CN116219446A - Precise cleaning method of target material for integrated circuit - Google Patents

Abstract

A precise cleaning method of a target material for an integrated circuit comprises the following steps: (1) Performing high-frequency ultrasonic cleaning on the target in a high-purity organic solvent cleaning agent; (2) Soaking the target subjected to ultrasonic cleaning in the step (1) in a high-purity azeotrope organic solvent cleaning agent for rinsing; (3) And (3) heating the high-purity organic solvent cleaning agent used in the step (2) by the target material in a steam drying box heater, heating the high-purity organic solvent cleaning agent to form steam for cleaning the target material, stopping heating the solvent, heating the target material independently, and drying to obtain the clean target material. The process method can avoid contact with water in the whole process of cleaning the target, effectively eliminates the possibility of electrochemical reaction on the surface of the target, and simultaneously can effectively remove the pollutants such as particles, greasy dirt and the like possibly existing on the surface of the target.

Description

A precision cleaning method for target materials for integrated circuits

technical field

The invention belongs to the technical field of processing high-purity metal materials, and in particular relates to a precision cleaning method for high-purity elemental metal or alloy targets used in integrated circuits.

Background technique

High-purity metal sputtering targets are key materials for integrated circuit manufacturing, and various thin-film functional materials are mainly obtained through magnetron sputtering technology during use. At present, according to the chemical composition, sputtering targets can be divided into: pure metal targets, such as aluminum, copper, titanium, tantalum, cobalt, etc.; alloy targets, such as aluminum copper, aluminum silicon, copper aluminum, copper manganese, tungsten titanium , nickel platinum, nickel cobalt, nickel vanadium, etc. According to Moore's Law, the integrated circuit manufacturing process continues to improve and iteratively updated, and higher and higher requirements are placed on the performance of various materials. First, the purity requirements of materials are getting higher and higher, and the purity requirements of pure metals are from 99.99%. To 99.9999%, or even to 99.99999%, the impurity content in the material is getting lower and lower. For alloy targets, in addition to the main elements, the content of impurity elements is usually controlled at the ppm level or even lower. High-purity metals and their alloy targets are key materials for integrated circuits. In addition to their purity, their microstructure and surface cleanliness also directly affect the performance of chips during sputtering coating. The impact of target surface cleanliness on the preparation and performance of integrated circuit metal thin films is mainly manifested in that when there are impurities on the target surface, when the plasma bombards the target surface, the impurities are likely to cause abnormal plasma discharge and ignition ( arcing), the particles formed by discharge falling on the wafer will cause circuit failure, which cannot meet the requirements of high-performance thin film preparation, resulting in scrapped wafers and a decrease in yield.

For high-purity material monomer targets and high-purity materials and copper alloys, aluminum alloys and other welding composite targets, in the processing environment, the materials are easily affected by the erosion of machining residual cutting fluid and moisture in the air. Oxidative discoloration occurs, so the cleanliness of the target surface is often difficult to guarantee. Especially for copper, copper alloy single targets and composite targets containing copper alloy backplanes, special attention should be paid to the problem of surface oxidation. Generally, cleaning agents for metal materials mainly include water-based cleaning agents and solvent-based cleaning agents. For solvent-based cleaning agents, they can be classified according to the types of solvents used. In the early days, traditional solvent cleaning agents such as gasoline and kerosene were widely used in the cleaning industry. However, these traditional cleaning agents are highly toxic, flammable and explosive. , there is a great potential safety hazard, so there are few practical applications. The patent "Cleaning Method of Copper or Copper Alloy Sputtering Target" (CN101724818 B) uses traditional organic solvent aviation kerosene to clean the target, which has safety risks. Water-based cleaning agents are widely used, and pure water is usually used in the target cleaning process. Usually, the target is cleaned by pure water ultrasonic cleaning to degrease, rinse, etc., and then organic solvents such as ethanol and isopropanol are used to accelerate the cleaning of the target. Dehydration, final drying to ensure its surface cleanliness, and then vacuum packaging. There are many patents for this kind of target cleaning. The problem with this method is that for high-purity targets with strong chemical activity such as copper and aluminum, Under the joint action of water, oxygen, etc. during cleaning, a series of electrochemical reactions are likely to occur on the surface of the target, resulting in corrosion and oxidation phenomena, and the target increases the risk of Particles when it participates in the chip sputtering process. With the continuous development of advanced integrated circuit technology, the process has begun to advance towards smaller 5nm and 3nm, which is getting closer and closer to the physical limit. Advanced integrated circuit manufacturing technology has higher and higher requirements on the purity and cleanliness of materials used in the process, especially for 1Xnm and below integrated circuits, the cleanliness of the target surface has become one of the important factors leading to target failure. The fine oil stains, oxides, and impurities on the surface of the target may cause the particles of the deposited film to exceed the standard, resulting in a decrease in chip yield. Cleaning the target with water machine cleaning agent, due to the limited ability of water to deal with pollutants such as oil stains and oxides on the surface of the material, and the ultrasonic frequency of ultrasonic cleaning in the current industrial cleaning is low (not higher than 40KHz), it is difficult to remove the micron level As well as impurity particles of smaller size, there are high-end targets for integrated circuits. The current cleaning method has the risk that the surface of the target is difficult to clean, and the waste generated during the cleaning process is more, and the cleaning process is also longer, which is not conducive to Energy saving and environmental protection. Therefore, it is urgent to develop a new high-efficiency and high-clean target cleaning method to avoid oxidation of the target during the cleaning process, especially for the urgent demand for high-cleanness targets in advanced integrated circuit manufacturing processes. cleaning method.

Contents of the invention

In order to overcome the problems existing in the existing methods, the present invention provides a precision cleaning method for high-purity elemental metal or alloy targets for integrated circuits. contact, the target will not be oxidized, and at the same time shorten the cleaning process, reduce the cleaning time, and achieve high-efficiency, high-cleaning and precision cleaning. The specific technical solutions are as follows:

A precision cleaning method for targets used in integrated circuits. The high-purity metal or alloy targets processed to the finished product size are transferred to a clean room with strictly controlled temperature and humidity, and then the targets are cleaned with high-purity organic solvents. Ultrasonic cleaning, rinsing, steam cleaning and drying are carried out in a fully enclosed cleaning machine with chemical agents, mainly including:

(1) The target is cleaned by high-frequency ultrasonic cleaning at room temperature in a high-purity solvent cleaning agent;

(2) The target after ultrasonic cleaning is soaked in a high-purity solvent cleaning agent for room temperature rinsing;

(3) The target is heated by the heater in the steam drying oven to the solvent used in step (2). The solvent is heated to form steam to clean the target, and then the heating of the solvent is stopped, and the target is heated separately, and a clean target is obtained after drying. .

In the above-mentioned precise cleaning method, the high-purity metal and alloy target material has a purity ≥99.99%, including metal and alloy materials such as copper, tantalum, titanium, aluminum, nickel, cobalt, and tungsten.

In the above precision cleaning method, in step (1), the solvent-based cleaning agent includes: monofluorodichloroethane, decafluoropentane, perfluorobutyl methyl ether, ethyl nonafluoroisobutyl ether, Non-flammable or non-flammable organic solvents such as tetrafluoroethyl trifluoroethyl ether.

In the above precision cleaning method, in step (2) and step (3), the high-purity organic solvent cleaning agent used for rinsing is one or more of the single solvent used in step (1) and high-purity ethanol. Mixed solvents in which organic solvents form azeotropes.

In the above precision cleaning method, in steps (1) and (2), the purity of the high-purity organic solvent cleaning agent is ≥99.5%, and the water content is ≤100ppm; the high-purity organic solvent has no flash point or The flash point is greater than 60°C.

In the above precision cleaning method, in step (1), the ultrasonic cleaning time is 30s-180s, and the ultrasonic frequency is not lower than 60KHz.

In the above precision cleaning method, in step (2), the time for rinsing is 30s-180s.

In the above precision cleaning method, in step (3), the steam cleaning and drying refers to that the target is placed above the evaporation drying box, and the bottom of the drying box contains a high-purity solvent cleaning agent for rinsing, and the solvent is built into Heaters, and heaters are also arranged in the space around the target, and the heating temperature of the heaters does not exceed 60°C.

Further, in the above-mentioned precise cleaning method, in step (3), a heater is used to heat in a steam drying oven, and the time for heating the organic solvent to form steam is 30s-90s, and after stopping the heating of the organic solvent, separate the target The material heating and drying time is 30s-60s.

Further, in the above precision cleaning method, in step (3), the steam formed by heating the solvent is condensed and recovered in the cleaning machine, filtered and recycled.

Further, in the above precision cleaning method, the ambient temperature of the clean room is controlled below 25° C., and the ambient humidity is controlled below 40%.

Compared with the existing processing methods of high-purity metal and alloy targets, the beneficial effects of the present invention are as follows:

(1) The present invention can greatly improve the cleaning effect. During high-frequency ultrasonic cleaning, solvent molecules are accelerated by high-energy sound waves and continuously impact the surface of the target, forming a stronger ultrasonic cavitation effect, which disperses and desorbs insoluble fine particles adsorbed on the surface to be cleaned, and accelerates the dissolution of soluble dirt. dissolve and diffuse. The organic solvent selected by the present invention has high purity and ultra-low water content. Compared with the method of using water-based cleaning agent, no water participates in the cleaning process, which avoids the electrochemical reaction of the target material due to the presence of water, and greatly improves the efficiency of the target material. Improve the cleanliness of the surface of the target and reduce the phenomenon of scrapping caused by surface quality problems of the target. Compared with single-component solvents, the azeotrope cleaning solvent used in rinsing and steam cleaning not only has stronger solvency, but also greatly reduces the boiling point of the solvent. It can be boiled below 60°C to achieve steam cleaning, ensuring that it dissolves in The oil in the cleaning agent will not remain on the target surface.

(2) The present invention can realize fast and efficient cleaning. Due to the low boiling point of the azeotrope mixed cleaning solvent, it can be dried quickly after cleaning, and all the cleaning uses organic solvents, which can remove the target surface passivation, hot air drying, drying, etc. after cleaning with water-based cleaning agents The whole cleaning process usually does not exceed 10 minutes, which can save 1-1.5 hours of time. The entire cleaning process is carried out in a fully closed system, and the cleaning agent can be recycled, reducing the cleaning cost per unit target.

Description of drawings

Fig. 1 is a flow chart of the precise cleaning method of the target according to the present invention.

Fig. 2 is a schematic diagram of high-frequency ultrasonic cleaning of a target in the present invention.

Fig. 3 is a schematic diagram of steam cleaning of the target in the present invention.

Among them, 1-target; 2-high-purity solvent cleaning agent; 3-cleaning tank; 4-high-frequency sound wave generator; 5-high-energy sound wave; 6-cavitation; 7-pollutant; 8-steam drying oven; 9 - bottom heating device; 10 - high-purity solvent vapor; 11 - side wall heating device.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The examples shown below do not in any way limit the content of the invention described in the claims. In addition, all the contents of the configurations shown in the following embodiments are not limited to be essential to the solution of the invention described in the claims.

The purity of high-purity metal and alloy targets for integrated circuits is ≥99.99%, including copper, tantalum, titanium, aluminum, nickel, cobalt, tungsten and other metals and alloy materials. These targets can be single high-purity material targets, or composite targets welded by high-purity materials and back plates, which are collectively called high-purity metal or alloy targets. First, the surface of the high-purity metal or alloy target that has been processed to the finished size is quickly rinsed and wiped, and then transported to a clean cleaning room. The temperature and humidity of the cleaning room are strictly controlled. Usually, the humidity of the environment has a greater impact on whether the target surface is oxidized. Great impact, when the target is placed in an environment with a humidity >40% for a long time, water condenses on the surface of the target and it is easy to react with the metal, especially for copper, which is very easy to be exposed to high temperature and humidity. Oxidized target. The ambient temperature of the clean room required by the present invention is controlled below 25° C., and the ambient humidity is controlled below 40%.

The target material 1 is placed in a cleaning tank 3 filled with a high-purity solvent cleaning agent 2, and the target material is soaked in the solvent cleaning agent for high-frequency ultrasonic cleaning at room temperature. High-purity solvent cleaning agents are specifically monofluorodichloroethane, decafluoropentane, perfluorobutyl methyl ether, ethyl nonafluoroisobutyl ether, tetrafluoroethyl trifluoroethyl ether, etc. The high-purity solvents used The purity is ≥99.5%, and the water content is ≤100ppm. A high-frequency sound wave generating device 4 is installed at the bottom of the cleaning tank, which can emit high-energy sound waves 5 not lower than 60KHz to form a high-frequency ultrasonic sound field in the cleaning tank. High-energy ultrasonic waves have cavitation effects in the solvent, forming a large number of small cavities 6, accelerating the continuous impact of the solvent on the target surface, and making the micron and submicron particles, cutting oil and other pollutants 7 adsorbed on the target surface rapidly disappear with the solvent. peel off. The ultrasonic cleaning time is 30s-180s.

After the cleaning is completed, the target is transferred to the rinsing tank. The high-purity solvent cleaning agent used is an azeotrope mixed solvent formed by a single solvent used for ultrasonic cleaning and one or more organic solvents such as high-purity ethanol. The cleaning ability of the organic solvent is usually stronger than that of a single solvent, its boiling point is generally ≤60°C, and the rinsing time is 30s-180s.

Subsequently, the target material that has been cleaned from the rinsing tank is placed in the steam drying box 8, and the heating device 9 at the bottom of the drying box is heated with the same azeotrope cleaning agent as that used for rinsing. Solvent steam 10, put the target in the steam to remove the liquid solvent and fine particles on the surface. Then stop heating the solvent, and use the side wall heating device 11 of the drying oven to heat and dry the target material. The temperature in the drying oven does not exceed 60°C, the time for heating the organic solvent to form steam is 30s-90s, and the heating and drying time for 30s-60s after stopping the heating of the organic solvent. The volatile substances remaining on the surface of the target in the steam volatilize rapidly, and the steam formed by solvent heating is condensed and recovered in the cleaning machine, filtered and recycled for reuse, which is highly efficient, energy-saving and clean.

Example 1:

In a clean room with a temperature of 22°C and a humidity of 38%, a 300mm wafer is precisely cleaned with a high-purity copper (purity ≥ 99.9999%) target. The main cleaning steps include:

(1) The ultrasonic cleaning time of the target in fluorodichloroethane with a purity ≥ 99.5% and a water content ≤ 100ppm is 100s, and the ultrasonic frequency is 60KHz;

(2) Rinse the target in 1-fluorodichloroethane with a purity ≥ 99.5% and a water content ≤ 100ppm for 60s;

(3) The target is heated in a steam drying oven at 45°C with a solvent to form steam to clean the target for 60 seconds, then stop heating the solvent, and heat the target for 30 seconds to obtain a clean target.

Example 2:

In the same environment as in Example 1, the purity of the solvent is basically the same. Different high-purity solvent cleaning agents and cleaning times are used to precisely clean the copper target for a 300mm wafer. Ultrasonic cleaning uses high-purity decafluoropentane, ultrasonic cleaning The cleaning time is 100s, and the ultrasonic frequency is 80KHz; high-purity decafluoropentane is used for rinsing, and the rinsing is 60s; the solvent is heated in a steam drying oven at 60°C, the target is cleaned with steam for 60s, and then the target is heated for 30s.

Example 3:

In the same environment as in Example 1, the purity of the solvent is basically the same. Different high-purity solvent cleaning agents and cleaning times are used to precisely clean the copper target for a 300mm wafer. Ultrasonic cleaning uses high-purity tetrafluoroethyl trifluoro Ethyl ether cleaning agent, ultrasonic cleaning time is 100s, ultrasonic frequency 80KHz; rinsing uses high-purity tetrafluoroethyl trifluoroethyl ether cleaning agent, rinsing for 60s; heat the solvent in a steam drying oven at 60°C, and steam clean the target for 60s , and then heat the target for 30s.

Example 4:

In the same environment as in Example 1, the purity of the solvent is basically the same. Different high-purity solvent cleaning agents and cleaning times are used to precisely clean the copper target for a 300mm wafer. Ultrasonic cleaning uses high-purity tetrafluoroethyl trifluoro Ethyl ether, the ultrasonic cleaning time is 100s, the ultrasonic frequency is 80KHz; the azeotrope solvent of high-purity tetrafluoroethyl trifluoroethyl ether and high-purity ethanol is used for rinsing, and the rinsing is 60s; the solvent is heated at 55°C in a steam drying oven, Clean the target with steam for 60s, and then heat the target for 30s.

Comparative example 1:

In the same environment as in Example 5, the purity of the solvent is basically the same. Different high-purity solvent cleaning agents and cleaning times are used to precisely clean the copper target for a 300mm wafer. Ultrasonic cleaning uses high-purity tetrafluoroethyl trifluoro Ethyl ether, the ultrasonic cleaning time is 100s, the ultrasonic frequency is 40KHz; the azeotrope solvent of high-purity tetrafluoroethyl trifluoroethyl ether and high-purity ethanol is used for rinsing, and the rinsing is 100s; the solvent is heated at 55°C in a steam drying oven, Clean the target with steam for 60s, and then heat the target for 30s.

Comparative example 2:

In a clean room with a temperature of 22°C and a humidity of 38%, a 300mm wafer is cleaned with a high-purity copper (purity ≥ 99.9999%) target with a water-based cleaning agent. The main cleaning steps include:

(1) The target is sprayed and cleaned with 0.5MPa high-pressure pure water for 180s;

(2) The ultrasonic cleaning time of the target in pure water is 180s, and the ultrasonic frequency is 40KHz;

(3) Rinse the target in pure water for 180s;

(4) The surface of the target is blown with hot nitrogen gas heated to 80°C for 180s;

(5) The target is placed in an oven for drying for 300s;

Comparative example 3:

In a clean room with a temperature of 22°C and a humidity of 38%, a 300mm wafer is cleaned with a high-purity copper (purity ≥ 99.9999%) target with a water-based cleaning agent. The main cleaning steps include:

(1) The target is sprayed and cleaned with 0.5MPa high-pressure pure water for 300s;

(2) The ultrasonic cleaning time of the target in pure water is 300s, and the ultrasonic frequency is 40KHz;

(3) Rinse the target in pure water for 180s;

(4) The surface of the target is blown with hot nitrogen gas heated to 80°C for 180s;

(5) The target is placed in an oven for drying for 300s;

For the cleaned target, use an optical surface analyzer to detect the particles on the target surface. At the same time, after the target is cleaned and dried, it is placed in a class 100 clean room for 30 minutes, and then the target surface is observed with a 5x magnifying glass. The surface cleanliness, the specific data are shown in the table below.

For the fine particles remaining on the surface of the target, precision optical instruments can be used to analyze the micron and submicron particles remaining on the surface of the material. Usually, the particles above 0.5 μm on the target surface will cause harm to sputtering. Through the above examples and comparative examples, it is found that the cleaning effect of high-purity solvent cleaning agent on the target is obvious, especially under the action of high-frequency ultrasonic cleaning, there are few residual fine particles on the surface of the target, and the target can be kept clean and non-oxidized after being placed for a long time. The present invention cleans the copper target material, completely avoids the possibility of oxidation on the surface of the target material, no particle problem caused by surface abnormality is found in the subsequent sputtering process of the target material, and the coating yield is significantly improved. In the comparative example, pure water was used to clean the surface of the target, which was difficult to clean and very clean, and there were many fine particle residues, and there was also a risk of surface oxidation of the target.

Compared with the traditional target cleaning process, the present invention proposes a new target precision cleaning method. In a clean room with strict temperature and humidity control, the high-purity metal target to be cleaned is placed in a solvent cleaning machine using high Pure solvent cleaning agent is used for ultrasonic cleaning, rinsing and drying to obtain a clean target. The cleaning process of the present invention can prevent the target from being in contact with water throughout the process of cleaning and packaging the finished product, without the possibility of surface oxidation of the target, and can effectively remove impurities such as particles and oil stains that may exist on the surface of the target. The cleaning process is simple and efficient, the cleaning solution can be recycled and reused, and the discharge is small, which realizes the precise cleaning of the target for integrated circuits. Especially for copper and copper alloy materials, the cleaning process completely avoids the possibility of contact with water, so there is no surface oxidation that leads to unqualified quality and scrapping of the target. The invention has important significance for the process simplification, efficiency improvement and product use performance improvement of integrated circuit high-purity metal and alloy sputtering target preparation.

Claims (10)

1. A precise cleaning method for the target material of integrated circuit includes such steps as transferring the target material of high-purity metal or alloy to be processed to finished product, cleaning it in a clean room with strictly controlled temp and humidity, ultrasonic cleaning, rinsing, steam cleaning and drying, and features that it has a high-purity solvent, and high-purity metal or alloy is used as the target material of integrated circuit:

(1) Performing room-temperature high-frequency ultrasonic cleaning on the target in a high-purity solvent cleaning agent;

(2) Soaking the target subjected to ultrasonic cleaning in the step (1) in a high-purity solvent cleaning agent for room-temperature rinsing;

(3) And (3) heating the high-purity solvent cleaning agent used in the step (2) by the target material in a steam drying box heater, heating the high-purity solvent cleaning agent to form a steam cleaning target material, stopping heating the solvent, heating the target material independently, and drying to obtain the clean target material.

2. The precise cleaning method according to claim 1, wherein the purity of the high-purity metal and alloy target is greater than or equal to 99.99%, and the high-purity metal and alloy target comprises copper, tantalum, titanium, aluminum, nickel, cobalt, tungsten and other metal and alloy materials.

3. The precision cleaning method according to claim 1, wherein in the step (1), the high-purity organic solvent cleaning agent used comprises: monofluorodichloroethane, decafluoropentane, perfluorobutyl methyl ether, ethylnonafluoroisobutyl ether or tetrafluoroethyltrifluoroethyl ether; in the step (2) and the step (3), the high-purity organic solvent cleaning agent is a mixed solvent of the single solvent and one or more organic solvents such as high-purity ethanol and the like to form an azeotrope.

4. The precise cleaning method according to claim 3, wherein the purity of the high-purity organic solvent cleaning agent is more than or equal to 99.5%, the water content is less than or equal to 100ppm, and the high-purity organic solvent cleaning agent has no flash point or has a flash point of more than 60 ℃.

5. The precise cleaning method according to claim 1, wherein in the step (1), the ultrasonic cleaning time is 30s-180s, and the ultrasonic frequency is not lower than 60KHz.

6. The precision cleaning method according to claim 1, wherein the rinsing time is 30s to 180s in the step (2).

7. The precise cleaning method according to claim 1, wherein in the step (3), the steam cleaning and drying means that the target is placed above an evaporation drying box, the bottom of the drying box is filled with a high-purity solvent cleaning agent for rinsing, a heater is arranged in the solvent, and a heater is arranged in the space around the target, and the heating temperature of the heater is not more than 60 ℃.

8. The precision cleaning method according to claim 7, wherein in the step (3), the heating of the organic solvent is performed for a steam time of 30s to 90s, and the heating of the target material alone is performed for a drying time of 30s to 60s after stopping the heating of the organic solvent.

9. The precision cleaning method according to claim 1, wherein in the step (3), the steam is dried, and the steam formed by heating the solvent is condensed and recovered in a cleaning machine, and is filtered and recycled.

10. The precision cleaning method according to claim 1, wherein the ambient temperature of the clean room is controlled below 25 ℃ and the ambient humidity is controlled below 40%.

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