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  Date: 08/07/2014

Variance linked yield challenge; A tough one for the semiconductor fab experts

When the smooth ball is rolled down on an extremely smooth slope by just placing over the surface, however smooth and uniform is the slope and the ball, most of the times the ball will not stop at exactly same point. The micro forces change the ball movement each time. If this is about a physically visible thing, think about semiconductor chip manufacturing at less than 20nm, where the changes happen at atomic scale level.

The variance bug is haunting the industry increasingly more from 28nm onwards. With double and triple patterning, semiconductor fabs could achieve some yield success up to 20nm . But further down at 16nm and 14nm, the difficulty level is as tough as like sending space capsule to deeper space. The consistent achievement in both fields is extremely challenging.

The variation in etching/doping and depositing is not man or machine triggered. They all as per present knowledge are not falling out of line, it is happening however the best rope-walk the semiconductor fab engineers are doing. It is the big wall, which need to understood lot deeper. So basically demanding atomic control of material properties.

Semiconductor manufacturing equipment vendor Lam Research has made a new equipment called 2300 Kiyo F Series conductor etch system, which Lam claims uses a breakthrough technology called the Hydra Uniformity System for cross-wafer process control that corrects for incoming pattern non-uniformities. The VECTOR ALD Oxide system uses atomic layer deposition (ALD) to create the highly conformal dielectric films that are used to define critical pattern dimensions in a multiple patterning sequence, say Lam.

Lam explains "Double and quadruple patterning schemes are being used by chipmakers to compensate for limitations in optical lithography. These techniques create smaller features than would be possible from single patterning by printing larger, less dense patterns and then shrinking both the size and the spacing by repeating some combination of lithography/etch/deposition steps to achieve the desired dimensions. With the increased number of process steps, variability challenges are exacerbated since each individual step contributes to overall non-uniformity. Because of this compounding effect, variability tolerances for etch and deposition need to be far more stringent in order for devices to function as intended. Process control is essential since variability can impact device performance, power consumption, and yield, which may lead to costly and time-consuming rework. In addition to variability control, high productivity is required to mitigate the increased manufacturing costs from additional process steps."

Lam's Hydra technology is said to correct for any critical dimension (CD) non-uniformities present on the incoming wafer, by mapping incoming CDs and adjusts etch process conditions in "micro" zones across the wafer to reduce variability, thereby compensating for variation from up-stream processes.

Lam claims VECTOR ALD Oxide system utilizes atomic-scale deposition to deliver highly conformal films with excellent thickness uniformity, high repeatability, and low defectivity.

Lam further explains in its release "These capabilities are essential for spacer-based multiple patterning approaches, where the deposited film becomes the mask and defines critical pattern dimensions for the subsequent step. The VECTOR ALD Oxide system can deposit films at low temperatures, enabling spacer formation on a wide variety of materials. In addition, the hardware design allows fast gas-switching, providing a productivity advantage over competitive systems."
Author: Srinivasa Reddy N
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