The CD metrology perspectives and future trends

Abstract

As we are moving towards the 32nm node and beyond, the tightening of CD control requirements is becoming very challenging for the semiconductor industry. Therefore, year after year the need for accuracy in CD measurement is becoming one of the major components in process control. In order to succeed reaching in a near future the 'true CD' that will guarantee high yield and high performances, the semiconductor industry has to quickly move into a new 'Industrial Reference Metrology Model'. Today the industrial configuration of CD Metrology relies on CD-SEM or Scatterometry techniques depending on the criticality of the level that is measured. Both techniques are challenged and tend to show strong fundamental limitations in term of accuracy when being used in their conventional configuration (conventional ellipsometry or reflectometry for Scatterometry and threshold algorithm for CD-SEM). Therefore a huge effort has to be made on reference metrology inside the industrial semiconductor environment. The calibration of CD-SEM through Pitch standard is definitely not enough because it does not guarantee any accuracy onto CD measurement which is the main output. In the same way, using Scatterometry in the industrial environment without several 'golden' standards that have been calibrated with a true reference technique is also definitely limited for future technological nodes in order to avoid correlation between outputs (CD, height, Sidewall Angle) that will inevitably lead to wrong process window definition and bad process control. In this paper we will present some experimental results illustrating in practical terms the needs for future CD metrology and the current limitations of industrial techniques. For example, we will talk about emerging 3D multiwires FET devices which require specific 3D metrology. Based on the conclusion which shows the increasingly need for accuracy in the industrial environment, we will discuss about a potential new Reference Metrology Landscape that take into account the limitations of standard industrial techniques (i.e CD-SEM and Scatterometry). These complementary metrology capabilities which will become mandatory in a near future will help the semiconductor industry to corner well with accurate measurement and Reference Metrology inside the fab.