PECVD를 이용한 ZrO2 박막의 제조와 특성연구

김기동, 신동근*, 조영아, 전진석, 최동수, 박종진*

한국가스공사 연구개발원

한양대학교 금속재료공학과

The Preparation and Characterization of ZrO2 thin films by PECVD

K.D.KIM, G.D.Shin*, Y.A.CHO, J.S.Jeon, D.Choi, J.J.Pak*

R & D Center KOGAS

Department of Metallugy and Material Engineering, Hanyang University*

1. Introduction

Zirconia is a very refractory material with a high melting point and similar to hafnia[1]. It has a relative dielectric constant and is characterized by low electric conductivity and extreme chemical inertness[2]. Also, the properties of zirconia ceramics, for example alumina-zirconia, partially stabilized zirconia etc., suggest that the combination of strength, toughness and chemical resistance should allow application of the materials in harsh environments under severe loading conditions. Applications for zirconia included such as dielectric films in microelectronics as well as for various other application such as oxygen sensors, fuel cell ,hydrogen production, glass etc.[3]

There are several types of zirconia which are thick, thin and bulk. Among those, it have been tried to prepare thin films of zirconia due to its own merits of thin film which are dense structure, low power consumption etc. Several methods for depositing thin films on the substrate (CVD/EVD, PVD including R.F sputtering ,sol-gel deposition etc.) have been reported[2,4]. Generally, CVD had better than PVD in step coverage of a film but requires high temperature for manufacture. High temperature deposition leads to thermal strain which generates defect states. Therefore there are much study in low temperature deposition for zirconia. In our study, thin films of zirconia were manufactured by the PEMOCVD(plasma enhanced metal organic chemical vapor deposition) method. Also, the properties of films were investigated.

2. Experimental

Deposition system

The depositions for zirconia have been conducted in a low pressure cold wall vertical reactor. The susceptor were plate of 4" diameter and plasma was sustained by Advanced Energy's rf generator of which frequency is 13.56MHz with matching network and dc bias voltage which occurred at upper electrode could be measured by readout unit. The bubbler of Zr source was heated to sublime at enough temperature. The working pressure was controlled by the amount of gas flow and a butterfly valve in back of reaction chamber. All gases were controlled by mass flow controller. Details of deposition conditions are represented in Table 1. On the lower electrode, the wafers of Si were placed as a substrate in reaction chamber.

Table. 1 The conditions of deposition for zirconia thin films

Substrate	SiO2(3,000Å) / Si single crystal
Temperature	Zr source[Zr(TMHD)4]	200~300℃
	Substrate	300~600℃
	Source feeding line	320℃, 300℃
Flow	He as carrier gas	0~100sccm
	Oxygen as oxidant	0~100sccm
Working Pressure	controlled by butterfly valve	0.1~1torr
Plasma generator	Advanced Energy Co.	Max. power 600W

Materials including reactant

Commercially available Zr(TMHD)4 were employed as solid precursors from Stream chemicals. As an oxidizing agent, high purity(99.99+%) oxygen flow was introduced and pre-mixed with carrier gas before entering the reactor. Also ultra high purity helium was used as carrier gas. Depositions were made on single crystal Si(100) p-type 4inch disk which has 5~10□□ of specific resistivity and have passivated by oxygen up to SiO2 3000Å.

Characterization

The material characterization of the thin films of zirconia prepared was performed by XRD for crystallography, SEM(EDS) for quantity analysis and Auger for depth profile, etc. The thicknesses of thin films were measured by Alpha-step.

3. Results and discussion

The structure of thin films deposited was investigated by XRD. Fig.1 shows the x-ray diffraction pattern of a zirconia film deposited at various temperatures. As shown in fig. 1, there is no crystalline structure in the films deposited below 350℃. The films obtained over 450℃ had cubic crystalline phase. While adhesion of all films was examined by tape test and scratch method, those deposited at low temperatures failed to that test or scratch. Also, if the film prepared at room temperature was done by heat treatment at 500℃ in O2 for 1hr, it was evaporated. In case of heat treatment of the film deposited at 250℃, it exhibits zirconia crystalline structure which did not exist before annealing. Variations of zirconia deposition as function of rf power supply is shown in fig. 2 and 3. In fig. 2, the high rf power was, the better the deposition of zirconia was at substrate temperature of 350℃. But at high temperature, the deposition seemed to have no relevant to rf power. It would be considered that high temperature provides Zr organic compound with enough energy and Zr MO was easy to be activated in the presence of plasma. Fig. 4 shows the effect of oxygen as oxidized agent for zirconia deposition. From fig. 4 , it could be deduced that oxygen is necessarily required for zirconia deposition.

Reference

1. Hugh O. Pierson, Handbook of Chemical Vapor Deposition, p238(1992)

2. Eui-Tae Kim and Soon-Gil Yoon, Thin Solid Films, 227, 7(1993)

3. Magnesium Elektron Ltd., Magnesium Elektron Publication No. 113

4. M.Balog and M.Schieber, J. Electrochemical Soc., 126, 7(1979), 1207