METHOD OF FABRICATING A BIPOLAR SEMICONDUCTOR DEVICE WITH SILICIDE CONTACTS

Abstract: A method for making a bipolar semiconductor device having silicide contacts (30) which is compatible with the processing steps used in the fabrication of MOS devices. The present invention includes the use of sidewall spacers (28) to limit the self-aligned implants of the extrinsic base (24) and the silicide contact (30). The device is annealed so that the diffusion of the polysilicon layer (22) which forms the emitter (38) may be controlled. Since the emitter (38) size may be controlled, the emitter (38) to base (18) contact area may be reduced resulting in improved device performance.

Description: Background of the Invention This invention generally pertains to a method of fabricating a bipolar semiconductor device having silicide contacts. Generally, in fabricating bipolar devices and the like, it is desirable to be able to use processing steps which are compatible with those used in a fabrication of MOS devices. This not only decreases the number of processing steps needed to fabricate a bipolar device, but also allows a bipolar device to be processed in conjunction with a MOS device thereby enabling composite integrated circuits to be more easily manufactured and used. The bipolar device fabrication will differ from that of an MOS device in that a active base must be formed and no gate dielectric layer is utilized. Therefore, this bipolar arrangement will have doped polysilicon directly on the substrate in its emitter region. Further, the emitter to base contact area is reduced which results in improved device performance. European Patent Application No. EP-A-0230689 teaches a bipolar semiconductor device fabrication method. A device area is isolated in an epitaxial layer on a substrate and an isolating layer is formed on the device area. A base region of a first conducitivity type is implanted in the device area and an emitter opening in said isolating layer is formed. An emitter region of a second conductivity type is implanted in the base region. A polysilicon layer is then deposited over the emitter region and an adjacent area of the isolating layer. Silicide contacts are then formed on the polysilicon layer to contact the emitter region and also to contact the base region. Summary of the Invention It is an object of the present invention to provide a new and improved method of making a bipolar semiconductor device with silicide contacts which is compatible with methods used to fabricate MOS devices. It is a further object of the present invention to provide a new and improved method for making a bipolar semiconductor device with silicide contacts which reduces the emitter to base contact area thereby resulting in increased device density and improved device performance. It is a further object of the present invention to provide a new and improved method for making a bipolar semiconductor device with silicide contacts having a reduced number of processing steps. The present invention pertains to a method for making a bipolar semiconductor device with silicide contacts. The method used in the present invention is one which is compatible with methods commonly used in the fabrication of MOS devices. In accordance with a first aspect of the present invention there is provided a method of processing a bipolar semiconductor device made by the steps of, providing a substrate; isolating a device region on said substrate; forming a first dielectric layer on said substrate; forming an active base of a first conductivity type in said device region of said substrate; defining an emitter opening in said first dielectric layer; depositing a polysilicon layer on said first dielectric layer and in said emitter opening; doping said polysilicon layer in a second conductivity type; masking and etching said polysilicon layer so that said polysilicon extends beyond said emitter opening; etching said first dielectric layer so that only the portion covered by said etched polysilicon layer remains; annealing said device to diffuse an emitter into said active base from said doped polysilicon layer; forming silicide contacts on said polysilicon layer and said base; forming a second dielectric layer on said device region; etching contact opening in said second dielectric layer, said contact openings extending to said silicide contacts; and metallizing said contact openings to create external contacts. Brief Description of the Drawings FIGS. 1-10 are highly enlarged cross-sectional views of a section of a bipolar device during various stages of processing in accordance with the present invention; and FIG. 11 is a highly enlarged cross-sectional view of a section of a bipolar device in accordance with the present invention. Description of the Preferred Embodiments Referring specifically to FIGS. 1-10, highly enlarged cross-sectional views of a section of a bipolar semiconductor device are shown during various stages of processing. It should be noted that the collector contact and buried layer regions are not shown in these figures. Initially, a substrate, 10, is provided. A device region, 12, is isolated on substrate 10 by isolation areas 14. This is well known in the art. Following the isolation of device region 12 on substrate 10, a first dielectric layer, 16 is formed on substrate 10. An active base, 18, is then implanted in device region 12 of substrate 10. An additional dielectric layer may be formed following the implantation if a thicker first dielectric layer is desired. Following the implantation of active base 18, an emitter opening, 20, is defined in first dielectric layer 16. Once emitter opening 20 has been defined, a polysilicon layer, 22, is deposited in emitter opening 20 and on first dielectric layer 16. After polysilicon layer 22 has been doped, it is masked and etched so that it extends beyond emitter opening 20. It should be understood that polysilicon layer 22 and active base 18 are of opposite conductivity types. In one embodiment of the present invention (see FIG. 6), an extrinsic base, 24, may be implanted in device region 12 of substrate 10. This is done by using etched polysilicon layer 22 so that a self-aligned implant may occur. In another embodiment of the present invention (see FIGS. 7 & 8), a conformal dielectric layer, 26, is formed on first dielectric layer 16 and etched polysilicon layer 22. Conformal dielectric layer 26 and first dielectric layer 16 are then etched so that sidewall spacers, 28, are formed. Commonly, an anisotropic etch of first dielectric layer 16 and conformal dielectric layer 26 is used to form sidewall spacers 28. Following the formation of sidewall spacers 28, extrinsic base 24 is implanted. Sidewall spacers 28 enable the self-aligned implantation of extrinsic base 24 to cover a lesser area than if sidewall spacers 28 were not employed. The size of sidewall spacers 28 enable the size of extrinsic base 24 to be controlled. It should be understood that sidewall spacers 28 may be employed after the implantation of extrinsic base 24 for reasons which will be discussed presently. After the formation of extrinsic base 24, the bipolar device is annealed so that the desired dopant profile and device characteristics may be obtained. This annealing causes an emitter, 38, to diffuse from doped polysilicon layer 22 beneath emitter opening 20. Since the annealing will control the size of emitter 38, the emitter to base contact area may be controlled. A reduced emitter to base contact area allows for improved device performance. Next, silicide contacts, 30, are formed. Sidewall spacers 28 may be used to control the size of silicide contacts 30 which are formed over active base 24. In addition to being formed over active base 24, a silicide contact 30 is formed over polysilicon layer 22 and serves as an emitter contact. Following the formation of silicide contacts 30, a second dielectric layer, 32, is formed over substrate 10. Following the formation of second dielectric layer 32, contact openings, 34, are etched in second dielectric layer 32. Contact openings 34 extend to the various silicide contacts 30. Referring specifically to FIG. 11, a highly enlarged cross-sectional view of a section of a bipolar semiconductor device having silicide contacts is shown. In this embodiment, it can be seen that contact openings 34 have been metallized and a plurality of metal contacts, 36, extend therefrom. However it should be understood that other contact means which are well known in the art may be used. Metal contacts 36 serve as emitter and base contacts accordingly in this figure.

Claims: A method of fabricating a bipolar semiconductor device comprising the steps of, providing a substrate (10); isolating a device region (12) on said substrate (10); forming a first dielectric layer (16) on said substrate (10); forming an active base (18) of a first conductivity type in said device region (12) of said substrate (10); defining an emitter opening (20) in said first dielectric layer (16); depositing a polysilicon layer (22) on said first dielectric layer (16) and in said emitter opening (20); doping said polysilicon layer (22) in a second conductivity type; masking and etching said polysilicon layer (22) so that said polysilicon extends beyond said emitter opening (20); etching said first dielectric layer (16) so that only the portion covered by said etched polysilicon layer (22) remains; annealing said device to diffuse an emitter (38) into said active base (18) from said doped polysilicon layer (22); forming silicide contacts (30) on said polysilicon layer (22) and said base (18); forming a second dielectric layer (32) on said device region (12); etching contact openings (34) in said second dielectric layer (32), said contact openings (34) extending to said silicide contacts (30); and metallizing said contact openings (34) to create external contacts (36). The method of claim 1 further comprising the step of forming an extrinsic base (24). The method of claim 2 wherein the steps of forming an active base (18) and forming an extrinsic base (24) are performed by implantation. The method of claim 3 wherein a self-aligned implant is performed to implant the extrinsic base (24) during or directly following the etching of the polysilicon layer (22). The method of claim 2 wherein after the etching of the polysilicon layer (22), a conformal dielectric layer (26) is formed over the device region (12) and said conformal dielectric layer (26) and the first dielectric layer (16) are etched to provide for sidewall spacers (28). The method of claim 5 wherein a self-aligned implant is performed to implant the extrinsic base (24) following the processing of the sidewall spacers (28). The method of claim 1 wherein the formation of the silicide contacts (30) is self-aligned.

Inventors: ALVAREZ, ANTONIO R., KIRCHGESSNER, JAMES A.
Applicants: MOTOROLA INC.
Application year: 1988
Main classification: H01L21
IPC codes: H01L29, H01L21