阅读说明：本技术 一种双阴极间断式抛光铜的方法 (Method for intermittently polishing copper by double cathodes ) 是由 郑辉 徐海波 张阳 郑梁 郑鹏 于 2020-12-31 设计创作，主要内容包括：本发明公开了一种双阴极间断式抛光铜的方法,旨在提供一种抛光效果好、效率高、操作方便的铜表面抛光的方法；该方法包括下述步骤：配制抛光溶液并置于反应皿中；将两个碳棒浸入溶液中作为阴极,将待抛光铜片置于两个阴极正中间作为阳极；接通电源进行间断式抛光,即先在一定的电流密度下(1.5-2.5A/cm～2)持续抛光一定的时间(10-20s),再将电流密度降为0,保持一定的时间(例如5-10min),随后再继续在一定的电流密度下(1.5-2.5A/cm～2)持续抛光一定的时间(10-20s),重复5-10次。其中,每100g抛光溶液包括64.7g纯度为85％的磷酸、0.3g纯度为99％的抗坏血酸、0.2g纯度为97％的乙烯硫脲,剩余34.8g为水的含量。(The invention discloses a double-cathode intermittent copper polishing method, aiming at providing a copper surface polishing method with good polishing effect, high efficiency and convenient operation; the method comprises the following steps: preparing a polishing solution and placing the polishing solution in a reaction vessel; immersing two carbon rods into the solution to be used as cathodes, and placing the copper sheet to be polished in the middle of the two cathodes to be used as an anode; the intermittent polishing is carried out by switching on the power supply, namely, the polishing is carried out under a certain current density (1.5-2.5A/cm) 2 ) Polishing for a certain time (10-20s), reducing the current density to 0, maintaining for a certain time (e.g. 5-10min), and continuing to polish at a certain current density (1.5-2.5A/cm) 2 ) Polishing is continued for a certain period of time (10-20s) and repeated 5-10 times. Wherein each 100g of the polishing solution contained 64.7g of phosphoric acid having a purity of 85%, 0.3g of ascorbic acid having a purity of 99%, 0.2g of ethylenethiourea having a purity of 97%, and the remaining 34.8g was the content of water.)

1. A method of double cathode interrupted polishing of copper comprising the steps of:

(1) preparing a polishing solution, wherein the polishing solution comprises 55 wt% of phosphoric acid, 0.3 wt% of ascorbic acid and 0.2 wt% of ethylene thiourea; the invention adopts phosphoric acid with the purity of 85 percent, ascorbic acid with the purity of 99 percent and ethylene thiourea with the purity of 97 percent; weighing 129.4g of phosphoric acid, 0.6g of ascorbic acid and 0.4g of ethylene thiourea, placing the mixture in a reaction vessel, adding 69.6g of water, stirring uniformly, and cooling to room temperature;

(2) immersing two carbon rods into the polishing solution prepared in the step (1) to be used as cathodes, simultaneously placing a copper sheet to be polished between the two carbon rods to be used as an anode, and switching on a power supply to simultaneously polish the front and back surfaces of the copper sheet;

(3) adopting an intermittent polishing technology for the testing device constructed in the step (2); that is, firstly, 1.5-2.5A/cm²The current density of (A) is continuously polished for 10-20s, the current density is reduced to 0, the polishing is kept for 5-10min, and then the polishing is continued at 1.5-2.5A/cm²Continuously polishing for 10-20s under the current density;

(4) repeating the step (3) for a certain number of times;

(5) and (4) taking out the copper sheet after the step (4) is finished, washing away residual phosphoric acid on the surface of the copper sheet by using a sodium bicarbonate solution, washing by using deionized water, and drying.

Technical Field

The invention belongs to the field of electrochemistry, relates to a method for electrochemically polishing copper, and particularly relates to a method for intermittently polishing copper by double cathodes so as to prepare a smooth and defect-free copper material.

Background

Copper has good thermal and electrical properties and is widely used in large scale integrated circuits. During the application process, the copper surface is often required to be polished to obtain a smooth and defect-free copper surface. The chemical mechanical polishing technology utilizes the synergistic action of chemistry and machinery to realize the complete polishing of the surface of the copper sheet, and is applied to the field of integrated circuit manufacturing for more than twenty years.

As the technology advances, the feature size of the copper interconnection layer becomes thinner and thinner, and the interlayer dielectric constant becomes smaller and smaller in order to eliminate the RC delay effect, so that the interconnection layer becomes more fragile and more easily damaged during the chemical mechanical polishing process. Therefore, ordinary chemical mechanical polishing has not been satisfactory. The electrochemical polishing has no mechanical force to participate in the polishing, and the requirements on the removal and the flatness of the surface material of the copper sheet are met by depending on the chemical reaction between the anode copper sheet and the polishing solution, so that the stress-free polishing is realized, and the damage of an interconnection layer and the damage of a dielectric layer caused by the mechanical force in the chemical mechanical polishing process are solved. Traditional electrochemical polishing only polishes the copper sheet single face, and copper sheet another side edge also has a little faint polishing reaction during the polishing, leads to the copper sheet overall material clearance different, and goes on along with the continuation of reaction, and solution temperature risees, and the resistivity increases, and polishing current increases, leads to reaction rate too fast, and copper surface roughness Ra is higher.

The invention adopts a double-cathode intermittent electrochemical polishing method, and the double-cathode method is used for polishing the front surface and the back surface of the copper sheet simultaneously, so that the material removal rate of the front surface and the back surface of the copper sheet are consistent, the surface roughness Ra is approximately the same, the process is reduced, and the polishing efficiency is improved. The intermittent polishing ensures that the temperature of the solution is always stabilized at room temperature in the polishing process, so that the safety of the whole polishing process is higher, the material removal rate is more stable, the surface roughness Ra of the copper is lower, the operation is simple, and the requirements on the integral and local flatness of the copper sheet are met.

Disclosure of Invention

The invention aims to provide a polishing method for globally and stably polishing a copper sheet, which is applied to the field of integrated circuits.

(1) A polishing solution was prepared, which contained phosphoric acid at a concentration of 55 wt%, ascorbic acid at 0.3 wt%, and ethylenethiourea at 0.2 wt%. The invention adopts phosphoric acid with the purity of 85 percent, ascorbic acid with the purity of 99 percent and ethylene thiourea with the purity of 97 percent. 129.4g of phosphoric acid, 0.6g of ascorbic acid and 0.4g of ethylene thiourea are weighed and placed in a reaction vessel, 69.6g of water is added, and the mixture is cooled to room temperature after being stirred uniformly.

(2) And (2) immersing two carbon rods into the polishing solution prepared in the step (1) to be used as cathodes, meanwhile, placing the copper sheet to be polished between the two carbon rods to be used as anodes, and switching on a power supply to simultaneously polish the front side and the back side of the copper sheet.

(3) And (3) adopting an intermittent polishing technology for the testing device constructed in the step (2). Namely, firstly, the current density is in a certain range (1.5-2.5A/cm)²) Polishing for a certain time (10-20s), reducing the current density to 0, maintaining for a certain time (e.g. 5-10min), and continuing to polish at a certain current density (1.5-2.5A/cm)²) Polishing was continued for a certain time (10-20 s).

(4) Repeating the step (3) for a certain number of times (5-10 times).

(5) And (4) taking out the copper sheet after the step (4) is finished, washing away residual phosphoric acid on the surface of the copper sheet by using a sodium bicarbonate solution, washing by using deionized water, and drying.

In the polishing solution, phosphoric acid has a good effect on polishing the copper surface, and a layer of adhesive film is formed on the copper surface during polishing to protect recesses on the copper sheet surface from being removed. The content of phosphoric acid also needs to be controlled, the content of phosphoric acid is too low, the reaction is slow, the viscosity of the polishing solution is low, and a sticky film layer is difficult to form by copper ions and phosphoric acid to protect the concave part on the surface of the copper sheet, so that the difference between the resistance of the solution mucous membrane at the microcosmic concave part and the resistance of the solution mucous membrane at the convex part on the surface of the copper sheet is not obvious enough, the convex part can not be reacted preferentially to achieve the leveling effect, and the. The content of phosphoric acid is too high, the mucosa layer formed on the surface of the anode is too thick, microscopic depressions and projections on the surface of the copper sheet are covered by the mucosa, the difference of the resistance of the mucosa is not obvious enough, and the effective leveling effect cannot be achieved.

The ascorbic acid can be combined with oxygen to be used as an oxidizing agent, has the function of passivating metal ions, can be combined with copper ions to generate stable metal salt, and forms a layer of passivation film consisting of copper salt on the surface of the copper sheet. The higher the concentration of the ascorbic acid is, the higher the integrity of the passivation film is, and the harder the copper surface is removed, so that the effect of controlling the Material Removal Rate (MRR) is achieved, and the MRR is reduced to an applicable value.

The roughness Ra of the copper surface is increased while the MRR is controlled by the ascorbic acid, and the ethylene thiourea is used as an additive and has a synergistic effect with the ascorbic acid, so that the requirements of controlling the MRR and meeting the Ra value of the copper surface are met.

Compared with the traditional electrochemical polishing method, the double-cathode intermittent electrochemical polishing method can simultaneously polish the front and back surfaces of the copper sheet, ensures that the material removal rates of the front and back surfaces of the copper sheet are consistent and the surface roughness Ra is approximately the same, reduces the process and improves the polishing efficiency. The power supply of the intermittent polishing method has enough rest time after working for a short time every time, the polishing process is safer, the temperature of the solution is stable and is always kept at room temperature, the material removal rate is more stable, the surface roughness Ra of copper is lower, and the requirements of the whole and local flatness of the copper sheet are met while the operation is simple.

The main equipment used by the invention is as follows: high-power adjustable direct current stabilized voltage power supply.

Drawings

FIG. 1 is a schematic diagram of an experiment according to the present invention;

FIG. 2 is a surface topography curve and a microscopic surface topography map of a copper sheet before polishing;

FIG. 3 is a graph of the surface topography and a microscopic surface topography of an example one obtained copper sheet;

FIG. 4 is a surface topography curve and a microscopic surface topography map of the copper sheet obtained in example two. In which example one employs conventional continuous polishing techniques and example two employs interrupted polishing.

Detailed Description

The experimental procedures used in the following examples are all conventional ones unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

Example one:

(1) a polishing solution was prepared, which contained phosphoric acid at a concentration of 55 wt%, ascorbic acid at 0.3 wt%, and ethylenethiourea at 0.2 wt%. This example used a phosphoric acid solution of 85% purity, ascorbic acid of 99% purity and ethylenethiourea of 97% purity. 129.4g of phosphoric acid, 0.6g of ascorbic acid and 0.4g of ethylene thiourea are weighed and placed in a reaction vessel, 69.4g of water is added, and the mixture is cooled to room temperature after being stirred uniformly.

(2) Two carbon rods are immersed into the reaction vessel to be used as cathodes, a copper sheet to be polished is placed between the two carbon rods to be used as an anode, and a power supply is switched on to simultaneously polish the front surface and the back surface of the copper sheet. Wherein the current density in the polishing process is 2A/cm²The polishing time was 90 s.

(3) And (4) taking out the copper sheet after polishing, washing away residual phosphoric acid on the surface of the copper sheet by using a sodium bicarbonate solution, washing by using deionized water, and drying.

Example two:

(1) a polishing solution was prepared, which contained phosphoric acid at a concentration of 55 wt%, ascorbic acid at 0.3 wt%, and ethylenethiourea at 0.2 wt%. This example used a phosphoric acid solution of 85% purity, ascorbic acid of 99% purity and ethylenethiourea of 97% purity. 129.4g of phosphoric acid, 0.6g of ascorbic acid and 0.4g of ethylene thiourea are weighed and placed in a reaction vessel, 69.4g of water is added, and the mixture is cooled to room temperature after being stirred uniformly.

(2) Two carbon rods are immersed in a reaction vessel to be used as cathodes, a copper sheet to be polished is placed between the two carbon rods to be used as an anode, and a power supply is switched on to simultaneously perform intermittent polishing on the front surface and the back surface of the copper sheet. Wherein the current density in the polishing process is 2A/cm²The polishing time is 15s each time, the interruption time is 5min, and the polishing times are 6 times.

(3) And (4) taking out the copper sheet after polishing, washing away residual phosphoric acid on the surface of the copper sheet by using a sodium bicarbonate solution, washing by using deionized water, and drying.

As can be seen from the surface topography curve chart and the microscopic surface topography chart of the copper sheet before polishing in FIG. 2, the roughness of the surface of the copper sheet before polishing is as high as 82.5nm, and the surface of the copper sheet is full of lines and uneven. As can be seen from the surface topography curve chart and the microscopic surface topography chart of the copper sheet obtained by continuously performing the electropolishing treatment for 90 seconds in the figure 3, the electropolishing can not only reduce the roughness of the surface of the copper sheet to 25.4nm, but also can remove the uneven lines on the surface of the copper sheet, but the solution temperature is increased, the current is increased, and the reaction speed is too high due to overlong continuous polishing time, so that the holes on the surface of the copper sheet are large and dense. As can be seen from the surface topography curve and the microscopic surface topography curve of the copper sheet obtained by the intermittent polishing in FIG. 4, Ra is reduced to 13.5nm, and the surface of the copper sheet has only a few tiny holes. Therefore, compared with the copper material obtained by the traditional polishing method, the intermittent polishing has lower surface roughness, fewer micro surface holes and better polishing effect.

The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.