WO1991016472A1

WO1991016472A1 - Method of controlling metallization baths

Info

Publication number: WO1991016472A1
Application number: PCT/DE1991/000312
Authority: WO
Inventors: Heinrich Meyer; Rolf Schumacher; Gerd Linka; Robert RÜTHER; Werner Richtering
Original assignee: Schering Aktiengesellschaft
Priority date: 1990-04-17
Filing date: 1991-04-12
Publication date: 1991-10-31
Also published as: DE4012556C1

Abstract

The invention describes methods for controlling metallization baths, in which the independent parameters mass, charge and impedance, plus surface tension and viscosity, of the liquid phase are measured using quartz resonators.

Description

Process for controlling metal deposition baths

description

Control parameters that are developed from the bulk phase of the electrolyte have so far been preferred for monitoring galvanic and electroless metal deposition baths. This means the tracking of process-relevant bath parameters via wet chemical, instrumental-analytical and physical measurement methods. On the basis of these measurement data, the dosages required for process control are carried out. A monitoring method for galvanic baths is known from DE-OS 30 43 066, in which the concentration of a bath substance is determined continuously or intermittently by measuring the electrical conductivity, the density or the refractive index.

The disadvantage of this methodology is that for

Surface processes, such as the metallization of

Substrate documents, the volume phase information of the

Electrolytes only in exceptional circumstances

Reflect surface directly. Measurement data that can be taken directly from the boundary layer area solid / liquid (in-situ) are more suitable.

In addition to the above-mentioned examination methods for process control, the following in-situ techniques are known, for example:

Cyclic voltammetry can be used to check the content of organic additives in galvanic baths; please refer . DAHMS, continuous monitoring of acidic copper electrolytes by cyclic voltammetry, Metallfläche 43, 345 (1989). Furthermore, impedance and mixed potential measurements have been successfully used to control copper baths without external current. These methods are electrochemical test methods and contain in-situ information about the surface process. It is the object of the present invention to continuously register independent variables such as mass, charge, impedance, elastic coating properties and viscosity of the liquid phase (electrolyte) by means of in-situ measurements using a detector (oscillating quartz crystal), and in particular in the case of continuous registration of mass changes to determine at least one or more of the quantities mentioned and to use the information obtained in this way about layer properties and the electrolyte to control the metallization process.

This object is achieved in that the quartz crystal surface, which is in contact with the electrolyte, is also the working electrode of the electrolytic cell, and in addition to changes in mass, other electrochemical in-situ variables such as charge flow and impedance can also be measured. In addition, this methodological approach is also suitable for tracking the elastic surface properties of the deposited coatings or the viscosity of the electrolyte.

With this detector, the following properties of the coatings can be determined:

The (texture-dependent) surface tension, or expressed as a synonym, the elastic coating properties as a function of the layer thickness, K.E. HEUSLER et al. , Ber. Bunsenges. Phys. Chem. 92, (1988), 1218 and H. SPÄHN, Metallfläche, 16, (1962), 109.

Porosity, compactness as a function of the layer thickness, Δmf / _lmq

Δmf = mass change due to frequency detuning f 4mq = mass change due to charge q R. Schumacher, Angewandte Chemie, 102, (1990), 347.

Impedance measurements to characterize roughness effects, AJ Bard, LR Faulkner, Electrochemical Methods, John Wiley and Sons, 1980. The following properties of the electrolyte can also be determined with this detector:

a. ) Changes in viscosity and density in the electrolyte, see K. KANAZAWA et al. , Anal. Chem. 57, (1985), 1771.

b.) The efficiency of galvanic and chemically reductive metal deposition processes. This is understood to mean the ratio of the deposited mass of the metal and the amount of charge required for this. For chemically reductive baths, the amount of charge is determined from the consumption of reducing agent.

To regenerate the quartz crystal, the metal film can be removed either chemically or in-situ by applying a suitable potential.

To extend the operating time of the quartz crystal, pulse technology can also be used as a measurement variant, i.e. H. the periodic switching on and off of the measuring probe.

The measuring probe is an electrochemical cell with a classic three-electrode arrangement, see Figure 1. The control takes place via a potentiostat and a function generator. The working electrode of this system is the side of the quartz crystal facing the electrolyte. A change in mass at this electrode leads to a detuning of the resonance frequency of the quartz oscillator, which is measured via a frequency counter and fed to the small computer for processing.

The charge is measured in the circuit between the counter electrode (CE) and working electrode (WE) using a coulometer.

To measure the impedance of the electrochemical boundary layer, a voltage pulse is impressed on the measuring probe and evaluated together with the current response as a Fourier transformation. Elastic coating properties correlate with frequency detuning which result from the tension effects of these layers; the measurement is carried out by pressure compensation on the quartz crystal side facing away from the electrolyte. The surface tension can be calculated from these measurement data.

To determine the viscosity of the metallization bath, the frequency detuning, which results only from the electrolyte contact, is measured. For this, the metallization process is carried out by appropriate

Potential setting on the working electrode interrupted. The measured frequency detuning is now compared with the frequency detuning of a reference solution.

The new control method is used for example at

1. Gold, copper and nickel plating without external current,

2. galvanic copper plating, galvanizing, nickel plating and chrome plating as well as galvanic precious metal deposition,

3. Cementation

Examples

In the following, the present invention is demonstrated by means of chemically reductively deposited nickel-phosphor coatings.

The process is based on a combined application of

Quartz microbalance and a periodically or continuously potential-controlled layer resolution, the

Determination of the mass change on the measurement of the

Frequency detuning is carried out as a function of the foreign mass assignment. At the same time, the mass can optionally be registered with the other sizes mentioned. The measurement takes place with oscillating, mass sensitive

Quartz crystals, which can be coated on both sides with metal films and usually only one side of the

Detector system has contact with the electrolyte. By the

Liquid contact will increase the sensitivity of the detection

_ Systems not influenced by a few ng / Hz cm,

R. Schumacher, Angewandte Chemie, 102, (1990), 347.

The process is based on the periodically repeated deposition and dissolution of the nickel / phosphor layers.

In the first step, the electroless (chemically reductive) deposition of nickel-phosphorus films takes place on the surface of the quartz crystal that is in contact with the electrolyte. From the detuning of the resonance frequency of the quartz crystal, the foreign mass assignment and thus the layer thickness and deposition speed can be directly determined. derive; G. SAUERBREY, Z. Phys. , 155, (1955), 206. - 6 -

In the second step, the coated side of the quartz crystal is switched as a working electrode in the three-electrode arrangement. The anodic dissolution takes place by means of a potential that is constant over time or a potential ramp. The chemical composition of the nickel-phosphorus layer can be determined by simultaneously registering the electrical charge converted during this process and the change in mass. The following reaction is used:

^Ni ( _{/ l} oo--) Px - ^ (00-χ) _Ni ²⁺ + _{x P} + [2 (Λ∞ - *) + 5c] e ~

The chemical composition of the layer can be inferred from the ratio of charge to mass change (Δ Q. / Δ m).

The deposition or dissolution takes place in a specially designed cell, see Figure 2, which enables rapid electrolyte exchange without the nickel-phosphorus layer coming into contact with the atmosphere. This makes step two of the method possible either in the deposition electrolyte or in any other, for example indifferent, electrolyte.

With the anodic resolution carried out potentiodynamically, a current-voltage curve is obtained, as shown in Figure 3. The stoichiometric composition can be determined from the change in mass registered at the same time via the charge / mass ratio. In addition, the analysis of the curve shape allows conclusions to be drawn about the structure, morphology and properties of the layer, for example the corrosion resistance.

In addition to the registration and documentation of the layer properties, it is also possible to control the process by means of measured variables such as peak height or peak area ratio or peak position using controlled variables such as temperature, pH value and bath composition. Examples 1-6:

Example 1:

In the cell shown schematically in Figure 2, an electrolyte becomes the composition

30 - 34 g / 1 nickel sulfate hexahydrate,

20 - 24 g / 1 sodium hypophosphite monohydrate and

35 - 45 g / 1 malic acid o at a temperature of 86 - 90 C and after rinsing with

Inert gas at various pH values (adjusted with sulfuric acid / ammonia water). Plates of nickel-phosphorus alloys are deposited on the quartz crystal.

After replacing the deposition solution with a 0.1 M sodium sulfate solution, which is also heated to 86 - 90 C and flushed with inert gas, the coatings deposited on the quartz crystal are switched as working electrodes in a three-electrode arrangement against a reference potential (saturated calomel electrode SCE) and a platinum counter electrode. The potentiodynamic current-voltage curves of nickel-phosphorus coatings recorded during anodic dissolution, which were deposited at different pH values, are shown in Figure 4. The courses show characteristic differences. The respective phosphorus content can be determined in situ from the charge-mass ratio measured during the dissolution. In addition, on the basis of the current-voltage curves by comparison with a target curve and an automatic pH adjustment, a process control is possible in such a way that layers with an exactly constant phosphorus content are obtained. Example 2:

A nickel-phosphorus layer is also deposited from a bath of the composition mentioned in Example 1 at temperatures between 86-90 ° C. at a pH of 4.8 after the addition of 5 × 10 mol / 1 thiourea. The current-voltage curves of the anodic dissolution (same conditions as mentioned in example 1) show a strong change compared to the layers that were deposited from a bath without addition (Figure 5). The current-voltage curves can be correlated with data on corrosion resistance, which are obtained from independent tests (such as salt spray test, "Kesternich test"). It is shown that the nickel-phosphorus alloys which are deposited from baths with additions of thiourea or other sulfur homologues have significantly poorer corrosion resistance. By analyzing the anodic current-voltage curves, it is possible to make a statement during the deposition, i.e. in-situ.

Further examples of compositions of chemical-reductive nickel baths which can be monitored and controlled using the described method are listed in Examples 3-6.

Example 3:

Deposition in a bath of the composition:

20 - 40 g / 1 NiSO ^ • 6H ₂ 0

20-33 g / 1 H00C-CH (0H) -C00H 2-20-g / l PbCl ^

Temperature: 80 - 92 ° C pH: 4.4 - 5.4, adjusted with KOH Example 4:

Deposition in a bath of the composition:

25 - 45 g / 1 NiSO ^. * 6H ₂ 0

5 - 20 g / 1 CgHgO? ^• H ^ O

2 - 7 g / 1 acetic acid

Temperature: 82 - 90 ° C pH: 4.4 - 5.0, adjusted with ammonia

Example 5:

Deposition in a bath of the composition:

18 - 34 g / 1 NiSO ^ 6H ₂ 0 17 - 25 g / 1 NaH ₂ P0 ₂ - H ^ O 12 - 20 g / 1 acetic acid 4 - 8 g / 1 CH ₂ (0H) -C00H

Temperature: 88 - 92 ° C pH: 4.0 - 4.4, adjusted with ammonia

Example 6:

Deposition in a bath of the composition:

18 - 34 g / 1 NiSO "6H ₂ 0 17 - 25 g / 1 NaH ₂ P0 ₂ 'H ₂ 0 12 - 20 g / 1 acetic acid

4-8 g / 1 CH2, (0H) -C00H 0.7- & "_ * /! 2-mercaptobenzothiazole

Temperature: 88 - 92 ° C pH: 4.6 - 5.2, adjusted with ammonia

Claims

1. A method for controlling metal deposition baths characterized in that the mutually independent variables of mass, charge, impedance and surface tension as well as viscosity of the liquid phase are measured using oscillating quartz crystals.

2. A method for controlling metal deposition baths according to claim 1, characterized in that at least one or more other variables such as charge, impedance and surface tension as well as viscosity of the liquid phase are measured with continuous registration of changes in mass.

3. A method for controlling metal deposition baths according to claim 1 or 2, characterized in that only one side of the oscillating for measuring the sizes

Quartz crystal has contact with the electrolytes.

4. A method for controlling metal deposition baths according to at least one of claims 1-3, characterized in that stoichiometric and / or structurally determined layer properties are determined during the deposition process (in situ) by deposition and / or dissolution cycles.