Electricity: measuring and testing – Electrolyte properties – Using a conductivity determining device
Reexamination Certificate
2000-09-11
2002-05-21
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
Using a conductivity determining device
C324S071100, C134S001300, C134S018000, C134S002000, C134S100100, C204S406000, C204S409000, C204S410000, C204S411000
Reexamination Certificate
active
06392417
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an arrangement for detecting the end of life of an aqueous bath utilized in semiconductor processing, comprising water, an amount of hydrogen peroxide and an amount of a predetermined chemical species, the species being either an acid or a base.
During manufacturing substrates, especially semiconductor substrates, impurities need to be removed from the substrate surface. One well-known technique is to rinse the substrate surface in an aqueous bath containing water, an amount of hydrogen peroxide and an amount of a chemical species. A solution called “SC1” frequently used for cleaning comprises ammonium hydroxide as such a chemical species.
As, for instance, summarized in the introduction to U.S. Pat. No. 5,472,516, such rinsing may be carried out using many different techniques, such as immersion in a bath, spray cleaning and megasonic cleaning. However, a small variation in the amount of either ammonium hydroxide or hydrogen peroxide will negatively affect the cleaning efficiency of the aqueous bath.
In commonly used cleaning solutions, the ammonium hydroxide concentration is about 0.01 to about 10% by weight of the cleaning solution, and the hydrogen peroxide concentration is about 0.01 to about 10% by weight of the cleaning solution.
Both the concentration of ammonium hydroxide and the concentration of hydrogen peroxide tend to vary substantially over time. The ammonium hydroxide can evaporate spontaneously from the solution whereas hydrogen peroxide decomposes.
Because exchanging an aqueous bath for a fresh aqueous bath results in high costs, and a premature exchange results in too much chemical disposal, there is a strong need to keep the concentrations of both ammonium hydroxide and hydrogen peroxide within desired ranges as long as possible.
One solution to that problem is called “spiking”. The technique of “spiking” is e.g. referred to in JP-A-07142435. This patent document proposes to control the concentration of ammonium hydroxide within a range of 2.0 to 3.5 wt. % by adding a predetermined quantity of aqueous solution of ammonium hydroxide at predetermined time intervals. The predetermined time intervals are equal to the time elapsed before the concentration of ammonium hydroxide has decreased from 3.5 wt. % to 2.0 wt. % and the predetermined quantity is equal to the quantity required for increasing the concentration of ammonium hydroxide from 2.0 wt. % to 3.5 wt. %.
U.S. Pat. No. 5,439,569 proposes to improve the technique of “spiking”. This document notes: “In order to manufacture even smaller submicron semiconductor devices, as well as improving the manufacturing yield, it is imperative that ultimated schemes for maintaining a tighter control on the chemical make-up of a liquid processing bath is desired.” Therefore this document proposes to continually monitor and, if necessary, appropriately adjust the concentration level of chemicals in an aqueous bath automatically. To this end, samples of the aqueous bath are continuously taken and processed by electrochemical sensors to determine the concentrations of the chemical species within the aqueous bath. The electrochemical sensors are used in a feedback loop such that the chemical species are added to the aqueous bath if the controlled parameters deviate too much from a desired value. End of life issues regarding the aqueous bath are not considered in this document.
In U.S. Pat. No. 5,472,516, referred to above, a similar approach as in U.S. Pat. No. 5,439,569 is taken. In U.S. Pat. No. 5,472,516 it is proposed to measure the pH of the cleaning solution in the aqueous bath, which is demonstrated to be a good indication of the concentration of hydrogen peroxide present in the solution, and to measure the conductivity of the cleaning solution, which is demonstrated to be a good measure of the concentration of ammonium hydroxide in the cleaning solution. In dependence on the pH and the conductivity measured, the arrangement adds hydrogen peroxide and/or ammonium hydroxide to the cleaning solution to maintain their concentrations within desired ranges.
U.S. Pat. No. 5,472,516 indicates that one can monitor the buildup of impurities in the solution by monitoring the amount of hydrogen peroxide added to the solution as a function of time. This can be attributed to the fact that impurities in the solution stimulate the decomposition of hydrogen peroxide. Since impurities in the solution are undesirable for a clean substrate, the aqueous bath must be exchanged for a fresh bath whenever the concentration of impurities in the solution is too high. A substantial increase in the rate at which the hydrogen peroxide is being added to the solution is an indication that the rate at which hydrogen peroxide is being catalyzed by metal impurities in the solution is much higher than when the bath was fresh. As a result, U.S. Pat. No. 5,472,516 proposes to exchange the aqueous bath for a fresh bath when the rate of adding hydrogen peroxide to the solution exceeds a predetermined level. This technique, however, cannot be used in the technique of “time spiking” since the latter presupposes that the same amount of hydrogen peroxide (and/or the same amount of ammonium hydroxide) is added after fixed time intervals.
JP-A-10326769 discloses a similar feedback loop as does U.S. Pat. No. 5,472,516.
JP-A-08017775 proposes to detect the end of life of an aqueous bath comprising ammonium hydroxide and hydrogen peroxide by monitoring the relationship of the concentration ratio between ammonium hydroxide and hydrogen peroxide.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an arrangement and a method for detecting the end of life of an aqueous bath utilized in semiconductor processing, the bath comprising water, an amount of hydrogen peroxide and an amount of a predetermined chemical species, for instance ammonium hydroxide, wherein the concentrations of hydrogen peroxide and the chemical species are controlled by adding predetermined amounts of at least one of them according to the “spiking” technique.
This object is achieved, in accordance with the invention, by an arrangement for detecting the end of life of an aqueous bath utilized in semiconductor processing, said bath comprising water, an amount of hydrogen peroxide and an amount of a predetermined chemical species, which is either an acid or a base, the arrangement being provided to:
add a predetermined additional amount of the hydrogen peroxide and/or said predetermined chemical species at predetermined time intervals;
measure at least one parameter of the aqueous bath, thereby obtaining a measured parameter value, the at least one parameter being selected from a set of parameters comprising bath pH and bath conductivity;
read a predicted value of the at least one parameter from a memory storing a curve of predicted values of the at least one parameter as a function of time, the curve depending on the predetermined additional amount of said hydrogen peroxide and/or the predetermined chemical species, and depending on the predetermined time intervals;
establish the end of life of said aqueous bath on the basis of a predetermined deviation between said measured parameter value and said predicted value.
By using such an arrangement, no feedback system is required for adding additional amounts of hydrogen peroxide and the predetermined chemical species. The inventors of the present invention have found out that, based on results obtained from simulations carried out by means of similar baths, one can predict the concentration of ammonium hydroxide and hydrogen peroxide present in the bath as a function of time in dependence on the amounts of ammonium hydroxide and hydrogen peroxide spiked into the bath. By monitoring the pH and/or the conductivity of the bath it is possible to obtain an indication of the increase of the impurity concentration within the bath. Curves showing the dependency of the pH and/or the conductivity of the bath, as a function of time, on the added amounts of hydrogen peroxide and/or
Knotter Dirk Maarten
Vleeshouwers Servatius Maria
Winters Leonardus Cornelus Robertus
Hamdan Wasseem H.
Koninklijke Philips Electronics , N.V.
Waxler Aaron
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