A Novel Retaining Ring in Advanced Polishing Head Design for Significantly Improved CMP Performance
- PDF / 1,640,349 Bytes
- 10 Pages / 417.6 x 639 pts Page_size
- 83 Downloads / 211 Views
mixed signal devices). EXPERIMENTAL A 4-head and 3-platen CMP tool (Mirra® CMP system) was used with 8" wafers throughout this work. Different retaining ring designs coupled with a Titan Head design were investigated for improved performance. The Titan Head design features a flexible membrane applying a uniform pressure to the backside of the wafer. The advanced polishing head is equipped with a retaining ring to prevent wafer slippage during polishing. A more important function of the retaining ring in a Titan Head design is to modulate the polishing removal rate near the edge of the wafer for a low within wafer non-uniformity (WIWNU) at reduced edge exclusions. This is achieved by independently controlled pressure applied onto the ring. Two different types of retaining ring materials were used in this work. The first type is a polymeric material requiring lapping. The second type used in different ring designs including the AEP design is the layered materials. The retaining ring made of the first type of material is called P ring in this paper. The new-generation retaining ring (AEP ring) requires no individual modification for fitting, no lapping and no adj ustments.
63
Mat. Res. Soc. Symp. Proc. Vol. 566 02000 Materials Research Society
Stacked IC IOO0/Suba IV pads (Rodel) were used for polishing and a Politex pad (Rodel) was used when buff is applied. For pad conditioning, an improved diamond disk manufactured by using a proprietary high temperature Ni-Cr brazing process was used in conjunction with an advanced conditioner head assembly design. [1] Cabot's SS-12 slurry was used as an oxide slurry. Consumables used in W and polysilicon CMP were described in previous work. [2, 3]. RESULTS AND DISCUSION Impact of Retaining Ring Design Types on WIWNU The retaining ring design has a significant impact on WIWNU due to the ring-pad-wafermembrane interaction (Fig. 1). In a Titan Head design, an independently-controlled pressure (P 1 )
is applied onto the retaining ring to absorb pad deformation around the wafer edge during polishing. Meanwhile, a uniform pressure (P2) is applied by a flexible membrane over the wafer backside to achieve a desirable polishing rate. To optimize WIWNU, the retaining rings of different designs were evaluated. The results are summarized in Table 1. The results indicate that an AEP ring design is critical to ensure low WIWNU. The AEP ring design can more effectively control pad deformation during wafer polishing as compared to the conventional P ring. As a results, better edge performance of an AEP ring was achieved than a P ring as shown in wafer scan (Fig. 2). Impact of Pressure and Speed on Removal Rate and Non-Uniformity Designed experiments were conducted to optimize the processes for high removal rate and low non-uniformity. The impact of retaining ring pressure and platen speed on removal rate and WIWNU is shown in a contour map (Fig. 3). The results indicate that WIWNU can be significantly improved by increasing retaining ring pressure in the range studied which is made possible
Data Loading...
