Adhesion, passivation, and resistivity of a Ag(Mg) gate electrode for an amorphous silicon thin-film transistor
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Changoh Jeong, Beomseok Cho, and Kyuha Chung R&D Team, AMLCD Division, Samsung Electronics Company, Ltd., Kiheung-Eup, Yongin 449-711, Korea
Eungu Lee Department of Materials Engineering, Chosun University, Kwangju 501-759, Korea (Received 29 January 2003; accepted 24 March 2003)
The effect of Mg in Ag(Mg)/SiO2/Si multilayers on the adhesion, passivation, and resistivity following vacuum annealing at 200–500 °C has been investigated. The annealing of Ag(Mg)/SiO2/Si multilayers produced surface and interfacial MgO layers, resulting in a MgO/Ag/MgO/SiO2/Si structure. The formation of a surface MgO/Ag bilayer structure provided excellent passivation against air and CF4 plasma chemistry. In addition, the adhesion of Ag to SiO2 was improved due to the formation of an interfacial MgO layer resulting from the reaction of segregated Mg with SiO2. However, the negligible solubility of Si in Ag prevented the dissolution of free silicon into the Ag(Mg) film produced from the reaction Mg + SiO2 ⳱ MgO + free Si, which in turn limited the reaction between Mg and SiO2, which led to a decrease in the adhesion of Ag to SiO2 at the higher temperature. The use of an O2 plasma prior to Ag(Mg) alloy deposition on SiO2 produced an oxygen-rich surface on the SiO2, which allowed for the enhanced reaction of the segregated Mg and SiO2 at the surface, thus resulting in markedly increased adhesion properties. I. INTRODUCTION
Ag has recently received attentions as a potential interconnection for ultra-large scale integration1,2 and large-area thin film transistor/liquid crystal displays3 as it shows the lowest resistivity of the metals, high electromigration resistance,4 and high thermal conductivity.5 In addition, no diffusion barrier is required to prevent the reaction between Ag and Si in Ag/Si contact structures3,6 because Ag with Si is thermodynamically stable and also has negligible solubility of Si. However, Ag metallization has serious drawbacks, such as poor adhesion to dielectrics, agglomeration7 upon annealing in ambient oxygen, Ag sulfidation (chlorination) in the corrosive environment,8 and difficulty when dry etching.2 Of these issues, this work will focus on the crucial problems, such as poor adhesion to SiO2, serious degradation from plasma chemistry, and agglomeration. To address these issues, alloying Ag with Mg was explored. The addition of Mg has shown good results for Cu metallization by forming a surface MgO layer on the Cu and an interfacial MgO layer at the SiO2 surface during anneal in ambient O2.9–12 However, Ag(Mg) metallization was shown to have a much thinner MgO layer at the interface of SiO2 upon annealing, compared with Cu(Mg). As a result, the adhesion obtained in Ag(Mg)/SiO2 is lower than that in Cu(Mg)/SiO2 after annealing at low temperatures. This J. Mater. Res., Vol. 18, No. 6, Jun 2003
can be attributed to the negligible solubility of Si in Ag, which limits the reaction of segregated Mg with SiO2 during annealing; the free Si generated from the reaction of Mg and SiO2 cannot dissolve in the Ag film an
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