Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/48—Electroplating: Baths therefor from solutions of gold
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D7/00—Electroplating characterised by the article coated
  • C25D7/12—Semiconductors
  • C25D7/123—Semiconductors first coated with a seed layer or a conductive layer

Definitions

• This application relates to the field of electroplating technologies, and specifically to a gold electroplating solution and an application thereof.
• gold electroplating solutions used for forming a gold bump may be classified into a cyanide electroplating solution and a non-cyanide electroplating solution based on whether a gold source is a cyanide.
• the non-cyanide electroplating solution has high costs, and the electroplating solution cannot compete with the cyanide electroplating solution in terms of stability.
• a gold bump formed by using a conventional cyanide electroplating solution has low hardness. Especially after heat treatment at a relatively high temperature (for example, at least 260°C), it is relatively difficult to ensure that the hardness is at least 90 HV. In addition, appearance uniformity and flatness of a surface of the gold bump are relatively poor.
• embodiments of this application provide a gold electroplating solution that can be used to make a high-hardness gold bump, to resolve a problem that it is difficult to make a gold bump obtained by using an existing cyanide gold electroplating solution have both high surface flatness and high hardness after heat treatment.
• a first aspect of embodiments of this application provides a gold electroplating solution, including an aurous cyanide salt serving as a gold source, an oxalate, a lead-containing compound, a water-soluble polysaccharide substance, and an organic acid conductive medium, where the organic acid conductive medium includes an organic phosphonic acid or a salt of the organic phosphonic acid.
• the electroplating solution can be used to form a gold bump with high surface flatness and high hardness after heat treatment, and the gold bump is particularly suitable for reliable electrical interconnection between a semiconductor substrate and a substrate between which there is a small spacing.
• an electrical conductivity of the electroplating solution at a room temperature ranges from 40 mS/cm to 90 mS/cm.
• the electrical conductivity of the electroplating solution can still meet a requirement of gold electroplating, and an obtained electroplated gold layer has a uniform appearance and high surface flatness.
• the electroplating solution does not include an inorganic acid conductive salt.
• the electrical conductivity of the electroplating solution is still appropriate, and an electroplated gold layer with a uniform thickness, a uniform appearance, and high surface flatness can be prepared by using the electroplating solution.
• a concentration of the organic acid conductive medium in terms of organic phosphonic acids ranges from 10 g/L to 100 g/L. In some implementations, in the electroplating solution, the concentration of the organic acid conductive medium in terms of organic phosphonic acids ranges from 55 g/L to 95 g/L. This is relatively beneficial for the electroplating solution to have appropriate viscosity and an appropriate conduction rate, and an electroplated gold layer obtained by using the electroplating solution has relatively high hardness and surface flatness.
• At least one of hydroxyethylidene diphosphonic acid, amino trimethylene phosphonic acid, and ethylenediamine tetramethylenephosphonic acid is selected as the organic phosphonic acid.
• the water-soluble polysaccharide substance includes at least one of dextrin, ⁇ -cyclodextrin, ⁇ -cyclodextrin, or dextran.
• a concentration of the water-soluble polysaccharide substance in the electroplating solution ranges from 0.1 g/L to 5 g/L.
• An appropriately low concentration of the water-soluble polysaccharide substance can cooperate with the lead-containing compound and the organic phosphonic acid to increase hardness of the electroplated gold layer after heat treatment, without affecting purity of the electroplated gold layer.
• a ratio of mass of the organic acid conductive medium in terms of organic phosphonic acids to mass of the water-soluble polysaccharide substance is (9-900): 1.
• a ratio of mass of the organic acid conductive medium in terms of organic phosphonic acids to mass of the water-soluble polysaccharide substance is (9-900): 1.
• pH of the electroplating solution ranges from 5 to 7.
• the lead-containing compound in the weakly acidic electroplating solution may have relatively high solubility, and it is not easy to precipitate.
• the aurous cyanide salt does not affect a gold electroplating effect due to precipitation in an excessively acidic system.
• a second aspect of embodiments of this application provides an application of the electroplating solution according to the first aspect of the embodiments of this application in gold electroplating.
• the application includes an application in preparing a semiconductor gold-electroplated part provided with a gold bump.
• the electroplating solution in this application can be used to form an electroplated gold layer that has a regular shape, a uniform appearance, low roughness, and high flatness and that still has relatively high hardness after heat treatment, so that a high requirement of gold electroplating in the semiconductor field can be better met.
• a third aspect of embodiments of this application provides a gold electroplating method, including:
• the method further includes: performing heat treatment at a temperature ranging from 260°C to 300°C; and hardness of the electroplated gold layer ranges from 90 HV to 120 HV after the heat treatment.
• the electroplated gold layer formed by using the foregoing electroplating solution provided in the embodiments of this application still has relatively high hardness, and can be better used in the semiconductor field.
• hardness of the electroplated gold layer ranges from 95 HV to 120 HV after the heat treatment.
• a fourth aspect of embodiments of this application provides a gold-electroplated part, including a substrate and an electroplated gold layer disposed on the substrate, where the electroplated gold layer may be formed through electroplating using the electroplating solution according to the first aspect of the embodiments of this application, or may be formed by using the gold electroplating method according to the third aspect of the embodiments of this application.
• the electroplated gold layer on the gold-electroplated part has a uniform appearance, high surface flatness, and relatively high hardness after heat treatment, and has a wider application prospect.
• surface roughness Ra of the electroplated gold layer falls within a range of 60 nm to 100 nm when a thickness of the electroplated gold layer ranges from 7 ⁇ m to 11 ⁇ m. Appropriately high Ra is conducive to alignment and bonding between the electroplated gold layer and the substrate.
• the electroplated gold layer is a gold bump
• the substrate is a semiconductor substrate.
• the gold-electroplated part in this case may be referred to as a semiconductor gold-electroplated part provided with a gold bump.
• hardness of the gold bump falls within a range of 90 HV to 120 HV; and a height difference between a point farthest to the substrate and a point nearest to the substrate on a surface that is of the gold bump and that is away from the substrate is less than 1.2 ⁇ m. This can reflect that the surface that is of the gold bump and that is away from the substrate has high flatness, and hardness of the gold bump is high after the heat treatment.
• the embodiments of this application further provide a gold-electroplated part, including a substrate and an electroplated gold layer disposed on the substrate, where the electroplated gold layer is formed through electroplating using an electroplating solution containing an aurous cyanide salt, and surface roughness Ra of the electroplated gold layer falls within a range of 60 nm to 100 nm when a thickness of the electroplated gold layer ranges from 7 ⁇ m to 11 ⁇ m.
• hardness of the electroplated gold layer falls within a range of 90 HV to 120 HV, and further falls within a range of 95 HV to 120 HV.
• the electroplated gold layer is a gold bump; and a height difference between a point farthest to the substrate and a point nearest to the substrate on a surface that is of the gold bump and that is away from the substrate is less than 1.2 ⁇ m.
• the foregoing electroplated gold layer has high surface flatness, high hardness, and good toughness, is conducive to alignment and bonding with the substrate, and has a wide application prospect.
• the electroplating solution further includes an oxalate, a lead-containing compound, a water-soluble polysaccharide substance, and an organic acid conductive medium, where the organic acid conductive medium includes an organic phosphonic acid or a salt of the organic phosphonic acid.
• the electroplated gold layer is formed through electroplating using the electroplating solution according to the first aspect of the embodiments of this application.
• the embodiments of this application further provide an electronic device.
• the electronic device includes the foregoing gold-electroplated part according to the embodiments of this application.
• FIG. 1 is a diagram of a process in which a gold bump 6 is formed by using a gold electroplating solution according to an embodiment of this application.
• (A) in FIG. 1 is a diagram of a structure of a to-be-electroplated part on which gold electroplating is to be performed.
• the structure shown in (A) in FIG. 1 includes a substrate 1, an electrode 2 disposed on a surface on one side of the substrate 1, and a passivation layer 3 covering the substrate 1 and the electrode 2.
• the passivation layer 3 is provided with a specific opening that exposes a part of the electrode 2.
• a lower metal layer 4 is formed on the passivation layer 3, the lower metal layer 4 covers the passivation layer 3 and the electrode 2 exposed from an opening 3a of the passivation layer 3, and the conductive lower metal layer 4 is a forming basis for gold electroplating.
• the lower metal layer 4 includes a TiW layer and a gold seed layer that are stacked, and the TiW layer is close to the electrode 2, so that bonding force between the electrode 2 and the gold seed layer can be increased.
• a photoresist layer 5 is formed on a surface of the lower metal layer 4, the photoresist layer 5 is provided with an opening part 5a that can allow a part of the lower metal layer 4 to be exposed, and the opening part 5a is located above the electrode 2.
• Gold electroplating is subsequently performed in the opening part 5a to form a gold bump 6, as shown in (B) in FIG. 1 .
• the structure may be bonded with a printed routing substrate and the like, which is specifically implemented by bonding the gold bump 6 with a substrate electrode on the printed routing substrate.
• Hardness of the gold bump 6 formed by using a conventional cyanide gold electroplating solution is usually not high. Especially after heat treatment is performed at a relatively high temperature (for example, at least 260°C), it is relatively difficult to ensure that the hardness of the gold bump 6 is at least 90 HV. In addition, surface flatness of the gold bump 6 is relatively poor, and a surface 601 that is of the gold bump 6 and that is away from one side of the electrode 2 fluctuates greatly. In other words, a distance between a point that is on the surface 601 and that is nearest to the substrate 1 (point a in the figure) and a point that is on the surface 601 and that is farthest to the substrate 1 (point b in the figure) is relatively long. This greatly reduces an effective contact area during bonding. Therefore, this application provides a cyanide gold electroplating solution that can be used to make a gold bump with both high surface flatness and high hardness after heat treatment.
• the gold electroplating solution provided in embodiments of this application includes an aurous cyanide salt serving as a gold source, an oxalate, a lead-containing compound, a water-soluble polysaccharide substance, and an organic acid conductive medium, where the organic acid conductive medium includes an organic phosphonic acid or a salt of the organic phosphonic acid.
• a specific organic acid conductive medium used in the foregoing cyanide gold electroplating solution can reduce resistance of the electroplating solution, increase an electrical conductivity of the electroplating solution, and ensure that a surface of an electroplated gold layer formed through electroplating using the electroplating solution is more uniform (for example, almost no protruding gold nodule is generated) and has higher flatness and better performance of filling a step-shaped opening part; and the organic acid conductive medium further has a function of increasing hardness of the electroplated gold layer to some extent.
• the oxalate as an organic acid conductive salt, may also help increase a conduction rate of the electroplating solution, and may prevent the electroplating solution from penetrating into a photoresist layer and prevent an electroplated gold film from being formed under the photoresist layer, thereby ensuring that gold electroplating is performed in a limited area.
• the water-soluble polysaccharide substance can increase hardness of the electroplated gold layer.
• the lead-containing compound can adjust crystallinity, crystal orientation, and the like of the obtained electroplated gold layer, improve a depolarization effect of the electroplating solution, reduce an electroplating voltage, and improve precipitation efficiency of the electroplating solution, and can also help increase the hardness of the electroplated gold layer.
• the electroplating solution can be used to form an electroplated gold bump with high surface flatness, and film hardness of the gold bump is relatively high after heat treatment.
• the hardness of the gold bump may be still at least 90 HV, for example, 95 HV to 120 HV.
• the gold bump with high surface flatness and high hardness is particularly suitable for reliable electrical interconnection between a semiconductor substrate and a substrate between which there is a small spacing.
• an electrical conductivity of the electroplating solution at a room temperature ranges from 40 mS/cm to 90 mS/cm.
• the electrical conductivity of the electroplating solution is relatively appropriate
• an electroplated gold layer formed through electroplating has a relatively uniform thickness and high surface flatness.
• the term "room temperature” may be any temperature from 20°C to 30°C, for example, 22°C, 25°C, or 28°C; and 25°C is relatively common.
• the electroplating solution does not include an inorganic acid conductive salt.
• the inorganic acid conductive salt may be inorganic phosphate (for example, potassium phosphate, sodium phosphate, or ammonium phosphate).
• the electrical conductivity of the electroplating solution is relatively appropriate. This is conducive to forming an electroplated gold layer with a uniform thickness, a uniform appearance, and high surface flatness. In addition, the electroplated gold layer still has relatively high hardness after heat treatment.
• the electroplating solution does not include the inorganic acid conductive salt is not limited to a case in which content of the inorganic acid conductive salt is definitely 0. When the content of the inorganic acid conductive salt in the electroplating solution is less than or equal to 100 mg/L, it may also be considered that the electroplating solution does not include the inorganic acid conductive salt.
• hydroxyethylidene diphosphonic acid HEDP
• amino trimethylene phosphonic acid ATMP
• ethylenediamine tetramethylenephosphonic acid ETMP
• the organic phosphonic acid is hydroxyethylidene diphosphonic acid and/or amino trimethylene phosphonic acid.
• the organic acid conductive medium is better for improving a leveling effect of the electroplating solution.
• a concentration of the organic acid conductive medium in terms of organic phosphonic acids ranges from 10 g/L to 100 g/L.
• a concentration of the organic phosphonic acid ranges from 10 g/L to 100 g/L; and when the organic acid conductive medium is organic phosphonate, a concentration of an organic phosphonic acid corresponding to the organic phosphonate ranges from 10 g/L to 100 g/L.
• concentration of the organic acid conductive medium can ensure that surface flatness of the electroplated gold layer formed by using the electroplating solution is obviously high, and does not excessively increase viscosity of the electroplating solution or reduce an electrical conduction rate.
• concentration of the organic acid conductive medium in terms of organic phosphonic acids may be 15 g/L, 20 g/L, 25 g/L, 30 g/L, 40 g/L, 50 g/L, 52 g/L, 55 g/L, 60 g/L, 70 g/L, 80 g/L, 90 g/L, 95 g/L, or the like.
• the concentration of the organic acid conductive medium in terms of organic phosphonic acids ranges from 10 g/L to 50 g/L. In some other implementations, the concentration of the organic acid conductive medium in terms of organic phosphonic acids ranges from 55 g/L to 95 g/L, and may further range from 55 g/L to 90 g/L, 55 g/L to 85 g/L, or the like. In this case, it is more beneficial for the foregoing electroplating solution to have appropriate viscosity, a higher electrical conduction rate, and a relatively high precipitation effect; and the obtained electroplated gold layer has appropriate hardness and higher surface flatness.
• the water-soluble polysaccharide substance includes at least one of dextrin, ⁇ -cyclodextrin, ⁇ -cyclodextrin, or dextran.
• a concentration of the water-soluble polysaccharide substance in the electroplating solution may range from 0.1 g/L to 5 g/L.
• the foregoing cyanide gold electroplating solution includes the foregoing organic acid conductive medium, so that content of the water-soluble polysaccharide substance can be appropriately low.
• the concentration of the water-soluble polysaccharide substance in the electroplating solution may be 0.1 g/L, 0.2 g/L, 0.3 g/L, 0.4 g/L, 0.5 g/L, 0.8 g/L, 1.0 g/L, 1.5 g/L, 2.0 g/L, 2.5 g/L, 3.0 g/L, 3.5 g/L, 4.0 g/L, 4.5 g/L, 4.8 g/L, 5.0 g/L, or the like.
• the concentration of the water-soluble polysaccharide substance in the electroplating solution may range from 0.1 g/L to 4.5 g/L, and may further range from 0.2 g/L to 4.5 g/L.
• a ratio of mass of the organic acid conductive medium calculated in terms of organic phosphonic acids to mass of the water-soluble polysaccharide substance is (9-900):1.
• the mass ratio may be 10, 11, 12, 13, 15, 18, 20, 50, 60, 65, 80, 100, 200, 300, 500, 550, 600, 650, 700, 800, or the like.
• the mass ratio is (11-900):1, and may further be (11-850): 1.
• the mass ratio is (13-850):1, and may further be (13-650):1.
• the aurous cyanide salt includes at least one of potassium aurous cyanide, sodium aurous cyanide, and ammonium aurous cyanide. Solubility of these cyanide salts of monovalent gold in the foregoing electroplating solution is relatively high.
• an amount of the aurous cyanide salt causes a concentration of gold ions ranging from 1 g/L to 15 g/L in the electroplating solution. In other words, a concentration of the aurous cyanide salt calculated in terms of gold ions ranges from 1 g/L to 15 g/L.
• the concentration of gold ions falls within this range, so that it can be ensured that precipitation efficiency of gold on a to-be-electroplated part at a cathode is not excessively low during electroplating, thickness distribution of an electroplated gold layer is relatively uniform. In addition, a case in which a gold source is wasted and production costs are increased due to the removal of the electroplating solution after electroplating is completed, and the like can be avoided.
• the concentration of gold ions in the electroplating solution is specifically 1 g/L, 2 g/L, 3 g/L, 4 g/L, 5 g/L, 6 g/L, 7 g/L, 8 g/L, 9 g/L, 10 g/L, 11 g/L, 12 g/L, 13 g/L, 14 g/L, 14.5 g/L, or the like.
• At least one of potassium oxalate, sodium oxalate, and ammonium oxalate is selected as the oxalate.
• a concentration of the oxalate in the electroplating solution ranges from 5 g/L to 80 g/L.
• An appropriate concentration of the oxalate can ensure that the electroplating solution can be effectively prevented from penetrating the photoresist layer; and can avoid a case in which excessively high oxalate content causes an undesirable appearance of the electroplated gold layer, for example, a phenomenon in which the electroplated gold layer is burnt.
• the concentration of the oxalate in the electroplating solution may be 5 g/L, 8 g/L, 10 g/L, 20 g/L, 30 g/L, 40 g/L, 50 g/L, 60 g/L, 70 g/L, 80 g/L, or the like. In some implementations, a concentration of the oxalate in the electroplating solution ranges from 10 g/L to 50 g/L.
• At least one of lead acetate, lead nitrate, lead citrate, and lead sulfate is selected as the lead-containing compound.
• a concentration of the lead-containing compound in terms of lead element ranges from 2 mg/L to 15 mg/L. In other words, a concentration of a lead element in the electroplating solution is 2 mg/L to 15 mg/L.
• the lead-containing compound of appropriately low content can ensure that crystallinity and hardness of the electroplated gold layer can be adjusted, and avoids a case in which purity of the electroplated gold layer is reduced due to the inclusion of excessive Pb impurities in the formed electroplated gold layer.
• the electroplating solution further includes a pH additive.
• the pH additive may be an acid or a base, where at least one of organic phosphonic acids used as the foregoing organic conductive medium may be selected as the acid; and at least one of potassium hydroxide, sodium hydroxide, ammonia water, and the like may be selected as the base.
• pH of the electroplating solution ranges from 5 to 7.
• the lead-containing compound has relatively good solubility in the weakly acidic electroplating solution, and is not easy to precipitate to avoid impact on an effect of the electroplating solution, so that the electroplating solution has good long-term stability.
• the aurous cyanide salt does not cause hydrogen cyanide volatilization and impact on a gold electroplating effect that are caused due to excessively low pH of the system.
• the pH of the electroplating solution may be specifically 5.0, 5.2, 5.5, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, or the like. In some implementations, the pH of the electroplating solution ranges from 5.5 to 7, and may further range from 6 to 7.
• the cyanide gold electroplating solution is an aqueous solution. It may be understood that the electroplating solution further includes water used as a solvent.
• the electroplating solution may be prepared after the foregoing components are completely dissolved in water.
• Each component may be added in a solid form or in a form of a corresponding aqueous solution.
• corresponding compounds may be directly added into water for complete dissolution.
• a gold source is added in a form of a solid salt, but an actual amount of the gold source is calculated based on a gold element.
• An actual amount of the lead-containing compound is also calculated based on an actually introduced lead element, and the lead-containing compound is usually added after pH of the system is adjusted to weakly acidic for dissolution.
• a method for preparing the electroplating solution includes: First, the organic phosphonic acid or a salt of the organic phosphonic acid is mixed with water to obtain a completely dissolved solution; then pH of the solution is adjusted to predetermined pH by using a pH regulator; then the oxalate and the gold source are added; after the solution is fully dissolved, the lead-containing compound and the water-soluble polysaccharide substance are added; and after the solution is completely dissolved, the mixture is adjusted to a predetermined volume and predetermined pH to obtain an electroplating solution, and the electroplating solution is allowed to meet a requirement for a concentration of each component.
• organic phosphonate for example, organic phosphonate potassium salt, organic phosphonate sodium salt, and organic phosphonate ammonium salt.
• An embodiment of this application further provides an application of the foregoing cyanide gold electroplating solution.
• the application may be specifically a function in preparing a gold-electroplated part, and may further be preparing a semiconductor gold-electroplated part.
• the application is an application in preparing a semiconductor gold-electroplated part provided with a gold bump.
• the foregoing cyanide gold electroplating solution provided in this application is particularly suitable for the semiconductor manufacturing field, and is suitable for electroplating a semiconductor substrate with a patterned photoresist layer, to obtain a semiconductor gold-electroplated part product provided with a gold bump, for example, a liquid crystal drive chip, a CMOS image sensor, and a fingerprint sensor.
• a semiconductor gold-electroplated part product provided with a gold bump for example, a liquid crystal drive chip, a CMOS image sensor, and a fingerprint sensor.
• Interconnection between a chip and a substrate may be implemented by using a flip technology TAB (Tape Automated Bonding), COG (Chip on glass), COF (Chip on Film), COP (Chip on Plastics), or the like.
• An electroplated gold layer prepared by using the foregoing electroplating solution provided in the embodiments of this application can meet technical requirements of the semiconductor field for hardness, flatness, roughness, and the like of the electroplated gold layer, and the prepared semiconductor gold-electroplated part has a good line forming capability, a regular shape, and no infiltration plating defect, and has a good application prospect in the semiconductor field.
• An embodiment of this application further provides a gold electroplating method, including:
• the to-be-electroplated part is usually used as a cathode, and may be partially or completely placed in an electroplating tank in which the electroplating solution is provided; and an anode may be placed in the electroplating tank.
• the anode may be, for example, a platinum-coated titanium plate.
• the cathode and the anode each may be electrically connected to an electroplating power supply through routing.
• the foregoing electroplating solution is used as an electrolyte, and the cathode and the anode jointly form a conducting loop to implement deposition of electroplated gold on a to-be-electroplated part.
• the electroplating apparatus 200 includes:
• the cathode 22 and the anode 23 are usually disposed opposite to each other, and are usually separated from each other, for example, separated by using a diaphragm 25.
• a diaphragm 25 In addition, in FIG. 2 , although the cathode 22 and the anode 23 are vertically placed in the electroplating tank 20, it may be understood that the cathode 22 and the anode 23 may also be horizontally placed in the electroplating tank 20 based on a specific requirement.
• a potential is usually applied to the cathode 22.
• a current is also applied to the to-be-electroplated part correspondingly.
• gold ions in the electroplating solution are reduced at the cathode 22 to form metal gold on the to-be-electroplated part.
• the applied current may be a direct current, a pulse current, or another suitable current.
• the to-be-electroplated part may be a substrate without a complex device structure, for example, an unpatterned wafer or a wafer with an epitaxially stacked structure.
• the to-be-electroplated part is a patterned wafer.
• the patterned wafer includes a substrate and a passivation layer disposed on the substrate, the passivation layer is provided with at least one opening formed by using a patterned photoresist layer, and one opening can expose one corresponding electrode on the substrate. Gold electroplating is specifically performed in the opening.
• the electroplated gold layer obtained through electroplating is usually protruded on the passivation layer, and is provided with a step. Therefore, the electroplated gold layer may be referred to as a "gold bump".
• the substrate is usually a semiconductor substrate, for example, a silicon substrate.
• the gold bump is usually formed on a semiconductor chip, and the gold bump is a key structure for implementing interconnection between the semiconductor chip and the substrate.
• the to-be-electroplated patterned wafer may be shown in (A) in FIG. 1 , and include a substrate 1, a patterned electrode 2, and a passivation layer 3 that covers the electrode 2 and the substrate 1, where the patterned electrode 2 and the passivation layer 3 are sequentially stacked on the substrate 1.
• a lower metal layer 4 is deposited in an opening 3a of the passivation layer 3, and a photoresist layer 5 is disposed on each of two sides of an opening 3a of the passivation layer 3.
• An opening part 5a (or referred to as a gap) between adjacent photoresist layers 5 allows a part of the lower metal layer 4 to be exposed.
• Electroplating may be performed in the opening part 5a, and an electroplated gold layer formed through electroplating in the opening part 5a may be referred to as a gold bump.
• a temperature of the electroplating ranges from 30°C to 50°C.
• the temperature is specifically 32°C, 35°C, 40°C, 45°C, 48°C, or 50°C.
• An appropriate electroplating temperature can ensure that the electroplating solution has relatively high precipitation efficiency, avoid a uniform appearance of an electroplated layer, and ensure high stability of the overall electroplating solution. In this way, a case in which it is difficult to manage the electroplating solution due to excessively rapid volatilization of the electroplating solution can be avoided.
• a current density during electroplating ranges from 0.1 A/dm 2 to 1.0 A/dm 2 (that is, ASD).
• the electroplated layer may have a non-uniform appearance, defect filling may occur, and the like.
• a total time of electroplating can be adjusted based on a size parameter of an electroplated gold layer to be formed and a concentration of each component in the electroplating solution.
• purity of gold in the electroplated gold layer formed by using the foregoing electroplating solution is relatively high, and the purity of gold may be greater than or equal to 99.9%.
• the method further includes: performing heat treatment at a temperature ranging from 200°C to 300°C for more than 5 minutes, so that hardness of the electroplated gold layer obtained after the heat treatment still falls within a range of 90 HV to 120 HV.
• Heat treatment can increase toughness of the electroplated gold layer, and ensure impact resistance of a connecting piece subsequently connected by using the electroplated gold layer.
• heat treatment causes a decrease in hardness of the electroplated gold layer to some extent.
• the electroplated gold layer formed by using the foregoing electroplating solution in this embodiment of this application still has relatively high hardness after heat treatment is performed at a relatively high temperature.
• the hardness of the electroplated gold layer is greater than or equal to 90 HV, for example, 90 HV to 120 HV, and may further range from 95 HV to 120 HV.
• a time for performing heat treatment may be 0.5h, 1.2h, 1h, 1.5h, 2h, or the like.
• the hardness of the electroplated gold layer is greater than or equal to 95 HV, for example, 95 HV to 120 HV.
• An embodiment of this application further provides a gold-electroplated part.
• the gold-electroplated part includes a substrate and an electroplated gold layer disposed on the substrate.
• the electroplated gold layer may be formed by using a cyanide electroplating solution containing an aurous cyanide salt.
• the electroplated gold layer is formed through electroplating using the foregoing cyanide electroplating solution in the embodiments of this application that includes an aurous cyanide salt, an oxalate, a lead-containing compound, a water-soluble polysaccharide substance, and an organic acid conductive medium, or is formed by using the foregoing gold electroplating method in the embodiments of this application.
• a gold-electroplated part 300 includes a substrate 1 and an electroplated gold layer 6' disposed on the substrate 1.
• the electroplated gold layer 6' is specifically a gold bump 6', and is T-shaped and provided with steps.
• the substrate 1 is usually a semiconductor substrate, for example, a silicon substrate, a silicon-on-insulator substrate, or a germanium substrate.
• the gold-electroplated part 300 in this case may be referred to as a "semiconductor gold-electroplated part provided with a gold bump". As shown in FIG.
• an electrode 2 and a passivation layer 3 that covers the electrode 2 and the substrate 1 are disposed on the substrate 1, the passivation layer 3 is provided with an opening 3a that can expose a part of the electrode 2, and the gold bump 6' includes an internal electroplated layer filled in the opening 3a and a surface electroplated layer deposited on the passivation layer 3.
• a thickness h' of the gold bump 6' may fall within a range of 7 ⁇ m to 11 ⁇ m. This is a common thickness of a gold bump in a semiconductor gold-electroplated part.
• a first surface 601' that is of the gold bump 6' and that is away from the substrate 1 is basically a plane, and flatness of the surface is relatively high.
• a height difference between a point that is on the first surface 601' of the gold bump 6' and that is farthest to the substrate 1 and a point that is on the first surface 601' and that is nearest to the substrate 1 may be less than or equal to 1.2 ⁇ m.
• the relatively small height difference may reflect that surface flatness of the first surface 601' that is of the gold bump 6' and that is away from the substrate 1 is relatively high. This can greatly increase an effective contact area during bonding with another substrate by using the electroplated gold layer 6', and increase stability of a bonding structure.
• the height difference may be less than or equal to 1.1 ⁇ m, less than or equal to 1.0 ⁇ m, or even less than or equal to 0.9 ⁇ m.
• the height difference may be measured by using surface roughness Rz of the gold bump 6'.
• Rz represents a maximum height of a profile, and may be represented by a distance between a profile peak line and a profile valley line within a sampling length.
• the surface roughness Rz of the gold bump 6' is less than or equal to 1.2 ⁇ m, or less than or equal to 1.1 ⁇ m, or less than or equal to 1.0 ⁇ m, or even less than or equal to 0.9 ⁇ m.
• hardness of the gold bump 6' may still fall within a range of 90 HV to 120 HV, or even fall within a range of 95 HV to 120 HV.
• the gold bump 6' with a thickness of 7 ⁇ m to 11 ⁇ m can have both high toughness and high hardness after heat treatment. In a case in which a horizontal size and a spacing of the gold bump 6' are relatively small, the gold bump 6' with relatively high hardness can ensure that in a process of thermal compression bonding between a chip provided with the gold bump 6' and a substrate, the gold bump 6' is not easily deformed to cause a connection between adjacent gold bumps and short circuiting of a line.
• surface roughness Ra of the first surface 601' that is of the gold bump 6' and that is away from the substrate 1 falls within a range of 60 nm to 100 nm, for example, 65 nm, 70 nm, 72 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 98 nm.
• Ra falls within a range of 70 nm to 95 nm, and may further fall within a range of 71 nm to 95 nm.
• Ra represents an arithmetic average deviation of the profile, and is represented by an arithmetic average value of absolute values of profile offsets within the sampling length L.
• the substrate 1 may be a semiconductor substrate, for example, a silicon substrate, a silicon-on-insulator substrate, or a germanium substrate.
• the electrode 2 is usually an aluminum (Al) electrode, and is usually formed on a side that is of the substrate 1 and on which a circuit layer is formed.
• the passivation layer 3 is usually an insulation dielectric material such as SiO 2 and silicon nitride.
• a lower metal layer 4 is further disposed between the passivation layer 3 and the electroplated gold layer 6'.
• the lower metal layer 4 may fill only the bottom of the opening 3a, or may cover both the passivation layer 3 and the electrode 2 exposed from the opening 3a of the passivation layer 3, as shown in FIG. 3 . Due to the presence of the lower metal layer 4, smooth electroplating of the electroplated gold layer 6' on the substrate 1 can be ensured.
• the lower metal layer 4 may include a TiW layer and a gold seed layer that are stacked, and the TiW layer is close to the electrode 2. Due to the presence of the TiW layer, bonding force between the electrode 2 and the gold seed layer can be increased.
• a plurality of electrodes 2 that are distributed at intervals may be disposed on the substrate 1.
• the substrate 1 is also provided with a plurality of gold bumps 6' that are distributed at intervals, to ensure electrical interconnection between the electrodes 2 and conductive parts on another substrate.
• the electroplated gold layer on the gold-electroplated part may not be a gold bump provided with a step, and may be specifically an electroplated gold layer without a step.
• a surface that is of the electroplated gold layer and that is close to the substrate is not a step surface, but a flat surface.
• the surface roughness Ra may also fall within a range of 60 nm to 100 nm.
• the surface roughness Ra is specifically 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, or 95 nm.
• Ra may fall within a range of 70 nm to 95 nm.
• the hardness of the electroplated gold layer falls within a range of 90 HV to 120 HV.
• the hardness of the electroplated gold layer is still greater than or equal to 90 HV, for example, 90 HV to 120 HV, and may further range from 95 HV to 120 HV.
• the electroplated gold layer has both relatively high toughness and hardness, and has a good application prospect.
• An embodiment of this application further provides an electronic device provided with the foregoing gold-electroplated part.
• the term "and/or" describes an association relationship between associated objects and may indicate that three relationships may exist.
• a and/or B may indicate the following cases: Only A exists, both A and B exist, and only B exists, where A and B may be singular or plural.
• the character "/" generally indicates an "or" relationship between the associated objects.
• At least one means one or more, and "a plurality of” means more than or equal to two.
• At least one of the following items (pieces/types) or a similar expression thereof means any combination of these items, including any combination of singular items (pieces) or plural items (pieces).
• "at least one item (piece) of a, b, or c" or "at least one item (piece) of a, b, and c" may indicate: a, b, c, a-b (namely, a and b), a-c, b-c, or a-b-c, where a, b, and c each may be singular or plural.
• HEDP hydroxyethylidene diphosphonic acid
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "65 g of HEDP" is replaced with "65 g of monopotassium phosphate”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "5 g of ⁇ -cyclodextrin" is replaced with "0.1 g of ⁇ -cyclodextrin".
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "10 mg of lead acetate” is replaced with “5 mg of lead acetate”, and “5 g of ⁇ -cyclodextrin” is replaced with "0.1 g of dextrin”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "10 mg of lead acetate” is replaced with “5 mg of lead acetate”, and "5 g of ⁇ -cyclodextrin” is replaced with "5 g of dextrin”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "10 mg of lead acetate” is replaced with “5 mg of lead acetate”, and "5 g of ⁇ -cyclodextrin” is replaced with “5 g of ⁇ -cyclodextrin”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "10 mg of lead acetate” is replaced with “5 mg of lead acetate”, and "5 g of ⁇ -cyclodextrin” is replaced with "0.1 g of ⁇ -cyclodextrin”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "65 g of HEDP” is replaced with "65 g of amino trimethylene phosphonic acid (ATMP)".
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "65 g of HEDP” is replaced with “65 g of amino trimethylene phosphonic acid (ATMP)", “10 mg of lead acetate” is replaced with “5 mg of lead acetate”, and “5 g of ⁇ -cyclodextrin” is replaced with "0.1 g of ⁇ -cyclodextrin”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 1 in that: "65 g of HEDP” is replaced with “65 g of amino trimethylene phosphonic acid (ATMP)", “10 mg of lead acetate” is replaced with “5 mg of lead acetate”, and “5 g of ⁇ -cyclodextrin” is replaced with "1 g of dextran”.
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 7 in that: "65 g of ATMP" is replaced with "30 g of ATMP".
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 7 in that: "65 g of ATMP" is replaced with "10 g of ATMP” .
• a gold electroplating solution is provided, and the gold electroplating solution differs from the gold electroplating solution in Embodiment 7 in that: "65 g of ATMP" is replaced with "90 g of ATMP".
• each of the electroplating solutions in the embodiments and the comparative example is placed in a Yamamoto vertical electroplating tank, a temperature of the electroplating solution is controlled to be maintained at 40°C, and electroplating is performed at a current density of 0.5 ASD for 32 min with a platinum-coated titanium plate as an anode and a fresh unpatterned gold-electroplated silicon wafer as a cathode, to obtain a gold-electroplated part. After the electroplating is completed, precipitation efficiency of each electroplating solution is calculated. Results are compiled in Table 1.
• hardness, before heat treatment, of electroplated layers formed on unpatterned gold-electroplated silicon wafers and hardness of the electroplated layers after heat treatment at 280°C for 30 min are tested by using a Vickers hardness tester. Results are compiled in Table 1.
• the precipitation efficiency of the electroplating solution may be measured by using a gravimetric method, after electroplating is completed.
• the parameter is specifically a ratio of a weight of gold obtained through electroplating to a theoretical weight of monovalent gold to which total electric charge that passes through during electroplating is converted.
• a load of 10 gf is applied to hold an indenter on a surface of the electroplated layer for 10s, to test the hardness of the electroplated layer.
• FIG. 4 compiles microscopic profile images of gold bumps obtained through electroplating on patterned silicon wafers using the electroplating solution in Embodiment 1 and the electroplating solution in Comparative Example 1 respectively, where magnifications are 500x.
• (a) in FIG. 4 is the image of the gold bump obtained by using the electroplating solution in Embodiment 1
• (b) in FIG. 4 is the image of the gold bump obtained by using the electroplating solution in Comparative Example 1. It can be learned from FIG. 4 that, the electroplated gold layer formed through electroplating using the electroplating solution with an organic phosphonic acid as a conductive medium in Embodiment 1 of this application has a relatively uniform appearance with almost no noticeably protruding particles.
• each image in FIG. 4 is divided into a plurality of rectangular areas with dimensions of 50 ⁇ m x 50 ⁇ m, and there are more than three gold nodules in each of the plurality of rectangular areas.
• a patterned silicon wafer is designed based on an actual requirement.
• the patterned silicon wafer is a patterned silicon wafer with an Au seed layer deposited on a surface.
• a specific structure of the patterned silicon wafer may be shown in (A) in FIG. 1 .
• a surface cross-sectional structure of a middle part of the patterned silicon wafer from bottom to top is Si/SiO 2 /Al/TiW/Au.
• the substrate 1 is a silicon substrate with SiO 2
• the electrode 2 is Al
• the lower metal layer 4 is a TiW layer and an Au seed layer that are stacked.
• a negative photoresist PR NR9-8000 (Futurrex) is used to form a bump opening. Dimensions of the bump opening are 80 ⁇ m (length) x 20 ⁇ m (width w) x 15 ⁇ m (depth h).
• a passivation layer with a height of 1.2 ⁇ m is designed on the aluminum electrode, and a width w 1 of an opening, in the passivation layer, that can expose the aluminum electrode is 12 ⁇ m.
• Gold electroplating is performed in the bump opening by using each electroplating solution.
• a temperature of the electroplating is 40°C
• a current density of the electroplating is 0.5 ASD
• duration of the electroplating is 32 min.
• the photoresist is removed by using an N-methylpyrrolidinone (NMP) solvent, to obtain a gold bump filled in the bump opening, and a shape and a height of the gold bump are measured by using VK-X3100.
• NMP N-methylpyrrolidinone
• FIG. 5 is a cross-sectional view of a patterned silicon wafer provided with a gold bump and formed through electroplating using the electroplating solution in Embodiment 1 of this application. It can be learned from FIG. 5 that a shape of the obtained gold bump is relatively regular, and no phenomenon of skipping plating or infiltration plating occurs.
• FIG. 6 compiles a top-view microscopic image (a in FIG. 6 ) of the patterned silicon wafer provided with the gold bump and obtained by using the electroplating solution in Embodiment 1, a top-view profile image (b in FIG. 6 ) of the gold bump, a top-view microscopic image (c in FIG. 6 ) of a patterned silicon wafer provided with a gold bump and obtained by using the electroplating solution in Comparative Example 1, and a top-view profile image (d in FIG. 6 ) of the gold bump, where magnifications in FIG. 6 are 500x.
• a shape of the gold bump obtained through electroplating is relatively regular, no phenomenon of skipping plating or infiltration plating occurs, and no photoresist dissolution or breakage occurs (a location at which the photoresist exists corresponds to gaps between long strip-shaped gold bumps in a and c in FIG. 6 ).
• a height of the gold bump prepared by using the electroplating solution in Embodiment 1 is 9.681 ⁇ m, and a height of the gold bump prepared by using the electroplating solution in Comparative Example 1 is 10.396 ⁇ m.
• a maximum height difference of a front end of a gold bump that is, a height difference between a point closest to the aluminum electrode and a point farthest to the aluminum electrode on a surface that is of the gold bump and that is away from a side of the electrode, that is, a height difference between two points a and b shown in (B) in FIG. 1
• a height difference of a front end of the gold bump obtained by using the electroplating solution in Comparative Example 1 is approximately 1.31 ⁇ m
• a height difference of a front end of the gold bump obtained by using the electroplating solution in Embodiment 1 is only approximately 0.90 ⁇ m.
• the electroplating solution in which an organic phosphonic acid is used to replace inorganic phosphate has relatively good leveling performance.
• High flatness of the front end of the gold bump can greatly increase an effective contact area between the gold bump and a substrate during thermal compression bonding, thereby ensuring a relatively high bonding success rate and a more reliable bonding structure.
• Table 1 further compiles data such as precipitation efficiency of electroplating solutions in other embodiments of this application when electroplating is performed on unpatterned silicon wafers by using the electroplating solutions, and hardness of electroplated layers before and after heat treatment. It can be learned from a comparison between Embodiment 1 and Embodiment 7 that, when concentrations of other components in the electroplating solutions are the same, concentrations of added organic phosphonic acids are the same, but types of the organic phosphonic acids are different, the electroplating solutions also have high precipitation efficiency, and hardness of electroplated layers after heat treatment is also high.
• Embodiment 6 and Embodiment 8 are also different in only types of added organic phosphonic acids in the electroplating solutions, so results in the two embodiments are also relatively close to each other.
• Embodiment 7 it can be learned from a comparison between Embodiment 7 and Embodiments 10 to 12 that, when mass of a same type of organic phosphonic acid added in the electroplating solutions is different, and concentrations of organic acid conductive media in the electroplating solutions in terms of organic phosphonic acids are allowed to be greater than 30 g/L, for example, in a range of 55 g/L to 90 g/L, the electroplating solutions have appropriate viscosity and relatively high precipitation effects, and obtained gold bumps have appropriate hardness and good surface flatness.
• hardness of each of electroplated layers obtained by using the electroplating solutions in the embodiments of this application may fall within a range of 95 HV to 120 HV, and may further fall within a range of 96 HV to 120 HV. Because hardness of an electroplated layer usually decreases with an increase of a heat treatment temperature, it may be understood that, for the electroplated layers obtained in the embodiments of this application, if heat treatment is performed at a relatively low temperature (for example, heat treatment is performed at 250°C for 0.5 hour), hardness of each electroplated layer after the heat treatment may definitely be greater than 95 HV, for example, may fall within a range of 100 HV to 120 HV.
• gold bumps formed on the patterned silicon wafers by using the electroplating solutions in Embodiments 2 to 12 of this application also have a similar effect as that in Embodiment 1.
• a shape of the gold bump is regular, and no skipping plating or infiltration plating occurs.
• a surface that is of the gold bump and that is away from the silicon substrate has a uniform appearance, and a maximum height difference (corresponding to Rz in Table 1) on the surface that is of the gold bump and that is away from the silicon substrate is also relatively low, and is basically less than 1.1 ⁇ m. This indicates that the surface of the gold bump is relatively flat, facilitating bonding between the patterned silicon wafer and a routing substrate, and the like.

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