JP2001262378A - Plasma processing method - Google Patents

Abstract

(57) [Problem] To provide a plasma processing method capable of suppressing re-oxidation after plasma processing and ensuring good processing quality. SOLUTION: In a plasma processing method for removing an oxide film on an electrode surface by performing a plasma processing on a substrate on which an electrode made of copper or a copper alloy is formed, a plasma generating gas containing a hydrogen gas as a reducing gas for the substrate. After performing the plasma treatment using the aging method, aging is performed by allowing the mixture to stand for a predetermined time while continuing to supply the plasma generating gas and cooling to room temperature. This can prevent the cleaned surface immediately after the plasma treatment from coming into direct contact with oxygen and suppress the progress of reoxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method for performing plasma processing on an object to be processed having an electrode made of copper or a copper alloy, such as a substrate for mounting electronic components.

[0002]

2. Description of the Related Art On a substrate on which a semiconductor element is mounted, an electrode to which the semiconductor element is electrically connected is subjected to plasma processing. This plasma treatment is performed for the purpose of improving the bonding property by cleaning the electrode surface, which is a bonding point of a metal conductor such as a wire or a bump used for connection. Conventionally, copper or a copper alloy is frequently used as a material of an electrode. These materials oxidize when exposed to the atmosphere, and particularly when heated to a high temperature by a heat treatment or the like, the oxidation proceeds and a thick oxide film is formed on the surface. In a plasma treatment for removing these oxide films, a reducing gas such as a hydrogen gas has been used as a gas for plasma generation.

[0003]

However, the conventional plasma processing using hydrogen gas for the above purpose has a problem that the electrode surface is re-oxidized when exposed to the atmosphere after the plasma processing is completed. This re-oxidation occurs when the electrode surface comes into contact with oxygen in the air when it is opened to the atmosphere.However, the oxidation reaction proceeds rapidly on the electrode surface that has been cleaned by plasma treatment and the temperature has risen. An oxide film having a thickness much larger than the oxide film thickness at the time of oxidation is generated in a short time. As described above, the conventional plasma processing method has a problem in that reoxidation progresses at the time of opening to the atmosphere after the plasma processing, and the intended purpose of the plasma processing cannot be achieved.

Accordingly, an object of the present invention is to provide a plasma processing method capable of suppressing re-oxidation after plasma processing and ensuring good processing quality.

[0005]

According to a first aspect of the present invention, there is provided a plasma processing method for removing an oxide film on an electrode surface by performing a plasma processing on an object having an electrode whose surface is made of copper or a copper alloy. A method, wherein a plasma processing is performed on the processing target using a plasma generating gas including a reducing gas, and a step of cooling the processing target to a normal temperature in a reducing gas atmosphere following the plasma processing. And

According to a second aspect of the present invention, there is provided the plasma processing method according to the first aspect, wherein the reducing gas is hydrogen gas.

According to the present invention, after performing plasma processing using a plasma generating gas containing a reducing gas, the object to be processed is cooled to room temperature in a reducing gas atmosphere following the plasma processing. It is possible to prevent the cleaned surface immediately after the plasma treatment from coming into direct contact with oxygen, thereby suppressing the progress of reoxidation.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a plasma processing apparatus according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view of a substrate to be subjected to plasma processing according to an embodiment of the present invention, and FIG. The flow chart of the plasma processing method, (Table 1) is a table showing the surface condition of the copper electrode surface to be plasma-processed.

[0009]

[Table 1]

First, the structure of the plasma processing apparatus will be described with reference to FIG. Reference numeral 1 denotes a base plate in which an electrode 2
Is provided. A high-voltage / high-frequency power supply 3 is connected to the electrode unit 2. A casing 4 is installed on the base plate 1 so as to be freely opened and closed. The space enclosed by the base plate 1 and the casing 4 forms a processing space for performing plasma processing.

The casing 4 is connected to a ground 5. A gas for plasma generation such as oxygen gas or a mixed gas containing oxygen gas is supplied from a gas supply unit 9 through a pipe 6 to the inside of the casing 4. The gas in the casing 4 is sucked in vacuum through the pipe 7. Reference numeral 8 denotes a vacuum suction pump.

A substrate 10 made of a resin material is mounted on the electrode portion 2. FIG. 2 shows the substrate 10. A metal electrode 1 made of copper or a copper alloy is provided on the upper surface of the substrate 10.
1 is formed, and an oxide film 12 having a thickness t of about 500 Å is formed on the surface of the electrode 11 by being heated in the heat treatment process. The oxide film 12 is a bonding property inhibitor that impairs bonding property in wire bonding in a later step, and therefore needs to be removed.

Next, the plasma processing performed to remove these bonding impediments will be described with reference to the flowchart of FIG. In FIG. 3, first, the substrate 10 is sent to the plasma processing step, and is mounted on the electrode unit 2 of the plasma processing apparatus shown in FIG. 1 (ST1). When the casing 4 is closed, the pump 8 is driven to vacuum-evacuate the inside of the casing 4 (ST2), and a plasma generating gas is supplied into the casing 4 through the pipe 6 (ST3). Here, a mixed gas containing H2 gas, which is a 10% reducing gas, and Ar gas is used as the plasma generating gas. The processing pressure at this time is set to about 10 Pa.

Next, the power supply 3 is inputted, a high-frequency voltage is applied to the electrode section 2, and plasma processing is performed for a predetermined time (ST).
4). That is, plasma of hydrogen and argon is generated in the casing 4 by the plasma discharge, whereby the oxide film 12 on the surface of the electrode 11 is removed. The processing time during the plasma processing is about 3 minutes. After the predetermined plasma processing time has elapsed, the power supply 3 is turned off to stop applying the high-frequency voltage (ST5). This stops the plasma discharge.

At this time, while the supply of the plasma generating gas into the casing 4 is continued as it is, the substrate 10 after the oxide film 12 is removed by the plasma treatment is cooled to room temperature in an atmosphere of a reducing gas. Is performed (ST6). Here, the aging time is set to about 3 minutes.

After a predetermined aging time has elapsed, nitrogen gas at normal pressure is introduced into the casing 4 through the pipe 6 (ST7). Thereby, the casing 4
The vacuum inside is broken, and the casing 4 can be opened. At the time of vacuum breaking, it is desirable to use nitrogen gas, but the atmosphere may be directly introduced after a predetermined aging with a reducing gas. After that, when the casing 4 is opened, the substrate 10 from which the oxide film has been removed on the electrode portion 2 is taken out (ST8), and the plasma processing is completed.

FIG. 4 shows the thickness of the oxide film and the composition ratio of oxygen and copper in the oxide film in various states of the electrode surface to be subjected to the plasma treatment. State 1 shows a state of spontaneous oxidation in which the substrate 10 is kept in the air at room temperature for a long time, and state 2 is a state in which the electrode 11 is kept at a high temperature (180 ° C.) by heat-treating the substrate 10. Indicates a state in which oxidation has progressed.

The state 5 is a state where the oxide film 12 is formed on the electrode 11 by the heat treatment in this manner.
Shows a state where plasma processing is performed under the conditions described in the present embodiment. According to this, it is found that the oxide film 12 formed on the surface of the electrode 11 by the heat treatment is improved by performing the above-described plasma treatment, compared to the oxidation state of the surface of the electrode 11 in the natural oxidation state (state 1). .

In states 3 and 4, the plasma processing using the same gas as the plasma generating gas used in the plasma processing described in this embodiment is performed for 30 seconds and 2 minutes, respectively, and then the state is opened to the atmosphere. State 6 shows a state in which aging has been performed using nitrogen gas after plasma treatment with the same gas.

According to these data, even if plasma treatment is performed using the same reducing gas, aging is performed by nitrogen gas without using the reducing gas, when the treatment is released to the atmosphere as it is. In each case, it is found that an oxide film thicker than the naturally oxidized state is formed in a short time, and good processing quality is not ensured.

As described above, after the plasma processing using a reducing gas for the purpose of removing an oxide film, the object to be processed is left as it is in the reducing gas for a predetermined time to perform aging. It is possible to suppress the progress of oxidation and to ensure good plasma processing quality.

[0022]

According to the present invention, after the plasma processing is performed using the plasma generating gas containing the reducing gas, the object to be processed is cooled to the normal temperature in the reducing gas following the plasma processing. Therefore, the cleaned surface immediately after the treatment can be prevented from coming into direct contact with oxygen and reoxidation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a plasma processing apparatus according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a substrate to be subjected to plasma processing according to one embodiment of the present invention;

FIG. 3 is a flowchart of a plasma processing method according to an embodiment of the present invention;

[Explanation of symbols]

 10 Substrate 11 Electrode 12 Oxide film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/32 H01L 21/302 NF term (Reference) 4G075 AA30 BA06 CA03 CA25 CA47 DA02 EC21 4K057 DA01 DB04 DD01 DE14 DE20 DK10 DN02 5E319 AA03 AA07 AB05 CD01 5F004 AA14 DA24 DB13 5F044 KK01

Claims (2)

[Claims] 1. A plasma processing method for removing an oxide film on an electrode surface by subjecting a processing object having an electrode whose surface is made of copper or a copper alloy to plasma treatment, wherein the processing object is treated with a reducing gas. A plasma processing method, comprising: performing a plasma process using a plasma generating gas including the plasma process; and cooling the process target to a normal temperature in a reducing gas atmosphere following the plasma process. 2. The plasma processing method according to claim 1, wherein said reducing gas is hydrogen gas.