Better than you will ever be able to.
Here is YMTC's illustration of their pseudo 3D NAND product.
The problem here is that die stacking is nothing new, even dissimilar products can be, and have been, joined to perform unique tasks for niche applications. Here is a NOR die stacked atop a NAND die and both are packaged together.
So to start, YMTC did not really innovate anything new. But going back to YMTC. What make YMTC's pseudo 3D NAND more expensive to produce is that it takes up two production lines: CMOS array and memory array.
Logistically, the first question involves wafer size. Which is 200 mm? Which is 300 mm? Is both 200 mm? Or is both 300 mm? Or is it one of each? If YMTC must use both 200 mm and 300 mm wafers, which array get the 300 mm wafer? Can
YOU make even an educated guess?
Here is an example of a wafer map.
In order to mate the CMOS and the memory arrays together, their dies' geographical boundaries must be identical. Maybe some allowances for slight differences to accommodate physical bonding, but at the μm level, any physical differences are irrelevant to the discussion. So what this mean, in reference to the wafer map example, is that the two product lines must be carefully managed as they progress thru the fab, post fab, and to BackEnd (BE) for extraction. If one line must use the 200 mm wafer, the tooling for that line will be different than the 300 mm wafer tools, and that will complicate the manufacturing lines even more.
Even though NAND and CMOS are established products, there are always manufacturing flaws, so not every die on a wafer will be shippable. Most edge dies are malformed dies, and those that are full formed, quite often because of them being edge dies, they often have inferior performance than dies on the main areas of the wafer. For example, a 300 mm wafer may produce 500 prime dies and a 200 mm wafer may produce 200 prime dies, now logistics is complicated even more to keep track of how many 200 mm wafers to how many 300 mm wafers in order to produce X number of final stacked pseudo 3D NAND packages. If both lines are 200 mm wafer or 300 mm wafer, then this complication would be dramatically reduced. That is not to say that YMTC was not creative. They were. But hardly 'groundbreaking'.
Already, I have at least %75 understanding of how YMTC did it. I would make a good ProcEng or TestEng for them.
That is a 26 yrs old SRAM 200 mm wafer atop some 64gb 300 mm NAND wafers. All of them are functionally dead. The NAND wafers were 'killed' by me personally for a special project that involved some important entities outside the normal customers list. Ain't that hard to make a fool out of you, little man.