# US 9,437,749 B2 · Semiconductor device and method for fabricating the same

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- Number: US 9,437,749 B2
- Document ID: US9437749B2
- Status: Granted
- Kind: B2
- Application number: 14/995,247
- Filed: 2016-01-14
- Published: 2016-05-12
- Granted: 2016-09-06
- Earliest claimed: 2012-08-10
- Assignees: Semiconductor Energy Laboratory Co., Ltd.
- Applicants: Semiconductor Energy Laboratory Co., Ltd.
- Inventors: Shunpei Yamazaki
- Web page: https://patentgrep.com/patent/US9437749B2

## CPC

- H10D 30/6756: {Amorphous oxide semiconductors}
- H10D 30/6729: {characterised by the electrodes}
- H10D 30/6739: {Conductor-insulator-semiconductor electrodes}
- H10D 30/6755: {Oxide semiconductors, e.g. zinc oxide, copper aluminium oxide or cadmium stannate}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

To provide a highly reliable semiconductor device exhibiting stable electrical characteristics. To fabricate a highly reliable semiconductor device. Included are an oxide semiconductor stack in which a first oxide semiconductor layer, a second oxide semiconductor layer, and a third oxide semiconductor layer are stacked, a source and a drain electrode layers contacting the oxide semiconductor stack, a gate electrode layer overlapping with the oxide semiconductor layer with a gate insulating layer provided therebetween, and a first and a second oxide insulating layers between which the oxide semiconductor stack is sandwiched. The first to the third oxide semiconductor layers each contain indium, gallium, and zinc. The proportion of indium in the second oxide semiconductor layer is higher than that in each of the first and the third oxide semiconductor layers. The first oxide semiconductor layer is amorphous. The second and the third oxide semiconductor layers each have a crystalline structure.

## Claims

### Claim 1

A semiconductor device comprising:
a transistor including a channel formation region, the channel formation region comprising silicon,
a first insulating layer over the transistor,;
a first gate electrode over the first insulating layer;
a second insulating layer over the first gate electrode;
a first oxide semiconductor layer over the second insulating layer, the first oxide semiconductor layer overlapping with the first gate electrode;
a second oxide semiconductor layer over the first oxide semiconductor layer, the second oxide semiconductor layer overlapping with the first gate electrode;
a third oxide semiconductor layer over the second oxide semiconductor layer, the third oxide semiconductor layer overlapping with the first gate electrode;
a source electrode and a drain electrode over the first oxide semiconductor layer and the second oxide semiconductor layer, the source electrode and the drain electrode electrically connected to the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer;
a third insulating layer over the third oxide semiconductor layer, the source electrode, and the drain electrode; and
a second gate electrode over the third insulating layer, the second gate electrode overlapping with the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer,
wherein each of the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer comprises at least one of indium, zinc, and gallium,
wherein the third oxide semiconductor layer and a side surface of the second oxide semiconductor layer are in contact with each other, and
wherein the third oxide semiconductor layer and a side surface of the first oxide semiconductor layer are in contact with each other.

### Claim 2 (depends on 1)

The semiconductor device according to claim 1, wherein the first insulating layer comprises aluminum and oxygen.

### Claim 3 (depends on 1)

The semiconductor device according to claim 1, wherein each of the second oxide semiconductor layer and the third oxide semiconductor layer has a crystalline structure.

### Claim 4 (depends on 1)

The semiconductor device according to claim 1, wherein the first oxide semiconductor layer has an amorphous structure.

### Claim 5 (depends on 1)

The semiconductor device according to claim 1, wherein a composition of the second oxide semiconductor layer and a composition of the third oxide semiconductor layer are different from each other.

### Claim 6 (depends on 1)

The semiconductor device according to claim 1, wherein the second insulating layer contains oxygen in excess of a stoichiometric composition.

### Claim 7 (depends on 1)

The semiconductor device according to claim 1, wherein a concentration of silicon or carbon in each of the first oxide semiconductor layer and the third oxide semiconductor layer is lower than or equal to 3×1018 atoms/cm3.

### Claim 8 (depends on 1)

The semiconductor device according to claim 1, wherein each of the source electrode and the drain electrode is in contact with the second insulating layer.

### Claim 9 (depends on 1)

The semiconductor device according to claim 1, wherein the source electrode and the drain electrode is positioned over the third oxide semiconductor layer.

### Claim 10

A semiconductor device comprising:
a transistor including a channel formation region, the channel formation region comprising silicon,
a first insulating layer over the transistor;
a first gate electrode over the first insulating layer;
a second insulating layer over the first gate electrode;
a first oxide semiconductor layer over the second insulating layer, the first oxide semiconductor layer overlapping with the first gate electrode;
a second oxide semiconductor layer over the first oxide semiconductor layer, the second oxide semiconductor layer overlapping with the first gate electrode;
a third oxide semiconductor layer over the second oxide semiconductor layer, the third oxide semiconductor layer overlapping with the first gate electrode;
a source electrode and a drain electrode over the first oxide semiconductor layer and the second oxide semiconductor layer, the source electrode and the drain electrode electrically connected to the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer;
a third insulating layer over the third oxide semiconductor layer, the source electrode, and the drain electrode; and
a second gate electrode over the third insulating layer, the second gate electrode overlapping with the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer,
wherein each of the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer comprises at least one of indium, zinc, and gallium,
wherein the third oxide semiconductor layer and a side surface of the second oxide semiconductor layer are in contact with each other,
wherein the third oxide semiconductor layer and a side surface of the first oxide semiconductor layer are in contact with each other, and
wherein one of the source electrode and the drain electrode is electrically connected to the transistor.

### Claim 11 (depends on 10)

The semiconductor device according to claim 10, wherein the first insulating layer comprises aluminum and oxygen.

### Claim 12 (depends on 10)

The semiconductor device according to claim 10, wherein each of the second oxide semiconductor layer and the third oxide semiconductor layer has a crystalline structure.

### Claim 13 (depends on 10)

The semiconductor device according to claim 10, wherein the first oxide semiconductor layer has an amorphous structure.

### Claim 14 (depends on 10)

The semiconductor device according to claim 10, wherein a composition of the second oxide semiconductor layer and a composition of the third oxide semiconductor layer are different from each other.

### Claim 15 (depends on 10)

The semiconductor device according to claim 10, wherein the second insulating layer contains oxygen in excess of a stoichiometric composition.

### Claim 16 (depends on 10)

The semiconductor device according to claim 10, wherein a concentration of silicon or carbon in each of the first oxide semiconductor layer and the third oxide semiconductor layer is lower than or equal to 3×1018 atoms/cm3.

### Claim 17 (depends on 10)

The semiconductor device according to claim 10, wherein each of the source electrode and the drain electrode is in contact with the second insulating layer.

### Claim 18 (depends on 10)

The semiconductor device according to claim 10, wherein the source electrode and the drain electrode is positioned over the third oxide semiconductor layer.