# Patent

## Title
Gate structure in a trench region of a semiconductor device and method for manufacturing the same

## Abstract

Disclosed are a gate structure in a trench region of a semiconductor device and a method for manufacturing the same. The semiconductor device includes a pair of drift regions formed in a semiconductor substrate; a trench region formed between the pair of drift regions; an oxide layer spacer on sidewalls of the trench region; a gate formed in the trench region; and a source and a drain formed in the pair of the drift regions, respectively.

## Background
This application is a divisional of U.S. patent application Ser. No. 11/646,837, filed on Dec. 27, 2006 now U.S. Pat. No. 7,541,641, which is incorporated herein by reference in its entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same.
2. Description of the Related Art
High voltage devices require a low-density drift region in a drain so as to have breakdown characteristics against high voltages. The drift region occupies the largest area in the high voltage device. Larger drift region is required in a horizontal direction as the higher breakdown characteristic is required for the high voltage device.
Further, in order to realize a high voltage breakdown characteristic, it is necessary for the high voltage device to increase the length of a channel region for preventing the punch through between a source and a drain. The channel region occupies the second largest area in the high voltage device.
Hereinafter, a high voltage device according to the related art will be described in detail with reference to the attached drawings.
FIG. 1 is a cross-sectional view of a high voltage device according to the related art.
Referring to FIG. 1, a low-density drift region 11 is formed on a predetermined region of a p-type semiconductor substrate 10. A gate oxide layer 12 is formed on an upper surface of the p-type semiconductor substrate 10, and a field oxide layer 13 for a field plate is formed on the semiconductor substrate 10 corresponding to a part of the drift region 11.
A gate 14 is formed on the gate oxide layer 12 and the field plate 13. A source 15 and a drain 16, i.e., n-type doped region 15 having a high-density are formed adjacent to both sides of the gate 14 and in the semiconductor substrate 10. At this time, the source 15 is spaced apart from the drift region 11, and the drain 16 is formed in the drift region 11.
The channel region 17 is formed between the source 15 and the drift region 11 in the semiconductor substrate 10 below the gate 14, and electrons 18 flow from the source region 15 to the drain region 16.
In the conventional high voltage device as described above, the drift region 11 needs to be increased in its horizontal length due to its horizontal structure so as to improve the breakdown characteristic. This may act as limitations in high-integration and miniaturization of the semiconductor device.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a semiconductor device and a method for manufacturing the same, which can reduce an area of a device while sustaining the breakdown strength.
To accomplish the above object of the present invention, there is provided a semiconductor device, which comprises a pair of drift regions formed in a semiconductor substrate; a trench region formed between the pair of drift regions; an oxide layer spacer formed on both sidewalls of the trench region; an insulating layer formed below the trench region; a gate formed in the trench region; and a source and a drain formed in the pair of the drift regions, respectively.
To accomplish the above object of the present invention, there is provided a method for manufacturing a semiconductor device, which comprises the steps of: forming a pair of drift regions in a semiconductor substrate; forming an oxide layer on the substrate in such a manner that the oxide layer is partially overlapped with the pair of drift regions; forming a trench region between the pair of drift regions; forming an oxide layer spacer on both sidewalls of the trench region; forming an insulating layer below the trench region; forming a gate in the trench region and on the oxide layer; and forming a source and a drain on the pair of drift regions, respectively.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a high voltage device according to the related art; and
FIGS. 2A to 2G are cross-sectional views showing a semiconductor device and a method for manufacturing the same according to a preferred embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment according to the present invention will be described in detail, with reference to the following drawings.
In the following description of the present invention, technologies which are generally known in the art and do not directly relate to the present invention will be omitted in order to avoid redundancy and to clarify the subject manner of the present invention. In the same manner, some of elements are exaggerated, omitted or simplified in the drawings and the elements may have sizes different from those shown in drawings, in practice.
FIG. 2A to 2G are cross-sectional views showing a semiconductor device and a method for manufacturing the same according to a preferred embodiment of the present invention.
First, as shown in FIG. 2A, a pair of drift regions 21, which are symmetrical to each other, are formed in a p-type semiconductor substrate 20.
The drift regions 21 are deeply formed in the vertical direction, and spaced apart from each other in the horizontal direction by a predetermined distance.
A method for forming the drift region 21 includes the steps of; forming a drift region mask pattern in the semiconductor substrate 20; implanting n-type low-density impurities; and driving-in the implanted impurities.
Next, as shown in FIG. 2B, an oxide layer 22 is formed on the surface of the substrate 20 such that the oxide layer 22 is partially overlapped with both drift regions 21. In other words, the length of the oxide layer 22 is larger than the distance between both drift regions 21.
A method for forming the oxide layer 22 includes the steps of; forming an oxide layer mask pattern on the substrate 20; etching the substrate 20 by a predetermined depth; depositing the oxide layer 22 over the entire surface; and planarizing the oxide layer 22.
As shown in 2C, a nitride layer 31 is formed on the substrate 20.
Next, as shown in 2D, a trench region 23 is formed between both drift regions and in the substrate 20.
The trench region 23 has a depth than equal to or shallower than that of the drift region 21, and a width shorter than the length of the oxide layer 22.
A method for forming the trench region 23 includes the steps of; forming a trench region mask pattern; and etching the substrate 20 by a predetermined depth.
Next, as shown in FIG. 2E, an oxide layer spacer 24 is formed on both sidewalls of the trench region 23. The oxide layer spacer 24 is used as a field plate of a high voltage device. A method for forming the oxide layer spacer 24 includes the steps of; depositing the oxide layer over the entire surface; and anisotropic dry etching the deposited oxide layer.
An insulating layer 32 is formed below the trench region 23. The insulating layer 32 is a thermal oxide layer formed by performing a thermal oxidation process.
Next, the nitride layer 31 is removed.
Next, as shown in FIG. 2F, a gate 25 is formed in the trench region 23 and on the upper surface of the oxide layer 22. After that, a nitride layer spacer 26 is formed on both sidewalls of the gate 25.
A method for forming the gate 25 includes the steps of; depositing a gate conductive layer so as to be completely filled in the trench region 23; forming a gate mask pattern; and etching the gate conductive layer. Further, a method for forming the nitride layer spacer 26 includes the steps of; depositing the nitride layer over the entire surface; and anisotropic dry etching the deposited nitride layer.
Next, as shown in FIG. 2G, a source 27 and a drain 28 are formed on both drift regions 21, respectively, by implanting n-type impurities having a high density.
Further, electrons 30 flow between the source 27 and the drain 28.
As described above, the semiconductor device is featured in that the drift regions 21 having a vertical structure are formed to be symmetrical to each other in the left and right direction.
In the high voltage device according to the present invention, since a depletion region is formed in a vertical direction when a high electric power is applied to the drain 28, both lengths of the drift region 21 and the channel region 29 can be shorter about a several μm than that of the conventional structure, thereby reducing the area of the high voltage device.
While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

## Claims

1. A method for manufacturing a semiconductor device, the method comprising the steps of:
forming first and second drift regions in a semiconductor substrate;
forming an oxide layer on the substrate such that the oxide layer partially overlaps the first and second drift regions;
forming a trench between the first and second drift regions;
forming an oxide spacer on sidewalls of the trench;
forming an insulating layer at a bottom of the trench;
forming a gate in the trench and on the oxide layer;
forming a spacer on sidewalls of the gate; and
forming a source in one of the first and second drift regions and a drain in the other of the first and second drift regions.

2. The method according to claim 1, wherein the step of forming the oxide layer includes:
forming a mask pattern on the substrate;
etching the substrate to a predetermined depth;
depositing the oxide layer over an entire surface of the semiconductor substrate; and
planarizing the oxide layer.

3. The method according to claim 1, wherein the trench has a depth equal to or less than that of the first and second drift regions and a width equal to or less than a length of the oxide layer.

4. The method according to claim 3, wherein the width of the trench is less than the length of the oxide layer.

5. The method according to claim 1, wherein the spacer comprises silicon nitride.

6. The method according to claim 1, wherein the first and second drift regions are symmetrical to and spaced apart from each other in a horizontal direction.

7. A method for manufacturing a semiconductor device, the method comprising the steps of:
forming first and second drift regions in a semiconductor substrate;
forming an oxide layer on the substrate such that the oxide layer overlaps with each of the first and second drift regions;
forming a nitride layer on the substrate;
forming a trench between the first and second drift regions;
forming an oxide spacer on sidewalls of the trench;
forming an insulating layer at a bottom of the trench;
removing the nitride layer;
forming a gate in the trench region and at least partially on the oxide layer; and
forming a source in one of the first and second drift regions and a drain in the other of the first and second drift regions.

8. The method according to claim 7, wherein the trench has a depth less than that of the first and second drift regions and a width less than a length of the oxide layer.

9. The method according to claim 7, further comprising forming a nitride spacer on sidewalls of the gate.

10. A method for manufacturing a semiconductor device, the method comprising the steps of:
forming first and second drift regions in a semiconductor substrate;
forming a mask pattern on the substrate;
etching the substrate to a predetermined depth;
depositing the oxide layer over an entire surface of the semiconductor substrate such that the oxide layer partially overlaps the first and second drift regions;
planarizing the oxide layer;
forming a trench between the first and second drift regions;
forming an oxide spacer on sidewalls of the trench;
forming an insulating layer at a bottom of the trench;
forming a gate in the trench and on the oxide layer; and
forming a source in one of the first and second drift regions and a drain in the other of the first and second drift regions.

11. The method according to claim 10, wherein the oxide layer has a length greater than the distance between the first and second drift regions.

12. The method according to claim 10, wherein the trench has (i) a depth equal to or less than that of the first and second drift regions and (ii) a width equal to or less than a length of the oxide layer.

13. The method according to claim 10, wherein the width of the trench is less than the length of the oxide layer.

14. The method according to claim 10, further comprising forming a nitride layer on the substrate prior to forming the trench between the first and second drift regions.

15. The method according to claim 14, further comprising removing the nitride layer after forming the insulating layer at the bottom of the trench.

16. The method according to claim 10, further comprising forming a nitride spacer on sidewalls of the gate.

17. The method according to claim 10, wherein the first and second drift regions are symmetrical to and spaced apart from each other in a horizontal direction.