Patent Publication Number: US-2022230909-A1

Title: Method for making deep trench isolation of cis device, and semiconductor device structure

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority to Chinese patent application No. CN 202110075783.X filed at CNIPA on Jan. 20, 2021, and entitled “METHOD FOR MAKING DEEP TRENCH ISOLATION OF CIS DEVICE, AND SEMICONDUCTOR DEVICE STRUCTURE”, the disclosure of which is incorporated herein by reference in entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of semiconductor manufacturing, in particular to a method for making a deep trench isolation of a CIS device, and a semiconductor device structure. 
     BACKGROUND 
     A CIS (CMOS Image Sensor) is a device that converts optical signals into electrical signals. 
     The light sensitivity of CIS devices is related to the size of a pixel region. The space of photodiodes is expanded vertically to improve the light sensitivity in a small pixel region. A method known to the inventors, in a CIS device manufacturing process, a pixel region is defined by a photolithography process, and then the pixel region is formed by an ion implantation process. 
     However, the inventors realized that the photolithography process is limited by the depth-to-width ratio of the photoresist and the ion implantation process is limited by ion implantation depth and concentration during a small pixel region manufacturing process. 
     SUMMARY 
     According to some embodiments in this application, a method for making a deep trench isolation of a CIS device is disclosed in the following steps: growing a first epitaxial layer on a substrate, and the conductive type of the first epitaxial layer being N type; forming a hard mask layer on the surface of the first epitaxial layer; performing photolithography and etching processes to form deep trenches arranged longitudinally and transversely in the first epitaxial layer; forming a second epitaxial layer in the deep trenches, sidewalls and bottoms of the deep trenches being completely covered by the second epitaxial layer, and the conductive type of the second epitaxial layer being P type; performing a thermal oxidation process to form a first oxide layer with a predetermined thickness on the surface of the second epitaxial layer in the deep trenches; completely filling the deep trenches with a polysilicon; performing a back-etching process to the substrate to expose sidewalls of the first oxide layer in the deep trenches; forming a second oxide layer on the top of the polysilicon in the deep trenches; removing the hard mask layer on the surface of the substrate and the first oxide layer above the second oxide layer; rapidly growing a third epitaxial layer, the third epitaxial layer covering tops of the deep trenches, and the conductive type of the third epitaxial layer being P type; performing a CMP process to form a deep trench isolation on the substrate. 
     A semiconductor device structure is manufactured in a process with the CIS devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of a method for making a deep trench isolation of a CIS device, according to one or more embodiments of the present application. 
         FIG. 2  shows the device cross sectional view after the first epitaxial layer is formed on the substrate. 
         FIG. 3  shows the device cross sectional view after the hard mask is formed on the device. 
         FIG. 4  shows the device cross sectional view after deep trenches formed in the first epitaxial layer, according to one or more embodiments of the present application. 
         FIG. 5  shows the device top view after deep trenches formed in the first epitaxial layer, according to one or more embodiments of the present application. 
         FIG. 6  shows the device cross sectional view after the second epitaxial layer is formed, according to one or more embodiments of the present application. 
         FIG. 7  shows the device cross sectional view after the first oxide layer is formed, according to one or more embodiments of the present application. 
         FIG. 8  shows the device cross sectional view after the polysilicon is deposited, according to one or more embodiments of the present application. 
         FIG. 9  shows the device cross sectional view after the back-etching process, according to one or more embodiments of the present application. 
         FIG. 10  shows the device cross sectional view after the second oxide layer is formed on the top of the polysilicon in the deep trenches, according to one or more embodiments of the present application. 
         FIG. 11  shows the device cross sectional view after the hard mask layer and the first oxide layer above the second oxide layer are removed, according to one or more embodiments of the present application. 
         FIG. 12  shows the device cross sectional view, according to one or more embodiments of the present application. 
     
    
    
     Reference numbers in the drawings are listed in the following:
           11 : substrate;  12 : first epitaxial layer;  13 : hard mask layer;  14 : deep trench;  15 : transverse deep trench;  16 : longitudinal deep trench;  17 : cross region of transverse deep trench and longitudinal deep trench;  18 : second epitaxial layer;  19 : first oxide layer;  21 : polysilicon;  22 : second oxide layer;  23 : third epitaxial layer.       

     DETAILED DESCRIPTION 
     The technical solutions in this application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the application, instead of all them. Based on the embodiments in the present application, all other embodiments obtained by one skilled in the art without contributing any inventive labor shall fall into the protection scope of the present application. 
     In the description of this application, it should be noted that the orientation or positional relationship indicated by the terms “center”, “upper”, “lower”, “left”, “right”, “vertical”, “horizontal”, “inside”, “outside”, or the like is based on the orientation or positional relationship shown in the drawings, is only for the convenience of describing this application and simplified description, and does not indicate or imply that the indicated device or element must have a specific orientation or be configured and operated in a specific orientation. Therefore, the orientation or positional relationship should not be construed as limitations on the present application. In addition, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed to indicate or imply relative importance. 
     In the description of this application, it should be noted that the terms “installation”, “connected”, and “connection” should be understood in a broad sense, unless explicitly stated and defined otherwise, for example, they may be fixed connection or removable connection, or integral connection; can be mechanical or electrical connection; can be direct connection, or indirect connection through an intermediate medium, or the internal communication of two elements, and can be wireless or wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood in specific situations. 
     In addition, the technical features involved in the different implementations of the present application described below can be combined with each other as long as they do not conflict with each other. 
     One or more embodiments of the present application provides a method for making a deep trench isolation of a CIS device, including the following steps illustrated in  FIG. 1 . 
     In step  101 , a first epitaxial layer is grown on a substrate. 
     The first epitaxial layer is a first conductive type, and the conductive type of the first epitaxial layer is N type. 
     Referring to  FIG. 2 , a first epitaxial layer  12  is grown on a substrate  11 . 
     The thickness and doping concentration of the first epitaxial layer are determined according to the actual situation, which are not limited in the embodiments of the present application. 
     In step  102 , a hard mask layer is formed on the surface of the first epitaxial layer. 
     In some embodiments, a hard mask is deposited by a CVD process, and the hard mask layer is used as a block layer for the etching processes. 
     Referring to  FIG. 3 , a hard mask layer  13  is formed on the surface of the first epitaxial layer  12 . 
     In step  103 , photolithography and etching processes are performed to form deep trenches arranged longitudinally and transversely in the first epitaxial layer. 
     The photoresist is coated on the surface of the hard mask layer, a mask with deep trench patterns is used for the exposure process, after development, the mask patterns are copied into the photoresist layer, the hard mask layer is etched by using the photoresist layer as a mask to copy the deep trench patterns into the hard mask layer, the photoresist is removed after the etching process of the hard mask layer, and then the first epitaxial layer is etched by using the hard mask layer as a mask, and thus deep trenches arranged longitudinally and transversely are formed in the first epitaxial layer. 
     Referring to  FIG. 4 , deep trenches  14  are formed in the first epitaxial layer  12 . Referring to  FIG. 5 , from the top view of the substrate, the deep trenches formed in the first epitaxial layer  12  crisscross, and the transverse deep trenches  15  and the longitudinal deep trenches  16  form cross regions  17 . 
     The number of deep trenches is determined according to the actual situation, and the depth of the deep trenches is equal to the thickness of the first epitaxial layer. 
     The deep trenches in the horizontal direction are parallel to each other, and the deep trenches in the vertical direction are parallel to each other. In the horizontal or vertical direction, two adjacent deep trenches are separated by a predetermined distance. The predetermined distance is determined according to the manufacturing process requirement of the CIS device. 
     In step  104 , a second epitaxial layer is formed in the deep trenches. 
     The second epitaxial layer is a second conductive type, and the conductive type of the second epitaxial layer is P type. 
     The second epitaxial layer grown in the deep trenches completely covers the sidewalls and the bottoms of the deep trenches, but the deep trenches are not completely filled with the second epitaxial layer. 
     Referring to  FIG. 6 , the sidewalls and the bottoms of the deep trench  14  are completely covered by the second epitaxial layer  18 , and there is still a gap in the deep trench  14 . 
     The thickness of the second epitaxial layer is determined according to the actual situation, which is not limited in the embodiment of the present application. 
     In step  105 , perform a thermal oxidation process to form a first oxide layer with a predetermined thickness. 
     The first oxide layer completely covers the second epitaxial layer. 
     The thermal oxidation process is performed to the substrate, and the second epitaxial layer in the deep trenches is oxidized. Referring to  FIG. 7 , in the deep trenches  14 , the first oxide layer  19  formed by the oxidation of the second epitaxial layer  18  completely covering the second epitaxial layer  18 . 
     The predetermined thickness of the first oxide layer is determined according to the actual situation. 
     After the thermal oxidation process, the deep trenches have not been completely filled, that is, there is still a gap in the deep trenches. 
     In step  106 , the deep trenches are completely filled with the polysilicon. 
     The polysilicon is deposited to completely fill the deep trenches. When the deep trenches are completely filled, there are excess polysilicon on the surface of the substrate. At this time, the cross regions of the transverse deep trenches and the longitudinal deep trenches are also completely filled with the polysilicon. 
     Referring to  FIG. 8 , the deep trenches are completely filled with the polysilicon  21 , the first oxide layer  19  and the second epitaxial layer  18 , and the top of the first epitaxial layer  12  is also covered by the polysilicon  21 . 
     In step  107 , the back-etched process is performed to the substrate to expose sidewalls of the first oxide layer in the deep trenches. 
     The substrate is back-etched to remove the polysilicon on the surface of the substrate and the polysilicon on upper portions in the deep trenches, and expose the sidewalls of the first oxide layer in the deep trenches. 
     Referring to  FIG. 9 , the polysilicon above the first epitaxial layer  12  is removed, the polysilicon on the upper portions in the deep trenches  14  is also removed, and the sidewalls of the first oxide layer  19  in the deep trenches  14  are exposed. In each deep trench  14 , the gap in the first oxide layer  19  is partially filled with the polysilicon  21 . 
     In step  108 , a second oxide layer is formed on a top of the polysilicon in the deep trenches. 
     In some embodiments, a second oxide layer is formed on a top of the polysilicon by the thermal oxidation process of the polysilicon. 
     The thermal oxidation process is performed to the polysilicon  21  in the deep trenches  14 , referring to  FIG. 10 , a second oxide layer  22  on a top of the polysilicon  21  is formed in the deep trenches  14 . 
     In step  109 , the hard mask layer on the surface of the substrate and the first oxide layer above the second oxide layer are removed. 
     After the hard mask layer and the first oxide layer above the second oxide layer  22  in the deep trenches  14  are removed, referring to  FIG. 11 , there is no the hard mask layer on the surface of the first epitaxial layer  12 ; the height of the second oxide layer  22  is the same as the height of the first oxide layer  19 ; the sidewalls of the second epitaxial layer  18  and the sidewalls of the deep trenches  14  are exposed. 
     In step  110 , a third epitaxial layer is rapidly grown. 
     The third epitaxial layer covers tops of the deep trenches. 
     The third epitaxial layer is the second conductive type, and the conductive type of the third epitaxial layer is P type. 
     The growth speed of the third epitaxial layer is higher than the growth speed of the second epitaxial layer. 
     Since the growth speed of the third epitaxial layer is faster, the third epitaxial layer fully fill the deep trenches, and the cross regions  17  of the longitudinal deep trenches and the transverse deep trenches, that is, to seal the cross regions of the trenches. Referring to  FIG. 12 , the third epitaxial layer  23  completely fills the gap in the deep trenches illustrated in  FIG. 11 . 
     In step  111 , the CMP process is performed to the substrate to form a deep trench isolation on the substrate. 
     The surface of the substrate is not flat after the third epitaxial layer is formed, perform the CMP process to the surface of the substrate to remove the excess third epitaxial layer. After the CMP process is performed, a deep trench isolation of the CIS device is formed on the substrate, referring to  FIG. 12 . 
     In summary, by forming a first epitaxial layer on a substrate, forming deep trenches arranged longitudinally and transversely in the first epitaxial layer, forming a second epitaxial layer covering sidewalls and bottoms of the deep trenches in the deep trenches, oxidizing the second epitaxial layer to form a first oxide layer, filling the deep trenches with polysilicon, oxidizing the top of the polysilicon to form a second oxide layer, then removing the hard mask layer and the first oxide layer in a region above the second oxide layer in the deep trenches, rapidly growing a third epitaxial layer to seal tops of the deep trenches, the sealing defect at the top of the cross region of the deep trench has been overcome. 
     In some embodiments, the first conductive type is N-type, the second conductive type and the third conductive type are P-type; or, the first conducting type is P-type, the second conducting type and the third conducting type are N-type. 
     In some embodiments, the doping concentration of the third epitaxial layer is higher than the doping concentration of the second epitaxial layer. 
     In some embodiments, a doped epitaxial growth process is performed to form the second epitaxial layer on the sidewalls and bottoms of the deep trenches. 
     In some embodiments, wet etching processes are performed to remove the hard mask layer on the surface of the substrate and the first oxide layer higher than the second oxide layer in the deep trenches. 
     In some embodiments, the material of the hard mask layer is silicon nitride or silicon dioxide. 
     In some embodiments, the polysilicon filled in the deep trenches is doped polysilicon. 
     According to the conductive type of the second epitaxial layer and the third epitaxial layer, the doping type of the doped polysilicon is determined. For example, the conductive type of the second epitaxial layer and the third epitaxial layer is P-type, and the polysilicon filled the deep trenches is a P-type doped polysilicon. 
     One embodiment of the present application provides a semiconductor device structure. The semiconductor device structure is formed in the manufacturing process of the CIS device.  FIG. 12  shows the device cross sectional view of the deep trench isolation, according to one or more embodiments of the present application. 
     The semiconductor device structure includes a substrate  11 , and above the substrate  11  is a first epitaxial layer  12 . 
     Deep trenches arranged longitudinally and transversely are formed in the first epitaxial layer  12 , and each deep trench is completely filled with a second epitaxial layer  18 , an oxide layer, a polysilicon  21  and a third epitaxial layer  23 . 
     In each deep trench, an outer side of the polysilicon  21  is a first oxide layer  19 , a top of the polysilicon  21  is covered by a second oxide layer  22 , an outer side of the first oxide layer  19  is the second epitaxial layer  18 , and the third epitaxial layer  23  completely covers the second epitaxial layer  18 , the first oxide layer  19  and the second oxide layer  22 . 
     Bottoms of the deep trenches are completely covered by the second extending layer  23 . 
     The conductive type of the first epitaxial layer  12  is N type, and the conductive type of the second epitaxial layer  18  and the third epitaxial layer  23  is P type. 
     Each deep trench which is completely filled with the third epitaxial layer  23 , the second epitaxial layer  18 , the first oxide layer  19 , the second oxide layer  22  and the polysilicon  21  is a deep trench isolation. 
     The cross regions of the longitudinal deep trenches and the transverse deep trenches are completely filled. 
     In some embodiments, the doping concentration of the third epitaxial layer is higher than the doping concentration of the second epitaxial layer. 
     In some embodiments, the polysilicon is doped polysilicon. 
     In some embodiments, the surface of the first epitaxial layer is covered by the third epitaxial layer. 
     The foregoing embodiments are merely for clear description of made examples, and are not limitations on the implementations. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. There is no need and cannot be exhaustive for all implementations. And, the obvious changes or modifications introduced thereby are still within the protection scope of this application.