Chemical mechanical polishing solution for removing polyimide film

Abstract

The invention relates to a chemical mechanical polishing solution for removing a polyimide film. The polishing solution comprises a grinding material, organic alkali, polyethylene glycol and water, the grinding material is aluminum oxide, and the particle size of the grinding material is 200-300 nm; the organic base is tetramethylammonium hydroxide. And the polishing pad is damping cloth during polishing. The hydroxyl free radicals promote the hydrolysis reaction of the surface of the polyimide film, and meanwhile, the polyimide film is rapidly removed through the interaction of the hard aluminum oxide abrasive and the soft damping cloth polishing pad on the polyimide film. According to the method, the surface quality of the polished polyimide film is improved, meanwhile, the removal rate is high, and the polyimide film with the smooth surface is efficiently prepared.

Description

Technical Field

[0001] This invention belongs to the field of chemical mechanical polishing for ultra-precision machining, and specifically relates to a chemical mechanical polishing fluid for removing polyimide films. Background Technology

[0002] With the continuous development of integrated circuits, traditional metal interlayer dielectrics are gradually failing to meet the demands. Polyimide films, with their excellent heat resistance, chemical stability, mechanical strength, and mechanical toughness as organic polymers, are highly valued in the microelectronics industry. Polyimide films have become a commonly used passivation polymer in integrated circuits. Furthermore, in more precise applications of integrated circuits, such as interlayer dielectrics and three-dimensional packaging, higher requirements are placed on planarization and surface quality.

[0003] Chemical mechanical polishing of polyimide films presents three main challenges: First, the high heat resistance (>400℃) and chemical inertness of polyimide make it difficult to achieve efficient polishing using traditional mechanical or chemical methods, easily leading to surface damage (such as scratches and residual stress) or inhomogeneity. Second, in microelectronics (such as multilayer wiring in integrated circuits and wafer-level packaging), when polyimide is used as a dielectric or buffer layer, nanoscale surface flatness (Ra<1nm) is required to ensure device reliability. Third, existing polishing slurries lack sufficient chemical compatibility with polyimide films, resulting in polishing rates below 350nm / min, low efficiency, and easy surface scratches. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a chemical mechanical polishing (CMP) slurry for removing polyimide films. This slurry utilizes an organic alkali, alumina abrasive, and a novel polishing method (using a soft material as a polishing pad) to reduce the mechanical forces during CMP polishing of polyimide films, ensuring the surface quality after polishing while introducing chemical action to increase the polishing rate. This invention achieves both improved surface quality of the polished polyimide film and a high removal rate, efficiently producing polyimide films with smooth surfaces.

[0005] The solution to the technical problem of this invention is:

[0006] A chemical mechanical polishing slurry for removing polyimide films, the slurry comprising: abrasive, organic base, polyethylene glycol and water;

[0007] The polishing slurry contains an abrasive concentration of 1.5–3.0% by mass, polyethylene glycol concentration of 0.1–0.5%, and a pH value of 11–13.

[0008] The abrasive is aluminum oxide with a particle size of 100–300 nm.

[0009] The organic base mentioned is tetramethylammonium hydroxide.

[0010] The method for preparing the chemical mechanical polishing slurry for removing polyimide films includes the following steps:

[0011] First, nano-alumina abrasive containing polyethylene glycol as a dispersant was prepared by high-energy ball milling. Then, water and tetramethylammonium hydroxide as a pH adjuster were added to adjust the pH to 11, and the abrasive concentration was diluted to the target concentration. Finally, the pH was adjusted to 12 with tetramethylammonium hydroxide.

[0012] The application of the high-efficiency polishing slurry for preparing high surface quality polyimide films is to polish polyimide films.

[0013] The conditions for chemical mechanical polishing of polyimide films using polishing slurry are:

[0014] The polishing machine model is Rui Xuan SSP-500, the polishing time is 3 minutes, the polishing pressure is 4.1 psi, the polishing fluid flow rate is 60 ml / min, the polishing head speed is 50 r / min, the polishing disc speed is 50 r / min, and the polishing pad is damping cloth.

[0015] The essential features of this invention are:

[0016] Current research uses hard polishing pads or adds highly corrosive modifiers such as ethylenediamine, which cannot achieve a high removal rate while ensuring surface quality. When using silica sol, the polishing fluid is negatively charged. Since the polyimide film is insoluble in water, the removed polyimide is easily left on the surface, causing scratches during further polishing.

[0017] In this invention, firstly, a weakly alkaline tetramethylammonium hydroxide is used as a pH adjuster, and its usage is much greater than that of the currently used potassium hydroxide adjuster. Therefore, there are more free hydroxyl groups in the solution, and the higher concentration of hydroxyl groups can accelerate the hydrolysis reaction on the surface of the polyimide film. Through the study of the particle size and zeta point of the polishing solution, it was found that the particle size distribution of the polishing solution is more uniform, and there are no large particles. Moreover, after adding tetramethylammonium hydroxide to the pH 12, the zeta potential of the polishing solution is positive, while the surface of the polyimide film is negatively charged. Therefore, it is more suitable for polishing polyimide films.

[0018] Secondly, by using soft materials as the polishing pad material, the combined effects of hard abrasives, soft polishing pads, and a strong alkaline environment allow the hard abrasives to remove surface protrusions through mechanical friction, achieving initial flattening. The soft material polishing pad can avoid excessive mechanical damage to the film surface from the hard abrasives, reducing scratches. The strong alkaline environment may cause the polyimide film molecular chains to break or hydrolyze, reducing the material hardness, which is easier to remove with mechanical grinding. Thus, it is possible to ensure good surface quality under high polishing rates.

[0019] The beneficial effects of this invention are:

[0020] This invention prepares an alkaline polishing slurry with strong chemical action on polyimide films and scratch-free removal under different mechanical strengths. The pH value of the polishing slurry is stable in the range of 11 to 13. With the action of a soft polishing pad, this invention has excellent polishing efficiency and performance for polyimide films, and can ultimately achieve a polyimide film removal rate of 623 nm / min, which far exceeds the polishing rate (100 to 350 nm / min) in CN119057651A, and the surface roughness Sq can reach 0.3 nm. Attached Figure Description

[0021] Figure 1 Original morphology diagram of polyimide film

[0022] Figure 2 This is a comparison chart of the polishing rates of polyimide films by organic and inorganic bases in Examples 1-2.

[0023] Figure 3 The images show a comparison of the surface quality of the soft material polishing pad (damping cloth) and the hard material polishing pad (non-woven fabric) in Examples 1 and 3.

[0024] Figure 4 The image shows the AFM test result after polishing the soft material (damping cloth) polishing pad in Example 1.

[0025] Figure 5 The image shows the AFM test results after polishing with the hard material (non-woven fabric) polishing pad in Example 3.

[0026] Figure 6 This is a comparison chart of the zeta potential tests of organic and inorganic bases in Examples 1-2.

[0027] Figure 7 This is a particle size test diagram from Example 1.

[0028] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] Step S1: Add alumina powder (mass m1), polyethylene glycol dispersant (mass m2), and zirconium oxide ball milling beads (mass m3) to deionized water, stir evenly, and then adjust the pH of the ball milling liquid to 11 using an organic base.

[0031] Step S2: After ball milling for 120 minutes, filter out the zirconium dioxide from the ball milling slurry and dilute the ball milling slurry at a liquid-to-water ratio of 1:10;

[0032] Step S3: Adjust the diluted ball milling slurry to pH 12 using an organic base, and stir the polishing slurry evenly.

[0033] In step S1 of the present invention, the mass m1 of the alumina powder is 60-120g, the average particle size is 100-300nm, the mass m2 of the dispersant polyethylene glycol is 1-5g, the mass m3 of the zirconia grinding beads is 180-360g, the organic base is a pH adjuster with a concentration of 30%, and the total mass of the grinding liquid is 400g.

[0034] In step S2 of the present invention, the water used to dilute the ball milling fluid is deionized water;

[0035] In step S3 of the present invention, the organic base is tetramethylammonium hydroxide.

[0036] Example 1

[0037] Prepare 400g of polishing slurry

[0038] (1) Alumina powder (average particle size 200 nm), polyethylene glycol dispersant, and zirconia grinding beads (particle size 0.3 mm) were added to deionized water. After stirring, the pH was adjusted to 11 with tetramethylammonium hydroxide to obtain a mixed solution. The mass ratio of grinding balls to abrasive in the mixed solution was 3:1. After ball milling (360 rpm) for 120 minutes, the zirconia in the ball milling liquid was filtered out to obtain the ball milling liquid (the mass concentration of alumina in the ball milling liquid was 20%, the mass concentration of polyethylene glycol was 1%, and the particle size D50 of the abrasive after ball milling was 239.1). Ball milling transformed the alumina powder into an alumina dispersion.

[0039] (2) Add 40g of the ball milling fluid obtained in the previous step to 300g of deionized water; after stirring evenly, add deionized water to the polishing fluid so that the total mass of the polishing fluid is 350g; adjust the pH of the polishing fluid to 12 using tetramethylammonium hydroxide; add the remaining amount to 400g with deionized water and stir evenly; finally, the abrasive concentration of the polishing fluid is 2wt% and the polyethylene glycol concentration is 0.1wt%.

[0040] (3) On a damping cloth (Politex Reg from DUPONT), the polyimide film was polished for three minutes at a pressure of 4.1 psi, a polishing fluid flow rate of 60 ml / min, a polishing head speed of 50 r / min, and a polishing disc speed of 50 r / min. The thickness was then measured using an F50 film thickness meter. The polishing rate was 623 nm / min. Figure 2 As shown in Figure 5, the surface roughness is 0.3 nm. The AFM test results are also shown in Figure 5. Figure 1 The original appearance is in contrast.

[0041] The polyimide film material used was PI 2610 from HD Microsystems. A planetary ball mill (YXQM-2L) manufactured by Changsha Miqi Instrument Equipment Co., Ltd. was used for ball milling. For polishing, a Rui Xuan SSP-500 chemical mechanical polishing machine was used, with the following process conditions: polishing fluid flow rate 60 ml / min, polishing head speed 50 r / min, and polishing disc speed 50 r / min. Two 2*2 cm polyimide films adhered to a 4-inch sapphire substrate were selected for chemical mechanical polishing. After cleaning the two 2*2 cm polyimide films adhered to the 4-inch sapphire substrate, their thickness was measured using an Filmetrics F50 film thickness meter. The particle size and zeta potential of the polishing fluid were measured using a Nicomp Z3000 laser nanoparticle size analyzer manufactured by Aofamejia. The surface morphology and surface roughness (Sq) were measured using an Agilent 5600LS atomic force microscope manufactured by Agilent Technologies, France. (The polishing and testing conditions for Examples 2-6 are the same.)

[0042] Example 2

[0043] The other steps are the same as in Example 1, except that tetramethylammonium hydroxide is replaced with potassium hydroxide.

[0044] like Figure 2 As shown, when the inorganic alkali was replaced as the pH adjuster, the polishing rate decreased from 623 nm / min to 230 nm / min. And as... Figure 6 The zeta potential of the polishing slurry changes from negative to positive, indicating the presence of large particles.

[0045] This is because when adjusting the pH to 12, only 1g of inorganic base is needed, while 10g of weak organic base is required. Therefore, there are more free hydroxyl groups in the solution, which promotes hydrolysis or molecular chain breakage during polishing. Methyl groups are positively charged and may adsorb onto the surface of the alumina abrasive, thus making the zeta potential of the polishing solution positively charged.

[0046] Example 3

[0047] The other steps are the same as in Example 1, except that the damping cloth polishing pad is replaced with a non-woven cloth polishing pad.

[0048] like Figure 5 As shown, the surface roughness Sq increased from 0.3nm to 2nm, and the polishing rate increased from 623nm / min to 730nm / min, but the roughness is far greater than the requirement of less than 0.5nm in integrated circuits.

[0049] This is because non-woven polishing pads are harder than damping cloth polishing pads. The squeezed abrasive undergoes strong mechanical friction with the polyimide film, resulting in increased removal but also increased surface roughness.

[0050] Example 4

[0051] The other steps are the same as in Example 1, except that 4g of polyethylene glycol is replaced with 10g of polyethylene glycol.

[0052] The resulting polishing slurry D50 is similar to that of Example 1;

[0053] Example 5

[0054] The other steps are the same as in Example 1, except that the 4.1 psi pressure is replaced with 1.8 psi pressure;

[0055] The surface roughness was 0.2 nm, and the polishing rate was 436 nm / min. After reducing the pressure, the surface roughness decreased and the polishing rate decreased.

[0056] Example 6

[0057] The other steps are the same as in Example 1, except that the pressure of 40g ball milling fluid is replaced with 60g ball milling fluid.

[0058] The surface roughness was 0.36 nm, and the polishing rate was 840 nm / min. Increasing the alumina abrasive concentration increased the roughness, and the polishing rate increased slightly.

[0059] Matters not covered in this invention are common knowledge.

Claims

1. A chemical mechanical polishing slurry for removing polyimide films, characterized in that, The polishing fluid consists of: abrasive, organic base, polyethylene glycol, and water; The polishing slurry contains an abrasive concentration of 1.5–3.0% by mass, polyethylene glycol concentration of 0.1–0.5%, and a pH value of 11–13. The abrasive is aluminum oxide; the organic base is tetramethylammonium hydroxide.

2. The chemical mechanical polishing slurry for removing polyimide films as described in claim 1, characterized in that, The alumina has a particle size of 100–300 nm.

3. The application of the chemical mechanical polishing slurry for removing polyimide films as described in claim 1, characterized in that, Used for polishing polyimide films; The conditions for polishing are: The polishing time was 3 minutes, the polishing pressure was 4.1 psi, the polishing fluid flow rate was 60 ml / min, the polishing head speed was 50 r / min, the polishing disc speed was 50 r / min, and the polishing pad was damping cloth.

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