Abstract:
A manufacturing method for reverse conducting insulated gate bipolar transistor, the manufacturing method is characterized by the use of polysilicon for filling in grooves on the back of a reverse conducting insulated gate bipolar transistor. The parameters of reverse conducting diodes on the back of the reverse conducting insulated gate bipolar transistor can be controlled simply by controlling the doping concentration of the polysilicon accurately, indicating relatively low requirements for process control. The reverse conducting insulated gate bipolar transistor manufacturing method is relatively low in requirements for process control and relatively small in manufacturing difficulty.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method of manufacturing a semiconductor device, and particularly relates to a method of manufacturing the reverse conducting insulated gate bipolar transistor. 
     BACKGROUND OF THE INVENTION 
     The insulated gate bipolar transistor (IGBT) generally is a common power switching device controlled by a voltage. It has the features of a large input capacitance, a high input resistance, high voltage resistance, a high work temperature, a simple control circuit and the like, and becomes a main device of the power electronics apparatus at the present stage. The reverse conducting insulated gate bipolar transistor is a new IGBT device, and it integrates an IGBT structure and a reverse conducting diode structure on a same chip, which can improve the passage of non-balanced carriers and optimizing the tail current. The reverse conducting IGBT device has many advantages of a small size, a high power density, a low cost, a high reliability and the like. 
     The method of manufacturing the reverse conducting diode structure at the back side of the device in the method of manufacturing the common reverse conducting IGBT has two main manners. A method of manufacturing the reverse conducting diode structure of the reverse conducting IGBT is implemented by using two back side photoetching processes. Particularly, a P+ type area is formed by firstly performing selective implantation and diffusion processes, and then an N+ type area is formed by performing selective implantation and diffusion processes again. As a result, the N+ and P+ areas can be formed at intervals on the back side of the reverse conducting IGBT. The interval N+ and P+ areas are the reverse conducting diode structure. The back side N+ area of the reverse conducting IGBT formed by using this manufacturing method is shallower, and has a higher requirement for controlling the process. Once the doping concentration of the N+ area becomes higher, when the formed reverse conducting IGBT is forward conducted, a large implantation effect can be formed, resulting in losing the function of the reverse conducting IGBT. 
     Another method of manufacturing the reverse conducting diode structure of the reverse conducting IGBT is described as follows. After the front side process is performed and the back side P+ layer is formed, digging of the trench is performed, and then the reverse conducting diode structure of the reverse conducting IGBT is finally formed by filling back side metal in the trench. The method of manufacturing the reverse conducting diode structure of the reverse conducting IGBT mainly use the means of digging of the trench and filling of the back side metal to form he reverse conducting diode structure. However, because the metal in the trench at the back side of the reverse conducting IGBT is limited by requirement of collector metal of the reverse conducting IGBT, the parameters of the reverse conducting diode can be adjusted only by adjusting the width and depth of the dug trench, resulting in troubling of the adjusting process and a high requirement of controlling the process. Therefore, from the above process methods, it can be understood that the common method of manufacturing the reverse conducting diode structure at the back side of the reverse conducting IGBT device has a higher requirement of controlling the manufacturing process, and a larger difficulty of manufacturing. 
     SUMMARY OF THE INVENTION 
     On the basis of this, it is necessary to provide a method of manufacturing a reverse conducting insulated gate bipolar transistor, which can reduce the requirement of controlling the process, and reduce the difficulty of manufacturing. 
     A method of manufacturing a reverse conducting insulated gate bipolar transistor includes: preparing an N-type substrate; growing a gate oxide layer at a front side of the N-type substrate; depositing a polysilicon gate on the gate oxide layer; forming a P well on the N-type substrate by photoetching, etching and ion-implanting processes; forming an N+ region and a front side P+ region in the P well by photoetching and ion-implanting processes; depositing a dielectric layer at the front side of the N-type substrate; depositing a protecting layer on the dielectric layer; grinding the N-type substrate by a back side grinding process; forming a back side P+ region by implanting a P-type impurity to a back side of the N-type substrate; forming a trench at the back side of the N-type substrate by photoetching and etching processes; filling the trench by depositing polysilicon at the back side of the N-type substrate, and etching polysilicon at an area outside of the trench; removing the protecting layer at the front side of the N-type substrate; selectively etching the dielectric layer, and forming a front side metal layer to form a contact hole for shorting the N+ region and the front side P+ region; depositing a passivation layer at the front side of the N-type substrate; and performing a back side metalized process at the back side of the N-type substrate and forming a back side metal layer. 
     In one of embodiments, after forming the back side metal layer by performing the back side metalized process at the back side of the N-type substrate, the method further comprises controlling a carrier lifetime at a partial area in the N-type substrate by a local radiation technique. 
     In one of embodiments, the local radiation technique radiates the N-type substrate by using electron or proton. 
     In one of embodiments, the trench formed at the back side of the N-type substrate is of a rectangle shape. 
     In one of embodiments, a depth of the trench formed at the back side of the N-type substrate is from 1 to 20 μm, a width thereof is from 1 to 30 μm, and a distance between two adjacent trenches is 50 to 300 μm. 
     In one of embodiments, the polysilicon deposited in the trench formed at the back side of the N-type substrate is N-type polysilicon. 
     In one of embodiments, a doping concentration of the polysilicon deposited in the trench formed at the back side of the N-type substrate is from 1E17 to 1E21 cm −3 . 
     In one of embodiments, from the N-type substrate to an external, the back side metal layer comprises aluminum, titanium, nickel and silver, which are laminated in that order. 
     In one of embodiments, the dielectric layer is made of silicon dioxide and boro-phospho-silicate glass. 
     In one of embodiments, the protecting layer is made of silicon nitride. 
     The method of manufacturing the reverse conducting insulated gate bipolar transistor described above uses polysilicon to fill the trench at the back side of the reverse conducting insulated gate bipolar transistor. The parameters of the reverse conducting diode at the back side of the reverse conducting insulated gate bipolar transistor can be controlled by only precisely controlling the doping concentration of polysilicon, resulting in a lower requirement of controlling the process. The method of manufacturing the reverse conducting insulated gate bipolar transistor has a lower requirement of controlling the manufacturing process, and a less difficulty of manufacturing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a flow chart of a method of manufacturing the reverse conducting insulated gate bipolar transistor in an embodiment; 
         FIGS. 2 to 17  are schematic diagrams of corresponding reverse conducting insulated gate bipolar transistor in the manufacturing method of the field stop insulated gate bipolar transistor shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIG. 1 , in an embodiment, the method of manufacturing the reverse conducting insulated gate bipolar transistor is provided, which includes the following steps. 
     In step S 111 , an N-type substrate  110  is prepared. As shown in  FIG. 2 , the N-type substrate  110  is an N-type silicon substrate. 
     In step S 112 , a gate oxide layer  121  is grown at a front side of the N-type substrate  110 . As shown in  FIG. 3 , the thickness of the gate oxide layer  121  is from 600 angstroms to 1500 angstroms. 
     In step S 113 , a polysilicon gate  122  is deposited on the gate oxide layer  121 , as shown in  FIG. 3 . 
     In step S 114 , a P well  123  is formed on the N-type substrate  110  by photoetching, etching and ion-implanting processes (referring to  FIG. 5 ). Referring to  FIG. 4 , an implantation window of the P well  123  is formed by selectively etching the polysilicon gate  122  and the gate oxide layer  121  by the photoetching process. Referring to  FIG. 5 , a P-type impurity is implanted to the implantation window of the P well  123  by the self-aligned implantation process, and the P well  123  is formed by a drive-in process. 
     In step S 115 , an N+ region  124  and a front side P+ region  125  are formed in the P well  123  by photoetching and ion-implanting processes (referring to  FIG. 7 ). Referring to  FIG. 6 , ions are selectively implanted to the P well  123  by the photoetching process, and the N+ region  124  is formed by the drive-in process. Referring to  FIG. 7 , ions are selectively implanted to the P well  123  by the photoetching process, and the front side P+ region  125  is formed by the drive-in process. The N+ region  124  is mainly configured as an emitter of the reverse conducting insulated gate bipolar transistor. 
     In step S 116 , a dielectric layer  126  is deposited at the front side of the N-type substrate  110 . As shown in  FIG. 8 , the dielectric layer  126  is made of silicon dioxide and boro-phospho-silicate glass. 
     In step S 117 , a protecting layer  127  is deposited on the dielectric layer  126 . As shown in  FIG. 9 , the protecting layer is made of silicon nitride. 
     In step S 118 , the N-type substrate  110  is ground by a back side grinding process. In step  118 , the N-type substrate  110  is ground to the required thickness. 
     In step S 121 , a back side P+ region  131  is formed by implanting a P-type impurity to a back side of the N-type substrate  110 , as shown in  FIG. 10 . 
     In step S 122 , a trench  132  is formed at the back side of the N-type substrate  110  by photoetching and etching processes. As shown in  FIG. 11 , in the embodiment, the trench  132  formed at the back side of the N-type substrate  110  is of a rectangle shape. Of course, the trench  132  formed at the back side of the N-type substrate  110  is of a circle, an oval, a trapezium and other appropriate shapes. When the trench  132  formed at the back side of the N-type substrate  110  is of a rectangle shape, a depth of the trench  132  is from 1 to 20 μm, a width thereof is from 1 to 30 μm, and a distance between two adjacent trenches  132  is from 50 to 300 μm. 
     In step S 123 , the trench  132  is filled by depositing polysilicon at the back side of the N-type substrate  110 , and the polysilicon at an area outside of the trench  132  is etched. As shown in  FIG. 12 , in step S 123 , the reverse conducting diode is formed by filling polysilicon in the trench  132 . The parameters of the reverse conducting diode at the back side of the manufactured reverse conducting insulated gate bipolar transistor can be adjusted by adjusting the doping concentration of polysilicon in the trench  132 , so that the difficulty of the adjusting process is low and it is easy to control the process. Therefore, the manufacturing difficulty of the reverse conducting insulated gate bipolar transistor can be reduced. Of course, the parameters of the reverse conducting diode at the back side of the reverse conducting insulated gate bipolar transistor can be also adjusted by adjusting a width and a depth of the trench  132 , or by adjusting the doping concentration of polysilicon in the trench  132  and the width and the depth of the trench  132  at the same time. Therefore, the difficulty of the adjusting process of the reverse conducting insulated gate bipolar transistor can be reduced, and then the manufacturing difficulty thereof is reduced. In the embodiment, the polysilicon deposited in the trench  132  formed at the back side of the N-type substrate  110  is N-type polysilicon. The doping concentration of the polysilicon deposited in the trench  132  is 1E17 to 1E21 cm −3 . 
     In step S 124 , the protecting layer  127  at the front side of the N-type substrate is removed, as shown in  FIG. 13 . 
     In step S 125 , a contact hole for shorting the N+ region  124  and the front side P+ region  125  is formed by selectively etching the dielectric layer  126 , and a front side metal layer  128  is formed. As shown in  FIG. 14 , from the manufacturing flow of the reverse conducting insulated gate bipolar transistor described above, it can be understood that step S 122  and step S 123  are performed after performing step S 116 . In other words, forming the trench  132  at the back side of the N-type substrate  110  and depositing the polysilicon in the trench  132  are performed after performing depositing the dielectric layer  126  at the front side of the N-type substrate  110  rather than after performing the whole front side process of the reverse conducting insulated gate bipolar transistor. Such a manufacturing method has the following advantages. Firstly, after the P-type impurity is implanted at the back side of the N-type substrate  110  in step S 121 , the following front side thermal processes such as the hole reflow process (the hole reflow process is in forming the contact hole for shorting the N+ region  124  and the front side P+ region  125  by selectively etching the dielectric layer  126  and forming a front side metal layer  128  of step S 125 , and the temperature of the step S 125  is about 850 degrees centigrade) and so on are performed. The activity of the P-type impurity at the back side of the N-type substrate  110  is very high without performing the annealing process individually. Therefore, the step of the thermal annealing of the P-type impurity at the back side of the N-type substrate  110  can be omitted. Further, the polysilicon in the trench  123  at the back side of the N-type substrate  110  and the polysilicon of the front side are processed separately, thus easily controlling the doping concentration of the polysilicon. 
     In step S 126 , a passivation layer  129  is deposited at the front side of the N-type substrate  110 . As shown in  FIG. 15 , here, a pad area is formed by performing the etching process. 
     In step S 127 , a back side metal layer  133  is formed by performing a back side metalized process at the back side of the N-type substrate  110 . In the embodiment, from the N-type substrate to an external, the back side metal layer  133  at the back side of the N-type substrate  110  comprises aluminum, titanium, nickel and silver, which are laminated in that order. In other words, the outermost layer is metal silver. 
     In step S 128 , a carrier lifetime at a partial area  111  in the N-type substrate  110  is controlled by a local radiation technique. As shown in  FIG. 17 , in the embodiment, the local radiation technique radiates the N-type substrate  110  by using electron or proton to control the life of the carrier at a partial area  111  in the N-type substrate  110 . Therefore, manufacturing of the reverse conducting insulated gate bipolar transistor is completed. 
     The method of manufacturing the reverse conducting insulated gate bipolar transistor described above uses polysilicon for filling the trench at the back side of the reverse conducting insulated gate bipolar transistor. Thus, the parameters of the reverse conducting diode at the back side of the reverse conducting insulated gate bipolar transistor can be controlled by only precisely controlling the doping concentration of polysilicon, resulting in a lower requirement of controlling the process. Therefore, the method of manufacturing the reverse conducting insulated gate bipolar transistor has a lower requirement of controlling the manufacturing process, and a less difficulty of manufacturing. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.