BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the nitride semiconductor device, and in particular to the epitaxial structure and fabrication method of the nitride semiconductor device.
2. The Prior Arts
According to prior arts, a conventional nitride semiconductor device such as a gallium-nitride (GaN) based light emitting diode (LED) has an epitaxial layer formed on top of a buffer layer, which in turn is formed on top of a substrate. Usually, the buffer layer within these conventional nitride semiconductor devices is formed by depositing aluminum-gallium-nitride (AlxGa1-xN, 1≧x≧0) or indium-gallium-nitride (InyGa1-yN, 1≧y≧0) under a low temperature (200-900° C.). The nitride epitaxial layer is then formed under a high temperature on the buffer layer. However, there is a huge difference between the substrate and the nitride epitaxial layer in terms of their lattice constants. This huge difference in the lattice structure causes the nitride epitaxial layer subsequently formed to have a defect density more than 1010/cm3. The nitride semiconductor device such as a GaN-based LED as fabricated has a poor resilience to electrostatic discharge, a short operation life, and inferior device characteristics.
Accordingly, the present invention is directed to overcome the foregoing disadvantages of conventional nitride semiconductor devices according to prior arts.
SUMMARY OF THE INVENTION
The present invention provides a structure and a fabrication method for a nitride semiconductor device so that the limitations and disadvantages from the prior arts can be obviated practically.
The present invention utilizes appropriate intermediate layers to replace the conventional buffer layer. With the present invention, the nitride epitaxial layer is deposited on top of an intermediate layer made of either silicon-nitride (SiiNj, i, j≧0) or magnesium-nitride (MgmNn, m, n≧0), which in turn is formed on top of another intermediate layer made of aluminum-gallium-indium-nitride (Al1-x-yGaxInyN x, y≧0, 1≧x+y≧0). The defect density of the nitride epitaxial layer can be reduced to below 1010/cm3 within this structure. Both intermediate layers are formed by the metalorganic chemical vapor deposition (MOCVD) technique. For the intermediate layer made of SiiNj (i, j≧0) or MgmNn (m, n≧0), ammonia (NH3) and silane (SiH4), or NH3 and disilane (Si2H6) are used to grow the SiiNj (i, j≧0) during the MOCVD process. On the other hand, NH3 and cyclopenta-dienyl-magnesium (CP2Mg) are used to grow MgmNn (m, n≧0) during the MOCVD process.
The present invention's reduction of the defect density of the nitride epitaxial layer lies in the phenomenon that, when the SiiNj (i, j≧0) or MgmNn (m, n≧0) intermediate layer is deposited on the A1-x-yGaxInyN (x, y≧0, 1≧x+y≧0) intermediate layer, the material SiiNj or MgmNn forms a mask having a random, clustered pattern. The nitride epitaxial layer subsequently deposited grows from the exposed Al1-x-yGaxInyN (x, y≧0, 1≧x+y≧0) intermediate layer not covered by the SiiNj (i, j≧0) or MgmNn (m, n≧0) mask, and then overflowed to the top of the mask, instead of directly from the top of the mask. A nitride epitaxial layer with lower defect density is thereby formed.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing the structure of the nitride semiconductor device according to the first embodiment of present invention.
FIG. 2 is a flow diagram showing the processing steps for forming the nitride semiconductor device as depicted in FIG. 1.
FIG. 3 is a schematic diagram showing the structure of the nitride semiconductor device according to the second embodiment of present invention.
FIG. 4 is a schematic diagram showing the structure of the nitride semiconductor device according to the third embodiment of present invention.
FIG. 5 is a flow diagram showing the processing steps for forming the nitride semiconductor device as depicted in FIG. 4.
FIG. 6 is a schematic diagram showing the structure of the nitride semiconductor device according to the fourth embodiment of present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, detailed description along with the accompanied drawings is given to better explain preferred embodiments of the present invention. Please be noted that, in the accompanied drawings, some parts are not drawn to scale or are somewhat exaggerated, so that people skilled in the art can better understand the principles of the present invention.
FIG. 1 is a schematic diagram showing the structure of the nitride semiconductor device according to the first embodiment of present invention. FIG. 2 is a flow diagram showing the processing steps for forming the nitride semiconductor device as depicted in FIG. 1. As shown in FIG. 1, the nitride semiconductor device is formed by stacking a first intermediate layer 102, a second intermediate layer 103, and a nitride epitaxial layer 104, sequentially in this order from bottom to top on a substrate 101. The second intermediate layer 103, when deposited, would form a mask having a random, clustered pattern on the first intermediate layer 102. The nitride epitaxial layer 104 subsequent deposited then grows from the exposed first intermediate layer 102 not covered by the mask of the second intermediate layer 103, and overflows to cover the top of the mask of the second intermediate layer 103. The processing steps, as shown in FIG. 2, include: on the substrate 101, forming the first intermediate layer 102 made of Al1-x-yGaxInyN (x, y≧0, 1≧x+y≧0) having a thickness between 5 Å and 10 Å by using a MOCVD process under a temperature between 200° C. and 1000° C. (step 201); forming the second intermediate layer 103 made of SiiNj (i, j≧0) having a thickness between 5 Å and 100 Å by using NH3 and SiH4 (or using NH3 and Si2H6) in a MOCVD process under a temperature between 200° C. and 1000° C. on the first intermediate layer 102 (step 202); and forming a nitride epitaxial layer 104 by using a MOCVD process under a temperature between 700° C. and 1100° C. on the second intermediate layer 103 (step 203).
The foregoing second intermediate layer 103 can also be made of MgmNn (m, n≧0) by using NH3 and CP2Mg in the MOCVD process.
When the second intermediate layer 103 is made of SiiNj (i, j≧0) or MgmNn (m, n≧0), the material SiiNj or MgmNn forms a mask having a random, clustered pattern on the first intermediate layer 102. The nitride epitaxial layer 104 subsequently deposited then grows from the exposed first intermediate layer 102 not covered by the SiiNj or MgmNn mask, and overflows to cover the top of the second intermediate layer 103, instead of directly from the top of the second intermediate layer 103. The nitride epitaxial layer 104 therefore has a lower defect density.
FIG. 3 is a schematic diagram showing the structure of the nitride semiconductor device according to the second embodiment of present invention. As shown in FIG. 3, the nitride semiconductor device contains multiple first and second intermediate layers 102 and 103 stacked alternately upon each other between the substrate 101 and the nitride epitaxial layer 104. More specifically, on the substrate 101, the steps 201 and 202 as depicted in FIG. 2 are performed in sequence to form the first pair of the first and second intermediate layers 102 and 103. But before the step 203 is performed, the steps 201 and 202 are repeated at least once so that additional pairs of the first and second intermediate layers 102 and 103 are formed and stacked upon one another. Each of the first intermediate layers 102 is made of Al1-p-qGapInqN (p, q≧0, 1≧p+q≧0) with a specific composition, and has a thickness between 5 Å and 10 Å. Similarly, each of the second intermediate layers 103 is made of SiaNb (a, b≧0) or MgcNd (c, d≧0) with a specific composition, and has a thickness between 5 Å and 100 Å. At last, the step 203 is performed to form the nitride epitaxial layer 104 on top of the topmost second intermediate layer 103.
As in the first embodiment of the present invention, the SiaNb or MgcNd of each of the second intermediate layer 103 forms a mask having a random, clustered pattern on the underlying first intermediate layer 102. The next first intermediate layer 102 or the nitride epitaxial layer 104 subsequent deposited then grows from the exposed, underlying first intermediate layer 102 not covered by the SiaNb or MgcNd mask, and then overflows to cover the top of the underlying second intermediate layer 103. The next first intermediate layer 102 or the nitride epitaxial layer 104 therefore has a lower defect density.
FIG. 4 is a schematic diagram showing the structure of the nitride semiconductor device according to the third embodiment of present invention. FIG. 5 is a flow diagram showing the processing steps for forming the nitride semiconductor device as depicted in FIG. 4. As shown in FIG. 4, the nitride semiconductor device is formed by stacking a lower first intermediate layer 402, a second intermediate layer 403, an upper first intermediate layer 402, and a nitride epitaxial layer 404, sequentially in this order from bottom to top on a substrate 401. The second intermediate layer 403, when deposited, would form a mask having a random, clustered pattern on the lower first intermediate layer 402. The upper first intermediate layer 402 subsequent deposited then grows from the exposed, lower first intermediate layer 402, and overflows to cover the top of the mask of the second intermediate layer 403. The upper first intermediate layer 402 is added to enhance the epitaxial quality of the nitride epitaxial layer 404. The processing steps, as shown in FIG. 5, include: on the substrate 101, forming the lower first intermediate layer 402 made of Al1-s-tGasIntN (s, t≧0, 1≧s+t≧0) having a thickness between 5 Å and 10 Å by using a MOCVD process under a temperature between 200° C. and 1000° C. (step 501); forming the second intermediate layer 403 made of SieNf (e, f≧0) having a thickness between 5 Å and 100 Å by using NH3 and SiH4 (or using NH3 and Si2H6) in a MOCVD process under a temperature between 200° C. and 1000° C. on the first intermediate layer 402 (step 502); forming the upper first intermediate layer 402 made of Al1-u-vGauInvN (u, v≧0, 1≧u+v≧0) having a thickness between 5 Å and 10 Å by using a MOCVD process under a temperature between 200° C. and 1000° C. on the second intermediate layer 403 (step 503); and forming a nitride epitaxial layer 404 through a common epitaxial technique under a temperature between 700° C. and 1100° C. on the upper first intermediate layer 402 (step 504).
The foregoing second intermediate layer 403 can also be made of MggNh (g, h≧0) by using NH3 and CP2Mg in the MOCVD process.
FIG. 6 is a schematic diagram showing the structure of the nitride semiconductor device according to the fourth embodiment of present invention. As shown in FIG. 6, the nitride semiconductor device contains multiple first and second intermediate layers 402 and 403 stacked alternately upon each other between the substrate 401 and the nitride epitaxial layer 404. More specifically, on the substrate 401, the steps 501, 502, and 503 as depicted in FIG. 5 are performed in sequence to form the lower first intermediate layer 402, the second intermediate layer 403, and the upper first intermediate layers 402. But before the step 504 is performed, the steps 502 and 503 are repeated so that additional pairs of the second and first intermediate layers 403 and 402 are formed and stacked upon one another, and the topmost layer is the first intermediate layer 402. Each of the first intermediate layers 402 is made of Al1-w-zGawInzN (w, z≧0, 1≧w+z≧0) with a specific composition and has a thickness between 5 Å and 10 Å. Similarly, each of the second intermediate layers 403 is made of SikN1 (k, 1≧0) or MgsNt (s, t≧0) with a specific composition, and has a thickness between 5 Å and 100 Å. At last, the step 504 is performed to form the nitride epitaxial layer 404 on top of the topmost first intermediate layer 402.
In the third embodiment and the fourth embodiments of the present invention, the SikN1 (k, 1≧0) or MgsNt (s, t≧0) of each of the second intermediate layer 403 forms a mask having a random, clustered pattern on the underlying first intermediate layer 402. The next intermediate layer 402 subsequent deposited then grows from the exposed, underlying first intermediate layer 402 not covered by the SikN1 or MgsNt mask, and overflows to cover the top of the second intermediate layer 403. The next first intermediate layer 402 therefore has a lower defect density. Accordingly, the nitride epitaxial layer 404 formed on the topmost first intermediate layer 402 also has a lower defect density.
Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.
Patent Application
20060049418
