Highly Attenuated Laser for RIE Endpoint Control

Highly Attenuated Laser for RIE Endpoint Control

       Conventional laser interferometry is widely used in-situ
endpoint detection in reactive ion etching (RIE)  The reflected laser
light from the material that being etched is monitored.  The
intensity of the light is superposition of the waves reflecting from
the numerous in the index of refraction within the material. in the
index of refraction result in changes in the nature of the reflected
light indicating an  With the conventionally used lasers (red light),
light is only slightly attenuated over the distances etched or the
distance between interfaces.

      Substituting such a radiant source by one which is attenuating
(blue light) over short distances in the being etched offers some
advantages for endpoint in certain applications.  One such example is
the etching of the ridges of an A1GaAs GRINSCH laser.  The depth of
the ridge etch must be carefully controlled. very thin dummy quantum
well of slightly different index refraction is inserted several
hundred nanometers from actual GRINSCH region as an end etch
indicator (Fig. 1). the highly attenuated beam, the amplitude of the
fluctuations of the reflected light increases as etching approaches
the interface.  Once past the the intensity remains constant until
the etch close to the next interface.  The abrupt flattening of
reflected clearly indicates that the end etch indicator has been
etched.  With sufficient light attenuation and spacing the inten...