探討在濺鍍過程中各濺鍍參數對生成FePt(001)和CoPt(001)薄膜之影響

Investigatng the influence of sputtering parameters on the formation of FePt(001) and CoPt (001) thin films

王顯文(Shien-Wen Wang)

指導教授 ： 郭博成

共同指導教授 ： 許仁華(Jen-Hwa Hsu)

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01049

摘要

本研究在探討調控濺鍍參數對於生成FePt(001)和CoPt(001)薄膜的影響，並希望藉由實驗之結果能達到降低其序化溫度的目的。本實驗利用磁控濺鍍的方式來鍍製FePt(001)及CoPt(001)薄膜，其膜層結構分別固定為Fe48Pt52(20 nm)/Pt(2 nm)/Cr91Ru9(120 nm)/glass substrate及CoPt(50 nm)/Pt(0 ~ 2 nm)/MgO(001) substrate。對於FePt來說，本實驗利用調控FePt層之濺鍍速率、基板載台之公轉轉速、濺鍍溫度及偏壓等濺鍍參數來討論其對薄膜的影響；至於CoPt方面，則利用調控Pt緩衝層厚度、濺鍍溫度、濺鍍速率及公轉轉速來探討其影響。X光繞射儀用來分析薄膜的晶相結構，震盪樣品磁性量測儀用來分析薄膜的各項磁性質。
本研究共針對FePt及CoPt兩材料系統來探討，首先在FePt方面，隨著濺鍍速率R由2.226 nm/min.降低至0.578 nm/min.，薄膜的序化度呈現明顯的上升，對10 rpm系列試片來說，在350℃下，序化度由0.57增加至0.82，此外，在薄膜的磁性質上也有明顯的提升，對於1 rpm系列來說，薄膜的S⊥值由0.165增加至0.557，而Hc⊥值則是由454 Oe增加至1923 Oe；而對於公轉轉速來說，在1 rpm的X光繞射圖中並無法觀測到FePt(001)繞射峰的存在，但當公轉轉速增加至10 rpm，其繞射峰強度有著大幅的提升，此時薄膜的序化度為0.68，而薄膜的Hc⊥值由1 rpm的665 Oe增加至10 rpm的1860 Oe，S⊥值也由0.21增加至0.89；而當負偏壓由0增加至300 V時，薄膜在300℃下的序化度也由0.43降低至無法計算的程度，而薄膜的磁性質也由未施加偏壓前的垂直異向性轉變為偏壓為-300 V下的水平異向性。
至於在CoPt方面，我們發現薄膜必須在550℃以上序化過程才能展開，且此時薄膜仍然為水平異向性，而要當溫度增加至650℃以上，薄膜才開始轉換為垂直易相性；此外，隨著濺鍍速率的降低，CoPt(002)繞射峰開始朝向高角度偏移，證明了薄膜序化度有著些微的提升，但濺鍍速率對於磁性質的影響較不明顯；而隨著公轉轉速由1 rpm增加至10 rpm，CoPt(001)繞射峰的強度有著大幅的提升，此外，CoPt(003)的繞射峰也開始出現，表示公轉轉速的增加的確有助於幫助薄膜的序化。
由我們的研究結果發現，降低磁性層的濺鍍速率以及增加基板載台之公轉轉速，對於薄膜序化度的提升有著明顯的助益，探究其原因主要是因為隨著濺鍍速率降低或公轉轉速的增加，薄膜單層所鍍上去的厚度就跟著變薄，因此對於Fe、Pt原子來說，序化所需要擴散的距離也就相對的縮短，薄膜的序化度也就由此提升。本實驗利用調控這兩種參數，成功的將FePt的序化溫度降低至300℃，這和先前使用相同膜層結構的文獻結果相比，序化溫度整整降低了50℃之多，若能有效的搭配其它相關的技術，FePt的序化溫度將有可能進一步降低至300℃以下，如此便能大幅增加FePt在工業界中實際應用的可能性。

關鍵字

FePt ； CoPt ； 濺鍍速率 ； 序化溫度

並列摘要

In this study, the dependence of sputtering parameters on the formation of FePt(001) and CoPt(001) films was investigated. Two series of samples with the structures of Fe48Pt52(20 nm)/Pt(2 nm)/Cr91Ru9(120 nm)/glass substrate and CoPt(50 nm)/Pt(0 ~ 2 nm)/MgO(001) substrate were sequentially planetary-sputtered using an ultra-high vacuum magnetron sputtering system, and the effect of sputtering parameters on the ordering of L10-FePt and L10-CoPt films were investigated. These parameters include negative bias, Pt layer thickness, sputtering rate, deposition temperature and rotational speed of the sample holder. Film structures were analyzed by X-ray diffractometry (XRD), and magnetic properties were measured by a vibrating sample magnetometer (VSM).
For the FePt series, the degree of chemical ordering increased as the sputtering rate decreased. For the film sputtered at 1 rpm, when the sputtering rate decreased from 2.226 to 0.578 nm/min., the out-of-plane squareness increased from 0.165 to 0.557, and the out-of-plane coercivity also increased from 454 to 1923 Oe. Furthermore, when the rotational speed of the sample holder increased from 1 to 10 rpm, the FePt films exhibit higher degree of ordering and improved magnetic properties. However, when the negative bias was applied, the degree of chemical ordering declined and the orientation of easy axis switched from out-of-plane to in-plane direction.
As for the CoPt series, it has been found that the development of perpendicular anisotropy of L10-CoPt (001) films is a two-step process. First, the ordering process onsets at the temperature of 550℃ with longitudinal anisotropy. Then the perpendicular anisotropy will dominate when the deposition temperature is increased above 650℃. Futhermore, The CoPt(002) peak shifted to higher angle as the sputtering rate decreased. Also, the intensities of CoPt(001) peak was greatly enhanced by increasing the rotational speed of the sample holder from 1 to 10 rpm. These phenomenon indicate that the degree of chemical ordering can be enormously improved by increasing the rotational speed of the sample holder similar to that of FePt(001) films. This is because when the rotational speed of the sample holder increased, the thickness of Fe or Pt layer formed per revolution was also reduced, which results in the reduction of the distance which the sputtered Fe and Pt atoms have to travel into the correct lattice sites of L10 phase. Therefore, the degree of chemical ordering increased. Decreasing the sputtering rate has a similar effect to that of increasing the rotational speed of the sample holder.
By combining low-sputtering-rate and high-rotaional-speed process, we successfully reduced the ordering temperature of FePt to 300℃, which is 50℃ lower than in previous reports. These results herein provide useful information on the fabrication of FePt(001) and CoPt (001) thin films in media use.

並列關鍵字

FePt ； CoPt ； sputtering rate ； ordering

參考文獻

[54] 蔡昀志，展透性FePt-MgO垂直記錄媒體的製作及磁化反轉行為，國立臺灣大學材料科學與工程學研究所碩士論文 (2007)

[3] D. Weller and A. Moser, IEEE Trans. Magn. 35, 4423 (1999).

[5] M. H. Kryder, Digest of Technical Papers Perpendicular Magnetic Recording　Conference 2003, joint NAPMRC 6.

[8] H. N. Bertram, H. Zhou, and R. Gustafson, IEEE Trans. Magn. 34, 1845 (1998)

[9] S. H. Charap, P.-L. Lu, and Y. He, IEEE Trans. Magn. 33, 978 (1997)