JP3960080B2 - Plasma processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method performed for the purpose of surface modification of a resin substrate.
[0002]
[Prior art]
In a substrate on which a semiconductor element is mounted, the surface of the substrate is subjected to plasma treatment prior to mounting of the semiconductor element by a flip chip method, wire bonding or resin sealing after the semiconductor element is mounted. This plasma treatment is performed for the purpose of improving the bondability by cleaning the surface of the bonding point of wire bonding, or for the purpose of improving the adhesion of the sealing resin by modifying the resin surface of the substrate. is there. Among these, in plasma processing performed for the purpose of surface modification, oxygen is used as a plasma generating gas, and the resin surface is modified by the chemical action of an active substance such as oxygen radicals generated by plasma discharge.
[0003]
[Problems to be solved by the invention]
However, in the above-described plasma treatment, a sputtering effect that removes a substance on the resin surface by a physical action caused by collision of charged particles such as oxygen ions and electrons occurs in addition to a surface modification effect by a chemical action of an active substance. . And if this sputtering is performed excessively, the resin surface is damaged, resulting in a decrease in adhesion with the sealing resin, which is contrary to the original processing purpose. For this reason, in the conventional plasma processing for the purpose of surface modification of the resin substrate, there is a problem that it is difficult to prevent the substrate from being damaged and to perform efficient plasma processing.
[0004]
Therefore, an object of the present invention is to provide a plasma processing method capable of efficiently performing plasma processing while preventing damage to the substrate in plasma processing for the purpose of surface modification of a resin substrate.
[0005]
[Means for Solving the Problems]
The plasma processing method according to claim 1 is a vacuum chamber, a pair of electrodes disposed opposite to each other in the vacuum chamber, and a resin substrate to be processed disposed in a plasma processing space between the electrodes. A substrate mounting portion on which is mounted, a high frequency power supply portion that applies a high frequency voltage to the electrode, a power supply control portion that controls the high frequency power supply portion, a vacuum exhaust portion that evacuates the vacuum chamber, A plasma processing method for modifying the surface of a resin substrate by a plasma processing apparatus having a gas supply unit for supplying a plasma generating gas containing a reactive gas in a vacuum chamber, wherein the output of the high-frequency power unit and the the Rukoto plasma is generated under the condition where the process pressure by controlling the process pressure in the plasma generating gas in the plasma processing space exceeds 50 [Pa], between the pair of electrodes Self-bias voltage is the processing pressure 50 of the pressure [Pa] or lower processing the resin substrate surface by charged particles generated in the plasma processing space by a plasma discharge between said smaller as compared with the case electrode in pressure conditions In addition to preventing the sputtering effect on the surface of the resin substrate from being damaged by sputtering, the surface of the resin substrate is modified by the chemical action of the active material generated in the plasma processing space.
[0007]
According to the present invention, the sputtering effect on the resin substrate surface by the charged particles generated in the plasma processing space by the plasma discharge between the electrodes is controlled by controlling the output of the high frequency power supply and the processing pressure of the plasma generating gas in the plasma processing space. By preventing the allowable upper limit from being exceeded, damage to the resin substrate surface due to sputtering can be prevented, and surface modification of the resin substrate can be performed by the chemical action of the active substance generated in the plasma processing space.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described 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 an explanatory diagram of a state of a plasma processing space in the plasma processing method of an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a graph showing the interelectrode voltage in the plasma processing method according to one embodiment of the present invention.
[0009]
First, the plasma processing apparatus will be described with reference to FIG. In FIG. 1, a pair of a lower electrode 3 and an upper electrode 5 are disposed inside the vacuum chamber 1 so as to face each other. The lower part of the lower electrode 3 penetrates the bottom surface of the vacuum chamber 1 through the insulator 2 and protrudes to the outside, and the upper part of the upper electrode 5 penetrates the upper surface of the vacuum chamber 1 and is connected to the grounding part 6. . A space between the lower electrode 3 and the upper electrode 5 is a plasma processing space 7, and a substrate 4 made of a resin material to be subjected to plasma processing is placed on the upper surface of the lower electrode 3. The upper surface of the lower electrode 3 serves as a substrate mounting portion for mounting the substrate 4 to be processed.
[0010]
Two openings 1a and 1b are provided on the bottom surface of the vacuum chamber 1, and the openings 1a and 1b are connected to a vacuum exhaust part 9 and a gas supply part 10, respectively. By driving the evacuation unit 9, the inside of the vacuum chamber 1 is evacuated. Further, by driving the gas supply unit 10, a plasma generating gas containing a reactive gas such as oxygen gas is supplied into the vacuum chamber 1.
[0011]
When the vacuum exhaust unit 9 and the gas supply unit 10 are driven, the control unit 12 controls the vacuum exhaust unit 9 and the gas supply unit 10 so that the degree of vacuum inside the vacuum chamber 1 and the plasma generated in the vacuum chamber 1 are generated. The supply amount of the working gas can be controlled, and therefore the pressure of the plasma generating gas (processing pressure) in the plasma processing space 7 in the vacuum chamber 1 can be set to a predetermined pressure.
[0012]
The lower electrode 3 is connected to a high frequency power supply unit 8 controlled by the power supply control unit 11. By driving the high frequency power supply unit 8, a high frequency voltage is applied between the upper electrode 5 and the lower electrode 3. The By driving the high frequency power supply unit 8 with the plasma generating gas supplied after the vacuum chamber 1 is evacuated, plasma of the plasma generating gas containing oxygen gas is generated in the plasma processing space 7. At this time, the processing pressure in the vacuum chamber 1 and the output of the high frequency power supply unit 8 are set to desired conditions by controlling the vacuum exhaust unit 9, the gas supply unit 10, and the power supply control unit 11 by the control unit 12. Can be done.
[0013]
Next, the state of the plasma processing space 7 when the plasma is generated by the plasma generating gas containing the oxygen gas will be described with reference to FIG. As shown in FIG. 2, a plasma discharge is generated by applying a high frequency voltage (interelectrode voltage) V between the lower electrode 3 and the upper electrode 5, whereby oxygen gas plasma (broken line) is generated in the plasma processing space 7. 13), and charged particles such as oxygen ions O ⁺ and electrons e ⁻ and oxygen radicals O ^* are generated. Oxygen ions O ⁺ and electrons e ⁻ are particles having a positive charge and a negative charge, respectively. The oxygen radicals O ^* are electrically neutral particles oxygen atom is activated. Here, an example is shown in which oxygen is used as the plasma generating gas, but chlorine, fluorine, bromine, or a mixture thereof may be used.
[0014]
When the substrate 4 to be processed is placed on the lower electrode 3 in a state where such plasma is generated, a physical action by charged particles such as the above-described oxygen ions O ⁺ and electrons e ⁻ is formed on the upper surface of the substrate 4. That is, a sputtering effect due to collision of these charged particles with the surface of the substrate 4 acts. Thereby, the surface of the resin material constituting the substrate 4 is partially removed. Simultaneously with the sputtering effect, the surface of the resin surface of the substrate 4 is modified by the chemical action of oxygen radical O ^* which is an active substance.
[0015]
Next, an example of the plasma processing method will be described with reference to FIGS. FIG. 3 shows the correlation between the etching rate and the processing pressure obtained based on the result of the systematic plasma processing test using the above-described plasma processing apparatus. That is, when the high-frequency output of the high-frequency power supply unit 8 is set to 600 W, the test is performed when the gas supply unit 10 is controlled to gradually increase the flow rate (horizontal axis) of oxygen gas supplied into the vacuum chamber 1. The surface removal amount (vertical axis) per unit time of the substrate is shown in a graph.
[0016]
As can be seen from FIG. 3, the etching rate gradually decreases as the flow rate of the oxygen gas is gradually increased to increase the processing pressure. It can be seen that the etching rate is almost zero at a specific processing pressure or higher, and that the sputtering effect on the resin surface hardly occurs. Incidentally, even when the sputtering effect does not occur, as long as the oxygen radicals O ^* generated by the plasma discharge is present in the vicinity of the surface of the substrate 4, the resin surface of the substrate 4 oxygen radical O ^* chemical The action is not affected and the surface modification effect is not impaired.
[0017]
That is, in the plasma processing method of the present embodiment, when the plasma processing for the purpose of surface modification of the resin substrate 4 is performed by the above-described plasma processing apparatus, the output of the high frequency power supply unit 8 and the plasma processing space 7 By controlling the processing pressure of the plasma generating gas, the sputtering effect on the surface of the substrate 4 by the charged particles generated in the plasma processing space 7 by plasma discharge does not exceed the allowable upper limit, and thus the excessive sputtering of the surface of the substrate 4 is performed. In addition to preventing damage, the surface modification of the substrate 4 is performed by the chemical action of the active substance (oxygen radical O ^* ) generated in the plasma processing space 7.
[0018]
Here, a specific example of processing conditions in the plasma processing method will be described. As described above, this processing condition is obtained from the results of tests performed using an actual plasma processing apparatus. As shown in FIG. 3, in the measured example of the etching rate when the high frequency output of the high frequency power supply unit 8 is set to 600 W, the etching rate is almost zero at the processing pressure of 57.5 [Pa]. Therefore, if a processing pressure (50 [Pa]) somewhat lower than this pressure is set as the lower limit of the practical processing pressure, the surface modification is performed without exerting an excessive sputtering effect on the resin surface of the substrate 4. Only the effect can be secured. That is, in the present embodiment, plasma treatment for surface modification is performed under the condition of a treatment pressure of 50 [Pa] or higher. Of course, it goes without saying that the pressure condition is such that stable plasma can be generated in relation to the high frequency output.
[0019]
Next, the interelectrode voltage V in the plasma processing will be described with reference to FIG. FIG. 4A shows an application pattern of a high-frequency voltage generated by the high-frequency power supply unit 8, and an alternating voltage having a regular stepped waveform is applied. On the other hand, FIG. 4B shows the interelectrode voltage V (lower part shown in FIG. 2) when the alternating voltage having the waveform shown in FIG. 4A is applied under the processing conditions where the processing pressure in the plasma processing space 7 is low. The potential difference actually generated between the electrode 3 and the upper electrode 5 is shown.
[0020]
That is, when an alternating voltage is applied between the electrodes, the charging state of the lower electrode 3 on which the substrate 4 is placed alternately repeats positive and negative. When the lower electrode 3 is charged with a positive charge, electrons e ⁻ which are negative charges among the charged particles generated in the plasma processing space 7 move toward the substrate 4 and reach the surface of the substrate 4. Thus, a negative charge is applied to the substrate 4. On the other hand, when the lower electrode 3 is charged with a negative charge, oxygen ions O ⁺ that are positive charges among the charged particles generated in the plasma processing space 7 move toward the substrate 4 and move to the surface of the substrate 4. It reaches and gives a positive charge to the substrate 4.
[0021]
At this time, since the electron e ⁻ has a remarkably smaller mass than the oxygen ion O ⁺ , the electron e ⁻ quickly reaches the surface of the substrate 4, and the electron e ⁻ reaches the substrate 4 within a unit time. There are many. Accordingly, a large amount of negative charge is applied to the substrate 4 per unit time, and as a result, the interelectrode voltage V decreases during application of the alternating voltage (see A shown in FIG. 4B). On the other hand, when the lower electrode 3 is negatively charged and the oxygen ions O ⁺ move with respect to the substrate 4, the moving speed is slow because the mass of the oxygen ions O ⁺ is large, and the substrate 4 within a unit time. The number of oxygen ions O ⁺ that reach is small. Accordingly, the positive charge given to the substrate 4 per unit time is very small, and the decrease in the interelectrode voltage V (negative voltage) during application of the alternating voltage is small (see B shown in FIG. 4B).
[0022]
By repeating such a voltage change every time an alternating voltage is applied, the interelectrode voltage V gradually moves to the negative side, and is biased by a voltage value on the negative side (self-bias voltage Vdc) in a steady state. It becomes a shape. The energy when the oxygen ions O ⁺ collide against the substrate 4 increases in accordance with the self-bias voltage Vdc increases, together with the oxygen ions O ⁺ by sputtering effect increases, electrons e ^- sputtering effect is to Superimposed.
[0023]
On the other hand, FIG. 4C shows the inter-electrode voltage V when the plasma is generated under a condition where the processing pressure in the plasma processing space 7 is high and exceeds 50 [Pa]. Under such high pressure processing conditions, the gas density in the vacuum chamber 1 is high, and since many particles such as oxygen ions O ⁺ and oxygen radicals O ^* exist in the plasma processing space 7, the electrons e ⁻ are generated. The probability of colliding with these particles in the process of moving toward the substrate 4 is high.
[0024]
Therefore, as compared with the case shown in FIG. 4B, the number of electrons e ⁻ reaching the surface of the substrate 4 is small, and the decrease in the interelectrode voltage V during application of the alternating voltage is small. As a result, the self-bias voltage Vdc is smaller than that under the low processing pressure condition shown in FIG. 4B, and the sputtering effect due to collision of oxygen ions O ⁺ against the substrate 4 can be suppressed. it can. Therefore, plasma processing for the purpose of surface modification of the substrate 4 can be efficiently performed without causing damage to the resin surface of the substrate 4 due to excessive sputtering.
[0025]
【The invention's effect】
According to the present invention, the sputtering effect on the resin substrate surface by the charged particles generated in the plasma processing space by the plasma discharge between the electrodes by controlling the output of the high-frequency power source and the processing pressure of the plasma generating gas in the plasma processing space. By preventing the above from exceeding the allowable upper limit, the resin substrate surface can be prevented from being damaged by sputtering, and the surface modification of the resin substrate can be performed by the chemical action of the active substance generated in the plasma processing space.
[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 an explanatory diagram of a state of a plasma processing space in a plasma processing method according to an embodiment of the present invention. FIG. 4 is a graph showing the correlation between the gas flow rate and the etching rate in the plasma processing method according to the embodiment. FIG. 4 is a graph showing the interelectrode voltage in the plasma processing method according to the embodiment of the invention.
DESCRIPTION OF SYMBOLS 1 Vacuum chamber 3 Lower electrode 4 Substrate 5 Upper electrode 7 Plasma processing space 8 High frequency power supply part 9 Vacuum exhaust part 10 Gas supply part 11 Power supply control part

Claims (1)

A vacuum chamber, a pair of electrodes arranged opposite to each other in the vacuum chamber, and a substrate platform on which a processing target resin substrate is placed and disposed in a plasma processing space between these electrodes; A high-frequency power supply unit that applies a high-frequency voltage to the electrodes, a power supply control unit that controls the high-frequency power supply unit, a vacuum exhaust unit that evacuates the vacuum chamber, and a plasma containing a reactive gas in the vacuum chamber A plasma processing method for modifying the surface of a resin substrate by a plasma processing apparatus including a gas supply unit for supplying a gas for generation,
The Rukoto plasma is generated under the condition in which the said treatment pressure output and the controls the process pressure of the plasma generating gas in the plasma processing space of the high-frequency power supply unit is more than 50 [Pa], between the pair of electrodes Resin substrate surface due to charged particles generated in the plasma processing space by plasma discharge between the electrodes by reducing the self-bias voltage of the voltage as compared with the case where the processing pressure is lower than 50 [Pa]. The surface of the resin substrate is modified by the chemical action of the active substance generated in the plasma processing space, while preventing the sputtering effect on the resin substrate from exceeding the allowable upper limit to prevent damage due to sputtering of the resin substrate surface. Plasma processing method.

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