Stack and semiconductor device

Abstract

A stack with excellent electrical characteristics and reliability is provided. The stack includes an insulator, a conductor, and a first oxide between the insulator and the conductor; the first oxide includes a first c-axis-aligned crystal region; and a c-axis of the first crystal region is substantially perpendicular to a plane of the first oxide on the insulator side. Alternatively, the stack includes an insulator, a conductor, a first oxide between the insulator and the conductor, and a second oxide facing the first oxide with the insulator therebetween; the first oxide includes a first c-axis-aligned crystal region; a c-axis of the first crystal region is substantially perpendicular to a plane of the first oxide on the insulator side; the second oxide includes a second c-axis-aligned crystal region; and a c-axis of the second crystal region is substantially perpendicular to a plane of the second oxide on the insulator side.

1 . A semiconductor device comprising a transistor, the transistor comprising:
 a first gate electrode over a substrate;   a first insulator over the first gate electrode, the first insulator functioning as a first gate insulator;   a first oxide semiconductor over the first gate insulator;   a second oxide semiconductor over and in contact with the first oxide semiconductor;   a second insulator over the second oxide semiconductor;   a third insulator over and in contact with the second oxide semiconductor, the third insulator functioning as a second gate insulator; and   a second gate electrode over the second gate insulator,   wherein the second oxide semiconductor comprises a crystal region,   wherein a c-axis of the crystal region is substantially perpendicular to a top surface of the first oxide semiconductor, and   wherein the third insulator and the second gate electrode are positioned inside a first opening of the second insulator.   
     
     
         2 . The semiconductor device according to  claim 1 , further comprising:
 a source electrode and a drain electrode electrically connected to the second oxide semiconductor,   wherein the source electrode is positioned inside a second opening of the second insulator, and   wherein the drain electrode is positioned inside a third opening of the second insulator.   
     
     
         3 . The semiconductor device according to  claim 1 ,
 wherein each of the first oxide semiconductor and the second oxide semiconductor comprises indium, gallium, and zinc.