Biolar transistor

• US 20040094823A1
• Filed: 09/05/2003
• Published: 05/20/2004
• Est. Priority Date: 03/07/2001
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Matsuno, Noriaki
• Granted Patent: US 7,023,072 B2
• Time in Patent Office: Days
• US Class Current: 257/565
• CPC Class Codes: H01L 29/1004 Base region of bipolar transistors
• CPC Class Codes: H01L 29/36 characterised by the concentration or distribution of impurities in the bulk material within semiconductor regions H01L29/06
• CPC Class Codes: H01L 29/7378 comprising lattice mismatched active layers, e.g. SiGe strained layer transistors

Abstract

In a bipolar transistor including a base layer made of SiGe, a non-did SiGe layer and a non-doped Si layer are provided between the base layer and an emitter layer. The composition ratio of Ge in the emitter side of SiGe base layer is decreased with increasing proximity to the emitter side, and the composition ratio of Ge in the non-doped SiGe layer is a smaller than the composition ratio of Ge at the emitter layer-side end of the SiGe base layer. In this manner, restriction is put on the diffusion of boron from the base layer to the emitter side, and the base-emitter junction capacitance C_BE reduced. Furthermore, the direct-current gain β can be improved by increasing the composition of Ge at the emitter end of the SiGe base layer to more than or equal to a predetermined value.

Claims

1. A bipolar transistor comprising a SiGe base layer and an emitter layer,

wherein a non-doped SiGe layer and a non-doped Si layer are provided between the SiGe base layer and the emitter layer, the non-doped SiGe layer is adjacent to the SiGe base layer, and the non-doped Si layer is adjacent to the non-doped SiGe layer and also is adjacent to the emitter layer.

2. The bipolar transistor according to claim 1,

wherein the composition ratio of Ge in the non-doped SiGe layer is smaller than the composition ratio of Ge in the SiGe base layer.

3. The bipolar transistor according to claim 1 or 2,

wherein the composition ratio of Ge continuously or stepwise decreases with increasing proximity to the emitter side in at least a part of the emitter side of the SiGe base layer.

6. The bipolar transistor according to any one of claims 1 to 5,

wherein the total film thickness is 5 nm or more, but 60 nm or less with respect to the non-doped SiGe layer and the non-doped Si layer.

7. The bipolar transistor according to any one of claims 1 to 6,

wherein the composition ratio of Ge is 3% or more at the emitter layer-side end of the SiGe base layer.

8. The bipolar transistor according to claim 7,

wherein the composition ratio of Ge is 6% or more at the emitter layer-side end of the SiGe base layer.

9. The bipolar transistor according to any one of claims 1 to 6,

wherein the composition ratio of Ge at the emitter layer-side end of the SiGe base layer is more than or equal to one-fifth the maximum value of the composition ratio of Ge in the SiGe base layer.

10. The bipolar transistor according to any one of claims 1 to 9,

wherein each of the non-doped SiGe layer and the non-doped Si layer comprises a layer having an impurity concentration of 1×

10¹⁷ cm<sup>−

3</sup> or less.

11. The bipolar transistor according to any one of claims 1 to 9,

wherein each of the non-doped SiGe layer and the non-doped Si layer comprises a layer having an impurity concentration of less than or equal to one-fiftieth the impurity concentration of the base region.

12. The bipolar transistor according to any one of claims 1 to 11,

wherein the non-doped SiGe layer and the non-doped Si layer constitute a space-charge region, and the band gap of the space-charge region in adjusted at a value between the hand gap of the emitter layer and the band gap of the base layer.

4. A bipolar transistor comprising:

a laminated structure composed of a collector layer, a SiGe base layer, a non-doped SiGe layer, a non-doped Si layer and an n-type emitter layer in that order,

wherein the composition ratio of Ge gradually decreases with increasing proximity to the emitter layer side in at least a part of the emitter layer side of the SiGe base layer, and the composition ratio of Ge in the non-doped SiGe layer is smaller than the composition ratio of Ge at the emitter-side end of the SiGe base layer.

5. A bipolar transistor comprising:

a laminated structure composed of a collector layer, a SiGe base layer, a non-doped SiGe layer, a non-doped Si layer and an n-type emitter layer in that order,

wherein the composition ratio of Ge stepwise decreases with increasing proximity to the emitter layer side in at least a part of the emitter layer side of the SiGe base layer, and the composition ratio of Ge in the non-doped SiGe layer is smaller than the composition ratio of Ge at the emitter layer-side end of the SiGe base layer.