CN111378372B

CN111378372B - Application of acetic acid in STI polishing

Info

Publication number: CN111378372B
Application number: CN201811627090.1A
Authority: CN
Inventors: 李守田; 尹先升; 贾长征; 王雨春
Original assignee: Anji Microelectronics Shanghai Co Ltd
Current assignee: Anji Microelectronics Shanghai Co Ltd
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2022-05-13
Anticipated expiration: 2038-12-28
Also published as: CN111378372A

Abstract

The invention provides the use of acetic acid in STI polishing. The acetic acid and the chemical mechanical polishing solution are mixed for use, the chemical mechanical polishing solution comprises a cerium oxide abrasive, and the cerium oxide abrasive is a colloid nano cerium oxide abrasive. The concentration of the acetic acid is 25-500 ppm. The pH value of the polishing solution is 4.5-4.8, and the surface of the cerium oxide abrasive is positively charged under the pH condition. The polishing solution has high silicon dioxide polishing rate and high silicon dioxide/silicon nitride polishing rate selection ratio, and can efficiently remove a silicon dioxide dielectric layer and stop polishing on a silicon nitride layer in the polishing process, so that a polished product meeting the industrial production requirement is obtained.

Description

Application of acetic acid in STI polishing

Technical Field

The invention relates to the field of chemical mechanical polishing, in particular to application of acetic acid in STI polishing.

Background

Semiconductor chips are typically fabricated by integrating hundreds of millions of active devices (e.g., NMOS and PMOS) on a silicon substrate material to design various circuits for complex logic and analog functions. To ensure electrical isolation between different devices, insulating materials are used to isolate them, and Shallow Trench Isolation (STI) is an industrial process for forming isolation regions between active devices. The STI structure is generally formed by depositing a silicon nitride layer on a semiconductor substrate, patterning the silicon nitride layer to form a hard mask, etching the substrate to form a steep trench between adjacent devices, and filling the trench with an oxide to form a device isolation structure. . Among them, planarization by a Chemical Mechanical Polishing (CMP) method is an important step in the manufacturing process of the STI structure. In the CMP process for STI structure fabrication, it is desirable that the CMP slurry has a high selectivity to silicon dioxide/silicon nitride polishing rates, preferably greater than 100: 1.

Chinese patent CN101568613A discloses a CMP polishing composition comprising proline and a fluorochemical surfactant at a pH of 9 to 11, the polishing composition having at least

And an oxide/nitride removal rate ratio of at least 5.

Cerium oxide is an important CMP polishing slurry abrasive, has more efficient polishing characteristics to silicon dioxide materials than traditional silica sol abrasives, and has been widely used for CMP polishing of STI and dielectric materials (ILD). However, the conventional cerium oxide-containing polishing solution generally has the problem of low selection rate of silicon dioxide/silicon nitride polishing rate, and cannot meet the industrial production requirement of the semiconductor product containing the STI structure.

Disclosure of Invention

The invention discloses a method for preparing cerium oxide polishing solution, which is characterized in that acetic acid is a conventional organic acid, is often used as a pH regulator or a buffering agent in the chemical mechanical polishing solution, and the acetic acid is added into the cerium oxide polishing solution, so that the polishing rate of silicon nitride can be greatly inhibited while the polishing rate of silicon dioxide is not influenced, and the selection ratio of the polishing rate of silicon dioxide/silicon nitride is improved. Accordingly, the present invention provides the use of acetic acid in STI polishing. The acetic acid is mixed with a chemical mechanical polishing solution for use, the chemical mechanical polishing solution comprises a cerium oxide abrasive, and the polishing rate selectivity of silicon dioxide/silicon nitride is high under the acidic pH condition.

In particular, the invention provides the use of acetic acid in STI polishing. Wherein the acetic acid is mixed with a chemical mechanical polishing solution for use, and the chemical mechanical polishing solution comprises a cerium oxide abrasive. The concentration of the acetic acid is 25-500 ppm. The pH value of the chemical mechanical polishing solution is 4.5-4.8.

Preferably, the cerium oxide abrasive is positively charged in the chemical mechanical polishing solution having a pH of 4.5 to 4.8.

Preferably, the concentration of acetic acid is 50-200 ppm.

Preferably, the concentration of acetic acid is 100-500 ppm.

Preferably, the content of the cerium oxide abrasive is 0.2wt% to 0.4 wt%.

Preferably, the cerium oxide abrasive is a colloidal nano cerium oxide abrasive. The chemical mechanical polishing solution of the present invention may further comprise other components of the polishing solution conventionally used in the art for polishing silicon dioxide and silicon nitride materials.

In the present invention, the pH of the CMP slurry can be adjusted by using a pH adjusting agent, such as ammonia, nitric acid, etc., which is conventional in the art.

In the invention, the acetic acid plays a role in chemical mechanical polishing, not only inhibits the polishing rate of silicon nitride, but also improves the polishing rate of silicon dioxide, thereby greatly improving the silicon dioxide/silicon nitride polishing rate selection ratio of the polishing solution.

Compared with the prior art, the invention has the technical advantages that: the polishing solution has high silicon dioxide polishing rate and high silicon dioxide/silicon nitride polishing rate selection ratio, and can efficiently remove a silicon dioxide dielectric layer and stop polishing on a silicon nitride layer in the polishing process, so that a polished product meeting the requirements is obtained. Meanwhile, the polishing solution can be applied to a wider polishing pressure range, can show a stable silicon dioxide/silicon nitride polishing rate selection ratio under various polishing pressures, and meets the requirements of STI polishing under various pressures.

Drawings

FIG. 1 is a graph of polishing solution to silica, silicon nitride polishing rate and silica/silicon nitride polishing rate selectivity ratio as a function of acetic acid concentration in accordance with the present invention.

Detailed Description

The advantages of the present invention will be described in detail with reference to the following examples, but the scope of the present invention is not limited to the following examples.

Table 1 shows the amounts of the abrasive, acetic acid and pH of the polishing solutions in examples 1 to 7 and comparative examples 1 to 2 of the chemical mechanical polishing solution of the present invention. In the comparative examples, acetic acid was not added, but acetic acid was added at different concentrations in the examples.

TABLE 1 comparative examples 1 to 7 and polishing solutions 1 to 8 according to the invention

The chemical mechanical polishing solutions of examples 1 to 7 and comparative examples 1 to 2 were used to polish silicon dioxide and silicon nitride blank wafers to obtain corresponding polishing rates, and the ratios of the polishing rates of the polishing solutions of the examples to the silicon dioxide and silicon nitride blank wafers were calculated, and the results are shown in tables 2 and 3, respectively.

Wherein the polishing conditions are as follows: a Mirra polishing machine is selected for polishing, the polishing pad is an IC1010 polishing pad, the rotating speeds of a polishing disc and the polishing head are 93rpm and 87rpm respectively, the pressure is 1.5psi-5psi, the flow rate of polishing liquid is 150mL/min, and the polishing time is 60 seconds.

TABLE 2 polishing rates for silicon dioxide and silicon nitride for comparative example 1 and examples 1-4 at different polishing pressures

TABLE 3 polishing rates for comparative example 2 and examples 5-7 for silicon dioxide and silicon nitride

As can be seen from table 2, the polishing liquids of examples 1 to 4 to which acetic acid was added in the present invention were able to suppress the polishing rate of silicon nitride while substantially maintaining the polishing rate of silicon dioxide, as compared with comparative example 1, and thus, the polishing liquids of the examples of the present invention significantly improved the silicon dioxide/silicon nitride polishing rate selectivity. Specifically, as can be seen by comparing comparative example 1 and example 1, the cerium oxide polishing solution containing no acetic acid exhibits not only a high polishing rate of silicon dioxide but also a high polishing rate of silicon nitride, and thus, the silicon dioxide/silicon nitride polishing rate selection thereof is small. In this example 1, a small amount (25ppm) of acetic acid was added, and the polishing solution obtained was capable of greatly suppressing the polishing rate of silicon nitride while maintaining the polishing rate of silicon dioxide at a low polishing pressure, thereby exhibiting a high silicon dioxide/silicon nitride polishing rate selectivity, but as the polishing pressure increased, the polishing rate of the polishing solution to silicon nitride increased, and the silicon dioxide/silicon nitride polishing rate selectivity increased, and it was found that when the amount of acetic acid added was small, the polishing solution was suitable for polishing an STI structure at a low pressure. However, it can be seen from examples 2 to 4 of the present invention that the polishing rate of silicon nitride under high pressure can be suppressed at a low polishing rate of silicon nitride under low pressure maintained with an increase in the amount of acetic acid added at the same silicon nitride content and pH. And with the increase of the acetic acid content, the polishing speed of silicon dioxide and silicon nitride which has wide covering polishing pressure range and is stable is shown, the selection ratio of the silicon dioxide/silicon nitride polishing speed is higher, and the requirement of polishing an STI structure can be well met.

The polishing rates for silicon dioxide and silicon nitride for inventive examples 5-7 and comparative example 2 without acetic acid at 3psi or 5psi polishing pressure for increasing the ceria content in the inventive examples are shown in table 3. As can be seen from Table 3, when the content of cerium oxide was increased to 0.4wt%, the polishing liquid having an acetic acid content of 100ppm or more exhibited a polishing rate of silicon oxide substantially identical to that of comparative example 2 containing no acetic acid at a polishing pressure of 3psi, while the polishing rate of silicon nitride was much lower than that of comparative example 2 containing no acetic acid, thereby exhibiting a higher silicon oxide/silicon nitride polishing rate selectivity. When the polishing pressure is increased to 5psi, the polishing rates of silicon oxide and silicon nitride of examples 5-7 of the present invention are increased simultaneously, thereby showing a stable silicon oxide/silicon nitride polishing rate selectivity ratio, and being capable of well satisfying the requirements of polishing the STI structure.

To better demonstrate the effect of acetic acid in the present invention in increasing the selectivity of polishing slurry to silicon dioxide/silicon nitride polishing rate, FIG. 1 shows the graph of the selectivity of silicon dioxide polishing rate, silicon nitride polishing rate and silicon dioxide/silicon nitride polishing rate as a function of acetic acid concentration for a polishing slurry with a cerium oxide abrasive content of 0.2wt% and a polishing pressure of 3 psi. As can be seen from the figure, the throw-away containing acetic acidThe polishing rate of the polishing solution to TEOS generally increases along with the increase of the acetic acid concentration, and particularly, after the acetic acid concentration reaches 50ppm, the polishing rate of the polishing solution to silicon dioxide continuously increases; the polishing rate of the polishing solution containing acetic acid to SiN is higher when the concentration of acetic acid is less than 25ppm

And when the concentration of acetic acid is 50ppm, it is less than

The polishing rate of silicon nitride is stably maintained as the concentration of acetic acid is increased

The following. Thus, when the concentration of acetic acid is close to 50ppm, the polishing rate selectivity of the polishing solution to silicon dioxide/silicon nitride is obviously increased and stabilized to more than 200.

In summary, the invention adds acetic acid with a certain concentration into the polishing solution containing cerium oxide, and greatly reduces the polishing rate of silicon nitride under the condition of basically maintaining the polishing rate of silicon dioxide, thereby improving the selectivity of the polishing solution to the polishing rate of silicon dioxide/silicon nitride. The polishing solution of the embodiment of the invention has a silicon dioxide/silicon nitride polishing rate selection ratio of over 100, and can completely meet the industrial production requirement of the STI structure.

It should be noted that the contents in the present invention are mass percent contents (wt%), unless otherwise specified.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the invention, are given by way of illustration only, since the invention is not limited to the specific embodiments described above. Any equivalent modifications and substitutions to those skilled in the art are also within the scope of the present invention. Accordingly, equivalent changes and modifications made without departing from the spirit and scope of the present invention should be covered by the present invention.

Claims

1. Use of acetic acid in STI polishing, wherein the acetic acid is used in combination with a chemical mechanical polishing solution, the chemical mechanical polishing solution comprises a cerium oxide abrasive, and the pH of the chemical mechanical polishing solution is 4.5-4.8; the cerium oxide abrasive is a colloid nano cerium oxide abrasive, and the concentration of acetic acid is 50-200 ppm; the content of the colloid nano cerium oxide abrasive is 0.2 to 0.4 weight percent; in the chemical mechanical polishing solution with the pH of 4.5-4.8, the colloidal nano cerium oxide abrasive is positively charged.

2. Use according to claim 1,

the concentration of the acetic acid is 100-500 ppm.