Trench MOSFET having shielded electrode integrated with trench Schottky rectifier

A trench MOSFET having shielded gate in parallel with trench Schottky rectifier is formed on a single chip to further increase the efficiency of the trench MOSFET having shielded electrode. As the size of present device is getting smaller and smaller, the trench Schottky rectifier of this invention is able to be shrink and, at the same time, to achieve lower forward voltage drop and lower reverse leakage current.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from application Ser. No. 12/659,639 filed Mar. 16, 2010 which is continuation in part of application Ser. No. 12/213,628 now U.S. Pat. No. 7,816,732.

FIELD OF THE INVENTION

This invention relates generally to the cell structure, device configuration of semiconductor devices. More particularly, this invention relates to an improved trench MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having shielded electrode integrated with trench Schottky rectifier on a single chip to improve operation efficiency.

BACKGROUND OF THE INVENTION

Trench MOSFET having gate electrode over shielded electrode structure provides advantages over conventional trench MOSFET, such as reduced gate to drain charge Qgd, and reduced on-resistance. See for example, U.S. Pat. Nos. 5,998,833 and 7,768,064. The superior performance of the trench MOSFET having shielded electrode is an excellent choice for DC/DC converter. Meanwhile, in order to further increase the efficiency of the trench MOSFET having shielded electrode, the parasitic PN body diode of the trench MOSFET must be prevented from turning on, because once the parasitic PN body diode is turned on, both electron and hole carriers are generated that requires longer time to eliminate these carriers through the electron-hole combinations, thus reducing the efficiency of the trench MOSFET. Therefore, a Schottky rectifier is chosen to be implemented as a clamping diode in parallel to the parasitic PN body diode to prevent the body diode from turning on because that, the Schottky rectifier is operated with a single carrier, e.g., the carriers consisted of electrons only, and this single type of carriers can be drawn from the drain electrode. Therefore, the Schottky rectifier is an effective and preferred clamping diode to increase the operational efficiency of the semiconductor power device. The Schottky clamping operation can be realized when the forward voltage Vf of the Schottky rectifier is less than the parasitic diode that is approximately 0.7 volts.

Accordingly, it would be desirable to provide a new and improved device configuration to further improving the characteristic of the trench MOSFET having shielded electrode by integrating a trench Schottky rectifier on a single chip.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a new and improved semiconductor power device such as an integrated circuit comprising a trench MOSFET having shielded electrode and a trench Schottky rectifier on a single chip for better operation performance. According to the present invention, there is provided an integrated circuit comprising a plurality of trench MOSFETs and a plurality of trench Schottky rectifiers horizontally disposed in two different areas further comprising: a substrate of a first conductivity type; an epitaxial layer of the first conductivity type over the substrate, the epitaxial layer having a lower doping concentration than the substrate; a plurality of gate trenches extending into the epitaxial layer; a trench MOSFET comprising a gate electrode over a shielded electrode in each the gate trench wherein the gate electrode and the shielded electrode insulated from each other by an inter-electrode insulation layer, and the gate electrode is insulated from a source region of the first conductivity type and body region of a second conductivity type by a first gate insulation layer and the shield electrode is insulated from the epitaxial layer by a second gate insulation layer; the first gate insulation layer along the gate trenches is less than the second insulation layer; the gate electrode surrounded by the source region encompassed in the body region above the shielded electrode; the gate electrode connected to a gate metal and the shielded electrode to a source metal; a contact insulation layer covering the integrated circuit with a source-body contact trench opened in the trench MOSFET through the source and extended into the body regions and filled with a contact metal plug overlying a barrier metal layer therein, the contact metal plug filled in the source-body contact trench connected with the source metal; a trench Schottky rectifier formed into the epitaxial layer in a different area from the trench MOSFET and having a Schottky barrier layer lined in a Schottky contact trench filled with the contact metal plug overlying the barrier metal layer directly contacting the Schottky contact trench bottom and sidewalls, and between a pair of adjacent gate trenches wherein the source and body regions do not exist, the contact metal plug filled in the Schottky contact trench connected with an anode metal; the gate trenches in the trench MOSFET and trench Schottky rectifier having a greater trench depth than the Schottky contact trench into the epitaxial layer; the Schottky rectifier formed at least along sidewalls of the Schottky contact trench in the epitaxial layer, separated from the pair of adjacent gate trenches by the epitaxial layer without having the source and body regions surrounding the Schottky contact trench sidewalls; at least a gate contact trench in the trench MOSFET opened through the contact insulation layer and extended into the gate electrode in a wide gate trench having a greater trench width than the gate trenches in the trench MOSFET, and filled with the contact metal plug overlying a barrier metal layer therein, the contact metal plug filled in the gate contact trench connected with the gate metal; and the source metal and the anode metal connected together as a source/anode metal.

In other preferred embodiments, this invention include one or more of following features: the gate trench in the trench Schottky rectifier is filled with the gate electrode over the shielded electrode wherein the gate electrode and the shielded electrode insulated from each other by an inter-electrode insulation layer, and the gate electrode is insulated from the epitaxial layer by the first gate insulation layer and the shielded electrode is insulated from the epitaxial layer by a second gate insulation layer; the first gate insulation layer along the gate trenches is thinner than the second insulation layer; the gate electrode in the trench Schottky rectifier extends to a wide gate electrode in a wide gate trench having a greater trench width than the gate trenches in the trench Schottky rectifier, and at least a gate contact trench in the trench Schottky rectifier opened through the contact insulation layer and extended into the wide gate electrode in the trench Schottky rectifier, and filled with the contact metal plug overlying a barrier metal layer therein, the contact metal plug filled in the wide gate electrode in the trench Schottky rectifier connected with the source/anode metal and separated from the gate electrode in the trench MOSFET; the gate trench in the trench Schottky rectifier is only filled with the shielded electrode wherein the shielded electrode insulated from the epitaxial layer by the second gate insulation layer; the shielded electrode in the trench Schottky rectifier extends to a wide shielded electrode in a wide gate trench having a greater trench width than the gate trenches in the trench Schottky rectifier, and at least a shielded contact trench in the trench Schottky rectifier opened through the contact insulation layer and extended into the wide shielded electrode in the Schottky rectifier, and filled with the contact metal plug overlying a barrier metal layer therein, the contact metal plug filled in the wide shielded contact trench connected with the source/anode metal; the barrier metal layer lines in the source-body contact and the Schottky contact trenches is Ti/TiN or Co/TiN; the contact metal plug overlying the barrier metal layer is tungsten; the Schottky barrier layer comprises TiSi2(Ti Silicide) or CoSi2(Co Silicide); the source/anode metal and the gate metal are Ti/Aluminum alloys, Ti/TiN/Aluminum alloys, or Ti/TIN/Copper disposed on top surface of the contact insulation layer and the contact metal plugs; the Schottky barrier layer lines along sidewalls and bottom of the Schottky contact trench; the Schottky barrier layer lines along only sidewalls of the Schottky contact trench in the epitaxial layer; the epitaxial layer is a single epitaxial layer; the epitaxial layer is a double epitaxial layer with a doping concentration of the top epitaxial layer less than that of the bottom epitaxial layer; the integrated circuit further comprises a body contact region of the second conductivity type formed only within the body region wrapping sidewalk and bottom of each the source-body contact trench, but not formed within the trench Schottky rectifier, wherein the body contact region has a higher doping concentration than the body region; the integrated circuit further comprises a Schottky barrier height enhancement region of the first conductivity type having doping concentration less than the epitaxial layer, formed within the epitaxial layer in the Schottky rectifier and wrapping sidewalls and bottom of each the Schottky contact trench; the integrated circuit further comprises a Schottky barrier layer enhancement region of the second conductivity type within the epitaxial layer in the Schottky rectifier and wrapping sidewalls and bottom of each the Schottky contact trench; the contact metal plug filled in the source-body contact trench and the gate contact trench in the trench MOSFET, and the Schottky contact trench in the trench Schottky rectifier extends to cover top surface of the contact insulation layer connected with the gate metal and the source/anode metal, respectively; the contact metal plug is tungsten layer deposited over a Ti/TiN or Co/TiN barrier metal layer, covering the contact insulation layer; the source/anode metal and the gate metal are Ti/Aluminum alloys, Ti/TIN/Aluminum alloys, or Ti/TiN/Copper disposed on top of the contact metal plug; the first gate insulation layer has a thickness along the gate trenches less than that of the second gate insulation layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Please refer toFIG. 1for a preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 1) on a single chip. The N-channel circuit is formed in an N epitaxial layer100supported on a heavily doped N+ substrate102which coated with back metal118on the rear side as drain/cathode metal. A plurality of gate trenches103are formed extending in the N epitaxial layer100, each of the gate trenches103is filled with a gate electrode104over a shielded electrode105, wherein the gate electrode104and the shielded electrode105is insulated from each other by an inter-electrode insulation layer106, the gate electrode104is insulated from an N+ source region107and a P body region108by a first gate oxide layer129and the shielded electrode105is insulated from the epitaxial layer100by a second gate insulation layer109, wherein the gate electrode104is surrounded by the N+ source region107encompassed in the P body region108above the shielded electrode105. The thickness along the gate trenches103of first gate insulation layer129is less than that of the second gate insulation layer109. The trench MOSFET further comprises a source-body contact trench110opened through an contact insulation layer111covering the integrated circuit, and further penetrating through the N+ source region107and extending into the P body regions108. The source-body contact trench110is filled with a contact metal plug112, for example tungsten plug, overlying a barrier metal layer113therein. In the P body region108between a pair of the gate trenches103in the trench MOSFET, a p+ body contact region114is formed wrapping sidewalls and bottom of the source-body contact trench110with higher doping concentration than the P body region108to further reduce the contact resistance between the P body region108and the contact metal plug112. The gate trenches103in the trench MOSFET further extends to a wide gate trench103′ with greater trench width than the gate trenches103and filled with a gate electrode104′ above a shielded electrode105′. A gate contact trench115is opened through the contact insulation layer111and extended into each the gate electrode104′ in each the wide gate trench103′, and filled with the contact metal plug112, for example tungsten plug, overlying the barrier metal layer113therein. The trench Schottky rectifier is formed in a different area from the trench MOSFET and having a Schottky barrier layer lined in a Schottky contact trench116which is penetrating through the contact insulation layer111and extending into the N epitaxial layer100. The Schottky contact trench116is filled with the contact metal plug112, for example tungsten plug, over the barrier metal layer113directly contacting sidewalls and bottom of the Schottky contact trench between a pair of adjacent gate trenches103wherein the source and body region do not exist, wherein the gate trenches103in the trench MOSFET and trench Schottky rectifier have a greater trench depth than the Schottky contact trench116into the N epitaxial layer100. The gate trenches103in the trench Schottky rectifier further extend to a wide gate trench103″ having a greater trench width than the gate trenches103, and filled with a gate electrode104″ above a shielded electrode105″. A gate contact trench117is opened through the contact insulation layer111and extended into each the gate electrode104″ in each the wide gate trench103″, and filled with the contact metal plug112, for example tungsten plug, overlying the barrier metal layer113therein. Onto the contact insulation layer111, a front metal layer is formed and patterned to act as a gate metal118and a source/anode metal119, wherein the gate metal118is contacting with the contact metal plug112in the gate contact trench115, and the source/anode metal119is contacting with the contact metal plugs112in the source-body contact trench110, the Schottky contact trench116and the gate contact trench117. Besides, the gate electrodes104,104′ and104″ are connected to the gate metal118and the shielded electrodes105,105′ and105″ are connected to the source/anode metal119. The barrier metal layer113can be implemented by Ti/TiN or Co/TiN, the Schottky barrier layer can be implemented by TiSi2(Ti Silicide) or CoSi2(Co Silicide), and the front metal can be implemented by Ti/Aluminum.

Please refer toFIG. 2for another preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 2) on a single chip. The integrated circuit inFIG. 2has similar configuration toFIG. 1except that, the Schottky contact trench216is formed between two adjacent gate trenches203only filled with the shielded electrode205in the trench Schottky rectifier which is different from other gate trenches203in the trench MOSFET filled with the gate electrode204over the shielded electrode205, wherein the shielded electrode205in the gate trenches203in the trench Schottky rectifier is insulate from the adjacent N epitaxial layer200and the P body region208by a second gate insulation layer209.

Please refer toFIG. 3for another preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 3) on a single chip which has similar configuration toFIG. 2except that, the integrated circuit inFIG. 3has double N epitaxial layers comprising a bottom N1epitaxial layer300and a top N2epitaxial layer300′, wherein the bottom N1epitaxial layer300has a higher doping concentration than the top N2epitaxial layer300′ to further reduce a forward voltage drop and a reverse leakage current for the trench Schottky rectifier.

Please refer toFIG. 4for another preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 4) on a single chip which has similar configuration toFIG. 1except that, the integrated circuit inFIG. 4has an n− Schottky barrier height enhancement region420surrounding bottom and sidewalls of the Schottky contact trench416within the N epitaxial layer400in the trench Schottky rectifier, wherein the n− Schottky barrier height enhancement region420has a lower doping concentration than the N epitaxial layer400.

Please, refer toFIG. 5for another preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 5) on a single chip which has similar configuration toFIG. 2except that, the integrated circuit inFIG. 5has an n− Schottky barrier height enhancement region520surrounding bottom and sidewalls of the Schottky contact trench516within the N epitaxial layer500in the trench Schottky rectifier, wherein the n− Schottky barrier height enhancement region520has a lower doping concentration than the N epitaxial layer500.

Please refer toFIG. 6for another preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 6) on a single chip which has similar configuration toFIG. 5except that inFIG. 6, the contact metal plugs612, for example tungsten plugs padded by a barrier metal layer613of Ti/TiN or Co/TiN filled in the source-body contact trench610and the gate contact trench615in the trench MOSFET and in the Schottky contact trench616in the trench Schottky rectifier extend to cover top surface of the contact insulation layer connected to the gate metal618and the source/anode metal619, respectively.

Please refer toFIG. 7for another preferred N-channel integrated circuit comprising a trench MOSFET and a trench Schottky rectifier (SKY, as illustrated inFIG. 7) on a single chip which has similar configuration toFIG. 6except that, the integrated circuit inFIG. 7has a p Schottky barrier height enhancement region720surrounding bottom and sidewalls of the Schottky contact trench716within the N epitaxial layer700in the trench Schottky rectifier.