JP4346593B2 - Wiring formation method - Google Patents

Description

  The present invention relates to a wiring formation method, and more particularly to a wiring formation method in which a conductor such as copper or silver is embedded in a fine recess for wiring formed on the surface of a semiconductor substrate such as a semiconductor wafer.

  In recent years, as a metal material for forming a wiring circuit on a semiconductor substrate, a movement of using copper (Cu) having a low electrical resistivity and a high electromigration resistance instead of aluminum or an aluminum alloy has become prominent. This type of copper wiring is generally formed by embedding copper in a fine wiring recess provided on the surface of the substrate. As a method of forming this copper wiring, there are methods such as CVD, sputtering and plating, and plating is generally used, but in any case, copper is formed on almost the entire surface of the substrate, and chemical mechanical polishing is performed. Unnecessary copper is removed by (CMP).

FIG. 16 shows a manufacturing example of this type of copper wiring board W in the order of steps. As shown in FIG. 16A, on a conductive layer 1a on a semiconductor substrate 1 on which a semiconductor element is formed, for example, An insulating film 2 made of SiO ₂ is deposited, a contact hole 3 and a wiring groove 4 are formed in the insulating film 2 by, for example, lithography / etching technique, and a barrier film 5 made of TaN or the like is further formed thereon. A copper seed layer 6 is formed thereon as a power supply layer for electrolytic plating by sputtering or the like.

  Then, as shown in FIG. 16 (b), the surface of the substrate W is plated with copper so that the contact holes 3 and the grooves 4 of the substrate W are filled with copper, and the copper layer 7 is formed on the insulating film 2. Deposit. Thereafter, the copper layer 7 and the barrier layer 5 on the insulating film 2 are removed by chemical mechanical polishing (CMP), and the surface of the copper layer 7 filled in the contact hole 3 and the wiring groove 4 and the insulating film 2 are removed. The surface of the surface is made substantially flush. Thereby, as shown in FIG. 16C, the wiring 8 composed of the copper seed layer 6 and the copper layer 7 is formed inside the insulating film 2.

  Here, as the miniaturization progresses, the wiring width becomes narrower and the aspect ratio (ratio of depth to width) becomes higher, the seed layer formed by sputtering or the like does not reach the bottom of the groove uniformly, and the seed The film thickness of the layer gradually decreases toward the bottom of the groove, or the seed layer may be interrupted and discontinuous without being deposited on a part of the side or bottom of the groove. As described above, when copper is embedded by electrolytic plating in a state where the seed layer is incomplete, a plating non-deposited portion (void) is generated inside the copper layer.

  In order to prevent this, it has been proposed to reinforce the seed layer by applying one of electroless plating or electrolytic plating to the surface of the seed layer, and then embed copper by electrolytic plating.

  However, when the seed layer is reinforced by electroless plating alone, the electroless plating is formed in a shape that follows the shape of the base (seed layer) because the rate of supply of reactive species dominates the plating. Although plating around the inside of the groove is good, if there are irregularities on the base, the irregularities are emphasized, and it is difficult to embed copper or the like without generating voids in subsequent electrolytic plating. On the other hand, if the seed layer is reinforced by electrolytic plating alone, conduction cannot be ensured when the base (seed layer) is discontinuous, and conversely, the seed layer is etched, so that the original intended seed layer cannot be reinforced. It is considered possible.

  The present invention has been made in view of the above circumstances, and provides a wiring formation method that can reinforce the seed layer even in a fine wiring with a high aspect ratio and can form a healthy wiring without voids. The purpose is to do.

  According to the first aspect of the present invention, a seed layer is formed on the surface of the substrate on which a fine recess for wiring is formed, the seed layer is reinforced by electroless plating with a first plating solution, and then the second layer is formed. A method of forming a wiring, wherein the seed layer is further reinforced by electrolytic plating using a pulse with a plating solution or PR pulse, and a conductor is embedded in the fine recess by electrolytic plating using a third plating solution It is.

  In this way, by reinforcing the seed layer by two-stage plating, electroless plating and electrolytic plating, the advantage of electroless plating is that the seed layer can be plated even when the seed layer is discontinuous, and electrolysis that can be plated more smoothly with less unevenness. By utilizing the advantages of plating, the seed layer can be reinforced more flatly and reliably.

  Moreover, by first reinforcing the seed layer by electroless plating, even if the seed layer is discontinuous, the seed layer is made continuous. By reinforcing the seed layer, the unevenness of the seed layer can be made uniform, and the film thickness of the seed layer can be made smoother.

  In electroplating, uniform electrodeposition and bottom-up properties (leveling properties) differ depending on the composition of the plating solution used and the current waveform used as the power source, but use a pulse or PR pulse as the current waveform. Thus, the seed layer can be reinforced in a smoother state over the entire surface.

The invention according to claim 2 is the wiring forming method according to claim 1, wherein the second plating solution is a plating solution capable of making the overvoltage higher than that of the third plating solution.
A third aspect of the present invention is the wiring forming method according to the first or second aspect, wherein the third plating solution is a copper sulfate plating solution.

According to a fourth aspect of the present invention, in the electroless plating, the electroless plating solution is dispersed from a plurality of spray nozzles and sprayed onto a surface to be plated of the substrate. It is a wiring formation method as described above.
A fifth aspect of the present invention is the wiring forming method according to any one of the first to fourth aspects, wherein the plated surface of the substrate is cleaned and cooled after the electroless plating process is completed.

  The invention according to claim 6 is characterized in that after the electrolytic plating treatment with the second plating solution is completed, the surface to be plated is rinsed and then dried. This wiring formation method.

  According to the present invention, even in the case of fine wiring with a high aspect ratio (for example, 0.1 μm or less), the seed layer can be reliably reinforced to form a healthy wiring without voids, thereby improving throughput. Can be made.

Embodiments of the present invention will be described below.
FIG. 1 is a plan layout view of a wiring forming apparatus used in a wiring forming method according to an embodiment of the present invention. This wiring forming apparatus is for reinforcement in which two load / unload units 10 that house a plurality of substrates W and one substrate processing unit (that is, one plating cell) 12 are shared in the same facility. An electroless plating apparatus 14, a reinforcing electrolytic plating apparatus 16 and an embedding electrolytic plating apparatus 18, and a transfer robot 20 that transfers a substrate W between the load / unload unit 10 and the substrate processing unit 12 are accommodated. It is configured.

  The reinforcing electroless plating apparatus 14 has a common substrate processing unit 12 and a first plating solution supply head 22. The reinforcing electrolytic plating apparatus 16 has a common substrate processing unit 12 and a second plating solution supply head 24, and the embedding electrolytic plating apparatus 18 has a common substrate processing unit 12 and a third plating solution supply head 26. Respectively. The first plating solution supply head 22 is held at the tip of a swing arm 30 that swings about the rotation shaft 28, swings between the substrate processing unit 12 and the retracting unit 32, and moves up and down. Is configured to do. The second plating solution supply head 24 is held at the tip of a swing arm 36 that swings about a rotation shaft 34, swings between the substrate processing unit 12 and the retracting unit 38, and moves up and down. The third plating solution supply head 26 is held at the tip of a swing arm 40 that swings around the rotation shaft 34 and swings between the substrate processing unit 12 and the retracting unit 42. At the same time, it is configured to move up and down.

  Further, on the side of the substrate processing unit 12, a precoat / recovery arm 44 and a fixed nozzle 46 for injecting a chemical solution such as pure water or ionic water toward the substrate W are arranged. A plurality of fixed nozzles 46 are installed, and one of them is used for supplying pure water.

  FIG. 2 shows a state in which the first plating solution supply head 22 is positioned above the substrate processing unit 12 and the reinforcing electroless plating apparatus 14 is configured. As shown in FIG. 2, the substrate processing unit 12 includes a substrate holding unit 50 that holds the substrate W with the surface to be plated facing upward, and a peripheral portion of the substrate holding unit 50 that is disposed above the substrate holding unit 50. The cathode 52 installed in this manner, and an annular sealing material 54 attached so as to cover the upper side of the cathode 52 are provided. Further, a bottomed cylindrical scattering prevention cup 56 that surrounds the periphery of the substrate holding unit 50 and prevents scattering of various chemicals used during processing is disposed. The substrate W may be fixed to the substrate holding unit 50 by a claw (not shown) provided on the substrate holding unit 50 or by vacuum suction.

  The cathode 52 and the sealing material 54 are configured so as not to move up and down and rotate integrally with the substrate holding unit 50. When the substrate holding part 50 is raised to the plating position B, the tip of the cathode 52 is pressed against the peripheral edge of the substrate W held by the substrate holding part 50 and energized. At the same time, the tip of the sealing material 54 is the peripheral edge of the substrate W. The upper surface (surface to be plated) of the substrate W is pressed against the upper surface of the substrate W and sealed in a water-tight manner to prevent the plating solution supplied to the upper surface (surface to be plated) from seeping out from the end of the substrate W. To prevent contamination.

  The substrate holding unit 50 moves up and down between a lower substrate delivery position A, an upper plating position B, and an intermediate pretreatment / cleaning position C, and the cathode 52 and the sealing material 54 at an arbitrary speed by a motor M. It is comprised so that it may rotate integrally. When the substrate holding part 50 is raised to the plating position B, the tip of the cathode 52 and the tip of the sealing material 54 come into contact with the peripheral edge of the substrate W held by the substrate holding part 50.

  The precoat / recovery arm 44 includes three nozzles (one is a precoat nozzle 58 for discharging a precoat liquid, and the other two nozzles are plating liquid recovery nozzles 60a and 60b for recovering a plating liquid). It is configured to be able to turn and move up and down around 62. In FIG. 2, the nozzles 58, 60 a, and 60 b are illustrated separately for convenience of illustration, but actually, they are integrally attached to the precoat / collection arm 44 as shown in FIG. 1.

  The first plating solution supply head 22 sprays an electroless plating solution for electroless plating dispersed in a shower form from a number of spray nozzles 66, and is attached to the tip of the swing arm 30. A lamp heater 68 is integrally installed inside the first plating solution supply head 22. That is, for example, a plurality of ring-shaped lamp heaters 68 having different radii are arranged concentrically, and a large number of injection nozzles 66 are opened in a ring shape from the gaps between the lamp heaters 68. The lamp heater 68 may be a single spiral lamp heater, or may be composed of lamp heaters having various other structures and arrangements. As a result, the electroless plating solution can be supplied from the spray nozzles 66 onto the surface to be plated of the substrate W in a substantially uniform manner, and the substrate heater W can be heated and kept warm easily, quickly and uniformly by the lamp heater 68.

  In FIG. 3, the second plating solution supply head 24 (or the third plating solution supply head 26) is positioned above the substrate processing unit 12, and the reinforcing electrolytic plating apparatus 16 (or the embedded electrolytic plating apparatus 18). The state which comprised is shown. The reinforcing electroplating apparatus 16 and the embedding electroplating apparatus 18 are the same except that the plating solution used is different, and only the reinforcing electroplating apparatus 16 will be described here.

  The second plating solution supply head 24 has an anode 72 attached to the lower surface of the housing 70, and a plating solution impregnated material 74 made of a water retaining material covering the entire surface of the anode 72 is attached to the lower surface of the anode 72. Is connected to a plating solution supply pipe 76. A large number of plating solution supply ports 72 a are provided in the anode 72, whereby the plating solution is supplied from the plating solution supply pipe 76 to the plating solution impregnated material 74 through the plating solution supply port 72 a. The plating solution impregnating material 74 is always used to prevent the black film formed on the surface of the anode 72 by the action of the plating solution from being dried or oxidized and falling off the anode 72 to form particles. It is provided to keep the surface of 72 wet. A substrate processing liquid supply mechanism is constituted by a mechanism for supplying the plating liquid from the plating liquid supply pipe 76 via the plating liquid supply port 72 a and the plating liquid impregnated material 74.

  In the second plating solution supply head 24, the gap between the substrate W held by the substrate holding unit 50 and the plating solution impregnated material 74 when the substrate holding unit 50 is at the plating position B is, for example, 0.5-3. The plating solution is lowered to about 0 mm, and in this state, the plating solution is supplied from the plating solution supply pipe 76 so that the plating solution is impregnated in the plating solution impregnated material 74, and plating is performed between the surface to be plated of the substrate W and the anode 72. Fill the solution and plate the surface to be plated.

Next, an example of wiring formation by this wiring forming apparatus will be further described with reference to FIGS.
First, in the first example, as a plating solution used for the reinforcing electroless plating apparatus 14 and a plating solution used for the reinforcing electroplating apparatus 16, divalent copper ions, copper ion complexing agents, A plating solution (electroless plating solution) having a reducing agent and a pH adjusting agent is used.

  As a supply source of the divalent copper ions, a cupric salt such as copper sulfate, copper chloride, or copper nitrate can be used. For example, it can be added in a concentration range of 0.001 to 1 mol / L. Examples of complexing agents for copper ions include oxycarboxylic acids such as tartaric acid and gluconic acid and salts thereof, aminocarboxylic acids such as ethylenediaminetetraacetic acid and iminodiacetic acid, and salts thereof, alkanolamines such as quadrol and triethanolamine, and the like. Those salts and the like can be used, and for example, they can be added in a concentration range of 0.001 to 5 mol / L.

As the reducing agent, glyoxylic acid, formaldehyde or the like can be used, and for example, it can be added in a concentration range of 0.001 to 1 mol / L. As the pH adjuster, ammonia, tetramethylammonium hydroxide, or the like can be used, and is added so that the pH of the plating solution is, for example, 6-14.
The treatment temperature of the plating solution is preferably about 20 to 70 ° C., and a known electroless copper plating stabilizer or surfactant can be contained as necessary.

  As a plating solution used in the electrolytic plating apparatus 16 for reinforcement, a plating solution having a divalent copper ion, a complexing agent and a pH adjusting agent in its composition, for example, 15 g / L of copper pyrophosphate and 92 g of pyrophosphoric acid A copper pyrophosphate plating solution excellent in uniform conductivity, containing / L, and having a pH of 9.5 by adding a pH adjusting agent such as choline may be used. As this plating solution, in addition to the copper pyrophosphate plating solution, a copper sulfate plating solution in which copper sulfate is dissolved to obtain divalent copper ions, and copper sulfonate is dissolved to obtain divalent copper ions. Arbitrary things, such as the sulfonic-acid copper plating solution which were made, can also be used.

  Here, since the copper pyrophosphate plating solution is based on copper pyrophosphate and a complexing agent such as pyrophosphoric acid is added thereto, the polarization is higher than that of a normal copper sulfate plating solution. Here, high polarization means that the ratio of the change in voltage to the change in current density is large, that is, the fluctuation in current density is small with respect to potential fluctuation. As a result, when used as an electrolytic plating solution, even if there is a difference in film thickness of the seed layer 6 (see FIG. 16) and a potential difference occurs during energization, fluctuations in current density can be reduced. For this reason, the deposition potential is raised, the uniformity of electrodeposition is improved, and the plating is deposited even on a thin portion of the seed layer, which is difficult to deposit with a normal copper sulfate plating solution.

  Moreover, as a plating solution used for the electrolytic plating apparatus 18 for embedding, the concentration of copper sulfate is high and the concentration of sulfuric acid is low, for example, copper sulfate 100 to 300 g / L (preferably 225 g / L), sulfuric acid 10 to 100 g / L. A copper sulfate plating solution having a composition of about 55 g / L (preferably 55 g / L) and containing an additive having improved leveling properties and excellent leveling properties is used.

  An additive having an effect of improving the leveling property is, for example, an organic nitrogen compound, specifically, a polyalkylenimine such as a phenatidine compound, a phthalocyanine compound, polyethyleneimine, polybenzylethyleneimine, and a derivative thereof, Thiourea derivatives such as N-dye substitution compounds, phenosafranine, safranine azonaphthol, safranine compounds such as diethyl safranine azophenol, dimethyl safranine dimethylaniline, polyepichlorohydrin and its derivatives, phenylthiazonium compounds such as thioflavine, acrylamide, Examples thereof include nitrogen-containing compounds such as amides such as propylamide and polyacrylic acid amide.

  Here, the leveling property means the property with respect to the surface flatness, and when plating is performed using a plating solution having excellent leveling property, the film growth at the entrance of the micro-dent is slowed down. While preventing the occurrence, copper can be uniformly filled in the fine recess without any gap, and the surface can be made flatter.

  First, the substrate W having the seed layer 6 (see FIG. 16) formed on the surface is taken out from the load / unload unit 10 by the transfer robot 20, and is placed on the substrate holding unit 50 of the substrate processing unit 12 with the surface to be plated facing upward. Install. At this time, the substrate holding part 50 is in the substrate delivery position A (see FIG. 2).

  Next, the substrate holding part 50 is raised to the plating position B. Then, as described above, the tip of the cathode 52 and the tip of the sealing material 54 come into contact with the peripheral edge of the substrate W, and the peripheral edge of the substrate W is sealed. In addition, since this plating is electroless plating, current supply by the cathode 52 is not performed.

  Then, the first plating solution supply head 22 located in the retracting portion 32 is swung and moved to the upper part of the substrate W, and the plating solution (electroless plating solution) having the above-described composition is ejected to form a shower on the surface to be plated. Pour evenly into Since the substrate W is surrounded by the sealing material 54 around the surface to be plated, all of the injected plating solution is held on the surface to be plated. The amount may be as small as 1 mm (about 30 mL) on the surface of the substrate W. The plating solution to be supplied is preheated and kept at a temperature optimum for the plating reaction (for example, 60 ° C.). At the same time, by heating and keeping the substrate W by the lamp heater 68, Keep the plating solution warm. In electroless plating, since the plating state varies depending on the temperature, a favorable plating process can be performed by providing the lamp heater 68 and keeping it at an optimum temperature as in this embodiment. Since the amount of the plating solution stored on the substrate W is small, the heat insulation by the lamp heater 68 can be easily performed.

  In addition, in order to wet the surface to be plated uniformly with the plating solution, the substrate W is instantaneously rotated by the motor M immediately after pouring the plating solution. After that, the surface to be plated is plated while the substrate W is stationary. Is preferable for uniform plating of the entire surface to be plated. Specifically, the substrate W is rotated at 100 rpm or less for 1 sec to uniformly wet the surface to be plated with the plating solution, and then is kept stationary to perform electroless plating for 1 min.

  Thus, the seed layer 6 formed in advance by sputtering or the like is reinforced, and an outline at this time is shown in FIG. That is, as the miniaturization progresses, the wiring width becomes narrower and the aspect ratio (ratio of depth to width) becomes higher, as shown in FIG. 4A, the seed layer 6 formed by sputtering or the like. Does not reach the bottom of the groove uniformly, and the film thickness of the seed layer 6 gradually decreases toward the bottom of the groove, or the seed layer 6 is interrupted in the middle without being deposited on a part of the side or bottom of the groove. Even in such a case, the electroless plating is formed in a shape that follows the shape of the base (seed layer) because the rate-determining rate of supply of the reactive species dominates the plating. As a result, plating around the holes and grooves is good, and a continuous seed layer is formed by the seed layer 6 and the reinforcing seed layer 6a formed at this time.

  After the plating process is completed, the first plating solution supply head 22 is returned to the retracting section 32, and then the precoat / collection arm 44 is moved down from the retracted position onto the substrate W, and the substrate W is removed from the plating solution recovery nozzle 60a. The remaining plating solution is recovered and returned to the retracted position. Then, the substrate holding part 50 is lowered from the plating position B to the pretreatment / cleaning position C, the rotation of the substrate W is started, pure water is supplied from the fixed nozzle 46 for pure water, and the surface to be plated is cooled at the same time. The electroless plating is stopped by diluting and washing the liquid, and at the same time, the sealing material 54 and the cathode 52 are washed with water, and the supply of pure water from the fixed nozzle 46 is stopped to increase the rotation speed of the substrate holding unit 50. And spin dry.

  Next, the precoat / collection arm 44 that has been in the retracted position is pivoted and lowered toward the upper surface of the substrate W, and while rotating the substrate holding unit 50, a precoat liquid made of, for example, a surfactant is supplied from the precoat nozzle 58. It discharges to the to-be-plated surface of the board | substrate W, and spreads over the to-be-plated surface. Next, the precoat / recovery arm 44 is returned to the retracted position, the rotation speed of the substrate holding unit 50 is increased, and the precoat liquid on the surface to be plated is shaken off and dried by centrifugal force.

  Next, the rotation of the substrate holding unit 50 is stopped (or slowed down) and raised to the plating position B. Then, as described above, the front end of the cathode 52 and the front end of the sealing material 54 come into contact with the peripheral portion of the substrate W to enable energization, and at the same time, the peripheral portion of the substrate W is sealed watertight.

  Then, the second plating solution supply head 24 located in the retracting portion 38 is turned and moved to the upper part of the substrate W, and is lowered to the above-described position on the substrate W. When the lowering of the second plating solution supply head 24 is completed, the plating solution (electroless plating solution in the first example or copper pyrophosphate plating solution in the second example) is supplied from the plating solution supply pipe 76. For example, 50 mL is supplied and supplied to the plating solution impregnated material 74 through the anode 72, and the plating solution is filled in a gap formed between the plating solution impregnated material 74 and the surface to be plated of the substrate W to flow a plating current. This deposits copper to further reinforce the seed layer 6 (see FIG. 16).

  The outline at this time is shown in FIG. As described above, by electroless plating, as shown in FIG. 4B, a continuous seed layer is formed by the seed layer 6 and the reinforcing seed layer 6a formed by electroless plating. The seed layer 6a emphasizes the unevenness of the seed layer 6 and has a considerably large unevenness on the surface. In this state, it is difficult to embed copper or the like without generating voids by electrolytic plating. Therefore, while ensuring energization with the continuous seed layer, the seed layer 6 is further reinforced by electrolytic plating, so that the unevenness of the reinforcing seed layer 6a is evenly uniform as shown in FIG. 4C. That is, the reinforcing seed layer 6a formed by electroless plating and the composite seed layer 6b having a flat surface are formed by copper deposition by electrolytic plating, and the seed layer 6 is reinforced by the composite seed layer 6b.

  At this time, it is preferable to use reverse electrolysis, a pulse, or a PR pulse as a current power source, and it has been confirmed that a flatter seed reinforcement can be performed by using a PR pulse in particular.

Examples of the waveform of the PR pulse used for the power source current of this electrolytic plating are shown in FIGS. In the figure, the vertical axis represents current density (A / dm ² ), the horizontal axis represents time (t), the upper side is a positive current (ON), and the lower is a reverse current (R). ). That is, FIGS. 5 (a) to 5 (c) are such that a positive waveform and a reverse current having simple waveforms are periodically made continuous, or a predetermined pause (OFF) is given when the current is reversed. 6 (a) and 6 (b) are obtained by changing one of the positive current and the reverse current stepwise. FIG. 7 uses an AC wave pulse (a DC current applied to an AC current), and FIG. 8 uses a triangular pulse. Further, FIG. 9 uses a so-called square wave differential pulse in which the peak of the current value rises at once and gradually falls, or the peak of the current value gradually rises and drops at once. These waveforms are arbitrarily combined.

  Thus, it is considered that the flat seed reinforcement can be performed by performing electrolytic plating using a PR pulse as a current power source for the following reason.

(1) Mass transfer in pulse plating Under conditions where plating is progressing in the electrolytic solution, the concentration of metal ions decreases at the electrode interface. The most important advantage of pulse electrolysis is that the diffusion layer formed during pulse application relaxes during rest and reverse electrolysis and is therefore high without causing side reactions (suboxides, hydroxides, etc.) under optimal conditions The point from which a current density is obtained is mentioned. That is, by using a pulse, the current density can be increased up to about 100 times compared with the case of direct current electrolysis, and plating can be performed with a higher activation overvoltage (voltage for deposition, also simply referred to as overvoltage). Further, a higher current density can be obtained by causing stirring, vibration, heat and other convection.

(2) Nucleation and growth in pulse plating The macroscopic electrodeposition pattern in pulse plating depends on the mass transfer phenomenon, but it is the nucleus that controls the microscopic properties (crystal grain size, preferred orientation, etc.). It is thought that this is a development and growth process. The nucleus growth rate is not significantly affected by the overvoltage, but the nucleus generation rate increases as the overvoltage increases. As a result, in the case of pulse plating using a high current density, microcrystalline precipitates are obtained. In addition, since the overvoltage is large, random nucleation occurs regardless of the non-uniformity of the electrode surface, and further, the generation of hydrogen and the reduction of defects (porous film) are also achieved.

(3) Surface morphology in pulse plating Since the thickness of the diffusion layer is kept thin in pulse plating, the smoothness of the plating surface is improved. That is, when the thickness of the diffusion layer is smaller than the unevenness on the electrode surface, the diffusion layer grows along the unevenness on the electrode surface, and the current distribution on the electrode surface becomes uniform, so that the thickness of the plating layer also becomes uniform. . If the thickness of the diffusion layer is equal to or greater than the unevenness of the electrode surface, the current is concentrated on the protrusions due to spherical diffusion, resulting in the formation of spherical crystals, needle crystals, dendritic crystals, powder crystals, etc. I think that.

(4) Electrodeposition crystal structure in pulse plating As the crystallization overvoltage increases, the critical radius and critical free energy of nucleation decrease, and the nucleation rate increases exponentially. That is, when the pulse current density (overvoltage) is increased, the average particle size decreases. On the other hand, the orientation changes with overvoltage. In pulse plating, concentration polarization can be reduced and overvoltage can be increased, so that an electrodeposit having a high index of preferred orientation axis can be obtained as compared with DC plating.

  When electrolytic plating using a PR pulse as a current power source is performed, as shown in FIG. 11, for example, copper forming the convex portion D of the seed layer 6 thickly deposited in the vicinity of the entrance of the wiring groove 4 or the like becomes a reverse current. When flowing, it is etched and melted, and the molten copper ions are used to recover the copper ion concentration at the bottom of the groove, and when positive current is passed, it precipitates at the bottom of the groove, thereby providing uniform reinforcement of the seed layer Is considered possible.

  When the reinforcement of the seed layer by electrolytic plating is completed, the second plating solution supply head 24 is raised and swiveled to retract to the retracting portion 38, and then the precoat / recovery arm 44 is moved from the retracted position onto the substrate W. The plating solution is recovered from the plating solution remaining on the substrate W through the plating solution recovery nozzle 60a. After this collection is completed, the precoat / collection arm 44 is returned to the retracted position, and pure water is discharged from the fixed nozzle 46 for pure water to the central portion of the substrate W for rinsing the surface to be plated of the substrate W. The holder 50 is rotated to replace the plating solution on the surface to be plated with pure water.

  After rinsing, the substrate holder 50 is lowered from the plating position B to the pretreatment / cleaning position C, and the pure water is supplied from the fixed nozzle 46 for pure water, while the substrate holder 50, the cathode 52 and the sealing material 54 are moved. Rotating and washing with water, the supply of pure water from the fixed nozzle 46 is stopped, the rotation speed of the substrate holding unit 50 is increased, and spin drying is performed.

  Next, the second third plating solution supply head 26 located in the retracting section 42 is turned and moved to the upper part of the substrate W, and the substrate W is plated in the same manner as the second plating solution supply head 24. Plating the surface and embedding copper. As a plating solution at this time, copper is deposited using the copper sulfate plating solution described above. The copper sulfate bath has lower electrodeposition due to the lower overvoltage than the pyrophosphoric acid bath, but the action of an additive that promotes precipitation makes it easier for current to concentrate inside the wiring, resulting in the bottom of the wiring From the bottom up. As a result, good plating without voids in the wiring can be performed.

  Then, after completing the copper embedding by electrolytic plating, the third plating solution supply head 26 is retracted to the retracting portion 42, and then the precoat / recovery arm 44 is moved from the retracted position onto the substrate W and lowered. The remaining plating solution on the substrate W is recovered from the plating solution recovery nozzle 60b of the substrate, and the precoat / recovery arm 44 is returned to the retracted position. Thereafter, as in the case of the second plating solution supply head 24, the substrate W Rinse, wash and spin dry the surface to be plated.

At this time, as described above, it is preferable to use reverse electrolysis, a pulse, or a PR pulse as the current power source. In particular, by using the PR pulse, copper can be embedded efficiently.
Next, the substrate holding unit 50 is stopped and lowered to the substrate delivery position A, and the substrate W is taken out from the substrate processing unit 12 by the transfer robot 20 and returned to the load / unload unit 10.

  Although this example shows an example in which the seed layer is reinforced by electroless plating and electrolytic plating, as described above, the plating solution is excellent in uniform electrodeposition such as a copper pyrophosphate plating solution. If a reverse current, pulse or PR pulse, especially PR pulse is used as the power supply current, reinforcement of the seed layer is omitted by electroless plating and the seed layer is reinforced by electrolytic plating alone. Thus, flat seed reinforcement can be performed.

  FIG. 12 shows another example of the wiring forming apparatus, which is composed of two load / unload units 10a that house a plurality of substrates W in the same equipment, and a single plating apparatus. The reinforcing electroless plating apparatus 14a, the reinforcing electroplating apparatus 16a and the embedding electrolytic plating apparatus 18a, the two cleaning apparatuses 80a and 80b, and the transfer robot 20a that transfers the substrate W between them are provided. It is housed and configured.

  Then, the substrate W on which the seed layer 6 (see FIG. 16) is formed is taken out from the load / unload unit 10a by the transfer robot 20a, and transferred to the reinforcing electroless plating apparatus 14a, where the electroless plating of the seed layer 6 is performed. Reinforce with. Then, this substrate W is transported to the first cleaning device 80a, the surface is cleaned and dried, and then transported to the reinforcing electroplating device 16a to reinforce the seed layer 6 by electrolytic plating. Thereafter, the substrate W is transported to the second cleaning device 80b, the surface is cleaned and dried, and then transported to the embedding electroplating device 18a to embed copper, and this embedding electroplating device. After the substrate is cleaned and dried inside 18a, it is returned to the load / unload section 10a.

  FIG. 13 is a plan layout view of still another example of the wiring forming apparatus, which includes two load / unload units 10b that house a plurality of substrates W in the same equipment, and reinforcement. Reinforcing plating apparatus 82 that serves as both an electroless plating apparatus and a reinforcing electrolytic plating apparatus, embedding electrolytic plating apparatus 18b, two cleaning apparatuses 80c and 80d, and transport for transferring the substrate W between them The robot 20b is accommodated.

  Then, the substrate W on which the seed layer 6 (see FIG. 16) is formed is taken out from the load / unload unit 10b by the transfer robot 20b and transferred to the reinforcing plating apparatus 82. In this reinforcing plating device 82, as described above, the same plating solution (electroless copper plating solution) is used to continuously reinforce the seed layer 6 by electroless plating and electrolytic plating. . Thereafter, the substrate W is transported to the second cleaning device 80d, the surface is cleaned and dried, and then transported to the embedding electroplating device 18b to embed copper, and this embedding electroplating device. The substrate is cleaned and dried inside 18b and then returned to the load / unload unit 10b.

  As described above, in the case where the seed layer is not reinforced by electroless plating, the reinforcing plating apparatus 82 uses the electrolysis plating using reverse electrolysis, pulse or PR pulse, particularly PR pulse as the power supply current. Then, the seed layer is reinforced, and thereafter, the seed layer is conveyed to the embedding electrolytic plating apparatus 18b to embed copper.

  Here, since the uniform electrodeposition and bottom-up properties in electrolytic plating depend on the power supply current waveform and plating solution used, a common plating solution is used for the reinforcing electrolytic plating apparatus and the embedding electrolytic plating apparatus. You may make it select the power supply current waveform used sometimes so that it may be suitable for each process.

Example 1
A sample in which a hole having a diameter of 0.18 μm and a depth of 1.0 μm (aspect ratio: 5.6) was formed on the surface of a semiconductor wafer and a copper seed layer having a thickness of 100 nm was formed by sputtering was prepared. Using the copper seed layer of this sample as a plating solution, a copper pyrophosphate plating solution (copper pyrophosphate: 15 g / L, pyrophosphoric acid: 92 g / L, pH: 9.5, solution temperature: 25 ° C.) Reinforced by electrolytic plating using the PR pulse (t _ON = 1337 ms, t _R = 562 ms, ON: 0.48 A / dm ² , R: 0.16 A / dm ² ) shown in FIG. Thereafter, copper was embedded by electrolytic plating using a copper sulfate plating solution having a bath temperature of 22.0 ° C. The state after reinforcing the copper seed layer and the state after embedding copper were observed with an SEM. FIG. 14 shows a drawing of the SEM photograph at this time. From FIG. 14A, by reinforcing the copper seed layer, the inner peripheral surface (side surface and bottom surface) of the hole 100 is integrally covered with the continuous copper seed layer 102 with a uniform film thickness, and FIG. From this, it can be seen that the copper layer 104 can be soundly embedded in the hole 100 by depositing the copper layer 104.

(Example 2)
A sample similar to that of Example 1 was prepared, and the power source current was a PR pulse (t _ON = 1337 ms, t _OFF = 100 ms, t _R = 562 ms, ON: 0.48 A / dm ² , R shown in FIG. : 0.16 A / dm ² ), and the copper seed layer was reinforced by electrolytic plating in which other conditions were the same as in Example 1, and copper was embedded under the same conditions as in Example 1. When the state at this time was observed with an SEM photograph, a state similar to that shown in FIG. 14 could be obtained.

(Example 3)
A sample similar to Example 1 was prepared, and the copper seed layer of this sample was used as a plating solution for a copper sulfate electroless plating solution (CuSO ₄ .5H ₂ O: 5 g / L, EDTA · 4H: 14 g / L, CHOCOOH: Electroless plating is performed for 1 minute using 18 g / L, pH: 11.5 (using TMAH), liquid temperature: 60 ° C., and then, as a power supply current, PR shown in FIG. Reinforcement was performed by electrolytic plating using a pulse (t _ON = 1337 ms, t _R = 562 ms, ON: 0.48 A / dm ² , R: 0.16 A / dm ² ). Next, copper was embedded under the same conditions as in Example 1. When the state at this time was observed with an SEM photograph, a state similar to that shown in FIG. 14 could be obtained.

(Comparative example)
A sample similar to that in Example 1 was prepared, a DC power source (current density: 0.48 A / dm ² ) was used as the power source current, and the copper seed layer was formed by electrolytic plating with the other conditions being the same as those in Example 1. Reinforcement and copper embedding were performed under the same conditions as in Example 1. The state after reinforcing the copper seed layer and the state after embedding copper were observed with an SEM. FIG. 15 shows a drawing of the SEM photograph at this time. From FIG. 15A, when the copper seed layer is reinforced, the copper seed layer 102 remains only on the inner peripheral surface of the hole 100, and when the copper layer 104 is deposited, as shown in FIG. It can be seen that the void (copper non-deposited portion) 106 is formed here without copper being deposited at the bottom of the hole 100. This is presumably because the copper seed layer at the bottom of the hole is etched away when the copper seed layer is reinforced.

It is a whole top view of the wiring formation apparatus used for the wiring formation method of embodiment of this invention. It is sectional drawing which shows a state when the electroless-plating apparatus is comprised with the board | substrate holding | maintenance part and plating solution supply head of FIG. It is sectional drawing which shows a state when an electroplating apparatus is comprised with the board | substrate holding | maintenance part and plating solution supply head of FIG. It is a figure showing roughly the state where a seed layer is reinforced with electroless plating and electrolytic plating. It is a figure which shows an example of PR pulse. It is a figure which shows the other example of PR pulse. It is a figure which shows the further another example of PR pulse. It is a figure which shows the further another example of PR pulse. It is a figure which shows the further another example of PR pulse. It is a figure which shows the further another example of PR pulse. It is a figure which shows typically the state by which the seed layer is reinforced to the uniform film thickness by the electroplating which uses PR pulse as a power supply current. It is a whole top view which shows the other example of a wiring formation apparatus. It is a whole top view which shows the further another example of a wiring formation apparatus. It is the figure which made the drawing after SEM observation the state after reinforcing the copper seed layer in the Example of this invention, and the state after embedding copper. It is the figure which made the drawing after SEM observation the state after reinforcing the copper seed layer in the comparative example of this invention, and the state after embedding copper. It is a figure which shows to CMP process of the copper wiring formation example in a semiconductor device in order of a process.

Explanation of symbols

6 seed layer 6a reinforcing seed layer 6b composite seed layer 7 copper layer 8 wiring 10, 10a, 10b load / unload section 12 substrate processing section 14, 14a reinforcing electroless plating apparatus 16, 16b reinforcing electrolytic plating apparatus 18, 18a 18b Embedding electroplating apparatus 22, 24, 24 Plating solution supply heads 30, 36, 40 Oscillating arm 44 Precoat / recovery arm 46 Fixed nozzle 50 Substrate holding part 52 Cathode 54 Sealing material 56 Spattering prevention cup 58 Precoat nozzle 60a, 60b Liquid recovery nozzle 66 Injection nozzle 68 Lamp heater 70 Housing 72 Anode 74 Plating liquid impregnated material 76 Plating liquid supply pipe 82 Reinforcing plating apparatus

Claims (6)

A seed layer is formed on the surface of the substrate on which fine depressions for wiring are formed,
Reinforcing the seed layer by electroless plating with a first plating solution;
Thereafter, the seed layer is further reinforced by electrolytic plating using a pulse with a second plating solution or a PR pulse,
A wiring forming method comprising embedding a conductor by electrolytic plating in the fine recess using a third plating solution.   The wiring forming method according to claim 1, wherein the second plating solution is a plating solution capable of increasing an overvoltage as compared with the third plating solution.   The wiring forming method according to claim 1, wherein the third plating solution is a copper sulfate plating solution.   5. The wiring forming method according to claim 1, wherein the electroless plating is performed by dispersing an electroless plating solution from a plurality of spray nozzles and spraying it onto a surface to be plated of the substrate.   The wiring formation method according to claim 1, wherein after the electroless plating process is completed, a surface to be plated is cleaned and cooled. The wiring forming method according to claim 1, wherein after the electrolytic plating treatment with the second plating solution is completed, the surface to be plated is rinsed and then dried.

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