Abstract:
A method for preparing a trench isolation structure, which comprises the following steps of: providing a substrate; forming an oxide layer on the substrate; successively generating an oxidation barrier layer and an ethyl orthosilicate layer on the surface of the oxide layer; etching the oxidation barrier layer and the ethyl orthosilicate layer; corroding the substrate to form a trench by using the oxidation barrier layer and the ethyl orthosilicate layer as mask layers; removing the ethyl orthosilicate layer, and oxidizing a side wall of the trench by using the oxidation barrier layer as a barrier layer; filling the trench with a polysilicon and then etching back the polysilicon, and removing the polysilicon on the surface of the oxidation barrier layer; and removing the oxidation barrier layer and the oxide layer on the surface of the substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to the technical field of semiconductor manufacturing, and particularly relates to a method of manufacturing a trench isolation structure. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the conventional manufacturing process (e.g., Silicon-On-Insulator, SOI), the manufacturing of the trench isolation structure typically chooses a tetraethyl orthosilicate (TEOS) layer as the etching hardmask. When such a method is employed to manufacture the trench isolation structure, the wet-etching is at a relatively large scale, a relatively large groove will be formed in the top of the trench, the flatness is unfavorable and the structure is vulnerable to the polysilicon residue problem causing a soft connection which affects the performance of the product. In addition, the trench isolation structure obtained by such a method is of a relatively large critical dimension. 
       SUMMARY OF THE INVENTION 
       [0003]    Accordingly, it is necessary to provide a method of manufacturing a trench isolation structure, the trench isolation structure manufactured accordingly has a better flatness on a top thereof and a relatively small critical dimension. 
         [0004]    A method of manufacturing a trench isolation structure includes: 
         [0005]    providing a substrate; forming an oxidation layer on the substrate; 
         [0006]    generating an oxidation barrier layer and an ethyl orthosilicate layer successively on a surface of the oxidation layer; 
         [0007]    etching the oxidation barrier layer and the ethyl orthosilicate layer; 
         [0008]    etching the substrate to form a trench using the etched oxidation barrier layer and the ethyl orthosilicate layer as masking layers; 
         [0009]    removing the ethyl orthosilicate layer, and oxidizing a sidewall of the trench using the oxidation barrier layer as a barrier layer; 
         [0010]    filling polysilicon in the trench, and then performing an etchback process to the polysilicon to remove the polysilicon on the surface of the oxidation barrier layer; and 
         [0011]    removing the oxidation barrier layer and the oxidation layer on the surface of the substrate. 
         [0012]    The foregoing method of manufacturing a trench isolation structure, the non-trench region can be masked by the oxidation barrier layer in the oxidation of the trench, thereby obstructing the oxidation to the non-trench region. As such, there is no need to remove the oxidation layer of the non-trench region by lots of wet-etching, the wet-etching volume is reduced whilst the lateral etching resulted from the wet-etching is avoided, such that the trench isolation structure is of a relatively small critical dimension. Additionally, a relatively large groove on the top of the trench isolation structure resulted from lots of wet-etching can be avoided, such that the top of the trench isolation structure is provided with a favorable flatness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The technical solutions of the present invention will be clearly and completely described in the following with reference to the accompanying drawings. It is obvious that the embodiments to be described are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by persons skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
           [0014]      FIG. 1  is a flowchart of a method of manufacturing a trench isolation structure according to an embodiment; 
           [0015]      FIG. 2  is a schematic view of a device after step S 130  in  FIG. 1 ; 
           [0016]      FIG. 3  is a schematic view of the device after a photolithography is performed to a photoresist layer according to the embodiment in  FIG. 1 ; 
           [0017]      FIG. 4  is a schematic view of the device after step S 140  in  FIG. 1 ; 
           [0018]      FIG. 5  is a schematic view of the device after the photoresist layer is removed according to the embodiment in  FIG. 1 ; 
           [0019]      FIG. 6  is a schematic view of the device after step S 160  in  FIG. 1 ; 
           [0020]      FIG. 7  is a schematic view of the device after the ethyl orthosilicate layer is removed according to the embodiment in  FIG. 1 ; 
           [0021]      FIG. 8  is a schematic view of the device after step S 170  in  FIG. 1 ; 
           [0022]      FIG. 9  is a schematic view of the device after filling polysilicon into the trench region according to the embodiment in  FIG. 1 ; 
           [0023]      FIG. 10  is a schematic view of the device after an etchback is performed to the polysilicon according to the embodiment in  FIG. 1 ; 
           [0024]      FIG. 11  is a schematic view of the device after step S 180  in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    The present invention will be described in the following with reference to the accompanying drawings and the embodiments. Preferable embodiments are presented in the drawings. However, numerous specific details are described hereinafter in order to facilitate a thorough understanding of the present disclosure. The various embodiments of the disclosure may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth hereinafter, and people skilled in the art can make similar modifications without departing from the spirit of the present disclosure. 
         [0026]      FIG. 1  is a flowchart of a method of manufacturing a trench isolation structure according to an embodiment, the method can be applied to semiconductor manufacture processes, such as the Silicon-On-Insulator (SOI) process. A method of manufacturing a trench isolation structure includes: 
         [0027]    Step S 110 , a substrate is provided. 
         [0028]    In the present embodiment, the trench isolation structure is manufactured on the basis of the SOI process, thus the SOI structure is required to be manufactured after the substrate is provided. That is, after step S 110 , it is also needed to execute the step of forming a burial oxidation layer and a top silicon successively to form the SOI structure. 
         [0029]    Step S 120 , an oxidation layer is formed on the substrate. 
         [0030]    In the present embodiment, as a SOI structure is formed, the step of forming an oxidation layer on the substrate is to form an oxidation layer on the surface of the top silicon. The oxidation layer is mainly used to separate the stress between the top silicon and the oxidation barrier layer, thus a relatively thin layer of oxidation will suffice. 
         [0031]    Step S 130 , an oxidation barrier layer and an ethyl orthosilicate layer are successively generated on the surface of the oxidation layer. 
         [0032]    The oxidation barrier layer can be made of substances that can block the thermal oxidation growth, such as silicon nitrides. In the present embodiment, the oxidation barrier layer is a silicon nitride layer. The silicon nitride has an extremely high compactness, thus it is an excellent barrier layer for wet-etching, which can stop exterior electric charges from entering the interior of the device, and thereby serving to protect the device and improving the operation reliability of the device. The ethyl orthosilicate layer is formed by low pressure chemical vapor deposition (LPCVD). The ethyl orthosilicate layer is a thin SiO 2  film generated using tetraethyl orthosilicate (TEOS) as the gas source.  FIG. 2  is a schematic view of a device after step S 130 . A burial oxidation layer  204  and a top silicon  206  are formed on the substrate  202 , thereby forming a SOI structure. An oxidation layer  208 , an oxidation barrier layer  210  and an ethyl orthosilicate layer  212  are successively formed on the surface of the top silicon  206 . 
         [0033]    Step S 140 , the oxidation barrier layer and the ethyl orthosilicate layer are etched. 
         [0034]    In the present embodiment, prior to etching the oxidation barrier layer  210  and the ethyl orthosilicate layer  212 , a photoresist layer  214  is required to be formed on the surface of the ethyl orthosilicate layer  212 , and photolithography is performed to the photoresist layer  214  to form a photolithography window, as shown in  FIG. 3 . As such, using the photoresist layer  214  as the barrier layer, the oxidation barrier layer  210  and the ethyl orthosilicate layer  212  are etched to form a window area. In the present embodiment, in the etching process, the corresponding position of the oxidation layer  208  is etched, the schematic diagram of the device after being etched is shown in  FIG. 4 . After the etching, the photoresist layer  214  is removed.  FIG. 5  is a schematic view of the device after the photoresist layer is removed. 
         [0035]    Step S 150 , the substrate is etched using the etched oxidation barrier layer and the ethyl orthosilicate layer as masking layers, thus forming a trench. 
         [0036]    Using the etched oxidation barrier layer  210  and the ethyl orthosilicate layer  212  as masking layers, the top silicon  206  is etched to form a trench.  FIG. 6  is a schematic view of a device after step S 150 . 
         [0037]    Step S 160 , the ethyl orthosilicate layer is removed, and the sidewall of the trench is oxidized using the oxidation barrier layer as a barrier layer. 
         [0038]    In the present embodiment, while removing the ethyl orthosilicate layer  212 , certain etching is also performed to the burial oxidation layer  204  in the trench, such that the trench region extends to the burial oxidation layer  204  area.  FIG. 7  is a schematic view of the device after the ethyl orthosilicate layer is removed. 
         [0039]    After the ethyl orthosilicate layer is removed, and using the oxidation barrier layer  210  as a barrier layer, the trench is oxidized. In the conventional trench manufacture process, merely the ethyl orthosilicate layer is used as a barrier layer, thus the whole wafer (non-trench region and trench region) is oxidized in the trench oxidation process. A typical oxidation layer is over thousands of angstroms, thus the oxidation layer of the active region must be removed in the subsequent process to define the active region, the required wet-etching load is great and causing the lateral etching to be relatively great, such that the critical dimension of the trench isolation structure is relatively great and a comparatively large groove will be formed at the top of the trench isolation structure, which is unfavorable to achieve the planarization of the surface of the trench isolation structure. In the present embodiment, the oxidation barrier layer  210  can shield the non-trench region, such that an oxidation layer is avoided to be formed in the non-trench region, thereby reducing the wet-etching load in subsequent process and hence avoid the lateral etching resulted from the wet-etching and the etching at the top of the trench isolation structure, which is advantageous to effect the miniaturization of the critical dimension as well as the planarization of the surface of the trench isolation structure.  FIG. 8  is a schematic view of the device after trench oxidation. 
         [0040]    Step S 170 , polysilicon is filled in the trench and then an etchback process is performed thereto and the polysilicon on the surface of the oxidation barrier layer is removed. 
         [0041]      FIG. 9  is a schematic view of the device after filling polysilicon  216  into the trench region. After the filling of the polysilicon  216 , in order to ensure that the polysilicon in the non-trench region is etched completely, the polysilicon  216  will be etched back, so as to remove the polysilicon on the surface of the oxidation barrier layer  210 . The etchback process to the polysilicon  216  is performed in a way to find the finishing point. When the polysilicon  216  is etched to a contacting surface between the oxidation layer  208  and the oxidation barrier layer  210 , it can be determined that the etching is completed. On this basis, a little etching time is added to form an over-etching, thus ensuring that the polysilicon  216  is completely etched away, such that the back-etched polysilicon  216  has a surface lower than the contacting surface between the oxidation layer  208  and the oxidation barrier layer  210 , and a polysilicon surface with an ideal morphology is obtained. In the present embodiment, as the oxidation layer  208  is relatively thin, the etchback can be finished upon arriving the contacting surface between the oxidation layer  208  and the oxidation barrier layer  210 , thereby avoiding a relatively great over-etching at the top of the trench isolation structure which will affect the surface planarization of the trench isolation structure.  FIG. 10  is a schematic view of the device after the etchback is performed to the polysilicon  216 . 
         [0042]    Step S 180 , the oxidation barrier layer and the oxidation layer on the surface of the substrate are removed. 
         [0043]    A SOI structure is formed in the present embodiment, therefore after the oxidation barrier layer and the oxidation layer on the surface of the top silicon are removed in present step, the manufacture of the trench isolation structure is completed. In the present embodiment, the oxidation barrier layer is removed by the chemical-mechanical polishing process, while the oxidation layer is removed by the wet-etching process. It should be understood that, in step  180 , the oxidation barrier layer and the oxidation layer on the surface of the substrate can be removed by other processes common in the art.  FIG. 11  is a schematic view of a device after step S 180 . 
         [0044]    According to the aforementioned method of manufacturing a trench isolation structure, the non-trench region can be shielded by the oxidation barrier layer during the process of oxidation of the trench, thereby preventing the non-trench region from being oxidized. As such, there is no need to remove the oxidation layer of the non-trench region by a large number of wet-etching, the wet-etching volume is reduced while the lateral etching resulted from the wet-etching is avoided, such that the trench isolation structure has a relatively small critical dimension. Additionally, a relatively large groove on the top of the trench isolation structure resulted from lots of wet-etching can be avoided, such that the top of the trench isolation structure is provided with a favorable flatness. 
         [0045]    The different technical features of the foregoing embodiments can have various combinations which are not described for the purpose of brevity. Nevertheless, to the extent the combining of the different technical features do not conflict with each other, all such combinations must be regarded as within the scope of the disclosure. 
         [0046]    The foregoing implementations are merely specific embodiments of the present disclosure, and are not intended to limit the protection scope of the present disclosure. It should be noted that any variation or replacement readily figured out by persons skilled in the art within the technical scope disclosed in the present disclosure shall all fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.