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The adhesion promoter Hexamethyldisilazane (HMDS) plays a crucial role in i-line lithography. According to HMDS
deposition forms, a hydrophobic surface defines upwardly directed, non-polar trimethysilyl groups. This condition is of
particular importance for wet chemical development and subsequent wet chemical etching processes, because the defined
hydrophobic surface prevents water from creeping beneath the resist mask. Undesirable effects, such as (partial) loss of
the resist structure or under etching can be prevented. Currently, a common and suitable method to control the success of
HMDS deposition is the contact angle measurement. There, a drop of water is applied to the substrate and the contact
angle / wetting angle is measured. As a result, conclusions can be drawn about the HMDS process.
Unfortunately, however, this simple to implement measurement method raises some problems. The measurement is
extremely dependent on the substrate, wherein the measurement results vary greatly. A possible reason for this is the
different surface properties of the wafers which are due to adsorbate films. Typically, a contact angle measurement is
performed just after the HMDS deposition. A difference between pre- and post-measurement cannot be determined. A
deviation of the contact angle can be caused by either an insufficient HMDS seeding, or just as well by other, unknown
surface properties.
The studies presented here were performed with the measuring system ChemetriQ 5000 from Qcept Technologies. This
measurement system was originally developed for Inspection on non-visible defects on the wafer level. It is able to
detect differences of work functions as a result of surface coverage by thin film / adsorbate, materials or residues. The
change in the surface work function due to the generated adsorbate layer during the HMDS deposition is determined by
the measuring system by means of a difference between pre- and post-measurement.
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