Patent Publication Number: US-9899375-B1

Title: Co-integration of self-aligned and non-self aligned heterojunction bipolar transistors

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to semiconductor structures and, more particularly, to co-integration of self-aligned and non-self aligned heterojunction bipolar transistors and methods of manufacture. 
     BACKGROUND 
     A heterojunction bipolar transistor (HBT) is a type of bipolar junction transistor (BJT) which uses differing semiconductor materials for the emitter and base regions, or base and collector regions, thereby creating a heterojunction. The HBT can handle signals of very high frequencies, up to several hundred GHz. The HBT is commonly used in radio-frequency (RF) systems, and in applications requiring a high power efficiency, such as RF power amplifiers in cellular phones. 
     BiCMOS technologies with very good low-noise amplifier (LNA) and very good power amplifier (PA) SiGe HBTs are difficult to integrate on the same wafer due to different optimization requirements. For example, LNA devices need high current gain beta, low Rb (base resistance) and low Ccb (collector-base capacitance) for low Noise Figure (NF) and high gain. A self-aligned emitter/base integration scheme is preferred for the LNA as it results in both lower Rb and lower Ccb. In LNA technologies, an implanted extrinsic base structure is typically used which results in high Rb and high base current (low beta). On the other hand, the PA devices need low Cbe (base-emitter capacitance) and high BVceo (for a given beta). In such PA implementations, a wide emitter is required and self-alignment of emitter-base is not essential. Accordingly, in current integration schemes, only one device can be optimized for performance, with the performance of the other device mostly restricted. 
     SUMMARY 
     In an aspect of the disclosure, a structure comprises at least two heterojunction bipolar transistor (HBT) devices integrated onto a same wafer with different epitaxial base profiles. An intrinsic base epitaxy for a second device of the at least two HBT devices acts as an extrinsic base for a first device of the at least two HBT devices. 
     In an aspect of the disclosure, a structure comprises: a first heterojunction bipolar transistor (HBT) device formed on a substrate and a second HBT device formed on the substrate. The first HBT device comprises: a collector region formed from the substrate; a self-aligned epitaxial base having a first profile formed in an opening above the collector region; and a self-aligned emitter region adjacent to the epitaxial base with the first profile. The second HBT device comprises: a collector region formed from the substrate; an epitaxial base having a second profile different than the first profile, which is formed in an opening above the collector region; and an emitter region adjacent to the epitaxial base with the second profile. 
     In an aspect of the disclosure, a method comprises: growing a first SiGe base with non-selective epitaxy for a first device; growing a second SiGe base for a second device, the first SiGe base and the second SiGe base having a different base profile; forming an emitter window and an undercut for the first device over the first SiGe base; linking an extrinsic base to an intrinsic base for first device within the undercut; forming an emitter window for the second device; and forming an emitter for both the first device and the second device, simultaneously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present disclosure. 
         FIG. 1  shows a starting structure and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 2  shows an opening for a base region of a first device and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 3  shows a base material within the opening in addition to several further material layers and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 4  shows a base opening and spacer formation for a base region of a second device and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 5  shows a base material within the opening for the second device, in addition to several further layers and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 6  shows an emitter opening and undercut for the first device and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 7  shows sidewall spacer formation and a growth in the opening of the first device, and an emitter opening for the second device in accordance with aspects of the present disclosure. 
         FIG. 8  shows emitters for the first device and the second device and respective fabrication processes in accordance with aspects of the present disclosure. 
         FIG. 9  shows two HBT devices with respective contacts and fabrication processes in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to semiconductor structures and, more particularly, to co-integration of self-aligned and non-self aligned heterojunction bipolar transistors and methods of manufacture. More specifically, the present disclosure provides an integration scheme to optimize two NPN devices, e.g., low-noise amplifier (LNA) and power amplifier (PA) devices. In embodiments, for example, the LNA and PA devices have optimized SiGe base profiles. In addition to optimizing SiGe base profiles for the PA and LNA, the integration scheme (i.e., emitter/base integration scheme) is also optimized specifically for the LNA and PA devices according to their specific needs. The integration scheme described herein is also applicable for other applications, e.g., high fT and high fmax devices or PA devices and high performance (HP) devices, amongst others. HP devices typically have very high ft/fmax for automotive radars, optical communication applications, etc. 
     In more specific embodiments, two HBT devices are integrated on a same wafer with two different SiGe epitaxy base profiles and two different integration schemes. For example, an intrinsic base epitaxy for one device can act as an extrinsic base poly for a second device. More specifically, in embodiments, dual-optimization can result from the use of non-selective epitaxy as part of the raised extrinsic base layer for the LNA device. In embodiments, the epitaxial profiles could differ in doping, thickness and Ge content in the base, as examples. The devices can also have the same emitter (formed simultaneously) and same or different collectors. In addition, one HBT (e.g., LNA device) can have a self-aligned emitter/base integration, whereas, another HBT (e.g., PA device) can have a non-self-aligned emitter/base integration. 
     The dual integration scheme of the present disclosure can be manufactured in a number of ways using a number of different tools. In general, though, the methodologies and tools are used to form structures with dimensions in the micrometer and nanometer scale. The methodologies, i.e., technologies, employed to manufacture the dual integration scheme of the present disclosure have been adopted from integrated circuit (IC) technology. For example, the structures are built on wafers and are realized in films of material patterned by photolithographic processes on the top of a wafer. In particular, the fabrication of the dual integration scheme uses three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask. 
       FIG. 1  shows a structure and respective fabrication processes in accordance with aspects of the present disclosure. As with all of the figures shown herein, the integration scheme shows a fabrication process for both an LNA device (on side “A”) and a PA device (on side “B”) in accordance with aspects of the present disclosure. It should be recognized by those of skill in the art that other devices are also contemplated using the integration schemes described herein. 
     In embodiments, the structure  10  includes shallow trench isolation (STI) structures  14  formed in a substrate  12 . In embodiments, the substrate  12  can be Si, silicon-on-insulator (SOI) or SiC, for examples. The area of the substrate  12  between the STI structures  14  can form the collector region of the HBTs, e.g., LNA device and PA device. In embodiments, a collector implant might be same between the devices. To form the STI structures  14 , for example, a resist is formed over the substrate  12  and exposed to energy (light) to form openings that correspond with the STI structures  14 . A trench is formed in the substrate  12  through the openings, by conventional etching processes, e.g., reactive ion etching (RIE). The resist is removed by a conventional stripant or oxygen ashing and an oxide material is then deposited in the trench, followed by a chemical mechanical polish (CMP). 
     Still referring to  FIG. 1 , an oxide material  16  is formed over the STI structures  14  and exposed surfaces of the substrate  12 . In embodiments, the oxide material  16  can be deposited by a conventional chemical vapor deposition (CVD) process to a thickness of about 100 Å to about 400 Å; although other thicknesses are also contemplated herein. A poly material  18  is deposited over the oxide material  16 . In embodiments, the poly material  18  can be deposited by a conventional CVD process to a thickness of about 100 Å to about 400 Å; although other thicknesses are also contemplated herein. 
     In  FIG. 2 , a window or opening  20  is formed through the oxide material  16  and the poly material  18  on the LNA side of the device, e.g., side “A”, to expose a surface of the underlying substrate  12 . In embodiments, the opening  20  is fabricated by forming a mask or resist on the poly material  18  and exposing it to energy to form an opening, followed by an etching (RIE) process to remove the oxide material  16  and the poly material  18  on the LNA side of the device. The resist can then be removed by a conventional stripant or oxygen ashing process. As shown in  FIG. 2 , the PA side of the device (e.g., side “B”) will not undergo any etching processes, as it remains protected by the resist. 
     In  FIG. 3 , a low temperature epitaxial material  22  is formed within the opening  20  (on the exposed surface of the substrate  12 ) and the exposed surfaces of the poly material  18  on both the LNA side and the PA side of the substrate. As should be understood by those of ordinary skill in the art, the low temperature epitaxial material  22  is a non-selective material that will grow as single crystalline SiGe on the substrate  12  on the LNA side of the device (e.g., side “A”); whereas, the low temperature epitaxial material  22  will grow as poly-crystalline or amorphous material on the surface of the poly material  18  and any dielectric material. In embodiments, the low temperature epitaxial material  22  can be other semiconductor materials known to those of skill in the art. The low temperature epitaxial material  22  can be grown to a thickness of about 300 Å to about 3000 Å; although other thicknesses are also contemplated by the present disclosure. 
     In embodiments, the SiGe material  22  will form a base region for the LNA device, which can be optimized. For example, the SiGe material  22  can have different concentrations of Ge to obtain a particular beta, e.g., high beta. For example, Ge concentration can be can be anywhere between about 5%-40%. In addition or alternatively, the SiGe material  22  can have a high base dopant in order to provide a low base resistance for the LNA device. For example, base Boron doping can be as high as 5E 20 /cm 3    
     Still referring to  FIG. 3 , in embodiments, an oxide material  24  and poly material  26  are sequentially deposited over the low temperature epitaxial material  22 , e.g., both single crystal SiGe and poly material. In embodiments, the oxide material  24  and poly material  26  are each deposited separately by a conventional deposition process, e.g., CVD. The oxide material  24  and poly material  26  can each be deposited to a thickness of about 200 Å; although other thicknesses are also contemplated herein. 
     Referring to  FIG. 4 , an opening  28  is formed in the base area on the PA side (e.g., side “B”). In embodiments, the opening  28  is formed by conventional lithography and etching processes, as described herein, to expose a surface of the substrate  12 . In embodiments, the LNA side of the substrate (e.g., side “A”) remains protected with the resist during the formation of the opening  28 . Optional spacers  30  are formed on the sidewalls of the opening  28 . In embodiments, the spacers  30  are nitride material formed by a conventional conformal deposition process, followed by an anisotropic etching process to remove spacer material from the horizontal surfaces. 
     In  FIG. 5 , a low temperature epitaxial material  32  is formed within the opening  30  (on the exposed surface of the substrate  12 ) and the exposed surfaces of the poly material  26  on both the LNA side and the PA side of the substrate. As previously noted, the low temperature epitaxial material  32  is a non-selective material that will grow as single crystal semiconductor material on the substrate  12 ; whereas, the low temperature epitaxial material  32  will grow as poly-crystalline or amorphous material on the surface of the poly material and any dielectric material, e.g., oxide material of the exposed STI region  14 . In this way, the intrinsic base epitaxy for the second device (e.g., PA device) acts as an extrinsic poly base for the first device (e.g., the LNA device). In embodiments, the low temperature epitaxial material  32  can be other semiconductor materials. 
     In embodiments, the SiGe material  32  will form a base region for the PA device, which can be optimized for low capacitance and high breakdown voltage. For example, the SiGe (semiconductor) material  32  can have different concentrations of Ge to obtain a particular beta for high BVceo. In addition or alternatively, the SiGe material  32  can have a base dopant or concentration in order to provide a low base and/or emitter capacitance for the PA device, as well as different thicknesses to adjust the breakdown voltage. For example, Ge concentration in the SiGe for the PA can be anywhere from about 5% to 25% and the base dopant for the NPN structure can be Boron with concentration as high as 2E 20 /cm 3 . Moreover, as an example, the low temperature epitaxial material  32  can be thicker layer than the material  22  of the LNA device, e.g., grown to a thickness of greater than 300 Å to about 3000 Å, to increase the breakdown voltage. In this way, it is now possible to integrate at least two HBT devices onto a same wafer with different epitaxial base profiles. Also, the non-selective epitaxy, e.g., low temperature epitaxial material  32 , can be used as part of the raised extrinsic base layer for the LNA device. 
     Still referring to  FIG. 5 , in embodiments, an oxide material  34  and nitride material  36  are sequentially deposited over the low temperature epitaxial material  32 , e.g., both single crystal SiGe and poly material. In embodiments, the oxide material  34  and nitride material  36  are each deposited separately by a conventional deposition process, e.g., CVD. The oxide material  34  and nitride material  36  can each be deposited to a thickness of about 200 Å; although other thicknesses are also contemplated herein. In embodiments, the layers  34  and  36  can be of same thickness over both “A” and “B”. Also layers  34  and  36  can be deposited over the entire structure shown on side “B” including regions outside spacer  30 . 
     As shown in  FIG. 6 , an emitter window or opening  38  is formed on the LNA side of the structure, e.g., side “A”. In embodiments, the emitter window or opening  38  is formed by conventional lithography and etching processes, e.g., RIE, with the oxide material  24  acting as an etch stop layer. The PA side of the structure, e.g., side “B” remains protected by a resist or mask material during the etching process. In embodiments, an emitter spacer  42  is formed on sidewalls of the emitter window or opening  38 . The emitter spacer  42  can be formed after removal of the resist material. In embodiments, the emitter spacer  42  is a nitride material formed by a conformal deposition process, followed by an anisotropic etching process to remove the emitter material from horizontal surfaces of the structure. 
     Following formation of the emitter spacer  42 , an undercut  40  can be formed in the oxide material  24 , aligned with the emitter window or opening  38 . The undercut  40  can be formed by a wet etching process of the oxide material  24  to expose the underlying semiconductor material  22 , e.g., low temperature epitaxial material. Depending on the etch time, for example, the undercut  40  can have different dimensions, e.g., ranging from about 500 Å to about 3000 Å. 
     Referring now to  FIG. 7 , semiconductor material  44 , e.g., Si material, is formed in the undercut  40  by a selective epitaxial growth process to link the raised extrinsic base to the intrinsic base on the LNA region of the structure, e.g., side “A”. As should be understood by those of skill in the art, the semiconductor material  44  will grow on the exposed surface of the low temperature epitaxial material  22  (e.g., SiGe), filling the undercut  40 . Also, as should be understood by those of skill in the art, the semiconductor material  44  will not grow on nitride material  36  formed on upper surfaces of both the LNA region and PA region of the structure due to selective growth conditions. Moreover, the oxide layer between the extrinsic base and the intrinsic base reduces the Ccb for the device resulting in higher gain. 
     As further shown in  FIG. 7 , after formation of the semiconductor material  44 , oxide material  46  and additional nitride material is blanket deposited on the structure and, in particular, over the semiconductor material  44 . The nitride material will extend the emitter spacer  42  to the semiconductor material  44 . The nitride material will undergo an anisotropic etching process to form another spacer  42 ′ and to remove any excess material from horizontal surfaces of the structure. 
     Still referring to  FIG. 7 , an emitter window or opening  48  is formed on the PA side of the structure, e.g., side “B”, using conventional lithography and etching processes, e.g., RIE, as already described herein. The emitter window or opening  48  will expose a surface of the low temperature epitaxial material  32 . 
     As shown in  FIG. 8 , the oxide material (e.g., oxide material  46 ) is removed from the opening  38  (and other surfaces), followed by deposition of emitter material  50  in both the openings  38  and  48 . In embodiments, the emitter material  50  can be in-situ doped polysilicon e.g., arsenic or phosphorous doped polysilicon. A nitride material  52  is formed over the emitter material  50 . In embodiments, the emitter material  50  and nitride material  52  can be deposited by a conformal deposition process, e.g., CVD, followed by a patterning process to simultaneously form the emitter  54  of the LNA device and the emitter  56  of the PA device. The patterning process can be a conventional lithography and etching process, as described herein, to form the emitter  54  of the LNA and the emitter  56  of the PA. 
     Still referring to  FIG. 8 , the structures then undergo an implant process to form the NPN structures. In embodiments, the implant process is a P+ implant, e.g., boron. The implant can have a dose of greater than 1E14. In addition, in embodiments, Ge or carbon can be added to reduce the diffusion of boron. The processes continue with an extrinsic base contact and collector contact for both LNA device and PA device using a same etching process (e.g., same mask for both the devices). 
     Accordingly, as should now be understood by those of skill in the art, the methods described herein form two SiGe epitaxy base profiles by growing the first SiGe base with nonselective epitaxy, depositing a sacrificial base oxide layer and poly-Si or a-Si layer and opening a window for second-type NPN (e.g., PA device). The method further comprises growing a second SiGe base, forming an emitter window for the first-type NPN (e.g., LNA device), and etching a cavity or undercut for selective epitaxy to link the extrinsic base to intrinsic base for the first-type NPN. An emitter window can be formed for the second-type NPN, e.g., PA device, with the emitter being formed for both types of NPNs, e.g., PA and LNA, simultaneously. In embodiments, the intrinsic base epitaxy for the second type device, e.g., PA, can be an extrinsic base for the first type device, e.g., LNA. 
     In addition, the following features are provided as shown in Table 1, below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 1st HBT device (e.g.,  
                 2nd HBT device (e.g., PA 
               
               
                   
                 LNA Device) 
                 Device) 
               
               
                   
               
             
            
               
                 Emitter/base 
                 Self-aligned 
                 Non-self-aligned 
               
               
                 integration 
                   
                   
               
               
                 Extrinsic Base 
                 Si seed layer + Implanted 
                 Implanted 2nd HBT device 
               
               
                   
                 2nd HBT device SiGe 
                 SiGe base 
               
               
                   
                 base 
                   
               
               
                 SiGe Intrinsic 
                 Non-selective SiGe (or 
                 Non-selective SiGe (or other 
               
               
                 Base 
                 other semiconductor 
                 semiconductor material) 
               
               
                   
                 material) epitaxy (1) 
                 epitaxy (2) 
               
               
                 Collector 
                 Dedicated SIC implant 
                 Dedicated implant 
               
               
                   
                 (or shared with 2nd HBT 
                   
               
               
                   
                 device) 
                   
               
               
                 Emitter 
                 Shared with 2nd HBT 
                 Shared with 1st HBT device 
               
               
                   
                 device 
                   
               
               
                 Sub-collector 
                 Shared with 2nd HBT 
                 Shared with 1st HBT device 
               
               
                   
                 device 
               
               
                   
               
            
           
         
       
     
       FIG. 9  shows two HBT devices with respective contacts and fabrication processes in accordance with aspects of the present disclosure. More specifically, the structure  100  of  FIG. 9  shows an emitter up device on side “A” and a collector up device on side “B”. In embodiments, the emitter up device includes an emitter region  110  above the substrate  120 , with the collector region  115  within the substrate  120 ; whereas, the collector up device includes the emitter region  110  within the substrate  120  and the collector region  115  above the substrate  120 . In embodiments, the emitter up device has a self-aligned emitter and base region and the collector up device has a non-self aligned collector and base region. The emitter regions, collector regions and remaining structures of the structure can be fabricated in the manner already described herein such that no further explanation is required for one of skill in the art to understand the fabrication processes. 
     Still referring to  FIG. 9 , in the emitter up device, a contact  110 ′ is contacting the emitter region  110  above the substrate  120 , with a contact  115 ′ contacting the collector region  115  on a side of the emitter region  110 . Similarly, in the collector up device, a contact  115 ″ is contacting the collector region  115  above the substrate  120 , with a contact  110 ″ contacting the emitter region  110  on a side of the collector region  115 . The contacts  110 ′,  110 ″,  115 ′ and  115 ″ can be fabricated with conventional lithography, etching and deposition processes as already described herein such that that no further explanation is required for one of skill in the art to understand the fabrication processes. 
     The method(s) as described above is used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
     The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.