CoPt及(CoPt)1-y(SiNx)y薄膜的製作與磁性質研究

Abstract

本研究以直流磁控濺鍍的方式於室溫鍍製Co50Pt50薄膜，搭配MgO、Ag底層及SiNx頂層，以形成Co50Pt50/MgO、Co50Pt50/Ag、SiNx/ Co50Pt50/Ag及(Co50Pt50)1-x(SiNx)x/Ag多層膜結構，探討MgO、Ag底層、SiNx頂層及製程參數對Co50Pt50薄膜之顯微結構、磁性質及其易磁化軸方向的影響。 關於MgO底層的製作，調整製程參數後發現Ar流量20 sccm、載台轉速0 rpm、Ar壓力5 mTorr、濺鍍功率150 w、厚度為360 nm的MgO薄膜具有最好的(200)結晶指向。對於CoPt (20 nm)/ MgO (360 nm)薄膜來說，在熱處理後，由於CoPt與MgO之間的介面粗糙以及CoPt原子會往MgO底層擴散，造成MgO (200)對CoPt薄膜的磊晶效果有限，無法藉由磊晶讓CoPt的易磁化軸垂直膜面。 在CoPt/Ag薄膜方面，Ag底層引入後有降低CoPt序化溫度的效果，序化溫度從單層CoPt的650°C降至500∼550°C，並且Ag底層有促進CoPt薄膜垂直膜面磁性質的效果。CoPt (20 nm)/ Ag (25 nm)於650°C退火30分鐘之後，具有最好的垂直磁性質，其Hc⊥值為13000 Oe、Hc∥值為12300 Oe、Ms值為420 emu/cm3、S⊥值為0.90、S∥值為0.38。 將32 nm的SiNx頂層鍍製到CoPt/Ag薄膜之上，經過650°C退火30分鐘後，CoPt (20 nm)/ Ag (25 nm)的 I001 / I111比值從未加SiNx頂層的13.05降到加上SiNx頂層之後的1.54，其Hc⊥值為11600 Oe、Hc∥值為9900 Oe、Ms值為520 emu/cm3、S⊥值為0.88、S∥值為0.41；SiNx頂層會抑制CoPt (001)指向並提升CoPt (111)指向，然而在高溫退火之後，SiNx頂層具保護CoPt薄膜減少氧化的效果，讓Ms值從420 emu/cm3提升到520 emu/cm3。 利用(Co50Pt50)1-y(SiNx)y (20 nm)/Ag (25 nm)薄膜來製作顆粒狀結構，經過650°C及700°C退火30分鐘後，發現添加SiNx到CoPt薄膜會嚴重地限制CoPt/Ag薄膜的垂直膜面磁異向性，陶瓷SiNx具有抑制CoPt (001)優選方位的效果；當SiNx＝4.3 vol%時，從TEM能觀察到薄膜具有部分的顆粒狀結構，但顆粒的大小及分佈都不均勻，當SiNx＝50 vol%時，顆粒的大小及分佈較均勻，然而此時CoPt的易磁化軸並非垂直，而是趨向於random。

Co50Pt50 films were deposited at room temperature by dc magnetron sputtering, and were combined with MgO underlayer, Ag underlayer, and SiNx capped layer to form Co50Pt50/MgO, Co50Pt50/Ag, SiNx/Co50Pt50/Ag, and (Co50Pt50)1-x(SiNx)x/Ag multilayer films on glass substrates. The effects of MgO underlayer, Ag underlayer, SiNx capped layer, and process parameters on the microstructure, magnetic properties, and magnetic easy axis of the film were investigated. For the fabrication of MgO underlayer with MgO(200) preferred orientation, the process parameters are 20 sccm Ar flow rate, 5 mTorr Ar pressure, 150 w rf power, and 360 nm film thickness. For the CoPt (20 nm)/ MgO (360 nm) films, the the effect of MgO(200) underlayer on the epitaxial growth of CoPt layer is not obvious due to the rough interface between CoPt and MgO and the diffusion of Co and Pt atoms into MgO underlayer during heat treatment. It can not make the magnetic easy axis of CoPt perpendicular to the film plane. For the CoPt/Ag films, the introduction of Ag underlayer could lower the ordering temperature of CoPt film. The ordering temperature decreases from 650°C of single-layered CoPt to 500~550°C and Ag underlayer has the effect of promoting out-of-plane magnetic properties of CoPt films. After annealing at 650°C for 30 minutes, the CoPt (20nm)/ Ag (25 nm) film shows best out-of-plane magnetic properties and its Hc⊥ value = 13000 Oe, Hc∥ value = 12300 Oe, Ms value = 420 emu/cm3, S⊥ = 0.9, and S∥ value= 0.38. A 32 nm SiNx capped layer was deposited on the top of CoPt/Ag film then annealed at 650°C for 30 minutes. The I001 /I111 ratio of CoPt (20 nm)/ Ag (25 nm) film decreases from 13.05 without SiNx capped layer to 1.54 with SiNx capped layer. Its Hc⊥ value = 11600 Oe, Hc∥ value = 9900 Oe, Ms value = 520 emu/cm3, S⊥ = 0.88, and S∥ value= 0.41. It was found that SiNx capped layer would inhibit CoPt(001) orientation growth and promote CoPt(111) preferred orientation. After annealing at high temperature, SiNx capped layer could reduce the oxidation of CoPt film, and the Ms value of the film was enhanced from 420 emu/cm3 to 520 emu/cm3. After annealing at 650°C and 700°C for 30 minutes, it is found that SiNx will limit the out-of-plane magnetic anisotropy of (Co50Pt50)1-y(SiNx)y (20 nm)/Ag (25 nm) granular films. SiNx would inhibit CoPt(001) preferred orientation. From the observation of TEM, when SiNx = 4.3 vol%, partial granular structure is observed, but the particle size and distribution are not uniform. When SiNx = 50 vol%, the uniformity of particle size and distribution is better, however, the magnetic easy axis is random and not perpendicular to the film plane.