Composite additive for semiconductor gold plating solution and application thereof

Abstract

The invention belongs to a gold plating solution, and particularly relates to a composite additive for a semiconductor gold plating solution and application of the composite additive. The tellurite derivative comprises tellurite and substituted benzaldehyde, wherein the substituted benzaldehyde is shown as a general formula I, wherein R is selected from sulfonyl or a derivative thereof. According to the technical scheme provided by the invention, through synergistic compounding of tellurite and substituted benzaldehyde, the grain refinement degree and grain orientation of the plating layer are remarkably improved, so that the surface of the plating layer is flat and bright, and the gold plating layer with high compactness and high conductivity is obtained. And the gold plating solution can meet the defect-free thickness requirement of 0.05-40 [mu] m. Besides, the hardness of the plating layer before annealing is 60-100 HV, the electroplating liquid can operate in a wide process window (the current density is 0.5-5 A / dm, and the temperature is 50-70 DEG C), and various application requirements of semiconductor gold wiring, gold bumps, RDL gold layers and the like can be met.

Description

Technical Field

[0001] This invention pertains to gold plating solutions, specifically relating to a composite additive for semiconductor gold plating solutions and its application. Background Technology

[0002] In the semiconductor and microelectronics packaging industry, gold plating has become a core choice for critical interconnect structures due to its unique material properties. Gold plating has low and stable contact resistance and is one of the most conductive materials among metals, effectively reducing electrical signal transmission losses. It is also highly chemically inert, not reacting with air, water, or most acids and alkalis at room temperature and pressure, providing long-term corrosion protection for devices. At the same time, gold has excellent thermal stability and bonding performance, enabling stable mechanical connections and electrical conduction in packaging processes such as wire bonding and flip-chip bonding. Therefore, it is widely used in various packaging structures from traditional discrete devices to advanced integrated circuits (ICs).

[0003] Compared to gold plating in other fields, gold plating in the semiconductor field requires extremely high flatness, density, and uniform current distribution. Cyanide gold plating solutions are stable, have excellent covering power, high current efficiency, and produce dense, defect-free plating. However, these solutions are significantly toxic, posing a huge threat to human survival and environmental remediation.

[0004] However, existing cyanide-free systems typically require the addition of highly toxic metal additives (such as antimony, arsenic, and thallium) to achieve bright and smooth coatings. For example, Chinese patent CN114934302A discloses a scheme for obtaining high-hardness gold bumps using additives containing antimony, arsenic, and thallium. These heavy metal ions, by adsorbing onto the cathode surface, alter the nucleation rate of metal deposition, thereby improving the appearance of the coating. Although the amount of these highly toxic metal additives used is small, their residue in the coating can lead to performance degradation in semiconductor devices. Summary of the Invention

[0005] This invention provides a composite additive for semiconductor gold plating solutions and its application, in order to solve the technical problem that current cyanide-free gold plating solutions require the addition of highly toxic metal additives to achieve a bright and smooth plating layer.

[0006] To address the aforementioned technical problems, the present invention provides a composite additive for semiconductor gold plating solutions, comprising tellurite and substituted benzaldehyde, wherein the substituted benzaldehyde is shown in general formula I:

[0007]

[0008] I

[0009] R is selected from sulfonyl groups or their derivatives.

[0010] The standard reduction potential of tellurite at the cathode is approximately -0.57 V, close to that of gold complexes (-0.38 V). The introduction of trace amounts of tellurium leads to partial distortion of the crystal structure, refining the grains to 50–100 nm. Substituted benzaldehyde forms an anion adsorption film on the cathode surface, while the aldehyde groups align along the surface electric field direction. Their polarity causes molecules to preferentially adsorb onto the micro-convex regions, inhibiting localized metal deposition. In the plating bath, tellurite micro-polarizes the cathode, increasing the local overpotential and promoting fine-grain deposition; while the substituted benzaldehyde forms a uniform adsorption layer, further improving grain orientation. The synergistic effect of these two factors achieves high gloss and smoothness over a wide current density range.

[0011] Optionally, the tellurite is selected from sodium tellurite and / or potassium tellurite.

[0012] Optionally, the sulfonyl group or its derivative is –SO3H, –SO3R1, or –SO3M, wherein R1 is a C1-C4 alkyl group and M is Na. + K + or NH4 + .

[0013] Optionally, the substituted benzaldehyde is selected from one or more of o-sulfonylbenzaldehyde, m-sulfonylbenzaldehyde, p-sulfonylbenzaldehyde, 2-sulfonylmethylbenzaldehyde, and sodium 2-sulfonate benzaldehyde.

[0014] Optionally, the ratio of the tellurite to the substituted benzaldehyde by mass is 2:1 to 1:8.

[0015] The present invention also provides a cyanide-free gold plating solution for semiconductors, comprising the above-mentioned composite additive for semiconductor gold plating solutions, and further comprising cyanide-free gold salt, complexing agent, conductive salt and stabilizer.

[0016] Optionally, the concentration of tellurite in the cyanide-free gold plating solution for semiconductors is 1~500 mg / L, preferably 2~50 mg / L, and more preferably 5~20 mg / L.

[0017] Optionally, the concentration of substituted benzaldehyde in the cyanide-free gold plating solution for semiconductors is 1~500 mg / L.

[0018] Optionally, the cyanide-free gold salt is selected from at least one of sodium gold sulfite, potassium gold sulfite, and ammonium gold sulfite.

[0019] Optionally, the complexing agent is selected from at least one of sodium sulfite, potassium sulfite, ammonium sulfite, sodium thiosulfate, potassium thiosulfate, and ammonium thiosulfate.

[0020] Optionally, the conductive salt is selected from at least one of sodium sulfate, potassium sulfate, and ammonium sulfate.

[0021] Optionally, the stabilizer is selected from at least one of ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine, and pentaethylenetetramine.

[0022] Optionally, the pH value of the cyanide-free gold plating solution for semiconductors is 7 to 8.4, preferably 7.5 to 8.2, and the pH adjuster is selected from at least one of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

[0023] If the pH value is too low, the stability of the plating solution cannot be guaranteed, and it will also cause the hydrolysis of sulfite or thiosulfate, reducing the life of the plating solution; if the pH value is too high, it will damage the photoresist.

[0024] Optionally, the concentration of gold ions in the cyanide-free gold plating solution for semiconductors is 5~20 g / L, the concentration of the complexing agent is 20~150 g / L, the concentration of the conductive salt is 20~150 g / L, and the concentration of the stabilizer is 1~50 g / L.

[0025] The gold ion concentration is calculated by converting the molar amount of gold ions in the plating solution into gold elemental concentration.

[0026] Optionally, the concentration of gold ions in the cyanide-free gold plating solution for semiconductors is preferably 3~18 g / L, more preferably 8~18 g / L.

[0027] Optionally, the complexing agent in the cyanide-free gold plating solution for semiconductors is sulfite, with a concentration of 30~120 g / L, preferably 40~80 g / L.

[0028] If the concentration of the complexing agent is too low, it cannot form a stable ligand with gold ions, resulting in an unstable plating solution; if the concentration of the complexing agent is too high, it will increase the viscosity of the plating solution, reduce the ion migration rate, and lead to a decrease in the deposition rate.

[0029] Optionally, the concentration of the conductive salt in the cyanide-free gold plating solution for semiconductors is preferably 30-120 g / L, more preferably 40-80 g / L.

[0030] Conductive salts can improve the conductivity of the plating solution, reduce the tank voltage, decrease energy consumption, and improve the uniformity of current distribution. If the conductive salt concentration is too low, the conductivity of the plating solution decreases, leading to an increase in tank voltage and energy consumption; if the conductive salt concentration is too high, the viscosity of the plating solution increases, which in turn reduces the ion migration rate.

[0031] Optionally, the stabilizer in the cyanide-free gold plating solution for semiconductors is ethylenediamine or diethylenetriamine, with a concentration of 5~40 g / L, preferably 10~30 g / L.

[0032] The role of stabilizers is to inhibit the oxidative decomposition of sulfite ions and adjust the pH value of the plating solution, thereby improving the long-term stability of the plating solution. If the stabilizer concentration is too low, it will not effectively inhibit the decomposition of sulfite ions, which is not conducive to the stability of the plating solution; if the concentration is too high, it will have a certain impact on the photoresist.

[0033] The technical solution provided by this invention significantly improves the grain refinement and orientation of the plating layer through the synergistic compounding of tellurite and substituted benzaldehyde, resulting in a smooth and bright plating surface and a gold plating layer with both high density and high conductivity. When used in gold plating solutions, it can meet the defect-free thickness requirement of 0.05–40 μm. Furthermore, the hardness of the plating layer before annealing is 60–100 HV, and the plating solution can operate within a wide process window (current density 0.5–5 A / dm², temperature 50–70 ℃), meeting the needs of various applications such as semiconductor gold wiring, gold bumps, and RDL gold layers. Attached Figure Description

[0034] Figure 1 This is a comparison chart of LSV curves of the cyanide-free gold plating solution for semiconductors described in Example 2 and the plating solution without the composite additives for semiconductor gold plating solutions. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Example 1: Gold plating bonding of semiconductor lead frames

[0037] Semiconductor leadframes serve as the connection carrier between chips and external circuits. The locally gold-plated areas (bonding areas) of these leadframes must possess high conductivity, high hardness, and excellent bonding performance to ensure the reliability of the wire bonding. This embodiment focuses on locally plating the bonding area (1 mm × 1 mm) of the leadframe.

[0038] The cyanide-free gold plating solution for semiconductors comprises: sodium gold sulfite (gold ion concentration 12 g / L), 60 g / L sodium sulfite, 40 g / L sodium sulfate, 30 g / L ethylenediamine, 20 mg / L potassium tellurite, and 10 mg / L p-sulfobenzaldehyde. The pH of the plating solution is adjusted to 8.2 using sodium hydroxide, and the remainder is deionized water.

[0039] Electroplating process conditions

[0040] Temperature: 60±2℃ (controlled by a constant temperature water bath, temperature fluctuation < ± 0.5℃);

[0041] Current density: 1.2 ASD;

[0042] Anode: Platinum electrode

[0043] Cathode: Semiconductor lead frame (substrate is Cu-Ni-Si alloy, pretreatment steps: degreasing → pickling → activation → pre-plating nickel);

[0044] Stirring speed: 600 rpm;

[0045] Electroplating time: 6 min;

[0046] Post-treatment: After electroplating, rinse twice with deionized water, and then dry at 80℃ for 5 minutes.

[0047] Coating performance test results

[0048] Thickness test: Using a white light interference microscope, five points were randomly selected in the bonding area of ​​the lead frame. The test results were 4.44 μm, 4.55 μm, 4.59 μm, 4.42 μm, and 4.53 μm, with an average value of 4.50 μm and a deviation of ±0.09 μm.

[0049] Surface roughness test: AFM test was used (scanning range 5 μm × 5 μm), Ra = 0.09 μm, which meets the requirement of < 0.1 μm;

[0050] Hardness test: The nano-indentation tester was used to test the hardness at 5 points randomly selected on the coating surface. The test results were 90 HV, 92 HV, 93 HV, 88 HV and 95 HV, with an average value of 92 HV.

[0051] Adhesion test: The cross-cut test was used (cross-cut spacing 1 mm, cross-cut depth to the substrate). After being pasted with 3M tape and then peeled off, the coating did not peel off, and the adhesion was ≥5 N / mm, which meets the requirements.

[0052] Conductivity test: The resistance was measured using a four-probe tester and was 2.6 mΩ / □, which meets the conductivity requirements of the semiconductor lead frame.

[0053] Example 2: Wafer Gold Bump Electroplating

[0054] Gold bumps on wafers are key interconnect structures in flip-chip packaging, used to achieve electrical connections between the chip and the substrate. Their performance directly affects the reliability of flip-chip bonding. This embodiment focuses on electroplating a gold bump array (bump diameter 30 μm, spacing 50 μm, array quantity 10,000) on an 8-inch silicon wafer.

[0055] The cyanide-free gold plating solution for semiconductors comprises: sodium gold sulfite (gold ion concentration 16 g / L), 40 g / L sodium sulfite, 40 g / L sodium sulfate, 20 g / L ethylenediamine, 10 mg / L potassium tellurite and 10 mg / L o-sulfobenzaldehyde, with the pH of the plating solution adjusted to 8.0 using sodium hydroxide, and the remainder being deionized water.

[0056] Electroplating process conditions

[0057] Temperature: 60±1℃ (controlled by constant temperature oil bath, temperature fluctuation <±0.3℃);

[0058] Current density: 1.2 ASD;

[0059] Anode: Platinum electrode (platinum purity 99.99%, area 25 cm², distance from wafer 5 cm);

[0060] Cathode: 8-inch silicon wafer (pre-processing steps: cleaning → photolithography → development → etching → activation, pattern is a bump array);

[0061] Stirring method: Magnetic stirring (stirrer speed 600 rpm);

[0062] Electroplating time: 6 minutes;

[0063] Post-processing: After electroplating, rinse twice with deionized water (30 seconds each time), then dry at 60°C for 3 minutes, and finally strip the photoresist.

[0064] Coating performance test results

[0065] Protrusion morphology and size test: An optical microscope (magnification 50x) was used. The diameter of the protrusions was 30±0.5 μm and the height was 1.5±0.07 μm. The height consistency was 4.7%, which meets the requirement of <5%.

[0066] Hardness test: The nano-indentation tester was used to test the coating surface. Five points were randomly selected. The test results were 80 HV, 82 HV, 79 HV, 78 HV and 84 HV, with an average value of 81 HV.

[0067] Annealing performance test: The wafer was annealed at 300 ℃ for 30 minutes. The hardness was tested and dropped to 45 HV, indicating that the ductility of the coating was improved after annealing, which can relieve stress during the bonding process.

[0068] Contact resistance test: The test was conducted using a probe station on 10 different bumps. The contact resistances were 0.9 mΩ, 1.1 mΩ, 1.0 mΩ, 1.2 mΩ, 0.8 mΩ, 1.0 mΩ, 1.1 mΩ, 0.9 mΩ, 1.2 mΩ, and 1.0 mΩ, with an average value of 1.0 mΩ.

[0069] MTO test

[0070] The plating solution was placed in an electroplating tank and continuously electroplated at 60°C and 1.2 ASD. Each MTO cycle was considered to consume 16 g / L of gold. The stability of the plating solution (whether gold precipitation occurred) and the performance of the coating were recorded after each half-cycle. The results are shown in Table 1. The plating solution in Example 2 remained stable after 3 MTO cycles, and the coating hardness remained at 80~88 HV.

[0071] Table 1

[0072] Plating bath life / MTO Plating solution stability Coating appearance Coating roughness / nm Average hardness / HV 0.5 Clear and without sediment Golden and smooth 50 81 1.0 Clear and without sediment Golden and smooth 70 84 1.5 Clear and without sediment Golden and smooth 61 82 2.0 Clear and without sediment Golden and smooth 56 85 2.5 Clear and without sediment Golden and smooth 75 86 3.0 Clear and without sediment Golden and smooth 80 82

[0073] The accelerated aging test (50℃, 30 days) showed that the solution was clear and free of precipitation, and the current efficiency remained above 98%. During 150 hours of continuous electroplating, the coating thickness fluctuation was less than ±5%, which is far superior to the traditional system.

[0074] Plating solution polarization curve test

[0075] The plating solution was placed in the electroplating tank. Using an electrochemical workstation, a three-electrode system was selected, with a platinum mesh electrode as the anode and Hg / HgO as the reference electrode. The test temperature was 333 K, and a linear sweep voltammetry curve was performed at a scan rate of 20 mV / s. Figure 1 By comparing the LSV curves of the gold plating solution with and without the added compound potassium tellurite and o-sulfobenzaldehyde solution in this embodiment, it can be observed that the gold deposition potential of the plating solution with the added compound potassium tellurite and o-sulfobenzaldehyde shifts significantly to the negative direction, thereby effectively obtaining gold-plated parts with low porosity, smooth and dense surface, and a bright golden appearance.

[0076] Example 3: Full Gold Plating of High-Frequency Semiconductor Devices

[0077] High-frequency semiconductor devices (such as power amplifiers for 5G base stations and receivers for satellite communications) typically transmit signals at frequencies above 10 GHz, requiring their internal conductive structures to possess low signal loss and high corrosion resistance. This embodiment focuses on fully gold-plating the metal casing (made of aluminum alloy) of the high-frequency device.

[0078] The cyanide-free gold plating solution for semiconductors comprises: sodium gold sulfite (gold ion concentration of 16 g / L), 60 g / L sodium sulfite, 60 g / L sodium sulfate conductive salt, 15 g / L diethylenetriamine, 20 mg / L potassium tellurite, and 150 mg / L o-sulfobenzaldehyde. The pH of the plating solution is adjusted to 8.0 using sodium hydroxide, and the remainder is deionized water.

[0079] Electroplating process conditions

[0080] Temperature: 65±2 ℃ (controlled by a constant temperature air bath, temperature fluctuation < ±0.5℃);

[0081] Current density: 2.5 ASD;

[0082] Anode: Platinum-titanium mesh (platinum coating thickness 5 μm, area 200 cm²);

[0083] Cathode: Metal casing of high-frequency device (pretreatment steps: degreasing → pickling → activation → pre-plating copper, pre-plating copper thickness 0.5 μm, to enhance adhesion);

[0084] Mixing method: air mixing + mechanical mixing (air flow rate 0.8 L / min, mechanical mixing speed 250 rpm);

[0085] Electroplating time: 8 minutes

[0086] Post-treatment: After electroplating, rinse three times with deionized water, and then dry at 100℃ for 10 minutes.

[0087] Coating performance test results

[0088] Thickness test: Using a white light interference microscope, 5 points were randomly selected in the bonding area of ​​the lead frame. The average coating thickness was 2.0 μm, with a deviation of ±0.1 μm.

[0089] Surface roughness test: AFM test (scanning range 10 μm × 10 μm) was used, Ra = 0.05 μm, which meets the requirement of < 0.1 μm;

[0090] Grain size test: XRD test was used, and the grain size was about 60 nm. The fine grain structure can reduce the scattering loss of high frequency signals.

[0091] Adhesion test: Tensile test was used, and the bonding strength between the coating and the substrate was 18 N / mm. 2 There is no peeling phenomenon, which meets the long-term use requirements of high-frequency devices.

[0092] Comparative Example 1:

[0093] Using the same basic formulation as in Example 1, 20 mg / L thallium acetate was used instead of tellurite, and o-sulfobenzaldehyde was not added.

[0094] Results: The appearance of the coating was similar to that of Example 1. Thickness test: the average thickness was 1.50 μm with a deviation of ±0.01 μm; the average hardness was 84 HV.

[0095] The above embodiments confirm that the cyanide-free gold electroplating solution provided by the present invention is environmentally friendly and non-toxic, has good stability, and produces a coating with excellent performance. It can effectively replace the trace amounts of highly toxic metal additives commonly added in traditional sulfurous acid systems.

[0096] Comparative Example 2

[0097] Referring to Example 1, p-sulfonylbenzaldehyde was removed, while other components remained unchanged. The cyanide-free gold plating solution comprises: sodium gold sulfite (gold ion concentration 12 g / L), 60 g / L sodium sulfite, 40 g / L sodium sulfate, 30 g / L ethylenediamine, 20 mg / L potassium tellurite, with the pH adjusted to 8.2 using sodium hydroxide, and the remainder being deionized water.

[0098] The plating process conditions were the same as in Example 1, and the plating performance test results are as follows:

[0099] Thickness test: Five points were randomly selected in the bonding area of ​​the lead frame using a white light interference microscope. The average thickness was 4.74 μm, with a deviation of ±0.15 μm.

[0100] Surface roughness test: AFM test was used (scanning range 5 μm × 5 μm), Ra = 0.16 μm, which does not meet the requirement of < 0.1μm, and the microstructure of the coating surface is black.

[0101] Comparative Examples 3-5

[0102] Using the same basic formulation as Example 1, Comparative Examples 3-5 used cerium nitrate, copper sulfate, or bismuth nitrate in the same molar amounts as in Example 1, respectively, instead of tellurite. The stability of the plating solution and the appearance and smoothness of the plating layer were scored, as shown in Table 1.

[0103] Grain refiner Plating solution stability Coating appearance Coating roughness (μm) Example 1 Potassium tellurite excellent Golden and shiny 0.09 Comparative Example 3 Cerium nitrate Difference Golden yellow, semi-glossy 0.14 Comparative Example 4 Copper sulfate excellent Reddish, shiny 0.17 Comparative Example 5 Bismuth nitrate excellent Grayish-white, glossy 0.08

[0104] Comparative Example 6

[0105] The same basic formulation as in Example 1 was used, but the potassium tellurite concentration was adjusted to 0.1 g / L and the p-sulfobenzaldehyde concentration to 10 mg / L. Under the same electroplating process conditions as in Example 1, the coating performance test results showed that the average coating thickness was 4.6 μm, with a deviation of ± 0.5 μm, and the smoothness was poor.

[0106] Based on the above embodiments and comparative examples, the cyanide-free gold electroplating solution provided by the present invention has the following advantages compared with traditional systems:

[0107] (1) Environmentally friendly and non-toxic: completely free of cyanide and heavy metal brighteners;

[0108] (2) High stability: No obvious precipitation occurred after storage at 50℃ for 30 days;

[0109] (3) The coating has excellent performance, with fine and dense grains, adjustable hardness (60–100 HV), and good adhesion.

[0110] (4) Strong process adaptability: suitable for gold plating of devices with complex morphology and microporous structure;

[0111] (5) The current efficiency is as high as 98% or more, and the gold utilization rate is high.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A complex additive for a semiconductor gold plating solution, characterized by, The compound additive for the gold plating solution for semiconductor includes a tellurite and a substituted benzaldehyde, wherein the substituted benzaldehyde is shown in general formula I: I wherein R is selected from a sulfonyl group or a derivative thereof.

2. The complex additive for a semiconductor gold plating solution according to claim 1, wherein The tellurite is selected from sodium tellurite and / or potassium tellurite.

3. The complex additive for a semiconductor gold plating solution according to claim 1, wherein The sulfonyl group or derivative thereof is -SO3H, -SO3R1, or -SO3M, wherein R1is C1-C4 alkyl and M is Na + , K + , or NH4 + .

4. The complex additive for a semiconductor gold plating solution according to claim 3, wherein The substituted benzaldehyde is selected from one or more of o-sulfobenzaldehyde, m-sulfobenzaldehyde, p-sulfobenzaldehyde, 2-sulfomethylbenzaldehyde and 2-sodium sulfobenzaldehyde.

5. The complex additive for a gold plating solution according to claim 1, wherein The mass ratio of the tellurite to the substituted benzaldehyde is 2:1 to 1:

8.

6. A cyanide-free gold plating solution for semiconductors, characterized by comprising: a gold salt; a complexing agent; a reducing agent; and a protective colloid. The compound additive for the gold plating solution for semiconductor includes a tellurite and a substituted benzaldehyde, wherein the substituted benzaldehyde is shown in general formula I:

7. The cyanide-free gold plating solution for a semiconductor according to claim 6, wherein The concentration of the tellurite in the cyanide-free gold plating solution for semiconductor is 1 to 500 mg / L, preferably 2 to 50 mg / L, and more preferably 5 to 20 mg / L.

8. The cyanide-free gold plating solution for a semiconductor according to claim 6, wherein The concentration of the substituted benzaldehyde in the cyanide-free gold plating solution for semiconductor is 1 to 500 mg / L.

9. The cyanide-free gold plating solution for a semiconductor according to claim 6, wherein The concentration of gold ions in the cyanide-free gold plating solution for semiconductor is 5 to 20 g / L, the concentration of the complexing agent is 20 to 150 g / L, the concentration of the conductive salt is 20 to 150 g / L, and the concentration of the stabilizer is 1 to 50 g / L.

10. The cyanide-free gold plating solution for a semiconductor according to claim 6, wherein The pH value of the cyanide-free gold plating solution for semiconductor is 7 to 8.4, preferably 7.5 to 8.2, and the pH value regulator is selected from at least one of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

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