Patent Publication Number: US-2007108477-A1

Title: Semiconductor structure

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a semiconductor structure. More particularly, the present invention relates to a semiconductor structure that can prevent noise interference.  
      2. Description of the Related Art  
      In very large scale integration (VLSI) and ultra large scale integration (ULSI) circuits, distance between integrated circuits are getting closer and closer to each other. As a result of the capacitive coupling between neighboring integrated circuits, noises or cross talk signals are frequently produced. With the continual reduction in the feature size of integrated circuits, their critical dimension also get smaller. Therefore, the intensity of capacitive coupling and noise between neighboring integrated circuits will intensify.  
       FIG. 1  is a top view of a conventional semiconductor structure, and  FIG. 2  is a cross-sectional view along line A-A′ of  FIG. 1 . As shown in  FIGS. 1 and 2 , the P-type substrate  100  has a P-type well  102 , an integrated circuit region  104 , an isolation structure  106 , an N-type well  108  and an N-type deep well  110 . At present, the most commonly used design for isolating noise includes setting up a guard ring made from the N-type region  108  or utilizing the N-type deep well  110  underneath the integrated circuit region formed outside the integrated circuit region  106 .  
      However, operating at a frequency higher than 10 GHz, a junction capacitance between the N-type well  108  and the P-type well  102 , between the N-type deep well  110  and P-type substrate  100 , between the N-type well  108  and P-type substrate  100  and between the N-type deep well  110  and the P-type deep well  102  is easily formed. Therefore, the noise may couple with the integrated circuit region  106  through the junction capacitance produced by the P-type substrate  100 . Ultimately, this may cause an average increase in the noise level of the integrated circuit region  106  or lead to disturbances that can forestall the operation of the integrated circuit.  
     SUMMARY OF THE INVENTION  
      Accordingly, at least one objective of the present invention is to provide a semiconductor structure that can effectively keep out noise signals so that noise is prevented from infiltrating into an integrated circuit region.  
      At least a second objective of the present invention is to provide a semiconductor structure that can prevent an integrated circuit from subjecting to noise interference.  
      To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a semiconductor structure. The semiconductor structure comprises a first conductive type substrate, a first conductive type well, an integrated circuit region, an isolation structure and a second conductive type doped region is described. The first conductive type well is disposed in the first conductive type substrate. The integrated circuit region is disposed in the first conductive type well. The isolation structure is disposed in the first conductive type substrate around the integrated circuit region. The second conductive type doped region is disposed in the first conductive type substrate around the isolation structure.  
      According to one preferred embodiment of the present invention, the aforementioned semiconductor structure further includes a second conductive type well disposed in the first conductive type substrate around the isolation structure. Furthermore, the second conductive type doped region is disposed in the second conductive type well.  
      According to one preferred embodiment of the present invention, the second conductive type doped region of the aforementioned semiconductor structure has a dopant concentration higher than the second conductive type well.  
      According to one preferred embodiment of the present invention, the second conductive type doped region of the aforementioned semiconductor structure is electrically connected to a preset voltage.  
      According to one preferred embodiment of the present invention, the preset voltage for the aforementioned semiconductor structure includes a ground connection.  
      According to one preferred embodiment of the present invention, the isolation structure of the aforementioned semiconductor structure includes a shallow trench isolation (STI) structure.  
      The present invention also provides an alternative semiconductor structure. The semiconductor structure comprises a first conductive type substrate, a first conductive type well, an integrated circuit region, an isolation structure; a second conductive type doped region, a second conductive type well and a second conductive type deep well. The first conductive type well is disposed in the first conductive type substrate. The integrated circuit region is disposed on the first conductive type well. The isolation structure is disposed in the first conductive type substrate around the integrated circuit region. The second conductive type well is disposed in the first conductive type substrate around the isolation structure. The second conductive type doped region is disposed in the second conductive type well around the isolation structure. The second conductive type deep well is disposed in the first conductive type substrate under the first conductive type well and connected to the second conductive type well.  
      According to one preferred embodiment of the present invention, the second conductive type doped region in the aforementioned semiconductor structure has a dopant concentration greater than the second conductive type well.  
      According to one preferred embodiment of the present invention, the second conductive type doped region in the aforementioned semiconductor structure is electrically connected to a preset voltage.  
      According to one preferred embodiment of the present invention, the preset voltage for the aforementioned semiconductor structure includes a ground connection.  
      According to one preferred embodiment of the present invention, the isolation structure of the aforementioned semiconductor structure includes a shallow trench isolation (STI) structure.  
      In the present invention, the semiconductor structure has a guard ring built using the second conductive type doped region so that noise signals are effectively shielded from the integrated circuit region. Thus, the integrated circuit can operate in a stable state. In addition, the second conductive type doped region in the semiconductor structure of the present invention can keep out most of the noise signals so that the amount of noise reaching the integrated circuit region through junction capacitance coupling is reduced.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
       FIG. 1  is a top view of a conventional semiconductor structure.  
       FIG. 2  is a cross-sectional view along line A-A′ of  FIG. 1 .  
       FIG. 3  is a top view of a semiconductor structure according to one preferred embodiment of the present invention.  
       FIG. 4  is a cross-sectional view along line B-B′ of  FIG. 3 .  
       FIG. 5  is a top view of a semiconductor structure according to another preferred embodiment of the present invention.  
       FIG. 6  is a cross-sectional view along line C-C′ of  FIG. 5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
       FIG. 3  is a top view of a semiconductor structure according to one preferred embodiment of the present invention.  FIG. 4  is a cross-sectional view along line B-B′ of  FIG. 3 . As shown in  FIGS. 3 and 4 , the semiconductor structure comprises a first conductive type substrate  200 , a first conductive type well  202 , an integrated circuit region  204 , an isolation structure  206  and a second conductive type doped region  208 .  
      The first conductive type substrate  200  is a P-type silicon substrate, for example.  
      The first conductive type well  202  is disposed in the first conductive type substrate  200 . The first conductive type well  202  is a P-type well region, for example. The method of forming the first conductive type well  202  includes performing an ion implant process on the silicon substrate using boron as the dopants, for example.  
      The integrated circuit region  204  is disposed on the first conductive type well  202 . The integrated circuit region  204  is an area with patterned integrated circuit (not shown). The integrated circuits within the integrated circuit region  204  comprise circuit devices including resistors, capacitors, inductors or metal-oxide-semiconductor (MOS) transistors, for example. In fact, anyone familiar with the knowledge in this field should notice that the integrated circuits could be a memory circuit, a digital-to-analogue converter circuit or an analogue/digital converter circuit. Hence, a detailed description is omitted.  
      The isolation structure  206  is disposed in the first conductive type substrate  200  around the integrated circuit region  204  for isolating the integrated circuit region  204  and other semiconductor devices or integrated circuit regions on the first conductive type substrate  200 . The isolation structure  206  is a shallow trench isolation (STI) structure fabricated using silicon oxide material, for example.  
      The second conductive type doped region  208  is disposed in the first conductive type substrate  200  around the isolation structure  206 . The second conductive type doped region  208  is an N-doped region, for example. The second conductive type doped region  208  is formed, for example, by performing an ion implant process using phosphorus as the dopants. The second conductive type doped region  208  is electrically connected to a preset voltage and the preset voltage is a ground connection, for example.  
      In addition, a second conductive type well  210  may also be disposed in the first conductive type substrate  200 . Furthermore, the second conductive type well  210  surrounds the isolation structure  206 . The second conductive type well  210  is an N-type well region, for example. The method of forming the second conductive type well  210  includes performing an ion implant process using phosphorus as the dopants, for example. The second conductive type doped region  208  has a dopant concentration higher than the second conductive well  210 .  
      Because the semiconductor structure includes a guard ring formed from the second conductive type well  210  and another guard ring formed from the second conductive type doped region  208 , the integrated circuit region  204  is effectively protected against noise interference. Furthermore, the second conductive type doped region  208  provides a shield for most of the noise signals. Therefore, the coupling of noise to the integrated circuit region  206  through the junction capacitance produced by the first conductive type substrate  200  is minimized.  
       FIG. 5  is a top view of a semiconductor structure according to another preferred embodiment of the present invention.  FIG. 6  is a cross-sectional view along line C-C′ of  FIG. 5 . As shown in  FIGS. 5 and 6 , the semiconductor structure comprises a first conductive type substrate  300 , a first conductive type well  302 , an integrated circuit region  304 , an isolation structure  306 , a second conductive type doped region  308 , a second conductive type well  310  and a second conductive type deep well  312 .  
      The first conductive type substrate  300  is a P-type silicon substrate, for example.  
      The first conductive type well  302  is disposed in the first conductive type substrate  300 . The first conductive type well  302  is a P-type well region, for example. The method of forming the first conductive type well  302  includes performing an ion implant process on the silicon substrate using boron as the dopants, for example.  
      The integrated circuit region  304  is disposed on the first conductive type well  302 . The integrated circuit region  304  is an area with patterned integrated circuit (not shown). The integrated circuits within the integrated circuit region  304  comprise circuit devices including resistors, capacitors, inductors or metal-oxide-semiconductor (MOS) transistors, for example. In fact, anyone familiar with the knowledge in this field should notice that the integrated circuits could be a memory circuit, a digital-to-analogue converter circuit or an analogue/digital converter circuit. Hence, a detailed description is omitted.  
      The isolation structure  306  is disposed in the first conductive type substrate  300  around the integrated circuit region  304  for isolating the integrated circuit region  304  and other semiconductor devices or integrated circuit regions on the first conductive type substrate  300 . The isolation structure  306  is a shallow trench isolation (STI) structure fabricated using silicon oxide material, for example.  
      The second conductive type well  310  is disposed in the first conductive type substrate  300  around the isolation structure  306 . The second conductive type well  310  is an N-type well region, for example. The second conductive type well  310  is formed, for example, by performing an ion implant process using phosphorus as the dopants.  
      The second conductive type doped region  308  is disposed in the second conductive type well  310  around the isolation structure  306 . The second conductive type doped region  308  is an N-doped region, for example. The second conductive type doped region  208  has a dopant concentration higher than the second conductive type well  310 . The second conductive type doped region  308  is formed, for example, by performing an ion implant process using phosphorus as the dopants. The second conductive type doped region  308  is electrically connected to a preset voltage and the preset voltage is a ground connection, for example.  
      The second conductive type deep well  312  is disposed in the first conductive type substrate  300  under the first conductive type well  302  and electrically connected to the second conductive type well  310 . The second conductive type deep well  312  is an N-type deep well, for example. The second conductive type deep well  312  is formed, for example, by performing an ion implant process using phosphorus as the dopants.  
      Because the semiconductor structure includes a guard ring formed from the second conductive type well  310  and another guard ring formed from the second conductive type deep well  312  and the second conductive type doped region  308 , noise is virtually isolated and the infiltration of noise into the integrated circuit region  304  is effectively suppressed. Furthermore, the second conductive type doped region  308  provides a shield for most of the noise signals. Therefore, the coupling of noise to the integrated circuit region  306  through the junction capacitance produced by the first conductive type substrate  300  is minimized.  
      Although the first conductive type refers to a P-type and the second conductive type refers to an N-type in the aforesaid embodiment, anyone familiar with the technique in this field may notice that the reverse is equally applicable. In other words, the same method can be applied to form a semiconductor structure with the first conductive type being the N-type and the second conductive type being the P-type. Hence, a detailed description of this aspect of the invention not repeated.  
      In summary, major advantages of the present invention includes at least the followings.  
      1. Because the semiconductor structure of the present invention incorporates a guard ring fabricated through the second conductive type doped region, the integrated circuit is effectively shielded from against noise interference.  
      2. With the provision of an effective means of shielding the semiconductor structure against noise, the integrated circuit can operate in a more stable condition.  
      3. Since the second conductive type doped region can isolate most of the noise signals, noise coupled to the integrated circuit through the junction capacitance is significantly reduced.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.