side by side table

Question

I am trying to figure out how to put these tables side by side (or at least in a proper form)

\begin{table} 
\caption{Initial measurement of photoresist step heights for $15$ and $30$ wafers ($A^\circ$)}
\label{tab:fonts}
\begin{center}      
\begin{minipage}[b]{0.33\linewidth}\centering 
\begin{tabular}{|l|l|} %% this creates two columns
%% |l|l| to left justify each column entry
%% |c|c| to center each column entry
%% use of \rule[]{}{} below opens up each row
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $1$  & 1.4725   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $3$  & 1.4725  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $6$  & 1.495  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $14$  &  1.492 \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $16$  &   1.465\\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $20$  & 1.2525 \\
\hline
\end{tabular}
\end{minipage}
\end{center}
\end{table}

\begin{table}
\caption{Post etch measurement of photoresist step heights for $15$ (4 mins) and $30$ (6 mins) wafers ($A^\circ$)}
\label{tab:fonts}
\begin{center}       
\begin{tabular}{|l|l|} %% this creates two columns
%% |l|l| to left justify each column entry
%% |c|c| to center each column entry
%% use of \rule[]{}{} below opens up each row
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $1$  & 1.5875   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $3$  & 1.575  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $6$  & 1.5925  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $14$  &  1.66 \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $16$  &   1.63\\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $20$  & 1.4625 \\
\hline
\end{tabular}
\end{center}
\end{table} 
\FloatBarrier
\begin{table} [h]
\caption{Post SPM treatment ($nm$)}
\label{tab:fonts}
\begin{center}       
\begin{tabular}{|l|l|} %% this creates two columns
%% |l|l| to left justify each column entry
%% |c|c| to center each column entry
%% use of \rule[]{}{} below opens up each row
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $1$  & 142.5   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $3$  & 142.5  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $6$  & 132.5  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $14$  &  190 \\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $16$  &   197.5\\
\hline
\rule[-1ex]{0pt}{3.5ex}    wafer $20$  & 192.5 \\
\hline
\end{tabular}
\end{center}
\end{table} 
\FloatBarrier

Second Part of question :

\begin{table}
\caption{Measurement of oxide thickness for blank wafer before etch (pre etch)} \label{tab:1}
\label{tab:fonts}
\begin{center}      
\begin{minipage}[b]{0.33\linewidth}\centering 
\begin{tabular}{|l|l|} %% this creates two columns
%% |l|l| to left justify each column entry
%% |c|c| to center each column entry
%% use of \rule[]{}{} below opens up each row
\hline
\rule[-1ex]{0pt}{3.5ex}    center & 5114 $A^\circ$   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    top  & 5236 $A^\circ$   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    right & 5196$A^\circ$ \\
\hline
\rule[-1ex]{0pt}{3.5ex}    bottom  &  5156$A^\circ$  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    left  &   5211$A^\circ$  \\
\hline
\end{tabular}
\end{minipage}
\end{center}
\end{table}

\begin{table}
\caption{Measurement of oxide thickness for blank wafer after etch (post etch)} \label{tab:2}
\label{tab:fonts}
\begin{center}      
\begin{minipage}[b]{0.33\linewidth}\centering 
\begin{tabular}{|l|l|} %% this creates two columns
%% |l|l| to left justify each column entry
%% |c|c| to center each column entry
%% use of \rule[]{}{} below opens up each row
\hline
\rule[-1ex]{0pt}{3.5ex}    center & 3088 $A^\circ$   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    top  & 3154 $A^\circ$   \\
\hline
\rule[-1ex]{0pt}{3.5ex}    right & 3133$A^\circ$ \\
\hline
\rule[-1ex]{0pt}{3.5ex}    bottom  &  3043$A^\circ$  \\
\hline
\rule[-1ex]{0pt}{3.5ex}    left  &   3112$A^\circ$  \\
\hline
\end{tabular}
\end{minipage}
\end{center}
\end{table}

Answer 1

The floatrow package lets you easily align captions by their top lines. No need to add invisible rules to add some padding to the rows: with the cellspace package, you can define minimal vertical spacing between a row and the above and below cells.

\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{caption, floatrow,cellspace}
\setlength\cellspacetoplimit{5pt}
\setlength\cellspacebottomlimit{5pt}
\DeclareFloatSeparators{mysep}{\hskip1.6em}
\begin{document}
\captionsetup{font=footnotesize}
\floatsetup{floatrowsep=mysep, capposition=TOP, captionskip =1.5ex}
\begin{table}[!hbt]
  \begin{floatrow}[3]
    \ttabbox[1.5\FBwidth]{\caption{Initial measurement of photoresist step heights for $15$ and $30$ wafers (\AA)}
      \label{tab:fontsa}}%
    {\begin{tabular}{|Sl|l|}
      \hline
      wafer $1$ & 1.4725 \\ \hline
      wafer $3$ & 1.4725 \\ \hline
      wafer $6$ & 1.495 \\ \hline
      wafer $14$ & 1.492 \\ \hline
      wafer $16$ & 1.465 \\ \hline
      wafer $20$ & 1.2525 \\ \hline
      \end{tabular}}%
    \hfill%
    \ttabbox[1.5\FBwidth]{\caption{Post etch measurement of photoresist step heights for $15$ (4 mins) and $30$ (6 mins) wafers (\AA)}%
      \label{tab:fontsb}}%
    {\begin{tabular}{|Sl|l|}
      \hline
      wafer $1$ & 1.5875 \\ \hline
      wafer $3$ & 1.575 \\ \hline
      wafer $6$ & 1.5925 \\ \hline
      wafer $14$ & 1.66\\ \hline
      wafer $16$ & 1.63 \\ \hline
      wafer $20$ & 1.4625 \\ \hline
      \end{tabular}}
    %
    \ttabbox{\caption{Post SPM treat\-ment ($nm$)} \label{tab:fonts3}}
    { \begin{tabular}{|Sl|l|} %% this creates two columns
      %% |l|l| to left justify each column entry
      %% |c|c| to center each column entry
      %% use of \rule[]{}{} below opens up each row
      \hline
      wafer $1$ & 142.5 \\ \hline
      wafer $3$ & 142.5 \\ \hline
      wafer $6$ & 132.5 \\ \hline
      wafer $14$ & 190 \\ \hline
      wafer $16$ & 197.5 \\ \hline
      wafer $20$ & 192.5 \\ \hline
      \end{tabular}}%
  \end{floatrow}
\end{table}
\end{document} 

Answer 2

Do you like to have something like this:

Above picture is generated by:

\documentclass{article}
    \usepackage{siunitx}

    \begin{document}
\begin{table}
    \begin{minipage}[b]{0.3\linewidth}\centering
\caption{Initial measurement of photoresist step heights for $15$ and $30$ wafers ($A^\circ$)}
\label{tab:fonts}
\begin{tabular}{|l|S[table-format=2.5]|}
    \hline
wafer $1$   &   1.4725   \\ \hline
wafer $3$   &   1.4725   \\ \hline
wafer $6$   &   1.495    \\ \hline
wafer $14$  &   1.492    \\ \hline
wafer $16$  &   1.465    \\ \hline
wafer $20$  &   1.2525   \\ \hline
\end{tabular}
    \end{minipage}
\hfill
    \begin{minipage}[b]{0.3\linewidth}\centering
\caption{Post etch measurement of photoresist step heights for $15$ (4 mins) and $30$ (6 mins) wafers ($A^\circ$)}
\label{tab:fonts}
\begin{tabular}{|l|S[table-format=2.5]|}
    \hline
wafer $1$   &   1.5875   \\ \hline
wafer $3$   &   1.575    \\ \hline
wafer $6$   &   1.5925   \\ \hline
wafer $14$  &   1.66     \\ \hline
wafer $16$  &   1.63     \\ \hline
wafer $20$  &   1.4625   \\ \hline
\end{tabular}
    \end{minipage}
\hfill
    \begin{minipage}[b]{0.3\linewidth}\centering
\caption{Post SPM treatment ($nm$)}
\label{tab:fonts}
\begin{tabular}{|l|S[table-format=4.2]|}
    \hline
wafer $1$   &   142.5   \\ \hline
wafer $3$   &   142.5   \\ \hline
wafer $6$   &   132.5   \\ \hline
wafer $14$  &   190     \\ \hline
wafer $16$  &   197.5   \\ \hline
wafer $20$  &   192.5   \\ \hline
\end{tabular}
    \end{minipage}
\end{table} 
    \end{document}

In your MWE the role of \rule[-1ex]{0pt}{3.5ex} is replaced it by \renewcommand{\arraystretch}{1.3}, which made similar height of cells as it was before. From question is not clear to me what you like to obtain with mix of "mini pages", "center" environments and use of \centering. I clear all this codes and form three minipages in which are tables centered by \centering command.

Beside this I add package siunitx and use its S column type for nicer typing of numbers in your tables.

Note: I didn't bother with caption formatting.

Addendum: Lets do the do-it-for-me service for added second part of question (I do this since I'm happy that after few hour of repairing my MikTeX installation it works again as desired ... ). The code is:

    \begin{table}
    \centering
    \renewcommand{\arraystretch}{1.3}
\begin{minipage}[b]{0.33\linewidth}\centering
\caption{Measurement of oxide thickness for blank wafer before etch (pre etch)} \label{tab:1}
    \label{tab:fonts}
\begin{tabular}{|l|S[table-format=5.0,
                     table-space-text-post=\si{\angstrom}]<{\si{\angstrom}\ }|}
    \hline
center  &   5114    \\  \hline
top     &   5236    \\  \hline
right   &   5196    \\  \hline
bottom  &   5156    \\  \hline
left    &   5211    \\  \hline
\end{tabular}
\end{minipage}
\hfil
\begin{minipage}[b]{0.33\linewidth}\centering
\caption{Measurement of oxide thickness for blank wafer after etch (post etch)} \label{tab:2}
\label{tab:fonts}
\begin{tabular}{|l|S[table-format=5.0,
                     table-space-text-post=\si{\angstrom}]<{\si{\angstrom}\ }|}
    \hline
center  &   3088    \\  \hline
top     &   3154    \\  \hline
right   &   3133    \\  \hline
bottom  &   3043    \\  \hline
left    &   3112    \\ \hline
\end{tabular}
\end{minipage}
\end{table}

In above code I assume, that $A^\circ$ mean unit Angstrom. I use standardizired notation for it as defined insiunitx` package (this was not considered in the first table).

Result: