Bipolar transistors with low-resistance emitter contacts
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IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
H01L-021/338
H01L-021/331
출원번호
US-0927914
(2004-08-27)
발명자
/ 주소
Ahn, Kie Y.
Forbes, Leonard
출원인 / 주소
Micron Technology, Inc.
대리인 / 주소
Schwegman, Lundberg, Woessner &
인용정보
피인용 횟수 :
2인용 특허 :
90
초록▼
Many integrated circuits include a type of transistor known as a bipolar junction transistor, which has an emitter contact formed of polysilicon. Unfortunately, polysilicon has a relatively high electrical resistance that poses an obstacle to improving switching speed and current gain of bipolar tra
Many integrated circuits include a type of transistor known as a bipolar junction transistor, which has an emitter contact formed of polysilicon. Unfortunately, polysilicon has a relatively high electrical resistance that poses an obstacle to improving switching speed and current gain of bipolar transistors. Current fabrication techniques involve high temperature procedures that melt desirable low-resistance substitutes, such as aluminum, during fabrication. Accordingly, one embodiment of the invention provides an emitter contact structure that includes a polysilicon-carbide layer and a low-resistance aluminum, gold, or silver member to reduce emitter resistance. Moreover, to overcome manufacturing difficulties, the inventors employ a metal-substitution technique, which entails formation of a polysilicon emitter, and then substitution or cross-diffusion of metal for the polysilicon.
대표청구항▼
1. A method of making an emitter contact for an emitter region of a bipolar transistor, the method comprising:forming a polysilicon structure over a base region of the transistor in a semiconductive substrate, the substrate having a surface bounding the base region; and cross-diffusing metal and at
1. A method of making an emitter contact for an emitter region of a bipolar transistor, the method comprising:forming a polysilicon structure over a base region of the transistor in a semiconductive substrate, the substrate having a surface bounding the base region; and cross-diffusing metal and at least a portion of the polysilicon structure to form a metal emitter contact entirely above the surface of the substrate at the emitter region position. 2. The method of claim 1 further including forming an emitter region within the base region after forming the polysilicon structure, wherein forming the emitter region occurs at a process temperature greater than a melting temperature of the metal emitter contact.3. The method of claim 2 wherein the polysilicon structure includes a doped layer and forming the emitter region comprises outdiffusing dopant from the doped layer into the base region.4. The method of claim 1 wherein cross-diffusing at least a portion of the provided metal and the portion of the polysilicon structure comprises:heating the provided metal and the polysilicon structure. 5. The method of claim 1 wherein the metal comprises at least one of aluminum, gold, and silver.6. The method of claim 1, wherein cross-diffusing at least a portion of the provided metal with at least a portion of the polysilicon structure comprises diffusing metal from a metal layer that contacts the polysilicon structure into the polysilicon structure and diffusing polysilicon into the metal layer.7. The method of claim 1, wherein cross-diffusing at least a portion of the provided metal with at least a portion of the polysilicon structure displaces polysilicon in the portion of the polysilicon structure.8. The method of claim 1, wherein the base region comprises a uniform or graded silicon-germanium Si1-XGeX composition, where x increases with distance from the emitter region.9. A method of making an emitter contact for an emitter region of a bipolar transistor, the method comprising:forming a polysilicon structure over a base region of a semiconductive substrate, the substrate having a surface bounding the base region, wherein forming the polysilicon structure comprises: forming a diffusion barrier layer comprising at least one of a silicon carbide, a silicon oxycarbide, and a titanium nitride; and forming a polysilicon layer on the diffusion barrier layer; providing a metal in contact with the polysilicon structure; and cross-diffusing at least a portion of the provided metal and at least a portion of the polysilicon structure to produce a metal emitter contact above the diffusion barrier layer and the surface of the substrate. 10. The method of claim 9, wherein the polysilicon layer includes polysilicon and germanium.11. The method of claim 9 wherein cross-diffusing at least a portion of the provided metal and the polysilicon structure comprises cross-diffusing the provided metal and substantially all of the polysilicon structure.12. A method of making an emitter contact for a bipolar transistor, the method comprising:forming a polysilicon structure on a base region of the transistor, the polysilicon structure including a doped diffusion barrier layer on the base region and a polysilicon layer on the diffusion barrier layer; depositing metal including at least one of aluminum, gold, and silver on the polysilicon layer; and heating at least the deposited metal and the polysilicon structure to urge diffusion of the deposited metal into the polysilicon layer, with the doped diffusion barrier layer inhibiting diffusion of the deposited metal into the emitter region position of the transistor. 13. The method of claim 12, wherein the diffusion barrier layer comprises at least one of the following: a silicon carbide, a silicon oxycarbide, and a titanium nitride.14. A method of making a metal contact for a bipolar transistor, the method comprising:forming a conductive diffusion barrier over a base region of the transistor; forming a polysilicon structure on the conductive diffusion barrier; forming a metal layer on the polysilicon structure; and cross-diffusing at least a portion of the metal layer and at least a portion of the polysilicon structure to form a metal contact having a lower-most surface overlying the conductive diffusion barrier. 15. The method of claim 14, further including forming an emitter region in the layer underneath and in contact with the polysilicon structure.16. The method of claim 15, wherein the polysilicon structure includes a doped layer contacting a region of the layer and forming the emitter region comprises diffusing dopant from the doped layer into the region.17. A method of reducing emitter resistance of a bipolar transistor, the method comprising:forming a bipolar transistor structure having a polysilicon emitter contact electrically coupled to an emitter region of the transistor structure, with the polysilicon emitter having an electrical resistance; forming a metal layer in contact with the polysilicon emitter; and cross-diffusing at least a portion of the metal layer and at least a portion of the polysilicon emitter contact to reduce the electrical resistance of the contact. 18. A method of making a bipolar transistor having self-aligned base contacts and self-aligned metal emitter contact, the method comprising:forming first and second polysilicon base contacts on a semiconductive layer, the contacts spaced apart to define an active region in the semiconductive layer; outdiffusing dopant from the first and second base contacts into the semiconductive layer to form extrinsic base regions aligned with the base contacts; implanting an intrinsic base region in the active region; forming a doped polysilicon structure on the intrinsic base region, wherein the polysilicon structure includes: a doped diffusion barrier layer on the intrinsic base region; and a polysilicon layer on the doped diffusion barrier layer; and forming an emitter region self-aligned with the doped polysilicon structure by outdiffusing dopant from the doped polysilicon structure into the intrinsic base region; forming a metal layer in contact with the emitter region, wherein the metal layer comprises a metal having a melting temperature lower than a processing temperature used while outdiffusing dopant from the doped polysilicon structure; and cross-diffusing at least a portion of the metal layer and substantially all of the polysilicon layer after forming the emitter region, thereby forming a metal emitter contact self-aligned with the emitter region. 19. A method of making a metal emitter contact for a bipolar transistor, the method comprising:forming a diffusion barrier layer over a base region of the transistor, wherein the diffusion barrier layer includes a dopant; forming a polysilicon layer on the diffusion barrier layer and over the emitter region position; forming a metal layer in contact with the polysilicon layer; and cross-diffusing at least a portion of the metal layer and at least a portion of the polysilicon layer to produce the metal emitter contact, the metal emitter contact electrically coupled to the emitter region through the diffusion barrier layer; and outdiffusing at least a portion of the dopant into the emitter region position at a temperature greater than a melting temperature of the metal emitter contact. 20. A method of making an emitter contact for a bipolar transistor, the method comprising:forming a polysilicon structure over a base region of a semiconductive substrate, the substrate having a surface bounding the base region; forming a metal layer over the polysilicon structure; and cross-diffusing at least a portion of the metal layer and at least a portion of the polysilicon structure to produce a metal emitter contact have a surface confronting the surface of the substrate. 21. The method of claim 20, further including forming an emitter region in the base region after forming the polysilicon structure.22. The method of claim 20, further including forming an emitter region in the base region after forming the polysilicon structure and before cross-diffusing at least a portion of the metal.23. The method of claim 20, wherein the polysilicon structure includes a doped layer and forming the emitter region comprises outdiffusing dopant from the doped layer into the base region at a process temperature greater than a melting temperature of the metal emitter contact.
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