**4.1 DPT Structure**

442 Recent Advances in Nanofabrication Techniques and Applications

the Root-Mean-Square (RMS) of three times the standard deviation of the 20-cycle measurements at each target, and combines static precision (occurring without any

standard deviation of the TIS in the measurements at each target. Where multiple tools are available, site-by-site tool matching (TM) is included. TM is three times the standard deviation of the difference in the average measurement from each tool at the same location.

2 22 ( ) ( 3) ( ) *TMU DYNP TIS TM*

The results for both DPT applications are summarized in Table 2. For the gate level DPT the dynamic precision is less than 0.1 nm and the TMU is 0.26 nm Average TIS is under 0.1nm. DBO matching data is between two tools (Atlas and FLX) with similar reflectometer optical heads. For the DPT structure on a silicon surface precision is 0.2nm. TIS and matching data

While LELE involving two process steps offers an adequate solution for DPT process steps, both are very expensive and slow. The alternative Litho-Freeze-Litho-Etch (LFLE, Fig. 1b) process reduces cost by replacing the intermediate etch step with a process step in the litho track.

(a) (b)

Fig. 11. DPT structure that has alternative photo resist lines with silicon over etch: (a) 65/390

**DYNP (nm)**

DPT Gate Patterning NOR Flash 0.07 -0.04 0.17 0.18 0.18 DPT Silicon Substrate 0.48 -0.37 0.31 0.57 DPT Gate Patterning NOR Flash 0.33 -2.05 6.03 6.04

**TIS Avg (nm)**

*<sup>T</sup>* (5)

**TIS 3 (nm)**

**Tool Match**

**TMU**

*<sup>T</sup>* is three times the

movement within the tool) and the effects of target reacquisition. *TIS3*

Matching data is not included in the DBO to IBO TMU comparison.

DPT Silicon Substrate 0.2

Table 2. Performance summary of DBO on two stacks discussed in Fig. 4.

is not available for this structure.

DBO

IBO

**TECHNOLOGY Process Step**

**4. Litho-freeze-litho-etch (LFLE)** 

Line/Pitch ratio, (b) 110/660 Line/Pitch ratio

An example LFLE DPT structure consists of ~120 nm photoresist lines with silicon over etch as shown in Fig. 11(a) and (b).
