JPH11274690A - Method of etching printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of etching a polyimide layer on a printed circuit board at a high speed. SOLUTION: A polyimide-made insulation layer formed between conductive layers is bored to form holes for taking the electric connection in the following conditions. (1) in a reactor vessel having a parallel flat plate type electrode structure, a plasma is produced by a high frequency of 10-100 MHz, using a gas composed of an O gas and F-based compd. gas mixed at vol. ratio of 1:0.1-1:1, (2) a printed circuit board is disposed on a cathode electrode and the cathode electrode is heated at 150-250 deg.C, and (3) the applied power density is over 2.00 W/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a polyimide layer, which is an insulating layer, at a high speed in a printed circuit board having a laminated structure of a conductive layer and an insulating layer.

[0002]

2. Description of the Related Art In recent years, in the electronics industry, there has been a demand for higher performance, higher functions, and more compact electronic devices, and accordingly, IC chips and boards for mounting the IC chips have become finer. , The density is increasing. I
In a C chip, a dry process using plasma is indispensable for fine patterning of silicon or the like. Further, a circuit board in which a copper foil as a conductive layer and a polyimide as an insulating layer are alternately laminated is widely used as an IC mounting board because of the excellent heat resistance, electrical characteristics, and the like of polyimide.

[0003] A mounting technique of a printed wiring board, particularly a technique of forming a through hole and a via hole in manufacturing a printed circuit board is particularly important. Through hole (Throug
Although there are dry processes such as a mechanical drilling method and a laser processing method as a method for forming a h hole and a via hole, a wet method is often used in terms of cost or processing ability (etching speed).

[0004] In recent years, various mechanical and electrical characteristics are required for a printed circuit board, and a polymer having a plurality of different structures may be used for a resin layer as an insulating layer.
For example, polyimide, which is a heat-resistant polymer, is often used for the insulating layer. Even when processing the polyimide layer by wet etching and forming a through hole and a via hole, the etching rate distribution occurs due to the small hole shape, and a part where the through hole and the via hole are not completely formed also occurs. There is a problem.

Further, in the case of wet etching, there are problems such as difficulty in handling the liquid, waste liquid treatment, contamination of the substrate, and the inability to freely control the etching shape. At present, the controllability of the etching shape is becoming more and more important with the refinement of circuit boards. Specifically, an anisotropic shape is required rather than an isotropic shape. On the other hand, the dry etching method using plasma is characterized in that the substrate is not contaminated, that there is no problem such as waste liquid, and that the processing shape can be controlled. However, in the case of etching using plasma, one of the reasons that the etching rate is slower than the wet method is not adopted in a practical process.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a hole in an insulating layer of a circuit board using plasma, and more particularly, to provide a technique for etching a polyimide layer which is an insulating layer at a high speed. It is in.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above-mentioned technology for boring a printed circuit board using polyimide as an insulating layer. As a result, the mixing ratio of fluorine-based compound gas to oxygen gas, etching, Control of substrate temperature at the time,
It has been found that controlling the applied power density to a constant condition significantly improves the etching rate. That is, the gist of the present invention is as follows.

(1) A printing method characterized in that a polyimide layer for making electrical connection is punched in an insulating layer made of polyimide formed between conductive layers under the following conditions. This is a method for etching a circuit board. (1) In a parallel plate type reaction vessel having an electrode structure, oxygen gas and fluorine compound gas are mixed at a mixing ratio of 1: 0.1 to 1: 1.
(Volume ratio) using a gas mixed in the range of 10 to 100
Plasma is generated by a high frequency of MHz. (2) The printed circuit board is placed on the cathode electrode, and the cathode electrode is heated to 150 to 250C. (3) The applied power density is 2.00 W / cm ² or more.

(2) The relation between the pressure X (Pa) of the plasma processing chamber and the bias potential Y (V) of the cathode electrode satisfies the following relational expressions (a) and (b) simultaneously (1). The method for etching a printed circuit board according to the above (2). Y ≦ 2.6X−520 (a) 1 ≦ X ≦ 200 (b)

(3) The method for etching a printed circuit board according to (1) or (2), wherein the fluorine-based compound gas is fluorine.

(4) The method for etching a printed circuit board according to (1) or (2), wherein the fluorine compound gas is nitrogen trifluoride.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit board used in the present invention can be applied to any circuit board as long as it is a circuit board in which a copper foil as a conductive layer and a polyimide layer as an insulating layer are laminated. If a specific example is shown as the polyimide layer, a commercially available polyimide film can be effectively used as a product name such as Kapton, Upilex, Apical or the like.
Further, acid anhydrides such as pyromellitic anhydride, biphthalic anhydride, benzophenonetetracarboxylic anhydride, oxydiphthalic anhydride, hydrofurandiphthalic anhydride, and methoxydiaminobenzene, 4,4′-oxydianiline , 3,4'oxydianiline, 3,3'oxydianiline, bisdianilinomethane, 3,3'-diaminobenzophenone, p, p-aminophenoxybenzene, p, m-aminophenoxybenzene, m, p- Aminophenoxybenzene, m, m-aminophenoxybenzene, chloro-m-aminophenoxybenzene, p-pyridineaminophenoxybenzene, m-pyridineaminophenoxybenzene, p-aminophenoxybiphenyl, m-aminophenoxybiphenyl, p-bisamino Phenoxybenzyl sulfone M-bisaminophenoxybenzylsulfone, p-bisaminophenoxybenzylketone, m-bisaminophenoxybenzylketone, p-bisaminophenoxybenzylhexafluoropropane, m-bisaminophenoxybenzylhexafluoropropane, m-bisaminophenoxy Benzylhexafluoropropane, p-bisaminophenoxybenzylpropane, o-bisaminophenoxybenzylpropane, m-bisaminophenoxybenzylpropane, p
Polyimides formed by reacting with and imidating amines such as -diaminophenoxybenzylthioether, m-diaminophenoxybenzylthioether, indanediamine, spirobidiamine, and diketonediamine can also be effectively used in the present invention.

The thickness of the insulating layer is not particularly limited. However, considering the role of the insulating layer of the circuit board, if it is too thin, it is difficult to maintain the insulating properties. In addition, problems arise in other aspects of performance. Therefore, the thickness of one insulating layer is 5 to
It is about 500 μm, preferably about 10-100 μm.

In the present invention, the etching of the insulating layer includes
It is industrially important to obtain an etching rate comparable to that of the conventionally used wet method. For this purpose, a printed circuit board is placed on a cathode electrode and heated, and oxygen gas and fluorine are used. Although it has been found that using plasma with a mixed gas of system compound gases is an effective means for improving the etching rate, the input power density is large in plasma etching using a parallel plate type high frequency power supply. It turned out to be meaningful. Considering that etching proceeds by a chemical reaction rather than a physical reaction, it is necessary to perform at a high temperature in order to improve the reaction rate, and particularly in an atmosphere heated near the glass transition temperature of the insulating layer. Was found to be the most responsive.

The substrate is placed on the cathode electrode not only to control the processing shape of the etching, but also to suppress the formation of a non-conductive film adhered to the circuit board. The optimum temperature (T) differs depending on the type of polyimide. For example, in the case of a polyimide having a heat resistance of Tg of 250 ° C. or more, if its glass transition temperature is Tg, 150 ° C. ≦ T
It was found that an etching rate higher than that performed at room temperature can be obtained in the temperature range of ≦ 250 ° C., and that this etching rate becomes highest at a temperature near Tg, that is, a temperature near 250 ° C. However, if the temperature is higher than Tg, the thermophysical properties of the polyimide greatly change, which may result in a defective circuit board after etching, which is not preferable.

Further, in addition to oxygen gas, a fluorine-based compound gas such as nitrogen trifluoride (NF ₃ )
It has been found that a system to which a gas or a fluorine (F ₂ ) gas is added is good, and in particular, a mixing ratio with an oxygen gas has a great influence on an etching rate. That is, in the case of NF ₃ , NF ₃ is 0.1 to 1 with respect to oxygen, and more effective is NF ₃ with respect to 1 with 0.1 to 0.5. In the case of F ₂ , it was found that the same mixing ratio as that of NF ₃ was preferable for improving the etching rate. Further, the reason why the addition of NF ₃ or F ₂ is effective is that F-F is higher than that of fluorine-based compound gas such as CF ₄ which is generally used as an etching species.
This is considered to be because the bond or the NF bond is lower than the CF bond energy and easily becomes a fluorine ion, an NFx ion, or a radical in plasma.

Further, with respect to the applied power density, the etching rate is drastically improved at a certain power density or more, that is, at 2.00 W / cm ² or more. It has been found that the etching rate can be obtained.

Further, it has been found that in order to increase the etching rate, it is important to perform etching under the condition that the relationship between the pressure of the plasma processing chamber and the bias potential of the cathode electrode satisfies the following relational expression. That is, assuming that the pressure of the plasma processing chamber is X (Pa) and the bias potential of the cathode electrode is Y (V), Y ≦ 2.6X−520 (a) 1 ≦ X ≦ 200 (b) It is important to control the plasma parameters such as pressure (X) and bias potential (Y) within the range. The relationship between the pressure and the bias potential is plotted in FIG. FIG.
In FIG. 5, the shaded area indicates a region that satisfies the relational expressions (a) and (b) at the same time (however, a region where the bias potential is −800 V or less is not shown).

In the present invention, the pressure can be controlled at 1 to 200 Pa from the equation (b), but it is more preferable to control the pressure at about 3 to 100 Pa in the balance between the etching rate and the processed shape.

In the present invention, a high-frequency power supply is used as a power supply for generating plasma, and its frequency is 10 MHz to 100 MHz, but 13.56 MHz or 27 MHz is preferably used in view of the Radio Law and handling. Can be Particularly, a frequency in this range is preferable for controlling the mobility of ions and radicals in the plasma. Further, this is an effective means for controlling the ion potential by applying a DC component to the high frequency independently of the high-frequency power supply, thereby controlling the selective etching by ions.

In the present invention, at least (a) a plasma processing chamber for performing plasma processing, which is provided with means for introducing a circuit board, means for holding the circuit board, and means for discharging the circuit board, (b) a power application device, and (c) vacuum evacuation Means, (d) a dry etching apparatus provided with substrate heating and temperature control means. Further, in order to improve the etching efficiency, (e) a loading chamber for loading a circuit board installed on the substrate holder, (f) a loading chamber for unloading, and (g) a plasma processing chamber from the loading chamber. It is preferable to use an apparatus provided with a transfer mechanism for transferring the substrate holder from the plasma processing chamber to the unloading chamber. This is because when the plasma processing is performed continuously, the processing chamber is in a high vacuum, so that the circuit board is held in a chamber in which a certain degree of vacuum is maintained in advance, and then the circuit board is transferred to the processing chamber where the etching processing is performed. Is to shorten the time until a high vacuum is achieved.
The spare room mentioned here refers to a (e) carry-in room and (f) carry-out room in a chamber in which a certain degree of vacuum is kept in advance. Here, (e) the loading chamber and (f) the unloading chamber are not particularly provided, that is, 13.56 of the parallel plate type shown in FIG.
A more specific description will be given using a processing apparatus using a high-frequency power supply of MHz as an example.

13.56 MHz high frequency (RF) power supply 3
1 and a plasma processing chamber 11 having a parallel-plate high-frequency electrode 32 into which a low-pass filter 22 to which a DC voltage can be independently applied is introduced, and a counter electrode 31 (ground).
The counter electrode 31 and the parallel plate high-frequency electrode 32 are provided with a mechanism capable of controlling the electrode temperature. Plasma processing chamber 11
Has a rotary pump 12 so that the inside can be evacuated,
The mechanical booster pump 13 is connected so that a higher degree of vacuum can be achieved. A gas line 14 (oxygen and NF ₃ ) used for etching is connected to the plasma processing chamber 11.

As a plasma etching method, first, a circuit board is placed on the parallel plate high-frequency electrode 32. At this time, a substrate holder may be used for fixing the substrate as necessary. After the substrate is installed, the gas line 1 is placed in the plasma processing chamber 11.
A gas is flowed through 4, and the power of the high-frequency power source 21 is turned on to generate plasma for a certain time to process the substrate. After the plasma processing (etching) for a predetermined time is completed, the discharge gas is stopped, the plasma processing chamber is opened to the atmosphere, and the substrate is taken out.

[0024]

The present invention will be described more specifically with reference to the following examples. Example 1 A copper thin film having a thickness of 18 μm and a pore diameter of 0.2 mmφ and a polyimide film having a low expansion coefficient (trade name: Kapton ENZ)
T, manufactured by Toray DuPont) and a thermoplastic adhesive polyimide PI-A (manufactured by Mitsui Chemicals, Inc .: thickness 3 μm, Tg =
A polyimide layer coated on both sides at about 200 ° C.) was used as an insulating layer, and a copper plate / polyimide / copper thin film laminate in which this and a 2 mm-thick copper plate were bonded together by a press was used as a circuit board. Mixed gas of oxygen gas and NF ₃ (composition ratio is 80: 2
0) was performed using the plasma etching apparatus shown in FIG. 1 (however, no DC voltage was applied by the low-pass filter 22). The etching conditions are shown below. Etching conditions: oxygen gas / NF ₃ gas flow rate 67/33 sccm processing chamber pressure 67 Pa RF power density 2.55 W / cm ² temperature 200 ° C. (processing chamber) The bias voltage of the cathode electrode at this time is −380.
V.

Example 2 The circuit board described in Example 1 was used. 1 using a mixed gas of oxygen gas and F ₂ (composition ratio: 80:20) (however, a low-pass filter 22).
The application of DC voltage was not performed). The etching conditions are shown below. Etching conditions: oxygen gas / F ₂ gas flow rate 80/20 sccm processing chamber pressure 6.7 Pa RF power density 2.55 W / cm ² temperature 200 ° C. (processing chamber) The self-bias potential of the cathode electrode at this time is -7
00V.

Example 3 The circuit board described in Example 1 was used. Using a mixed gas of oxygen gas and NF ₃ (composition ratio: 80:20), the plasma etching apparatus shown in FIG.
2 was applied). The etching conditions are shown below. Etching conditions: Oxygen gas / NF ₃ gas flow rate 67/33 sccm Processing chamber pressure 67 Pa RF power density 2.08 W / cm ² DC voltage −300 V Temperature 200 ° C. (Processing chamber) The bias of the cathode electrode at this time Voltage is -580
V.

Example 4 The circuit board described in Example 1 was used. Using a mixed gas of oxygen gas and F ₂ (composition ratio: 75:25), the plasma etching apparatus shown in FIG.
The application of DC voltage was not performed). The etching conditions are shown below. Etching conditions: oxygen gas / F ₂ gas flow rate 80/20 sccm processing chamber pressure 13.3 Pa RF power density 2.30 W / cm ² temperature 180 ° C. (processing chamber) The self-bias potential of the cathode electrode at this time is -5
It was 20V.

Example 5 The circuit board described in Example 1 was used. Using a mixed gas of oxygen gas and NF ₃ (composition ratio is 67:33), the plasma etching apparatus shown in FIG.
2 was applied, and the etching was performed. The etching conditions are shown below. Etching conditions: oxygen gas / NF ₃ gas flow rate 67/33 sccm processing chamber pressure 133 Pa RF power density 2.55 W / cm ² temperature 240 ° C. (processing chamber) The bias voltage of the cathode electrode at this time is −250.
V.

Example 6 The circuit board described in Example 1 was used. Using a mixed gas of oxygen gas and NF ₃ (composition ratio is 67:33), the plasma etching apparatus shown in FIG.
2 was applied, and the etching was performed. The etching conditions are shown below. Etching conditions: oxygen gas / NF ₃ gas flow rate 67/33 sccm processing chamber pressure 13.3 Pa RF power density 2.08 W / cm ² temperature 180 ° C. (processing chamber) The bias voltage of the cathode electrode at this time was − 450
V.

Example 7 The circuit board described in Example 1 was used. Using a mixed gas of oxygen gas and NF ₃ (composition ratio is 67:33), the plasma etching apparatus shown in FIG.
2 was applied, and the etching was performed. The etching conditions are shown below. Etching conditions: oxygen gas / NF ₃ gas flow rate 67/33 sccm processing chamber pressure 133 Pa RF power density 2.08 W / cm ² temperature 240 ° C. (processing chamber) The bias voltage of the cathode electrode at this time is −150.
V.

Comparative Example 1 Using the circuit board described in Example 1, etching was performed with a hydrazine solution.

Comparative Example 2 The circuit board described in Example 1 was used. Etching was performed in the same manner as in Example 1. However, the temperature of the processing chamber was kept constant at room temperature (about 20 ° C.). Etching conditions: oxygen gas / NF ₃ gas flow rate 67/33 sccm processing chamber pressure 67 Pa RF power density 2.55 W / cm ² temperature 20 ° C. (processing chamber) The bias voltage of the cathode electrode at this time is −380.
V.

Comparative Example 3 The circuit board described in Example 1 was used. Etching was performed in the same manner as in Example 1. However, the gas composition ratio is NF ₃ :
This was performed with oxygen at a ratio of 2: 1. Etching conditions: oxygen gas / NF ₃ gas flow rate 33/67 sccm processing chamber pressure 67 Pa RF power density 2.55 W / cm ² temperature 200 ° C. (processing chamber) The bias voltage of the cathode electrode at this time is −360.
V.

Comparative Example 4 The circuit board described in Example 1 was used. Etching was performed in the same manner as in Example 1. However, the input power density is 1.27
A DC voltage of W / cm ² was applied by a low-pass filter 22. Etching conditions: oxygen gas / NF ₃ gas flow rate 67/33 sccm processing chamber pressure 67 Pa RF power density 1.27 W / cm ² DC voltage −200 V temperature 200 ° C. (processing chamber) In this case, the bias of the cathode electrode was used. Voltage is -380
V.

Test Example 1 In Examples 1 to 5 and Comparative Examples 1 to 4, the time required for forming a hole in the polyimide layer was measured and summarized in Table 1. The etched shape was also evaluated, and the anisotropy was evaluated as +, ±,-(a large anisotropy (those with an aspect ratio of 3 or more) was +, and an anisotropic one (aspect ratio)). And 1-2) are indicated by-, and intermediates are indicated by ±).

In Examples 1 to 7, those in the region shown in FIG. 2 are plotted with ○, and those outside this region are plotted with □. It can be seen that all the particularly short time required for forming the holes in the polyimide layer is within the hatched portion in FIG.

[0037]

[Table 1]

[0038]

According to the present invention, the same etching rate as that of the conventional wet etching can be achieved by the plasma etching.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus.

FIG. 2 is a diagram showing the relationship between pressure and bias potential.

[Description of Signs] 11: Plasma processing chamber 12: Rotary pump 13: Mechanical booster pump 14: Gas line 21: RF electrode 22: Low pass filter for applying DC voltage 31: Counter electrode 32: Parallel plate high frequency electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Moruji Morita, 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Chemicals, Inc.

Claims (4)

[Claims] 1. A printed circuit, wherein a polyimide layer for making an electrical connection is punched in an insulating layer made of polyimide formed between conductive layers under the following conditions. Substrate etching method. (1) In a parallel plate type reaction vessel having an electrode structure, oxygen gas and fluorine compound gas are mixed at a mixing ratio of 1: 0.1 to 1: 1.
(Volume ratio) using a gas mixed in the range of 10 to 100
Plasma is generated by a high frequency of MHz. (2) The printed circuit board is placed on the cathode electrode, and the cathode electrode is heated to 150 to 250C. (3) The applied power density is 2.00 W / cm ² or more. 2. The relation between the pressure X (Pa) of the plasma processing chamber and the bias potential Y (V) of the cathode electrode satisfies the following relational expressions (a) and (b) at the same time. 3. The method of etching a printed circuit board according to claim 1. Y ≦ 2.6X−520 (a) 1 ≦ X ≦ 200 (b) 3. The method for etching a printed circuit board according to claim 1, wherein the fluorine-based compound gas is fluorine. 4. The method for etching a printed circuit board according to claim 1, wherein the fluorine-based compound gas is nitrogen trifluoride.