My brand new 1/6 Star Wars setup. These are in progress shots along with some detailed photos of what I do when I combine units together like I have done several times.
Here is an image of the tool that I used to make the holes. I have no clue what it is called but I found it at Lowes.
official term for them are pocket holes, the brand most known for them is Kreg.
if there is tension pulling on those shelves, I'd be careful about using pocket screws in ikea particle board material. they weren't really meant for that.