# Patent

## Title
Narrow semiconductor trench structure

## Abstract

Systems and methods for narrow semiconductor trench structures. In a first method embodiment, a method for forming a narrow trench comprises forming a first layer of insulating material on a substrate and creating a trench through the first layer of insulating material and into the substrate. A second insulating material is formed on the first layer and on exposed portions of the trench and the second insulating material is removed from the first layer of insulating material and the bottom of the trench. The trench is filled with an epitaxial material and the first layer of insulating material is removed. A narrow trench is formed by the removal of remaining portions of the second insulating material.

## Background
RELATED APPLICATION
This Application claims benefit of U.S. Provisional Patent Application Ser. No. 60/661,198, filed Mar. 11, 2005, to Chau et al., which is hereby incorporated herein by reference in its entirety.


TECHNICAL FIELD
Embodiments of the present invention relate to the fields of manufacturing semiconductors, and more particularly to systems and methods for forming narrow trench structures in semiconductors.
BACKGROUND
The inexorable decrease of feature size, e.g., critical dimension, of modern semiconductor devices is increasing semiconductor density in a wide variety of types of semiconductor devices. However, conventional methods for fabricating trenches in semiconductors, for example, as commonly used in power semiconductors and memory semiconductors, e.g., dynamic random access memory, are challenged to construct ever-narrower trenches corresponding to such decreases in semiconductor process critical dimension. In addition, some semiconductor applications have power density and/or voltage requirements that mitigate against decreasing process dimensions.
SUMMARY
Therefore, there is a need for systems and methods for narrow semiconductor trench structures.
Accordingly, systems and methods for narrow semiconductor trench structures are disclosed. In a first method embodiment, a method for forming a narrow trench comprises forming a first layer of insulating material on a substrate and creating a trench through the first layer of insulating material and into the substrate. A second insulating material is formed on the first layer and on exposed portions of the trench and the second insulating material is removed from the first layer of insulating material and the bottom of the trench. The trench is filled with an epitaxial material and the first layer of insulating material is removed. A narrow trench is formed by the removal of remaining portions of the second insulating material.
In accordance with another embodiment of the preset invention, a semiconductor device includes a trench characterized as having a width dimension of less than one tenth of the critical dimension of the semiconductor process used to manufacture the semiconductor device.
In accordance with another method embodiment of the preset invention, a first trench in a semiconductor substrate is formed. A first layer of material is applied adjacent to and parallel to an edge of the first trench. A second layer of material is applied adjacent to and parallel to an edge of the first layer of material. The first layer of material is removed while retaining the second layer of material to form a narrow trench.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1, 2, 3, 4, 5 and 6 illustrate side sectional views of a wafer in intermediate stages of forming a narrow trench, in accordance with embodiments of the present invention.
FIG. 7 illustrates a side sectional view of a wafer with a completed narrow trench, in accordance with embodiments of the present invention.
FIG. 8 illustrates a method of forming a narrow trench, in accordance with embodiments of the present invention.



BEST MODES FOR CARRYING OUT THE INVENTION
Reference will now be made in detail to the various embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.
Narrow Semiconductor Trench Structure
Conventional semiconductor processing techniques are generally unable to produce a vertical trench narrower, e.g., of less width, than the critical dimension (CD) of a semiconductor process. Usually, a minimum trench width is determined by the lithographic process capability.
Utilizing a process with a smaller critical dimension in order to create narrower trenches is not always commercially feasible. For example, at any given point in time there is a minimum process geometry available. Further, there are many cases in which an improved process geometry is prohibitively expensive for its beneficial return, but in which case narrower trenches would be advantageous none-the-less.
FIG. 1 illustrates a side sectional view of a wafer in an intermediate stage of forming a narrow trench, in accordance with embodiments of the present invention. FIG. 1 illustrates a first insulating layer 110, for example oxide or nitride, that has been grown on top of a substrate 101. It is appreciated that embodiments of the present invention are well suited to a wide variety of substrates, e.g., Silicon or Germanium, as well as to a wide variety of doping levels, including formation in and/or on epitaxial layers.
FIG. 2 illustrates a side sectional view of a wafer in an intermediate stage of forming a narrow trench, in accordance with embodiments of the present invention. FIG. 2 illustrates a trench 120, formed via conventional trench etching techniques, through first insulating layer 110 and into substrate 101. In general, the depth of trench 120 is a function of the design of the semiconductor device utilizing the trench.
After formation of the trench 120, a second insulating film 115 is deposited or grown on all the exposed surfaces. For example, second insulating film 115 is deposited or grown on top of first insulating layer 110 and on the walls and bottom of trench 120.
FIG. 3 illustrates a side sectional view of a wafer in an intermediate stage of forming a narrow trench, in accordance with embodiments of the present invention. FIG. 3 illustrates the trench structure after second insulating film 115 has been removed from the top and bottom of trench 120 via a blanket dry etching process.
FIG. 4 illustrates a side sectional view of a wafer in an intermediate stage of forming a narrow trench, in accordance with embodiments of the present invention. FIG. 4 illustrates the trench 120 filled with crystal epitaxial fill 130 via a selective epitaxial growth process. Embodiments in accordance with the present invention are well suited to an epitaxial fill 130 comprising n-type or p-type doped or undoped material. Epitaxial fill 130 should be grown up to at least to the bottom of first insulating layer 110.
FIG. 5 illustrates a side sectional view of a silicon wafer in an intermediate stage of forming a narrow trench, in accordance with embodiments of the present invention. FIG. 5 illustrates the trench 120 after a chemical mechanical polishing operation has removed remaining portions of first insulating layer 110.
FIG. 6 illustrates a side sectional view of a wafer in an intermediate stage of forming a narrow trench, in accordance with embodiments of the present invention. FIG. 6 illustrates the fill 130 after an etching operation has removed remaining portions of second insulating layer 115 (FIG. 5).
It is to be appreciated that the removal of second insulating material 115 (FIG. 5) along the side portions of fill 130 produces narrow trenches 140, in accordance with embodiments of the present invention.
FIG. 7 illustrates a side sectional view of a wafer with a completed narrow trench, in accordance with embodiments of the present invention. FIG. 7 illustrates narrow trenches 140 after a high temperature anneal operation in a Hydrogen-ambient atmosphere has smoothed out the trench corners and/or surface.
It is to be appreciated insulating material 115 can generally be formed to a thickness that is much thinner, e.g., smaller, than a critical dimension of a semiconductor process. Consequently, trenches formed in semiconductors in accordance with embodiments of the present invention can be thinner (narrower) than a critical dimension of the semiconductor process utilized to create the semiconductor. For example, prototype trenches of 200 Å to 300 Å wide have been constructed utilizing a 1.0-micron process. Simulation results predict that trenches less than about 100 Å wide may be fabricated in this manner. Such trenches can be excess of 1000 times smaller than the process critical dimension.
FIG. 8 illustrates a semiconductor manufacturing process 800 of forming a narrow trench, in accordance with embodiments of the present invention. In 810, a first layer of insulating material is formed on a substrate. The insulating material may be deposited, e.g., PECVD, or thermally grown.
In 820, a trench is created through the first layer of insulating material and into the substrate. In 830, a second insulating material is formed on the first layer and on exposed portions of the trench.
In 840, the second insulating material is removed from the first a layer of insulating material and the bottom of the trench, for example, via a blanket dry etching process.
In 850, the trench is filled with an epitaxial material, for example via a selective epitaxial growth process. In 860, the first layer of insulating material is removed, for example via a chemical mechanical polishing process.
In 870, a narrow trench is formed by the removal of the remaining portions of the second insulating material.
In optional 880, a high temperature anneal is conducted in a Hydrogen-ambient atmosphere to smooth the trench surface.
While the method of the embodiment illustrated in flow chart 800 shows specific sequences and quantity of operations, the present invention is suitable to alternative embodiments. For example, not all the operations provided for in the methods are required for the present invention. Furthermore, additional operations can be added to the operations presented in the present embodiment. Likewise, the sequences of operations can be modified depending upon the application.
In this novel manner, a narrow trench having a width very much less than a critical dimension of a semiconductor process can be formed. Such narrow trenches advantageously increase density of vertical channel semiconductors as well as beneficially decrease on resistance of such devices, e.g., in vertical power metal oxide semiconductors (MOSFETs).
Thus, embodiments in accordance with the present invention provide systems and methods for narrow semiconductor trench structures. Additionally, in conjunction with the aforementioned benefit, embodiments of the present invention provide systems and methods for narrow semiconductor trench structures that enable constructing trenches having a width very much less than a critical dimension of a semiconductor process. As a further benefit, in conjunction with the aforementioned benefits, systems and methods of narrow semiconductor trench structures are provided in a manner that is compatible and complimentary with existing semiconductor processing systems and manufacturing processes.
Embodiments in accordance with the present invention, narrow semiconductor trench structure, are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims.

## Claims

1. A semiconductor device comprising:
a substrate having a substrate top surface,
a void within said substrate,
wherein said substrate surrounds said void on the sides and bottom of said void;
a region of epitaxial material formed on said bottom of said void and having a top surface substantially planar with said substrate top surface; and
a trench having said substrate on one side and said epitaxial material on the other side,
wherein said trench is characterized as having a width dimension of less than one hundredth of the critical dimension of the semiconductor process used to manufacture said semiconductor device,
wherein epitaxial material is disposed only on one side of said trench,
wherein said critical dimension is 1.0 micron;
wherein said epitaxial material is of opposite carrier type of the substrate; and
further comprising a vertical channel adjacent to said trench.

2. The semiconductor device of claim 1 wherein said trench is characterized as having a width dimension of less than one thousandth of the critical dimension of the semiconductor process used to manufacture said semiconductor device.