CN114999899A - Wafer cleaning method - Google Patents
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- CN114999899A CN114999899A CN202210941181.2A CN202210941181A CN114999899A CN 114999899 A CN114999899 A CN 114999899A CN 202210941181 A CN202210941181 A CN 202210941181A CN 114999899 A CN114999899 A CN 114999899A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02041—Cleaning
- H01L21/02057—Cleaning during device manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
- B08B3/04—Cleaning involving contact with liquid
- B08B3/08—Cleaning involving contact with liquid the liquid having chemical or dissolving effect
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K13/00—Etching, surface-brightening or pickling compositions
- C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
- C09K13/08—Etching, surface-brightening or pickling compositions containing an inorganic acid containing a fluorine compound
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02041—Cleaning
- H01L21/02057—Cleaning during device manufacture
- H01L21/02068—Cleaning during device manufacture during, before or after processing of conductive layers, e.g. polysilicon or amorphous silicon layers
- H01L21/02074—Cleaning during device manufacture during, before or after processing of conductive layers, e.g. polysilicon or amorphous silicon layers the processing being a planarization of conductive layers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract
The invention provides a wafer cleaning method, which comprises the following steps: providing HNO to a cleaning machine 3 Mixed acid cleaning solution with HF, HNO in the mixed acid cleaning solution 3 The volume concentration ratio of the hydrogen fluoride to HF is 20: 1-100: 1; and performing a cleaning process to remove by-products on the surfaces of the wafers one by one, and supplementing a predetermined amount of HF into the mixed acid cleaning solution at a predetermined time interval from the beginning of the cleaning process so as to maintain the etching rate of the mixed acid cleaning solution within an effective etching rate range. According to the wafer cleaning method provided by the invention, the etching stability and the use efficiency of the mixed acid cleaning solution are improved, the use cost of the mixed acid cleaning solution is reduced, and the problem of reduced productivity of a cleaning machine caused by frequent replacement of the mixed acid cleaning solution is solved.
Description
Technical Field
The invention relates to the field of semiconductor manufacturing, in particular to a wafer cleaning method.
Background
Nitric acid (HNO) 3 ) A mixed acid cleaning solution (hereinafter, referred to as a mixed acid cleaning solution) containing hydrofluoric acid (HF) is widely used for cleaning wafers due to its excellent chemical properties. Particularly, the mixed acid cleaning solution has excellent cleaning capability on a plurality of metals, such as copper, and is often used in a cleaning process for removing metal byproducts on the surface of a wafer, so that device short circuit caused by metal residues on the surface of the wafer can be effectively prevented, and metal cross contamination caused by mixed use of machines can be effectively reducedThe risk of (c).
The cleaning principle of the mixed acid cleaning solution is as follows: by using HNO 3 The strong oxidizing property and the acidity of the silicon wafer dissolve away metal byproducts on the surface of the silicon wafer, the metal byproducts comprise metal and/or metal oxide, and SiO on the surface of the silicon wafer is corroded away by utilizing the strong coordination of fluorine ions in HF 2 By-product, then HNO 3 And HF etching the exposed silicon layer and releasing the metallic by-products diffused into the silicon layer, and finally HNO 3 And dissolving and removing the metal by-product diffused into the silicon layer, thereby ensuring the removal effect of the metal by-product.
In the actual cleaning process, HNO-rich is generally selected 3 To ensure the removal effect on the metal by-products, the HNO-enriched cleaning solution 3 In the mixed acid cleaning solution of (1), HNO 3 The content is far higher than HF content, HNO 3 The volume concentration ratio of the HF to the hydrogen fluoride is usually 20: 1-100: 1. Enriched HNO 3 In the process of circularly cleaning the wafer, along with the consumption of HF in the mixed acid cleaning solution, the concentration of the HF is gradually reduced, so that the etching rate of the mixed acid cleaning solution is reduced, and when the etching rate is reduced to be out of the range of the stable etching rate, the instability of the etching rate is caused. Furthermore, after a certain period of cyclic cleaning, the etching rate of the mixed acid cleaning solution is continuously reduced to be outside the effective etching rate range (the effective etching rate range can be determined according to specific process standards), and at this time, the mixed acid cleaning solution is considered to be invalid, so that the mixed acid cleaning solution needs to be replaced to ensure the quality of the cleaning process. Frequent replacement of mixed acid cleaning solution reduces the capacity of the cleaning machine, and the replaced mixed acid cleaning solution contains a large amount of underutilized HNO 3 The use efficiency of the mixed acid cleaning solution is low, and the use cost and the recovery cost of the mixed acid cleaning solution are high due to the low use efficiency.
Disclosure of Invention
In view of this, the present invention provides a wafer cleaning method to improve the utilization efficiency and etching rate stability of the mixed acid cleaning solution.
A method of cleaning a wafer, comprising:
providing HNO to a cleaning machine 3 Mixed acid cleaning solution with HF, HNO in the mixed acid cleaning solution 3 The volume concentration ratio of the hydrogen fluoride to HF is 20: 1-100: 1;
and (3) performing a cleaning process, removing the by-products on the surfaces of the wafers one by one, and supplementing a predetermined amount of HF (hydrogen fluoride) into the mixed acid cleaning solution at a predetermined time interval from the beginning of the cleaning process so as to maintain the etching rate of the mixed acid cleaning solution within an effective etching rate range.
Preferably, the wafer comprises a silicon wafer.
Preferably, the wafer surface comprises a wafer backside.
Preferably, the preset time interval is 200 s-800 s, and the preset amount of HF is 0.01V mol/L-0.02V mol/L of HF, wherein V is the volume of the mixed acid cleaning solution.
Preferably, the supplementing of the predetermined amount of HF to the mixed acid cleaning solution at the predetermined time interval from the start of the cleaning process comprises: and supplementing a predetermined amount of HF into the mixed acid cleaning solution every 500-800 s within a time period of 0-40 min after the cleaning process starts, and supplementing a predetermined amount of HF into the mixed acid cleaning solution every 200-300 s within a time period of 41-80 min after the cleaning process starts.
Preferably, the by-product comprises a metal and/or a metal oxide, the metal comprising copper and the metal oxide comprising copper oxide.
Preferably, the process parameters of the cleaning process include: the cleaning time of each wafer is 3 s-60 s, the temperature of the mixed acid cleaning solution is 23 ℃ to 28 ℃, and the flow rate of the mixed acid cleaning solution is 750ml/min to 850 ml/min.
Preferably, HNO in the cleaning solution 3 The volume concentration ratio to HF was 50: 1.
Preferably, the cleaning station comprises a single wafer cleaning station.
Preferably, the time of the cleaning process is less than 6000 s.
Compared with the prior art, the wafer cleaning method provided by the invention has the following advantages:
according to the wafer cleaning method provided by the invention, the preset amount of HF is supplemented into the mixed acid cleaning solution according to the preset time interval, so that the etching rate of the mixed acid cleaning solution is maintained within the effective etching rate range, the use efficiency of the mixed acid cleaning solution is improved, the use cost of the mixed acid cleaning solution is reduced, and the problem that the productivity of a cleaning machine is reduced due to frequent replacement of the mixed acid cleaning solution is avoided; meanwhile, the wafer cleaning method provided by the invention improves the problem of unstable etching rate caused by the reduction of the etching rate of the mixed acid cleaning solution.
Drawings
FIG. 1 is a flowchart illustrating a wafer cleaning method according to one embodiment;
FIG. 2 is a graph showing the variation of the etching rate of a mixed acid cleaning solution with etching time in a wafer cleaning method of the prior art;
FIG. 3 is a graph showing the variation of the etching rate of the mixed acid cleaning solution with the etching time in the wafer cleaning method according to the embodiment;
FIG. 4 is a graph showing the variation of the etching rate of the mixed acid cleaning solution with the etching time in the wafer cleaning method according to another embodiment;
fig. 5 is a histogram comparing the copper content before and after the back side cleaning in another embodiment of the wafer cleaning method shown in fig. 4.
Detailed Description
To make the objects, advantages and features of the present invention more apparent, a wafer cleaning method according to the present invention is further described in detail with reference to the accompanying drawings. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
The inventor finds that the process of cleaning the wafer back of the silicon wafer by the mixed acid cleaning solution mainly comprises two steps of etching by-products and etching a silicon layer, wherein the by-products comprise silicon oxide and metal by-products, and the metal by-products comprise metal and/or metal oxide. Taking the wafer back cleaning process containing the copper byproduct as an example, the cleaning process includes the following chemical reactions:
SiO 2 + 4HF → SiF 4 ↑+ 2H 2 O （1）
Cu + 4HNO 3 → Cu(NO 3 ) 2 + 2NO 2 ↑+ 2H 2 O （2）
CuO + 2HNO 3 → Cu(NO 3 ) 2 + H 2 O （3）
Si + HNO 3 + 6HF → H 2 SiF 6 + HNO 2 + H 2 O + H 2 ↑（4）
the cleaning process of the mixed acid cleaning solution is to clean the surface byproduct firstly. The surface layer comprises SiO formed by natural oxidation 2 Film layer and the SiO 2 A small amount of particles of metals and metal oxides deposited on the membrane layer and/or the membrane layer. This process takes place in chemical reactions (1), (2) and (3).
After the surface layer is cleaned away, a thickness of the silicon layer below the surface layer is then etched. Because of the diffusivity of the metal, a small amount of metal by-products will diffuse into the silicon layer, so in the actual cleaning process, to ensure that the metal by-products can be completely removed, it is usually necessary to etch away a certain thickness of the silicon layer, and this process takes place with a chemical reaction (4). The chemical reaction (4) is a total reaction, and the step-by-step reaction comprises the following steps: first, HNO is utilized 3 Oxidizing Si to + 4-valent Si 4+ Then Si 4+ And F - Coordination reaction to form H 2 SiF 6 . During the etching of the silicon layer, the metal by-products diffused into the silicon layer are exposed, and thus the chemical reactions (2) and (3) occur simultaneously. Since the metal by-product content is very low and the nitric acid is sufficient, it is considered that reactions (2) and (3) occur immediately. Therefore, the etching rate of etching the silicon layer is mainly determined by the reaction rate of the chemical reaction (4).
Since the etched-away silicon layer thickness (over 1500 a) is much larger than the etched-away surface layer thickness (tens of a) in the cleaning process, chemical reaction (4) mainly occurs; and the etching time of the surface layer is very short compared with that of the silicon layer and can be ignored, so that the etching rate of the whole cleaning process and the consumption condition of the cleaning agent are mainly determined by the step of etching the silicon layer. In the cleaning process, in order to ensure the metal pairGood removal effect of the product, and avoidance of over severe etching of the silicon layer (rapid reaction rate of chemical reaction (4) and large amount of heat release), the HNO-rich material is generally selected 3 The mixed acid cleaning solution of (1), wherein HNO is contained in the mixed acid cleaning solution 3 Higher content and lower HF content. As can be seen from the chemical reaction (4), the cleaning process consumes much HF. Therefore, as the cleaning process is carried out, the concentration of HF is reduced, the etching rate of the mixed acid cleaning solution is unstable and even fails, and the quality of the cleaning process is reduced.
In order to solve the problems, the invention provides a convenient and feasible solution, and the method ensures the effectiveness of the mixed acid cleaning solution by supplementing HF to the mixed acid cleaning solution in time so as to maintain the etching rate of the mixed acid cleaning solution within an effective etching rate range. In the invention, two standards which are commonly used in the industry for evaluating the effectiveness of the mixed acid cleaning solution are adopted: and the first standard and the second standard are used for detecting the effectiveness of the mixed acid cleaning solution at different moments of the cleaning process at any time. The first criterion is: the mixed acid cleaning solution is used for cleaning SiO formed by thermal oxidation 2 The etching rate of the film layer is stable in an effective etching rate range of 205A/min-245A/min, and the standard can ensure that the cleaning process can be effectively carried out; the second standard is as follows: after the mixed acid cleaning solution cleans the back of the wafer after Chemical Mechanical Polishing (CMP) in the copper plating process, the copper content of the back of the wafer reaches the ICPMS standard, namely the number of copper atoms is less than 5 multiplied by 10 9 /cm 2 The standard can ensure that the mixed acid cleaning solution has good metal removing effect. When the mixed acid cleaning solution simultaneously meets the first standard and the second standard, the effectiveness of the mixed acid cleaning solution can be judged.
Referring to fig. 1, the present invention provides a wafer cleaning method, including the following steps:
s1: providing HNO to a cleaning machine 3 Mixed acid cleaning solution with HF, wherein HNO in the mixed acid cleaning solution 3 The volume concentration ratio of the hydrogen fluoride to HF is 20: 1-100: 1;
s2: and (3) performing a cleaning process, removing by-products on the surfaces of the wafers one by one, and supplementing a predetermined amount of HF (hydrogen fluoride) into the mixed acid cleaning solution at a predetermined time interval from the beginning of the cleaning process so as to maintain the etching rate of the mixed acid cleaning solution within an effective etching rate range.
In this embodiment, the cleaning process is performed in an existing single wafer cleaning machine, and each wafer is continuously cleaned one by one in a flow manner, where the number of cleaned wafers and the time of the cleaning process (and the total etching time of the mixed acid cleaning solution) are in a linear relationship.
HNO in the mixed acid cleaning solution 3 The volume concentration ratio of the mixed acid cleaning solution to HF is preferably 50:1, but the volume concentration ratio is not limited to the preferred range, and the volume concentration ratio can be any value between 20:1 and 100:1 so as to ensure HNO in the mixed acid cleaning solution 3 The content is much greater than the HF content. The mixed acid cleaning solution also comprises a certain amount of deionized water, and the deionized water is used for diluting so as to ensure that HNO is generated 3 With HF to a desired concentration and to ensure that at the desired concentration the mixed acid cleaning solution meets the first criterion, namely for SiO formed by thermal oxidation 2 The etching rate of the film layer is within the effective etching rate range of 205A/min-245A/min; under the proper concentration, the etching rate of the mixed acid cleaning solution to the silicon wafer is 500A/s-800A/s.
In this embodiment, a silicon wafer after Chemical Mechanical Polishing (CMP) in a copper (Cu) process is taken as an example for explanation, so that the by-products to be removed by the cleaning process include SiO 2 And Cu by-products (including Cu and CuO), the wafer surface preferably being the wafer backside. One skilled in the art will appreciate that the byproducts may also include other metal byproducts, and the wafer surface may also be the wafer front side.
In order to ensure the stability of the etching rate in the cleaning process, the process parameters of the cleaning process are controlled. Preferred process parameters include: the cleaning time of each wafer is 3-60 s, the temperature of the mixed acid cleaning solution is 23-28 ℃, the flow rate of the mixed acid cleaning solution is 750-850 ml/min, and the spray cleaning mode is scanning spray cleaning. The temperature of the cleaning liquid influences the rate of chemical reaction generated in the etching process, so that the influence on the etching rate is large, and the temperature range of the cleaning liquid is preferably 23-28 ℃ after experimental tests. The flow rate of the cleaning liquid also has certain influence on the etching rate, and after experimental tests, the flow rate of the cleaning liquid is determined to be 750 ml/min-850 ml/min. In addition, the scanning spray may exhibit better surface etch rate uniformity than the center spray.
In the wafer cleaning method provided by the invention, in order to ensure that the etching rate of the mixed acid cleaning solution is maintained within an effective etching rate range, a predetermined amount of HF needs to be supplemented into the mixed acid cleaning solution according to a predetermined time interval.
Preferably, the predetermined time interval is 200 s-800 s, and the certain amount of HF is 0.01V mol/L-0.02V mol/L of HF, wherein V is the volume of the mixed acid cleaning solution. It can be understood that the time interval is preferably 200 s-800 s, which can ensure timely replenishment of HF consumed in the cleaning process, and the HF replenishment times are typically dozens of times within the effective time of the mixed acid cleaning solution (the time for maintaining effective etching of the cleaning solution, typically thousands of seconds), which is convenient for operation. The predetermined amount of HF should not be too small and not too large, too small may result in a weak effect of maintaining the etching rate of the mixed acid cleaning solution in step S2, too large may result in a large increase in the etching rate of the mixed acid cleaning solution in a short time just after the HF is added, causing an oscillation in the etching rate, and may even result in an etching rate exceeding an expected etching rate range, which is not favorable for maintaining the stability of the etching rate of the mixed acid cleaning solution. The operation of replenishing the predetermined amount of HF may be performed by replenishing an aqueous HF solution, the mass fraction of HF in the aqueous HF solution is preferably not less than 5%, so as to avoid the change in volume of the mixed acid cleaning solution caused by adding more water to the mixed acid cleaning solution when HF is replenished.
On the basis of the above, preferably, the supplementing a predetermined amount of HF to the mixed acid cleaning solution at predetermined time intervals from the start of the cleaning process includes: and (3) supplementing 0.01-0.02V mol/L of HF to the mixed acid cleaning solution every 500-800 s within 0-40 min, and supplementing 0.01-0.02V mol/L of HF to the mixed acid cleaning solution every 200-300 s within 41-80 min, wherein V is the volume of the mixed acid cleaning solution.
Hereinafter, features and advantages of the step S2 will be described with reference to fig. 2 to 4. Fig. 2 to 4 show the change curves of the etching rate of the mixed acid cleaning solution with the etching time in the cleaning method for supplementing HF in different ways. It should be noted that the etching rate of the ordinate in fig. 2 to fig. 4 refers to SiO formed by thermal oxidation of the mixed acid cleaning solution in the furnace tube manufacturing process 2 The etching rate (collecting a proper amount of the mixed acid cleaning solution to thermally oxidize SiO formed in the process of manufacturing the furnace tube) 2 Etching is performed, and the etching rate is measured), not the etching rate of the cleaning process on the surface of the wafer. The etching rate of the mixed acid cleaning solution to the surface of the wafer is high and generally reaches 500A/s-800A/s, and the fluctuation of the etching rate is large, so that the accurate value of the etching rate of the mixed acid cleaning solution to the surface of the wafer is difficult to measure; and the effectiveness of the mixed acid cleaning solution is generally evaluated and judged by the aforementioned first standard in the industry, which is: the mixed acid cleaning solution is used for cleaning SiO formed by thermal oxidation 2 The etching rate of the film layer is stable at 205A/min-245A/min. The etching time of the abscissa in fig. 2 to fig. 4 refers to the total time of etching each wafer by the mixed acid cleaning solution, in a general single wafer cleaning process, the etching time of each wafer is fixed, and the mixed acid cleaning solution cleans the wafers one by one and continuously, so that the total time of etching each wafer by the mixed acid cleaning solution is proportional to the number of cleaned wafers, and the total time is generally equal to the duration time of the cleaning process. In each cleaning process corresponding to fig. 2 to 4, except for different ways of supplementing HF, other process parameters are the same, and the specific process parameters include: the cleaning time of each wafer is 5s, the temperature of the mixed acid cleaning solution is 23-28 ℃, the flow rate of the mixed acid cleaning solution is 750-850 ml/min, and the volume of the mixed acid cleaning solution is 40L. And the cleaning processes corresponding to fig. 2-4 are all performed in a single-wafer type cleaning machine, the cleaning objects are all the wafer backs after the copper process, the mixed acid cleaning solution etches the surface of each wafer back one by one in batches, and the wafer back cleaning process is performed for 80min in total. Thus, it is possible to provideThe number of cleaned wafers is linearly increased along with the etching time of the mixed acid cleaning solution. It can be understood that, in fig. 2 to 4, the etching rates of the mixed acid cleaning solution at a limited number of different moments are measured, and a variation curve of the etching rate of the mixed acid cleaning solution with etching time is simulated according to the limited number of etching rates.
Referring to fig. 2, fig. 2 is a graph showing the variation of the etching rate of the mixed acid cleaning solution with the total etching time in the wafer cleaning method without supplying HF (in the prior art). Wherein, the etching rate gradually decreases with the consumption of HF in the mixed acid cleaning solution, and is at 1200s (t in FIG. 2) 1 ) Thereafter, the etch rate has dropped out of 215A/min (v in FIG. 2) 2 ) To 235A/min (v in FIG. 2) 3 ) The stable etching rate range is generally considered that the mixed acid cleaning solution loses the stability of the etching rate at the moment; further, at 2000s (t in FIG. 2) 2 ) Thereafter, the etch rate has been less than 205A/min (v in FIG. 2) 1 ) And the effective etching rate range (205 a/min-245 a/min) mentioned in the first standard is dropped, at which point the mixed acid cleaning solution no longer meets the requirements of the cleaning process and needs to be replaced. T in FIG. 2 1 The etching speed can be defined as the stable etching time of the mixed acid cleaning solution, namely the time for keeping the stable etching speed of the mixed acid cleaning solution; t in FIG. 2 2 Can be defined as the effective etching time of the mixed acid cleaning solution, namely the time for maintaining the effective etching rate of the mixed acid cleaning solution. In an effective etching time of 2000s, when the cleaning time per wafer is 5s, the number of cleaned wafers is 400. Increasing said t 1 And t 2 The etching stability and the effective etching time of the mixed acid cleaning solution can be improved, so that the quality of the cleaning process can be improved.
Referring to fig. 3, fig. 3 is a graph showing a variation curve of the etching rate of the mixed acid cleaning solution with the etching time in the wafer cleaning method according to an embodiment, in the cleaning method, a manner of supplementing HF is as follows: and supplementing 0.02V mol/L of HF to the mixed acid cleaning solution every 600s, wherein V is the volume of the mixed acid cleaning solution. In contrast to FIG. 2, the etch rate in FIG. 3 is initially replenished with HThe etching time after F is improved to a certain extent, and the etching time t is stabilized 1 (t in FIG. 3 1 ) I.e. the etching rate is maintained at 215A/min (v in FIG. 3) 2 ) To 235A/min (v in FIG. 3) 3 ) The time within the range of stable etching rate is increased to 2500 s; the etching rate of the mixed acid cleaning solution is greater than 205A/min during the whole cleaning process (the cleaning process time reaches 4800 s) (v in FIG. 3) 1 ) Therefore, the mixed acid cleaning solution is effective in the whole cleaning process, and the effective etching time t 2 (t in FIG. 3 2 ) Reaching 4800 s. Compared with the prior art (the wafer cleaning method corresponding to fig. 2), in the wafer cleaning method provided by an embodiment, the stable etching time t of the mixed acid cleaning solution is 1 (t in FIG. 3 1 ) The effective etching time t is increased by one time (from 1200s to 2500 s) 2 (t in FIG. 3 2 ) At least one fold increase (from 2000s to at least 4800 s). In the effective etching time of at least 4800s, when the cleaning time per wafer is 5s, the number of cleaned wafers is at least 960, that is, compared with the prior art, the cleaning capability of the mixed acid cleaning solution in one embodiment is improved by at least one time. Therefore, the wafer cleaning method provided by the embodiment can effectively improve the stability of the etching rate and the use efficiency of the mixed acid cleaning solution.
The etching rate shown in FIG. 3 is still unstable (the etching rate falls out of the stable etching rate range of 215A/min-235A/min) in the second half (after 40 min) of the cleaning process, so that the stability of the etching rate of the mixed acid cleaning solution can be further improved by further optimizing the manner of supplementing HF.
Referring to fig. 4, fig. 4 is a graph showing a variation curve of the etching rate of the mixed acid cleaning solution with the etching time in the wafer cleaning method according to another embodiment, in the wafer cleaning method according to the embodiment, a sectional HF supplementing manner is adopted, that is: and (3) supplementing HF at intervals of 500s within 0-40 min, and supplementing HF at intervals of 250s within 41-80 min, wherein V is the volume of the mixed acid cleaning solution. The embodiment corresponding to fig. 4 is a wholeIn the second half (after 40 min) of the cleaning process, the replenishment frequency of HF is accelerated, and the etching rate of the mixed acid cleaning solution in the second half is effectively increased, thereby ensuring that the etching rate of the mixed acid cleaning solution is maintained at 215 a/min (v in fig. 4) 2 ) To 235A/min (v in FIG. 4) 3 ) Within a stable etch rate range. Compared with the prior art (the wafer cleaning method corresponding to fig. 2), the wafer cleaning method provided by another embodiment corresponding to fig. 4 stabilizes the etching time t 1 (t in FIG. 4 1 ) At least three times (from 1200s to 4800 s), and at least one time (from 2000s to 4800 s), so that the etching rate stability and the use efficiency of the mixed acid cleaning solution can be effectively improved by the wafer cleaning method provided by another embodiment corresponding to fig. 4. Compared with the embodiment corresponding to fig. 3, the wafer cleaning method provided by the other embodiment corresponding to fig. 4 has the advantage that the stable etching time is increased by about one time (from 2500s to at least 4800 s), and the quality of the cleaning process is further improved.
It is to be understood that, in the above embodiments, the specific parameters involved in the manner of supplementing HF are selected to be certain values, and these specific parameters may be varied within a suitable range only for convenience of explanation. For example, after extensive testing experiments, the inventors finally concluded that a better way to supplement HF includes: and (3) supplementing HF of 0.01-0.02V mol/L every 500-800 s within 0-40 min, and supplementing HF of 0.01-0.02V mol/L every 200-300 s within 41-80 min, wherein V is the volume of the mixed acid cleaning solution. In the expression, the amount of the supplemented HF can be any value between 0.01V mol/L and 0.02V mol/L, and the time interval of the supplemented HF can also be a proper value between 200s and 800 s; and under the same supplementary HF mode, the time intervals of supplementary HF can be different, and the quantity of the supplementary HF can also be different.
And as mentioned above, the amount of HF supplied each time needs to be within a suitable range, and in the embodiments described above, when HF is supplied each time at 0.01V mol/L to 0.02V mol/L (where V is the volume of the mixed acid cleaning solution), the increase in etching rate in a short time is not more than 10 a/min, so that oscillation of the etching rate caused by HF supply is avoided, and the stability of the etching rate is ensured, as shown in fig. 3 and 4.
Meanwhile, according to the second standard, the metal removing effect of the mixed acid cleaning solution in the above embodiments is evaluated, so as to further illustrate the advantages of the present invention. Taking another embodiment corresponding to fig. 4 as an example, the metal copper content before and after cleaning of the wafers 1, 2, 3, 4, and 5 that are cleaned at different times of the cleaning process, 1000s, 2000s, 3000s, 4000s, and 4500s, is detected to form a histogram of the copper content before and after cleaning shown in fig. 5. According to the histogram of copper content comparison before and after cleaning and according to the second standard, it can be determined whether the removing capability of the mixed acid cleaning solution of another embodiment corresponding to fig. 4 to the metal by-product meets the standard. As can be seen from FIG. 5, the number of copper atoms on the backside of each wafer was 10 before cleaning 10 /cm 2 In order of magnitude, the number of the crystal back copper atoms after cleaning is not more than 0.15 multiplied by 10 9 /cm 2 (shown by the dashed line in fig. 5), the second criterion is satisfied, and thus the removal capability of the metal by-product can be considered to be good. The mixed acid cleaning solution in the other embodiments described above, after being detected by the second standard, also has good removing capability for metal by-products. Thus, the effectiveness of the mixed acid cleaning solution was further demonstrated.
In summary, according to the wafer cleaning method provided by the invention, the predetermined amount of HF is supplemented to the mixed acid cleaning solution according to the predetermined time interval, so that the etching rate of the mixed acid cleaning solution is maintained within the effective etching rate range, and the effective etching time of the mixed acid cleaning solution is increased, thereby increasing the use efficiency of the mixed acid cleaning solution, and solving the problems of low use efficiency of the mixed acid cleaning solution and reduced productivity of a cleaning machine caused by frequent replacement of the mixed acid cleaning solution in the existing cleaning process; meanwhile, the wafer cleaning method provided by the invention can also improve the stable etching time of the mixed acid cleaning solution, improve the stability of the etching rate of the mixed acid cleaning solution and improve the quality of the cleaning process.
In addition, it is to be understood that while the present invention has been described in conjunction with the preferred embodiments thereof, it is not intended to limit the invention to those embodiments. It will be apparent to those skilled in the art that many changes and modifications can be made, or equivalents employed, to the presently disclosed embodiments without departing from the intended scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed. It is to be further understood that the present invention is not limited to the particular methodology, compounds, materials, manufacturing techniques, uses, and applications described herein, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a step" means a reference to one or more steps and may include sub-steps. All conjunctions used should be understood in the broadest sense. Thus, the word "or" should be understood to have the definition of a logical "or" rather than the definition of a logical "exclusive or" unless the context clearly dictates otherwise. Structures described herein are to be understood as also referring to functional equivalents of such structures. Language that can be construed as approximate should be understood as such unless the context clearly dictates otherwise.
Claims (10)
1. A wafer cleaning method is characterized by comprising the following steps:
providing HNO to a cleaning machine 3 Mixed acid cleaning solution with HF, wherein HNO in the mixed acid cleaning solution 3 The volume concentration ratio of the hydrogen fluoride to HF is 20: 1-100: 1;
and (3) performing a cleaning process, removing by-products on the surfaces of the wafers one by one, and supplementing a predetermined amount of HF into the mixed acid cleaning solution at a predetermined time interval from the beginning of the cleaning process so as to maintain the etching rate of the mixed acid cleaning solution within an effective etching rate range.
2. The wafer cleaning method of claim 1, wherein the wafer comprises a silicon wafer.
3. A method according to claim 1, wherein the wafer surface comprises a wafer backside.
4. The wafer cleaning method as claimed in claim 1, wherein the predetermined time interval is 200 s-800 s, and the predetermined amount of HF is 0.01V mol/L-0.02V mol/L HF, where V is the volume of the mixed acid cleaning solution.
5. The wafer cleaning method as claimed in claim 4, wherein the supplementing of the predetermined amount of HF to the mixed acid cleaning solution at predetermined time intervals from the start of the cleaning process comprises: and supplementing a predetermined amount of HF into the mixed acid cleaning liquid every 500-800 s within a time period of 0-40 min after the cleaning process starts, and supplementing a predetermined amount of HF into the mixed acid cleaning liquid every 200-300 s within a time period of 41-80 min after the cleaning process starts.
6. The wafer cleaning method according to any one of claims 1 to 5, wherein the by-product comprises a metal and/or a metal oxide, the metal comprises copper, and the metal oxide comprises copper oxide.
7. The wafer cleaning method according to any one of claims 1 to 5, wherein the process parameters of the cleaning process comprise: the cleaning time of each wafer is 3-60 s, the temperature of the mixed acid cleaning solution is 23-28 ℃, and the flow rate of the mixed acid cleaning solution is 750-850 ml/min.
8. The wafer cleaning method of claim 1, wherein the HNO in the cleaning solution 3 The volume concentration ratio to HF was 50: 1.
9. A method as claimed in claim 1, wherein the cleaning tool comprises a single wafer cleaning tool.
10. The wafer cleaning method of claim 1, wherein the cleaning process time is less than 6000 s.
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| CN115494887A (en) * | 2022-11-16 | 2022-12-20 | 合肥新晶集成电路有限公司 | Etching liquid replenishing method and device and etching equipment |
| CN115579311A (en) * | 2022-12-02 | 2023-01-06 | 湖北江城芯片中试服务有限公司 | Control method and device for mixed acid activation state, computer equipment and storage medium |
| CN115707527A (en) * | 2022-10-08 | 2023-02-21 | 杭州中欣晶圆半导体股份有限公司 | DK furnace tube cleaning method |
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