1. Field of the Invention
The present invention generally relates to hybrid inspectors.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor water using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to drive higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail.
Currently used methods of inspection have effectively not changed for more than 20 years. Inspection solutions essentially have the following characteristics. A substantially slow electron beam type system allows a user to identify and verify problems for physical defects. Separately, a fast but coarse optical inspection is performed that covers the entire wafer, but is often limited to a single layer of inspection. These two systems are typically physically separated from each other.
Conventional lithographic scaling (at the 193 nm wavelength) appears to have stalled as of 2014-2015. It has been replaced by multi-patterning lithography processes, which appear to be here to stay for the next 10 years or so even if extreme ultraviolet (EUV) appears on the scene. Multi-patterning lithography processes have resulted in the use of an enormous number of process steps (e.g., greater than 20) just to complete a FINFET transistor whereas just a few generations ago, the conventional planar MOSFET transistor was just a few layers. In a sense, to maintain control in one dimension, complexity has been added in the z dimension. The added complexity in the z dimension has resulted in much tighter requirements for critical dimension (CD) and overlay control. Noise has increased for optical inspectors by a factor of 10× at a given layer. In fact, one can make the argument that inspection at a given layer is an ill posed problem.
There are several limitations of current stand alone optical inspectors for physical inspection. In particular, optical tools are affected by the following in the era of post CMOS scaling: post layer noise (optical systems can “see” through layers, which can be a major disadvantage if prior layers have more noise); color noise (optical systems are affected by phase changes such as local and global dimension changes in the z direction, film thickness, etc.); line edge roughness (LER), which when combined with phase based detection apertures can lead to further noise; and core resolution limitations of optics.
There are also several limitations of electron beam inspection and review tools. For example, electron beam inspectors and review platforms have the advantage of physical resolution and are increasingly being adopted but have limitations including: inability to detect process systematic defects which requires relatively wide coverage; relatively poor defect to pixel ratio for LER defects (most detection algorithms are comparison based); relatively poor defect to pixel ratio due to local charging (most detection algorithms are comparison based); and substantially limited penetration to see defects in the z direction.
Accordingly, it would be advantageous to develop systems and methods for detecting defects on a specimen that do not have one or more of the disadvantages described above.