Electronic – Difference between Logic Chip and Memory Chip front-end manufacturing process

That's not how I learned it. It has to do with energy gaps between valence band where the electrons at the highest energy are, and the conduction band, where an electron can come free of its atom. In metals these bands overlap and electrons move free within the metal's lattice, and that's what gives metals their typical shine.

Pure semiconductors are isolators at cryo-temperatures. But doping them with N-type material will cause doping atoms to bond with the semiconductor, and then there's one superfluous electron which, like in metals, can move freely through the lattice, and thus conduct electricity.

A useful way to visualize the difference between conductors, insulators and semiconductors is to plot the available energies for electrons in the materials. Instead of having discrete energies as in the case of free atoms, the available energy states form bands. Crucial to the conduction process is whether or not there are electrons in the conduction band. In insulators the electrons in the valence band are separated by a large gap from the conduction band, in conductors like metals the valence band overlaps the conduction band, and in semiconductors there is a small enough gap between the valence and conduction bands that thermal or other excitations can bridge the gap. With such a small gap, the presence of a small percentage of a doping material can increase conductivity dramatically.

An important parameter in the band theory is the Fermi level, the top of the available electron energy levels at low temperatures. The position of the Fermi level with the relation to the conduction band is a crucial factor in determining electrical properties.

(from this excellent site)

It is. Microcontrollers generally contain logic, Flash, and SRAM all on one die. But they are not designed to be high performance chips, and they are generally made with 'old' processes.

This is generally not done for high performance devices for several reasons. First is process optimization. The optimal process characteristics for high performance DRAM, high performance Flash, and high performance logic are generally different and comprimises must be made to combine them on one chip. Second, yield. If your RAM array doesn't test out, the chip gets canned even though the flash and logic are good. So it is generally not done for very complex chips because the yield would be too low to be economical. It also means that the flash and RAM sizes are fixed so it is not possible to select different sizes of Flash or RAM for different applications.

Flash and RAM also take up a huge amount of silicon area and there is far more demand for flash and RAM than for any given CPU design, so economies of scale drive down the cost flash and RAM chips far more than the CPUs. Because of this, designers try to make the CPU dies as small as possible to minimize the cost of production - all else being equal, the cost per area of the CPU die will be higher the cost per area of off-the-shelf memory chips.

This is also the main reason devices like FPGAs do not often contain flash memory - it is hard enough to get the programmable logic working that they really don't want to sacrifice yields by adding a flash array that is only used on power up.