Run to run control in tungsten chemical vapor deposition using H-2/WF6 at low pressures

Citation
R. Sreenivasan et al., Run to run control in tungsten chemical vapor deposition using H-2/WF6 at low pressures, J VAC SCI B, 19(5), 2001, pp. 1931-1941
Citations number
21
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Material Science & Engineering
Journal title
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B
ISSN journal
1071-1023 → ACNP
Volume
19
Issue
5
Year of publication
2001
Pages
1931 - 1941
Database
ISI
SICI code
1071-1023(200109/10)19:5<1931:RTRCIT>2.0.ZU;2-T
Abstract
Run to run control with an Internal Model Control (IMC) approach has been u sed for wafer state (thickness) control in the tungsten chemical vapor depo sition (CVD) process. The control implementation was preceded by establishi ng a stable wafer state thickness metrology using in situ mass spectrometry . Direct reactor sampling was achieved from an Ulvac ERA-1000 cluster tool module during the H-2/WF6 W CVD process at 0.5 Torr for temperatures 350-40 0 degreesC using a 300 amu closed ion source Inficon Transpector system. Si gnals from HF product generation were used for in-process thickness metrolo gy and compared to ex situ, postprocess thickness measurements obtained by microbalance mass measurements, providing a metrology accuracy of about 7% (limited primarily by the very low conversion efficiency of the process use d, similar to2%-3%). A deliberate systematic process drift was introduced a s a -5 degreesC temperature change for each successive wafer, which would h ave led to a major (similar to 50%) thickness decrease over ten wafers in a n open loop system. A robust run to run (RtR) control algorithm was used to alter the process time in order to maintain constant HF sensing signal obt ained from the mass spectrometer, resulting in thickness control comparable to the metrology accuracy. The efficacy of the control algorithm was also corroborated by additional experiments that utilized direct film weight mea surements through the use of the microbalance. A set of simulations in Matl ab (R) preceded the control implementation and helped in tuning the control ler parameters. These results suggest that in situ chemical sensing, and pa rticularly mass spectrometry, provide the basis for wafer state metrology a s needed to achieve RtR control. Furthermore, since the control was consist ent with the metrology accuracy, we anticipate significant improvements for processes used in manufacturing, where conversion rates are much higher (4 0%-50%) arid corresponding signals for metrology will be much larger. (C) 2 001 American Vacuum Society.