Semiconductor device and manufacturing method thereof
A semiconductor device capable of high speed operation is provided. Further, a semiconductor device in which change in electric characteristics due to a short channel effect is hardly caused is provided. An oxide semiconductor having crystallinity is used for a semiconductor layer of a transistor. A channel formation region, a source region, and a drain region are formed in the semiconductor layer. The source region and the drain region are formed by self-aligned process in which one or more elements selected from Group 15 elements are added to the semiconductor layer with the use of a gate electrode as a mask. The source region and the drain region can have a wurtzite crystal structure.
1. A semiconductor device comprising:
an oxide semiconductor layer including a channel formation region, a source region and a drain region,
wherein:
the oxide semiconductor layer contains zinc, indium and gallium;
the channel formation region includes crystals;
the crystals are c-axis-oriented in a direction substantially perpendicular to a surface of the oxide semiconductor layer;
the crystals comprise atoms arranged to have a triangular or hexagonal shape in an a-b plane;
each of the source region and the drain region includes at least one element selected from Group 15 elements;
each of the source region and the drain region comprises a wurtzite crystal structure, and
a crystal structure of each of the source region and the drain region is different from a crystal structure of the channel formation region.
2. The semiconductor device according to claim 1 , wherein:
a concentration of the at least one element selected from Group 15 elements included in the source region is higher than or equal to 5×10 19 atoms/cm 3 and lower than or equal to 1×10 22 atoms/cm 3 ; and
a concentration of the at least one element selected from Group 15 elements included in the drain region is higher than or equal to 5×10 19 atoms/cm 3 and lower than or equal to 1×10 22 atoms/cm 3 .
3. The semiconductor device according to claim 1 , wherein the at least one element is nitrogen.
4. The semiconductor device according to claim 1 , further comprising an insulating layer under the oxide semiconductor layer, wherein:
an amount of oxygen released from the insulating layer is greater than or equal to 3.0×10 20 atoms/cm 3 in thermal desorption spectroscopy when the amount of oxygen is converted into oxygen atoms;
the insulating layer contains oxygen and is capable of supplying oxygen to the oxide semiconductor layer; and
the insulating layer contains SiO x where x is larger than 2.
5. The semiconductor device according to claim 1 , further comprising a gate electrode over the oxide semiconductor layer, wherein the source region and the drain region are formed by self-aligned process with respect to the gate electrode.
6. A semiconductor device comprising:
an oxide semiconductor layer including a channel formation region, a source region and a drain region;
a source electrode electrically connected to the source region; and
a drain electrode electrically connected to the drain region,
wherein:
the channel formation region includes crystals;
the crystals are c-axis-oriented in a direction substantially perpendicular to a surface of the oxide semiconductor layer;
the crystals comprise atoms arranged to have a triangular or hexagonal shape in an a-b plane;
each of the source electrode and the drain electrode is a metal electrode;
an energy gap of the channel formation region is larger than an energy gap of each of the source region and the drain region;
the energy gap of the channel formation region is 2.5 eV or more, and
a crystal structure of each of the source region and the drain region is different from a crystal structure of the channel formation region.
7. The semiconductor device according to claim 6 , wherein:
each of the source region and the drain region includes at least one element selected from Group 15 elements;
a concentration of the at least one element selected from Group 15 elements included in the source region is higher than or equal to 5×10 19 atoms/cm 3 and lower than or equal to 1×10 22 atoms/cm 3 ; and
a concentration of the at least one element selected from Group 15 elements included in the drain region is higher than or equal to 5×10 19 atoms/cm 3 and lower than or equal to 1×10 22 atoms/cm 3 .
8. The semiconductor device according to claim 7 , wherein the at least one element is nitrogen.
9. The semiconductor device according to claim 6 , further comprising an insulating layer under the oxide semiconductor layer, wherein:
an amount of oxygen released from the insulating layer is greater than or equal to 3.0×10 20 atoms/cm 3 in thermal desorption spectroscopy when the amount of oxygen is converted into oxygen atoms;
the insulating layer contains oxygen and is capable of supplying oxygen to the oxide semiconductor layer; and
the insulating layer contains SiO x , where x is larger than 2.
10. The semiconductor device according to claim 6 , further comprising a gate electrode over the oxide semiconductor layer, wherein the source region and the drain region are formed by self-aligned process with respect to the gate electrode.
11. The semiconductor device according to claim 6 , wherein:
a work function of the channel formation region is larger than a work function of the source region; and
the work function of the source region is larger than a work function of the source electrode.
12. The semiconductor device according to claim 6 , wherein the energy gap of the channel formation region is 3 eV or more.
13. The semiconductor device according to claim 6 , wherein:
the crystals include a first crystal and a second crystal; and
directions of an a-axis and a b-axis on the a-b plane of the first crystal are different from those of the second crystal.
14. A semiconductor device comprising:
an oxide semiconductor layer including a channel formation region, a source region and a drain region,
wherein:
the oxide semiconductor layer contains zinc, indium and gallium;
the channel formation region includes crystals;
the crystals are c-axis-oriented in a direction substantially perpendicular to a surface of the oxide semiconductor layer;
the crystals comprise atoms arranged to have a triangular or hexagonal shape in an a-b plane;
each of the source region and the drain region includes at least one element selected from Group 15 elements;
each of the source region and the drain region comprises a wurtzite crystal structure;
an energy gap of the channel formation region is larger than an energy gap of each of the source region and the drain region;
the energy gap of the channel formation region is 2.5 eV or more, and
a crystal structure of each of the source region and the drain region is different from a crystal structure of the channel formation region.
15. The semiconductor device according to claim 14 , wherein:
a concentration of the at least one element selected from Group 15 elements included in the source region is higher than or equal to 5×10 19 atoms/cm 3 and lower than or equal to 1×10 22 atoms/cm 3 ; and
a concentration of the at least one element selected from Group 15 elements included in the drain region is higher than or equal to 5×10 19 atoms/cm 3 and lower than or equal to 1×10 22 atoms/cm 3 .
16. The semiconductor device according to claim 14 , wherein the at least one element is nitrogen.
17. The semiconductor device according to claim 14 , further comprising an insulating layer under the oxide semiconductor layer, wherein:
an amount of oxygen released from the insulating layer is greater than or equal to 3.0×10 20 atoms/cm 3 in thermal desorption spectroscopy when the amount of oxygen is converted into oxygen atoms;
the insulating layer contains oxygen and is capable of supplying oxygen to the oxide semiconductor layer; and
the insulating layer contains SiO x where x is larger than 2.
18. The semiconductor device according to claim 14 , further comprising a gate electrode over the oxide semiconductor layer, wherein the source region and the drain region are formed by self-aligned process with respect to the gate electrode.
19. The semiconductor device according to claim 14 , further comprising a source electrode electrically connected to the source region, wherein:
a work function of the channel formation region is larger than a work function of the source region; and
the work function of the source region is larger than a work function of the source electrode.
20. The semiconductor device according to claim 14 , wherein the energy gap of the channel formation region is 3 eV or more.