Copper etching liquid and etching method for semiconductor packaging

Abstract

The invention discloses a copper etching solution for semiconductor packaging, which mainly comprises, by mass percentage, 1% to 8% of an oxidant, 21% to 40% of an inorganic acid, 6% to 30% of an organic carboxylic acid, 0.001% to 15% of a chelating agent, 0% to 3% of a corrosion inhibitor, and the balance of deionized water; the organic carboxylic acid is composed of a first carboxylic acid and a second carboxylic acid, the first carboxylic acid is selected from at least one of a monocarboxylic acid and a dicarboxylic acid, and the second carboxylic acid is at least one of a tricarboxylic acid or higher. The copper etching solution for semiconductor packaging of the invention reduces the etching speed and improves the etching accuracy by optimizing the organic carboxylic acid and adjusting the etching solution component content, completely etches and removes the copper seed layer, and reduces the side loss of the copper etching solution to other copper layers in the redistribution layer and the metal bump, so that the morphology of the redistribution layer and the metal bump is more regular, and the structural stability of the redistribution layer and the metal bump is improved. The invention also discloses an etching method based on the copper etching solution for semiconductor packaging.

Description

Technical Field

[0001] The invention relates to the technical field of electronic chemicals, and in particular to a copper etching solution and an etching method for semiconductor packaging. Background Art

[0002] In the wafer-level packaging process, the redistribution layer (RDL) is a metal wiring formed by depositing a metal layer and a dielectric layer on the surface of the wafer. The common materials of the redistribution layer are copper or gold, which have poor adhesion to the substrate silicon dioxide / silicon, so a metal adhesion layer (titanium or titanium tungsten) is set between the redistribution layer and the silicon dioxide / silicon. Copper is sputtered on the surface of the adhesion layer as the copper seed layer of the redistribution layer, and the under bump metallurgy (UBM) includes the above adhesion layer and copper seed layer. After the redistribution layer is plated, the excess under bump metallurgy layer in the non-graphic area on the substrate needs to be etched away, including two steps: first, the non-graphic area of ​​the copper seed layer is etched away to obtain a stacked structure of the redistribution layer and the graphic area of ​​the copper seed layer; then the non-graphic area of ​​the adhesion layer is etched away to obtain a stacked structure of the redistribution layer, the copper seed layer and the graphic area of ​​the adhesion layer.

[0003] The metal bump is stacked above the contact of the metallization layer under the bump, serving as the contact area connecting the internal leads of the chip with the external package solder balls. The solder ball on the top of the metal bump will diffuse and deform during connection, and the copper pillar under the solder ball can maintain its shape, so the copper pillar is mostly used in high-density interconnection and fine-pitch chips. The copper seed layer at the bottom of the metal bump is connected to the polyimide through an adhesion layer (usually a titanium layer), and the stacked structure from the titanium layer to the top of the bump can be selected as titanium-copper-nickel-tin-silver, titanium-copper-nickel-copper-tin-silver. After the tin-silver ball is implanted on the top of the bump, the non-patterned area of ​​the second seed layer needs to be etched away to obtain the second seed layer and the metal bump stacked structure thereon.

[0004] In order to provide higher interconnection density, the line width and line spacing of the redistribution layer metal wiring are getting smaller and smaller. The thickness of the copper seed layer of the metallization layer under the bump is usually 10 3 The thickness of the redistribution layer and the copper seed layer is usually in the order of nanometers, such as 0.2μm to 0.5μm, while the sum of the thickness of the stacked structure of the redistribution layer and the copper seed layer is usually in the order of micrometers, such as about 2μm. The above small-size packages require higher etching accuracy of the etching solution. While the copper etching solution etches away the copper seed layer, it reacts with the top and side surfaces of the redistribution layer. Similarly, while etching away the copper seed layer at the bottom of the bump, the copper pillars in the metallization layer under the bump will also be undercut and undercut. Excessive local undercutting around the bump will directly affect the structural stability of the tin bump and even cause the bump to collapse.

[0005] How to reduce the etching rate of the copper etching solution on the side of the stacked structure in the graphic area on the basis of completely etching away the copper seed layer, and improve the versatility of the same etching solution in etching the redistribution layer and the metal bump copper seed layer, is the main problem that technicians in this field need to overcome. Summary of the invention

[0006] One of the purposes of the present invention is to overcome the defects in the prior art and provide a copper etching solution for semiconductor packaging. By optimizing the mass fraction of each component of the copper etching solution and the organic carboxylic acid composition, the copper etching solution can be used for etching the copper seed layer of the redistribution layer and the metal bump, and the lateral loss of the copper layer in the redistribution layer and the metal bump during the etching process can be effectively controlled.

[0007] In order to achieve the above object, the technical solution of the present invention is: a copper etching solution for semiconductor packaging, characterized in that, by mass percentage, the main components are: 1% to 8% oxidant, 21% to 40% inorganic acid, 6% to 30% organic carboxylic acid, 0.001% to 15% chelating agent, 0 to 3% corrosion inhibitor and the balance deionized water;

[0008] The organic carboxylic acid is composed of a first carboxylic acid and a second carboxylic acid, wherein the first carboxylic acid is at least one selected from a monocarboxylic acid and a dicarboxylic acid, and the second carboxylic acid is at least one of a tricarboxylic acid or higher.

[0009] Furthermore, the mass percentage of the corrosion inhibitor in the copper etching solution for semiconductor packaging is 0.001% to 3%.

[0010] The copper etching solution for semiconductor packaging does not contain organic base components, and the organic base includes organic amine and quaternary ammonium base.

[0011] The preferred technical solution is that the mass percentage of the first carboxylic acid is 6% to 22%, and the mass percentage of the second carboxylic acid is 0% to 7%; further, the mass percentage of the first carboxylic acid is 6% to 12%, and the mass percentage of the second carboxylic acid is 0.5% to 6%.

[0012] A preferred technical solution is that the first carboxylic acid is at least one selected from lactic acid, glycolic acid, malic acid, tartaric acid, and malonic acid; and the second carboxylic acid is at least one selected from citric acid and ethylenediaminetetraacetic acid.

[0013] A preferred technical solution is that the inorganic acid is phosphoric acid.

[0014] The preferred technical solution is that the mass fraction of phosphoric acid in the copper etching solution is 24% to 35%; specifically, 24%, 26%, 28%, 30%, 32%, 34%, 35% point values ​​or a data interval with any two of the above point values ​​as the maximum and minimum values ​​can be selected; further, the mass fraction of phosphoric acid in the copper etching solution is 28% to 33%.

[0015] The preferred technical solution is that the oxidant is hydrogen peroxide; further, the mass fraction of hydrogen peroxide in the copper etching solution is 2% to 6%, and 2%, 3.5%, 4%, 4.5%, 5%, 6% or any two of the above points can be selected as the maximum and minimum data intervals; further, the mass fraction of hydrogen peroxide in the copper etching solution is 2.5% to 5%. Hydrogen peroxide is added to the copper etching solution composition in the form of hydrogen peroxide.

[0016] The preferred technical solution is that the mass percentage of the chelating agent is 0.01% to 5%, which can be selected as 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 1.2%, 1.7%, 2%, 2.2%, 2.7%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, 5% point value or a data interval with any two of the above points as the maximum and minimum values. Further, the mass percentage of the chelating agent is 0.1% to 2%; further, the mass percentage of the chelating agent is 0.1% to 0.8%.

[0017] A preferred technical solution is that the chelating agent is at least one selected from an organic phosphonic acid chelating agent and sodium gluconate; further, the chelating agent is at least one selected from an organic phosphonic acid chelating agent.

[0018] The preferred technical solution is that the corrosion inhibitor is selected from azole inhibitors; further, the corrosion inhibitor is at least one selected from triazole inhibitors, tetrazole inhibitors, and thiazole inhibitors; further, the nitrogen-containing heterocyclic ring of the corrosion inhibitor has amino and / or thiol substituents. Furthermore, on the basis that the chelating agent is at least one selected from organic phosphonic acid chelating agents, the use of a corrosion inhibitor having a nitrogen-containing heterocyclic ring with amino and / or thiol substituents is beneficial to obtain a better morphology of the redistribution layer and the metal bump.

[0019] The second object of the present invention is to provide an etching method, using the above-mentioned copper etching solution for semiconductor packaging to etch a semiconductor element, the semiconductor element includes a copper seed layer, a first copper layer of a predetermined pattern is stacked on the surface of the copper seed layer, further, the first copper layer is connected to the copper seed layer, and / or an intermediate metal layer is sandwiched between the first copper layer and the copper seed layer. The intermediate metal layer can be a nickel layer.

[0020] Furthermore, the etching temperature is 15 to 30°C, preferably 20 to 25°C.

[0021] The advantages and beneficial effects of the present invention are:

[0022] The copper etching solution for semiconductor packaging of the present invention reduces etching speed and improves etching precision by optimizing organic carboxylic acid and adjusting the content of etching solution components, and while completely removing the copper seed layer by etching, makes the morphology of the redistribution layer and the metal bump more regular, reduces the lateral loss of the copper etching solution to other copper layers in the redistribution layer and the metal bump, and improves the structural stability of the redistribution layer and the metal bump. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of a semiconductor component before and after RDL etching;

[0024] Figure 2 It is a schematic diagram of the structure of a semiconductor component before and after bump etching;

[0025] Figure 3 is 75% OE Example 1 ( Figure 3 Left side) and Comparative Example 1 ( Figure 3 Right) Photographs of the RDL side morphology;

[0026] Figure 4 is 75% OE Example 1 ( Figure 4 Left side) and Comparative Example 3 ( Figure 4 Left side) Photographs of the morphology after BUMP etching. DETAILED DESCRIPTION

[0027] The specific implementation of the present invention is further described below in conjunction with the examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0028] Components of copper etching solution for semiconductor packaging

[0029] Oxidants

[0030] The main function of the oxidant is to react with copper to generate copper oxide. The oxidant may include hydrogen peroxide, potassium persulfate, sodium persulfate, preferably hydrogen peroxide.

[0031] Inorganic acid

[0032] The main function of the inorganic acid is to dissolve copper oxide, and the inorganic acid may include nitric acid, sulfuric acid, and phosphoric acid, preferably nitric acid and phosphoric acid. The oxidizing property of nitric acid limits its content in the copper etching solution. Usually, the upper limit of nitric acid content is 2%, and the etching speed is too fast, and the difficulty of controlling the etching speed increases. Therefore, phosphoric acid is more preferred.

[0033] Organic carboxylic acid

[0034] The main function of organic carboxylic acids is to provide H +. The organic carboxylic acid is composed of a first carboxylic acid and a second carboxylic acid. The first carboxylic acid may include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, lactic acid, glycolic acid, hydroxybutyric acid, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid, tartaric acid, malonic acid, and maleic acid; the second carboxylic acid may include citric acid, ethylenediaminetetraacetic acid, and ethylenediaminetriacetic acid. The preferred content range of the organic carboxylic acid in the etching solution system is 6% to 20%. The greater the content of the organic carboxylic acid within this content range, the better the etching morphology of the obtained bump and RDL line.

[0035] Chelating agents

[0036] The main function of the chelating agent is to chelate the copper ions produced by the dissolution of copper oxide by inorganic acid. The organic phosphonic acid chelating agent can be selected from hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, aminodi(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), hexamethylenediaminetetramethylenephosphonic acid.

[0037] The combined use of organic phosphonic acid chelating agent, sodium gluconate and inorganic phosphoric acid is beneficial to maintaining the stability of hydrogen peroxide in the etching solution system and delaying the decomposition of hydrogen peroxide.

[0038] Corrosion Inhibitors

[0039] The main function of the corrosion inhibitor is to make etching and metal protection proceed simultaneously, and to work together with the oxidant, inorganic acid, and organic carboxylic acid that play an etching role to reduce the roughness of the top surface of the redistribution layer bump after etching, and the roughness of the top surface of the redistribution layer bump meets the adhesion of polyimide. The corrosion inhibitor containing nitrogen heterocyclic rings with amino and / or mercapto substituents can be selected including mercaptobenzotriazole, 5-amino-1H-tetrazole, 5-mercapto-1-methyltetrazole (MMT), 5-(methylthio)-1H-tetrazole, aminotriazole, aminotetrazole, 1-aminobenzotriazole, and 3-amino-5-phenyl-1,2,4-triazole.

[0040] Other components

[0041] The copper etching solution for semiconductor packaging can be optionally composed of an oxidant, an inorganic acid, an organic carboxylic acid, a chelating agent and a corrosion inhibitor, or in addition to the above components, it can also include components commonly used in wet etching compositions such as surfactants, and play the corresponding functions of the components.

[0042] The following chemicals used in the examples were all commercially available analytically pure.

[0043] Oxidant: Hydrogen peroxide (add 31% hydrogen peroxide to the etching solution)

[0044] Inorganic acid: phosphoric acid

[0045] Organic carboxylic acids: lactic acid, citric acid, malonic acid, ethylenediaminetetraacetic acid;

[0046] Chelating agents: aminotrimethylenephosphonic acid (ATMP), sodium gluconate;

[0047] Corrosion inhibitors (referred to as inhibitors in the table): aminotetrazole, 5-(methylthio)-1H-tetrazole, 1-aminobenzotriazole;

[0048] Solvent: deionized water.

[0049] The examples (abbreviated as S) and comparative examples (abbreviated as D) were prepared according to the following table:

[0050]

[0051]

[0052] The etching solutions of the embodiments and comparative examples were used for etching of the following semiconductors:

[0053] 1. Copper etching redistribution layer copper seed layer of semiconductor components

[0054] The structure of the semiconductor element before etching for preparing the redistribution layer is as follows Figure 1 As shown: the blank and shaded parts between the dotted line and the substrate represent the copper seed layer, the blank part of the layer above the dotted line and the shaded parts on the top and side of the blank part represent the bumps (electroplated copper layer) based on the copper seed layer; the shaded part represents the part to be removed by etching, and the blank parts above and below the dotted line represent the redistribution layer RDL after etching; L1 represents the thickness of the copper seed layer of the redistribution layer, and L2 represents the side loss of the Cu-1 layer; L1 of the etched sample is

[0055] Etching test conditions for redistribution layer semiconductor components: etching temperature is 23±1℃, normal pressure; based on EPD (etching end point detection), the sample is overetched by 70%, and the side loss of OE70% is obtained, see the table below:

[0056]

[0057] 2. Copper etching metal bumps copper seed layer of semiconductor components

[0058] The structure of the semiconductor element before etching for preparing metal bumps is as follows Figure 2 As shown in the figure: the blank and shaded part between the dotted line and the substrate represent the copper seed layer, and the Cu-2 layer, nickel layer, Cu-3 layer, and tin-silver layer are above the dotted line in order. The shaded part in the figure represents the part to be removed by etching, and the blank part above and below the dotted line represents the metal bump; L3 represents the thickness of the copper seed layer of the metal bump, L4 represents the side loss of the Cu-2 layer, and L5 represents the side loss of the Cu-3 layer.

[0059] Take L3 of the etched sample as

[0060] The 75% OE samples L4 and L5 are similar, so they are expressed with the same side loss value. Etching test conditions for redistribution layer semiconductor components: etching temperature is 23±1℃, normal pressure; based on EPD (etching end point detection), the sample is overetched by 70%, and the side loss of OE70% is obtained, see the table below:

[0061]

[0062] *The slight undercut of Cu-3 has little effect on the structural stability of the metal bump;

[0063] **Cu-3 moderate undercut and severe undercut have a significant impact on the structural stability of the metal bump, so it is judged as NG.

[0064] From the etching results, we can see that:

[0065] Comparison of S1, D1, and D2 shows that the combined use of the first carboxylic acid and the second carboxylic acid has a synergistic effect on improving the RDL line and bump morphology;

[0066] The preferred etching solution system of hydrogen peroxide, phosphoric acid and organic carboxylic acid is also conducive to further improving the RDL line and bump morphology. The side loss of the RDL line is stably controlled within a range of less than 0.5 μm, and the side loss of the bump is stably controlled within a range of less than 1 μm.

[0067] The above data proves that the etching solution system of the embodiment meets the etching requirements of both the RDL line and the bump.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A copper etching solution for semiconductor packaging, characterized in that: The main components are, by mass percentage, 1% to 8% of an oxidant, 21% to 40% of an inorganic acid, 6% to 17% of an organic carboxylic acid, 0.001% to 15% of a chelating agent, 0% to 3% of a corrosion inhibitor, and the balance of deionized water; the organic carboxylic acid is composed of a first carboxylic acid and a second carboxylic acid. The first carboxylic acid is at least one selected from lactic acid, glycolic acid, malic acid, tartaric acid, and malonic acid; the second carboxylic acid is at least one selected from citric acid and ethylenediaminetetraacetic acid; The mass percentage of the first carboxylic acid is 6% to 12%, and the mass percentage of the second carboxylic acid is 0.5% to 6%; The inorganic acid is phosphoric acid; The oxidant is hydrogen peroxide.

2. The copper etching solution for semiconductor packaging according to claim 1, characterized in that The mass fraction of phosphoric acid in the copper etching solution is 24% to 35%.

3. The copper etching solution for semiconductor packaging according to claim 2, characterized in that: The mass fraction of phosphoric acid in the copper etching solution is 28% to 33%.

4. The copper etching solution for semiconductor packaging according to claim 1, characterized in that The mass fraction of hydrogen peroxide in the copper etching solution is 2% to 6%.

5. The copper etching solution for semiconductor packaging according to claim 4, characterized in that: The mass fraction of hydrogen peroxide in the copper etching solution is 2.5% to 5%.

6. The copper etching solution for semiconductor packaging according to claim 1, characterized in that: The mass percentage of the chelating agent is 0.01% to 5%.

7. The copper etching solution for semiconductor packaging according to claim 1, characterized in that: The chelating agent is at least one selected from organic phosphonic acid chelating agents and sodium gluconate.

8. The copper etching solution for semiconductor packaging according to claim 1, characterized in that: The corrosion inhibitor is selected from azole inhibitors.

9. The copper etching solution for semiconductor packaging according to claim 8, characterized in that: The corrosion inhibitor is at least one selected from a triazole inhibitor, a tetrazole inhibitor, and a thiazole inhibitor.

10. The copper etching solution for semiconductor packaging according to claim 8, characterized in that: The nitrogen-containing heterocyclic ring of the corrosion inhibitor has amino and / or mercapto substituents.

11. An etching method, characterized in that: A semiconductor element is etched using the copper etching solution for semiconductor packaging as claimed in any one of claims 1 to 10, wherein the semiconductor element comprises a copper seed layer, and a first copper layer with a predetermined pattern is stacked on the surface of the copper seed layer.

12. An etching method according to claim 11, characterized in that: The first copper layer is connected to the copper seed layer, and / or an intermediate metal layer is sandwiched between the first copper layer and the copper seed layer.

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