Patent Publication Number: US-11641739-B2

Title: Semiconductor non-volatile memory devices

Description:
FIELD OF THE INVENTION 
     The disclosed subject matter relates generally to semiconductor devices, and more particularly to semiconductor non-volatile memory devices and methods of forming the same. 
     BACKGROUND 
     Memory devices are widely used in semiconductor devices and can be generally divided into volatile memory devices and non-volatile memory (NVM) devices. Volatile memory devices require a supply of electric power to retain stored information but lose the information when the supply of electric power is interrupted. NVM devices, on the other hand, retain the stored information even without a supply of electric power. 
     NVM devices may be operated by employing a charge retention mechanism to store information such as, but not limited to, a charge storage mechanism or a charge trapping mechanism. For example, charges may be stored in a floating gate structure during a program operation and charges may be expelled from the floating gate structure during an erase operation of an NVM device. 
     As the semiconductor industry continues to progress, it is desirable to provide NVM devices having optimized performance and methods of forming the same. 
     SUMMARY 
     To achieve the foregoing and other aspects of the present disclosure, non-volatile memory (NVM) devices and methods of forming the same are presented. 
     According to an aspect of the present disclosure, a memory device is provided. The memory device includes an active region in a substrate, an electrically-isolated electrode, and a dielectric layer. The electrically-isolated electrode is disposed over the active region. The dielectric layer is disposed between the electrically-isolated electrode and the active region and has a first dielectric portion having a first thickness and a second dielectric portion having a second thickness. 
     According to another aspect of the present disclosure, a memory device is provided. The memory device includes a first and a second active region in a substrate, an isolation region, a first and a second electrically-isolated electrode, and a dielectric layer. The isolation regions are disposed between the first and second active regions. The first electrically-isolated electrode is disposed over the first active region and the second electrically-isolated electrode is disposed over the second active region. The dielectric layer is disposed between the first electrically-isolated electrode and the first active region and has a first dielectric portion having a first thickness and a second dielectric portion having a second thickness. 
     According to yet another aspect of the present disclosure, a method of fabricating a memory device is provided. The method includes forming a first active region and a second active region in a substrate and forming a dielectric layer over the first and second active regions. The dielectric layer has a first dielectric portion of a first thickness and a second dielectric portion of a second thickness. A first electrically-isolated electrode and a second electrically-isolated electrode are formed over the first and second active regions, respectively, and the first and the second electrically-isolated electrodes are electrically coupled to define a floating gate for the memory device 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the present disclosure will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawings: 
         FIG.  1    is a cross-sectional view of a non-volatile memory (NVM) device, according to an embodiment of the disclosure. 
         FIG.  2    is a cross-sectional view of a non-volatile memory (NVM) device, according to another embodiment of the disclosure. 
         FIGS.  3 A to  3 D  are cross-sectional views of a non-volatile memory (NVM) device, illustrating various stages of forming the NVM device, according to embodiments of the disclosure. 
     
    
    
     For simplicity and clarity of illustration, the drawings illustrate the general manner of construction, and certain descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the device. Additionally, elements in the drawings are not necessarily drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help improve understanding of embodiments of the device. The same reference numerals in different drawings denote the same elements, while similar reference numerals may, but do not necessarily, denote similar elements. 
     DETAILED DESCRIPTION 
     The present disclosure relates to semiconductor non-volatile memory (NVM) devices having optimized performance and methods of forming the same. Various embodiments of the present disclosure are now described in detail with accompanying drawings. It is noted that like and corresponding elements are referred to by the use of the same reference numerals. The embodiments disclosed herein are exemplary, and not intended to be exhaustive or limiting to the disclosure. 
       FIG.  1    is a cross-sectional view of an NVM device  100 , according to an embodiment of the disclosure. The NVM device  100  may be arranged in a memory cell region of a semiconductor device and the NVM device  100  may be part of a plurality of NVM devices arranged in an array configuration of rows and columns in the memory cell region. Only one NVM device is illustrated for clarity purposes. In an embodiment of the disclosure, the NVM device  100  may be a multi-time-programmable (MTP) NVM device or a flash memory cell having a floating gate. 
     The NVM device  100  may include a plurality of active regions in a substrate (not shown). The plurality of active regions may have different dopant conductivity types, such as P-type or N-type conductivity, as well as different dopant depths and different dopant concentrations. P-type conductivity dopants may include, but not limited to, boron, aluminum, or gallium. N-type conductivity dopants may include, but not limited to, arsenic, phosphorus, or antimony. The dopant concentrations and/or dopant depths in the substrate, for example, may vary depending on the technology node and design requirements for the NVM device  100 . 
     The plurality of active regions may include a first active region  102   a  having a first conductivity type and a second active region  102   b  having a second conductivity type in a substrate (not shown). The first active region  102   a  may be disposed laterally adjacent to the second active region  102   b . In an embodiment of the disclosure, the first active region  102   a  may be of P-type conductivity and the second active region  102   b  may be of N-type conductivity. 
     The NVM device  100  may include a field-effect transistor (FET)  104  formed in the first active region  102   a . The FET  104  may further include a first doped region  106   a , a second doped region  106   b , a first electrode  108 , a dielectric layer  112 . The first doped region  106   a  and the second doped region  106   b  may be disposed in the first active region  102   a  at opposing sides of the first electrode  108 , such that the first doped region  106   a  and the second doped region  106   b  define a channel  110  therebetween. In an embodiment of the disclosure, the first and second doped regions ( 106   a  and  106   b , respectively) may be of N-type conductivity. In another embodiment of the disclosure, the first doped region  106   a  may serve as a drain region of the FET  104  and the second doped region  106   b  may serve as a source region of the FET  104 . 
     The NVM device  100  may further include a capacitor  114  formed in the second active region  102   b . The capacitor  114  may further include a second electrode  116  and at least one doped region  106   c . The at least one doped region  106   c  may be disposed in the second active region  102   b  that is adjacent to the second electrode  116 . In an embodiment of the disclosure, the at least one third doped region  106   c  may be of N-type conductivity. 
     The dielectric layer  112  may be disposed over the first and second active regions ( 102   a  and  102   b , respectively). The dielectric layer  112  over the first active region  102   a  separates the first electrode  108  from the first active region  102   a  and the dielectric layer over the second active region  102   b  separates the second electrode  116  from the second active region  102   b . In an embodiment of the disclosure, the dielectric layer  112  is formed of silicon dioxide. As will be appreciated by those skilled in the art, other suitable dielectric materials known in the art may be also applicable to the embodiments disclosed herein. 
     The first electrode  108  of the FET  104  and the second electrode  116  of the capacitor  114  may be electrically isolated electrodes and they may be electrically coupled together to define a floating gate  118 ; the electrical coupling indicated generally by a line. A floating gate is an electrically-isolated gate structure that serves as charge storage for an NVM device. The electrical coupling between the first electrode  108  and the second electrode  116  may serve to balance the two electrodes in the same potential while each of them varies in voltage levels. In an embodiment of the disclosure, the first electrode  108  and the second electrode  116  may be formed of polycrystalline silicon. 
     Although not shown in the accompanying drawings, isolation regions may be provided for isolating or separating the FET  104  from the capacitor  114  and the NVM device  100  from neighboring conductive features. For example, the isolation regions may include shallow trench isolation (STI) regions, deep trench isolation (DTI) regions, or the like. Additionally, it is understood that other features, such as sidewall spacers, lightly doped diffusion (LDD) regions, and silicidation may be further applied to the NVM device  100 . 
     An NVM device may be programmed by utilizing a hot carrier injection (HCI) mechanism and may be erased by utilizing a Fowler-Nordheim (FN)-tunneling mechanism. In order to increase the performance of the NVM device during a program operation, it is desirable to increase the coupling ratio of the NVM device. 
     Coupling ratio is one of the factors that affect the program performance of an NVM device. The term “coupling ratio” as used herein refers to the ratio of the capacitance of the control gate C CG  to the total capacitance C TOTAL  of the NVM device. The C TOTAL  of the NVM device is a summation of the capacitance between all terminals of the NVM device and the floating gate, including the capacitance between the control gate and the floating gate C CG , between the source terminal and the floating gate C s , between the drain terminal and the floating gate C d , and between the substrate and the floating gate C b . The coupling ratio of an NVM device affects both the operating voltage and the device operating speed. Generally, a high coupling ratio advantageously enables usage of lower operating voltage while maintaining a comparable device operating speed, thereby achieving an optimized program performance of the NVM device and improving the device margin of the NVM device. The coupling ratio of the NVM device may be increased by decreasing the capacitative coupling between the floating gate and the first active region; achievable by increasing the thickness of the dielectric layer therebetween. 
     However, the thicker dielectric layer potentially renders an erase operation ineffective. The electric field necessary for an effective FN-tunneling mechanism to function may not be sufficient to repel the charges from the floating gate to the active region through the thicker dielectric layer. 
     Therefore in order to balance the program and erase performances of using a thicker dielectric layer, the dielectric layer  112  may have different thicknesses. As illustrated in  FIG.  1   , the dielectric layer  112  has a first dielectric portion  112   a  having a first dielectric thickness and a second dielectric portion  112   b  having a second dielectric thickness. In an embodiment of the disclosure, the second portion of the dielectric layer  112   b  is thinner than that of the first portion of the dielectric layer  112   a . In another embodiment of the disclosure, the dielectric layer  112  of the FET  104  has the second portion of the dielectric layer  112   b  may be arranged adjacent to the second doped region  106   b . In yet another embodiment of the disclosure, the dielectric layer  112  of the capacitor  114  has the second portion of the dielectric layer  112   b  arranged between the second electrode  116  and the second active region  102   b.    
     The dielectric layer  112 , having different dielectric thicknesses, advantageously optimizes the program and erase performances of the NVM device  100 . The first portion of the dielectric layer  112   a , being relatively thicker, reduces the capacitive coupling of the first electrode  108  to the first active region  102   a , thereby increasing the coupling ratio of the FET  104  and achieving an optimized program operation performance. Additionally, the second portion of the dielectric layer  112   b , being relatively thinner, maintains the effectiveness of an erase operation. 
     Although it is illustrated in  FIG.  1    that the first and second portions of the dielectric layer ( 112   a  and  112   b , respectively) as having substantially similar lengths at the first active region  102   a , it is understood that the lengths of the first and second portions of the dielectric layer ( 112   a  and  112   b , respectively) may not be the same at the first active region  102   a . In an embodiment of the disclosure, it is preferably that the length of the first portion of the dielectric layer  112   a  is longer than that of the second dielectric portion  112   b  at the first active region  102   a . Having a greater proportion of a thicker dielectric layer advantageously lowers the capacitive coupling of the NVM device  100  to substrate and drain even further, thereby further improving the coupling ratio of the NVM device  100 . 
     In an embodiment of the disclosure, the first portion of the dielectric layer  112   a  has a dielectric thickness of approximately 250 Å. In another embodiment of the disclosure, the second portion  112   b  of the dielectric layer has a dielectric thickness of at least 80 Å. In yet another embodiment, the first portion of the dielectric layer  112   a  may have a dielectric thickness of no more than three times the thickness of the second dielectric portion  112   b.    
     As illustrated in  FIG.  1   , a plurality of terminals may be connected to the NVM device  100 . In an embodiment of the disclosure, a first operating voltage V 1  may be supplied to a first terminal to bias the first doped region  106   a , a second operating voltage V 2  may be supplied to a second terminal to bias the second doped region  106   b , and a third operating voltage V 3  may be supplied to a third terminal to bias the third doped region  106   c . The third terminal may electrically couple the second active region  102   b  to capacitively bias the second electrode  116 . In an embodiment of the disclosure, the third operating voltage V 3  may be supplied by a control gate of the NVM device  100 . 
     The first, second, and third operating voltages may be provided by on-chip or external circuitry, or a combination thereof, as will be appreciated by those skilled in the art. 
       FIG.  2    is a cross-sectional view of an NVM device  200 , according to another embodiment of the disclosure. The NVM device  200  may be arranged in a memory cell region of a semiconductor device and the NVM device  200  may be part of a plurality of NVM devices arranged in an array configuration of rows and columns in the memory cell region. Only one NVM device is illustrated for clarity purposes. In an embodiment of the disclosure, the NVM device  200  may be a multi-time-programmable (MTP) NVM device or a flash memory cell having a floating gate. 
     Similarly to the embodiment of NVM device  100  in  FIG.  1   , the NVM device  200  may include a FET  204  and a capacitor  214  arranged over a first active region  202   a  and a second active region  202   b , respectively. 
     The FET  204  may include a first electrode  208 , a first doped region  206   a , a second doped region  206   b , and a dielectric layer  212 ; the dielectric layer  212  separates the first electrode  208  from the first active region  202   a . The first doped region  206   a  and the second doped region  206   b  are spaced apart defining a channel  210  therebetween and are disposed at opposite sides of the first electrode  208 . 
     The capacitor  214  may include a second electrode  216 , at least one third doped region  206   c , and the dielectric layer  212  separating the second electrode  216  from the second active region  202   b . The first electrode  208  of the FET  204  may be electrically coupled to the second electrode  216  of the capacitor  214  to define a floating gate  218 ; the electrical coupling indicated generally by a line. 
     The dielectric layer  212  of the FET  204  may also have different thicknesses, similar to the dielectric layer  112  in the embodiment of NVM  100  in  FIG.  1   . The dielectric layer  212  may have a first dielectric portion  212   a  having a first thickness, a second dielectric portion  212   b  having a second thickness, and a third dielectric portion  212   c  having a third thickness, such that the second dielectric portion  212   b  may be disposed between the first and third portions of the dielectric layer ( 212   a  and  212   c , respectively). In an embodiment of the disclosure, the third thickness may be substantially equal to the first thickness. In other embodiments of the disclosure the third thickness may be a different thickness from the first and second thicknesses. 
     In this embodiment of the disclosure, the first and third portions of the dielectric layer ( 212   a  and  212   c , respectively) decrease the capacitive coupling of the first electrode  208  to the first active region  202   a  for an optimized program operation of the NVM device  200  using HCI mechanism. The second portion of the dielectric layer  212   b , being relatively thinner, advantageously provides an effective erase operation of the NVM device using the FN-tunneling mechanism. 
       FIGS.  3 A to  3 C  are cross-sectional views of the NVM device  100 , illustrating a method of forming the NVM device  100 , according to embodiments of the disclosure. Certain structures may be conventionally fabricated, for example, using known processes and techniques, and specifically disclosed processes and methods may be used to achieve individual aspects of the present disclosure. 
     As illustrated in  FIG.  3 A , a first active region  102   a  and a second active region  102   b  may be provided in a substrate (not shown). The first and second active regions ( 102   a  and  102   b , respectively) may be regions defined to form a FET  104  and a capacitor  114 , respectively, for the NVM device  100 . The first active region  102   a  and the second active region  102   b  may be formed by introducing dopants into the substrate. 
     A dielectric layer  112  may be deposited over the first and second active regions ( 102   a  and  102   b , respectively). The dielectric layer  112  may be deposited using various deposition techniques such as, but not limited to, chemical vapor deposition (CVD) or plasma-enhanced CVD. In an embodiment of the disclosure, the dielectric layer  112  may be deposited to a thickness of approximately 250 Å. 
       FIG.  3 B  illustrates the NVM device  100  after patterning the dielectric layer  112 , according to an embodiment of the disclosure. The dielectric layer  112  may be patterned using various patterning techniques such that portions of the dielectric layer  112  may be removed, leaving a first portion of the dielectric layer  112   a  over the first active region  102   a.    
     As used herein, “patterning techniques” include deposition of patterning material or photoresist, patterning, exposure, development, etching, cleaning, and/or removal of the patterning material or photoresist as required in forming a described pattern, structure or opening. Exemplary examples of techniques for patterning include, but not limited to, wet etch lithographic processes, dry etch lithographic processes, or direct patterning processes. Such techniques may use mask sets and/or mask layers. 
     The deposition of the dielectric layer and the patterning of the first portion of the dielectric layer  112   a , as described above in  FIGS.  3 A and  3 B , may be performed concurrently with other active devices, such as transistors in other regions of the semiconductor device, having similar dielectric thicknesses. No additional patterning mask or layer is required to specifically pattern the first portion of the dielectric layer  112   a.    
       FIG.  3 C  illustrates the NVM device  100  after forming a second portion of the dielectric layer  112   b , according to an embodiment of the disclosure. A layer of dielectric material may be deposited to form the second portion of the dielectric layer  112   b . The second portion of the dielectric layer  112   b  may be deposited over the first active region  102   a  adjacent to the first portion of the dielectric layer  112   a  and the second active region  102   b . The second portion of the dielectric layer  112   b  may share a patterning mask or layer with other active devices having similar dielectric thicknesses, such as transistors, in other regions of the semiconductor device and may be fabricated concurrently with those active devices. 
     In an embodiment of the disclosure, the first portion of the dielectric layer  112   a , among other regions, may be protected with a layer of material, such as a patterning layer or a photoresist layer, such that the second layer of dielectric material may not be deposited over the first portion of the dielectric layer  112   a . The first and second portions of the dielectric layer ( 112   a  and  112   b , respective) form the dielectric layer  112  the NVM device  100 . 
     The second portion of the dielectric layer  112   b  may be deposited to a thickness that is thinner than the first dielectric portion  112   a . In an embodiment of the disclosure, the second portion of the dielectric layer  112   b  may be deposited to a thickness of about 80 Å. In another embodiment, the second portion of the dielectric layer  112   b  may be deposited to a thickness of no less than one-third of that of the first portion  112   a . In an embodiment of the disclosure, the dielectric layer  112  includes silicon dioxide. 
       FIG.  3 D  illustrates the NVM device  100  after forming a first electrode  108  and a second electrode  116 , according to an embodiment of the disclosure. A layer of conductive material may be deposited over the first active region  102   a  and the second active region  102   b , covering the dielectric layer  112 . The layer of conductive material may be patterned using various patterning techniques to form the first electrode  108  over the first active region  102   a  and the second electrode  116  over the second active region  102   b . The first electrode  108  in the first active region  102   a  and the second electrode  116  in the second active region  102   b  may be coupled together to define a floating gate  118 ; the electrical coupling indicated generally by a line. In an embodiment of the disclosure, the layer of conductive material may include polycrystalline silicon. 
     The NVM device  100  may undergo further fabrication steps to form a FET  104  and a capacitor  114 . A plurality of doped regions, similar to the embodiment NVM device  100  illustrated in  FIG.  1   , may be fabricated. A first doped region  106   a  and a second doped region  106   b  may be disposed at opposite sides of the first electrode  108  forming a channel  110  therebetween the first and second doped regions ( 106   a  and  106   b , respectively). At least one third doped region  106   c  may be disposed adjacent to the second electrode  116   
     It is understood that other fabrication steps such as, but not limited to, forming contact structures, depositing interlayer dielectric layers, and forming interconnect structures may be further performed to the NVM device  100 . 
     As presented above, various embodiments of an NVM device having different thicknesses of a dielectric layer have been described. The NVM device may be arranged in a memory cell region of a semiconductor device and the NVM device may be part of a plurality of NVM devices arranged in an array configuration of rows and columns in the memory cell region. 
     The dielectric layer, having different dielectric thicknesses, advantageously optimized the performance of the NVM device  100 . The thicker portion of the dielectric layer improves the coupling ratio of the NVM device for an optimized program operation using the HCI mechanism, while the thinner portion of the dielectric layer enables an effective erase operation using FN-tunneling mechanism. The dielectric thicknesses may be adjusted accordingly to achieve the desired performance of an NVM device. 
     The NVM device may be operated by applying appropriate operating voltages. Memory access operations may include a program operation, an erase operation, or a read operation. As the floating gate is inherently an electrically isolated gate structure, the voltage may be supplied to the floating gate through a capacitively-coupled control gate. 
     Table 1 below shows a set of exemplary voltages that may be supplied to an NVM device for the different memory access operations. It is understood that other suitable types of voltage values may be supplied, depending on the design and technology node of the NVM device. Programming and erasing NVM devices have known techniques in the art. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Drain 
                 Source 
                 Control 
                   
               
               
                   
                 Region 
                 Region 
                 Gate 
               
               
                   
                 (V 1 ) 
                 (V 2 ) 
                 (V 3 ) 
                 Substrate 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Program Operation 
                 4 V 
                 ~9 V 
                 ~9 V 
                 0 V 
               
               
                 Erase Operation 
                 0 V 
                 ~9 V 
                  0 V 
                 0 V 
               
               
                 Read Operation 
                 1.2 V     
                  0 V 
                 ~1 V to 3.5 V 
                 0 V 
               
               
                   
               
            
           
         
       
     
     The terms “top”, “bottom”, “over”, “under”, and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the devices described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. 
     Additionally, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. 
     Similarly, if a method is described herein as involving a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise”, “include”, “have”, and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or device that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or device. Occurrences of the phrase “in an embodiment” herein do not necessarily all refer to the same embodiment. 
     In addition, unless otherwise indicated, all numbers expressing quantities, ratios, and numerical properties of materials, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. 
     While several exemplary embodiments have been presented in the above detailed description of the device, it should be appreciated that a number of variations exist. It should further be appreciated that the embodiments are only examples, and are not intended to limit the scope, applicability, dimensions, or configuration of the device in any way. Rather, the above detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the device, it being understood that various changes may be made in the function and arrangement of elements and method of fabrication described in an exemplary embodiment without departing from the scope of this disclosure as set forth in the appended claims.