etch.tex

\section{Mesa etching}

\textbf{Aim}:
Remove the 2DEG layer which is not under the mesa pattern. The thickness to remove is around \SI{210}{\nano\meter} for Sandia, and \SI{110}{\nano\meter} for Gossard
and \SI{130}{\nano\meter} for Manfra.

\subsubsection{Needs}
\begin{itemize}[noitemsep]
\item Mesa Etch, DI Water beakers
\item measuring cylinders for \ce{H2O2}, \ce{H2SO4}, \ce{H2O}
\item one big beaker
\item 2 pipettes
\item timer
\end{itemize}

\subsubsection{Steps}
\begin{enumerate}
\item Open the water tap and let it flow
\item Be sure your gloves are fitted properly (you might want to double glove)
\item Prepare the acid etch solution. Remember \underline{always acid in water}, and \ce{H2O2} last. The recipe is:
  \begin{itemize}
  \item 240ml of \ce{H2O}
  \item 1ml of \ce{H2SO4}
  \item 8ml of \ce{H2O2}
  \end{itemize}
\item Rinse used beakers and measuring cylinders thoroughly. Acids and \ce{H2O2} go down the drain, not in with solvents.
\item Mix acid solution with tweezers
\item Put some of the solution in the 'mesa etch beaker'
\item Put the chip in the solution for 50 sec (the etch rate should be around 2nm/sec)
\item Put the chip in water, rinse thoroughly for 30 sec.
\item Blow dry
\end{enumerate}
\subsection{Measure the etch depth}
\begin{itemize}
\item Use the Dektak to measure the depth of the etch
\item Measure at the same points than when the height of the resist was measured. The height of the resist is not uniform around the chip so it
is important to use the same locations when measuring.
\item Use measurements before etch to compute the etching rate (depth after etch (\AA) - depth before etch (\AA))/ etching time (sec) = etching rate ((\AA)/sec)
\item Deduce the etching time needed to etch at a total depth of 110 nm (etching more will reveal impurities)
\end{itemize}
\newpage

\section {HF Etch}
\textbf{Aim}:
Remove an oxide layer from the wafer. This process is normally done after ALD.

\subsubsection{Needs}
\begin{itemize}[noitemsep]
\item Dedicated DI \ce{H2O} beaker
\item Plastic basket and tweezers
\item HF Dress: Goggles, Apron, Oversleeves
\end{itemize}

\subsubsection{Steps}
\begin{enumerate}
\item Open the water tap and let it flow. Place the DI \ce{H2O} beaker under the flowing water on top of the stand.
\item Dress for the etch. Note the following is required:
\begin{enumerate}
  \item Oversleeves
  \item Second pair of gloves, pulled over the sleeves
  \item Apron, hanging next to fume hood
  \item Goggles
\end{enumerate}
\item Prepare basket, timer and samples on a piece of filter paper in the fume hood.
\item Remove the cover from the etch solution, ensuring that no solution drips. Keep the cover upside down inside the fume hood.
\item Place the chips in the basket and the basket in the solution and start the timer. The basket should be lowered slowly to ensure the chips do not fall out.
\item As soon as the etch finishes, transfer the basket into the \ce{H2O} beaker. Rinse for at least 60 sec.
\item Remove from water and blow dry. Replace the cover onto the etch solution and clean up.
\end{enumerate}