1. Field of the Invention
The present invention relates to the field of semiconductor techniques, and more specifically, relates to an apparatus and a method for detecting a mark in a layer of a semiconductor device as well as to a semiconductor device processing system.
2. Description of the Related Art
During the fabrication of a semiconductor device, a process of forming multiple layers on a wafer by using a mask plate is typically involved. In the formation process of the multiple layers, patterning of each layer by etching or the like may be involved. It is known that, in order to make patterns between multiple layers that are overlapped on a wafer align with respect to each other, alignment marks may be formed on each of these layers. By the alignment between the mask plate of the current layer and the alignment mark of the previous layer, it is possible to align the formed pattern on the current layer with the pattern on the previous layer. These alignment marks may have phase contrast (e.g. “topographical” contrast) or reflectivity contrast. Background lighting (generally, visible light) in a process environment is utilized to detect the phase contrast or the reflectivity contrast to obtain a phase contrast signal or a reflectivity contrast signal, thereby optically detecting or imaging these alignment marks.
Alignment marks may be covered by the current layer or by multiple layers that include the current layer. For the aforementioned prior art, in a case where the current layer to be patterned is a layer opaque to the visible light or a layer of low transmissivity to the visible light, or in a case where there is a layer opaque to the visible light or a layer of low transmissivity to the visible light between the current layer to be patterned and the layer with alignment marks, the visible light may be reflected or absorbed by the opaque layer or the layer of low transmissivity, and thus, may not reach the layer with alignment marks, as illustrated in FIG. 1 (in FIG. 1, layer 4 has for example a low transmissivity to the visible light and layer 3 is for example a layer substantially opaque to the visible light). In this case, the obtained phase contrast signal or reflectivity contrast signal may be significantly reduced, resulting in the inability to clearly image the marks. Directed to the problems existing in the prior art as found by the inventor, a new technical solution according to the present invention is proposed.