CN116604122A - 激光回流方法 - Google Patents
激光回流方法 Download PDFInfo
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- CN116604122A CN116604122A CN202310118054.7A CN202310118054A CN116604122A CN 116604122 A CN116604122 A CN 116604122A CN 202310118054 A CN202310118054 A CN 202310118054A CN 116604122 A CN116604122 A CN 116604122A
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Abstract
本发明提供激光回流方法,能够抑制半导体芯片的外周部的连接不良。激光回流方法包含如下的步骤:准备步骤,准备被加工物,该被加工物包含基板以及半导体芯片,该半导体芯片在一个面上具有凸块并经由该凸块而载置于该基板上;以及激光束照射步骤,从位于该一个面的相反侧的另一个面向该半导体芯片照射激光束而对该被加工物的被照射区域所包含的凸块进行回流。在该激光束照射步骤中,从该被照射区域中的包含外周部的区域朝向该被照射区域中的包含中央部的区域,一边阶段性地变更照射范围一边照射激光束。
Description
技术领域
本发明涉及激光回流方法。
背景技术
在半导体器件的制造工艺中,作为将芯片与外部端子电连接的方法之一,有使芯片的电极与封装基板上的电极相对并经由凸块进行连接的倒装芯片(flip chip)安装方式。
通常在倒装芯片安装中,采用将基板整体加热而进行接合的批量回流(MassReflow)工艺、通过将各芯片加热、加压而进行接合的TCB(Thermo-Compression Bonding:热压接接合)工艺等。但是,批量回流工艺中,将基板整体加热而导致的热应力成为课题,TCB工艺中,接合头的冷却花费时间等导致的生产率差成为课题。
作为相对于上述那样的工艺具有优越性的工艺,提出了通过激光照射将芯片与基板上的电极连接的激光回流工艺(参照专利文献1、2)。在激光回流工艺中,具有如下的优点:由于没有对基板整体施加热,因此能够降低热应力,并且通过对多个芯片照射激光束,能够得到比TCB工艺高的生产率。
专利文献1:日本特开2008-177240号公报
专利文献2:日本特开2021-102217号公报
但是,逐渐认识到在激光回流工艺中,与其他工艺相比略多地发现芯片的外周部处的接合不良。关于其原因,本申请人进行了验证,推测是由于芯片的中央部与外周部的热的传递方式不同,芯片的中央部先进行接合而产生芯片翘曲,由此引起外周部的接合不良。
发明内容
由此,本发明的目的在于提供能够抑制半导体芯片的外周部的连接不良的激光回流方法。
根据本发明,提供激光回流方法,其中,该激光回流方法具有如下的步骤:准备步骤,准备被加工物,该被加工物包含基板以及半导体芯片,该半导体芯片在一个面上具有凸块并经由该凸块而载置于该基板上;以及激光束照射步骤,从位于该一个面的相反侧的另一个面向该半导体芯片照射激光束而对该被加工物的被照射区域所包含的凸块进行回流,在该激光束照射步骤中,从该被照射区域中的包含外周部的区域朝向该被照射区域中的包含中央部的区域,一边阶段性地变更照射范围一边照射激光束。
优选在该激光束照射步骤中,伴随该照射范围的变更而变更激光束的功率密度。
优选在该激光束照射步骤中,设定成照射至阶段性地变更的该照射范围中的规定的照射范围的激光束的功率密度小于等于照射至比该规定的照射范围靠该外周部侧的照射范围的激光束的功率密度。
根据本发明,能够抑制半导体芯片的外周部的连接不良。
附图说明
图1是示出实施方式的激光回流方法的流程的流程图。
图2是在图1所示的准备步骤中准备的被加工物的立体图。
图3是图2所示的被加工物的主要部分剖视图。
图4是示出图1所示的激光束照射步骤中的被加工物的一个状态的主要部分剖视图。
图5是示出实施图1所示的激光束照射步骤的激光回流装置的光学***的结构例的图。
图6是在被加工物的被照射区域中示出第一阶段的照射范围的平面图。
图7是在被加工物的被照射区域中示出第二阶段的照射范围的平面图。
图8是在被加工物的被照射区域中示出第三阶段的照射范围的平面图。
图9是在被加工物的被照射区域中示出第四阶段的照射范围的平面图。
图10是示出比较例的照射范围的平面图。
标号说明
10:被加工物;11:被照射区域;12:外周部;13:中央部;14、14-1、14-2、14-3、14-4、14-5:照射范围;20:基板;30:半导体芯片;31:正面(一个面);32:背面(另一个面);40:凸块;61:激光束。
具体实施方式
以下,参照附图对本发明的实施方式进行详细说明。本发明并不被以下实施方式所记载的内容限定。另外,在以下所记载的构成要素中包含本领域技术人员能够容易想到的内容、实质上相同的内容。另外,以下所记载的结构可以适当组合。另外,可以在不脱离本发明的主旨的范围内进行结构的各种省略、置换或变更。
根据附图,对本发明的实施方式的激光回流方法进行说明。图1是示出实施方式的激光回流方法的流程的流程图。如图1所示,激光回流方法具有准备步骤1和激光束照射步骤2。
(准备步骤1)
图2是在图1所示的准备步骤1中准备的被加工物10的立体图。图3是图2所示的被加工物10的主要部分剖视图。如图2和图3所示,被加工物10包含基板20以及具有凸块40的半导体芯片30。
准备步骤1是准备在基板20上载置有半导体芯片30的被加工物10的步骤。此时,半导体芯片30在使具有凸块40的一个面(正面31)朝下的状态下经由凸块40而载置于正面21侧朝上的基板20的正面21侧。
在实施方式中,基板20是矩形状。基板20例如是PCB基板(Printed CircuitBoard:印刷电路板)、分割成芯片之前的器件晶片等。在基板20的正面21侧经由凸块40而配置有多个半导体芯片30。半导体芯片30在正面31上具有多个凸块40。凸块40是设置于半导体芯片30的正面31的突起状的端子。
凸块40被加热并熔化从而半导体芯片30与基板20上的电极连接。即,关于在准备步骤1中准备的被加工物10,预想利用激光束61(参照图4)对凸块40进行回流从而将半导体芯片30倒装安装于基板20。
另外,被加工物10除了实施方式中的半导体芯片30经由凸块40而排列在基板20的被加工物10以外,还可以是将多个半导体芯片30层叠且在各个半导体芯片30间存在凸块40的被加工物10等。
(激光束照射步骤2)
图4是示出图1所示的激光束照射步骤2中的被加工物10的一个状态的主要部分剖视图。图5是示出实施图1所示的激光束照射步骤2的激光回流装置50的光学***的结构例的图。激光束照射步骤2是对半导体芯片30照射激光束61而对被加工物10的被照射区域11所包含的凸块40进行回流的步骤。
实施方式的激光束照射步骤2通过具有图5所示的光学***的激光回流装置50来实施。激光回流装置50具有加工工作台51、激光束照射单元60、未图示的移动单元、未图示的拍摄单元以及未图示的控制器。
加工工作台51将被加工物10保持于保持面52。激光束照射单元60对加工工作台51所保持的被加工物10照射激光束61。未图示的移动单元使加工工作台51和激光束照射单元60相对地移动。未图示的拍摄单元对加工工作台51上的被加工物10进行拍摄,用于将被加工物10的位置和照射激光束61的照射部的位置进行对准。未图示的控制器对各构成要素进行控制。
如图5所示,激光束照射单元60包含:激光光源62、均匀照射单元63、导光单元64、空间光调制单元65、成像***66、放大成像透镜67以及远心透镜68。
激光光源62射出激光束61。激光光源62例如包含光纤激光器、具有单一的激光二极管(LD)的单一光源或配置有多个激光二极管的多光源等。从激光光源62射出的激光束61是对于被加工物10(半导体芯片30)具有吸收性的波长的连续波(CW)。
均匀照射单元63配置于激光光源62的后段。均匀照射单元63用于通过从均匀照射单元63射出的激光束61对后述的空间光调制单元65形成均匀照射面。在该均匀照射面中,激光束61的功率密度均匀。
在激光光源62为多光源的情况下,特别优选设置均匀照射单元63。关于均匀照射单元63,即使在单一光源的情况下,优选为了在呈高斯分布的光源的情况下形成完全的平顶(top-hat)分布而设置均匀照射单元63,另外,即使在呈平顶分布的光源的情况下,优选为了形成更完整的平顶分布而设置均匀照射单元63。
作为均匀照射单元63,例如可以利用:通过准直透镜与非球面透镜的组合来形成均匀照射面的单元;通过准直透镜、DOE(Diffractive Optical Element;衍射光学元件)和聚光透镜的组合来形成均匀照射面的单元;通过棒状透镜(由玻璃构成的筒状部件)或光导管(是由镜围绕的中空的筒状部件,也被称为均化(homogenizer)棒)和导光单元(中继透镜合光纤)的组合来形成均匀照射面的单元;通过准直透镜、第一透镜阵列以及第二透镜阵列(将多个棒状透镜捆扎而形成为阵列状的结构、将透镜面加工成阵列状的结构)和聚光透镜的组合来形成均匀照射面的单元;等等。
导光单元64是用于将通过均匀照射单元63形成的均匀照射面的光转移至空间光调制单元65的单元。另外,在激光束照射单元60未包含均匀照射单元63的情况下,导光单元64将直接来自激光光源62的光转移至空间光调制单元65。导光单元64例如由光纤或中继透镜(组透镜)构成。
空间光调制单元65包含空间光调制元件,能够控制所射出的激光束61的强度(功率密度)的空间密度分布,被称为SLM(Spatial Light Modulator:空间光调制器)。空间光调制单元65通过控制激光束61的功率密度的空间密度分布而控制向被加工物10照射激光束61时的被加工物10的被照射区域11(参照图4和后述的图6至图9)中的激光束61的照射范围14的形状。作为空间光调制单元65,例如可以利用周知的反射型液晶LCOS(Liquid-Crystal on Silicon:硅基液晶)、透过型液晶LCP(Liquid Crystal Panel:液晶面板)、变形反射镜(Deformable Mirror)、DMD(Digital Micro-mirror Device:数字微镜设备)等周知的SLM器件。实施方式的空间光调制单元65是LCOS。
成像***66将所入射的激光束61成像。成像***66由单一的透镜或包含组透镜的成像透镜构成,在图5所示的一例中,构成为依次配置有双凸透镜和双凹透镜。另外,在空间光调制单元65通过空间光调制元件还兼具成像***66(成像透镜)的功能的情况下,可以省略成像***66。
放大成像透镜67将利用成像***66形成的像(共轭像)放大而成像于被加工物10的激光被照射面(被照射区域11)。另外,可以省略放大成像透镜67。
远心透镜68用于使激光束61垂直地入射即与光轴平行地入射至被加工物10的激光被照射面(被照射区域11)。另外,也可以将成像***66构成为远心透镜68,另外也可以省略远心透镜68而构成光学***。
实施方式的激光束照射单元60通过包含成像***66、放大成像透镜67和远心透镜68在内的成像单元将激光束61成像于加工工作台51上的被加工物10中的与半导体芯片30的背面32对应的区域。另外,在激光束照射单元60中,可以对多个半导体芯片30同时进行照射。
在激光束照射步骤2中,首先将被加工物10保持于加工工作台51的保持面52。此时,处于保持面52对基板20的背面22侧进行保持而基板20在正面21侧经由凸块40而载置有半导体芯片30的状态。接着,通过拍摄单元(未图示)对加工工作台51上的被加工物10进行拍摄,通过移动单元(未图示)使加工工作台51和激光束照射单元60相对地移动,执行对准也就是将被加工物10的位置与激光束照射单元60的照射部的位置对位。
在激光束照射步骤2中,从半导体芯片30的与具有凸块40的一个面(正面31)相反侧的另一个面(背面32)对半导体芯片30照射激光束61。此时,激光束61的被照射区域11与半导体芯片30的整个背面32对应。在实施方式的激光束照射步骤2中,对被照射区域11照射1秒钟的激光束61。
图6是在被加工物10的被照射区域11中示出第一阶段的照射范围14-1的平面图。图7是在被加工物10的被照射区域11中示出第二阶段的照射范围14-2的平面图。图8是在被加工物10的被照射区域11中示出第三阶段的照射范围14-3的平面图。图9是在被加工物10的被照射区域11中示出第四阶段的照射范围14-4的平面图。
在激光束照射步骤2中,如图6至图9所示,对被照射区域11一边阶段性地变更激光束61的照射范围14一边照射激光束61。在实施方式的激光束照射步骤2中,分成四个阶段照射激光束61。另外,在实施方式中,激光束61的照射范围14的变更通过空间光调制单元65控制激光束61的功率密度的空间密度分布而实施。
即,在执行了被加工物10的位置与激光束照射单元60的照射部的位置的对准之后,在激光束照射步骤2中,通过空间光调制单元65将激光束61的照射范围14的形状变更成图6所示的第一阶段的照射范围14-1。
如图6所示,第一阶段的激光束61的照射范围14-1包含被照射区域11中的外周部12。外周部12是被照射区域11的外周缘及其附近的环形状的区域,是与半导体芯片30的外周部12对应的区域。实施方式的照射范围14-1是沿着矩形状的半导体芯片30的外周缘的矩形的框形状。
在激光束照射步骤2中,通过对第一阶段的照射范围14-1照射激光束61,对与照射范围14-1对应的包含外周部12的区域中所包含的凸块40进行回流,将包含半导体芯片30的外周部12的与照射范围14-1对应的环形状(矩形状)的部分接合于基板20。
在激光束照射步骤2中,接着通过空间光调制单元65将激光束61的照射范围14的形状变更成图7所示的第二阶段的照射范围14-2。如图7所示,第二阶段的激光束61的照射范围14-2是与图6所示的照射范围14-1的内侧邻接的环形状的区域。实施方式的照射范围14-2是矩形的框形状。
在激光束照射步骤2中,在对第一阶段的照射范围14-1照射了激光束61之后,对第二阶段的照射范围14-2照射激光束61,由此对与照射范围14-2对应的区域中所包含的凸块40进行回流,将比半导体芯片30的外周部12靠内侧的与照射范围14-2对应的环形状(矩形状)的部分在外周部12之后接合于基板20。
在激光束照射步骤2中,接着通过空间光调制单元65将激光束61的照射范围14的形状变更成图8所示的第三阶段的照射范围14-3。如图8所示,第三阶段的激光束61的照射范围14-3是进一步与图7所示的照射范围14-2的内侧邻接的环形状的区域。实施方式的照射范围14-3是矩形的框形状。
在激光束照射步骤2中,在对第二阶段的照射范围14-2照射了激光束61之后,对第三阶段的照射范围14-3照射激光束61,由此对与照射范围14-3对应的区域中所包含的凸块40进行回流,将比半导体芯片30的照射范围14-2靠内侧的与照射范围14-3对应的环形状(矩形状)的部分在与照射范围14-2对应的部分之后接合于基板20。
在激光束照射步骤2中,接着通过空间光调制单元65将激光束61的照射范围14的形状变更成图9所示的第四阶段的照射范围14-4。如图9所示,第四阶段的激光束61的照射范围14-4进一步与图8所示的照射范围14-3的内侧邻接且包含被照射区域11中的中央部13。中央部13是与半导体芯片30的中央部13对应的区域。实施方式的照射范围14-4是矩形状。
在激光束照射步骤2中,在对第三阶段的照射范围14-3照射了激光束61之后,对第四阶段的照射范围14-4照射激光束61,由此对与照射范围14-4对应的包含中央部13的区域中所包含的凸块40进行回流,将包含半导体芯片30的中央部13的与照射范围14-4对应的矩形状的部分在与照射范围14-3对应的部分之后接合于基板20。
这样,在激光束照射步骤2中,在1秒钟的照射时间中,从被加工物10的被照射区域11中的包含外周部12的区域朝向包含中央部13的区域,一边阶段性地变更照射范围14一边照射激光束61。由此,在激光束照射步骤2中,对被照射区域11所包含的凸块40从半导体芯片30的外周部12朝向中央部13依次进行回流。
在激光束照射步骤2中,可以伴随照射范围14的变更而变更激光束61的功率密度。在该情况下,功率密度设定成照射至包含外周部12的区域的激光束61的功率密度比照射至包含中央部13的区域的激光束61的功率密度大。
在按照三个阶段以上变更照射范围14的情况下,可以在所有的变更时变更功率密度,也可以在至少任意阶段的变更时变更功率密度。即,设定成照射至阶段性变更的照射范围14中的规定的照射范围14(例如照射范围14-3)的激光束61的功率密度小于等于照射至比规定的照射范围14靠外周部12侧的照射范围14(例如照射范围14-2)的激光束61的功率密度即可。在该情况下,关于实施方式的照射范围14中的激光束61的功率密度,(照射范围14-1的功率密度)≥(照射范围14-2的功率密度)≥(照射范围14-3的功率密度)≥(照射范围14-4的功率密度)的关系成立。
另外,可以从外周部12朝向中央部13依次减小功率密度。在该情况下,关于实施方式的照射范围14中的激光束61的功率密度,(照射范围14-1的功率密度)>(照射范围14-2的功率密度)>(照射范围14-3的功率密度)>(照射范围14-4的功率密度)的关系成立。
图10是示出比较例的照射范围14-5的平面图。比较例的照射范围14-5包含被照射区域11的整个区域。即,在比较例的激光束照射步骤2中,对被照射区域11均匀照射1秒钟的激光束61。在比较例的情况下,半导体芯片30的外周部12与外部气体接触,因此热容易逃逸,与中央部13相比温度不容易上升,因此关于利用比较例的激光束照射步骤2对凸块40进行回流的半导体芯片30,中央部13先接合,由此产生芯片翘曲。
与此相对,实施方式的激光回流方法在激光束照射步骤2中从外周部12向中央部13阶段性地照射激光束61。由此,能够使外周部12比中央部13先接合,因此能够抑制产生由于中央部13先接合所导致的芯片翘曲。因此,能够抑制半导体芯片30的外周部12的连接不良。
另外,本发明并不限于上述实施方式。即,可以在不脱离本发明的主旨的范围内进行各种变形并实施。例如激光束61的照射范围14的变更在实施方式中使用空间光调制单元65(LCOS)来实施,但例如可以预先准备将激光束61的一部分遮光的掩模,并通过使掩模机械式地移动而实施变更。
另外,关于阶段性地变更的多个照射范围14,在实施方式中,外周部12侧的照射范围14(例如照射范围14-2)与中央部13侧的照射范围14(例如照射范围14-3)邻接,但在本发明中,可以设定成外周部12侧的照射范围14与中央部13侧的照射范围14一部分重叠。
Claims (3)
1.一种激光回流方法,其中,
该激光回流方法具有如下的步骤:
准备步骤,准备被加工物,该被加工物包含基板以及半导体芯片,该半导体芯片在一个面上具有凸块并经由该凸块而载置于该基板上;以及
激光束照射步骤,从位于该一个面的相反侧的另一个面向该半导体芯片照射激光束而对该被加工物的被照射区域所包含的凸块进行回流,
在该激光束照射步骤中,
从该被照射区域中的包含外周部的区域朝向该被照射区域中的包含中央部的区域,一边阶段性地变更照射范围一边照射激光束。
2.根据权利要求1所述的激光回流方法,其中,
在该激光束照射步骤中,伴随该照射范围的变更而变更激光束的功率密度。
3.根据权利要求1或2所述的激光回流方法,其中,
在该激光束照射步骤中,设定成照射至阶段性地变更的该照射范围中的规定的照射范围的激光束的功率密度小于等于照射至比该规定的照射范围靠该外周部侧的照射范围的激光束的功率密度。
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