Question

Explain the DC breakdown voltage vs. electrode distance curve (Paschen’s law) and how it is relevant to dry etching. How is miniaturization of an electrode set equivalent to creating a local vacuum?

Answer 1

The simplest configuration employed for striking a gas discharge is a parallel electrode geometry.Two plane metal plates are separated by a distance, d, in a chamber reactor filled with a particular gas at a pressure, p. Breakdown of the gas is achieved by applying an electric field of direct-current (dc) with cathode and anode biased negatively and positively, respectively. When the voltage between the plates is low, the gas is a near-perfect insulator. As the voltage is increased, a small fraction of electrons present in a gas are accelerated towards the anode making collisions with the background atoms. Some of these collisions create positive ions which are then accelerated towards the cathode. When the ions strike the cathode, electrons are liberated from the metal surface as a result of neutralization .This process gives rise to an entire avalanche of electrons leading to gas breakdown and discharge formation. The voltage at which breakdown occurs is described by Paschen’s law.

Over the past decades, plasma etching has been widely used in the fabrication of silicon based integrated circuits.In the micro-electronics industry, glow discharge plasmas are often used for etching of surfaces, in order to generate topographical patterns on chips as an alternative to wet chemical etching. Low-temperature plasma processing offers important advantages over wet-chemical methods. First, plasma-processing is dry and safe. Secondly plasma-etching provides finer resolution, sharper etching and less under cutting than can be obtained with chemical ethantes. Thirdly, plasma-processing makes possible to perform sequential etching and stripping operations in the same machine. Finally, plasma-processing creates no pollution problems. Plasma etch equipment can be divided into twoclassifications. The first is the parallel-plate diode configured etches system, where the wafers are positioned on the electrode surface. The second classification is the high-pressure plasma etcher where the wafers are positioned in a rack that enables the wafers to float in the plasma. The cathode set-up uses the dc discharge experiments . This arrangement defines the etching area and makes it possible to calculate the current density.

Miniaturization  is the trend to manufacture ever smaller mechanical, optical and electronic products and devices. Examples include miniaturization of mobile phones, computers and vehicle engine downsizing