Inline metrology of high aspect ratio hole tilt and center line shift using small-angle x-ray scattering

Abstract

High aspect ratio (HAR) structures found in three-dimensional NAND memory structures have unique process control challenges. The etch used to fabricate channel holes several microns deep with aspect ratios beyond 50:1 is a particularly challenging process that requires exquisitely accurate and precise control. It is critical to carefully analyze multiple aspects of the etch process, such as hole profile, tilt, uniformity, and quality during development and production. X-ray critical dimension (XCD) metrology, which is also known as critical dimension small-angle x-ray scattering, is a powerful technique that can provide valuable insights on the arrangement, shape, and size of periodic arrays of HAR features. XCD is capable of fast, nondestructive measurements in the cell-area of production wafers, making XCD ideal for in-line metrology. Through several case studies, we will show that XCD can be used to accurately and precisely determine key properties of holes etched into hard mask, multilayer oxide/nitride film stacks and slit trenches. We show that the measurement of hole and slit tilt can be achieved without the aid of a structural model using a Fast Tilt methodology that provides sub-nanometer precision. Measurements were performed across several production wafers to determine the etch uniformity and quality. Particular attention was given at the edge of the wafers to account for large variations observed. In addition, we used a detailed physical model to characterize the HAR structures beyond linear tilt. This approach provides a more complete picture of the etch quality.

Cross-evaluation of critical dimension measurement techniques

“…Tools manufacturers, such as KLA, Rigaku, or Bruker, started to supply equipment, but these are restrained to high aspect ratio (HAR) contact holes for 3D-NAND structures for which the scattered signal is strong enough to be measurable in a clean room with process-compatible times. [17][18][19][20][21] Although some structure, such as HAR, are favorable for a quick measurement, short structures are challenging to measure and still require long measurement times. Moreover, significant progress was done to automatize the data processing.…”

Global tilt extraction for BEOL contact landing displacement control

“…Except the X-ray signal collections, the detail structures, film stacks, ideal CD and layout information should be included for preliminary model construction as well. There are already several use cases reported in previous studies [4,5]. However, the major applications of X-ray metrology still focuses on the channel hole structure measurements, and rarely used for other HAR structures.…”

Small angle x-ray scattering overlay metrology for advanced nodes

“…Reche et al also developed the method for line edge roughness measurement [15,16]. SAXS however lacks of powerful sources to be fit to structures others than High Aspect Ratio (HAR) in High Volume Manufacturing (HMV) [17][18][19], and sources 100 times brighter than conventional rotating anode sources are needed according to the International Roadmap for Devices and Systems (IRDS) [1].…”