Method for controlling surface concave-convex rate difference by adopting abrasive-free copper CMP (Chemical Mechanical Polishing) solution

Abstract

The invention relates to the technical field of chemical mechanical polishing, particularly discloses a method for controlling the surface concave-convex rate difference by adopting an abrasive-free copper CMP (Chemical Mechanical Polishing) solution, aims to realize abrasive-free chemical mechanical polishing so as to solve the problem of surface scratch caused by the abrasive action in the polishing process, and is suitable for a substrate polishing solution containing a copper metal layer. The polishing solution comprises a macromolecular chelating agent with the molecular weight of 300-500 g / mol, wherein the optimal molecular weight is 400 g / mol. The alkalescent copper polishing solution prepared by utilizing the macromolecular chelating agent has the advantages that the removal rate of concave parts is low and the polishing rate of convex parts is high through strong chemical reaction under the conditions of no abrasive and no corrosion inhibitor, so that the high-speed difference of the concave parts and the convex parts is generated, and the planarization is realized. Under the condition of alkalescence, no grinding material and no corrosion inhibitor, the polishing solution has high correction capacity on the height difference of the copper surface, and the problems of high polishing pressure, many surface scratches and difficulty in cleaning caused by a traditional method are solved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical mechanical polishing, in particular to a method for controlling the difference in surface concave-convex rate by using a copper CMP polishing liquid without abrasive. Background Art

[0002] Copper metal can be filled into the wiring groove by electrochemical plating (ECP). Since copper is plated on the wiring groove and the barrier layer at the same time, there will be a height difference on the surface of the graphic sheet after the electroplating. The purpose of copper CMP is to eliminate the surface height difference and achieve flattening. The traditional international flattening technology route is: adding corrosion inhibitor benzotriazole (BTA) and its derivatives to the polishing liquid to produce an organic passivation film to protect the copper in the concave part from chemical corrosion, and the convex part relies on the strong mechanical action provided by the abrasive to obtain a high polishing rate, thus forming a high removal rate difference between the concave and convex parts to achieve flattening. With the continuous development of technology nodes, the width of copper lines has become narrower, and surface defects after polishing will seriously affect the chip production yield and reliability. Among them, abrasives are the root cause of the above defects. In addition, the introduction of ultra-low-k dielectric materials requires low-pressure polishing, which makes the copper CMP process more biased towards the chemical action of the polishing liquid rather than the mechanical action. The formed BTA organic passivation film is not conducive to post-CMP cleaning, and requires strong mechanical force to remove, which is easy to damage the structure of the ultra-low-k dielectric material, resulting in delamination and shedding of the dielectric layer surface. The future development direction of copper polishing liquid is: mainly based on chemical action, low pressure, weak alkalinity, no abrasive and no corrosion inhibitor polishing.

[0003] Invention patent publication number CN101333419B discloses an abrasive-free alkaline copper CMP polishing liquid and obtains a polished surface with low scratches and low roughness, but does not involve research on the efficiency of flattening the surface height difference. Generally speaking, abrasive-free polishing mainly relies on chemical action to increase the polishing rate. Enhancing the chemical action of the polishing liquid will increase the removal rate of both the concave and convex parts at the same time, and cannot eliminate the performance height difference. According to the traditional flattening method, the abrasive can provide a strong mechanical force to remove the passivation film at the convex part and improve the line concave and convex rate difference. For the abrasive-free polishing liquid, the mechanical force is weak, and the passivation film at the convex part cannot be effectively removed. The presence of the passivation film hinders the progress of the chemical reaction, resulting in the corrosion inhibitor inhibiting the copper chemical reaction at the convex and concave parts of the line at the same time, and flattening cannot be achieved. How to solve the excellent selective removal ability of the copper line concave and convex parts in the abrasive-free polishing liquid based on chemical action is the main bottleneck restricting its wide application. Therefore, it is very necessary to invent a method for controlling the surface concave and convex rate difference using an abrasive-free copper CMP polishing liquid to achieve abrasive-free polishing. Summary of the invention

[0004] The purpose of the present invention is to provide a method for controlling the surface roughness rate difference by using abrasive-free copper CMP polishing liquid to solve the problems raised by the above-mentioned background technology in view of the defects of the prior art.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for controlling the surface roughness rate difference using a non-abrasive copper CMP polishing liquid, the specific steps are as follows:

[0006] Step 1: Under the condition of no abrasive and no corrosion inhibitor, 2-6% of macromolecular chelating agent, 2-6% of active agent, 2-5% of oxidant and 4-6% of pH regulator and deionized water are selected to prepare a rough polishing solution;

[0007] Step 2: Add coarse polishing liquid to the polishing machine;

[0008] Step 3: Using the mechanical energy difference between the concave and convex parts of the wafer surface during polishing, the macromolecular chelating agent in the rough polishing solution chelates the copper ions at a fast chemical reaction rate at the convex parts and a slow chemical reaction rate at the concave parts, thereby enhancing the chemical action of the copper CMP polishing solution while controlling the difference in the concave and convex rates of the copper surface;

[0009] Step 4: Taking advantage of the low removal rate in the concave areas, a high polishing rate is obtained in the convex areas through a strong chemical reaction, thereby creating a high rate difference between the concave and convex areas to achieve planarization.

[0010] As a preferred technical solution of the present invention, the macromolecular chelating agent comprises one or more monomers selected from tris(2-hydroxyethyl)ammonium ethylenediaminetetraacetate, hydroxyethylethylenediaminetriacetic acid trisodium salt, 1,2,3,4,5,6-[hexa-(2-methylamine oxime)ethoxy]hexane, and diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt.

[0011] As a preferred technical solution of the present invention, the molecular weight of the macromolecular chelating agent is 300-500 g / mol.

[0012] As a preferred technical solution of the present invention, the molecular weight of the macromolecular chelating agent is 400 g / mol.

[0013] As a preferred technical solution of the present invention, the active agent is ammonium dodecyl sulfate.

[0014] As a preferred technical solution of the present invention, the oxidant is hydrogen peroxide.

[0015] As a preferred technical solution of the present invention, the pH regulator is sodium hydroxide.

[0016] As a preferred technical solution of the present invention, the pH adjusted by the pH adjuster is 8-10.

[0017] As a preferred technical solution of the present invention, the method for preparing a rough polishing liquid in step 1 has the following specific steps: take deionized water, add an active agent and an oxidant with stirring, adjust the pH to 8-10 with a pH adjuster, add a macromolecular chelating agent with stirring, stir evenly and then make up the required weight with deionized water, and continue to stir evenly to obtain a rough polishing liquid.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The conventional CMP planarization method adds a corrosion inhibitor to inhibit the chemical reaction of copper in the concave part, while the convex part relies on abrasive particles to remove the corrosion inhibitor film to obtain high polishing removal, thereby generating a high rate difference. The present invention solves the problems of high polishing pressure and large mechanical action causing surface scratches in the conventional method, and the corrosion inhibitor film is toxic and difficult to clean.

[0020] Under the weakly alkaline condition without abrasive or corrosion inhibitor, the polishing liquid of the present invention has a high correction ability for the height difference of the copper surface, thereby solving the problems of high polishing pressure, many surface scratches and difficult cleaning caused by the traditional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The change of the height difference of the copper surface of the present invention with the polishing time;

[0022] Figure 2 This is a comparison diagram of the flattening of surface height differences by different non-abrasive polishing liquids in Example 1 of the present invention;

[0023] Figure 3 This is a comparison diagram of the flattening of surface height differences by different non-abrasive polishing liquids in Example 2 of the present invention;

[0024] Figure 4 The surface roughness after polishing with the polishing liquid without abrasive particles in Example 3 of the present invention; DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0026] The present invention provides a method for controlling the surface concave-convex rate difference by using abrasive-free copper CMP polishing liquid, thereby realizing the correction of the surface height difference. The specific implementation method principle is as follows:

[0027] The copper surface in contact with the polishing liquid includes unoxidized elemental copper, cuprous oxide (Cu2O) and cupric oxide (CuO), which are represented by [Cu], Cu(I) and Cu(II) respectively. T represents the total material on the copper surface during polishing, so the copper surface can be expressed as:

[0028] [Cu] T =[Cu]+[Cu(Ι,Π)] (1)

[0029] Here, Cu(Ⅰ,Ⅱ) represents the total oxide of copper in one and two valences, and [Cu(Ⅰ,Ⅱ)] represents its molar concentration. The reaction of copper with oxidant can be expressed as follows:

[0030]

[0031] OX in formula (2) represents oxide, so the oxidation reaction rate υ1 can be expressed as:

[0032] υ1=k1[Cu(Ι,Π)][OX] (3)

[0033] Where k1 represents the reaction rate constant of the copper oxidation reaction formula (2), and [OX] represents the concentration of the oxidant. The generated copper oxide can undergo a chelating reaction with the chelating agent, which can be expressed as:

[0034]

[0035] In formula (4), L represents a chelating agent, Cu 1+L,2+L represents the monovalent and divalent chelate products of copper, so the chelate reaction rate υ2 can be expressed as:

[0036] υ2=k2[Cu(Ι,Π)][L] (5)

[0037] Wherein k2 represents the reaction rate constant of the chelating reaction formula (4), and [L] represents the concentration of the chelating agent.

[0038] According to the law of conservation of mass, the generation rate of Cu(Ⅰ,Ⅱ) on the copper surface can be expressed as:

[0039]

[0040] Substituting formula (1) into formula (6) yields the following formula:

[0041]

[0042] The integral of formula (7) yields:

[0043]

[0044] When the polishing rate reaches a stable state, the amount of oxide material on the copper surface is a constant, and formula (8) can be expressed as follows:

[0045]

[0046] Abrasive-free copper chemical mechanical polishing mainly relies on chemical action to remove copper materials. The traditional chemical reaction rate is determined by the Arrhenius equation:

[0047]

[0048] Where A and R are constants, and U and T are the activation energy and temperature of the reaction, respectively. The energy provided by the polishing machine includes: (1) the kinetic energy generated by the high-speed rotation of the polishing head and the polishing disk, and (2) the friction energy generated by the friction between the copper and the polishing pad due to the low pressure. During the CMP process, the convex part of the polishing sheet has greater kinetic energy, greater friction energy, and higher temperature than the concave part, so the chemical reaction rate of the convex part of the surface is higher than that of the concave part. Therefore, the Arrhenius equation that determines the chemical reaction rate during the CMP process should be modified as follows:

[0049]

[0050] The subscript convex in formula (11) represents the convex part, E represents the kinetic energy and friction energy provided to the convex part by the pressure and rotation speed, and ΔT represents the temperature rise of the surface. On the contrary, the copper material in the concave part of the line is not affected by mechanical friction and is in a quasi-static environment, and its chemical reaction rate remains basically unchanged:

[0051]

[0052] The subscript concave in formula (12) represents a concave.

[0053] Therefore, the copper removal rate expression at the copper line convex part is:

[0054]

[0055] Similarly, the copper removal rate in the recess can be obtained as:

[0056]

[0057] Since the copper polishing rate is high at the convex part of the line and the copper removal rate is low at the concave part, it is beneficial to eliminate the surface height difference of the copper line. The reduction rate of the surface height difference h of the copper line is:

[0058]

[0059] In the formula, the negative sign indicates that the height difference is decreasing. Usually, the difference in chemical reaction rate during CMP of convex and concave parts is proportional to the height h, and the proportionality coefficient is λ, then:

[0060]

[0061] The solution of equation (16) is as follows:

[0062] h=h0e-λt (17)

[0063] Its h0 is the initial surface height difference.

[0064] The graph of equation (17) is as follows Figure 1 As shown: as time goes by, the height difference h approaches 0, that is, as time goes by, the height difference on the surface of the polished copper line gradually disappears and gradually tends to be flat.

[0065] The copper rough polishing liquid used to achieve the purpose of the present invention comprises 2-6% of chelating agent, 2-6% of activating agent, 2-5% of oxidizing agent, 4-6% of pH adjusting agent to adjust the pH to 8-10, and the balance is deionized water.

[0066] The chelating agent is a macromolecule with a molecular weight of 300-500 g / mol, with a molecular weight of 400 g / mol being preferred.

[0067] The active agent is ammonium dodecyl sulfate.

[0068] The oxidant is hydrogen peroxide.

[0069] The pH regulator is sodium hydroxide.

[0070] The macromolecular chelating agent comprises one or more monomers selected from tris(2-hydroxyethyl)ammonium ethylenediaminetetraacetate, hydroxyethylethylenediaminetriacetic acid trisodium salt, 1,2,3,4,5,6-[hexa-(2-methylamineoxime)ethoxy]hexane, diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt, and triethylenetetraaminehexaacetate.

[0071] Example 1: Preparation method and experimental method of copper rough polishing liquid;

[0072] Prepare 1000g rough polishing liquid: take 500ml deionized water, stir and add 5g ammonium dodecyl sulfate and 10ml hydrogen peroxide successively, adjust the pH to 8.9 with sodium hydroxide, stir and add 20g diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt, the molecular weight of diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt is 400g / mol, stir evenly and make up to 1000g with deionized water, continue to stir evenly to obtain polishing liquid A; take 500ml deionized water, stir and add 5g ammonium dodecyl sulfate and 10ml hydrogen peroxide successively, adjust the pH to 8.9 with sodium hydroxide, stir and add 15g ethylenediamine, stir evenly and make up to 1000g with deionized water, continue to stir evenly to obtain polishing liquid B.

[0073] Test: Use the prepared polishing liquid A and B in the French Alpsitec-E460E polishing machine; working pressure: 1.5psi; polishing disc speed 85 rpm; polishing head speed 95 rpm; polishing flow rate 300ml / min. Polishing a 300mm graphic piece for 1min, the initial surface height difference is 380nm, after polishing and cleaning, use a step meter to test the height difference after polishing. The results are as follows Figure 2 Shown

[0074] Example 1 shows that, compared with small molecule ethylenediamine, the abrasive-free and corrosion inhibitor-free alkaline copper polishing liquid configured by the present invention has a higher correction effect on the height difference of the copper surface.

[0075] Example 2: Preparation method and experimental method of copper rough polishing liquid;

[0076] Prepare 1000g rough polishing liquid: take 500ml deionized water, stir and add 5g ammonium dodecyl sulfate and 10ml hydrogen peroxide successively, adjust the pH to 8.9 with sodium hydroxide, stir and add 20g diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt, the molecular weight of diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt is 300g / mol, stir evenly and make up to 1000g with deionized water, continue to stir evenly to obtain polishing liquid A; take 500ml deionized water, stir and add 5g ammonium dodecyl sulfate and 10ml sodium hydroxide successively, adjust the pH to 8.9 with sodium hydroxide, stir and add 13g glycine, stir evenly and make up to 1000g with deionized water, continue to stir evenly to obtain polishing liquid C.

[0077] Test: Use the prepared polishing liquid A and C in the French Alpsitec-E460E polishing machine; working pressure: 1.5psi; polishing disc speed 85 rpm; polishing head speed 95 rpm; polishing flow rate 300ml / min. Polishing a 300mm graphic piece, the initial surface height difference is 380nm, after polishing and cleaning, the height difference after polishing is tested with a step meter. The results are as follows Figure 3 Shown

[0078] Example 2 shows that, compared with small molecule glycine, the abrasive-free and corrosion inhibitor-free alkaline copper polishing liquid configured by the present invention has a higher correction effect on the height difference of the copper surface.

[0079] Example 3: Preparation method and experimental method of copper rough polishing liquid;

[0080] Prepare 1000g of rough polishing liquid: take 500ml of deionized water, add 5g of ammonium dodecyl sulfate and 10ml of hydrogen peroxide in succession with stirring, adjust the pH to 8.9 with sodium hydroxide, add 20g of diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt with stirring, the molecular weight of diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt is 500g / mol, stir evenly, make up to 1000g with deionized water, continue stirring evenly to obtain polishing liquid A;

[0081] Test: Use the prepared polishing liquid A in the French Alpsitec-E460E polishing machine; working pressure: 1.5psi; polishing disc speed 85 rpm; polishing head speed 95 rpm; polishing flow rate 300ml / min. Polishing a 300mm copper sheet for 1 minute. After polishing and cleaning, the surface roughness is tested with an atomic force microscope. The results are as follows Figure 4 Shown

[0082] Example 3 shows that the abrasive-free and corrosion inhibitor-free alkaline copper polishing solution configured by the present invention has low surface roughness after polishing and cleaning.

[0083] Examples 1-3 illustrate that the present invention provides a method for controlling the difference in surface roughness rate using an abrasive-free copper CMP polishing liquid. The configured abrasive-free and corrosion inhibitor-free alkaline copper polishing liquid is mainly based on chemical action, has a high correction effect on the height difference of the copper surface, and obtains a low surface roughness.

[0084] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A method for controlling the surface unevenness rate difference using a non-abrasive copper CMP polishing liquid, characterized in that: The specific steps are as follows: Step 1: Under the condition of no abrasive and no corrosion inhibitor, 2-6% of macromolecular chelating agent, 2-6% of active agent, 2-5% of oxidant and 4-6% of pH regulator and deionized water are selected to prepare a rough polishing solution; Step 2: Add coarse polishing liquid to the polishing machine; Step 3: Using the mechanical energy difference between the concave and convex parts of the wafer surface during polishing, the macromolecular chelating agent in the rough polishing solution chelates the copper ions at a fast chemical reaction rate at the convex parts and a slow chemical reaction rate at the concave parts, thereby enhancing the chemical action of the copper CMP polishing solution while controlling the difference in the concave and convex rates of the copper surface; Step 4: Taking advantage of the low removal rate in the concave areas, a high polishing rate is obtained in the convex areas through a strong chemical reaction, thereby creating a high rate difference between the concave and convex areas to achieve planarization.

2. The method for controlling the surface roughness rate difference using abrasive-free copper CMP polishing liquid according to claim 1, characterized in that: The macromolecular chelating agent comprises one or more monomers selected from tris(2-hydroxyethyl)ammonium ethylenediaminetetraacetate, hydroxyethylethylenediaminetriacetic acid trisodium salt, 1,2,3,4,5,6-[hexa-(2-methylamine oxime)ethoxy]hexane, and diethylenediaminetetraacetic acid tetrahydroxyethylethylenediamine salt.

3. The method for controlling the surface unevenness rate difference using abrasive-free copper CMP polishing liquid according to claim 2, characterized in that: The molecular weight of the macromolecular chelating agent is 300-500 g / mol.

4. The method for controlling the surface roughness rate difference using abrasive-free copper CMP polishing liquid according to claim 3, characterized in that: The molecular weight of the macromolecular chelating agent is 400 g / mol.

5. The method for controlling the surface roughness rate difference using abrasive-free copper CMP polishing liquid according to claim 1, characterized in that: The active agent is ammonium lauryl sulfate.

6. The method for controlling the surface roughness rate difference using abrasive-free copper CMP polishing liquid according to claim 5, characterized in that: The oxidant is hydrogen peroxide.

7. The method for controlling the surface unevenness rate difference using abrasive-free copper CMP polishing liquid according to claim 6, characterized in that: The pH regulator is sodium hydroxide.

8. The method for controlling the surface roughness rate difference using abrasive-free copper CMP polishing liquid according to claim 7, characterized in that: The pH adjusted by the pH adjuster is 8-10.

9. The method for controlling the surface roughness rate difference using abrasive-free copper CMP polishing liquid according to claim 1, characterized in that: The method for preparing the rough polishing liquid in step 1 has the following specific steps: take deionized water, add the activator and the oxidant in succession with stirring, adjust the pH to 8-10 with a pH adjuster, add the macromolecular chelating agent with stirring, stir evenly and then make up the required weight with deionized water, and continue stirring evenly to obtain the rough polishing liquid.

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