For the Bosch deep silicon dry etch process with SF6–C4F8 a quantitative approach is developed. Essential plasma surface interactions and the transport properties of ions and radicals in high aspect ratio structures are unravelled. Balancing the interactions during etching and passivation pulses is essential for maximal profile control. In the anisotropic regime the etch rate is aspect ratio dependent largely due to depletion of fluorine radicals and with some involvement of passivation polymer redeposition. The anisotropic process tends to stop at a limiting aspect ratio because of improper removal of polymer passivation at the trench bottom. Both higher ion flux and ion energy are found to be crucial to push the Bosch process to higher achievable aspect ratios. Practical process implications are discussed. In situ ellipsometry shows that the polymer passivation step is a complex process with an ion induced component. More efficient removal of the passivation layer at the trench bottom by adjusting the plasma chemistry could further improve the Bosch plasma etch process.

High density fluorocarbon etching of silicon in an inductively coupled plasma: Mechanism of etching through a thick steady state fluorocarbon layer A quantitative study of dry etch behavior in deep silicon trenches in high density plasmas ͑electron cyclotron resonance, inductively coupled plasma͒ at low temperatures ͑160-210 K͒ is presented. The quantitative approach implies etch behavior being studied in relation to the relevant particle fluxes ͑atomic F and O and ions͒ as measured by in situ diagnostics. Two etch modes are observed. In one mode faceting shows up as due to crystallographic orientation preference, i.e., Si͗111͘ being etched slower than Si͗100͘. In the other mode the normal anisotropic ion-induced behavior is observed. Controlled switch from one mode to the other is studied under influence of process parameters like pressure, ion energy, and substrate temperature. The second part of this study deals with aspect ratio dependent etching ͑ARDE͒. Both vertical and horizontal trenches have been taken into account as to distinguish between radical and ion-induced effects. The flux of radical species into the deep trench is governed by Knudsen transport, with a reaction probability of atomic fluorine of about 0.5. As a consequence depletion of the fluorine content at the bottom is the main reason for ARDE. With the bottleneck identified, the plasma process has been readily tuned to the aspect ratio independent etch regime. This regime coincides with the crystallographic preference mode where surface reaction kinetics form the rate limiting step. Detailed surface analysis studies by x-ray photoelectron spectroscopy, in situ ellipsometry, and transmission electron microscopy have been used to characterize the surface reaction process.

A novel technique for the controlled fabrication of π-conjugated oligomers bonded to a substrate is presented. On a gold substrate, monolayers of small monomeric organic units are alternately deposited from solution. They order and connect to the previous layer by self-assembly. In each deposition step, chemisorption takes place on top of the previous monolayer through a condensation reaction. The oligomer chain growth has been analyzed by scanning tunneling microscopy, ellipsometry, and X-ray photoelectron spectroscopy. The azomethine molecules order approximately perpendicular to the gold surface. This growth process allows for flexible preparation of a range of oligomers in a self-assembled monolayer with variable electronic properties.

Inductively coupled Cl2/Ar plasma etching of 4H–SiC has been studied. The SiC etch rate has been investigated as a function of average ion energy, Ar concentration in the gas mixtures, inductively coupled plasma power, work pressure and substrate temperature. The etch mechanism has been investigated by correlating the ion current density and relative atomic chlorine content to the etch rate under various etch conditions. For the first time, it has been found that the etch rate of SiC increases by about 50% at lower substrate temperatures (−80°C) than at high substrate temperatures (150°C) with the highest SiC etch rate of 230 nm min−1 being achieved at a substrate temperature of −80°C.

Articles you may be interested inFormation of three-dimensional and nanowall structures on silicon using a hydrogen-assisted high aspect ratio etching J.High aspect ratio silicon etch: A review An advanced, time-multiplexed plasma etch process for high aspect ratio structures is presented. Compared to the two pulse Bosch process, the technique consists of a sequence of three pulses. The third pulse is tailored to improved depassivation of the trench bottom prior to each etch pulse. Several depassivation chemistries are explored: O 2 , CO 2 , and SO 2 . In a further extension the bias voltage is also pulsed, with the aim to balance the radical and ion-enhanced components in the passivation of the sidewalls and trench bottom. The process extensions lead to improved mask selectivity and substantial range for profile control from fully anisotropic to strongly negatively tapered. The maximum aspect ratio obtained in the Bosch process could not be improved, because the ion angular distribution probably remains the limiting factor. The role of the ions in passivation and etching has been quantified in separate experiments.