Temperature measurement in the semiconductor industry has become critical in many processing area. The need to ensure that temperature budget is maintained within the required range necessitates the necessary instrument to monitor the temperature distribution in the semiconductor equipment. One of the critical area that requires close temperature monitoring is the backend dielectric deposition step. The importance of temperature monitoring at this step is due to the fact that a shift in the temperature might induce a change in the metal grain which might affect reliability performance of the circuit or might even lead to metal distortion which will eventually lead to wafer scrap incurring loss to the company.
One of the most popular and common used temperature probe uses the optical pyrometry method. In the optical pyrometry method, the system utilizes infrared radiation that is been emitted by the substrate to determine the temperature of the wafers. This phenomena was then discovered by planck and eventually lead to the planck theorem which stipulates that electromagnetic radiation emitted by a black body in thermal equilibrium at a certain temperature. Basically what it says is that the amount of radiation emitted by a a black body has a direct correlation with the temperature of that body.
From this law, optical pyrometry uses the radiation from the body to actually determine the temperature of the body based on certain wavelength which normally is near the infrared region. Further improvement in the temperature measurement eventually creates an emissivity measurement reading of the wafer substrate as well. Since the emission that is been emitted by a certain body is relatively link to the emissivity of the wafers itself. Some of the factors that affects this emissitivy is the doping on the wafer, the roughness of the wafers which will lead to light scattering and thus creating multiple reflection of the radiation and also the distance and cavity between the wafers and the temperature probe. The temperature probe normally is made of sapphire rod which is able to transmit signal with minimum loss. The optical pyrometry reads the wafer emission which is the function of the wafer emissivity and temperature based on the wavelength.
One of the problem that we encountered so far is that we are seeing a temperature mismatch between wafers that is running in DUV compared to wafers that is been processed in ILINE. Further experiment shows that by removing the BARC from the DUV process we were able to match the temperature during the oxide deposition during the IMD layer. But what we are still yet to decipher is how does the BARC is able to affect our subsequent temperature since eventually the BARC is supposed been removed during the etch process and should not leave any trace of the layer before the IMD deposition. If the phenomena that we are seeing is true then the only reason that the temperature is going to be different is because the heat transfer from the residual barc layer causes a different temperature reading.
Hence what we are going to do is to try to understand the difference between a BARC process and a non BARC process. Few of the suspect that we have are, the BARC actually changes the chemistry or surface of the metal itself. To verify this a surface roughness measurement will be conducted to look at the surface of the metal after post etch process. Another possible hypothesis is that there is a residual BARC that is shifting the temperature and causing the radiation to be different compared to the non BARC process.
This is an interesting problem that I would like to understand. Hopefully i would be able to find the answer to this perplexing problem before the year end....
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