Abstract:
A novel semiconductor device structure includes a first-conductivity-type semiconductor substrate, an isolated region, a first-conductivity-type MOS region, and a second-conductivity-type MOS region. A first-conductivity-type MOS transistor locates in the first-conductivity-type MOS region with a second-conductivity-type well surrounding, and a first-conductivity-type deep well surrounding the second-conductivity-type well with a second-conductivity-type deep well surrounding. In the second-conductivity-type MOS region, a second-conductivity-type MOS transistor is formed with a first-conductivity-type well surrounding. The first-conductivity-type deep well and the second-conductivity-type deep well are sufficiently reducing the noise and current leakage from other devices or from the semiconductor substrate.

Description:
BACKGROUND 
     A transistor s an element that is utilized extensively in semiconductor devices. There may be millions of transistors on a single integrated circuit (IC). A common type of transistor used in semiconductor device fabrication is a metal oxide semiconductor field effect transistor (MOSFET) with either P or N channel transistors. A complementary MOS (CMOS) devices use both positive and negative channel devices in complementary configurations. N-type metal oxide semiconductors (NMOS) are fabricated within P-type wells within a P-type substrate; P-type metal oxide semiconductors (PMOS) within N-type wells situated within the same P-type substrate. 
     With the increased density of devices and the combination of various types of circuitry, such as logic and radio frequency processing circuits, noise generated in the ICs becomes intense. Such noise is detrimental in the ICs because the integrity of a signal may be compromised, which causes a loss of data or errors in logic or signal processing. In CMOS structures, noise from other nearby devices would interfere with the circuit function, and substrate noise coupling is also an effect that is of concern because it can adversely affect the operation of various other devices. In this regard, transistors in the CMOS structures often require isolation from each other to prevent disturbance from unwanted noise. In the NMOS, deep N-wells surrounding the P-type wells region may be used to electrically shield the device against possible perturbations of noise from those devices. The P/N junction diodes formed between the deep N-well regions and the P-type substrate prevent current flow and the deep N-wells also act as an electrical potential shield. 
     However, Since N-type wells naturally reduce the noise disturbance from P-type substrate due to small nature P/N junction diodes, the P-type transistors located in the N-type wells still have higher noise disturbance from the P-type substrate than N-type transistors located in the P-type wells within the deep N-wells. The noise and leak current from substrate will have big impact on the operation of the CMOS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a cross-sectional view of a CMOS semiconductor structure according to various embodiments of the present disclosure. 
         FIG. 2  is a cross-sectional view of a CMOS semiconductor structure according to various embodiments of the present disclosure. 
         FIG. 3A-E  are cross-sectional views at various stages of manufacturing a CMOS semiconductor structure according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of semiconductor structures and a method for manufacturing the same of the present disclosure are discussed in detail below, but not limited the scope of the present disclosure. The same symbols or numbers are used to the same or similar portion in the drawings or the description. And the applications of the present disclosure are not limited by the following embodiments and examples which the person in the art can apply in the related field. 
     The singular forms “a,” “an” and “the” used herein include plural referents unless the context clearly dictates otherwise. Therefore, reference to, for example, a semiconductor well includes embodiments having two or more such semiconductor wells, unless the context clearly indicates otherwise. Reference throughout this specification to “one embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, the figures are intended; rather, these figures are intended for illustration. 
     Modern CMOS technology is capable of providing transistors having the capability of operating at frequencies of 1 GHZ or more. This enables CMOS to provide functionality in radio frequency (RF) communications. RF-CMOS semiconductor structures can be used for the detection, processing or transmission of radio waves or microwaves having a frequency range about 10 kHz to 1000 GHz. These circuits need to be made from high switching speed capable components operating usefully at radio wave. But noise disturbance from other devices and the semiconductor substrate can cause a loss of data or errors in logic or signal processing in the RF-CMOS semiconductor structures. Therefore, reducing the noise disturbance to promote the RF-CMOS semiconductor structures efficiency is important. 
     The general CMOS semiconductor structure includes a first-conductivity-type, e.g., an N-type or a P-type, semiconductor substrate and an isolated region separating the first-conductivity-type semiconductor substrate into a first-conductivity-type MOS region and a second-conductivity-type MOS region. Generally, the second-conductivity-type deep well in the second-conductivity-type MOS region reduces the noise and leak current from the semiconductor substrate into a second-conductivity-type MOS transistor. But in the first-conductivity-type MOS region, without the deep well protection, the transistor is still under noise disturbance propagation from the semiconductor substrate. 
     According to various embodiments of the present disclosure, a RF-CMOS transistor in a semiconductor substrate is provided to have low noise disturbance. Referring to  FIG. 1 , a RF-CMOS semiconductor structure  1000  includes a first-conductivity-type semiconductor substrate  1100 , and an isolated region  1200  separating the first-conductivity-type semiconductor substrate  1100  into a first-conductivity-type MOS region  1300  and a second-conductivity-type MOS region  1400 . The first-conductivity-type MOS region  1300  has a second-conductivity-type deep well  1310 , a first-conductivity-type deep well  1320 , a second-conductivity-type well  1330 , and a first-conductivity-type MOS transistor  1340 . The second-conductivity-type MOS region  1400  has a second-conductivity-type deep well  1410 , a first-conductivity-type well  1420 , and a second-conductivity-type MOS transistor  1430 . 
     The first-conductivity-type semiconductor substrate  1100  may be made of semiconductor material such as silicon, germanium, silicon germanium, silicon carbide, and those consisting essentially of III-V compound semiconductors (e.g., GaAs and Si/Ge). In embodiments, the first-conductivity-type semiconductor substrate  1100  is slightly doped with the first-conductivity-type dopants. 
     In embodiments, the isolated region  1200  is a shallow trench isolation (STI) structure. 
     The second-conductivity-type deep well  1410  in the second-conductivity-type MOS region  1400  has opposite conductivity type to the first-conductivity-type semiconductor substrate  1100 . Then any noise contributions from the first-conductivity-type semiconductor substrate  1100  cannot interfere with the signals of the second-conductivity-type MOS transistor  1430 . Because the P/N junction between the opposite conductivity type regions forms the diode protection shields noise disturbance. Where the P/N junction diode only permits the electrical flow from the P-type semiconductor into the N-type semiconductor. 
     A particular feature in the embodiments is that the RF-CMOS semiconductor structure  1000  also has a second-conductivity-type deep well  1310  in the first-conductivity-type MOS region  1300 , and furthermore a first-conductivity-type deep well  1320  within the second-conductivity-type deep well  1310 . Because the P/N junction diode forms between the regions with opposite conductivity type, there will form two P/N junction diodes. One is located at the interface between the first-conductivity-type semiconductor substrate  1100  and the second-conductivity-type deep well  1310 , and another is located at the interface between the first-conductivity-type deep well  1320  and the second-conductivity-type deep well  1310 . The P/N junction diodes insurance the first-conductivity-type MOS transistor  1340  against possible perturbations of noise from those devices outside it or from the first-conductivity-type semiconductor substrate  1100 . 
     In the first-conductivity-type MOS region  1300 , the P/N junction diode also forms between the second-conductivity-type well  1330  and the first-conductivity-type deep well  1320 . In the second-conductivity-type MOS region  1400 , the P/N junction diode also forms between the first-conductivity-type well  1420  and the second-conductivity-type deep well  1410 . The P/N junction diodes here enhance the noise reduction ability and to protect the sensitive transistors  1340  and  1430  within the well region. 
     The first-conductivity-type well  1420 , and the first-conductivity-type deep well  1320  may be lightly or intermediately doped with dopants of the first-conductivity-type. The dopant concentration may depend on the maximum voltage requirement of the RF-CMOS semiconductor structure  1000 . 
     The second-conductivity-type well  1330 , the second-conductivity-type deep well  1310  in the first-conductivity-type MOS region  1300 , and the second-conductivity-type deep well  1410  in the second-conductivity-type MOS region  1400  may be lightly or intermediately doped with dopants of the second-conductivity-type. The dopant concentration may depend on the maximum voltage requirement of the RF-CMOS semiconductor structure  1100 . 
     The first-conductivity-type MOS transistor  1340  also includes a first gate oxide layer  1342 , a first gate  1344 , a first-conductivity-type source  1346 , and a first-conductivity-type drain  1348 . 
     The second-conductivity-type MOS transistor  1430  also includes a second gate oxide layer  1432 , a second gate  1434 , a second-conductivity-type source  1436 , and a second-conductivity-type drain  1438 . 
     The first gate oxide layer  1342  is located above the second-conductivity-type well  1330  and the second gate oxide layer  1432  is located above the first-conductivity-type well  1420 . In embodiments, the gate oxide layers  1342  and  1432  are made of silicon dioxide, and having a thickness in a range of 10 to 5000 angstroms, depending on operating voltage of the first gate  1344  and the second gate  1434 . 
     The first gate  1344  and the second gate  1434  are respectively disposed on the first gate oxide layer  1342  and the second gate oxide layer  1432 . In embodiments, the first gate  1344  and the second gate  1434  are made of polysilicon. 
     The first-conductivity-type source  1346  and the first-conductivity-type drain  1348  are respectively within the second-conductivity-type well  1330  and on opposite sides of the first gate  1344 . The first-conductivity-type source  1346  and the first-conductivity-type drain  1348  are heavily doped with the first-conductivity-type dopants. 
     The second-conductivity-type source  1436  and the second-conductivity-type drain  1438  are respectively within the first-conductivity-type well  1420  and on opposite sides of the second gate  1434 . The second-conductivity-type source  1436  and the second-conductivity-type drain  1438  are heavily doped with the second-conductivity-type dopants. 
     In embodiments, the first-conductivity-type is an N-type and the second-conductivity-type is a P-type, or the first-conductivity-type is a P-type and the second-conductivity-type is an N-type. 
     In embodiments, N-type dopants such as arsenic, phosphorus, antimony or a combination thereof are used for doping N-type regions. And P-type dopants such as boron, gallium, indium or a combination thereof are used for doping P-type regions. 
       FIG. 2  is a cross-sectional view of a RF-CMOS semiconductor structure  2000  according to some embodiments of the present disclosure. Among the RF-CMOS semiconductor structure  2000 , the first-conductivity-type is an N-type and the second-conductivity-type is a P-type. The RF-CMOS semiconductor structure  2000  includes an N-type semiconductor substrate  2100 , and an isolated region  2200  separating the N-type semiconductor substrate  2100  into an NMOS region  2300  and a PMOS region  2400 . The NMOS region  2300  has a P-type deep well  2310 , an N-type deep well  2320 , a P-type well  2330 , and an NMOS transistor  2340 . The PMOS region  2400  has an N-type well  2410 , and a PMOS transistor  2420 . 
     The NMOS transistor  2340  also includes a gate oxide layer  2342 , a gate  2344 , an N-type source  2346 , and an N-type drain  2348 . And the PMOS transistor  2420  also includes a gate oxide layer  2422 , a gate  2424 , a P-type source  2426 , and a P-type drain  2428 . 
       FIGS. 3A-3E  are cross-sectional views at various stages of manufacturing the RF-CMOS semiconductor structure  1000  according to various embodiments of the present disclosure. To clarify description and avoid repetition, like numerals and letters used to describe the RF-CMOS semiconductor structure  1000  above are used for the various elements in the coming figures. Also, reference numerals described previously may not be described again in detail herein. 
     As shown in  FIG. 3A , a first-conductivity-type semiconductor substrate  1100  is provided, and an isolate region  1200  is formed to separated the first-conductivity-type semiconductor substrate  1100  into a first-conductivity-type MOS region  1300  and a second-conductivity-type MOS region  1400 . In embodiments, the isolated region  1200  is formed by a STI process sequence. In which, trench (commonly  200  to  500  nanometers deep) is etched into the first-conductivity-type semiconductor substrate  1100 , electrically passivated, (commonly by growing a thermal oxide layer on sidewalls of the trenches) and filled with insulating material, typically silicon dioxide. The method includes a high density plasma (HDP) process or an ozone based thermal chemical vapor deposition (CVD) process. 
     Continuing in  FIG. 3B , in the first-conductivity-type MOS region  1300 , a second-conductivity-type deep well  1310 , a first-conductivity-type deep well  1320 , and a second-conductivity-type well  1330  are then formed therein. On the other side, a second-conductivity-type deep well  1410  and a first-conductivity-type well  1420  are formed in the second-conductivity-type MOS region  1400 . 
     In embodiments, the first-conductivity-type well  1420  and the first-conductivity-type deep well  1320  are formed by implanting dopants of the first-conductivity-type in selective areas of the first-conductivity-type semiconductor substrate  1100 . The second-conductivity-type well  1330  and the second-conductivity-type deep wells  1310  and  1410  are formed by implanting dopants of the second-conductivity-type in another selective areas of the first-conductivity-type semiconductor substrate  1100  prior or next to the step of forming the first-conductivity-type well  1420  and the first-conductivity-type deep well  1320 . 
     Referring now to  FIG. 3C , an oxide layer  3100  is formed covering the surface of the first-conductivity-type semiconductor substrate  1100  by thermally grown or deposition. Then a gate material layer  3200  is formed covering the surface of the oxide layer  3100  by low pressure chemical vapor deposition (LPCVD). 
     Continuing in  FIG. 3D , a first gate oxide layer  1342  is formed above the second-conductivity-type well  1330  and a second gate oxide layer  1432  is formed above the first-conductivity-type well  1420 . A first gate  1344  and a second gate  1434  are formed respectively on the first gate oxide layer  1342  and on the second gate oxide layer  1432 . In embodiments, the first gate oxide layer  1342 , the second gate oxide layer  1432 , the first gate  1344 , and the second gate  1434  are formed with the method of selectively etching the oxide layer  3100  and the gate material layer  3200  region which without photoresist protection. 
     As shown in  FIG. 3E , a first-conductivity-type source  1346  and a first-conductivity-type drain  1348  are formed on opposite sides of the first gate  1344 , and a second-conductivity-type source  1436  and a second-conductivity-type drain  1438  are formed on opposite sides of the second gate  1434  by any conventional method. In embodiments, an ion implantation process is performed by implanting the first-conductivity-type dopants into the selective areas within the second-conductivity-type well  1330 , and implanting the second-conductivity-type dopants into the selective areas within the first-conductivity-type well  1420 . 
     The embodiments of the present disclosure discussed above have advantages over existing structures and methods, and the advantages are summarized below. In various embodiments, the second-conductivity-type deep well  1310  and the first-conductivity-type deep well  1320  in the first-conductivity-type MOS region  1300  increasingly reduce the noise disturbance from the first-conductivity-type semiconductor substrate  1100 , which protect the first-conductivity-type MOS transistor  1340  in the first-conductivity-type MOS region  1300 . The P/N junction diodes forming at the interface between the opposite conductivity type region resist the unwanted noise and leak current from other devices, or the semiconductor substrate. It will be helpful for noise reduction and improve the signal noise (SN) ratio on sensitive RF-CMOS semiconductor structures. 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.