Semiconductor memory system

A semiconductor device comprising:

• a substrate;
• and
• a plurality of nonvolatile semiconductor memories on the substrate,
• wherein the substrate includes:
• a first metal layer having a first pattern density, the first metal layer being electrically connected to the nonvolatile semiconductor memories and being located on a first side of the substrate;
• a second metal layer having a second pattern density, the second metal layer being located on a second side of the substrate;
• a plurality of third metal layers disposed between the first and second metal layers and having respective third pattern densities;
• and
• insulating layers provided between the first metal layer and a first one of the third metal layers adjacent to the first metal layer, between the second metal layer and a second one of the third metal layers adjacent to the second metal layer, and between adjacent ones of the third metal layers,
• a first group of metal layers includes n metal layers including the first metal layer and (n−1) adjacent third metal layers, a second group of metal layers includes n metal layers including the second metal layer and (n−1) adjacent third metal layers different from the (n−1) third metal layers in the first group, a first density obtained from the first and third pattern densities of the first group of metal layers is substantially equal to a second density obtained from the second and third pattern densities of the second group of metal layers,
• at least one of the first and third pattern densities of the first group of metal layers and the second and third pattern densities of the second group of metal layers is 80% or greater, and
• a fourth metal layer is one of the third metal layers that faces the second metal layer with one or more of the insulating layers between the fourth metal layer and the second metal layer, wherein a pattern density of the fourth metal layer is 80% or greater.