Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1996-10-22
1998-05-26
Wong, Don
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
25033908, G01N 2135
Patent
active
057570035
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a method to determine the extent of oxygen clusters in silicon.
BACKGROUND OF THE INVENTION
Crystalline silicon that is used to produce integrated circuits is usually so called Cz-silicon. These silicon crystals are produced according to the Czochralski method and contains relatively high concentrations of oxygen. The presence of oxygen has both advantages and disadvantages. Advantages are a more mechanically stable material and the so called gettering effect, which means that precipitates of oxygen can be used to absorb other undesirable contaminations. Disadvantages are i.a. that areas of different kinds of silicon oxides can develop within the crystals and that electrically active oxygen defects, so called thermal donors, can be created in the temperature range 350.degree.-500.degree. C., a range that is of interest today for producing integrated circuits of very high packaging density.
The oxygen in the Cz-silicon originates from the walls of the quarts container containing the silicon melt and amounts typically to a concentration of 4.multidot.10.sup.17 -1.multidot.10.sup.18 atoms/cm.sup.3. This concentration corresponds to the solubility of oxygen atoms in melted silicon. At lower temperatures the solubility is lower and the supersaturation of oxygen that will therefore occur results in local clusters of silicon-oxygen compounds, Si.sub.x O.sub.y, where different values of x and y are conceivable. These clusters have other electrical properties than silicon and can therefore disturb the functioning of a IC-circuit. The development towards smaller and smaller active elements in the silicon technology means that these clusters are able to affect the function and yield of circuit manufacturing more and more.
In spite of the fact that the thermal donors created during heat treatment processes in the range 350.degree.-500.degree. C. have been studied since the middle of the 1950's, no method exists up to now that directly measures the content of the silicon-oxygen complexes that are the underlying cause.
SUMMARY OF THE INVENTION
The present invention solves this problem and gives an image of the extent of micro clusters and in which configurations they exist by being designed in the way that measures the absorption coefficients for one or more specific wave numbers using the standard spectrometer method for the infrared interval known for determining oxygen atoms in interstitial position and carbon atoms in substitutional position. In the known standard method, the absorption coefficient measurement for the oxygen atoms and the carbon atoms is carried out at the wave numbers 1106 and 605 cm.sup.-1, respectively, and the absorption measurements are carried out at room temperature, standardizing the measurement results with respect to the thickness of the sample and multiplying the results with a known calibration constant. However, in the present invention, one or more different wave numbers are used in the standard method to determine for the first time the extent of oxygen clusters in the silicon. The wave numbers discovered according to the present invention for measuring the absorption coefficients are one or more of the wave numbers 728.+-.1, 734.+-.1, 740.+-.1, 795.+-.1, 988.+-.1, 1000.+-.1, 1006.+-.1 and 1012.+-.1 cm.sup.-1. The method according to the invention is an important complement to the standard methods existing today to determine the concentrations of individual oxygen and carbon atoms in silicon and are based on knowledge from optical and electrical measurements, by which a correlation between vibrational absorption of oxygen atoms and different electrically active centres have been established. The measurement is carried out at room temperature in a spectrometer for the infra-red interval and means that the intensity of the absorption bands corresponding to the wave numbers 728.+-.1, 734.+-.1, 740.+-.1, 975.+-.1, 988.+-.1, 1000.+-.1, 1006.+-.1 and 1012.+-.1 cm.sup.-1 are measured and standardized for the thickness of the sample.
REFERENCES:
patent: 4429047 (1984-01-01), Jastrzebski et al.
patent: 4809196 (1989-02-01), Miller
patent: 5066599 (1991-11-01), Kaneta et al.
patent: 5444246 (1995-08-01), Kitagawara et al.
Hallberg Tomas
Lindstrom Lennart
Forsvarets Forskningsanstalt
Wong Don
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