JPH0360184A - Manufacture of ceramic substrate with copper wiring - Google Patents

Abstract

PURPOSE:To prevent the local abnormal growth of a plated section produced when plating of a metal, such as nickel, etc., other than copper is performed by an electroplating method so as to improve the reliability of the title substrate by using copper which is less in oxygen or sulfur content for copper to be used as the source of vapor deposition. CONSTITUTION:When a copper layer 3 is formed on a ceramic substrate 1 by vapor deposition, a kind of copper which is >=99.99% in purity and <=2ppm in oxygen content or another kind of copper which is 99.99% in purity and <=0.7ppm in the sum of oxygen and sulfur contents when the copper contains both oxygen and sulfur is used as the source of vapor deposition. The reason why the upper limit of the sum of oxygen and sulfur contents is suppressed is considered to be that, when oxygen and sulfur coexist, the copper is easily gasified due to the sulfur dioxide gas produced from the oxygen and sulfur. When a kind of copper which is >2ppm in oxygen content is used, whisker- or fin-like abnormal growth of a plated section occurs at the time of nickel plating. When the oxygen content is <=2ppm, such abnormal growth hardly occurs and, even when it occurs, the length of the abnormal section is short. Such abnormal growth can be eliminated completely, when the oxygen content is reduced to <=0.3ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a copper wiring board, particularly a copper wiring ceramic board which is finally coated with a metal other than copper by electroplating.

[Conventional technology]

A PGA (pin grid array) substrate is an IC package that can be mounted at high density. PGA substrates for applications requiring high reliability have often been made of ceramic and have aluminum wiring layers. Recently, however, copper, which has low electrical resistance, has been used in place of aluminum to accommodate the increasing speed of electronic circuits. Copper is easily oxidized not only at high temperatures but also at room temperature, and cannot be passed through wire bonding as it is, so copper wiring layers are usually plated with nickel or gold with a nickel base. For example, as shown in FIG. 2, titanium 1i2 and conductive copper N3 are formed on a ceramic substrate 1 by a normal vapor deposition method, a circuit pattern is formed by photoetching (called buttering), and then electroplating is performed. As a result, a gold plating film 6 is applied using a film 7 of a metal other than copper such as nickel, for example, nickel as the base 5.

[Problem to be solved by the invention]

However, according to the conventional copper wiring ceramic board manufacturing method,
A copper conductive layer is formed on a ceramic substrate by vapor deposition,
After forming a circuit pattern by photoetching (called patterning), when applying a coating of a metal other than copper such as nickel or a coating of a noble metal such as gold using nickel as a base by electroplating, a plating layer of nickel etc. Abnormal growth often occurred locally in the form of whiskers as shown in Figure 3a) or horizontally in the form of fins as shown in Figure 3b). In FIG. 2, whisker-like abnormal growth is indicated by 5a. In extreme cases, the lead parts 8, which should originally be electrically independent, may be short-circuited or almost short-circuited. To give a specific example, when the average plating thickness is 1 μm, the length of abnormal growth is 10 μm or more, and in some cases even reaches 40 μm (this means that the abnormal growth rate is 10 to 40 times the average plating speed). (means that electrodeposition is occurring). Such abnormal growth of the plating portion seriously impairs the reliability of the manufactured copper wiring board.

The object of the present invention is to prevent local abnormal growth of the plated portion that occurs when plating a metal other than copper such as nickel by electroplating after forming a circuit pattern on a dissipating conductive layer formed by vapor deposition. An object of the present invention is to provide a method for manufacturing a highly reliable copper wiring ceramic substrate.

[Means to solve the problem]

In order to achieve the above object, in the present invention, copper having a purity of 99.99% or more and an oxygen content of 2 ppm or less is used as a vapor deposition source when forming a copper vapor deposition layer, or copper with a purity of 99.99% or more is used as a vapor deposition source. In the above, copper having a sulfur content of 4 ppm or less was used.

However, if oxygen and sulfur coexist in copper with a purity of 99.99% or higher, the sum of the oxygen content and sulfur content is 0. lp
pm or less. The reason why the upper limit of the total content of oxygen and sulfur is small is thought to be that when oxygen and sulfur coexist, gasification tends to occur due to the production of sulfur dioxide.

The copper vapor deposited layer in the present invention includes a copper layer formed by physical vapor deposition (PVD) such as ion blating, cluster ion beam method, sputtering method, etc. in addition to vacuum evaporation method.

The method of the present invention consists of the following steps.

(1) Step of depositing a copper layer on a ceramic substrate The ceramic used as the substrate may be any of alumina, mullite, magnesia, aluminum nitride, zirconia, silicon carbide, etc.

This invention applies to ceramic substrates! In the process of vapor depositing the PI layer, copper with a purity of 99.99% or more and an oxygen content of 2 ppm or less is used as a vapor deposition source, or copper with a purity of 99.99% or more and a sulfur content of 4 ppm or less is used. It is characterized by using

Preferably, copper with an oxygen content of 0.3 ppm or less or copper with a sulfur content of 1 ppm or less is used.

If copper with an oxygen content of more than 2 ppm is used, abnormal growth such as whisker-like or fin-like shapes as described above will occur during nickel plating. If the oxygen content is 2 ppm or less, there will be very little abnormal growth in the plated area, and even if there is abnormal growth, the length will be short. If it is 0.3 ppm or less, there will be no abnormal growth.

To obtain copper with a purity of 99.99% or more and an oxygen content of 2 ppm or less, the method described in JP-A-60-244054 and the like can be used.

Similarly, when copper with a sulfur content exceeding 4 ppm is used, abnormal growth of the plated portion occurs. Sulfur content 14ppm
If it is below, there will be very little abnormal growth in the plated area, and even if there is abnormal growth, the length will be short. If the sulfur gold content is kept below ippm, there will be no abnormal growth.

To obtain copper with a purity of 99.99% or more and a sulfur content of 4 ppm or less, Japanese Patent Application Laid-open Nos. 57-16187 and 57-161
88, JP-A No. 61-84389, etc. can be used.

Before depositing copper, a layer 1 of a metal other than copper, such as one or more of aluminum, titanium, zirconium, chromium, molybdenum, tungsten, nickel, etc., is formed by vapor deposition as a base on the ceramic substrate. Good too.

The thickness to be deposited is usually about 1 μm to 20 μm, and 3
It is often set to 10 μm.

(2) Formation of circuit pattern by photoetching A circuit pattern is formed on the copper vapor deposited layer obtained in the above step (1) by a conventional photoetching method.

(3) Process of plating a metal other than copper on the copper wiring layer The copper wiring layer obtained in step (2) above is plated with a metal other than copper, such as nickel, or with a base layer of nickel, etc., using an electroplating method. Furthermore, precious metal plating is applied. The metal used for plating can be selected from nickel, cobalt, chromium, molybdenum, tungsten, etc., but the effect of the present invention is remarkable in the case of metals that tend to cause dendritic growth during plating, such as nickel, cobalt, and chromium. be.

If necessary, another metal, particularly a noble metal such as gold, may be further plated on the above metal plating other than copper.

There are no particular restrictions on the plating method, conditions, etc., and the usual methods may be used. The thickness of plating of metals other than copper such as nickel is 0.
The thickness of gold or other plating applied on top of nickel or other base plating is approximately 1 to 5μm. 1 to 2μ
It is about m.

[Effect]

According to the method of the present invention, copper with a purity of 99.99% or more and an oxygen content of 2 ppm or less is used as a deposition source, or copper with a purity of 99.99% or more and a sulfur content of 4 ppm or less is used.
A copper conductive layer is deposited on a ceramic substrate using copper of ppm or less, and after forming a circuit pattern on the formed copper conductive layer, plating with a metal other than copper such as nickel or gold etc. with nickel as a base is performed by electroplating. By performing noble metal plating, plating can be performed without local abnormal growth of the plated portion, and a copper wiring ceramic substrate can be manufactured.

If the content of oxygen or sulfur in the copper deposited film is small, fewer crystal grains will be lost on the surface of the copper deposited layer during etching, resulting in a smoother etched surface. When the etched surface becomes smooth, the current distribution during plating becomes relatively uniform, thereby preventing the occurrence of abnormal growth.

Hereinafter, the method of the present invention will be explained in detail with reference to Examples.

〔Example〕

As shown in Fig. 1, a titanium layer 2 is formed by vacuum-depositing titanium to a thickness of 0.03 μm on an alumina substrate l with a thickness of 2 mm.
After forming 11 types of copper vapor deposition materials with a purity of 99.99% and different oxygen and sulfur contents as shown in Table 1,
A copper deposition layer 3 was formed by vacuum deposition to a thickness of 66 mL at a substrate temperature of 300'C5 and a vacuum degree of 3X10-bTorr. The metal layer 4 (copper/titanium r*>) was etched using a copper chloride solution using a normal photoetching method, and the line width was 40 μm.
, 1000 linear wiring patterns (lead parts) with a line spacing of 40 μm and a length of 20 mm were formed in parallel to each other. The thus obtained copper wiring pattern on the alumina substrate is plated with nickel to a thickness of 0.5 μm using a normal electroplating method to form a nickel film 5, and then gold is coated with 0.5 μm of gold.
An electroplated gold film 6 was formed to a thickness of m. The plating conditions were as follows: For nickel plating, a standard Watt bath was used;
The hot water temperature was 60°C, the current density was 2.0A/dm", and for gold plating, a cyanogen potassium bath was used, and the temperature was 50°C.
C, and the current density was 1.0 A/dm''.Thus, the wiring lead portion 8 was formed on the ceramic straw substrate 1.

In FIG. 1, 4 indicates a layer formed by vapor deposition (vapor deposition N), and 7 indicates a plating layer.

The surface of the wiring pattern was observed after nickel plating and after gold plating. The results are shown in Table 1.

In Table 1, oxygen content t4ppm (test number 1), sulfur content 7ppm (test number 5), oxygen 0.5ppm, sulfur 1
．． The column of 0 ppm (Test No. 9) corresponds to a comparative example outside the scope of the present invention.

In Table 1, the abnormal growth occurrence rate indicates the percentage of the number of leads in which abnormal growth has occurred out of 1000 leads, and the number of short circuits indicates the number of leads in which short circuits have occurred between adjacent leads out of 1000 leads. .

Table 1 As is clear from Table 1, according to the present invention, copper with a purity of 99.99%, no detectable sulfur, and an oxygen content of 2 ppm or less (test number 2, 3, 4L or with a purity of 99.99%)
%, no oxygen was detected and copper with a sulfur content of 4 ppm or less (test numbers 6 and 7.8) was used for vapor deposition, no shortening of the line distance due to abnormal growth occurred. Oxygen content fi1.8
ppm or 3.5 ppm sulfur content, overgrowth occurred at a rate of just over 10%, but no shorting occurred. Oxygen content is 0.2 ppm or sulfur content is 0.8
In the case of ppm (test numbers 4 and 8), there was no abnormal growth. On the other hand, even if the purity is 99°99%, the oxygen content exceeds 2 ppm or the sulfur content is 4 ppm.
(Test Nos. 1 and 5)
) had a high rate of abnormal growth and short circuits between lines.

On the other hand, when 99.99% pure copper containing 0.5 ppm oxygen and ippm sulfur was used, short circuits between wires occurred although the incidence of abnormal growth was low. However, Q.
When using 99.99% pure copper containing 3 ppm oxygen and 0.3 ppm sulfur (the sum of oxygen and sulfur is 0.6 ppm), no abnormal growth occurred and no short circuit between wires occurred. Ta.

〔Effect of the invention〕

According to the method of the present invention, steaming number 1 is placed on a ceramic substrate.
), sulfur content 7 ppm (test number 5), oxygen 0.5 p
pm, sulfur 1.0 ppm (Test No. 9) column corresponds to a comparative example outside the scope of the present invention.

In Table 1, the abnormal growth occurrence rate indicates the percentage of the number of leads in which abnormal growth occurs out of 1,000 leads, and indicates that the phenomenon of abnormal growth such as whiskers does not occur, and the leads that must be electrically independent. A short circuit or near-short circuit condition is prevented. The method of the present invention is particularly useful for depositing copper conductive layers on ceramic substrates.

In the present invention, when copper with a low oxygen content or sulfur content is used as the vapor deposition source, abnormal growth of the plating layer does not occur in the subsequent plating process, as described above.
If the content of oxygen or sulfur is small, crystal grains on the surface of the copper vapor deposited layer will not be missing during etching, and the surface after etching will have less unevenness, so the current distribution during plating will be relatively uniform. It is.

According to the method of the present invention, there is not only no abnormal growth when plating a metal other than copper on a copper vapor deposited layer, but also the unevenness of the edges of the circuit pattern after plating is reduced, resulting in a sharp circuit pattern. As a result, it becomes possible to make the pattern finer.

According to the method of the present invention, it is possible to plate a metal other than copper, such as nickel, on a copper wiring layer deposited on a ceramic substrate without causing abnormal growth of the plating layer as described above. It is possible to create a ceramic wiring board suitable for wire bonding using copper with low electrical resistance, and it can be used to increase the calculation speed of electronic circuits, for example. The method of the present invention can be applied to, for example, PGAC pin grid array), TAB (tape automated bonding), FPC (flexible printed circuit board), and the like.

The method of the present invention is useful not only when depositing copper directly onto a ceramic substrate, but also when depositing copper through a base layer of another metal provided by vapor deposition or the like on a ceramic substrate. .

The method of the present invention is also useful when plating a metal other than the copper plate, such as nickel, on a power-dissipating conductive layer on which a circuit pattern is formed, and then plating a noble metal such as gold or silver using this layer as a base. be.

According to the method of the present invention, it is possible to increase the current density and the speed of electroplating, thereby increasing production efficiency.

[Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view of a wiring layer on a ceramic substrate obtained in an example of the present invention, and FIG. 2 is an enlarged cross-sectional view of an abnormally grown portion of a wiring layer on a ceramic substrate manufactured by a conventional method. , Fig. 3 is an explanation showing the abnormal growth of whiskers (Fig. 3a)) and fins (Fig. 3b)) that occur when nickel or the like is electroplated on a vapor-deposited copper wiring layer on a ceramic substrate. It is a diagram. Explanation of symbols 1------1...Ceramic substrate 2--...-
--- Titanium vapor deposition layer 3 --- Copper deposition layer
4・−・−・・−・・Vapour-deposited layer 5−・−1−−−・Nickel plating layer 5a−・−・−Abnormally elongated portion of nickel plating layer 6−・・・・−・−Gold plating layer

Claims (4)

[Claims] (1) In a method for manufacturing a copper wiring ceramic substrate, in which a copper conductive layer is formed on a ceramic substrate by a vapor deposition method, a circuit pattern is formed on the copper conductive layer, a coating of a metal other than copper is applied by an electroplating method. As a vapor deposition source for forming a vapor deposition layer, a purity of 99.99% or more and an oxygen content of 2p
pm or less, and when containing sulfur, the sum of oxygen content and sulfur content is 0.7 ppm or less. (2) The method for manufacturing a copper wiring ceramic substrate according to claim 1, wherein the metal other than copper is selected from nickel, cobalt, and chromium. (3) A method for manufacturing a copper wiring ceramic substrate, in which a copper conductive layer is formed on a ceramic substrate by vapor deposition, a circuit pattern is formed on the copper conductive layer, and then a coating of a metal other than copper is applied by electroplating. A vapor deposition source for forming a vapor deposition layer with a purity of 99.99% or more and a sulfur content of 4p
pm or less, and when containing oxygen, the sum of the oxygen content and sulfur content is 0.7 ppm or less. (4) The method for manufacturing a copper wiring ceramic substrate according to claim 1, wherein the metal other than copper is selected from nickel, cobalt, and chromium.