An Investigation of the Plasma Chemistry Involved in the Synthesis of ZnO by PECVD

Abstract

Plasma-enhanced chemical vapor deposition ͑PECVD͒ of zinc oxide was accomplished using diethyl zinc, oxygen, and argon in a capacitively coupled reactor. The plasma chemistry was studied by optical emission spectroscopy ͑OES͒ with particular focus on the effects of reactant composition and rf power. Process-property relationships were established by comparing plasma behavior with resulting film properties as characterized by the Hall effect, spectroscopic ellipsometry, and X-ray diffraction. In our studies of stoichiometry it was observed that the plasma chemistry was very similar to hydrocarbon combustion, so much so that the results were interpreted by borrowing the concept of the equivalence ratio, . For fuel-rich conditions ( Ͼ 1) deposition was dominated by incorporation of atomic Zn, the films were randomly oriented, and electrically insulating. In contrast fuel-lean conditions produced conducting films with a preferred ͑0 0 2͒ orientation. The results indicate that OES may be useful for calibrating oxide PECVD systems that employ bubblers to deliver organometallic precursors. It was also shown that increasing the plasma power had the same effect of decreasing , which was to drive the chemistry toward complete combustion. Electrical properties improved exponentially with both increased substrate temperature and decreased growth rate, highlighting the importance of surface migration in establishing carriers and controlling mobility.

Plasma‐Enhanced Atomic Layer Deposition of Semiconductor Grade ZnO Using Dimethyl Zinc

“…The reactor used to deposit the ZnO thin films is a parallel plate, capacitively-coupled system that has been described in detail previously [48]. Full Paper The DMZ was stored in a temperature controlled bubbler (À15 8C) and its flow rate (F DMZ ) was controlled by altering the bubbler pressure (P B ) using a needle valve.…”

The Role of Oxygen Dissociation in Plasma Enhanced Chemical Vapor Deposition of Zinc Oxide from Oxygen and Diethyl Zinc

“…(1) For these same advantages PEC-VD has recently been extended to the synthesis of numerous metal oxide thin films including advanced dielectrics (Ta 2 O 5 , (2) HfO 2 , (3,4) ZrO 2 , (5,6) Ga 2 O 3 , (7) ), electrochromics (WO 3 , (8,9) V 2 O 5 (10,11) ), transparent conductors (SnO 2 , (12,13) ZnO (14,15) ), optical coatings (Al 2 O 3 , (16,17) TiO 2 (18) ), and complex oxides (yittria-stabilized zirconia, (19,20) BaTiO 3 , (21) SrTiO 3 (20,22) ). For the most part the efforts to date have been experimental, focused on intrinsic film properties and relationships to device performance.…”

“…(5)(6)(7)(8)(9)(12)(13)(14)(17)(18)(19)(20)(21) However, to date there has been little or no plasma modeling performed on these systems. Plasma modeling has proven to be a particularly useful tool for microelectronic manufacturing.…”

“…As such PECVD modeling has been essentially limited to its derivatives including a-Si, (25) Si 3 N 4 , (26) and SiO 2 . (1,27) Metal oxide thin films besides silica are typically derived from either metal halide (8)(9)(10)12,19) or metalorganic (2)(3)(4)(5)(6)(7)10,(13)(14)(15)17,(20)(21)(22) sources. In the latter case, precursor dissociation results in extensive hydrocarbon chemistry.…”

“…(28) In our experimental investigation of zinc oxide synthesis using diethyl zinc (DEZ) it was found that the dependence of plasma composition on the equivalence ratio (φ) bore a number of similarities to combustion chemistry. (14) A DEZ:O 2 ratio of 7:1 corresponds to an equivalence ratio of unity, which is the amount of oxygen required to fully combust DEZ to CO 2 , H 2 O, and ZnO. In this paper, we take advantage of this relationship to develop a model of this plasma environment.…”