Patent Publication Number: US-6911374-B2

Title: Fabrication method for shallow trench isolation region

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority benefit of Taiwan application serial no. 92108333, filed on Apr. 11, 2003. 
   BACKGROUND OF INVENTION 
   1. Field of Invention 
   The present invention relates to a fabrication method for a shallow trench isolation region. More particularly, the present invention relates to a method for preventing void generation in a shallow trench isolation region. 
   2. Description of Related Art 
   The shallow trench isolation technique typically employs anisotropic etching to form a trench in a semiconductor substrate and filling an oxide material in the trench thereafter to form an isolation region for a device. The dimension of an isolation region formed by the shallow trench isolation technique can be adjusted. Further, the problem of bird&#39;s beak resulted in the conventional LOCOS is prevented. Therefore, shallow trench isolation is a preferred isolation technique in the sub-micron metal oxide semiconductor process. 
   Along with the increase of the integration of integrated circuits, the device dimension also gradually decreases. As the dimension of a shallow trench isolation region is being reduced when the integration of integrated circuits increases, problems that are associated with a high aspect ratio, for example, an incomplete filling of the trench or void generation in the subsequently formed shallow trench isolation region, will eventually surface. The isolation capability of a shallow trench isolation region would become inferior, leading to problems, such as, current leakage and undesirable reliability of the device. 
   SUMMARY OF INVENTION 
   Accordingly, the present invention provides a fabrication method for a shallow trench isolation structure, wherein the generation of voids in the shallow trench isolation structure is avoided to prevent poor isolation capability in the shallow trench isolation structure. 
   The present invention further provides a trench filling method, wherein the problem of an incomplete filling of the trench due to a high aspect ratio after the miniaturization of device is resolved. 
   The present invention provides a fabrication method for a shallow trench isolation region. This method comprises forming a mask layer over a substrate. Using the mask layer as an etching mask, the substrate is patterned to form a trench, wherein the trench comprises a first aspect ratio. A portion of the trench is filled with a first insulation layer, wherein the trench filled with the first insulation layer comprises a second aspect ratio, wherein the second aspect ratio is equal or smaller than the first aspect ratio. A first surface treatment process is performed to form a treated layer on the surface and sidewall of a part of the first insulation layer. In the present invention, the surface treatment process includes a tilted ion implantation process. Thereafter, a wet etching process is performed to remove the surface treated layer on the surface and sidewall of the first insulation layer. Further, the trench depth, after the removal of the treated layer, is substantially the same as that before the removal of the treated layer. However, the trench width, after the removal of the treated layer, is greater than that before the removal of the treated layer. Therefore, after the removal of the treated layer, the trench comprises a third aspect ratio, wherein the third aspect ratio is smaller than the second aspect ratio. Thereafter, a second insulation layer is formed over the first insulation layer, filling the trench. The mask layer is subsequently removed to form a shallow trench isolation region. 
   The present invention also provides a trench filling method, wherein this method provides a substrate having an opening already formed therein. The opening comprises a first aspect ratio. A portion of the opening is filled with a first material layer, wherein after filling with the first material layer, the opening comprises a second aspect ratio. Further, the second aspect ratio is equal or smaller than the first aspect ratio. Thereafter, a treated layer is formed on the surface of a part of the first material layer. In the present invention, the treatment process is, for example, a tilted ion implantation process. A wet etching process is then performed to remove the surface treated layer. The depth of the opening is substantially the same before and after the removal of the treated layer. However, the width of the opening, after the removal of the treated layer, is wider than the width of the opening before the removal of the treated layer. Therefore, subsequent to the removal the treated layer, the opening comprises a third aspect ratio. Further, the third aspect ratio is smaller than the second aspect ratio. Thereafter, a second material layer is formed over the first material layer to fill the opening. 
   In accordance to the present invention, filling a portion of the opening with a first material layer followed by removing a portion of the first material layer can lower the aspect ratio of the opening. Therefore, the present invention can mitigate the problem of an incomplete trench filling due to a high aspect ratio. 
   The fabrication method for a shallow trench isolation region further prevents the generation of voids. Therefore, the shallow trench isolation region formed provides a more desirable isolation effect. 
   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 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. 
       FIGS. 1A  to  1 G are schematic, cross-sectional views illustrating the process flow for fabricating a shallow trench isolation region according to one aspect of the present invention. 
   

   DETAILED DESCRIPTION 
     FIGS. 1A  to  1 G are schematic, cross-sectional views illustrating the process flow for fabricating a shallow trench isolation region according to one aspect of the present invention. 
   Referring to  FIG. 1A , a pad oxide layer  102  and a mask layer  104  are formed over a substrate  100 . The pad oxide layer  102  and the mask layer  104  are formed by, for example, performing a thermal oxidation process to form a thin oxide layer (not shown) on a surface of the substrate  100 , followed by depositing a silicon nitride layer on the thin oxide layer and performing photolithography and etching to pattern the silicon nitride layer to form the mask layer  104 . Further using the mask layer  104  as an etching mask, an etching process is performed to pattern the thin oxide layer and the substrate  100  to form the pad oxide layer  102  and a trench  106 . The trench  106  comprises a depth “H” and a width “W”. The aspect ratio of the trench  106  is “H/W”. 
   Referring to  FIG. 1B , an insulation layer  108  is formed over the substrate  100 , wherein the insulation layer  108  partially fills the trench  106 . The thickness of insulation layer  108  is about 20% to 30% of the depth of the trench  106 . The trench that is subsequent to the filling of the insulation layer  108  is depicted with the reference number  106   a , wherein the trench  106   a  has a height “H″”, a width “W″” and an aspect ratio “H″/W″”. Further, the aspect ratio “H″/W″” of the trench  106   a  is smaller than the aspect ratio “H/W” of the trench  106 . In one aspect of the present invention, the insulation layer  108  is formed with a material that includes silicon oxide. Further, The insulation layer  108  is formed by a method, such as, chemical vapor deposition, and preferably, a high density plasma chemical vapor deposition method. 
   Continuing to  FIG. 1C , a surface treatment step  110  is performed to form a treated layer  112  on the surface of the insulation layer  108 . The surface treatment step  110  includes, for example, a tilted ion implantation process. Further, the tilted ion implantation process is conducted at an angle of about 30 degrees to about 60 degrees. The dopants used in the tilted ion implantation process comprise, for example, an nitrogen gas, an argon gas or other inert gas. In addition, the tilted angle ion implantation process is conducted at an energy level of about 20 KeV to about 100 KeV with a dopant concentration of about 1E15/cm 2  to about 1E16/cm 2 . 
   Since the implanted angle in the above surface treatment process  110  is about 30 degrees to about 60 degrees, only a portion of the surface of the insulation layer  108  is implanted with dopants to form a treated layer  112 . Further, the treated layer  112  and the insulation layer  108  have different etching rates. If the dopants used in the above tilted ion implantation process is nitrogen, the etching rate of the treated layer  112  is about 155 to 165 angstroms/minute. If the dopants used in the above tilted ion implantation process is argon, the etching rate of the treated layer  112  is about 195 to 205 angstroms/minute, whereas the etching rate of the insulation layer  108  without any implanted dopants is about 120 to 125 angstroms/minute. 
   Referring to  FIG. 1D , an etching, preferably a wet etching process, is performed to remove the treated layer  112  on the surface of the insulation layer  108 . The trench, after the removal of the treated layer  112 , is designated with the reference number  106   b . The trench  106   b  has a depth “H″”, a width “W″?, and an aspect ratio “H″/W″”. One point that is worth noting is that the depth “H″” of the trench  106   b  is substantially the same as the depth “H″” of the trench  106   a . However, the width “W″” of the trench  106   b  is greater than the width “W″” of the trench  106   a . In other words, there is no significant change in the depth of the trench before and after the removal of the treated layer  112 . However, after the removal of the treated layer  112 , the width of the trench is increased. Therefore, the aspect ratio “H″/W″” of the trench  106   b  is smaller than the aspect ratio “H″/W″” of the trench  106   a . As a result, to fill the trench  106   b  with an insulation material, the trench  106   b  can be filled completely. 
   Referring to  FIG. 1E , a insulation layer  114  is formed filling the trench  106   b , wherein the insulation layer  108   a  and the insulation layer  114  together serve as an insulation material layer  116  for the shallow trench isolation region. In this aspect of the present invention, the insulation layer  114  is, for example, silicon oxide. Further, forming the insulation layer  114  includes, for example, performing chemical vapor deposition, and preferably, high density plasma chemical vapor deposition. 
   As discussed in the above, the aspect ratio “H″/W″” of the trench  106   b  is significantly reduced compared to the aspect ratio “H″/W″” of the trench  106   a . Therefore, in accordance to the fabrication method of the present invention, the trench can be completely filled with the insulation material layer  116  without the formation of voids therein. 
   As shown in  FIG. 1F , the insulation material layer  116  is partially removed until the mask layer  104  is exposed. Removing a portion of the insulation layer  116  includes performing chemical mechanical polishing or etching back. 
   As shown in  FIG. 1G , the mask layer  104  and the pad oxide layer  102  are removed to complete the fabrication of a shallow trench isolation region. 
   The fabrication method for a shallow trench isolation region of the present invention comprises filling a part of the trench of the first insulation layer, followed by removing a portion of the first insulation layer to lower the aspect ratio of the trench. The trench is then completely filled. Therefore, in accordance to the present invention, the trench can be completely filled without the formation of voids. The shallow trench isolation region can thus provide a superior isolation capability. 
   By improving the trench filling effect of the insulation material during the fabrication of a shallow trench isolation region of the present invention, the generation of voids in the isolation region is effectively prevented. Therefore, to lower the aspect ratio of an opening by filling a material layer into a part of the opening followed by removing a portion of the material layer can be applied to other filling processes, other than the shallow trench isolation process, for example, the filling process with an organic material or a metal material. 
   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.