Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D1/00—Resistors, capacitors or inductors
  • H10D1/60—Capacitors
  • H10D1/62—Capacitors having potential barriers
  • H10D1/64—Variable-capacitance diodes, e.g. varactors 

Definitions

• the present invention relates to a semiconductor structure that includes a hyperabrupt junction varactor that is tunability and has a high quality factor, Q as well as a process for fabricating such a semiconductor structure.
• the inventive semiconductor structure which includes a hyperabrupt junction varactor with a compensated cathode contact, is highly suitable for use in complementary metal oxide semiconductor (CMOS) and/or bipolar technologies.
• CMOS complementary metal oxide semiconductor
• the inventive structure is highly suitable for use as a component in mobile or cellular phones, personnel digital assistances (PDAs) and other high radio frequency (RF) electronic devices.
• Varactors form a class of tunable semiconductor capacitors typically derived from pn-junctions, where the pn-junction is operated in a reverse bias state.
• the varactor' s capacitance can be varied by adjusting the reverse bias voltage.
• varactors can be characterized by a CV tuning curve.
• Varactors are especially useful in oscillation circuits, especially voltage-controlled oscillators (VCOs), where the varactor' s tunability is used to tune the oscillation frequency of the circuit. Varactors thus find use in cellular or mobile phones, PDAs, televisions, radios, computers, active filters, and wherever a first signal is synchronized to a second signal.
• Hyperabrupt junction varactors Varactors that include an ion-implanted hyperabrupt junction are known and are referred to in the art as "hyperabrupt junction varactors". See, for example, U.S. Patent Nos. 4,226,648 to Goodwin, et al, 4,827,319 to Pavlidis, et al, 5,557,140 to Nguyen, et al. and 6,521,506 to Coolbaugh, et al. The term “hyperabrupt” is used to denote the profile of the pn junction. Hyperabrupt junction varactors have a doping profile that changes in a controlled non-linear way with density of the dopants increasing towards the junction and abruptly dropping to zero at the junction.
• Hyperabrupt junction varactors have a higher tuning range than pn- diode varactors, Schottky diode varactors and metal oxide semiconductor (MOS) diode varactors. Moreover, hyperabrupt junction varactors have an almost linear CV characteristic along with a high quality factor Q. These figures of merit, i.e., tunability, high Q, and linear CV, make the hyperabrupt junction varactor the device of choice for designers of VCOs.
• PARA 5 In order to implement a hyperabrupt junction varactor, which is independent of critical CMOS and BiCMOS processes, the prior art technique requires that at least two unique critical implant mask levels be implemented. For example, one implant mask level is needed to form the subcollector and/or the n-type implant for the hyperabrupt junction varactor and another implant mask level is needed to implement the p+ implant and/or the hyperabrupt implant to form the anode device.
• p+ source/drain implant or the emitter implant will cause multiple issues in the future since it is common practice to adjust the p+ implant to tune specific devices, e.g., pFETs, p+ polySi resistors, p+ diffusion resistors and bipolar transistors back to specification. Any minor adjustments to the energy or the dose can cause a large shift in the hyperabrupt junction varactor using it.
• FIG. 1 shows a cross sectional view of a typical prior art semiconductor structure 1OA that includes a one cathode contact and a hyperabrupt junction varactor.
• the hyperabrupt junction varactor of the prior art structure was fabricated using at least two critical masking levels.
• the structure 1OA shown in FIG. 1 includes a Si-containing substrate 12 that comprises a buried subcollector/cathode 14, a collector 16, trench isolation regions 18, reach-through implant region 20 and hyperabrupt dopant region 24.
• the reach-through implant region 20 is in contact with the subcollector/cathode 14 at one point in this prior art structure.
• the buried subcollector 14, collector 16, and reach-through implant region 20 are comprised of the same conductivity type dopant (p-type or n-type, with n-type being preferred). The dopant concentration within regions 14, 16 and 20, however, is different. For example, the buried subcollector 14 and the reach-through implant 20 are more heavily doped than the collector 16.
• Atop the substrate 12 there is shown a suicide region 32 which is in contact with the reach-through implant region 20.
• Dielectric film 30 is also shown atop the substrate 12 and it is located atop the trench isolation regions 18.
• a base region 25 comprising, for example, doped poly Si, is located atop the substrate 12 as well.
• the base region 25 comprises a monocrystalline portion 26 over the Si-containing substrate 12, and a polycrystalline portion 27 over the trench isolation regions 18 and dielectric film 30.
• a suicide region 34 is also located atop the base region 25.
• FIG. 2 The reference numerals used in FIG. 2 are the same as those used in FIG. 1 therefore the elements depicted in the two-cathode design shown in FIG. 2 are the same as that described above in regard to FIG. 1.
• the hyperabrupt junction varactor of the prior art structure shown in FIG. 2 was also made using at least two critical masking levels. (PARA 9) In both prior art structures mentioned above, two critical masking levels are required to form the hyperabrupt dopant region.
• the present invention provides a semiconductor structure including a hyperabrupt junction and a compensated cathode contact.
• the hyperabrupt junction varactor of the inventive structure including the hyperabrupt junction is highly tunable, has a high Q and a linear CV curve.
• the cathode contact which is located in a region of a substrate adjacent the hyperabrupt junction, is compensated.
• 'compensated' it is meant that the cathode contact of the present invention has a high enough dopant concentration of one type to effectively counter dope an opposite type dopant.
• the inventive semiconductor structure comprises:
• PARA 12 a hyperabrupt junction located in an anode region of a semiconductor substrate
• PARA 13 at least one compensated cathode contact located adjacent to, yet isolated from, said hyperabrupt junction, said at least one compensated cathode provides a first conductivity type dopant region at a surface of a reach-through dopant region, said reach-through dopant region is in contact with an underlying first dopant region which is a subcollector and/or a cathode.
• the inventive semiconductor structure can be used as a substrate in
• CMOS and/or bipolar technologies in which one or more CMOS and/or bipolar devices are located thereon.
• the present invention also provides a method of fabricating such a structure in which a single masking level is used to form the hyperabrupt junction, the subcollector/cathode and the collector/well region.
• the present invention provides a method of fabricating a semiconductor structure, particularly a hyperabrupt junction varactor in CMOS or BiCMOS processing, that does not include the use of an epitaxial growth process, which is a common process used in fabricating prior art hyperabrupt junction varactors.
• the present invention provides a method of fabricating a hyperabrupt junction varactor that is vertical using a single implant mask to form the hyperabrupt junction, the subcollector/cathode and the collector/well region.
• the method of the present invention used in forming the inventive semiconductor structure comprises the steps of: (PARA 17) providing a semiconductor substrate including a plurality of isolation regions located therein, said plurality of isolation regions defining an anode region and at least one cathode region within said semiconductor substrate;
• PARA 19 forming a subcollector/cathode, a collector/well region and a hyperabrupt junction in said semiconductor substrate using a single implant mask, said hyperabrupt junction is located in both said anode and cathode regions;
• PARA 20 selectively implanting into the cathode region so as to convert the hyperabrupt junction located therein into a compensated cathode contact.
• the forming of the inventive hyperabrupt junction includes the implantation of the upper dopant region thereof which is performed at high enough doses to form a diode layer of the varactor, yet low enough to be compensated for in the cathode contact region.
• FIG. 1 is a pictorial representation (through a cross sectional view) illustrating a prior art structure including a hyperabrupt junction and a single cathode contact.
• FIG. 2 is a pictorial representation (through a cross sectional view) illustrating a prior art structure including a hyperabrupt junction and two cathode contacts or a wrap-around cathode contact.
• FIGS. 3A-3D are pictorial representations (through cross sectional views) illustrating the basic processing steps that are used in the present invention for fabricating a substrate that includes a hyperabrupt junction and a compensated cathode contact.
• FIG. 4 is a pictorial representation (through a cross sectional view) illustrating the substrate of FIG. 3D after silicidation of the exposed semiconductor regions.
• FIG. 5 is a pictorial representation (through a cross sectional view) illustrating a similar substrate as shown in FIG. 4 except that a single cathode contact is formed; this substrate is made using the same basic processing steps as shown in
• FIGS 3A-3D except that a single reach-through implant region is formed.
• the present invention which provides a semiconductor structure including a hyperabrupt junction varactor with a compensated cathode contact as well as a method of fabricating the same in which a single mask is used to form the subcollector/cathode, collector/well, and hyperabrupt junction, will now be described in greater detail by referring to the drawings that accompany the present application.
• the drawings of the present application are provided herein for illustrative purposes and they are thus not drawn to scale.
• FIGS. 3A-3D illustrate the basic process flow that is used in the present invention to form the one mask hyperabrupt junction varactor with a compensated cathode contact.
• FIG. 3A illustrates an initial structure 40 that can be used in the present invention.
• the initial structure 40 comprises a semiconductor substrate 42 having a plurality of isolation regions 44 formed therein.
• the semiconductor substrate 42 comprises any semiconductor material including, but not limited to: Si, SiGe, SiC, SiGeC, GaAs, InAs, InP, layered semiconductors such as Si/SiGe, Si/SiGeC, silicon-on-insulators (SOIs) and silicon germanium-on-insulators (SGOIs).
• the semiconductor substrate 42 comprises a Si-containing semiconductor such as Si.
• the plurality of isolation regions 44 may include trench isolation regions (as shown), or alternatively, the isolation regions 44 may comprise field oxide (FOX) isolation regions (not shown).
• the isolation regions 44 are formed utilizing techniques that are well known in the art. For example when the isolation regions 44 are FOX isolation regions, a conventional local oxidation of silicon process can be used. Alternatively when the isolation regions 44 are comprised of trench isolation regions, the trench isolation regions 44 are formed by lithography, etching and trench fill.
• the lithographic step includes applying a photoresist to the surface of the substrate 42, exposing the photoresist to a desired pattern of radiation and developing the exposed photoresist using a conventional resist developer.
• the etching step using in forming the trench isolation regions 44 comprises a dry etching process, such as, for example, reactive-ion etching, ion beam etching, plasma etching or laser ablation, or a wet etching process in which a chemical etchant is used.
• the trench fill process includes the deposition of a trench dielectric material such as an oxide.
• the formation of the trench isolation regions 44 may further include a densification and/or planarization process.
• the plurality of isolation regions 44 defines various regions of the substrate including cathode contact regions IOOA and IOOB and an anode region 102. Although showing two cathode contact regions, the inventive method also contemplates a structure that includes a single cathode contact region.
• PARA 32 Next, and as shown in FIG. 3B, a first dopant region 46 is formed into exposed portions of the substrate in the cathode contact regions IOOA and 10OB, for example.
• the first dopant region 46 may also be referred to as a reach-though dopant region.
• the first dopant region 46 i.e., reach-through dopant region, contains a first conductivity type dopant which can be either an n-type dopant or a p-type dopant.
• a first conductivity type dopant which can be either an n-type dopant or a p-type dopant.
• the first dopant region 46 contains an n-type dopant.
• PARA 33 The first dopant region 46 is formed by lithography and ion implantation. The ion implantation step is performed utilizing conventional ion implantation conditions that are well known to those skilled in the art.
• Typical conditions for forming the first dopant region 46 which includes an n-type dopant, such as As, Sb or P include, but are not limited to: selecting an ion dose from about 10 14 to about 10 16 atoms/cm 3 and an energy from about 20 to about 800 keV.
• This first dopant region 46 can be formed by utilizing standard CMOS FET wells or could also be formed by utilizing BiCMO S/Bipolar reach-through/shunt processing which is commonly practiced to electrically contact the subcollector of a bipolar device. (PARA 34)
• concentration of dopant within the first dopant region 46 various depending about the dose and type of ion employed.
• a typical concentration range for an n-type dopant within the first dopant region 46 is from about 10 18 to about 10 20 atoms/cm 3
• a typical concentration range for a p-type dopant within the first dopant region 46 is from about 10 18 to about 10 20 atoms/cm 3 .
• the implant mask used in forming the first dopant region 46 is then removed from the structure utilizing a conventional stripping process.
• Another implant mask (not shown) is then formed on the structure and is used in forming a second dopant region 48, a third dopant region 50, a fourth dopant region 52 and a fifth dopant region 54.
• the second dopant region 48 represents either a subcollector/cathode region
• the third dopant region 50 represents a collector/well region.
• the fourth dopant region 52 represents the lower dopant region of the hyper abrupt junction
• the fifth dopant region 54 denotes the upper dopant region of the hyperabrupt junction.
• FIG. 3 C shows the structure including these various dopant regions.
• the second dopant region 48, the third dopant region 50 and the fourth dopant region 52 each contain the same conductivity type dopant, e.g., first conductivity type dopant, as the first dopant region 46, while the fifth dopant region 54 includes a second conductivity dopant that is opposite to the first conductivity type.
• dopant regions 46, 48, 50 and 52 contain an n-type dopant, while region 54 contains a p-type dopant.
• the opposite doping configuration is also contemplated herein.
• the interface 53 formed between the fifth dopant region 54 and the fourth dopant region 52 forms the junction of the hyperabrupt junction varactor.
• the depth D2 of the second dopant region 48 is deeper than the depth D3 of the third dopant region 50, while the depth D3 of the third dopant region 50 is deeper than the depth D4 of the fourth dopant region 52, while the depth D4 of the fourth dopant region 52 is deeper than the depth D5 of the fifth dopant region 54. That is D2>D3>D4>D5.
• the second dopant region 48 is typically first formed, followed by the formation of the fourth dopant region 52 and the fifth dopant region 54; the third dopant region 50 forms during the forming of the second dopant region 52.
• the third dopant region 50 forms during the forming of the second dopant region 52.
• PARA 39 In particular, a photomask is applied to the surface of the structure shown in FIG. 3B utilizing a conventional deposition process. A lithographic process is then used to open the photomask over the entire structure.
• a second implant step is then performed to create the second dopant region (subcollector/cathode) 48 under the surface of the substrate 42 such that it is in contact with the first dopant region 46, i.e., reach-through implant region.
• the shallower tail of this second implant step effectively creates the third dopant region 50 atop the second dopant region 48, as shown in FIG. 3C.
• the second dopant region 48 is created by implanting a dopant of the first conductivity type, preferably n-type, into the structure using ion implantation conditions that are capable of forming a subcollector/cathode into the substrate 42.
• the ion implant conditions used in forming the second dopant region 48 may vary depending on the type of dopant ion used.
• an ion dose from about 5xlO 13 to about 10 15 atoms/cm 2 and an energy from about 300 to about 1500 keV is typically utilized.
• an ion dose from about 5xl0 13 to about 10 15 atoms/cm 2 and an energy from about 200 to about 800 keV is typically utilized.
• the concentration of dopants within the second dopant region 48 is dependent on the ion dose used during the implant.
• the second dopant region 48 has an n-type dopant concentration from about 10 18 to about 10 20 atoms/cm 3 .
• a typical concentration for a p-type dopant would be from about 10 18 to about 10 20 atoms/cm 3 .
• the second dopant region 48 has a higher doping concentration than the third dopant region 50, which is formed during this second implant step as well.
• the third dopant region 50 represents a shallower dopant tail of the second dopant region 48.
• the third dopant region 50 thus comprises the same conductivity type dopant as that of the second dopant 48 however, the third dopant region 50 has a lower dopant concentration than that of the second dopant region.
• the third dopant region 50 e.g., the collector or well region, has an n-type dopant concentration from about 10 17 to about 10 19 atoms/cm 3 .
• a typical p- type dopant concentration for the third dopant region 50 would be within the range from about 10 17 to about 10 19 atoms/cm 3 .
• the fourth dopant region 52 i.e., the lower dopant region of the hyperabrapt junction, is formed via ion implantation of a first conductivity dopant into the exposed portions of the substrate 42.
• the fourth dopant region 52 comprises an n-type dopant.
• the ion implantation step used in forming the fourth dopant region 52 includes an ion dose from about 10 3 to about 10 14 atoms/cm 2 and an energy from about 30 to about 300 keV depending on what dopant species is utilized.
• the implant conditions include an ion dose from about 10 13 to about 10 14 atoms/cm 2 and an energy from about 10 to about 300 keV.
• the fourth dopant region 52 is a heavily doped region as compared to the underlying third dopant region 50.
• the fourth dopant region 50 has an n-type dopant concentration from about 10 17 to about 10 19 atoms/cm 3 .
• a typical p-type dopant concentration for the fourth dopant region 52 would be within the range from about 10 17 to about 10 19 atoms/cm 3 .
• the fifth dopant region 54 e.g., the upper layer of the hyperabrapt junction, is formed by another implant step.
• the implant step used in forming the fifth dopant region 54 utilizes a second conductivity type dopant, which differs in conductivity from the first conductivity type dopant.
• the fifth dopant region 54 comprises a p-type dopant. The opposite dopant configuration is also contemplated.
• the implant conditions include an ion dose from about 5x10 14 to about 10 16 atoms/cm 2 and an energy from about 5 to about 30 keV.
• the implant conditions used in forming the fifth dopant region 54 include a dose from about 5xlO 14 to about 10 16 atoms/cm 2 and an energy from about 10 to about 150 keV.
• the concentration of second conductivity type dopant within the fifth dopant region 54 is typically from about 10 19 to about 10 21 atoms/cm 3 .
• a standard source/drain implant from CMOS FET processing with a first conductivity type dopant is performed which forms highly doped region 56 within the cathode regions IOOA, and IOOB, as shown.
• highly doped region it is meant a dopant region having a dopant concentration of about 10 20 atoms/cm 3 or greater.
• this implant compensates the fifth dopant region 54 at the surface of the first dopant region 46 creating a first conductivity type dopant region from the surface of first dopant region 46 down to the ) second dopant region 48, as is shown in FIG. 3D.
• the implant mask used in the highly doped region 56 is removed from the structure and thereafter suicide contacts 58 are formed utilizing a conventional silicidation process.
• the suicide contacts 58 are formed by depositing a metal that is capable of reacting with silicon on the surface of the structure shown in FIG. 3D.
• the metal used in forming the suicide comprises a conductive metal such as, for example, Ti, Ta, Ni, Co, W, Pd, Pt, Rh, Ir, Au and alloys thereof.
• a silicon-containing layer such as, for example, epi-Si, can be formed on the surface of the substrate prior to forming the metal.
• the metal is formed utilizing a conventional deposition process such as, for example, chemical vapor deposition, plasma enhanced chemical vapor deposition, sputtering, evaporation, atomic layer deposition, chemical solution deposition or other like processes.
• the thickness of the metal layer may vary and is not critical so long as it is sufficiently thick to cause suicide formation.
• the structure including the metal is then annealed under conditions which cause reaction between the metal and silicon and subsequent formation of a stable suicide that is in its lowest resistance phase.
• the suicide anneal may include a single anneal step, followed by an etching step that removes any non-reacted metal, or a two step anneal in which a second anneal, typically at higher temperatures than the first anneal, is performed.
• the conditions of the anneals i.e., time and temperature, may vary depending on the type of suicide to be formed and such conditions are well known to those skilled in the art.
• FIG. 4 shows the structure that is formed after the silicidation formation which forms suicide contacts 58 over the cathode regions IOOA and IOOB and the anode region 100.
• FIG. 5 shows a structure that is similar to the one depicted in FIG. 4 except that a single cathode contact is illustrated.
• PARA 47 The structures shown in FIGS. 4 or 5 can be used as a substrate in which one or more bipolar devices, CMOS devices or a combination thereof (BiCMOS devices) can be formed. The fabrication of these various devices is well known to those skilled in the art and thus the fabrication of CMOS and/or bipolar devices is not needed to be mentioned herein.

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• 2005
  • 2005-01-06 US US10/905,486 patent/US7518215B2/en not_active Expired - Lifetime
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