Compositions: coating or plastic – Coating or plastic compositions – Heavy metal compound containing
Reexamination Certificate
2001-03-30
2003-03-25
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Heavy metal compound containing
C438S003000
Reexamination Certificate
active
06537361
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to integrated circuit fabrication and, more particularly, to a method of synthesizing and controlling PGO spin-coating precursor solutions.
BACKGROUND OF THE INVENTION
Lead Germanium Oxide (PGO or Pb
5
Ge
3
O
11
) thin films have broad application in ferroelectric 1T transistor devices. The methods of preparing PGO thin films include metal organic chemical vapor deposition (MOCVD), sputtering and spin-coating. For both MOCVD and sputtering methods, the thin film deposition processes are complex, and the equipment required is prohibitively expensive. Comparatively, the spin-coating technology is relatively simple and inexpensive.
The precursors for PGO ferroelectric thin film deposition are known in the art. The lead and germanium sources typically are lead acetate trihydrate (Pb(OAc)
2
•3H
2
O) and germanium alkoxide (Ge(OR)
4
(wherein R=C
2
H
5
or CH(CH
3
)
2
)). The organic solvents are 2-methoxyethanol and di(ethylene glycol) ethyl ether (DEGEE). In the prior art synthesis route, the first step is normally the distillation of Pb(OAc)
2
•3H
2
O in an organic solvent and then removal of the water. After mixing with the Ge(OR)
4
organic solution, the PGO solution is further heated in a di(ethylene glycol) ethyl ether solution. The PGO solution is not heated in the 2-methoxyethanol composition due to solid precipitation during the distillation. During heating in the di(ethylene glycol) ethyl ether, the PGO solution gradually changes to a black color.
According to Applicant's experiments, there are several disadvantages to the reported PGO spin-coating precursor solution preparation. First, the 2-methoxyethanol PGO solution is not stable in air and is moisture sensitive. Second, in the DEGEE solution, the presence of a black color signifies decomposition of the PGO solution, which involves the reduction of Pb
2+
to Pb
+
(Pb
2
O). Third, monitoring the quality of the precursor is necessary. Therefore, problems remaining in the reported synthesis route include determining the correct PGO solution heat treatment method, determining the correct PGO precursor solution monitoring method, and determining the correct PGO solution spin-on property control method.
SUMMARY OF THE INVENTION
The present invention is directed toward providing a heat treatment method, controlling the properties of the synthesized solution, and monitoring the solution so as to provide a suitable PGO spin-coating precursor solution. The method includes utilizing the starting materials of lead acetate trihydrate (Pb(OAc)
2
•3H
2
O) and germanium alkoxide (Ge(OR)
4
(wherein R=C
2
H
5
or CH(CH
3
)
2
)). The organic solvent is di(ethylene glycol) ethyl ether (DEGEE). The mixed solution of Pb(OAc)
2
•3H
2
O and DEGEE (the lead DEGEE solution) is heated in an atmosphere of air, not Argon, at a temperature no greater than 190° C., and preferably no greater than 185° C. for a time period in a range of thirty minutes to four hours. During the heating step the color of the solution is monitored by UV spectroscopy to determine when the reaction is complete and when decomposition of the desired reaction product begins to take place. A certain amount of DEGEE is then added into the lead DEGEE solution to adjust the solution to a desired lead concentration To this lead DEGEE solution, a pre-mixed germanium DEGEE solution having a desired concentration is added to form a PGO precursor solution. The formed PGO precursor solution is then subjected to a second heating step of the process. This second step also entails heating the solution to a temperature no greater than 190° C. for a time period in a range of 0.5 to 2.0 hours in an air atmosphere. The process results in a PGO precursor solution, having a desired concentration, suitable for use in spin-coating processes.
Accordingly, an object of the invention is to provide a method of synthesizing PGO ferroelectric spin-coating solutions.
Another object of the invention is to provide a method of determining the correct PGO solution heat treatment method.
Still another object of the invention is to provide a method of monitoring PGO ferroelectric precursor spin-coating solutions.
A further object of the invention is to provide a method of controlling the properties of a PGO spin-coating solution.
REFERENCES:
patent: 3754975 (1973-08-01), Spiller
patent: 6372034 (2002-04-01), Zhuang et al.
Article by C. J. Kim, D. S. Yoon, J. S. Lee, C. G. Choi and K. No, published in Japanese Journal of Applied Physics 33, (1994), pp. 2675-2678, entitled, “Effects of Substrate and Bottom Electrodes on the Phase Formation of Lead Zirconate Titanate Thin Films Prepared by the Sol-Gel Method”.
Article by J. J. Lee and S. K. Dey, published in Appl. Phys. Lett. 60 (20), (May 18, 1992), pp. 2487-2488 entitled, “Processing of a Uniaxial Ferroelectric Pb5Ge3O11Thin Film at 450° C with C-Axis Orientation”.
Hsu Sheng Teng
Maa Jer-Shen
Zhang Fengyan
Zhuang Wei-Wei
Krieger Scott C.
Rabdau Matthew D.
Ripma David C.
Sharp Laboratories of America Inc.
LandOfFree
Method of the synthesis and control of PGO spin-coating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of the synthesis and control of PGO spin-coating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of the synthesis and control of PGO spin-coating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3028064