Abstract:
A method of forming a trench in a semiconductor device formed of a substrate and a first layer formed over the substrate includes forming an initial trench that passes through the first layer to the substrate, the initial trench having a diameter that decreases from a first diameter to a second diameter, the second diameter being measured at a distance closer to the substrate than the first diameter; exposing the trench to a dopant via an orthogonal ion implant to form doped regions sidewalls of the trench; and etching the trench to remove at least some of the doped regions.

Description:
BACKGROUND 
     The present invention relates to semiconductors and, and more specifically, to forming semiconductor wafers having deep trenches. 
     Semiconductor wafers may include a base substrate layer covered by one or more layers (upper layers) formed on top of the base substrate. It may be required, in some instances, to etch the substrate after the other layers have been deposited over it. To that end, a trench is formed through the upper layers to expose the substrate layer. In some instances, a liner material is deposited on the sides of the trench before the substrate is etched. 
     In some cases, the substrate may be etched by a plasma etching process. The etching plasma components and sputtered material erode may the liner. This may be noticed particularly at the bottom of trench where the BOX-Si interface structure may be undercut leading to structural damage causing leakage and yield issues. This is inherent in the available plasma etch tools. Indeed, dielectric chambers are limited to fluorocarbon chemistry due to chamber materials and to provide anisotropy during silicon oxide etch. One solution is to apply a thicker liner material. The thicker liner material may reduce the width of the hole and, therefore, increase size. 
     SUMMARY 
     According to one embodiment of the present invention, a method of forming a trench in a semiconductor device formed of a substrate and a first layer formed over the substrate is disclosed. The method includes forming an initial trench that passes through the first layer to the substrate, the initial trench having a diameter that decreases from a first diameter to a second diameter, the second diameter being measured at a distance closer to the substrate than the first diameter; exposing the trench to a dopant via an orthogonal ion implant to form doped regions sidewalls of the trench; and etching the trench to remove at least some of the doped regions. 
     According to another embodiment of the present invention, a semiconductor device that includes a substrate and a first layer disposed over the substrate is disclosed. The first layer has in this embodiment been exposed to an orthogonal doping procedure and an etching procedure to remove at least some non-vertical portions therefrom. 
     According to yet another embodiment of the present invention, a semiconductor device that includes a substrate and a first layer formed over the substrate is disclosed. The first layer includes initial trench that passes through the first layer to the substrate that was formed having a diameter that decreases from a first diameter to a second diameter, the second diameter being measured at a distance closer to the substrate than the first diameter, and wherein the trench was exposed to a dopant via an orthogonal ion implant to form doped regions sidewalls of the trench and etched to remove at least some of the doped regions. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  shows an example of a workpiece having a trench formed therein; 
         FIG. 2  shows the workpiece of  FIG. 1  after being exposed to an orthogonal doping procedure; and 
         FIG. 3  shows the workpiece of  FIG. 2  after the trench sidewalls have been made more vertical by removing the doped portions. 
     
    
    
     DETAILED DESCRIPTION 
     As discussed above, a substrate may be etched by a plasma etching process that causes erosion of the liner covering upper layers disposed over the substrate. It has been discovered that such erosion may be more prevalent at the junction of two layers due to the non-vertical edges created at these locations. Accordingly, embodiments of the present invention may remove or reduce non-vertical edges within a trench. 
     In one embodiment, the one or more layers forming the walls of the trench may be orthogonally exposed to an appropriate dopant and concentration variation (e.g., doped with an n-type dopant such as arsenic) so that the doped portion may be selectively removed. This will selectively reduce non-vertical components of the trench and result in less angle of incidence for attack of the liner during subsequent processing steps. 
       FIG. 1  shows an example of a workpiece  100  having a trench  101  formed therein. The workpiece  100  may include a substrate  102 . On top of the substrate one or more upper layers  104  are disposed. In the example shown in  FIG. 1 , the upper layers  104  may include a first upper layer  106  disposed over the substrate  102 . The upper layers  104  may also include a second upper layer  108  disposed over the first upper first upper layer  106  and a third upper layer  110  disposed over the second upper layer  108 . Of course the number of layers is not limited to the three layers shown in  FIG. 1 . In one embodiment, only the first upper layer may be included. In one embodiment, the first upper layer  106  may be a buried oxide (BOX) layer. In one embodiment, the substrate  102  is silicon substrate and the upper layers  104  may include a silicon oxide layer and a pad nitride layer all covered by a sacrificial layer. 
     The trench  101  passes completely through at least one layer of the upper layers  104 . In one embodiment, the trench passes completely through all of the upper layers  104  so to expose at least a portion of the substrate  102 . 
     Depending on the depth of the trench  101  or the available processing means, the situation may exist where the walls  112  of the trench  101  curve inward narrowing the diameter of the trench  101  from the a first diameter d 1  to a second diameter d 2 . The second diameter d 2  is measured at a location closer to the substrate  102  than the first diameter d 1 . 
     As discussed above, if the curved walls  112  are covered by a liner layer, subsequent processing may cause holes or other damage to be formed in the liner layer. Accordingly, in one embodiment of the present invention, the walls  112  are made more vertical. Stated differently, in one embodiment, the curvature of the walls  112  is reduced making the values of d 1  and d 2  closer to one another. 
       FIG. 2  shows a close up one of the sides of the trench  101  shown in  FIG. 1  after being exposed to a. The sides of the trench  101  are exposed to an orthogonal ion implant as indicated by arrows  200 . In one embodiment, the ion implant  200  causes the non-vertical portions of the curved walls to be N-doped. This may be accomplished by doping the non-vertical portions with arsenic. Of course, other dopants could utilized. 
     The result of orthogonal doping is that at least a portion of the non-vertical portions of the sidewalls become doped. As shown in  FIG. 2 , the substrate  102  has a doped portion  202 , the first upper layer  106  has a doped portion  206  and the second upper layer  108  has a doped portion  208 . In one embodiment, the doped portions  202 ,  206  and  208  are N-doped. The size of the doped portions on each level may vary from that shown in  FIG. 2 . 
       FIG. 3  shows the trench  101  after it has been etched to remove the doped portions. The sidewalls  112  are more vertical than in  FIG. 1 . As shown, the sidewalls  112  are perfectly vertical. Of course, some curvature may still exist. In one embodiment, the processing described with respect to  FIG. 2  may be repeated if desired. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.