Optical profile analysis of diffused and ion-implanted silicon

Abstract

I n doping profiles used by modern semiconductor technology exist extremly large gradients of the complex refractive index which produce significant spectra of integral optical reflectivity and transmission by "internal reflection". I n this case the calculus of geometrical optics approximation cannot be used. It is shown, that it is possible to calculate the spatial distribution of the optical constants and the local free carrier concentration, respectively, using the matrices calculation of mult,ilayer structures and the Drude Theory. The concentration profiles which are used for example are present in boron diffused (surface concentration up to No = 3.4 x lo2" and ion implanted (fluence of implanted boron ions: N D ,~ = 10l6 ions/cm2 a t 150 keV) silicon samples. After successive isochronally annealing (700 to 950 "C) the implanted ions are electrical activated as an increasing modified Gauss profile. Another interesting aspect is the question of transmission and reflectance if the direction of wave propagation is changed in connection with the theorem of reciprocity. I n agreement to the theory the integral transmission is symmetrical, but the integral reflection is asymmetrical.I n den in der modernen Halbleitertechnologie iiblichen Dotierungsprofilen traten extrem groBe Gradienten des komplexen Brechungsindex auf, die durch ,,interne Reflexion" signifikante Spektren des integralen optischen Reflexionsvermogens und der Transmission hervorrufen. I n diesem Falle 1a5t sich die geometrisch optische Naherung nicht anwenden. E s wird gezeigt, daB es moglich ist, die raumliche Verteilung der optischen Konstanten und die lokale Konzentrrttion freier Trager unter Benutzung der Matrizenrechnung von Mehrschichtstrukturen und der Drudetheorie zu berechnen. Die Konzentrationsprofile, die als Beispiele betrachtet werden, liegen in Bordiffundierten (Oberflachenkonzentrationen bis zu No = 3,4 x 102O om+) und ionenimplantierten (Dosis der implantierten Borionen: N D , 0 = 10l6 Ionen/cm2 bei 150 keV) Siliziumproben vor. Nach sukzessiver isochroner Temperung (700 bis 950 "C) werden die implantierten Ionen als wachsendes modifiziertes GanlJprofil elektrisch aktiviert. Ein anderer interessanter Aspekt ist die Frage der Transmission und des Reflexionsvermogens, wenn die Richtung der Wellenausbreitung geandert wird im Zusammenhang mit dem Reziprozitatstheorem. I n ubereinstimmung mit der Theorie ist die integrale Transmission symmetrisch, die integrale Reflexion jedoch asymmetrisch.

Optical Effects of High Energy Implantations in Semiconductors

“…I n the case of the transmission set-up (see [69], 0.15 MeV boron-implanted silicon, P = 5.9) it has been proved experimentally that this theorem holds very well for small absorption coefficients. On the other hand, for most ionimplanted semiconductors the reflection depends strongly on the sample side which is being illuminatedsee Fig.…”

“…The main difference between reflection and absorption measurements is expressed by the so-called reciprocity theorem : the radiation flux density should remain unchanged by exchanging the direction of probing light into the opposite one (exchange of the light source and detector for transmission measurements, change of the sample sides for reflection measurements). I n the case of the transmission set-up (see [69], 0.15 MeV boron-implanted silicon, P = 5.9) it has been proved experimentally that this theorem holds very well for small absorption coefficients. On the other hand, for most ionimplanted semiconductors the reflection depends strongly on the sample side which is being illuminatedsee Fig.…”

“…On the other hand, for most ionimplanted semiconductors the reflection depends strongly on the sample side which is being illuminatedsee Fig. 10, taken from [69]. This happens because implantation creates complicated profiles of free carriers, due to the introduced impurity atoms and defects.…”