InsituFourier transform infrared (FTIR) spectroscopy has been utilized to detect gas‐phase product species resulting from the dry etching of aluminum and heavily dopedn‐type polycrystalline silicon (n+poly‐Si) in Cl2. The products of aluminum etching in Cl2were investigated in the presence and absence of a plasma. With the plasma off, Al2Cl6was the only infrared‐active etch product detected at both low (50 °C) and high (>120 °C) sample temperatures. With the discharge on, the spectrum was more complex, indicating partial fragmentation of the dimer etch product in the plasma forming AlCl3and, perhaps, AlCl. Silicon tetrachloride was the only infrared‐absorbing product detected during the Cl2plasma etching ofn+poly‐Si. Unsaturated silicon chlorides (SiClx,x=1–3) were not present at detectable levels. These results are compared with those of ultrahigh vacuum (UHV) beam studies; in comparing UHV results with those obtained in a processing plasma, allowances must be made for the considerable difference in pressure, and therefore, in species’ fluxes in these two experimental environments. Unlike UHV studies,insituFTIR measurements permit detection of etch products under typical processing conditions. When interpreting the results, however, the possibility that the products leaving the sample surface react further upon entering the plasma must be considered.