Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2002-12-27
2004-09-28
Norton, Nadine G. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C438S693000, C438S696000, C438S700000
Reexamination Certificate
active
06797626
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of polishing a copper layer of a substrate, e.g., a build-up substrate, used for example as a semiconductor wafer.
Some multi-layered circuit boards, on which electronic parts, e.g., semiconductor chips, etc. will be mounted, are made by a build-up method.
The build-up method will be explained.
Firstly, as shown in
FIG. 9
, an insulating resin layer
12
is formed on lower cable patterns
11
, and then via-holes
13
are formed so as to expose a part of each lower cable pattern
11
.
Next, as shown in
FIG. 10
, a copper layer
14
is formed in the via-holes
13
and a surface of the insulating resin layer
12
by non-electrolytic plating and electrolytic plating. In some cases, the copper layer
14
fills an inner space of each via-hole
13
. The copper layer
14
formed by plating is apt to be thick in the vicinity of edges of the insulating resin layer
12
. Therefore, parts of the copper layer
14
corresponding to the via-holes
13
are projected upward, so that flatness of the surface of the copper layer
14
must be low.
To make the surface of the copper layer
14
flat, firstly the surface of the copper layer
14
is removed by a roll-buff. Then, the copper layer
14
is etched to form into prescribed cable patterns (upper cable patterns). With this method, the upper cable patterns are electrically connected to the lower cable patterns
11
. This method will be repeated prescribed times to form the multi-layered circuit board.
In the case of forming circuits on a semiconductor wafer, connecting terminals, e.g., copper bumps, are formed in the wafer after the circuits are formed therein. The copper bumps are formed by the steps of: forming a resist mask having opening sections, which correspond to the copper bumps, on the wafer; plating parts of circuit sections exposed in the opening sections with copper; and removing the resist mask. With this method, the copper bumps can be projected from the surface of the wafer. Note that, the wafer having the copper bumps will be cut and divided into a plurality of semiconductor chips. Each of the semiconductor chips will be electrically connected to a circuit board by the copper bumps as terminals.
In some cases, copper bumps are formed in a circuit board so as to electrically connect a semiconductor chip(s) to the circuit board.
However, the above described conventional methods have following disadvantages.
The roll-buff is made of hard abrasive grains, which are bound by binders and formed into a cylindrical shape. The roll-buff is rolled on the surface of the copper layer so as to remove the projected parts of the copper layer. The projections can be removed by the roll-buff, but waviness in a wide area cannot be removed by the roll-buff, so that it is difficult to form the copper layer having uniform thickness. Further, the surface of the copper layer is scratched by the roll-buff, so that reliability of an electric element must be lower.
On the other hand, height of the copper bumps must be equal so as to securely connect the copper bumps. It is desirable to remove the copper bumps to make their height equal, but there are no effective methods.
SUMMARY OF THE INVENTION
The present invention has been invented to solve the problems of the conventional methods.
An object of the present invention is to provide a method of polishing a copper layer of a substrate, which is capable of improving a stock removal rate, forming a copper layer having uniform thickness, restricting scratches on a surface of the copper layer, and forming copper bumps having equal height.
Namely, the method of the present invention comprises the steps of:
supplying a substrate having a copper layer onto a polishing pad on a polishing plate with the copper layer facing the polishing pad;
pressing the substrate onto the polishing pad, with a backing pad, by a press head;
relatively rotating the press head with respect to the polishing plate, with supplying polishing slurry onto the polishing pad, so as to polish the copper layer,
wherein the backing pad is made of a material whose Asker C hardness is 75-95 and whose compressibility is 10% or less,
and the polishing slurry includes a chelating agent for chelating copper, an etching agent for etching the surface of copper layer, an oxidizing agent for oxidizing the surface of copper layer, and water.
Copper bumps formed in the substrate can be effectively removed by the invention. Height of the copper bumps can be made equal, and the surface of the substrate can be uniformly polished.
Further, a copper layer formed in a build-up substrate can also be effectively polished by the invention.
In the method of the present invention, a hard and low compressible backing pad, whose Asker C hardness is 75-95 and compressibility is 10% or less, is used.
Therefore, the substrate is held by the press head and the backing pad contacts a back side of the substrate when the copper layer (a front side) of the substrate is polished.
In this case, if the backing pad is too soft, a pressing force applied to projections in the front side or a counter force from the polishing pad is transmitted to the backing pad and the backing pad is depressed by the projections. Namely, the parts of the substrate, which correspond to the projections, are buried in the backing pad, so that it is difficult to remove the projections in the front side of the substrate and the copper layer cannot be uniformly polished.
On the other hand, if the backing pad is too hard, e.g., Asker C hardness is 96-100, the back side of the substrate becomes a standard face for the polishing. If there are small projections in the back side of the substrate, the projections are not buried in the backing pad, so that the projections badly influence the polishing. Uniformity of the polished copper layer must consequently be lower.
In the method of the present invention, the backing pad has the prescribed hardness and compressibility, so that projections in the back side of the substrate can be removed by the backing pad, and the backing pad is not badly influenced by projections in the copper layer. Therefore, the copper layer can be polished uniformly, and the copper layer having uniform thickness can be produced.
In the method, the backing pad may be made of polyurethane foam.
Further, the polishing slurry used in the method is capable of increasing the stock removal rate without scratching the surface of the copper layer, so that manufacturing efficiency can be improved. Namely, the polishing slurry includes a chelating agent for chelating copper, an etching agent for etching the surface of the copper layer,
an oxidizing agent for oxidizing the surface of the copper layer, and water. The copper layer is chemically etched by the etching agent.
The chelating agent catches copper grains, which are removed and separated by the etching agent and the abrasive grains in the case of the polishing slurry includes abrasive grains, and acts as the accelerator of the polishing.
Further, the chelating agent prevents the surface of the copper layer from being scratched by copper grains, so that no surface defects are formed on the surface of the copper layer.
In the method, the chelating agent may be organic carboxylic acid. For example, it may be at least one selected from the group consisting of: amino acid; quinoline-2-carboxylic acid (quinaldic acid); 2-pyridine carboxylic acid; 6-pyridine carboxylic acid; and quinine. Preferably, amino acid is selected due to good environmental conditions and high stock removal rate. Further, the chelating agent may be at least one amino acid selected from the group consisting of: neutral amino acid, such as glycine, &agr;-alanine, -alanine, valine, leucine, L-isoleucine, D-isoleucine, L-alloisoleucine, D-alloisoleucine, serine, L-threonine, D-threonine, L-allothreonine, D-allothreonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, cystine; and basic amino acid, such as lysine, arginine, histidine. Especially, the preferable chelating agent is at le
Hasegawa Tsuyoshi
Inada Yasuo
Kitamura Tadahiro
Miyairi Noriko
Sakai Kenji
Fujikoshi Machinery Corp.
Jordan and Hamburg LLP
Norton Nadine G.
Tran Binh X.
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