Interstitial copper (CUi) drift induced transient capacitance signals of a Schottky barrier are analysed after copper indiffusion at various temperatures and thermal quenching. Against the general expectation we show that most Cu impurities remain interstitially dissolved. Consequently, such transient ion drift analyses can be used to detect copper in silicon with a detection limit of the order of 1011cm−3. We applied the method to study Cu contamination of silicon samples after chemical cleaning and high temperature annealing. After a short dip into a copper contaminated aqueous solution and subsequent annealing at 1000C for 10 minutes, a strong correlation is found between the bulk copper concentration and the copper density in the solution. A density as low as 50 atomic parts per billion is found to be sufficient to induce a bulk copper concentration of about 5.1013cm−3.