CN112805403A - 氧化镁溅射靶 - Google Patents

氧化镁溅射靶 Download PDF

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CN112805403A
CN112805403A CN201980066087.3A CN201980066087A CN112805403A CN 112805403 A CN112805403 A CN 112805403A CN 201980066087 A CN201980066087 A CN 201980066087A CN 112805403 A CN112805403 A CN 112805403A
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sputtering
sputtering target
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magnesium oxide
crystal grains
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梶田博树
涩谷义孝
成田里安
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Jks Metal Co ltd
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Abstract

一种溅射靶,所述溅射靶包含氧化镁烧结体,其特征在于,所述氧化镁烧结体中的在一个晶粒内存在的针孔的数量为20个以上的晶粒的比例为50%以下。本发明的课题在于提供一种包含氧化镁烧结体并且在溅射时粉粒的产生少的溅射靶。

Description

氧化镁溅射靶
技术领域
本发明涉及适合于磁盘装置用磁记录介质、隧道磁阻(TMR)元件等电子器件中的氧化镁(MgO)层的形成的氧化镁溅射靶,特别涉及在溅射时粉粒的产生少的氧化镁溅射靶。
背景技术
随着磁盘的小型化、高记录密度化,进行了磁记录介质的研究和开发,并对磁性层、基底层等进行了各种改进。另外,在非易失性存储器的领域中,例如,自旋扭矩型磁阻存储器(MRAM)通过流过TMR元件的电流的经由隧道结流动的电子的自旋来控制磁化,由此与以往类型的MRAM相比,能够实现低功耗且小型化。
在将氧化镁(MgO)用于该TMR元件的隧道结部分时,显著地改善其特性,因此如何制作MgO隧道结成为关键。作为MgO膜的制作方法,存在使用镁(Mg)靶作为溅射靶并在成膜后使其氧化的方法和使用氧化镁(MgO)靶进行成膜的方法,一般认为后者的磁阻效应大,能够得到高特性。
一直以来,已知将MgO烧结体用作溅射靶。例如,在专利文献1中公开了适合于利用溅射法进行MgO保护膜的成膜的MgO靶。根据该文献,记载了能够应对1000/分钟以上的溅射成膜速度。但是,这样的现有产品存在以下问题:在溅射时产生大量粉粒,从而使产品的成品率大幅降低。
另外,在专利文献2中公开了使大量(111)面取向的MgO烧结体靶。根据该文献,记载了靶的机械性质和导热性良好。另外,在专利文献3中公开了平均晶粒尺寸为8μm以下、并且利用X射线衍射得到的峰强度比I(111)/I(200)大于等于8%且小于25%的氧化镁烧结体溅射靶,根据该文献,记载了能够制作具有优异的绝缘耐性和均质性的溅射膜。
可以通过对MgO粉末进行烧结来制作氧化镁烧结体,制作本身并不太困难,但是包含MgO烧结体的溅射靶有时特别容易产生粉粒。但是,对于在上述专利文献中公开的烧结体而言,存在不能充分减少粉粒的问题。特别是近年来,在作为TMR元件的主要部分的隧道结部分中,对容许的粉粒的要求越来越严格。
现有技术文献
专利文献
专利文献1:日本特开平10-130827号公报
专利文献2:日本特开2009-173502号公报
专利文献3:国际公开第2013/065564号
发明内容
发明所要解决的问题
本发明的课题在于提供一种包含氧化镁烧结体并且在溅射时粉粒的产生少的溅射靶。
用于解决问题的手段
为了解决上述问题,本申请提供以下的发明。
1)一种溅射靶,所述溅射靶包含氧化镁烧结体,其特征在于,所述氧化镁烧结体中的在一个晶粒内存在的针孔的数量为20个以上的晶粒的比例为50%以下。
2)如上述1)所述的溅射靶,其特征在于,所述溅射靶的抗弯强度为150MPa以上。
3)如上述1)或2)所述的溅射靶,其特征在于,所述溅射靶的平均晶粒尺寸为30μm以上且400μm以下。
4)如上述1)~3)中任一项所述的溅射靶,其中,所述溅射靶的相对密度为99.7%以上。
发明效果
本发明的包含氧化镁烧结体的溅射靶具有能够抑制溅射时的粉粒的产生的优异效果。由此,例如在形成TMR元件的隧道势垒(绝缘层)时,具有以下优异效果:能够改善其器件特性,并且能够提高成品率。
附图说明
[图1]为示出在溅射靶中在特定的晶粒内局部存在针孔的电子显微镜(SEM)照片(倍数:3000倍)。
[图2]为图1的SEM照片的示意图。
[图3]为示出实施例1的溅射靶的在晶粒内存在的针孔的SEM照片(倍数:300倍)。
[图4]为示出实施例1的溅射靶的在晶粒内存在的针孔的SEM照片(倍数:3000倍)。
具体实施方式
氧化镁溅射靶通常使用热压等烧结法制作,但是对以这样的方式制作的氧化镁烧结体的晶体组织进行观察发现,在其晶粒内产生了针孔(直径为约1μm的微小气孔)。一般认为,当这样的针孔出现在溅射面上时,由于优先从此处开始溅射,因此粉粒的产生增加。
进一步反复进行了研究,结果发现所述针孔不是均匀地分散存在于氧化镁的晶体组织中,而是局部地大量存在于一部分晶粒内。而且,随着局部地存在大量针孔的晶粒的比例增加,观察到粉粒的数量增加的倾向。由此发现,如果能够降低存在大量针孔的晶粒的比例,则能够抑制粉粒的产生。
基于上述见解,本发明的溅射靶的特征在于,所述溅射靶包含氧化镁烧结体,并且所述氧化镁烧结体中的在一个晶粒内存在的针孔的数量为20个以上的晶粒的比例为50%以下。所述比例优选为40%以下。这样的氧化镁溅射靶能够减少在溅射时产生的粉粒的数量。
针孔是在制造氧化镁烧结体的过程中出现的直径为约1μm的气孔。在图1中示出MgO烧结体溅射靶的电子显微镜(SEM)照片,并且在图2中示出临摹该SEM照片而得到的示意图(用圆形圈住针孔密集的位置)。如图2所示,针孔不是均匀地分散在晶体组织中,而是在一部分的晶粒内局部地存在多个(20个以上)针孔,这样的晶粒对粉粒的产生起到很大作用。
在此,存在的针孔的数量为20个以上的晶粒的比例通过以下方法计算:对氧化镁烧结体(溅射靶)的表面进行研磨,然后使用离子铣削装置进行加工,利用显微镜对包含约100个晶粒的视野进行观察,然后根据下式计算。
(存在的针孔的数量为20个以上的晶粒的比例)=(存在20个以上针孔的晶粒的数量)/(视野内的全部晶粒的数量)×100
需要说明的是,离子铣削的条件设定为:加速电压为4kV、氩气流量为0.08sccm、试样倾斜20°、加工时间为1小时,并且使用日立高新技术公司制造的离子铣削装置作为装置。
另外,本发明的溅射靶的平均晶粒尺寸优选为30μm以上且400μm以下。随着局部地存在大量针孔的晶粒的比例增加,晶粒趋于细化,因此平均晶粒尺寸优选为30μm以上。另一方面,当晶粒过大时,抗弯强度降低,从而减少粉粒的效果降低,因此平均晶粒尺寸优选为400μm以下。
在本公开中,平均晶粒尺寸使用以下的方法测定并计算。
首先,利用激光显微镜观察溅射靶的溅射面(研磨面),从而得到组织照片。接着,在该组织照片上划直线,并对位于线上的晶界的个数进行计数。然后,将线的长度设为L(μm)、将晶界的个数设为n(个),由d=L/n计算出晶粒尺寸d(μm)(切片法)。此时,在照片上划出的线的数量为纵向(以照片的短边方向作为纵向)、横向(以照片的长边方向作为横向)等间隔地各2条,在一张照片(视野)中,将共计4条线的平均值作为一个视野的晶粒尺寸。需要说明的是,在照片的长度为相同程度的情况下,将任一者作为纵向,并且将另一者作为横向。
接着,对如下共计5个点进行与上述同样的操作,将该5个点的平均值定义为本发明中的平均晶粒尺寸,所述5个点为:溅射靶(圆盘状)的溅射面的中心1个点;以及对于以连接中心与溅射面的端部的线为半径、该半径的1/2处的圆周上的点,以中心为基准以90°间隔选择的4个点。
需要说明的是,倍数设定为在纵向上约7个~约14个晶界位于一条线上、在横向上约10个~约20个晶界位于一条线上的倍数。需要说明的是,在照片的长度为相同程度的情况下,设定为约7个~约20个晶界位于纵向和横向的任意一个方向的一条线上的倍数。
本发明的溅射靶的抗弯强度优选为150MPa以上。当作为烧结体(溅射靶)的强度的指标的抗弯强度降低时,减少粉粒的效果降低。因此,溅射靶的抗弯强度优选为150MPa以上。
在本公开中,抗弯强度根据JIS R1601:2008进行测定。
本发明的溅射靶的相对密度优选为99.7%以上。如上所述,通过减少存在多个针孔的晶粒的比例,能够减少粉粒的数量,但是通过制成致密的烧结体,能够进一步得到抑制粉粒的效果。
在本公开中,从作为溅射靶的烧结体中切出样品,通过阿基米德法计算出表观密度,然后将表观密度除以理论密度(3.585g/cm3)并乘以100倍而得到的值定义为相对密度(%)。
本发明的氧化镁溅射靶(烧结体)可以通过以下方法制作。
首先,准备平均粒径为5μm以下的MgO粉末作为原料。只要是平均粒径在该范围内的MgO粉末,也可以使用市售品。当原料粉末的粒径超过该范围时,由于烧结性的降低,局部存在大量针孔的晶粒的比例趋于增加,因此是不优选的。优选使用原料的纯度为99.99重量%以上的原料。这是因为,杂质的存在对半导体器件的成品率降低产生很大的影响。
接着,在真空中、在最高烧结温度:1400℃~1800℃、载荷:250kg/cm2~350kg/cm2的条件下对该MgO粉末进行单轴加压烧结(热压)。当最高烧结温度小于1400℃时,局部存在大量针孔的晶粒的比例趋于增加,另一方面,当最高烧结温度大于1800℃时,由于晶粒生长,晶粒容易变得粗大,因此是不优选的。另外,当载荷小于250kg/cm2时,局部存在大量针孔的晶粒的比例趋于增加,当载荷大于350kg/cm2时,晶粒容易变得粗大,因此是不优选的。
另外,最高烧结温度下的保持时间优选设定为3小时~6小时。通过在达到最高温度后放置充分的时间,温度分布变小,烧结的进行变得均匀,能够使烧结体内外的烧结状态变得均匀。另外,为了降低局部存在多个针孔的晶粒的比例,在热压后进行HIP(热等静压)处理也是有效的。
需要说明的是,对于烧结条件而言,例如,即使像烧结温度为1400℃、保持时间为3小时、载荷为250kg/cm2这样将各烧结条件设定在上述范围内,有时也不能降低局部存在大量针孔的晶粒的比例。但是,通过高温、高载荷、长时间的烧结,局部存在多个针孔的晶粒的比例趋于减少,因此通过适当地调节这些条件,能够得到所期望的晶粒。
通过利用车床等将以如上方式得到的氧化镁烧结体加工成所期望的形状,从而制成溅射靶。以如上方式得到的氧化镁溅射靶能够显著地抑制溅射时的粉粒的产生。
实施例
以下,基于实施例和比较例进行说明。需要说明的是,本实施例只是一个例子,不受该例子的任何限制。即,本发明只受权利要求书的限制,包含本发明中所含的实施例以外的各种变形。
(实施例1)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1550℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
将利用电子显微镜(SEM)观察溅射靶的溅射面而得到的结果示于图3、图4中。如图3、图4中所示的在晶粒内存在20个以上针孔的晶粒的比例为38%。另外,平均晶粒尺寸为60μm,抗弯强度为220MPa。对靶的密度进行测定,结果相对密度为99.9%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果为30个以下,非常少。
将以上的结果示于表1中。
Figure BDA0003009639520000081
(实施例2)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1600℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为35%。另外,平均晶粒尺寸为120μm,抗弯强度为190MPa。对靶的密度进行测定,结果相对密度为99.9%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果少至30个~50个以下。
(实施例3)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1700℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为30%。另外,平均晶粒尺寸为250μm,抗弯强度为180MPa。对靶的密度进行测定,结果相对密度为99.9%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果少至30个~50个以下。
(实施例4)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1750℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为30%。另外,平均晶粒尺寸为350μm,抗弯强度为160MPa。对靶的密度进行测定,结果相对密度为99.9%。
接着,将靶安装在溅射装置上,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果少至50个~100个以下。
(实施例5)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1400℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为45%。另外,平均晶粒尺寸为35μm,抗弯强度为220MPa。对靶的密度进行测定,结果相对密度为99.7%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果少至30个~50个以下。
(实施例6)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1400℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。对以如上方式得到的烧结体进行HIP(热等静压)处理。将HIP处理的条件设定为温度1400℃、压力1500kgf/cm2、保持时间2小时。
然后,使用车床等将该烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为35%。另外,平均晶粒尺寸为45μm,抗弯强度为210MPa。对靶的密度进行测定,结果相对密度为99.9%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果为30个以下,非常少。
(实施例7)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1550℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。对以如上方式得到的烧结体进行HIP(热等静压)处理。将HIP处理的条件设定为温度1800℃、压力1500kgf/cm2、保持时间2小时。
然后,使用车床等将该烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为20%。另外,平均晶粒尺寸为400μm,抗弯强度为150MPa。对靶的密度进行测定,结果相对密度为99.9%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果少至30个~50个以下。
(比较例1)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1350℃,并以300kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为80%。另外,平均晶粒尺寸为25μm,抗弯强度为230MPa。对靶的密度进行测定,结果相对密度为99.7%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果为100个以上。
(比较例2)
准备平均粒径为1μm、纯度为4N(99.99%)的MgO粉末作为原料粉末。接着,将2400g该MgO粉末填充到内径为206mm的石墨模具中,使用热压装置进行成型和烧结。将热压的条件设定为真空气氛、最高温度为1550℃,并以150kg/cm2进行加压。另外,将保持时间设定为6小时。使用车床等将以如上方式得到的烧结体精加工成靶形状。
利用SEM观察溅射靶的溅射面,结果在晶粒内存在20个以上针孔的晶粒的比例为55%。另外,平均晶粒尺寸为45μm,抗弯强度为135MPa。对靶的密度进行测定,结果相对密度为99.5%。
接着,将靶安装在溅射装置中,实施溅射,在硅基板上成膜。对于硅基板上的薄膜,使用粉粒计数器调查0.06μm以上的粉粒的个数,结果为100个以上。
产业实用性
本发明的氧化镁(MgO)溅射靶具有能够抑制粉粒的产生的优异的效果。本发明的MgO溅射靶作为用于尖晶石型MRAM的TMR元件的隧道膜特别有用。

Claims (4)

1.一种溅射靶,所述溅射靶包含氧化镁烧结体,其特征在于,所述氧化镁烧结体中的在一个晶粒内存在的针孔的数量为20个以上的晶粒的比例为50%以下。
2.如权利要求1所述的溅射靶,其特征在于,所述溅射靶的抗弯强度为150MPa以上。
3.如权利要求1或2所述的溅射靶,其特征在于,所述溅射靶的平均晶粒尺寸为30μm以上且400μm以下。
4.如权利要求1~3中任一项所述的溅射靶,其特征在于,所述溅射靶的相对密度为99.7%以上。
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