Anodic Processing for Multilevel LSI
Anodic Processing for Multilevel LSI
复制标题
多级LSI的阳极处理
DOI：
10.1149/1.2132760
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发表时间：
1976
影响因子：
3.9
通讯作者：
V. Platter
中科院分区：
文献类型：
--
作者：
G. Schwartz;V. Platter
多级LSI的阳极处理很有吸引力，因为可以制作平面结构。为了设计的完全灵活性，有利的是互连金属化的第一层的部分最初与硅隔离，并且使用后续层上的立交桥来实现与硅的所需接触。前面描述的阳极工艺要求每个要定义的焊盘都与硅直接接触。这种限制可以通过在互连冶金沉积之前沉积薄导电层并最终将其转化为绝缘体来规避。给出了合适底层的要求，并解释了为此目的的铪选择。描述和讨论了阳极处理的细节。将底层转变为绝缘体需要阳极氧化直至阻挡层生长停止，并在高温下进行氧化； 450~ 在蒸汽中持续 30 场雨，效果极佳。与之前描述的阳极工艺相比，通过使用这种垫层工艺，紧密间隔的导体之间的漏电流大大降低。对于LSI中的多层铝或铝合金焊盘系统，阳极处理与传统的减法蚀刻相比具有两个主要优点。首先，可以制造平面结构。这消除了与用绝缘体覆盖大且通常陡峭的金属边缘相关的可靠性风险。光刻难度也降低了。其次，横截面积的损失大大减少。因此，阳极形成的导体的载流能力大于使用相同掩模常规形成的导体。阳极处理将不需要的金属转化为绝缘膜，以去除不需要的金属。由于电路需要相对较厚 (10,000 A) 的金属膜，因此由于阻挡层生长受到限制，不需要的金属会转化为多孔阳极氧化物。在完全平面工艺（1）中使用草酸作为电解质，因为它与光刻胶兼容，它可以在阳极处理完成时分解，并且在适当的电流密度下，电压适合半导体器件的制造。所有先前描述的阳极工艺（1、2、3）都要求要定义的每个焊盘都与硅直接接触。这一要求是由于在阳极氧化表面上完成后需要向焊盘提供电流，使得附着在焊盘边缘上、在紧密间隔的导体之间形成桥的残留铝可以转化为绝缘阳极氧化物。但为了具有多层金属化的集成电路设计的完全灵活性，通常需要首先将第一层金属化的部分与硅隔离，并在后续层上使用“立交桥”。为了能够在阳极上隔离这种电“浮动”导体，我们采用了 Romankiw (4) 开发的阳极处理方案，进行必要的更改以实现集成电路所需的极低泄漏水平，但不适用于 Romankiw 设计其程序的应用。在沉积用于互连图案的铝或铝合金膜之前，Romankiw提出沉积一层薄金属膜以将电流传送到未与硅连接的焊盘。随后必须将该薄膜转变成绝缘体。我们得出的结论是，用作衬垫的金属必须满足某些要求：(i)
Anodic processing for multilevel LSI is attractive because planar structures can be made. For complete flexibility of design, it is advantageous that portions of the first level of intereonnection metallization be isolated initially from silicon, and that the required contact to silicon be made using overpasses on a subsequent level. Anodic processes previously described required that there be a direct contact to silicon for each land to be defined. This restrictior~ can be circumvented by depositing a thin conductive layer before deposition of the interconnection metallurgy and eventually converting it to an insulator The requirements for a suitable underlay are given, and the choice of hafnium for this purpose is explained. The details of the anodic processing are described and discussed. Conversion of the underlay to an insulator requires both anodization until barrier layer growth ceases and oxidation at elevated temperature; 450~ in steam for 30 rain yields excellent results. The leakage current between closely spaced conductors is decreased substantially by the use of this underlay process as compared to the previously descibed anodic processes.For multilevel aluminum or aluminum alloy land systems in LSI, anodic processing has two main advantages over conventional subtractive etching. First, planar structures can be fabricated. This eliminates the reliability hazards associated with covering large and often steep metal edges with an insulator. Also photolithography difficulties are reduced. Second, there is substantially less loss in cross-sectional area. Therefore the current-carrying capability of a conductor formed anodically is greater than that formed conventionally using the same mask. Anodic processing substitutes conversion of the unwanted metal to an insulating film for the removal of unwanted metal. Because relatively thick (10,000 A) metal films are required for the circuitry, the unwanted metal is converted to porous anodic oxide as barrier layer growth is limited. Oxalic acid is used as the electrolyte in the completely planar process (1) since it is compatible with photoresist, it can be decomposed at the completion of anodic processing, and, at the appropriate current densities, the voltages are suitable for semiconductor device fabrication. All previously described anodic processes (1, 2, 3) had required that there be a direct contact to silicon for every land to be defined. This requirement arises from the need to supply current to the lands after the anodization is apparently complete, so that the residual aluminum which clings to the edges of the lands forming bridges between closely spaced conductors can be converted to insulating anodic oxide. But for complete flexibility of design of integrated circuits with multilevel metallization, it is often desirable to isolate from silicon, initially, portions of the firstlevel metallization and use" overpasses" on a subsequent level. To be able to isolate, anodically, such electrically" floating" conductors, we have adopted a scheme developed by Romankiw (4) for anodic processing, making the changes necessary to achieve the very low leakage levels required for integrated circuits, but not for the applications for which Romankiw designed his procedure. Before deposition of the aluminum or aluminum alloy film used for the interconnection pattern, Romankiw proposed that a thin metal film be deposited to carry current to the lands which are not connected to silicon. This film must subsequently be converted to an insulator. We have concluded that the metal used as an underlay must meet certain requirements:(i) it