JPS6263681A - System for monitoring etching rate - Google Patents

Abstract

PURPOSE:To easily monitor an etching rate and to make a criterion exact by impressing an AC voltage of a prescribed frequency between a material to be etched and counter electrode and measuring the polarization resistance. CONSTITUTION:The electrode which is the material to be etched and the counter electrode of the material electrochemically nobler than said material are immersed in an etching soln., then the AC voltage of a low frequency and AC voltage of a high frequency are impressed between the above-mentioned two electrodes. The above-mentioned low frequency is so adjusted that the impedance by the interface capacity of the electrodes and the etching soln. is made substantially higher than the polarization resistance of the electrodes. The above- mentioned high frequency is so adjusted that the impedance by the above- mentioned interfacial capacity is made substantially smaller than the polarization resistance of the electrodes. The above-mentioned polarization resistance is then measured and the etching rate of the material to be etched is monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an etching rate monitoring system for metal materials, and more particularly to an etching rate monitoring system capable of monitoring the etching rate with a meter and automating etching.

<Prior art> In the etching of metal materials, particularly in the manufacturing process of lead frames by etching, a pattern is formed on both sides of the material to be etched using a photoresist film, and the pattern is immersed in an etching solution or sprayed with the etching solution. An operation is performed to remove soil by etching the parts not covered with the photoresist film. At this time, it is extremely important to monitor the etching rate to determine the end of etching and the etching time. If the etching end point and etching time are not appropriate, the lead frame will not be etched and will be connected, or on the contrary, the etching will be excessive and the lead frame will become thinner due to overetching, which will reduce the yield.

As a conventional method for monitoring etching speed.

(1) Judgment is made based on the operator's 11 vision.

(2) The etching time required for each material for each etching solution is determined through experiments, and judgments are made based on the etching time.

However, each of these conventional methods has the following drawbacks.

The visual inspection method (1) relies heavily on the intuition of the worker, so there are large individual differences and the criteria for judgment often differ.

In the method (2) using etching time, the concentration, temperature, ratio, etc. of the etching solution must be maintained at standard values.
This is extremely difficult.

For this reason, in the IC hard mask etching system, the chrome mask and platinum electrode are immersed in the etching solution, an ammeter is connected, and the electrochemical current flowing between the chrome mask and the platinum electrode is measured. There is a mechanism that detects the end point of etching by observing changes in current during the etching stage and detecting the decrease in current at the end of etching.

However, such an etching end point detection mechanism has a problem in that the etching speed cannot be monitored.

<Problems to be Solved by the Invention> The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art and to improve the etching speed at which it is possible to manufacture inexpensive lead frames with good etching dimensional accuracy through appropriate etching. The objective is to provide a monitoring system.

<Problems to be Solved by the Invention> In the first invention, when etching a metal material, the material to be etched is used as an electrode, a material that is electrochemically more noble than the material to be etched is used as a counter electrode, and these materials are etched in an etching solution. An alternating current voltage of such a low frequency that the impedance due to the interfacial capacitance between the electrode and the etching solution is sufficiently larger than the polarization resistance of the electrode is applied between the two electrodes, and an alternating voltage of such a low frequency that the impedance due to the interfacial capacitance is sufficiently smaller than the polarization resistance. applying a high frequency alternating current voltage and measuring the polarization resistance;
This is an etching rate monitoring system characterized by monitoring the etching rate of a material to be etched.

In etching a metal material, the material to be etched 4 is used as an electrode, a material that is electrochemically more noble than the material to be etched is used as a counter electrode, and the electrode and the etching solution are placed between these two electrodes in an etching solution. An alternating current voltage with a low frequency such that the impedance due to the interfacial capacitance with the electrode is sufficiently larger than the polarization resistance of the electrode, and an alternating current voltage with a high frequency such that the impedance due to the interfacial capacitance is sufficiently smaller than the polarization resistance. The etching rate monitoring system is characterized in that the polarization resistance is measured, the correlation between the polarization resistance value and the etching rate is calculated, and the etching time is controlled.

Here, it is preferable to determine that etching has ended when the polarization resistance value between the two electrodes has decreased to a predetermined value.

The present invention will be explained in detail below.

The method is based on the principle of electrochemical corrosion.

That is, as shown in FIG. 1a, a patterned material such as a photoresist or the like, for example, a chrome mask shade, is used to conduct wiring such as aluminum, iron, copper, gold, silver, or other metals or alloys. A metal material with a pattern formed thereon is used as the electrode 1, and a material more electrochemically noble than the material to be etched, such as titanium or platinum, is used as the counter electrode 2, and these electrodes 1.2 are etched. liquid 3
and apply an alternating voltage between these electrodes.

The electrical equivalent circuit at the interface between the electrode 1 and the etching liquid 3 of the counter electrode 2 is as shown in FIG.
and a polarization resistor Rc connected in parallel. The impedance of this equivalent circuit is as follows: Cd1Cd2, Rcl R
If it is e2.

・・・・・・(1) f: frequency R8: Solution resistance It is.

Here, a voltage ■9 of a low frequency (for example, about 10 Hz, hereinafter referred to as low frequency) such that the impedance due to the interfacial capacitance 1-Cd is sufficiently larger than the polarization resistance Rc.
and the impedance due to the interfacial capacitance Cd is the polarization resistance Re
A high enough frequency (for example,
Using a voltage vh of about 10 KHz (hereinafter referred to as high frequency), cross the voltage between the electric current J4i1 and the counter electrode 2! f to ■Q and vh
is applied, then the impedance zQ at low frequency is (1
) Formula % Formula % (2) Since the impedance zh at high frequency is from formula (1), Zh=Rs ・・・・・・・・・(3
), and the polarization resistance is from equations (2) and (3).

Rc1+Rc2=ZQZ h""(4) is shown. Here, when AC is applied, Re2 is constant because it uses pt, etc., and can be determined experimentally in advance, so Rcl + Rc2 = (Zg - Zh) / 2Rc =
(Zu-Zh)/2-Re2...(4)
′.

Any method may be used to measure the polarization resistance Rc shown in this way. The oscillation circuit 11 preferably includes a circuit that automatically measures Rc and outputs the measurement result as digital data.
- by way of example, the frequency switching signal is a logic "0"
When , the above-mentioned low frequency vg is emitted by the oscillation circuit 11, and when the frequency switching signal is logic "1", the above-mentioned high frequency vh
is configured so that it is transmitted. AC voltage vQ or vh
The constant current circuit 12 generates a constant voltage 'm, i, and the electrode 1
, applied to the counter electrode 2, the voltage V
Measure. The measured voltage V is.

v=Rci・・・・・・・・・(
5), and since i is constant, the polarization resistance Re is measured by measuring V.

The etching rate Er is generally given by the following equation.

E r = k / Rc ・・・・・・
(6) FIG. 3 shows an example of the measurement results of polarization resistance Re with respect to etching time t.

In the etching speed monitoring system of the present invention, if the polarization resistance Rce at the etching end point is experimentally measured in advance, when similar etching is performed, the polarization resistance will be the value of Rce determined experimentally in advance. It is preferable that the etching end point can be judged accurately when the etching is finished, and the end point of the etching can be judged without any skill.

Actual etching is carried out in a solution by applying a direct current, and the etching rate is monitored by applying an alternating voltage in pulses at, for example, 1 second intervals.

FIG. 3 shows the change in polarization resistance with respect to etching time. As is clear from FIG. 3, the polarization resistance exhibits a small value at the initial stage of etching, but as the etching progresses, the polarization resistance increases rapidly. By monitoring the polarization resistance, the etching rate of the metal material could be monitored. Also.

By monitoring the point at which the polarization resistance is saturated, it was possible to determine the end of etching and further control the etching time.

As shown in FIG. 2, the second invention includes a system for monitoring the etching rate by measuring polarization resistance as described in L, including an arithmetic device 6 and a data display device 7.

This is an etching speed monitoring system comprising a data recording device 8 and a data storage device 9.

The polarization resistance measured by the polarization resistance measuring device 5 such as the digital voltmeter 13 (see FIG. 1a) is calculated by the calculation unit 216 as follows: (1), (2), (3), (4), (
4'), (5), and (8) perform the desired arithmetic processing, and monitor and control the etching rate. At the same time, data such as polarization resistance, etching time, etching speed, etc. are displayed on the data display device 7, recorded on the data recording device 8, and further stored in the data storage device 9, and the necessary data can be retrieved when necessary. output and perform calculation processing.

Arithmetic device 6. Data display device7. Data record bag; 8.8
, the data storage device 9 preferably uses a suitable computer system.

<Example> The material to be etched was a 42AIIoy (42% Ni-Fe) plate with a pattern formed with water-soluble resist (PVA-Cr), and platinum (Pt) was used as the counter electrode.
Then, the substrate was immersed in a 40% FeCJ13 solution at 40° C., and AC voltage was applied in pulses at 1 second intervals, and the polarization resistance during etching was continuously measured. As a result, the change in polarization resistance during etching was as shown in FIG. 3, making it possible to monitor the etching rate.

<Effects of the Invention> According to the method of the present invention, by measuring the polarization resistance between the material to be etched and the counter electrode, (1) the etching speed can be monitored with a meter without depending on the operator's skill or intuition; But it can be done accurately.

(2) Since the etching/soching speed can be monitored by a meter, there is almost no effect on the temperature or concentration of the etching solution.
1 can be accurately determined as the end point.

(3) There is no risk of over-etching or under-etching.

Further, according to the second invention, the measured polarization resistance allows
Since calculation processing, data display processing, etc. can be performed, the etching process can be precisely managed and automation is possible.

[Brief explanation of the drawing]

FIG. 1a shows a circuit diagram of the etch rate monitoring system of the present invention, and FIG. 1b shows the electrical equivalent circuit of this circuit at the interface between the electrode and the counter-electrode etching solution. FIG. 2 is a system diagram of an embodiment of the etching rate monitoring system according to the second invention. FIG. 3 is a graph of measurement results of polarization resistance versus etching time t. Explanation of symbols 1...electrode, 2...counter electrode, 3...etching liquid,
4... Etching tank, 5... Polarization resistance measuring device, 6
...Arithmetic unit, 7...Data display screen. 8... Data recording device, 9... Data storage device, V
,...Low frequency AC voltage, vh...High frequency AC voltage, Rs...Solution resistance, Rc
l... Polarization resistance of electrode 1, Rc2... Polarization resistance of electrode 2, Cd,... Interfacial capacitance of electrode 1, Cd2... Interfacial capacitance of electrode 2, 10... Frequency switching signal input L stage. 11... Transmission circuit, ■?・・・Constant current circuit, 13...
・Digital portometer, i...constant current, V...
A [II constant voltage

Claims (3)

[Claims] (1) In etching a metal material, the material to be etched is used as an electrode, a material that is electrochemically more noble than the material to be etched is used as a counter electrode, and in an etching solution, between these two electrodes,
An alternating current voltage with a low frequency such that the impedance due to the interfacial capacitance between the electrode and the etching solution is sufficiently larger than the polarization resistance of the electrode, and an alternating current voltage with a high frequency such that the impedance due to the interfacial capacitance is sufficiently smaller than the polarization resistance. An etching rate monitoring system characterized in that the etching rate monitoring system is characterized in that the etching rate of a material to be etched is monitored by applying the polarization resistance and measuring the polarization resistance. (2) Etching is determined to be completed when the polarization resistance value between the two electrodes decreases to a predetermined value.
Etching rate monitoring system as described in Section. (3) In etching a metal material, the material to be etched is used as an electrode, a material that is electrochemically more noble than the material to be etched is used as a counter electrode, and in the etching solution, between these two electrodes,
An alternating current voltage with a low frequency such that the impedance due to the interfacial capacitance between the electrode and the etching solution is sufficiently larger than the polarization resistance of the electrode, and an alternating current voltage with a high frequency such that the impedance due to the interfacial capacitance is sufficiently smaller than the polarization resistance. An etching rate monitoring system characterized in that the etching rate monitoring system is characterized in that the etching time is controlled by applying the above polarization resistance, measuring the polarization resistance, and calculating the correlation between the polarization resistance value and the etching rate.