A process for reducing particles on a polished surface of a silicon wafer

Abstract

The present application relates to the technical field of semiconductor material manufacturing, and in particular to a process method for reducing particles on a polished surface of a silicon wafer, comprising the following steps performed in sequence: megasonic tank cooperating with a wax removal active agent, N+1 times UPW overflow tank, ultraviolet ozone, SC1 cleaning, N+1 times UPW overflow tank, ultraviolet ozone, HF solution immersion, N+1 times UPW overflow tank, ultraviolet ozone, N+1 times UPW overflow tank, and IR. The present application changes surface chemical groups (-Si-OH / -Si-H) by increasing RCA cleaning, ultraviolet ozone (UV-O3) treatment, and cooperating with the process method of HF rotary immersion, so as to finally reduce particle residues and improve the yield of silicon wafers.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material manufacturing technology, and in particular to a process method for reducing grain particles on the polished surface of silicon wafers. Background Technology

[0002] In silicon wafer processing, particles can have a variety of negative impacts on process stability and device performance, including the following: 1. Decreased process stability In the cleaning process, residual silicon wafer particles reduce cleaning efficiency. Particles can obscure surfaces and clog deep trenches, leading to incomplete cleaning in certain areas and requiring additional cleaning steps or time. Secondly, it increases the risk of secondary contamination, as unremoved particles can release metal ions or adhere with the liquid flow, expanding contamination. It also exacerbates surface damage, as strong cleaning conditions can corrode silicon wafers, destroying flatness and forming hidden defects. Furthermore, it reduces cleaning uniformity, as particles alter local hydrophilicity and hydrophobicity, causing uneven spreading of the cleaning solution and making it prone to defects after drying.

[0003] In photolithography, residual particles on the silicon wafer surface can reduce the accuracy of pattern transfer. Particles can cause uneven photoresist coating and the formation of bumps, especially in high-NA lithography systems, where even small height differences can affect imaging. They can also cause mask contamination and damage. In contact / proximity lithography, particles can easily cause permanent defects in the mask, accounting for 20%-30% of the total defects in photolithography. They can also reduce alignment accuracy, as particles covering alignment marks can increase alignment errors. Furthermore, they can cause exposure dose deviations, leading to changes in critical dimensions and pattern distortion.

[0004] 2. Device performance degradation Residual particles on the silicon wafer surface can increase leakage current in semiconductor devices, cause defects in the insulating layer, and form conductive channels, affecting power consumption and stability. They can also cause threshold voltage drift, alter the doping or surface potential of the active region, and affect the switching characteristics of the device. Furthermore, they can reduce carrier mobility, increase surface roughness and scattering centers, especially affecting the performance of high-mobility devices. They can also lower the breakdown voltage, and particles can become electric field concentration points, easily causing premature breakdown of power devices. Additionally, they can increase contact resistance, hindering the contact between the metal and the semiconductor, and affecting the device's conduction performance.

[0005] 3. Reduced long-term reliability of devices Particle residues on the silicon wafer surface can exacerbate the hot carrier effect, with particles forming defect centers that trap charge carriers, accelerating the aging of MOS devices and shortening their lifespan; increase the risk of electromigration, as metal particles alter current distribution, easily leading to interconnect voids or short circuits; exacerbate stress migration, as particles form stress concentration points, causing deformation and cracking of multilayer metal structures; accelerate corrosion and oxidation, as metal particles release corrosive substances under specific environments, damaging devices; and increase radiation sensitivity, as particle defects become charge trapping centers, exacerbating radiation damage.

[0006] 4. Reduced uniformity and consistency of device performance. Particle residue can increase parameter dispersion because the particles are unevenly distributed on the silicon wafer surface, and the devices at different locations are affected to varying degrees; functional failure points may appear, and particles in critical locations can cause local device failure, especially reducing the yield of high-density integrated circuits; matching performance may degrade, affecting the accuracy of circuits such as operational amplifiers that require precise parameter matching; noise performance may deteriorate, as particles increase the 1 / f noise of devices and reduce the signal-to-noise ratio of circuits such as low-noise amplifiers. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a process method for reducing the particles on the polished surface of an 8-inch silicon wafer.

[0008] The technical solution of the present invention is as follows: A process for reducing particles on the polished surface of silicon wafers includes the following steps performed sequentially: mega-acoustic bath cleaning with dewaxing agent → N+1 times UPW overflow bath → ultraviolet ozone → SC1 cleaning → N+1 times UPW overflow bath → ultraviolet ozone → HF solution immersion → N+1 times UPW overflow bath → ultraviolet ozone → N+1 times UPW overflow bath → IR.

[0009] In a further embodiment, during the ultraviolet ozone step, ultraviolet light excites O2 in the air to generate ozone, and O3 oxidizes organic pollutants or non-polar groups on the surface of the silicon wafer, while simultaneously oxidizing surface silicon atoms to SiO2, thereby forming a -Si-OH oxide film.

[0010] In a further embodiment, during the SC1 cleaning step, hydrogen peroxide oxidizes the silicon wafer surface into a thin layer of SiO2, and NH3·H2O further promotes the generation of a large number of silanol groups on the SiO2 surface, while removing surface particles.

[0011] In a further embodiment, the composition of SC1 is NH3·H2O:H2O2:H2O=1:1:5~1:2:10.

[0012] In a further embodiment, the HF solution is used for immersion in a rotating manner to ensure that each area of ​​the silicon wafer is in contact with HF for the same amount of time. HF reacts with SiO2 to remove the oxide layer, and at the same time, silicon atoms on the surface of the silicon wafer directly combine with hydrogen atoms to form silicon-hydrogen bonds.

[0013] The beneficial effects of this invention are: By adding and adjusting RCA cleaning, ultraviolet ozone (UV-O3) treatment, and combining it with HF rotary immersion process, the surface chemical groups (-Si-OH / -Si-H) are changed, ultimately reducing particle residue and improving silicon wafer yield.

[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0015] Figure 1 This is a flowchart of an embodiment of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0017] Particulate contamination is an unavoidable challenge in silicon wafer manufacturing and processing. These particles can originate from various stages, including crystal growth, cutting, grinding, polishing, and cleaning. When particles adhere to the silicon wafer surface, they not only affect the smooth progress of subsequent processes but also have a profound impact on the electrical performance and long-term reliability of the final device.

[0018] To prevent contamination of subsequent processes, it is necessary to ensure the cleanliness of the silicon wafer surface, thereby improving the adhesion of subsequent materials; at the same time, reducing the generation of surface defects will improve the silicon wafer manufacturing yield and provide a guarantee for the stable electrical performance and long-term reliability of the device.

[0019] This embodiment provides a process method for reducing graininess on the polished surface of silicon wafers, such as... Figure 1 As shown, it includes the following steps: The process involves cleaning in a megahertz tank with a dewaxing agent (surfactant) → (N+1) UPW overflow tank cleaning → UV ozone → SC1 cleaning → (N+1) UPW overflow tank cleaning → UV ozone → HF solution immersion → (N+1) UPW overflow tank cleaning → UV ozone → (N+1) UPW overflow tank cleaning → IR infrared drying. N≥0, and the specific value is determined according to process requirements.

[0020] In the above cleaning steps, the ultraviolet ozone step involves directly irradiating the air with UV light, decomposing the O2 in the air into gaseous O3. Its purpose is to oxidize surface organic matter and non-polar groups, forming a thin layer of SiO2 on the surface, and subsequently generating silanol groups (-Si-OH), paving the way for subsequent SC1 solution wetting and particle removal. In this embodiment, the O3 used is obtained by directly irradiating the air with UV light, decomposing the O2 in the air into gaseous O3, and the effects of O3 vary in each step. The specific effects are as follows: The purpose of the first ultraviolet ozone treatment is to oxidize the organic matter and non-polar groups on the surface to form a thin layer of SiO2, which in turn generates silanol-Si-OH on the surface, making the surface hydrophilic and paving the way for subsequent SC1 solution wetting and particle removal.

[0021] The purpose of the second ultraviolet ozone treatment is to further remove the residual trace organic matter and non-polar groups on the surface after SC1; and to lightly oxidize and repair the surface again, to reorganize the SiO2 thin oxide layer and -Si-OH hydroxyl groups, so as to homogenize the surface state and perform interface pretreatment for HF pickling.

[0022] The purpose of the third ultraviolet ozone treatment is to oxidize and decompose the trace organic pollutants adsorbed after HF pickling, and to generate a uniform SiO2 oxide thin layer on the lightly oxidized silicon surface, thereby improving surface cleanliness.

[0023] SC1 cleaning (NH3·H2O:H2O2:H2O=1:1:5~1:2:10) uses hydrogen peroxide (H2O2) to oxidize the silicon wafer surface into a thin layer of SiO2. NH3·H2O further promotes the formation of a large number of silanol groups (-Si-OH) on the SiO2 surface, while removing surface particles. Then, ultrapure water (UPW) is used to rinse the residual chemical solution to prevent impurities from covering the hydroxyl groups, ultimately forming a highly hydrophilic surface.

[0024] During HF immersion, a rotating immersion method is used to ensure that all areas of the silicon wafer are in contact with HF for the same amount of time. The surface -Si-OH readily adsorbs CO2 or organic matter from the air, causing the hydrophilicity to decrease over time. When the hydrophilic silicon wafer (with a SiO2 layer on the surface) is immersed in HF, HF reacts with SiO2 (SiO2 + 4HF → SiF4↑ + 2H2O), removing the oxide layer. At the same time, silicon atoms on the surface of the silicon wafer directly combine with hydrogen atoms to form silicon-hydrogen bonds (-Si-H) (nonpolar groups).

[0025] Compared with existing RCA, this embodiment reduces ≥120nm particles by about 78%, ≥65nm particles by about 75%, and metal residue by about 87%, stably meeting the requirements of advanced processes. Specific data are shown in Table 1.

[0026] Table 1: Comparison of Cleaning Effects The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A process for reducing graininess on the polished surface of silicon wafers, characterized in that, The process includes the following steps performed sequentially: cleaning in a mega-sound tank with surfactant → N+1 times in a UPW overflow tank → ultraviolet ozone → SC1 cleaning → N+1 times in a UPW overflow tank → ultraviolet ozone → HF solution immersion → N+1 times in a UPW overflow tank → ultraviolet ozone → N+1 times in a UPW overflow tank → IR.

2. The process for reducing graininess on the polished surface of silicon wafers according to claim 1, characterized in that: In the ultraviolet ozone step, ultraviolet light excites O2 in the air to generate ozone, and O3 oxidizes organic pollutants or non-polar groups on the surface of the silicon wafer, while oxidizing the surface silicon atoms to SiO2, thereby forming a -Si-OH oxide film.

3. The process method for reducing grain particles on the polished surface of silicon wafers according to claim 1, characterized in that: In the SC1 cleaning step, hydrogen peroxide oxidizes the silicon wafer surface into a thin layer of SiO2, and NH3·H2O further promotes the generation of a large number of silanol groups on the SiO2 surface, while removing surface particles.

4. The process method for reducing grain on the polished surface of silicon wafers according to claim 3, characterized in that: The composition of SC1 is NH3·H2O:H2O2:H2O=1:1:5~1:2:

10.

5. The process method for reducing grain particles on the polished surface of silicon wafers according to claim 1, characterized in that: During the HF solution immersion, a rotating immersion method is used to ensure that each area of ​​the silicon wafer is in contact with HF for the same amount of time. HF reacts with SiO2 to remove the oxide layer, and at the same time, silicon atoms on the surface of the silicon wafer directly combine with hydrogen atoms to form silicon-hydrogen bonds.

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