(Digital Presentation) Advanced Process Control of Dual Patterns for FinFET Mass Production

Abstract

ABSTRACT Advanced Process Control (APC) has been widely applied in state-of-the-art semiconductor industries for the everlasting pursuit of cycle time reduction, higher yield and zero scrap. Inline metrology is thus valuable input feeds for the improvement of wafer-to-wafer and within-wafer CD variations originated from either abnormality or noise of different processes. Implementing a suitable APC scheme to process flow remains a challenging task for engineers. In most cases, it is enough to implement the APC to only one single pattern on Chip. However, for multi-purpose chip design, the CD control of multiple patterns is becoming important. In this paper, we presented a workflow of APC to control the CD of two different patterns. It is shown that, with the same amount of APC process layers, we were able to improve from single pattern CD control to dual pattern CD control. The final process variations of two patterns can be controlled within ±0.5 nm. INTRODUCTION Abnormality and noise are two inevitable root causes of systematic yield loss and mis-process during semiconductor manufacturing processes [1]. Within-wafer uniformity is another important indication of process control capability. Lam tools implement Hydra Electro Static Chuck (ESC) combining the 4 radially-tunable zones with grid-heating elements, where additional CDU tuning is made possible for radial and non-radial uniformity [2].APC schemes are normally applied to a single pattern as the anchor point to control the CD and CDU. However, for multi-purpose chip layouts, areas of different CDs and pitches are designed. For instance, CD controlling of both Logic and SRAM are important for yield improvement and device performance. When APC is implemented to different processes across the production flow, it is possible to utilize properly the inline metrology data of different patterns across processes for a dual pattern control. For this purpose, The APC CD control scheme of dual patterns is demonstrated in this work. SETUP The process flow is divided into 4 stages. In stage 1, a hard mask (HM) is patterned with a Lithograph-Etching (LE) process. An added CD trimming process of stage 2 is added to cover the LE etch bias (EB) incapability. Pattern B is covered by photoresist materials to trim the CD of pattern A HM to the target value. In stage 3, a thin Atomic Layer Deposition (ALD) layer is deposited on the HM of both patterns A and B for etching protection. In stage 4, the final etch process is completed with the HMs of target CDs. RESULTS and DISCUSSIONS For single pattern APC, pattern A is designated as the anchor pattern for this scheme. For stage 1, the Hydra function is applied to pattern A to improve its CDU. Here we assume that the Hydra function barely improves the CD or CDU of pattern B, due to the fact that pattern A and pattern B have different line CDs and Pitches. In stage 2, APC is turned on using inline data of pattern A from stage 1. Pattern A is exposed for the isotropic plasma dry etching process until target CD is reached. Pattern B is covered in photoresist materials, and its CD is not changed during this process. And the photoresist materials are removed afterward. In stage 3. Fixed-amount ALD process is applied for HM protection on both Pattern A and B. In stage 4, HM is used to etch the pattern into substrate Si with Hydra function turned on for pattern A only. During this process flow, CD and CDU APC are applied to pattern A only. The process variation of stage 1 on pattern B is transferred all the way down to the final stage 4 without any APC functioning on Pattern B.Figure 1 shows the new APC flow. In stage 1, HM of pattern A and pattern B are etched with Hydra function working on pattern A only. However, inline metrology is applied to pattern B for APC of stage 3. In stage 2, Pattern A trimming changed from APC-mode to fixed time mode. The APC function is turned on for stage 3 for a global CD control of both pattern A and pattern B using ALD. And Hydra function is turned on for stage 4 for a CDU control on pattern A. It is shown that the CD variation originated from stage 1 is compensated on stage 3. With the same amount of APC stages, the effect of the APC can be improved from pattern A CD/CDU only, to pattern A CD/CDU and pattern B CD control. Figure 1