam welding, rapid cutting of thermosetting plastics, cross-linking of thermoplastics to improve their physical properties, promote or increase plasma chemical activity, to invert the population of a gas laser and give rise to light amplification (from the soft X-ray region to the far infrared) [13], to control thermonuclear reactions via plasma heating [5], to process of surface treatment and depollution of high-volume exhaust streams [13], to support externally nonself-sustained discharges, or to study stellar plasma. Some of these listed applications combine an electron beam interacting with a plasma.…”

Large area radio frequency plasma for microelectronics processing

“…In order to explore broadening of the operating pressure window of the dc ring plasma 2 we tried an auxiliary ICP discharge and a cusp shaped magnetic field separately. First, we combined the planar rf ICP discharge with a ring shaped cold cathode dc discharge, but the impedance of the dc discharge dropped by only 10% with the simple addition of rf.…”

“…[2][3][4] Commercial ICP processing still has several major unsolved problems and here we focus on wide area plasma uniformity and undesired antenna window erosion caused by the plasma. Our present design employs a unique vacuum and antenna structure with a novel matching circuit to achieve larger area planar ICP plasmas with good spatial uniformity.…”