This invention generally relates to a method for manufacturing a multilayer semiconductor structure that includes a layer of irregular material. In an embodiment, the method includes providing a layer of irregular material on a donor substrate, creating a weakened zone in the donor substrate, providing an intermediate layer that covers the surface of the irregular layer and provides a substantially flat surface, bonding the substantially flat surface of the intermediate layer to a receiver substrate, and detaching the donor substrate along the weakened zone to form the multilayer semiconductor structure.
The words “donor” and “receiver” correspond to the “active layer” and to the “support” of the wafer, respectively. These terms may also mean “top” and “base”, respectively, at times. In addition, the expression “layer of irregular material” means a layer having at least one surface which is not regular (according to this definition, a layer of single-crystal silicon is typically a regular layer).
A layer of irregular material is, within this text, understood to be a layer of which at least one free surface has a roughness and a flatness greater than a value of a few angstroms expressed in terms of root mean square (RMS) values. Conversely, in this text, a layer is regular if the roughness of its free surfaces is less than such a value.
For example, a layer of irregular material can be made of CVD diamonds, of Si3N4, of AIN or even of a poly-crystal material such as, notably, poly-crystal silicon, and the like. Such rough materials can, for example, be implemented in a SOI (Silicon on Insulator) type structure to improve the heat conductive properties of such a wafer. It is contemplated that the insulator layer of such a wafer would not be made of SiO2 (whose heat conducting properties are poor), but may be made of one or several materials that have high heat conductivity, such as diamonds or Si3N4. Layers of such materials are generally obtained via epitaxy. However the surface of such epitaxial layers is rough.
The table below presents examples of the heat conductivity coefficients for different materials.
MaterialHeat conductivity W/m/KBuried oxide of the SIMOX structure1.6CVD diamond2 × 103AIN>250Si3N4>150Si168
The word “bonding” means putting two surfaces into close contact so that links (for example. Van der Waals forces or hydrogen links) are created between the two surfaces (For example, see “Semiconductor Wafer Bonding Science and Technology”, Wiley, 1999, Q.-Y Tong and U. Gösele). Such processes are known. In particular, the published International Application No. WO 01/97282 describes a process in which a zone of weakness is created by implanting atomic species. This type of process allows the fabrication of multilayer wafers including a layer of irregular material. Such implementation allows detachment along the weakened zone such that the remainder of the donor substrate which is present after detachment can be recycled. In addition, this type of process results in a wafer whose surface is homogenous (notably in terms of thickness), after detachment along the weakened zone. This type of process thus has a certain number of advantages. Moreover, this type of process results in a wafer whose layer of irregular material (for example in diamond) has one irregular face turned towards the useful layer of the wafer.
It is to be understood that the useful layer of the wafer is a superficial layer (a layer located in the immediate neighborhood of the wafer surface), in which components will be created. In addition, it would be of interest to obtain multilayer wafers in which a layer of irregular material has a regular face that is turned towards the useful layer of the wafer. Returning to the example of SOI type wafers having an insulator layer that is made of one or several irregular materials, this would allow the manufacture of an interface between the useful layer and the insulator layer that is as regular as possible. Such a structure would in particular improve the electric characteristics of the wafer.