| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 95 === Dual damascene process has been used for copper interconnect.There are many schemes to fabricate dual damascene structure. The most common integration approaches for the dual damascene architecture are via first, trench first and buried hard mask. Which mask
first, using etch stop and hard masks or not and the use of ultra low k materials in advanced interconnect make dual damascene process very complicated.
No matter which dual damascene scheme used all of them need two masks and two lithography process. One advanced mask cost about two million NT$ and one metal layer needs two masks. With the increasing trend of metal layers of modern IC, the mask cost will add additional burden on already high manufacture cost. With rapidly decreasing chip feature size, the misalignment tolerance is not that far from critical dimension (CD). The existence of misalignment between via and trench mask will cause more rework on lithography steps. The increases of metal layers and higher rework rate on high cost lithography steps can only make things worse. Misalignment will also degrade the process and product yield. It is also a reliability killer.
This thesis is to develop a differential exposure lithography process between via and trench using partial transmission on trench. On the mask, it combines via and trench pattern layout. To achieve one exposure having dual damascene shape on photo resist, we need different exposure energy settings or conditions at via and trench areas at the same time. This thesis used light’s partial transmission technique to weaken the exposure energy on trench to obtain partial exposure. Semi-transparent chromium(Cr) film on trench area was used to absorb
some energy of the exposure light to create partial exposure on trench.Via area can be simply clear (no Cr for positive resist) to obtain full exposure. Dry etching was then used to transfer the dual damascene shape photoresist to underlying substrate.
The thesis also used KLA Tencor’s Prolith v.9.2 to simulate the combined mask structures to optimize mask design and exposure conditions.
Using this unique single mask instead of two traditional masks, we can obtain photoresist dual damascene structure in one exposure. This dual damascene structure can be transferred to underlying dielectric via selective etch process. This cuts the high mask cost in half. With
one mask, we need only one lithography step, one etch, one ash and one clean instead of two each. It saves process cost a lot, simplifies the complicated two mask dual damascene processes and completely removed two masks’ misalignment problems. Besides saving mask and process cost, without misalignment’s issues. It will also boost yield and improves product reliability.
|
|---|
