Abstract
Metal contacts on semiconductors devices are normally defined by lift-off process, because no well-defined etch processes exist for some rare metals. In this work, an RIE process for gold contacts is introduced which requires a high-density plasma, generated by electron cyclotron resonance. The proof is given by the residual-free etching without fence-generation and micromasking in the vicinity of the mask.
Highlights
The first contacts on semiconductors were developed by Lepselter at Bell Labs in the late 1950s.1 It consisted of a sandwich of the three metals titanium, platinum and gold to fulfil these requirements: 1. ohmic contact to the p-doped top region of the semiconductor; 2. good adhesion of this film to surfaces of semiconductor(s) and oxides; 3. ease of bonding, high resistance to corrosion, high elongation to allow thermal expansion mismatch with the substrate; 4. suitability for further high-resolution electroforming.It is obvious that in order to satisfy these diverging purposes, more than one metal is required
Since the first two qualities can be fulfilled by titanium or chromium, and the last two by gold, which severely degrades the electrical quality of the p+ zone, we have to add a third metal to serve as a low-ohmic diffusion barrier
This article does not deal with features like etch rate and loading effect as a function of discharge pressure and power input, because the thickness of the metal layer is always small compared with the depth of the structures which are carved into the semiconductor
Summary
The first contacts on semiconductors were developed by Lepselter at Bell Labs in the late 1950s.1 It consisted of a sandwich of the three metals titanium, platinum and gold to fulfil these requirements: 1. ohmic contact to the p-doped top region of the semiconductor; 2. good adhesion of this film to surfaces of semiconductor(s) and oxides; 3. ease of bonding, high resistance to corrosion, high elongation to allow thermal expansion mismatch with the substrate; 4. suitability for further high-resolution electroforming. This contact remained standard for more than twenty years and was followed by replacing the top layer (gold) by aluminum in silicon processing technology, whereas for p-contacting of III/V compound semiconductors, the Bell contact has still survived. With these metals as contact, the lowest contact resistivities challenge the limits of measuring accuracy which are possible with the transmission line method (TLM) or contact hole.[2,3] since no suitable etchants for all three layer components are known, the most usual way is to use a simple lift-off technique. In this study we focus on real etching of gold layers with an etchant that is highly selective to III/V semiconductors
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