The chief motivation for developing 64 bit processore was that, as their name suggests, their registers are 64 bits wide and they can theoretically access a maximum of 18,446,744,070Gb of memory, compared to "only" 4Gb of memory for a 32 bit processor. The 64 bit processors which are currently in production cannot actually access all that memory, but they could do so in the future, and, even in their current state, they can access orders of magnitude more memory than 32 bit processors.
maybe there are more registers on the cilicon chip(phyically)?
The 64 bit processors have acquired eight more general purpose register, because the x86 architecture was generally thought of as being a bit short of them. But still, the big difference is that the registers have grown from 32 bits to 64 bits, and in the process been renamed. Eax has become rax, ebx has become rbx, and so on - as well as the new r8-r16 64 bit registers. Whether the registers are physically wider as measured in nanometers, I don't know.