JP2003064479A - Pre-treatment of electroless plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the selectivity of electroless plating by removing negative charge on the surface of an insulating film of a substrate. SOLUTION: A pre-treatment of electroless plating for forming a plating film on the substrate 51 by electroless plating is carried out to remove negative charge on the surface of the substrate 51 by applying AC power from an AC power source 18 on the surface of the substrate 51 opposite from the surface on which the plating film of the substrate 51 is formed by dipping the substrate 51 into an electrolyte 41. As the pre-treatment, the negative charge on the surface of the substrate 51 may be removed by applying DC bias power while applying AC power or may be removed while applying pulse power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for electroless plating, and more particularly to a pretreatment method for electroless plating for forming a thin film of a metal or a metal compound used in a semiconductor device.

[0002]

2. Description of the Related Art Copper wiring provides lower resistance, lower capacitance, and higher reliability than aluminum wiring, and therefore becomes more important in fine prevention in which circuit delay due to parasitic resistance and parasitic capacitance of the wiring dominates. Is coming. Grooved wiring technology (eg, damascene process) is widely accepted as the most common method of forming copper wiring. However, a silicon nitride (SiN) film having a high relative permittivity of 7 is used as a cap film in order to cover the copper surface which is easily oxidized, and as a result, there is a disadvantage that the parasitic capacitance of the entire wiring system is increased.

Further, although copper has the physical properties expected to have high electromigration resistance,
Since the surface is chemically unstable, the interface between copper and silicon nitride acts as a preferential diffusion path for copper, and there is a problem that the expected high electromigration resistance (reliability) cannot be obtained. Therefore, a cobalt tungsten phosphorus (CoWP) film formed by electroless plating is used for the purpose of simplifying the complicated copper wiring process, which is the above-mentioned problem, and not using the silicon nitride film, which has many problems in terms of reliability and parasitic capacitance. (S. Lopatin et al., Pr
oc. of Advanced Metallization Conference (1997) p.
See 437).

The CoWP film is selectively formed only on copper exposed by electroless plating. This film-forming selectivity is obtained by coating the copper surface with palladium by substitution electroless plating with copper before carrying out CoWP electroless plating, so that CoWP film formation uses palladium as a catalyst over palladium. It is due to occurring only in. Once the palladium surface was coated with CoWP, the continuous deposition of CoWP on CoWP was
Proceeding while maintaining selective film formation by self-catalytic plating using WP confidence as a catalyst.

[0005]

However, palladium obtains a negative charge (free electron) from copper and coats the copper surface. Therefore, in order to maintain high selectivity, it is very important to completely eliminate the negative charges on the insulating film.

[0006]

The present invention is a pretreatment method for electroless plating, which has been made to solve the above problems.

The first pretreatment method for electroless plating according to the present invention is a pretreatment method for electroless plating in which a plating film is formed on a substrate by electroless plating. A pretreatment for removing negative charges on the surface of the substrate is performed while applying AC power to the side of the substrate opposite to the side where the plating film is formed.

In the first electroless plating pretreatment method, the substrate is immersed in an electrolytic solution different from the plating solution, and an alternating current is applied to the side of the substrate opposite to the side where the plating film is formed (the back surface of the substrate). Is applied. As a result, the side of the substrate on which the plated film is formed (the substrate surface) is negatively charged, so that negative charges such as negative ions remaining on the substrate surface are removed. The reason why an AC voltage is applied to the back surface of the substrate is that, unlike DC, the polarity of the voltage is switched, so that charge-up of the substrate can be prevented. Therefore, it is possible to sufficiently suppress the influence on the device. Further, after removing the negative charges on the surface of the substrate, the substrate is immersed in an electroless plating solution to form CoWP or NiWP. In addition, a frequency at which ions in the electrolytic solution can sufficiently follow may be selected as the alternating current frequency.

A second pretreatment method for electroless plating according to the present invention is a pretreatment method for electroless plating in which a plating film is formed on a substrate by electroless plating, wherein the substrate is immersed in an electrolytic solution and A pretreatment is performed to apply a DC bias power to the side of the substrate opposite to the side where the plating film is formed and to remove the negative charges on the surface of the substrate while applying an AC power.

In the second pretreatment method for electroless plating, the substrate is immersed in an electrolytic solution different from the plating solution, and DC bias power is applied to the side of the substrate opposite to the side where the plating film is formed. In addition, since the pretreatment for removing the negative charges on the surface of the substrate is performed while applying the AC power, the substrate can be always negatively biased. As described above, by applying the DC voltage and the AC voltage in combination, it is possible to always apply the negative bias to the substrate and efficiently remove the negative charges. As a result, the side of the substrate on which the plated film is formed (the substrate surface) is negatively charged, so that negative charges such as negative ions remaining on the substrate surface are removed. Further, after removing the negative charges on the surface of the substrate, the substrate is immersed in an electroless plating solution to form CoWP or NiWP. Also,
As the frequency of the alternating current, a frequency with which the ions in the electrolytic solution can sufficiently follow may be selected. Further, as the frequency of the alternating current applied to the substrate, it is sufficient to select a frequency at which the ions serving as the film-forming species for plating can sufficiently follow.

A third electroless plating pretreatment method of the present invention is an electroless plating pretreatment method of forming a plating film on a substrate by electroless plating, wherein the substrate is immersed in an electrolytic solution to form Pretreatment is performed to remove negative charges on the surface of the substrate while applying pulsed power to the side of the substrate opposite to the side where the plated film is formed.

In the third pretreatment method for electroless plating, the substrate is immersed in an electrolytic solution different from the plating solution, and pulsed power is applied to the side of the substrate opposite to the side where the plated film is formed. While performing the pretreatment for removing the negative charges on the substrate surface, the insulating film (not shown) formed on the substrate is prevented from being charged, as in the first electroless plating pretreatment method. The uniformity of the film thickness distribution in the surface of the substrate is improved without affecting the reliability of.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, an example of a pretreatment apparatus used in the first pretreatment method for electroless plating of the present invention will be described with reference to the schematic sectional view of FIG.

As shown in FIG. 1, a first pretreatment device 1
Is provided with an electrolytic solution tank 11. An electrode 12 is installed, for example, at the bottom of the electrolytic solution tank 11. A DC power supply 13 is connected to this electrode 12.

Further, the electrolytic solution tank 11 is provided with a substrate holding portion 14 for holding the substrate 51 at a position facing the electrode 12. The substrate holding portion 14 is provided with an electrode 15 for supplying electric power to the conductive film 52 formed on the surface of the substrate 51 held on the electrode 12 side of the substrate holding portion 14. This electrode 15 is grounded, for example.

Further, the AC applying electrode 17 is insulated from the electrode 15 by an insulating material 16, and the AC applying electrode 17 is attached to the substrate holding portion 1.
It is provided so as to be connected to the back surface side of the substrate 51 held by No. 4. An AC power supply 18 is connected to the AC applying electrode 17. This AC power source 18 is, for example, 10 Hz
It consists of a device that oscillates an alternating current having a frequency of about 1 kHz.

The electrolytic solution tank 11 is filled with an electrolytic solution 41. As the electrolytic solution 41, for example, ionic water, ammonia water, an aqueous potassium hydroxide solution, or the like can be used.

In the first pretreatment apparatus 1, the AC applying electrode 17 is connected to the side (rear side) of the substrate 51 opposite to the side where the plating film is formed, and AC power is applied to the AC applying electrode 17. Since the AC power supply 18 for applying the voltage is provided, when performing the pretreatment of the substrate 51, it is possible to apply the DC power from the DC power supply 13 to the electrode 12 and the AC power supply to the substrate 51. Therefore, when an AC voltage is applied to the back surface of the substrate 51, the voltage is switched between positive and negative, unlike DC.

As the frequency of the alternating current applied to the substrate 51,
It suffices to select a frequency at which the ions to be the pretreatment species can sufficiently follow.

Next, an embodiment of the first pretreatment method for electroless plating according to the present invention will be described with reference to the schematic diagram of FIG.

As an example, a case will be described in which the AC power supply 18 shown in FIG. 1 is one that generates AC power having a frequency of 350 Hz, and the pretreatment is performed by applying AC power of 350 Hz to the substrate 51. As an example of this pretreatment condition, ion water is used as the electrolytic solution 41 and the electrolytic solution temperature is set to 1
At 8 ° C., the DC pretreatment voltage applied to the electrode 12 from the DC power supply 13 is 1.3 V, and the AC application electrode 17 is applied from the AC power supply
AC power to be applied to the
0 Hz) was set to 30 W and pretreatment was performed for 1 minute.

After that, a CoWP film was formed by electroless plating. As a result, the CoWP film could be formed only on copper without breaking the selectivity.

In the first electroless plating pretreatment method, direct current is applied to the electrode 12 from the direct current power source 13 and alternating current power is applied to the side of the substrate 51 opposite to the side on which the plating film is formed. However, since a plating film is formed on the substrate 51, when an AC voltage is applied to the back surface of the substrate 51, the positive / negative of the voltage is switched unlike the direct current.

As the frequency of the alternating current applied to the substrate 51,
It suffices to select a frequency at which the ions forming the plating film formation species can sufficiently follow. For example, when the film formation species is copper, 10
It is preferable to select about Hz to 1 kHz. If 1
When an alternating current having a frequency of less than 0 Hz is applied,
The in-plane uniformity of the pretreatment surface is likely to deteriorate, and when the frequency of the alternating current exceeds 1 kHz, the trackability of ions of the film-forming species deteriorates.

As described above, by applying an alternating current of 10 Hz to 1 kHz to the substrate 51, the insulating film (not shown) formed on the substrate 51 is prevented from being charged, and the reliability of the device is not affected. The negative charges on the surface of the insulating film (not shown) formed on the substrate 51 can be removed.

Next, an example of the second pretreatment apparatus used in the second pretreatment method for electroless plating of the present invention will be described with reference to the schematic diagram of FIG.

As shown in FIG. 2, the second pretreatment device 2
Is provided with an electrolytic solution tank 11. An electrode 12 is installed, for example, at the bottom of the electrolytic solution tank 11. A DC power supply 13 is connected to this electrode 12.

Further, the electrolytic solution tank 11 is provided with a substrate holding portion 14 for holding the substrate 51 at a position facing the electrode 12. The substrate holding portion 14 is provided with an electrode 15 for supplying electric power to the conductive film 52 formed on the surface of the substrate 51 held on the electrode 12 side of the substrate holding portion 14. This electrode 15 is grounded, for example.

Further, the bias applying electrode 27 is provided so as to be connected to the back side of the substrate 51 held by the substrate holding portion 14 while being insulated from the electrode 15 by the insulating material 16. A negative side of a DC power supply 28 is connected to the bias applying electrode 27, and an AC power supply 18 is connected to the positive side of the DC power supply 28. That is, the bias applying electrode 27, the DC power supply 28, and the AC power supply 18 are connected in series. The AC power source 18 is, for example, 10 Hz-
It consists of a device that oscillates an alternating current with a frequency of about 1 kHz.

The electrolytic solution tank 11 is filled with an electrolytic solution 41. As the electrolytic solution 41, for example, ionic water, ammonia water, an aqueous potassium hydroxide solution, or the like can be used.

In the second electrolytic plating apparatus 2, the substrate 5
The bias applying electrode 27 is connected to the side opposite to the side where the plating film of No. 1 is formed, and the DC power is applied to the bias applying electrode 27. In order to pretreat the substrate 51, the direct current power supply 13 applies a direct current to the electrode 12 and the substrate 12 It is possible to apply a combination of a DC voltage and an AC voltage to the back surface of the substrate 51, which allows the substrate 51 to be always negatively biased.

Further, as the frequency of the alternating current applied to the substrate 51, it is sufficient to select a frequency at which the ions to be the pretreatment species can sufficiently follow.

Next, an embodiment of the second pretreatment method for electroless plating according to the present invention will be described with reference to the schematic diagram of FIG.

As an example, the AC power supply 18 shown in FIG. 1 is one that generates AC power having a frequency of 100 Hz, and the AC power of 100 Hz is applied to the substrate 51 and a negative bias is applied by the DC power supply 28. Then, the case where pre-processing is performed will be described. As an example of this pretreatment condition, ammonia water is used as the electrolytic solution 41 and the electrolytic solution temperature is set to 1
At 8 ° C., a DC pretreatment voltage applied from the DC power supply 13 to the electrode 12 is 1.3 V, a DC voltage applied from the AC power supply 18 to the bias applying electrode 27 is 2 V, and AC power (for example, 100 Hz as low frequency AC power) is applied. Set to 30W, 30
Pretreatment for 2 seconds was performed.

After that, a CoWP film was formed by electroless plating. As a result, the CoWP film could be formed only on copper without breaking the selectivity.

In the second pretreatment method for electroless plating, direct current is applied to the electrode 12 from the direct current power source 13 and at least direct current bias power is applied to the side of the substrate 51 opposite to the side on which the plating film is formed. Since the substrate 51 is pre-processed while being applied, the substrate 51 can always be negatively biased.

Further, as the frequency of the alternating current applied to the substrate 51, it is sufficient to select a frequency at which the ions as the pretreatment species can sufficiently follow. For example, it is preferable to select about 10 Hz to 1 kHz. If an alternating current having a frequency of less than 10 Hz is applied, the in-plane uniformity of the pretreated surface tends to deteriorate, and if the alternating current frequency exceeds 1 kHz, the followability of the ions of the pretreated species deteriorates. .

As described above, since the negative bias can be applied to the center of the substrate 51, the insulating film (not shown) formed on the substrate 51 is prevented from being charged, and the reliability of the device is affected. First, it becomes possible to remove the negative charges on the surface of the insulating film (not shown) formed on the substrate 51.

Next, an example of a third pretreatment apparatus used in the third pretreatment method for electroless plating of the present invention will be described with reference to the schematic configuration diagram of FIG.

As shown in FIG. 3, as shown in FIG. 3, the third pretreatment apparatus 3 includes an electrolytic solution tank 11. An electrode 12 is installed, for example, at the bottom of the electrolytic solution tank 11.
A DC power supply 13 is connected to this electrode 12.

Further, the electrolytic solution tank 11 is provided with a substrate holding portion 14 for holding the substrate 51 at a position facing the electrode 12. The substrate holding portion 14 is provided with an electrode 15 for supplying electric power to the conductive film 52 formed on the surface of the substrate 51 held on the electrode 12 side of the substrate holding portion 14. This electrode 15 is grounded, for example.

Further, the pulse wave applying electrode 37 is provided so as to be connected to the back surface side of the substrate 51 held by the substrate holding portion 14 while being insulated from the electrode 15 by the insulating material 16. A pulse wave generating power source 38 is connected to the pulse wave applying electrode 37.

The electrolytic solution tank 11 is filled with the electrolytic solution 41. As the electrolytic solution 41, for example, ionic water, ammonia water, an aqueous potassium hydroxide solution, or the like can be used.

In the third pretreatment apparatus 3, the pulse wave applying electrode 37 is connected to the side of the substrate 51 opposite to the side where the plating film is formed, and pulse power is applied to the pulse wave applying electrode 37. Since the pulse wave applying power source 38 is provided, the insulating film (not shown) formed on the substrate 51 is prevented from being charged, as in the case of the first pretreatment apparatus 1, thus affecting the reliability of the device. It is possible to remove the negative charges on the surface of the insulating film of the substrate 51 without applying the charge.

Next, an embodiment relating to the third pretreatment method for electroless plating of the present invention will be described with reference to the schematic configuration diagram of FIG.

As an example, a case will be described in which the pulse wave power source 38 shown in FIG. 3 applies pulse wave power to the back surface of the substrate 51 to perform pretreatment for electroless plating. As an example of this pretreatment condition, an aqueous solution of potassium hydroxide is used as the electrolyte 41, the temperature of the electrolyte is 18 ° C., the DC pretreatment voltage applied from the DC power supply 13 to the electrode 12 is 1.3 V, and the pulse wave application power supply is used. The pulse wave voltage applied from 38 to the pulse application electrode 37 is -2 V (pulse cycle: 3 ms, pulse width 3
0 μs) and plating was performed for 1 minute and 30 seconds.

After that, a CoWP film was formed by electroless plating. As a result, the CoWP film could be formed only on copper without breaking the selectivity.

In the third pretreatment method for electroless plating, direct current is applied to the electrode 12 from the direct current power source 13 and pulse power is applied to the side of the substrate 51 opposite to the side where the plated film is formed. However, since the substrate 51 is subjected to the pretreatment, as in the first electroless plating pretreatment method,
The insulating film (not shown) formed on the substrate 51 is prevented from being charged, and the reliability of the device is not affected.
It becomes possible to remove the negative charges on the surface of the first insulating film (not shown).

In each of the above-mentioned embodiments, the pretreatment for forming the CoWP film by electroless plating has been described. However, the pretreatment method for electroless plating of the present invention is performed when electrolessly plating another material. It can also be applied to pretreatment.
For example, it can be applied to a pretreatment for forming a nickel tungsten phosphorus (NiWp) film in electroless copper plating with a palladium catalyst.

[0050]

As described above, according to the first pretreatment method for electroless plating of the present invention, the AC power is applied to the side of the substrate opposite to the side where the plated film is formed. Since the pretreatment of the substrate is performed, the insulating film formed on the substrate can be prevented from being charged, and the negative charge on the substrate surface can be removed without affecting the reliability of the device.

According to the second pretreatment method for electroless plating of the present invention, the pretreatment of the substrate is performed while applying at least DC bias power to the side of the substrate opposite to the side where the plated film is formed. Therefore, the substrate can always be negatively biased. Therefore, the insulating film formed on the substrate can be prevented from being charged, the reliability of the device is not affected, and the negative charge on the substrate surface can be removed.

According to the third pretreatment method for electroless plating of the present invention, the pretreatment of the substrate is performed while applying the pulse power to the side of the substrate opposite to the side where the plated film is formed.
The insulating film formed on the substrate can be prevented from being charged, and the negative charge on the surface of the insulating film on the substrate can be removed without affecting the reliability of the device.

Therefore, by any of the pretreatment methods,
For example, the negative charges attached to the surface of the insulating film formed on the substrate can be removed. Therefore, for example, it becomes impossible to supply free electrons to palladium except for the surface of copper, which is a metal. For this reason, CoW is maintained with high selectivity.
It is possible to selectively form a film of P, NiWP or the like by electroless plating. Further, since AC is used also in the surface treatment, the selectivity of electroless plating can be improved without affecting the reliability of the device.

[Brief description of drawings]

FIG. 1 is a schematic configuration sectional view showing an embodiment of a first pretreatment method for electroless plating according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an embodiment of a second pretreatment method for electroless plating according to the present invention.

FIG. 3 is a schematic cross-sectional view showing an embodiment of a third pretreatment method for electroless plating of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pretreatment apparatus, 17 ... AC application electrode, 18 ... AC power supply, 51 ... Substrate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuru Taguchi             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Naoki Komai             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F-term (reference) 4K022 AA02 AA05 AA41 BA06 BA14                       BA16 BA24 BA32 CA16 CA29                       DA01                 4M104 BB04 BB05 BB18 BB36 DD21                       DD47 DD53 FF16                 5F033 HH07 HH11 HH15 HH19 MM01                       MM05 MM13 PP28 QQ00

Claims (3)

[Claims] 1. A pretreatment method of electroless plating for forming a plating film on a substrate by electroless plating, wherein the side of the substrate on which the plating film is formed by immersing the substrate in an electrolytic solution. A pretreatment method for electroless plating, which comprises performing a pretreatment for removing negative charges on the surface of the substrate while applying AC power to the opposite side. 2. A pretreatment method of electroless plating for forming a plating film on a substrate by electroless plating, wherein the side of the substrate on which the plating film is formed by immersing the substrate in an electrolytic solution. A pretreatment method for electroless plating, characterized in that a pretreatment for removing negative charges on the surface of the substrate is performed while applying DC bias power to the opposite side and applying AC power. 3. A pretreatment method of electroless plating for forming a plating film on a substrate by electroless plating, wherein the side of the substrate on which the plating film is formed by immersing the substrate in an electrolytic solution. A pretreatment method for electroless plating, which comprises performing a pretreatment for removing negative charges on the surface of the substrate while applying pulsed power to the opposite side.