1. Field of the Invention
The present invention relates to a method and a system for manufacturing semiconductor epitaxy structure, and more particularly to a method and a system for manufacturing semiconductor epitaxy structure without epitaxy layer cracks.
2. Description of the Prior Art
It is an important technology to grow epitaxy layers on a large size substrate, such as growing a thicker gallium nitride (GaN) epitaxy layer on a silicon (Si) substrate. In this structure, a major problem is surface cracks after cooling down and lead to the device failure. In order to prevent surface cracks, the design of epitaxy structure can be changed to control strain.
During the cooling down process, the tensile stress in the GaN epitaxy layer is generated by the different thermal expansion coefficients of the GaN epitaxy layer and the Si substrate. In order to compensate the tensile stress, GaN epitaxy layer should be in a compressive stress state before cooling down process. Then, the crack-free GaN epitaxy layer on Si substrate will be obtained. The compressive stress of GaN epitaxy layer is usually on aluminum nitride (AlN) layers, so that AlN is usually used as buffer layer between GaN epitaxy layer and Si substrate. In the structure of GaN layer and AlN layer on Si substrate, it is difficult to get 1 μm GaN epitaxy layer without cracks on 6 inch Si substrate. But for high power device applications, thicker GaN epitaxy layer is required.
The concept of strain engineering is used to get thicker GaN epitaxy layer on large size Si substrate. For example, different structures with sequential layers are designed to control the strain which enables the growth of thicker epitaxy structure without cracks. However, it is difficult to control the strain of the structure because of the variation of process conditions, such as temperature, or lattice defects etc. For example, accumulated compressive stress drives the lattice relaxation, which results in the curvature value with tensile tendency during the cooling down process. In other case, excessive compressive stress with plastic deformation cannot be dissipated during the cooling down process so that the structure shows the compressive tendency after the cooling down process.
Accordingly, it is highly desirable to determine deposition time or thickness of the layers on the substrate to control the strain of the structure.