LDPMOS STRUCTURE FOR ENHANCING BREAKDOWN VOLTAGE AND SPECIFIC ON RESISTANCE IN BICMOS-DMOS PROCESS
An LDPMOS structure having enhanced breakdown voltage and specific on-resistance is described, as is a method for fabricating the structure. A P-field implanted layer formed in a drift region of the structure and surrounding a tightly doped drain region effectively increases breakdown voltage while maintaining a relatively low specific on-resistance.
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This application is a divisional of U.S. application Ser. No. 12/797,896 (Att. Docket P980083), filed on Jun. 10, 2010, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates generally to semiconductors and, more particularly, to power metal-oxide-semiconductor transistors and methods of fabricating and using same.
2. Description of Related Art
A lateral double-diffused metal-oxide-semiconductor (LIMOS) field effect transistor (MOSFET) is a MOSFET fabricated with coplanar drain and source regions. LDMOS devices with a P-channel may be referred to as LDPMOS devices. These devices are typically used in high voltage applications. When designing such LDPMOS devices, it is important for the device to have a very high breakdown voltage (BVD) whilst also exhibiting, during operation, a low specific on-resistance (Ronsp). By designing LDPMOS devices with low Ronsp and high BVD, low power loss can be achieved in high voltage applications. In addition, a low Ronsp can facilitate a high drain current (Idsat) when the transistor is in saturation. One problem encountered when designing such LDPMOS devices is that approaches tending to maximize BVD tend also adversely to affect the Ronsp and vice versa. In other words, a trade-off (e.g., inverse relationship) is typically presented between the optimization of BVD and Ronsp.
A need thus exists in the prior art for a lateral power MOSFET arrangement that can provide an effective compromise between large BVD and small Ronsp.
SUMMARY OF THE INVENTIONThe present invention addresses this need by providing a semiconductor structure that exhibits an efficient trade-off between breakdown voltage (BVD) and specific on-resistance (Ronsp). The invention herein disclosed comprises, according to one embodiment, a substrate formed of a first conductivity type with an epitaxial layer formed over the substrate. A first well region of a second conductivity type may be formed in the epitaxial layer with a second well region of the second conductivity type likewise formed in the epitaxial layer and spaced apart from the first well region. A third well region of the first conductivity type may be formed between the first well region and the second well region. A field region of the first conductivity type may be formed in a surface of the third well region and spaced apart from the first and second well regions, the field region having a drain region of the first conductivity type formed on a surface thereof and extending into the field region.
Another embodiment of the present invention further comprises a buried region of the second conductivity type formed in the epitaxial layer and extending into the substrate. According to this embodiment, the first well region extends from a surface of the epitaxial layer to an upper extent (e.g., surface) of the buried region, the first well region overlying a portion of the buried region and extending laterally beyond (e.g., past a right extent of) the buried region. The second well region of this embodiment also extends from the surface of the epitaxial layer to the upper extent of the buried region, overlies a portion of the buried region, and extends laterally beyond (e.g., past a left extent of) the buried region. The field region is spaced apart from the buried region.
While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless indicated otherwise, are not to be construed as limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents.
Any feature or combination of features described or referenced herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one skilled in the art. In addition, any feature or combination of features described or referenced may be specifically excluded from any embodiment of the present invention. For purposes of summarizing the present invention, certain aspects, advantages and novel features the present invention are described or referenced. Of course, it is to be understood that not necessarily all such aspects, advantages or features will be embodied in any particular implementation of the present invention. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims that follow.
Embodiments of the invention are now described and illustrated in the accompanying drawings, instances of which are to be interpreted to be to scale in some implementations while in other implementations, for each instance, not. In certain aspects, use of like or the same reference designators in the drawings and description refers to the same, similar or analogous components and/or elements, while according to other implementations the same use should not. According to certain implementations, use of directional terms, such as, top, bottom, left, right, up, down, over, above, below, beneath, rear, and front, are to be consumed literally, while in other implementations the same use should not. The present invention may be practiced in conjunction with various integrated circuit fabrication and other techniques that are conventionally used in the art, and only so much of the commonly practiced process steps are included herein as are necessary to provide an understanding of the present invention. The present invention has applicability in the field of semiconductor_devices and processes in general. For illustrative purposes, however, the following description pertains to lateral double-diffused metal-oxide-semiconductor field effect transistors (MOSFETs) and related methods of use and manufacture.
Referring more particularly to the drawings,
A device illustrated
A typical embodiment of the structure just described exhibits a specific on-resistance (Ronsp) ranging from about 50 to 150, an example being, 95, mΩ-mm2 while maintaining a breakdown voltage (BVD) of about −25 to −45, an example being −35, volts. As such, the present invention may be noted to provide an efficient trade-off between BVD and Ronsp.
The characteristics of the embodiment of
As an attempt to improve Ronsp properties of the prior-art device of
Returning to
It will be understood by one skilled in the art that respective references to N- and P-type materials, implantations, depositions, and so on may be replaced, respectively, by P- and N-type references. That is, N- and P-type references may be interchanged throughout this disclosure, which then may describe an LDNMOS, rather than LDPMOS structure. The description of an LDPMOS structure, for at least this reason, as an example is not intended to limit the scope of the present invention.
With combined reference to
First and second N-wells 315 and 320 (FIGS, 3 and 5C) may be formed in the epitaxial layer 110 at step 415, using, for example, a photolithographic method similar to that already described and/or that is well understood, to implant the N-wells 315 and 320 with atoms of N-type material at a concentration of about 1012 to 1013, an example being 9×1012, atoms/cm2. According to one embodiment, the first N-well 315 has a width of about 1.5 to about 3.5, an example being 2.5, microns and extends partially over (e.g., contacting) a first part (e.g., edge) of the NBL 305. The second N-well 320 may have a width of about 4 to about 6, an example being 5, microns extending partially over (e.g., contacting) another part (e.g., opposing part or end) of the NBL 305, At step 420, first and second P-wells 325 and 355 may be formed in the epitaxial layer 110, the first P-well 325 being formed. between the first and second N-wells 315 and 320, the second P-well 355 being formed adjacent the second N-well 320 opposite the first P-well 325. Forming of the first and second P-wells 325 and 355 may include patterning/implanting regions corresponding to their footprints (e.g., the space between N-wells 315 and 320 and that adjacent the second N-well 320) with atoms of P-type material (e.g., boron) at a concentration of about 1012 to 1013, an example being 8×1012, atoms/cm2. A suitable drive-in procedure may be performed at step 425 to drive-in the N- and P-wells 315, 320, 325, and 355 to a depth about the same as that of an upper extent of the NBL 305, which can be about 2 to 4, an example being 3, microns.
At step 430, the P-field 335 (
Field oxide (FOX) regions 345, 346, and 347 (
A portion of the first FOX region 345 may include a thin region 351 (
A gate electrode 350 (
At step 445, the N+/N− region 360 (i.e., an N-type lightly-doped drain [NLDD] module) may be formed by implanting N-type atoms into a surface of a first portion of a space between the first and third FOX regions 345 and 347 (e.g., and contacting third FOX region 347). A first portion of the N+/N− region 360 may be lightly doped (N−), with a second portion being doped to a higher concentration of N-type atoms (N+). For example, the (N−) portion may be doped to a concentration of about 1013 to 1014, an example being 3×1013, atoms/cm2, while the (N+) portion may be doped to a concentration of about 1015 to 1016, an example being 3×1015, atoms/cm2. At step 450, the PLDD 340 may be formed by implanting atoms of P-type material between (e.g., and contacting) the first and second FOX regions 345 and 346 as shown in
Although the disclosure herein refers to certain illustrated embodiments, it is to be understood that these embodiments have been presented by way of example rather than limitation. The intent accompanying this disclosure is to have such embodiments construed in conjunction with the knowledge of one skilled in the art to cover all modifications, variations, combinations, permutations, omissions, substitutions, alternatives, and equivalents of the embodiments, to the extent not mutually exclusive, as may fall within the spirit and scope of the invention as limited only by the appended claims.
Claims
1. A method, comprising:
- forming a buried layer in a first-conductivity type substrate;
- depositing an epitaxial layer of the first conductivity type over the substrate and the buried layer;
- forming first and second wells of a second conductivity type in the epitaxial layer;
- forming a third well of the first conductivity type between the first and second wells;
- forming a field region of the first conductivity type in the third well, the field region being spaced apart from the first and second wells and the buried layer; and
- forming a. drain region of the first conductivity type in the field region.
2. The method as set forth in claim 1, wherein:
- the first conductivity type is P-type;
- the second conductivity type is N-type; and
- the forming of a field region is preceded by driving in the first, second, and third wells.
3. The method as set forth in claim 1, wherein:
- the first conductivity type is N-type;
- the second conductivity type is P-type; and
- the forming of a field region is preceded by driving in the first, second, and third wells.
4. The method as set forth in claim 1, wherein:
- the buried layer is formed of material having the second conductivity type;
- the forming of the first and second wells comprises implanting atoms of the second conductivity type into a surface of the epitaxial layer; and
- the forming of the third well comprises implanting atoms of the first conductivity type into the surface of the epitaxial layer.
5. The method as set forth in claim 4, wherein the forming of the first, second, and third wells further comprises driving the wells to a depth about the same as that of an upper extent of the buried layer.
6. The method as set forth in claim 1, further comprising:
- forming a first insulation layer overlying a portion of the second well, a portion of the third well, and a portion of the field region; and
- forming a second insulation layer overlying a portion of the first well, a portion of the third well, and a portion of the field region, the first insulation layer being separated from the second insulation layer.
7. The method as set forth in claim 6, wherein the forming of the first and second insulation layers comprises:
- depositing an oxide layer; and
- patterning and etching the oxide layer.
8. The method as set forth in claim 6, wherein the forming of the first and second insulation layers comprises local oxidation of silicon.
9. The method as set forth in claim 1, further comprising:
- forming a lightly doped drain region of the first conductivity type in the field region in a space between the first and second insulation regions; and
- forming a source region in a surface of the second well.
10. The method as set forth in claim 6, wherein the forming of the source region comprises:
- forming a first region having the second conductivity type; and
- forming a second region having the first conductivity type.
11. A semiconductor structure fabricated according to the method set forth in claim 1.
Type: Application
Filed: Oct 10, 2012
Publication Date: Feb 14, 2013
Applicant: MACRONIX INTERNATIONAL CO., LTD. (Hsinchu)
Inventors: Yin-Fu Huang (Tainan City), Miao-Chun Chung (Miaoli County), Shih-Chin Lien (Taipei County)
Application Number: 13/648,964
International Classification: H01L 29/78 (20060101); H01L 21/336 (20060101);