TW201910015A - Semiconductor wafer cleaning method - Google Patents

Abstract

This invention provides a method for washing a semiconductor wafer comprising: conducting a first washing to a wafer to have a positive Zeta potential; washing the wafer by an acidic washing fluid to remove residual metals thereon; conducting a second washing to the wafer, wherein the second washing fluid has a positive Zeta potential at the initial washing, and the wafer has a negative Zeta potential at the completion of the second washing. The present method is able to avoid reattachment of microparticles on the wafer surface caused by opposite potentials between the wafer and the microparticles in the fluid, thereby the washing efficiency increases.

Description

Method for cleaning semiconductor wafer

The present invention relates to the field of semiconductor technology, and in particular, to a method for cleaning a semiconductor wafer.

Before manufacturing integrated circuits, semiconductor wafers need to be polished to improve wafer flatness. The final polishing of a semiconductor wafer is to use a polishing solution (Slurry) and a polishing pad (Pad) on a final polisher to finalize the front side of a wafer such as a 300 mm wafer by chemical mechanical reaction. Polished to improve frontal roughness, flatness and nano topography, and remove particles. Final polishing determines the final flatness and nano-morphology of the wafer. In general, the final polishing removal is about 1 μm, and the polishing liquid is generally a mixture of alkaline silica and some other additives. After the final polishing is completed, the wafer needs to be cleaned to remove organics, particles and metals.

Final polishing cleaning includes pre-cleaning and final cleaning. After pre-cleaning, a series of measurements, such as flatness and visual inspection, are performed, and then final cleaning is performed before wafer shipment. The final cleaning is mainly to remove the metal contamination brought in during the measurement, and to further reduce the particles on the wafer surface.

At present, the general cleaning process after final polishing uses the RCA cleaning method (that is, SC1 (NH ₄ OH + H ₂ O ₂ ), SC2 (HCL + H ₂ O ₂ )). Among them, SC1 mainly removes particles, of course, it also has effects on some metals, and SC2 mainly removes metals. However, the main problem of the RCA cleaning method is that after SC1 removes particles, due to the difference in the subsequent PH value of each tank, the Zeta Potential on the wafer surface and the particles in the subsequent solution (SC2 and rinsed DIW (deionized water)) The opposite situation of the kinematic potential exists, causing particles to reattach to the wafer surface, reducing the overall cleaning effect.

Therefore, it is necessary to propose a cleaning method for semiconductor wafers to solve the above problems.

In view of the shortcomings of the prior art, the present invention proposes a method for cleaning semiconductor wafers, which can avoid the re-attachment of particles on the wafer surface due to the fact that the electric potential of the wafer surface is opposite to the dynamic potential of the particles in the subsequent solution. Problems that improve the cleaning effect.

In order to overcome the existing problems, the present invention provides a method for cleaning a semiconductor wafer, which includes the following steps: performing a first cleaning on the wafer to change the interface potential of the wafer to a positive value; cleaning using an acidic cleaning solution The wafer to remove the metal remaining on the wafer; performing a second cleaning on the wafer, and during the second clearing process, the wafer enters the initial stage of the rinsing tank, and the The liquid interface potential is positive, and the interface potential of the wafer is changed to a negative value after the second cleaning is completed.

Optionally, a mixed solution of deionized water and an acidic surfactant is used in the first cleaning.

Optionally, performing the first cleaning on the wafer to change the interface potential of the wafer to a positive value includes the following steps: cleaning the wafer in a deionized water tank; and injecting into the deionized water tank The acidic surfactant continues to clean the wafer.

Optionally, the acidic cleaning solution is a mixed solution of SC2 and hydrofluoric acid.

Optionally, a mixed solution of deionized water and an acidic surfactant is used in the second washing.

Optionally, performing the second cleaning on the wafer includes the following steps: after injecting the acidic surfactant into a deionized water tank, cleaning the wafer with a mixed solution of deionized water and acidic surfactant ; Stop injecting the acidic surfactant into the deionized water tank, and continue cleaning the wafer in the deionized water tank.

Optionally, before performing the first cleaning on the wafer to change the interface potential of the wafer to a positive value, the method further includes the following steps: removing particles and some metal remaining on the wafer.

Optionally, the steps of removing particles and metals remaining on the wafer include the following steps: cleaning the wafer with a first cleaning solution; cleaning the wafer with deionized water.

Optionally, before removing the particles and some metal remaining on the wafer, the method further includes the following steps: washing the wafer with deionized water.

Optionally, after performing the second cleaning on the wafer, the method further includes the following steps: cleaning the wafer with deionized water; and performing a hydrophilic treatment on the wafer.

According to the method for cleaning a semiconductor wafer according to the present invention, before using an acidic cleaning solution to remove metal remaining on the wafer, first perform a first cleaning on the wafer so that the interface potential of the wafer is positive, so that when the acidic cleaning solution is entered In the bath, because the interface potential of the particles in the wafer and the acid cleaning solution tank are positive, the two are mutually exclusive so that the wafer will not adsorb the particles; and after using the acid cleaning solution to remove the metal remaining on the wafer, the During the second clearing process, when the wafer enters the rinsing tank, the liquid interface potential in the rinsing tank is positive, and after the second cleaning is completed, the interface potential of the wafer is changed to a negative value. During the second clearing process, the interface potential of the wafer will not change suddenly and affect the cleaning effect. When the wafer is subsequently cleaned with deionized water, since the interface potentials of the wafer and the particles in the deionized water are both It is a negative value, and the two are mutually exclusive so that the wafer does not adsorb particles, so the cleaning method after the final polishing of the semiconductor wafer according to the present invention improves the overall cleaning effect.

Numerous specific details are provided below to facilitate a thorough understanding of the invention. However, those skilled in the art can easily understand that in some embodiments, one or more of the details may be omitted and still implemented. In other embodiments, in order to avoid confusion with the present invention, some technical features that are known in the art are not described.

It should be understood that the present invention can be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, the embodiments provided are sufficient to completely and completely disclose the technical features of the present invention, and can completely pass the scope of the present invention to those skilled in the art. It should be noted that the drawings are all in simplified form and all use inaccurate proportions, which are only used to facilitate and clearly explain the purpose of the embodiments of the present invention. The same component symbol indicates the same component.

It will be understood that when an element or layer is referred to as being "on", "adjacent", "connected to" or "coupled to" another element or layer, it can be directly on the other element or layer, with Are adjacent, connected or coupled to other elements or layers, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers present. It should be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, without departing from the teachings of the present invention, a first element, component, region, layer or section mentioned may be referred to as a second element, component, region, layer or section.

Spatial relation terms such as "below", "below", "below", "below", "above", "above", etc. are used herein for ease of description. Can be used to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientations shown in the figures, the terms of spatial relationship may include different orientations of the device in use and operation, for example: if the device in the figure is turned over, then described as "below other elements" or "below other elements" "Beneath" or "below" elements or features will be oriented "above" other elements or features; therefore, the exemplary terms "below" and "below" may include both an orientation of up and down. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptors used herein interpreted accordingly.

The terminology used herein is used to describe specific embodiments and is not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular forms "a", "an" and "said / the" may include plural forms. It should also be understood that when the terms "composition" and / or "including" are used in the specification, the existence of the described features, integers, steps, operations, elements and / or components is determined, but one or more other features are not excluded , Integers, steps, operations, elements, parts, and / or groups. As used herein, the term "and / or" includes any and all combinations of the listed solutions.

In order to thoroughly understand the present invention, detailed structures and steps will be provided below to explain the technical solution proposed by the present invention. The preferred embodiments of the present invention are described in detail below, but the present invention can also cover other embodiments.

At present, the cleaning machine after the final polishing generally uses the RCA cleaning method, that is, SC1 (a mixture of NH ₄ OH and H ₂ O ₂ ) and SC2 (a mixture of HCL and H ₂ O ₂ ) are used for cleaning. The cleaning process shown in Figure 1 includes deionized water cleaning, SC1 cleaning, deionized water cleaning, SC2 cleaning, deionized water cleaning, ozone water cleaning, and drying. However, because the isoelectric point of silicon is 3 to 4, the isoelectric point of silicon dioxide is 1.5 to 3.7, and the wafer ’s SC1 in Zeta Potential is negative. The particles in the water tank (the particle interface potential in the deionized water tank is also generally negative) are mutually exclusive in principle and will not adsorb each other. However, when entering the SC2 tank from the deionized water tank, since the interface potential of the particles in SC2 is positive and the interface potential of the wafer is negative, there will be an attractive force between the two, causing the particles to adhere to the wafer. In addition, after SC2 cleaning is completed, the interface potential of the wafer becomes positive, so that when it enters the subsequent deionized water tank, the particles with a negative interface potential adsorb each other again, which reduces the overall effect of RCA cleaning.

Based on this, the present invention provides a method for cleaning a semiconductor wafer. As shown in FIG. 2, the cleaning method includes: Step S201, performing a first cleaning on the wafer, so that the interface potential of the wafer is converted to a positive value. Step S202: washing the wafer with an acidic cleaning solution to remove metal remaining on the wafer; step S203, performing a second cleaning on the wafer, and during the second cleaning process, the At the initial stage of the wafer entering the rinsing tank, the liquid interface potential in the rinsing tank is positive, and after the second cleaning is completed, the interface potential of the wafer is changed to a negative value.

According to the method for cleaning a semiconductor wafer according to the present invention, before using an acidic cleaning solution to remove metal remaining on the wafer, first perform a first cleaning on the wafer so that the interface potential of the wafer is positive, so that when the acidic cleaning solution is entered In the bath, the interface potentials of the particles in the wafer and the acidic cleaning solution tank are positive, and the two are mutually exclusive, so that the wafer will not adsorb the particles; and after using the acidic cleaning solution to remove the metal remaining on the wafer, The wafer performs a second cleaning. During the second clearing process, the wafer enters the rinsing tank at an early stage. The potential of the liquid interface in the rinsing tank is positive, and the interface of the wafer after the second cleaning is completed. The potential changes to a negative value, so that not only does the potential of the interface where the wafer is located during the second clearing process not change suddenly and affect the cleaning effect, and when the wafer is subsequently cleaned with deionized water, the wafer and The interface potential of the particles in the deionized water is negative, and the two are mutually exclusive so that the wafer does not adsorb the particles. Therefore, the cleaning method after the final polishing of the semiconductor wafer according to the present invention improves the overall cleaning effect. .

It can be understood that the semiconductor wafer cleaning method according to the present invention can be applied not only to the cleaning of the semiconductor wafer after final polishing, but also to the cleaning of the semiconductor wafer at other stages in the fabrication of integrated circuits, which can improve the overall performance. Cleaning effect.

Hereinafter, a method for cleaning a semiconductor wafer according to an embodiment of the present invention will be described in detail with reference to FIG. 3.

As shown in FIG. 3, the method for cleaning a semiconductor wafer according to this embodiment includes: Step S301, cleaning the wafer with deionized water.

Wherein, the deionized water tank is cleaned by overflow method, and the overflow speed during cleaning is 5 liters / minute (L / min) to 30 L / minute, preferably 20 L / minute.

Illustratively, the resistivity of deionized water is 18 M ohm-cm (Ω · cm). The cleaning temperature is from normal temperature to 85 degrees Celsius, preferably normal temperature. The washing time is 3 to 7 minutes, preferably 5 minutes.

In step S302, particles and some metals remaining on the wafer are removed.

In this step, the first cleaning solution is used to remove particles and some metals remaining on the circle. Exemplarily, the first cleaning liquid is SC1.

Specifically, this step includes the following process: sequentially cleaning the wafer using SC1 and deionized water, that is, sequentially putting the wafer into the SC1 tank and the deionized water tank for cleaning, thereby removing particles and some metal remaining on the wafer .

Wherein, the deionized water tank is cleaned by overflow, and the overflow speed during cleaning is 5 L / min to 30 L / min, preferably 20 L / M. The SC1 tank is immersed for cleaning.

Exemplarily, the resistivity of deionized water is 18M ohm-cm; SC1 is a mixture of ammonia, hydrogen peroxide and deionized water; the concentration of ammonia water is 5% to 40%, preferably 23.6%; the concentration of hydrogen peroxide is 5% to 20 %, Preferably 11.8%.

SC1 cleaning temperature is from normal temperature to 85 degrees Celsius, preferably 45 degrees Celsius. The temperature for cleaning with deionized water is normal temperature.

The cleaning time for SC1 cleaning and deionized water cleaning is 3 to 7 minutes, preferably 5 minutes.

Optionally, an ultrasonic wave may be added during the cleaning process, and the ultrasonic frequency ranges from 1000 KHZ to 3000 KHZ, preferably 1200 KHZ. Through the vibration of ultrasonic waves, particles and some metals remaining on the wafer can be better removed.

Depending on the situation, the above SC1 and deionized water cleaning process can be repeated twice.

In step S303, a first cleaning is performed on the wafer, so that the interface potential of the wafer after being cleaned by the first cleaning liquid becomes a positive value.

Exemplarily, a mixed solution of deionized water and an acidic surfactant is used in the first cleaning.

More specifically, the process or operation of the first cleaning is: first, rinsing with deionized water in a deionized water tank, where, for example, the resistivity of the deionized water is 18M ohm-cm; the cleaning temperature is from normal temperature to 85 ° C Degrees, preferably room temperature. The deionized water tank is cleaned by overflow. The overflow speed during cleaning is 5 L / min to 30 L / min, preferably 20 L / min. The cleaning time is 1 to 4 minutes, preferably 2 minutes.

Next, an acidic surfactant, such as citric acid, is injected into the deionized water tank until the liquid pH in the tank reaches 3 to 3.7 (preferably 3.3). Optionally, the injection of the acidic surfactant is completed within 30 seconds, and then the wafer is lifted. Exemplarily, the cleaning temperature in this process is from normal temperature to 85 degrees Celsius, preferably normal temperature. The overflow cleaning is also adopted, and the overflow speed during cleaning is 2 L / min to 20 L / min, preferably 5 L / min.

In the above process, as the pH in the deionized water tank decreases, the interface potential of the wafer changes from a negative value to a positive value.

In the above process, cleaning with deionized water first can avoid the sudden change in the interface potential of the wafer after SC1 cleaning affects the cleaning effect, and can change the interface potential of the wafer to a positive value after the first cleaning.

In addition, it should be understood that when the injection of the acidic surfactant is stopped after the wafer is lifted out, and the overflow mode is maintained, the overflow speed at this time is 5 L / min to 60 L / min, preferably 35 L / min. The overflow time is 1 to 4 minutes, preferably 2.5 minutes. The pH value in the deionized water tank is restored to the original value through the overflow for a period of time, so as to perform the above-mentioned first cleaning process on other wafers.

Optionally, ultrasonic waves can be added in the cleaning at the previous stage, and the frequency is, for example, 1000 KHZ to 3000 KHZ, and preferably 1200 KHZ. The ultrasonic vibration can better clean the wafer.

In step S304, the metal remaining on the wafer is removed.

In this step, the wafer is cleaned with an acidic cleaning solution to remove metal remaining on the wafer. Exemplarily, the acidic cleaning solution is a mixed solution of SC2 and diluted hydrofluoric acid (DHF), that is, cleaning is performed in a tank including a mixed solution of hydrochloric acid, hydrogen peroxide, hydrofluoric acid, and deionized water. Cleaning.

Exemplarily, the concentration of hydrochloric acid is 0.1% to 2%, preferably 0.6%; the concentration of hydrogen peroxide is 0% to 2%, preferably 0.1%; and the concentration of DHF is 0% to 2%, preferably 0.2%.

Exemplarily, the cleaning temperature is from normal temperature to 85 degrees Celsius, preferably normal temperature.

Exemplarily, the cleaning time is 3 to 7 minutes, preferably 5 minutes.

In step S305, a second cleaning is performed. During the second cleaning process, when the wafer enters the rinsing tank, the liquid interface potential in the rinsing tank is a positive value, and the interface potential of the wafer after the second cleaning is completed. Change to a negative value.

Exemplarily, a mixed solution of deionized water and an acidic surfactant is used in the second washing.

More specifically, the second cleaning process or operation is: first, cleaning in a mixed solution of an acidic surfactant and deionized water, the acidic surfactant is exemplified by citric acid, and the pH of the mixed solution liquid is exemplified by 3 To 3.7, preferably 3.3. The cleaning temperature is from normal temperature to 85 degrees Celsius, preferably normal temperature. This process adopts overflow cleaning. The overflow speed during cleaning is 2 L / min to 20 L / min, preferably 5 L / min.

More specifically, the wafer is put into a deionized water tank while an acidic surfactant such as citric acid is injected to clean the wafer using a mixed solution of the acidic surfactant and deionized water. Exemplarily, the injection of the acidic surfactant is completed within 30 seconds.

Then, the injection of the acidic surfactant is stopped, and the cleaning is continued, and the cleaning temperature is from normal temperature to 85 degrees Celsius, preferably normal temperature. The cleaning method is still overflow cleaning, and the overflow speed during cleaning is 5 L / minute to 30 L / minute, preferably 20 L / minute. The cleaning time is 1 to 4 minutes, preferably 4 minutes.

In the above process, when the wafer enters the rinsing tank at the initial stage, because the rinsing tank is a mixed solution of an acidic surfactant and deionized water, the interface potential of the solution is positive, and the subsequent injection of the acidic surfactant is stopped , The pH in the deionized water tank increases from low, so that the interface potential of the wafer changes from a positive value to a negative value.

It should be noted that the general name of various cleaning tanks in the rinsing tank, for example, a deionized water tank is a rinsing tank that is connected with deionized water.

In addition, after the wafer is lifted out, the acidic surfactant is re-injected, and the overflow mode is maintained, preferably reaching a liquid pH of 3 to 3.7, preferably 3.3 in 30 seconds, for the second cleaning of other wafers .

In step S306, the wafer is cleaned with deionized water.

Wherein, the deionized water tank is cleaned by overflow, and the overflow speed during cleaning is 5 L / min to 30 L / min, preferably 20 L / min.

Illustratively, the resistivity of deionized water is 18 M ohm-cm. The cleaning temperature is from normal temperature to 85 degrees Celsius, preferably normal temperature. The washing time is 3 to 7 minutes, preferably 5 minutes.

Step S307: performing a hydrophilic treatment on the wafer.

Exemplarily, the wafer is cleaned by using ozone water, that is, the wafer is put into the ozone water tank for cleaning, so as to form a dense oxide layer on the surface of the wafer, so that the surface of the wafer is hydrophilic, so that the wafer after cleaning is made. Particles do not easily adhere to it.

The ozone water tank is cleaned by an overflow method, and the overflow speed during cleaning is 5 L / minute to 30 L / minute, preferably 20 L / minute.

Exemplarily, the resistivity of deionized water in ozone water is 18 M ohm-cm; the ozone concentration of ozone water is 10 ppm to 35 ppm, preferably 25 ppm.

Exemplarily, the cleaning temperature is from normal temperature to 85 degrees Celsius, and the preferred temperature is normal temperature.

Exemplarily, the cleaning time is 3 to 7 minutes, preferably 5 minutes.

In step S308, the wafer is dried.

Exemplarily, a pure water pull-drying method or an infrared drying method or a combination of the two commonly used in wafer drying may be used, and details are not described herein again.

In the above cleaning process, since the interface potential of the wafer after SC1 cleaning is negative, and the interface potential of the particles during SC2 and DHF cleaning is positive, in order to avoid wafer and particle adsorption during SC2 and DHF cleaning, SC2 and DHF Perform a first cleaning before cleaning to change the interface potential of the wafer to a positive value. In this way, when SC2 and DHF cleaning, the interface potentials of the wafer and the particles in the SC2 and DHF tank are positive, which are mutually exclusive. So that the wafer does not adsorb particles; and after SC2 and DHF are used to remove the metal remaining on the wafer, a second cleaning is performed on the wafer, and in the second clear process, the wafer enters the initial stage of the rinsing tank, The potential of the liquid interface in the rinsing tank is positive, and the interface potential of the wafer is changed to a negative value after the second cleaning is completed, so that in the second clear process, the wafer enters the initial stage of the rinsing tank, The potential of the liquid interface in the rinsing tank is positive, and the interface potential of the wafer is changed to a negative value after the second cleaning is completed. When the wafer is subsequently cleaned with deionized water, the The interface potentials are Value, so that the wafer does not adsorb both exclusive particles, thus improving the overall effect of the cleaning method of cleaning a semiconductor wafer after the final polishing of the present invention.

The content of the specific embodiments described above is used to describe the present invention in detail. However, these embodiments are only used for illustration and are not intended to limit the present invention. Those skilled in the art can understand that various changes or modifications made to the present invention without departing from the scope defined by the scope of the attached patent application fall into a part of the present invention.

S201, S202, S203, S301, S302, S303, S304, S305, S306, S307, S308‧‧‧Steps

FIG. 1 is a schematic flowchart showing a conventional RCA cleaning method.

FIG. 2 is a schematic flowchart of a method for cleaning a semiconductor wafer according to an embodiment of the present invention.

FIG. 3 is a more detailed schematic flowchart showing a method for cleaning the semiconductor wafer shown in FIG. 2.

Claims (10)

A method for cleaning a semiconductor wafer, comprising the following steps: performing a first cleaning on the wafer to change the interface potential of the wafer to a positive value; cleaning the wafer with an acidic cleaning solution, and Removing the remaining metal on the wafer; performing a second cleaning on the wafer, and during the second clearing process, when the wafer enters the rinsing tank in the initial stage, the liquid interface potential in the rinsing tank is positive And after the second cleaning is completed, the interface potential of the wafer is changed to a negative value. The cleaning method according to item 1 of the scope of the patent application, wherein a mixed solution of deionized water and an acidic surfactant is used in the first cleaning. The cleaning method according to item 2 of the scope of the patent application, wherein performing the first cleaning on the wafer to change the interface potential of the wafer to a positive value includes the following steps: In a deionized water tank Cleaning the wafer; injecting the acidic surfactant into the deionized water tank, and continuing to clean the wafer. The cleaning method according to item 1 of the scope of patent application, wherein the acidic cleaning solution is a mixed solution of SC2 and hydrofluoric acid. The cleaning method according to item 1 of the scope of patent application, characterized in that a mixed solution of deionized water and an acidic surfactant is used in the second cleaning. The cleaning method according to item 5 of the scope of patent application, wherein performing the second cleaning on the wafer includes the following steps: after injecting the acidic surfactant into a deionized water tank, using deionization A mixed solution of water and an acidic surfactant cleans the wafer; stop injecting the acidic surfactant into the deionized water tank, and continue cleaning the wafer in the deionized water tank. The cleaning method according to any one of claims 1 to 6, wherein before performing the first cleaning on the wafer so that the interface potential of the wafer becomes a positive value, The method comprises the following steps: removing particles and a part of metal remaining on the wafer. The cleaning method according to item 7 of the scope of the patent application, wherein the removing of particles and some metals remaining on the wafer includes the following steps: cleaning the wafer with a first cleaning solution; cleaning with deionized water Wafer. The cleaning method according to item 7 of the scope of patent application, characterized in that, before removing the particles and some metal remaining on the wafer, the method further comprises the following steps: cleaning the wafer with deionized water. The cleaning method according to item 7 of the scope of patent application, wherein after performing the second cleaning on the wafer, the method further includes the following steps: cleaning the wafer with deionized water; and hydrophilicizing the wafer. Sexual treatment.