HEMT with stair-like compound layer at drain

An HEMT with a stair-like compound layer as a drain includes a first III-V compound layer. A second III-V compound layer is disposed on the first III-V compound layer. The composition of the first III-V compound layer and the second III-V compound layer are different from each other. A source electrode, a gate electrode and a drain electrode are disposed on the second III-V compound layer. The gate electrode is disposed between the source electrode and the drain electrode. A first P-type III-V compound layer is disposed between the drain electrode and the second III-V compound layer. The first P-type III-V compound layer is stair-like.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high electron mobility transistor (HEMT) with a stair-like compound layer.

2. Description of the Prior Art

Due to their semiconductor characteristics, III-V semiconductor compounds may be applied in many kinds of integrated circuit devices, such as high power field effect transistors, high frequency transistors, or high electron mobility transistors (HEMTs). In the high electron mobility transistor, two semiconductor materials with different band-gaps are combined and a heterojunction is formed at the junction between the semiconductor materials as a channel for carriers. In recent years, gallium nitride (GaN) based materials have been applied in high power and high frequency products because of their properties of wider band-gap and high saturation velocity.

A two-dimensional electron gas (2DEG) may be generated by the piezoelectric property of the GaN-based materials, and the switching velocity may be enhanced because of the higher electron velocity and the higher electron density of the 2DEG.

However, trapped electrons are generated during the operation of the HEMT, which affects the performance of the HEMT.

SUMMARY OF THE INVENTION

In view of this, an HEMT with a stair-like compound layer as a drain is provided in the present invention to remove trapped electrons without increasing on-resistance.

According to a preferred embodiment of the present invention, an HEMT with a stair-like compound layer as a drain includes a first III-V compound layer. A second III-V compound layer is disposed on the first III-V compound layer, wherein composition of the first III-V compound layer and composition of the second III-V compound layer are different from each other. A source electrode, a gate electrode and a drain electrode are disposed on the second III-V compound layer, wherein the gate electrode is disposed between the source electrode and the drain electrode. A first P-type III-V compound layer is disposed between the drain electrode and the second III-V compound layer, wherein the first P-type III-V compound layer has a stair-like shape.

According to another preferred embodiment of the present invention, an HEMT with a stair-like compound layer as a drain includes a first III-V compound layer. A second III-V compound layer is disposed on the first III-V compound layer, wherein composition of the first III-V compound layer and composition of the second III-V compound layer are different from each other. A source electrode, a gate electrode and a drain electrode disposed on the second III-V compound layer, wherein the gate electrode is disposed between the source electrode and the drain electrode, the drain electrode includes a first part and a second part, material of the first part is different from material of the second part. A first P-type III-V compound layer is disposed between the drain electrode and the second III-V compound layer, wherein the first P-type III-V compound layer has a stair-like shape, and Schottky contact is between the first part and the first P-type III-V compound layer.

According to yet another preferred embodiment of the present invention, a fabricating method of an HEMT with a stair-like compound layer as a drain includes providing a III-V compound layer. Next, P-type III-V compound layer formed to cover the III-V compound layer. Subsequently, the P-type III-V compound layer is segmented to form a first P-type III-V compound layer and a second P-type III-V compound layer. Later, the first P-type III-V compound layer is patterned to make the first P-type III-V compound layer to have a stair-like shape. After patterning the first P-type III-V compound layer, a source electrode, a gate electrode and a drain electrode are formed, wherein the gate electrode is disposed on the second III-V compound layer, the drain electrode is disposed on the first P-type III-V compound layer.

DETAILED DESCRIPTION

FIG.1toFIG.6depict a fabricating method of a high electron mobility transistor (HEMT) with a stair-like compound layer as a drain according to a first preferred embodiment of the present invention.

As shown inFIG.1, a substrate10is provided. The substrate10may include a silicon substrate and a barrier. Next, a first III-V compound layer12, a second III-V compound layer14and a P-type III-V compound layer16are formed in sequence to cover the substrate10. The P-type III-V compound layer16covers and contacts the second III-V compound layer14. The second III-V compound layer14covers and contacts the first III-V compound layer12. The first III-V compound layer12covers and contacts the barrier of the substrate10. The barrier may be III-V compounds such as aluminum gallium nitride. The P-type III-V compound layer16is preferably P-type gallium nitride. The second III-V compound layer14is preferably aluminum gallium nitride. The first III-V compound layer12is preferably gallium nitride. However, based on different product requirements, the barrier, the P-type III-V compound layer16, the second III-V compound layer14, the first III-V compound layer12may be independently selected from aluminum gallium nitride, aluminum indium nitride, aluminum indium gallium nitride, aluminum nitride or other III-V compounds.

As shown inFIG.2, the P-type III-V compound layer16is segmented to form a first P-type III-V compound layer16aand a second P-type III-V compound layer16b. According to a preferred embodiment of the present invention, the P-type III-V compound layer16can be segmented by an etching process.

Next, the first P-type III-V compound layer16ais patterned to make the first P-type III-V compound layer16ato have a stair-like shape. In details, as shown inFIG.3, a first patterned photoresist18ais formed to cover the second P-type III-V compound layer16b, the second III-V compound layer14and part of the first P-type III-V compound layer16a. The first P-type III-V compound layer16afarther from the second P-type III-V compound layer16bis exposed from the first patterned photoresist18a. Later, the exposed first P-type III-V compound layer16ais etched to form a recess20awithin the surface of the first P-type III-V compound layer16a. As shown inFIG.4, after the first patterned photoresist18ais removed, a second patterned photoresist18bis formed to cover the second P-type III-V compound layer16b, the second III-V compound layer14and part of the first P-type III-V compound layer16a. Only part of the recess20ais exposed through the second patterned photoresist18b. Subsequently, the recess20awhich is exposed is etched to form another recess20b. A vertical distance between the recess20band the second III-V compound layer14is smaller than a vertical distance between the recess20aand the second III-V compound layer14. The fabricating stages of forming recess20a/20bcan be repeated several times to make the first P-type III-V compound layer16ato have a stair-like shape. It is note-worthy that the steps constituting the stair-like shape go down toward a direction away from the second P-type III-V compound layer16b.

As shown inFIG.5, after the second patterned photoresist18ais removed, a gate electrode G is formed to contact and cover the second P-type III-V compound layer16b. Schottky contact is between the gate electrode G and the second P-type III-V compound layer16b. For example, the gate electrode G includes nickel or gold. As shown inFIG.6, a drain electrode D and a source electrode S are formed simultaneously. The drain electrode D covers and contacts the first P-type III-V compound layer16aand contacts the second III-V compound layer14. Source electrode S covers and contacts the second III-V compound layer14. The drain electrode D is at one side of the gate electrode G. The source electrode S is at another side of the gate electrode G which is opposed to the drain electrode D. Moreover, Ohmic contact is between the drain electrode D and the first P-type III-V compound layer16aand between drain electrode D and the second III-V compound layer14. Ohmic contact is also between the source electrode S and the second III-V compound layer14. The drain electrode D and the source electrode S may include titanium, aluminum, nickel, gold or titanium nitride. For example, the drain electrode D and the source electrode S can respectively be composite materials formed by stacking titanium, aluminum, nickel and gold in sequence or formed by stacking titanium, aluminum, titanium and titanium nitride in sequence. After the drain electrode D and the source electrode S are formed, an insulating layer22such as silicon oxide is formed to cover and contact the drain electrode D, the source electrode S, the gate electrode G and to fill up space between the drain electrode D, the source electrode S, the gate electrode G. Now, an HEMT100awith a stair-like compound layer as a drain of the present invention is completed.

FIG.7depicts a fabricating method of an HEMT with a stair-like compound layer as a drain according to a second preferred embodiment of the present invention, wherein elements which are substantially the same as those in the first preferred embodiment are denoted by the same reference numerals; an accompanying explanation is therefore omitted. The difference between the second preferred embodiment and the first preferred embodiment is that both Ohmic contact and Schottky contact are between the drain electrode D and the first P-type III-V compound layer16a. Other elements are the same as that in the first preferred embodiment. In details, after fabricating stages inFIG.1toFIG.4are completed, as shown inFIG.7, the second patterned photoresist layer18bis removed. Then, a first part D1of the drain electrode D and the gate electrode G are formed simultaneously. The first part D1of the drain electrode D covers and contacts the top surface of the first P-type III-V compound layer16a. Schottky contact is between the first part D1of the drain electrode D and the first P-type III-V compound layer16a. Similarly, Schottky contact is also between the gate electrode G and the second P-type III-V compound layer16b.

Later, the second part D2of the drain electrode D and the source electrode S are formed. The second part D2of the drain electrode D covers and contacts the first part D1of the drain D, and also contacts the second III-V compound layer14and an end of the first P-type III-V compound layer16a. Ohmic contact is between the second part D2of the drain electrode D and the first P-type III-V compound layer16a. Later, an insulating layer22such as silicon oxide is formed to cover and contact the drain electrode D, the source electrode S, the gate electrode G and to fill up space between the drain electrode D, the source electrode S, the gate electrode G. Now, an HEMT200awith a stair-like compound layer as a drain of the present invention is completed.

FIG.6depicts an HEMT with a stair-like compound layer as a drain fabricated by the stages disclosed in the first preferred embodiment, wherein elements which are substantially the same as those in the first preferred embodiment are denoted by the same reference numerals; an accompanying explanation is therefore omitted. As shown inFIG.6, an HEMT100awith a stair-like compound layer as a drain includes a first III-V compound layer12. The second III-V compound layer14is disposed on the first III-V compound layer12. The composition of the first III-V compound layer12and the composition of the second III-V compound layer14are different from each other. A source electrode S, a gate electrode G and a drain electrode D are disposed on the second III-V compound layer14, wherein the gate electrode G is disposed between the source electrode S and the drain electrode D. A first P-type III-V compound layer16ais disposed between the drain electrode D and the second III-V compound layer14, wherein the first P-type III-V compound layer16ahas a stair-like shape. The steps constituting the stair-like shape go down toward a direction away from the gate electrode G. The drain electrode D contacts the first P-type III-V compound layer16a, and the second III-V compound layer14. In details, the first P-type III-V compound layer16aincludes numerous steps, the bottommost step of steps includes a vertical sidewall24, and the drain electrode D contacts the vertical sidewall24. Ohmic contact is between the drain electrode D and the first P-type III-V compound layer16a. A second P-type III-V compound layer16bis disposed between the gate electrode G and the second III-V compound layer14. In this embodiment, the drain electrode D is farther from the gate electrode G, and the source electrode S is closer to the gate electrode G. However, based on different product requirements, the distance between the drain electrode D and the gate electrode G can be the same as the distance between the source electrode S and the gate electrode G.

FIG.8depicts a varied type of an HEMT according toFIG.6, wherein elements which are substantially the same as those inFIG.6are denoted by the same reference numerals; an accompanying explanation is therefore omitted. The HEMT100bwith a stair-like compound layer as a drain includes a third P-type III-V compound layer16cdisposed between the source electrode S and the second III-V compound layer14, wherein a symmetry line L of the gate electrode G is perpendicular to a top surface of the second III-V compound layer14. Based on the symmetry line L, the source electrode S and the drain electrode D are mirror symmetry, and the third P-type III-V compound layer16cand the first P-type III-V compound layer16aare mirror symmetry. That is, both of the third P-type III-V compound layer16cand the first P-type III-V compound layer16ahave stair-like shapes. The source electrode S covers and contacts the third P-type III-V compound layer16c. Because the distance between the drain electrode D and the gate electrode G is the same as the distance between the source electrode S and the gate electrode G, the drain electrode D and the source electrode S of the HEMT100bcan be exchanged during operation.

FIG.7depicts an HEMT with a stair-like compound layer as a drain fabricated by the stages disclosed in the second preferred embodiment, wherein elements which are substantially the same as those in the second preferred embodiment are denoted by the same reference numerals; an accompanying explanation is therefore omitted. As shown inFIG.7, An HEMT200awith a stair-like compound layer as a drain includes a first III-V compound layer12. A second III-V compound layer14is disposed on the first III-V compound layer12, wherein the composition of the first III-V compound layer12and the composition of the second III-V compound layer14are different from each other. A source electrode S, a gate electrode G and a drain electrode D are disposed on the second III-V compound layer14, wherein the gate electrode G is disposed between the source electrode S and the drain electrode D. The drain electrode D includes a first part D1and a second part D2. The material of the first part D1is different from material of the second part D2. A first P-type III-V compound layer16ais disposed between the drain electrode D and the second III-V compound layer14. A second P-type III-V compound layer16bis disposed between the gate electrode G and the second III-V compound layer14. The first P-type III-V compound layer16ahas a stair-like shape. The steps constituting the stair-like shape go down toward a direction away from the gate electrode G. Schottky contact is between the first part D1and the first P-type III-V compound layer14. The first part D1is between the second part D2and the first P-type III-V compound layer16a. Moreover, the first P-type III-V compound layer16aincludes numerous steps, the bottommost step of the steps includes a vertical sidewall24, the second part D2contacts the vertical sidewall24and the second part D2also contacts the second III-V compound layer14. Ohmic contact is between the second part D2and the vertical sidewall24. In this embodiment, the drain electrode D is farther from the gate electrode G, and the source electrode S is closer to the gate electrode G. However, based on different product requirements, the distance between the drain electrode D and the gate electrode G can be the same as the distance between the source electrode S and the gate electrode G.

FIG.9depicts a varied type of an HEMT according toFIG.7, wherein elements which are substantially the same as those inFIG.7are denoted by the same reference numerals; an accompanying explanation is therefore omitted. The HEMT200bwith a stair-like compound layer as a drain includes a third P-type III-V compound layer16cdisposed between the source electrode S and the second III-V compound layer14, wherein a symmetry line L of the gate electrode G is perpendicular to a top surface of the second III-V compound layer14. Based on the symmetry line L, the source electrode S and the drain electrode D are mirror symmetry. Therefore, the source electrode S also has a first part S1and a second part S2. The third P-type III-V compound layer16cand the first P-type III-V compound layer16aare mirror symmetry. That is, both of the third P-type III-V compound layer16cand the first P-type III-V compound layer16ahave stair-like shapes. Because the distance between the drain electrode D and the gate electrode G is the same as the distance between the source electrode S and the gate electrode G, the drain electrode D and the source electrode S of the HEMT200bcan be exchanged during operation.

FIG.10depicts an HEMT according an example of the present invention, wherein elements which are substantially the same as those in the first preferred embodiment are denoted by the same reference numerals; an accompanying explanation is therefore omitted.

Comparing to the HEMTs inFIGS.6to9, the first P-type III-V compound layer16′ of the HEMT300inFIG.10doesn't have stair-like shape. The first P-type III-V compound layer16′ is used to remove trapped electrons within the first III-V compound layer12and the second III-V compound layer14. However, the first P-type III-V compound layer16′ decreases density of two-dimensional electron gas (2DEG) which is below the first P-type III-V compound layer16′. In this way, the on-resistance of the HEMT300will increase.

The density of 2DEG below the first P-type III-V compound layer16awith stair-like shape inFIGS.6to9is higher than the density of 2DEG below the first P-type III-V compound layer16′ without stair-like shape inFIG.10. Therefore, the first P-type III-V compound layer16awith stair-like shape can remove trapped electrons and decrease on-resistance.

Furthermore, the HEMTs200a/200binFIGS.7and9have Schottky contact at the drain electrode D. Comparing to the drain electrodes D inFIGS.6and8which only use Ohmic contact, the drain electrode D with Schottky contact can increase the breakdown voltage of the HEMT.