Control of electroless plating baths

Claim 3

The method of claim 1 characterized in that it is used to control the plating solution and that the addition of one or more constituents is controlled in accordance with said electrochemical analysis.

Claim 4

The method of claim 1 characterized in that the metallic ions of the plating solution are copper ions and the reducing agent is formaldehyde and said analysis determines the formaldehyde concentration.

Claim 5

The method of claim 1 characterized in that the metallic ions of the plating solution are nickel ions and the reducing agent is a hypophosphite.

Claim 6

The method according to claim 1 wherein the metallic ions of the plating solution are copper ions and the reducing agent is selected from the group con­sisting of formaldehyde compounds and boron hydrides.

Claim 8

The method of claim 6 characterized in that the addition of the reducing agent to the bath solution is controlled in accordance with the departure of the calculated concentration from the desired concentration.

Claim 9

The method of claim 6 characterized in that the metal ions are copper ions, the reducing agent is formaldehyde,and the calculated formaldehyde concen­tration is calculated from said peak current.

Claim 11

The method of claim 9 characterized in that the metallic ions are copper ions, the reducing agent is formaldehyde, and the ratio between said anodic and said cathodic reaction rates indicates the cooper plating quality.

Claim 12

The method of claim 10 characterized in that the composition of the plating solution is controlled by periodic additions of copper ions and/or formalde­hyde according to concentration departures from re­spective set points; and that the set point for copper concentration is increased and/or the set point for formaldehyde concentration is decreased as said ratio approaches 1.1.

Claim 13

The method of claim 9 characterized in that at least one of said electrodes is provided with a re­producible surface between successive applications of sweep potentials by electrochemically stripping and re­surfacing in the plating solution.

Claim 14

The method for analyzing an electroless plating solution comprising metallic ions and a reducing agent for said metallic ions according to claim 1, character­ized that it further comprises the steps of providing at least two electrodes in the plating solution, one being a test and the other being a counter electrode, the counter electrode having a surface layer composed of the metal of said metallic ions; carying out an electro­chemical reaction on the surface of said test electrode with said metallic ions or said reducing agent by apply­ing a potential across said electrodes; measuring the electrochemical reaction; and providing a reproducible surface on said measuring electrode by electrochemically stripping said surface layer and resurfacing said test electrode in the plating solution with a fresh surface layer comprised of the metal of said metallic ions to prepare for the next cycle.

Claim 15

The method of claim 13 characterized in that the measurement of the electrochemical reaction de­termines the intrinsic reaction rate of said metallic ion or reducing agent.

Claim 16

The method of claim 14 characterized in that the measurement of the electrochemical reaction de­termines the concentration of said metallic ion or said reducing agent.

Claim 19

The method of claim 16 characterized in that sensors for measuring temperature (16) and pH (14) are also placed in said plating solution and that said tem­perature and pH are included in said formaldehyde con­centration calculation.

Claim 20

The method of claim 16 characterized in that the stabilizer concentration of the plating solution is determined as a function of the bath potential at said peak current.

Claim 21

The method of claim 18 characterized in that it further includes controlling the addition of stabi­lizer to the plating solution in accordance with the de­ parture of said stabilizer concentration from the de­sired stabilizer concentration.

Claim 22

The method of claim 16 charcterized in that a potential is applied to said counter (10) and test electrodes (11) after said sweep potential to deplate at least one of the electrodes prior to a new measure­ment cycle, and that said deplated electrode is plated with fresh copper from the solution prior to appli­cation of a subsequent sweep potential.

Claim 23

The method of claim 16 characterized in that it further includes a sensor (17) for measuring the copper concentration in the plating solution, and that copper addition to the solution is controlled in accord­ance with departure of said copper concentration from the desired value.

Claim 24

The method of claim 21 characterized in that it further includes determination of copper plating quality index and adjusting the set points for desired copper and formaldehyde concentrations in accordance with the copper plating quality index.