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CN106378583A - 一种高温封装用Sn/Cu/Sn冷压预制片的制备方法 - Google Patents

一种高温封装用Sn/Cu/Sn冷压预制片的制备方法 Download PDF

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CN106378583A
CN106378583A CN201610822937.6A CN201610822937A CN106378583A CN 106378583 A CN106378583 A CN 106378583A CN 201610822937 A CN201610822937 A CN 201610822937A CN 106378583 A CN106378583 A CN 106378583A
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cold
pressing
temperature
pressed
interconnection
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CN106378583B (zh
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张志昊
李明雨
操慧珺
杨海峰
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Xiamen University
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Xiamen University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
    • B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B21D28/24—Perforating, i.e. punching holes
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • C21—METALLURGY OF IRON
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    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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    • C23G1/103—Other heavy metals copper or alloys of copper
    • C—CHEMISTRY; METALLURGY
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Abstract

一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，涉及半导体器件封装互连。包括以下步骤：1)一个制备Sn/Cu/Sn冷压金属箔的步骤；2)一个加工Sn/Cu/Sn冷压预制片的步骤；3)一个Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连的步骤。原材料价格低廉、加工工艺简单、对设备要求低、方便存储运输、材料加工性好、便于批量制造。可短时间内在低温下形成耐高温无铅焊点，完全避免了高温、长时间的回流过程对芯片可靠性造成的不利影响及对能源的浪费。互连原理简单、对准精度高、互连缺陷少；可解决高温半导体器件中大互连间隙无铅耐高温焊点难以快速制造的技术瓶颈。

Description

一种高温封装用Sn/Cu/Sn冷压预制片的制备方法
技术领域
本发明涉及半导体器件封装互连，尤其是涉及一种高温封装用Sn/Cu/Sn冷压预制片的制备方法。
背景技术
半导体工业的进步促使微电子器件持续向小型化、集成化和多功能化的方向发展。更小的体积与更多的功能使得器件的功率密度显著提高，进而加剧了器件的产热；更大的集成密度则极大地压缩了器件的散热空间，最终导致器件的工作温度急剧上升(DanielLu,C.P.Wong.Materials for Advanced Packaging.Springer；2009.p.1-62)。尤其是对于那些本身就应用于航天航空、高速列车、石油勘探、通信化工等高温环境下的半导体器件，其工作温度已经突破250℃(A.Mona Kumar,C.Zhong.IEEE Trans.Adv.Packag.2007,30:68-72)。由于目前主流的硅基半导体器件在高于150℃时会导致结温效应，使其使用寿命急剧缩短，因此工业界已积极开发新型耐高温半导体材料(如碳化硅、氮化镓等，稳定工作温度可达500℃)，用来取代硅基半导体器件应用于第三代高温半导体器件中(Z.H.Zhang,M.Y.Li,C.Q.Wang.Intermetallics.2013,42:52-55)。
制造第三代高温半导体器件要求器件内部的封装互连材料同样具有耐高温性能，同时还应兼具低温互连能力及较低的材料制造成本。目前可用于高温半导体封装互连的焊点材料多以Pb95Sn5、Pb90Sn10、Pb95.5Sn2Ag2.5等高铅合金为主，其加热互连温度约为300℃，工作使用温度最高可达250℃，在一定程度上满足了现阶段高温半导体封装的使用要求(Y.C.Liang,H.W.Lin,H.P.Chen,C.Chen,K.N.Tu,Y.S.Lai.Scripta Mater.2013,69:25-28)。不过，铅元素对人体健康及水土环境有极大的破坏性，因此世界各国争相颁布无铅化禁令(如欧洲环保指令《RoHs》等)以限制含铅半导体器件的使用(F.Y.Ouyang,K.N.Tu,Y.S.Lai.Mater.Chem.Phys.2012,136:210-218)。目前无铅焊点已经广泛应用于半导体器件的低温互连领域，然而对于应用于高温半导体互连领域的高铅焊点，由于无法找到合适的替代材料使含铅焊点一直享有豁免；不过，全球对半导体封装互连材料的无铅化已经达成共识，因此开发新型无铅耐高温焊点对半导体工业的发展有重大价值。
新型无铅耐高温焊点应具备与第三代半导体材料匹配的耐高温能力，从而减少芯片辅助制冷设计，满足芯片微型化发展要求。研究发现，虽然无铅Sn系互连焊点的工作温度较低(<150℃),但是其与互连Cu焊盘发生冶金反应所形成的界面金属间化合物(Cu6Sn5和Cu3Sn)具有极高的耐高温性能。其中，Cu6Sn5熔点为415℃，弹性模量为85～125GPa，硬度为4.5～6.5GPa，电阻率为8.9μΩ·cm；Cu3Sn熔点为675℃，弹性模量为110～140GPa，硬度为5.5～7GPa，电阻率为17.5μΩ·cm(Z.H.Zhang,M.Y.Li,Z.Q.Liu,S.H.Yang.ActaMater.2016,104:1-8)。考虑到Cu6Sn5和Cu3Sn皆具有较高的机械性能与导电性能，因此可作为良好的无铅耐高温互连封装焊点材料。不过在一般软钎焊条件下(250℃加热1min)，Cu6Sn5的生长速率仅为2～3μm/min，而Cu3Sn的生长速率更是只有100～200nm/min；这意味着如果要实现常规封装尺寸(如：互连间距20μm)的金属间化合物基垂直互连焊点需要对无铅Sn基焊点进行长时间的持续加热，这无疑损害了半导体芯片的互连封装效率。因此，如何快速实现大互连间距的金属间化合物基垂直互连焊点已经成为目前高温半导体器件制造的主要技术瓶颈。
发明内容
鉴于目前半导体工业在高温封装互连领域面临的主要技术挑战，本发明提供一种工艺简单、成本低廉的一种高温封装用Sn/Cu/Sn冷压预制片的制备方法。
本发明包括以下步骤：
1)一个制备Sn/Cu/Sn冷压金属箔的步骤；
2)一个加工Sn/Cu/Sn冷压预制片的步骤；
3)一个Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连的步骤。
在步骤1)中，所述制备Sn/Cu/Sn冷压金属箔的具体步骤包括：
a)Sn、Cu金属箔的清洗：将商用Sn、Cu金属箔分别浸泡于丙酮溶液中，超声清洗去除箔片表面油污后，再浸泡于质量浓度为0.5％～2％的盐酸酒精的腐蚀溶液中，按照浸泡产物与腐蚀液体积比1︰10的比例添加腐蚀溶液，超声清洗去除箔片表面氧化物后，再浸泡于质量浓度为0.5～2％的硝酸酒精的腐蚀溶液中，按照浸泡产物与腐蚀液体积比1︰10的比例添加腐蚀溶液，超声清洗去除箔片表面难溶氯化物后，再浸泡于酒精溶液中，超声清洗，冷风吹干；
b)Sn、Cu金属箔的预压成型：将清洗后的Sn、Cu金属箔分别通过双辊冷压机进行滚压加工，滚压速度为1～9mm/s；其中，商用Sn金属箔的初始厚度为0.1～1mm，经冷压5～10次后，压缩至10～50μm；商用Cu金属箔的初始厚度约为0.1～10mm，经冷压5～10次后，压缩至0.02～1mm；
c)Sn/Cu/Sn预压箔的冷压成型：将预压成型的Sn、Cu金属预压箔，按照Sn、Cu、Sn的放置次序放入双辊冷压机内，滚压速度为1～9mm/s，实现冷压多层箔的成型，其中，Sn/Cu/Sn结构可由三层扩展为多层，并按照Sn/Cu/…/Cu/Sn的方式依次放置。首次冷压时，1号滚轮设置的间隙宽度应略小于金属预压箔的总厚度，用以夹持并向2号滚轮输送；2号滚轮设置的间隙宽度应小于1号间隙宽度的一半，以便于多层预压箔一次性预压成型，消除微气孔等缺陷，实现层间机械啮合及界面纳米尺度连接，保持滚轮间隙宽度不变，重复冷压3次，以消除金属的冷压弹性变形，稳定厚度方向上的塑性变形；调整2号滚轮间隙2～9次，使得冷压箔最终达到预期厚度且表层Sn层控制在1～20μm之间，在随后的挤压过程中，界面处的纳米扩散结合区面积将逐渐扩大，最终Sn/Cu/Sn预压箔结构将形成紧密结合；
d)冷压箔的回火处理：将Sn/Cu/Sn冷压箔放入真空加热炉内，真空压力设置为1～0.1Pa，温度为120～150℃，保温0.5～2h后随炉冷却备用。
在步骤2)中，所述加工Sn/Cu/Sn冷压预制片的具体步骤包括：
a)Sn/Cu/Sn冷压箔的切割处理：将不规则的Sn/Cu/Sn冷压薄箔用激光切割机切割成50mm×50mm或100mm×100mm等规整图案，其中，激光切割机的激光功率为50～200W,切割速度为0.01～0.5mm/s；当冷压箔的整体厚度小于200μm时，激光功率优选为100W，切割速度优选为0.4mm/s；当冷压箔的整体厚度大于200μm时，激光功率优选为200W，切割速度优选为0.1mm/s；
b)Sn/Cu/Sn冷压箔的冲模：将切割后的Sn/Cu/Sn冷压箔放入冲模夹具的底座中，冲模夹具的顶座放置于底座的固定槽内，顶座与底座不加定位销以便于快速取料；冲模顶座由压台、冲模顶出杆、弹簧三部分组成；顶座与底座开通孔，当顶座放置于底座固定槽后，顶座与底座的通孔将自动对齐，并与冲模顶出杆形成紧密配合；通过对压台施加载荷(1～10MPa)，使得冲模顶出杆由顶座与底座组成的固定滑道内顶出，落料即为所需Sn/Cu/Sn预制片；每次冲模完成后，释放压力，压台将由弹簧回复原先位置；冲模后的Sn/Cu/Sn冷压片的尺寸由底座所开通孔尺寸决定，厚度由初始Sn/Cu/Sn冷压箔决定；
c)Sn/Cu/Sn冷压预制片的回火处理：将Sn/Cu/Sn冷压预制片浸泡于酒精溶液中，超声清洗后冷风吹干，再放入真空加热炉内，真空压力设置为1～0.1Pa，温度为120～150℃，保温0.5h。
在步骤3)中，所述Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连的具体步骤包括：
a)Sn/Cu/Sn冷压预制片的放置：将冷压预制片表面涂敷助焊剂，再放置在互连焊盘表面中心；
b)Sn/Cu/Sn冷压预制片的加热：对预制片加热，加热温度为钎料熔点以上30～50℃，加热时间30s，通过加热使预制片的底部Sn层与接触焊盘快速润湿互连；
c)Sn/Cu/Sn冷压预制片的倒装：将冷却后的预制片表层重新涂敷助焊剂，倒置整个互连结构并放置在与其匹配的倒装互连焊盘顶部；
d)Sn/Cu/Sn冷压预制片的回流：对倒装芯片结构加热，加热温度为150～350℃，加热时间30～600s。根据控制加热温度与加热时间可生成4种不同结构的互连焊点，分别为：全Cu3Sn金属间化合物焊点、Cu3Sn/Cu/Cu3Sn复合结构焊点、Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点和Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点。其中，前两种类型的互连焊点可在675℃的环境温度下稳定服役，后两种类型的互连焊点可在415℃的环境温度下稳定服役。另外，对Sn/Cu/Sn冷压预制片的Cu层进一步覆Ni、Ag、Au等金属后，可形成多种Sn基金属间化合物(如Ni3Sn4、Ag3Sn、AuSn2等)，形成以上述4种复合焊点结构为基础的更为复杂的金属化合物基高温互连焊点。
本发明相对于现有技术的优点及有益效果在于：
1、本发明制备的Sn/Cu/Sn预制片具有制片原材料价格低廉、加工工艺简单、对设备要求低、方便存储运输、材料加工性好、便于批量制造等优点。
2、所述Sn/Cu/Sn预制片可短时间内在低温下形成耐高温无铅焊点，完全避免了高温、长时间的回流过程对芯片可靠性造成的不利影响及对能源的浪费。
3、本发明采用的Sn/Cu/Sn冷压箔的冲模装置，具有工作原理简单、成本低、可靠性高、可批量制造高精度预制片的优点。
4、本发明采用的Sn/Cu/Sn冷压预制片与Cu基焊盘的冶金互连方法，具有互连原理简单、对准精度高、互连缺陷少的优点；该方法与传统倒装焊芯片工艺兼容，因此对封装设备的要求较低，而且互连操作仅需30～600s，这对与半导体器件封装的互连效率提升有重要意义。
5、本发明制造的耐高温互连焊点，当其由全Cu3Sn或Cu3Sn/Cu/Cu3Sn复合结构组成时，服役温度最高可达675℃；当其由Cu3Sn/Cu6Sn5/Cu3Sn或Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn组成时，其服役温度最高可达415℃。因此，上述耐高温无铅焊点完全满足碳化硅、氮化镓等新型高温半导体器件的高温服役要求。
6、本发明获得的Sn/Cu/Sn冷压预制片及形成的耐高温无铅互连焊点将对第三代高温半导体器件的可靠封装有重大实用价值。本发明利用该预制片结构可解决高温半导体器件中大互连间隙无铅耐高温焊点难以快速制造的技术瓶颈。
附图说明
图1为Sn/Cu/Sn冷压过程示意图。
图2为Sn/Cu/Sn冷压箔的冲模装置的冲模前截面示意图。
图3为Sn/Cu/Sn冷压箔的冲模装置的冲模后截面示意图。
图4为Sn/Cu/Sn冷压箔的冲模装置的冲模装置顶视图。
图5为Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连工艺流程图。
图6为Sn/Cu/Sn冷压预制片的超声扫描检测结果。
图7为Sn/Cu截面扫面电镜照片。
图8为6μm-Sn/30μm-Cu/6μm-Sn冷压预制片与Cu焊盘在250℃下加热0～1200s后的截面结构。图8中，(a)0s；(b)60s；(c)180s；(d)300s；(e)600s；(f)1200s。
图9为10μm-Sn/40μm-Cu/10μm-Sn冷压预制片与Cu焊盘在240℃下截面CuSn金属间化合物厚度随加热时间的曲线图。
图10为10μm-Sn/40μm-Cu/10μm-Sn冷压预制片与Cu焊盘在280℃下截面CuSn金属间化合物厚度随加热时间的曲线图。
具体实施方式
下面将对本发明的实施例做详细说明，本实施例在本发明技术方案为前提下进行实施，给出详细的实施方式和具体的操作过程，但本发明的保护范围不限于下述实施例。
本发明包括以下步骤：
1)一个制备Sn/Cu/Sn冷压金属箔的步骤；
2)一个加工Sn/Cu/Sn冷压预制片的步骤；
3)一个Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连的步骤。
在步骤1)中，所述制备Sn/Cu/Sn冷压金属箔的具体步骤包括：
a)Sn、Cu金属箔的清洗：将商用Sn、Cu金属箔分别浸泡于丙酮溶液中，超声清洗15min，用于去除箔片表面油污；将上述金属箔浸泡于质量浓度为0.5～2％的盐酸酒精的腐蚀溶液中，按照浸泡产物与腐蚀液体积比1︰10的比例添加腐蚀溶液，超声清洗5min，用于去除箔片表面氧化物；将上述金属箔浸泡于质量浓度为0.5～2％的硝酸酒精的腐蚀溶液中，按照浸泡产物与腐蚀液体积比1︰10的比例添加腐蚀溶液，超声清洗5min，用于去除箔片表面难溶氯化物；将上述金属箔浸泡于酒精溶液中，超声清洗15min后冷风吹干备用。
b)Sn、Cu金属箔的预压成型：将清洗后的Sn、Cu金属箔分别通过双辊冷压机进行滚压加工，滚压速度为1～9mm/s。其中，商用Sn金属箔的初始厚度约为0.1～1mm，经冷压5～10次后，压缩至10～50μm(具体数据参见表1)；商用Cu金属箔的初始厚度约为0.1～10mm，经冷压5～10次后，压缩至0.02～1mm(具体数据可参见表2)。滚压速度决定了Sn、Cu预压箔的厚度均匀性：滚压速度不易过快，速度太快将导致Sn、Cu金属箔的塑性变形时间缩短，使得滚压后的金属层厚度不均；速度太慢则会降低生产效率，导致生产成本增加。
表1Sn金属箔的冷压成型厚度与2号辊轮间隙调整次数之间的关系
表2Cu金属箔的冷压成型厚度与2号辊轮间隙调整次数之间的关系
c)Sn/Cu/Sn预压箔的冷压成型(如图1)：将预压成型的Sn、Cu金属预压箔，按照Sn/Cu/Sn的放置次序整齐的放入双辊冷压机内，滚压速度为1～9mm/s。通过控制双辊冷压机的2号棍轮间隙宽度、冷压次数，实现特定厚度冷压多层箔的快速成型(具体数据参见表3)。
表3Sn/Cu/Sn预压箔的冷压成型厚度与2号辊轮间隙调整次数之间的关系
其中，Sn/Cu/Sn结构可由三层扩展为多层，并按照Sn/Cu/…/Cu/Sn的方式依次放置。首次冷压时，1号滚轮设置的间隙宽度应略小于金属预压箔的总厚度，用以夹持并向2号滚轮输送；2号滚轮设置的间隙宽度应小于1号间隙宽度的一半，以便于多层预压箔一次性预压成型，消除微气孔等缺陷，实现层间机械啮合及界面纳米尺度连接。保持滚轮间隙宽度不变，重复冷压3次，以消除金属的冷压弹性变形，稳定厚度方向上的塑性变形；调整2号滚轮间隙2～9次，使得冷压箔最终达到预期厚度且表层Sn层控制在1～20μm之间。注意到：Cu、Sn预压箔在大变形量冷压过程中，表面氧化膜将逐步破裂使内部清洁表面暴露在裂缝间；这些清洁表面将与对位表面相互接触时形成紧密的纳米扩散结合区；在随后多次的挤压过程中，界面处的纳米扩散结合区面积将逐渐扩大，最终Sn/Cu/Sn预压箔结构将形成紧密结合。利用超声扫描技术对本专利所制备的Sn/Cu/Sn预制片进行无损检测，检测结果表明：Sn/Cu界面层完全结合，未发现预制片中含有明显的气孔或未结合区域(图6)；在扫描电子显微镜下取样观测预制片截面，发现预制片中Sn层厚度与Cu层厚度基本均匀(图7)。
d)冷压箔的回火处理：将Sn/Cu/Sn冷压箔放入真空加热炉内，真空压力设置为1～0.1Pa，温度为120～150℃，保温0.5～2h后随炉冷却备用。回火处理前，Sn/Cu层间结合主要靠机械啮合及纳米尺度的扩散连接，界面连接强度实测结果可达1.6～4.5MPa；经回火处理后，Sn/Cu结合界面形成有数百纳米的Sn/Cu金属间化合物层，其连接强度大幅提升，实测结果可达10.1～18.7MPa。其次，由于回火时间短，冷压箔内Sn/Cu界面处金属间化合物层极薄，因此其界面脆性小、可加工性良好。另外，回火处理后预制片在室温干燥环境下可长期存储。
所述2)Sn/Cu/Sn冷压预制片的加工方法，具体步骤包括：
a)Sn/Cu/Sn冷压箔的切割处理：将不规则的Sn/Cu/Sn冷压薄箔用激光切割机切割成50mm×50mm或100mm×100mm等规整图案。其中，激光切割机的激光功率为50～200W,切割速度为0.01～0.5mm/s。切割速度与切割功率的设置与冷压箔的厚度直接相关，优选结果为：当冷压箔的整体厚度小于200μm时，激光功率100W，切割速度0.4mm/s；当冷压箔的整体厚度大于200μm时，激光功率200W，切割速度0.1mm/s。
b)Sn/Cu/Sn冷压箔的冲模：如图2～4所示，将切割后的Sn/Cu/Sn冷压箔放入冲模夹具的底座中，冲模夹具的顶座放置于底座的固定槽内，顶座与底座不加定位销以便于快速取料；冲模顶座由压台、冲模顶出杆、弹簧三部分组成；顶座与底座开通孔，当顶座放置于底座固定槽后，顶座与底座的通孔将自动对齐，并与冲模顶出杆形成紧密配合；通过对压台施加载荷(1～10MPa)，使得冲模顶出杆由顶座与底座组成的固定滑道内顶出，落料即为所需Sn/Cu/Sn预制片；每次冲模完成后，释放压力，压台将由弹簧回复原先位置；冲模后的Sn/Cu/Sn冷压片的尺寸由底座所开通孔尺寸决定(一般直径为10～500μm)，厚度由初始Sn/Cu/Sn冷压箔决定；另外，Sn/Cu/Sn冷压片还可加工成其他形状，以满足特殊互连窗口需求。
c)Sn/Cu/Sn冷压预制片的回火处理：将Sn/Cu/Sn冷压预制片浸泡于酒精溶液中，超声清洗15min后冷风吹干；将其放入真空加热炉内，真空压力设置为1～0.1Pa，温度为120～150℃，保温0.5h；将其放入密封袋内低温长期储存。冷压预制片必须进行回火处理的原因在于：冲模处理后预制片内将有残余应力产生，该应力可能导致预制片表面产生大量Sn晶须，从而影响后续预制片在半导体封装中的应用；而经过回火处理后，预制片内残余应力将得到快速释放，从而有效抑制预制片表面Sn晶须的生长。
所述3)Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连方法，具体步骤包括(如图5)：
a)Sn/Cu/Sn冷压预制片的放置：将冷压预制片表面涂敷适当助焊剂，使用真空吸笔将其准确的放置在互连焊盘表面中心。助焊剂应选用免清洗型；真空吸笔的放置误差应小于5μm，并通过光学显微镜对放置后的预制片的位置进行校准。通过光学显微镜对冷压预制片的放置位置校准，可以有效降低后续加热过程可能出现的互连焊点虚焊问题。
b)Sn/Cu/Sn冷压预制片的加热：使用热风或电磁等加热装置对预制片加热，加热温度为钎料熔点以上30～50℃，加热时间30s，通过短时快速加热使预制片的底部Sn层与接触焊盘快速润湿互连。由于熔融Sn钎料具有自对准特性，因此Sn/Cu/Sn冷压预制片结构可以矫正它与互连焊盘的放置误差。另外，由于对预制片加热温度低、时间短，预制片顶部Sn层不会与预制片的内层Cu完全反应，从而保证了预制片在随后倒装-回流过程中可以与倒装焊盘实现润湿互连，进而形成可靠的垂直互连焊点。
c)Sn/Cu/Sn冷压预制片的倒装：将冷却后的预制片表层重新涂敷助焊剂，倒置整个互连结构并放置在与其匹配的倒装互连焊盘顶部，放置误差应小于5μm。
d)Sn/Cu/Sn冷压预制片的回流：使用加热装置对倒装芯片结构加热，加热温度为150～350℃，加热时间30～600s。根据控制加热温度与加热时间可生成4种不同结构的互连焊点，分别为：全Cu3Sn金属间化合物焊点、Cu3Sn/Cu/Cu3Sn复合结构焊点、Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点和Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点。其中，前两种类型的互连焊点可在675℃的环境温度下稳定服役，后两种类型的互连焊点可在415℃的环境温度下稳定服役。另外，对Sn/Cu/Sn冷压预制片的Cu层进一步覆Ni、Ag、Au等金属后，可形成多种Sn基金属间化合物(如Ni3Sn4、Ag3Sn、AuSn2等)，形成以上述4种复合焊点结构为基础的更为复杂的金属化合物基高温互连焊点。
以下给出具体实施例。
实施例1
通过预压8次，将100μm厚Sn箔压至厚度为10μm；通过预压10次，将500μm厚Cu箔压至厚度为60μm。使用丙酮溶液、1％盐酸酒精溶液、1％硝酸酒精溶液及酒精对Cu、Sn预压箔进行表面处理。设置真空压力设置为0.1Pa，温度为150℃，对预压箔进行回火处理1h。将回火处理后的Cu、Sn预压箔按照Sn/Cu/Sn结构叠放入双棍冷压机，控制1号滚轮间隙为79μm，2号滚轮间隙为40μm，速度为4mm/s，重复滚压3次，最终获得滚压后的Sn/Cu/Sn冷压金属箔厚度为3μm/34μm/3μm。
实施例2
通过预压9次，将500μm厚Sn箔压至厚度为30μm；通过预压10次，将500μm厚Cu箔压至厚度为60μm。使用丙酮溶液、1％盐酸酒精溶液、1％硝酸酒精溶液及酒精对Cu、Sn预压箔进行表面处理。设置真空压力设置为0.1Pa，温度为150℃，对预压箔进行回火处理1h。将回火处理后的Cu、Sn预压箔按照Sn/Cu/Sn结构叠放入双棍冷压机，控制1号滚轮间隙为119μm，2号滚轮间隙为60μm，速度为2mm/s，滚压3次；随后控制双棍间隙为50μm且速度保持2mm/s，滚压3次。最终获得滚压后的Sn/Cu/Sn冷压金属箔厚度为10μm/30μm/10μm。
实施例3
通过预压10次，将500μm厚Sn箔压至厚度为20μm；通过预压10次，将500μm厚Cu箔压至厚度为60μm。使用丙酮溶液、1％盐酸酒精溶液、1％硝酸酒精溶液及酒精对Cu、Sn预压箔进行表面处理。设置真空压力设置为0.1Pa，温度为150℃，对预压箔进行回火处理1h。将回火处理后的Cu、Sn预压箔按照Sn/Cu/Sn结构叠放入双棍冷压机，控制1号滚轮间隙为99μm，2号滚轮间隙为50μm，速度为2mm/s，滚压3次；其次控制双棍间隙为46μm且速度保持2mm/s，滚压3次；再次控制双棍间隙为42μm且速度保持2mm/s，滚压3次。最终获得滚压后的Sn/Cu/Sn冷压金属箔厚度为6μm/30μm/6μm。
实施例4
采用实施例2所制备的Sn/Cu/Sn冷压金属箔，控制激光功率为100W，切割速度0.4mm/s，将冷压金属箔切割成50mm×50mm的方块。将切割后冷压金属箔放置于冲模夹具中，模具的冲孔直径为60μm，压力10MPa，进行冲模操作。落料放入真空干燥箱内，设置真空压力设置为0.1Pa，温度为120℃，对其进行回火处理0.5h。最终获得的即为厚度为10μm/40μm/10μm的Sn/Cu/Sn冷压预制片。
实施例5
采用实施例3所制备的Sn/Cu/Sn冷压金属箔，控制激光功率为80W，切割速度0.2mm/s，将冷压金属箔切割成100mm×100mm的方块。将切割后冷压金属箔放置于冲模夹具中，模具的冲孔直径为50μm，压力10MPa，进行冲模操作。落料放入真空干燥箱内，设置真空压力设置为0.1Pa，温度为120℃，对其进行回火处理0.5h。最终获得的即为厚度为6μm/30μm/6μm的Sn/Cu/Sn冷压预制片。
实施例6
采用实施例5中所制备的预制片与铜焊盘冶金互连。回流加热温度为250℃加热时间为0～1200s。将互连后的冶金截面进行抛光处理，观察结果如图8所示。根据图8中的a可知，Sn/Cu/Sn冷压预制片的初始Sn层厚度为6μm；经加热60～600s后，冷压预制片的初始Sn层的截面已经转变为Cu3Sn/Cu6Sn5/Cu3Sn结构(整体应为：Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点)，该焊点结构可在415℃下长期服役。经加热1200s后，冷压预制片的初始Sn层的截面已经完全转变为Cu3Sn结构(整体应为：Cu3Sn/Cu/Cu3Sn复合结构焊点)，该焊点结构可在675℃下长期服役。
实施例7
采用实施例4所制备的预制片与铜焊盘冶金互连。回流加热温度为240℃加热时间为0～600s。将互连后的冶金截面进行抛光处理，如图9可知：经加热360s后，冷压预制片的初始Sn层的截面已经转变为Cu3Sn/Cu6Sn5/Cu3Sn结构(整体应为：Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点)，该焊点结构可在415℃下长期服役。
实施例8
采用实施例4所制备的预制片与铜焊盘冶金互连。回流加热温度为280℃加热时间为0～600s。将互连后的冶金截面进行抛光处理，如图10可知：经加热360s后，冷压预制片的初始Sn层的截面已经转变为Cu3Sn/Cu6Sn5/Cu3Sn结构(整体应为：Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点)，该焊点结构可在415℃下长期服役。
本发明提供一种利用冷压加工方式获得特定厚度Sn/Cu/Sn预制片结构的制造方法，以及基于该预制片结构制造高温半导体器件中大互连间隙无铅耐高温焊点的技术方案。通过冷压加工方式制造的Sn/Cu/Sn冷压预制片，其结构可由三层扩展为多层(如Sn/Cu/Sn/Cu/Sn等)；Sn层可由其他低熔点钎料如Sn-Pb、Sn-Ag、Sn-Cu、Sn-Bi、Sn-In、Sn-Zn、Sn-Ag-Cu等合金替代；Cu层表面可覆Ni、Ag、Au等金属镀层。本发明制造的Sn/Cu/Sn冷压预制片总厚度为10～1000μm，其中表面Sn层厚度控制在1～20μm之间。预制片经冲孔、切割等工序可获得与高温半导体器件互连封装窗口匹配的形状与尺寸，随后通过倒装芯片焊接工艺，在150～350℃的温度范围内加热30～600s，最终形成大互连间隙无铅耐高温焊点。
根据控制Sn/Cu/Sn冷压预制片厚度、加热温度及加热时间可实现：全Cu3Sn金属间化合物焊点、Cu3Sn/Cu/Cu3Sn复合结构焊点、Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点和Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点。当互连焊点由全Cu3Sn或Cu3Sn/Cu/Cu3Sn复合结构组成时，其服役温度最高可达675℃；当互连焊点由Cu3Sn/Cu6Sn5/Cu3Sn或Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构组成时，其服役温度最高可达415℃。另外，对Sn/Cu/Sn冷压预制片的Cu层进一步覆Ni、Ag、Au等金属后，可形成多种Sn基金属间化合物(如Ni3Sn4、Ag3Sn、AuSn2等)，形成以上述4种复合焊点结构为基础的更为复杂的金属化合物基高温互连焊点。
本发明实现的Sn/Cu/Sn冷压预制片具有制造工艺简单、成本低廉的优点；预制片与芯片互连的封装工艺可与传统倒装芯片焊接工艺兼容，可在低温下快速有效的形成耐高温的无铅互连焊点；所形成的耐高温互连焊点具有极高的剪切强度、良好的导电性能与散热性能。本发明有望解决目前高温半导体封装领域(如大功率半导体器件、三维高密度集成电路等)使用的互连材料价格昂贵、难以实现大互连间隙无铅化高温焊点、焊点成形所需温度高且时间长、互连焊点耐高温能力差且可靠性不佳等一系列技术问题。

Claims (7)

1.一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于包括以下步骤：
1)一个制备Sn/Cu/Sn冷压金属箔的步骤；
2)一个加工Sn/Cu/Sn冷压预制片的步骤；
3)一个Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连的步骤。
2.如权利要求1所述一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于在步骤1)中，所述制备Sn/Cu/Sn冷压金属箔的具体步骤包括：
a)Sn、Cu金属箔的清洗：将商用Sn、Cu金属箔分别浸泡于丙酮溶液中，超声清洗去除箔片表面油污后，再浸泡于质量浓度为0.5％～2％的盐酸酒精的腐蚀溶液中，按照浸泡产物与腐蚀液体积比1︰10的比例添加腐蚀溶液，超声清洗去除箔片表面氧化物后，再浸泡于质量浓度为0.5～2％的硝酸酒精的腐蚀溶液中，按照浸泡产物与腐蚀液体积比1︰10的比例添加腐蚀溶液，超声清洗去除箔片表面难溶氯化物后，再浸泡于酒精溶液中，超声清洗，冷风吹干；
b)Sn、Cu金属箔的预压成型：将清洗后的Sn、Cu金属箔分别通过双辊冷压机进行滚压加工，滚压速度为1～9mm/s；其中，商用Sn金属箔的初始厚度为0.1～1mm，经冷压5～10次后，压缩至10～50μm；商用Cu金属箔的初始厚度约为0.1～10mm，经冷压5～10次后，压缩至0.02～1mm；
c)Sn/Cu/Sn预压箔的冷压成型：将预压成型的Sn、Cu金属预压箔，按照Sn、Cu、Sn的放置次序放入双辊冷压机内，滚压速度为1～9mm/s，实现冷压多层箔的成型，首次冷压时，1号滚轮设置的间隙宽度应略小于金属预压箔的总厚度，用以夹持并向2号滚轮输送；2号滚轮设置的间隙宽度应小于1号间隙宽度的一半，以便于多层预压箔一次性预压成型，消除微气孔等缺陷，实现层间机械啮合及界面纳米尺度连接，保持滚轮间隙宽度不变，重复冷压3次，以消除金属的冷压弹性变形，稳定厚度方向上的塑性变形；调整2号滚轮间隙2～9次，使得冷压箔最终达到预期厚度且表层Sn层控制在1～20μm之间，在随后的挤压过程中，界面处的纳米扩散结合区面积将逐渐扩大，最终Sn/Cu/Sn预压箔结构将形成紧密结合；
d)冷压箔的回火处理：将Sn/Cu/Sn冷压箔放入真空加热炉内，真空压力设置为1～0.1Pa，温度为120～150℃，保温0.5～2h后随炉冷却备用。
3.如权利要求2所述一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于在步骤c)中，Sn/Cu/Sn结构由三层扩展为多层，并按照Sn/Cu/…/Cu/Sn的方式依次放置。
4.如权利要求1所述一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于在步骤2)中，所述加工Sn/Cu/Sn冷压预制片的具体步骤包括：
a)Sn/Cu/Sn冷压箔的切割处理：将不规则的Sn/Cu/Sn冷压薄箔用激光切割机切割成50mm×50mm或100mm×100mm规整图案，其中，激光切割机的激光功率为50～200W,切割速度为0.01～0.5mm/s；
b)Sn/Cu/Sn冷压箔的冲模：将切割后的Sn/Cu/Sn冷压箔放入冲模夹具的底座中，冲模夹具的顶座放置于底座的固定槽内，顶座与底座不加定位销以便于快速取料；冲模顶座由压台、冲模顶出杆、弹簧三部分组成；顶座与底座开通孔，当顶座放置于底座固定槽后，顶座与底座的通孔将自动对齐，并与冲模顶出杆形成紧密配合；通过对压台施加载荷(1～10MPa)，使得冲模顶出杆由顶座与底座组成的固定滑道内顶出，落料即为所需Sn/Cu/Sn预制片；每次冲模完成后，释放压力，压台将由弹簧回复原先位置；冲模后的Sn/Cu/Sn冷压片的尺寸由底座所开通孔尺寸决定，厚度由初始Sn/Cu/Sn冷压箔决定；
c)Sn/Cu/Sn冷压预制片的回火处理：将Sn/Cu/Sn冷压预制片浸泡于酒精溶液中，超声清洗后冷风吹干，再放入真空加热炉内，真空压力设置为1～0.1Pa，温度为120～150℃，保温0.5h。
5.如权利要求4所述一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于在步骤a)中，当冷压箔的整体厚度小于200μm时，激光功率为100W，切割速度为0.4mm/s；当冷压箔的整体厚度大于200μm时，激光功率为200W，切割速度为0.1mm/s。
6.如权利要求1所述一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于在步骤3)中，所述Sn/Cu/Sn冷压预制片与Cu基焊盘冶金互连的具体步骤包括：
a)Sn/Cu/Sn冷压预制片的放置：将冷压预制片表面涂敷助焊剂，再放置在互连焊盘表面中心；
b)Sn/Cu/Sn冷压预制片的加热：对预制片加热，加热温度为钎料熔点以上30～50℃，加热时间30s，通过加热使预制片的底部Sn层与接触焊盘快速润湿互连；
c)Sn/Cu/Sn冷压预制片的倒装：将冷却后的预制片表层重新涂敷助焊剂，倒置整个互连结构并放置在与其匹配的倒装互连焊盘顶部；
d)Sn/Cu/Sn冷压预制片的回流：对倒装芯片结构加热，加热温度为150～350℃，加热时间30～600s。
7.如权利要求6所述一种高温封装用Sn/Cu/Sn冷压预制片的制备方法，其特征在于在步骤d)中，根据控制加热温度与加热时间生成4种不同结构的互连焊点，分别为：全Cu3Sn金属间化合物焊点、Cu3Sn/Cu/Cu3Sn复合结构焊点、Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点和Cu3Sn/Cu6Sn5/Cu3Sn/Cu/Cu3Sn/Cu6Sn5/Cu3Sn复合结构焊点；其中，前两种类型的互连焊点在675℃的环境温度下稳定服役，后两种类型的互连焊点在415℃的环境温度下稳定服役。
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