Preparation of stable iron nitride films by high speed reactive sputtering

氮化铁薄膜是一种很有前途的记录材料。尤其是GaNMA-Fe_4N复合薄膜，由于具有较大的饱和磁化强度和合理的矫顽力，有望成为一种新型的记录介质。在实际应用中，薄膜织构(包括颗粒尺寸和高温下的相稳定性)对于获得合适的薄膜性能是非常重要的。因此，本课题通过两个步骤进行：一是寻找一种简单有效的制备方法，二是通过控制沉积工艺参数，建立合适的氮化铁膜的制备条件。主要研究结果如下：对双面靶式直流溅射装置进行了有效的改造，在溅射过程中加入氮气，制备了氮化铁薄膜。一对直径为10 cm的铁靶在高电源供电下获得高沉积速率是非常有效的。虽然在目前的条件下没有生成Fe16N_2化合物，但沉积参数可以很好地控制沉积膜中的氮含量。沉积时的薄膜是亚稳态的，很容易转变为另一个稳定的相。发现在200ﾟC以上的高温下可以得到稳定的氮化铁薄膜。在实际的薄膜制备中必须考虑这种衬底加热系统。这里采用的高抽气系统有效地减少了残余杂质伽马S，并缩短了成膜时间。为了生产更稳定。然而，氮化铁薄膜必须考虑沉积薄膜和衬底之间的关系：氮化铁膜和衬底晶体之间的晶格对应可能是最重要的因素之一。

Iron nitride films are promising recording materials. Especially, ganma-Fe_4N compound film is expected as one of new recording media because of large saturation magnetization with a reasonable coercive force. In practice, film texture including grain size and the phase stability at elevated temperatures are very important to get appropriate film properties. Therefore, this project was carried out through two following steps: One is to find a simple/effective preparation method, and the other is to establish suitable preparation conditions for structure-stable iron nitride films by controlling deposition parameters using the above method. Main results are as follows: A two-facing target type dc sputtering apparatus was effectively modified so as to prepare iron nitride films by adding a nitrogen gas to a sputtering argon gas during sputtering. A pair of iron target 10 cm in diameter was very effective to get a high deposition rate together with high power supply. Nitrogen content in deposited films was found to be controlled well by deposition parameters, although Fe16N2 compounds were not produced under the present conditions. As-deposited films were metastable and were easily transformed into another stable phase. Stable iron nitride films were found to be prepared at elevated temperatures more than 200ﾟC. This substrate heating system must be taken into consideration in practical film fabrication.A high evacuation system employed here vas effective to reduce a residual impurity ga s as well as a total film preparation time. In order to produce more stable. iron nitride films, however, a relationship between the deposited film and the substrate must be taken into consideration: The lattice corresponderxe between the iron nitride film and the substrate crystal may be one of the most important factors.