Bake and cure of low-k dielectric layers
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Koyo Thermo Systems furnaces are available for many processes. Koyo Thermo Systems has an application laboratory in Tenri, Nara, Japan and an application center in Uppsala, Europe in cooperation with the University of Uppsala. The technology of new furnaces and new processes are developed in close contact with the customers. Koyo Thermo Systems can also assist the customer to fulfill special process demands. On this page, we discuss the cure process of low-k dielectrica, for which furnaces from Koyo Thermo Systems are suited very well.
For the production of 0,18 µm devices, dielectrics with an equivalent silicon oxide thickness of 4nm are required. For 0,13µm structures, the required equivalent oxide thickness goes down to only 2nm. For further down scaling the use of silicon dioxide becomes more and more critical and alternative materials will have to be used. In the near future, low-k dielectrics will emerge as a replacement for silicon dioxide.
Low-k materials can be used in advanced semiconductor factories for multi-level interconnects, for interlayer dielectrics (ILDs), passivation layers, shallow trench isolation and masking for deep trench isolation. Low-k dielectrics can be used in combination with traditional aluminum contact layers or can be implemented in copper dual-damascene process architectures.
Low-k dielectric materials can be categorized as follows: Doped oxide, organic, highly fluorinated, and porous materials. The porous class of materials introduces microporosity into the other base materials to reduce the net capacitance. Commonly used silicon dioxide (SiO2) has dielectric constant of 4.2. Air is considered the perfect insulator. It has a dielectric constant of 1. Porous materials, using most of the base materials can achieve therefore lower dielectric constants than the constituent materials. These materials are development for <0.10µm design rules, since dielectric constants between 2 and 3 can be obtained. Oxides, doped oxides, organics, or even highly fluorinated materials will be used as the constituent materials with the appropriate pore morphology.
Low-k materials can be deposited either by spin-on or CVD methods. Porous materials are typically spun on, with controlled evaporation of solvent providing the desired pore structure. The necessary baking of the material is normally done in a batch furnace. Today, in most cases vertical furnaces are used for this application in order to achieve the required high temperature uniformity. However, the bake temperature is typically between 350°C - 400°C, which is quite demanding to standard vertical furnaces.
Koyo Thermo Systems has long years experience with the similar SOG bake process and developed a special furnace with a very low thermal mass LGO heating element for this process. Now KLL has designed again a special vertical furnace for low-k dielectric bake. The same type of LGO heating element is used also successfully since years in Koyo Thermo Systems semiconductor tube furnaces for other typical low temperature processes like polyimide bake and hydrogen anneal.
For the performance of the low-k cure process, it is very important, that the oxygen content during the process is less than 20ppm. In the Koyo furnace, values down to 8 ppm oxygen can be achieved. This low oxygen content does not require evacuation! Koyo Thermo Systems developed an atmospheric furnace (which is much cheaper), that can fulfil the needs for the low-k cure process and deliver excellent process results. In the graph you can see the decrease of the oxygen level over the time (from right to left, using several scale changes for the oxygen concentration).
Koyo Thermo Systems produces vertical furnaces for low-k dielectric bake for batches of 100 - 150 wafers. The 6" and 8" versions are available with carrousel loading (VF5100) and with an integrated stocker (VF5300). For 12" wafers, Koyo Thermo Systems developed a FOUP loaded, large-batch version (VF5900) as well as a mini-batch system (VF5700).
For pilot lines, mini-batch versions with manual boat loading are available for wafers from 6" to 12" (VF1000).
Please contact us in order to receive more information about low-k cure and about our equipment. Test runs can be done on our furnace installed in the Tenri application laboratory.