Wafer surface processing method and semiconductor device
By converting the copper precipitated on the wafer surface into copper ions and generating color precipitates, and removing copper precipitates in combination with electrochemical reactions, the pit defect problem caused by copper precipitation is solved, efficient and low-cost detection and removal effects are achieved, and the production efficiency of semiconductor devices is improved.
Patent Information
- Application Number
- CN202411828487.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-11
- Publication Date
- 2025-03-28
AI Technical Summary
During semiconductor device manufacturing, copper precipitation will cause pit defects on the wafer surface, affecting subsequent needle testing and packaging. The existing detection methods have problems such as high cost, in real time, and inability to effectively detect small-sized copper precipitation.
The copper precipitated on the wafer surface is converted into copper ions and a color-containing precipitate is generated using a precipitant agent to generate a copper-containing precipitate with color, so as to detect and remove copper precipitate. Electrochemical reaction is used to convert copper into copper ions, and the copper precipitation is removed by controlling the voltage and current density to avoid damage to aluminum metal.
Effective detection and removal of copper precipitation on the wafer surface is achieved, avoiding the occurrence of pit defects, improving the yield and efficiency of subsequent testing and packaging, and the method is simple to operate and low cost.
Smart Images
Figure CN119725224A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a wafer surface processing method and a semiconductor device. Background Art
[0002] The metal wiring process is one of the important processes in the back-end support of semiconductor chips. The metal wiring process uses a metal wiring layer to connect hundreds of millions of transistors on the wafer.
[0003] During the wafer manufacturing process, the metal wiring layer on the wafer often uses two processes: copper wire and aluminum wire. The aluminum wire process generally contains 0.5% copper-aluminum alloy. During the aluminum wire deposition process, or the subsequent etching and annealing process of the passivation layer covering the aluminum wire, copper in the copper-aluminum alloy will be precipitated. After the copper on the wafer surface is precipitated, it will react with the wet etching solution during the subsequent wet etching, resulting in pit defects. At present, due to the small size of the copper precipitation, when the metal texture or metal grains on the surface of the metal layer are too heavy, it cannot be effectively scanned by the inspection machine. If the copper precipitation on the wafer cannot be detected in time, the pit defects that appear in the subsequent wet cleaning process will affect the subsequent wafer needle test and wafer packaging. Summary of the invention
[0004] In view of the above shortcomings of the prior art, the purpose of the present invention is to provide a wafer surface processing method and a semiconductor device to avoid the influence of copper precipitation on subsequent wafer needle testing and packaging, thereby improving the inspection yield and efficiency.
[0005] In order to achieve the above-mentioned object and other related objects, the present invention provides a method for processing a wafer surface, comprising:
[0006] Providing a wafer, on which a metal interconnection layer is formed, the metal interconnection layer comprising copper;
[0007] Convert the copper precipitated on the surface of the wafer into copper ions;
[0008] A precipitant is used to convert the copper ions into a colored copper-containing precipitate.
[0009] According to one aspect of the present invention, there is also provided a semiconductor device, which is obtained by the above-mentioned wafer surface processing method, and the semiconductor device comprises:
[0010] Semiconductor substrate;
[0011] at least one transistor formed in or above a semiconductor substrate;
[0012] a metal interconnect layer formed above at least one transistor and electrically connected to at least one transistor;
[0013] The passivation layer is formed on the metal interconnection layer and exposes at least a portion of the metal interconnection layer.
[0014] Compared with the prior art, the wafer surface processing method and semiconductor device of the present invention have at least the following beneficial effects:
[0015] The wafer surface processing method of the present invention comprises providing a wafer, on which a metal interconnection layer is formed, and the metal interconnection layer contains copper. The copper precipitated on the surface of the wafer is converted into copper ions. The copper ions are converted into a colored copper-containing precipitate by using a precipitant. Thus, the present invention can detect the copper precipitation on the wafer surface by converting copper into copper ions and generating a colored copper-containing precipitate. Since the precipitate has a color development reaction, the presence of copper precipitation can be directly determined based on the detection machine. Subsequently, the precipitate can be directly cleaned and removed to achieve the removal of the copper precipitation on the wafer surface, and since the method used is appropriate, no damage to the wafer is caused. Furthermore, the present invention can avoid the generation of pit defects on the wafer surface caused by copper precipitation, which is beneficial to the subsequent needle piercing test and packaging of the wafer.
[0016] Furthermore, the present invention converts copper into copper ions by electrochemical reaction. In this process, in order to well control the copper precipitation on the aluminum surface to be completely converted into copper ions without affecting the copper component in the copper-aluminum alloy, an AC voltage of 1V to 10V is applied between the anode and the cathode, and the current density is controlled to be between 0.5A / dm 2 ~5A / dm 2 Due to the principle that copper is oxidized preferentially over aluminum in electrochemistry, this potential setting can effectively remove copper precipitation on the aluminum surface without damaging the aluminum metal. Moreover, the electrochemical reaction can effectively control the reaction process by controlling the AC voltage and current density. Compared with chemical methods to remove copper precipitation, its reaction controllability is good and the efficiency is higher.
[0017] Furthermore, the present invention converts copper into copper ions by means of electrochemical reaction, and the subsequent product of copper ions and precipitants can be directly formed in the electrolyte, thereby avoiding the subsequent process of cleaning the wafer to remove the precipitate and simplifying the preparation process.
[0018] The semiconductor device of the present invention is formed by adopting the above-mentioned wafer surface processing method and also has the above-mentioned technical effects. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 This is a scanning electron microscope photo of copper precipitation on the wafer surface;
[0020] Figure 2This is a scanning electron microscope photo of the pit defect caused by copper precipitation on the wafer surface after wet etching;
[0021] Figure 3 is a flowchart of the steps of a method for processing a wafer surface in an embodiment of the present invention;
[0022] Figure 4 Schematic diagram of the structure of an electrochemical device for converting copper precipitation on the wafer surface into copper precipitate in an embodiment of the present invention.
[0023] List of reference numerals:
[0024] 001 Pit defect
[0025] 100 Electrochemical working platform
[0026] 200 Electrolytic Cell
[0027] 300 Wafer
[0028] 400 Inert Metal DETAILED DESCRIPTION
[0029] The following specific embodiments illustrate the embodiments of the present invention, and those familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.
[0030] It should be noted that the diagrams provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Although the diagrams only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, the form, quantity and proportion of each component can be changed at will during actual implementation, and the layout of the components may also be more complex. The structures, proportions, sizes, etc. illustrated in the drawings of the specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions that can be implemented in this application, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in this application without affecting the effects and purposes that can be achieved by the present invention.
[0031] During the wafer manufacturing process, the metal interconnect layer is deposited with an aluminum alloy containing 0.5% copper. Due to the process deposition problem of aluminum or the subsequent etching or annealing process of forming the passivation layer, copper precipitation may occur. After copper precipitation, when the wafer is wet-etched, the aluminum in the metal wiring layer and the precipitated copper will have a discharge reaction in the wet etching solution, resulting in the generation of pit 001 defects, such as Figure 2 As shown. At present, copper precipitation is mainly detected by laboratory energy dispersive X-ray spectroscopy or atomic emission spectroscopy. The above two methods have the following disadvantages: 1) Both methods obtain the average metal content of the wafer surface by scanning, and cannot obtain the distribution map of a certain metal within the surface. Since the aluminum metal in the metal interconnect layer itself has a copper content of 0.5%, when there is a deviation in the detection, the copper content cannot be accurately detected, and it is impossible to determine whether copper precipitation exists. 2) The above method needs to be tested in an environment outside the wafer factory, the operation is cumbersome, and the detection is not time-effective. 3) Since the detection is performed by scanning the surface of the wafer, the surface scanning effect of the patterned wafer is poor. 4) The detection cost is high, and taking the wafer out of the wafer factory for detection will increase the risk of scrapping the detection piece. 5) The size of the copper precipitation is small. In contrast to the metal texture on the surface of the metal interconnect layer or the metal grains are too heavy, the copper precipitation cannot be effectively scanned or determined by the detection machine. The scanning photo of the copper precipitation on the wafer surface is as follows. Figure 1 shown.
[0032] Based on the background technology and the above-mentioned technical problems, this embodiment provides a wafer surface processing method and a semiconductor device, which can effectively detect copper precipitation and remove the copper precipitation to avoid surface defects during subsequent wet etching, thereby affecting the testing and packaging of the wafer.
[0033] The present invention is described in detail below with reference to specific embodiments.
[0034] Example 1
[0035] This embodiment provides a method for processing a wafer surface. Figure 3 , the wafer surface processing method includes:
[0036] S1: providing a wafer, on which a metal interconnection layer is formed, the metal interconnection layer comprising copper;
[0037] Specifically, a wafer is provided, on which a plurality of transistors are formed. The transistors may be CMOS devices, logic devices, etc. A metal interconnection layer is formed above the plurality of transistors and electrically connects the plurality of transistors. In the present embodiment, the metal interconnection layer is a copper-aluminum alloy layer, for example, the copper metal content in the copper-aluminum alloy layer is 0.5%. In one example, a passivation layer is also formed on the metal interconnection layer, and a portion of photoresist remains on the passivation layer. The wafer is a wafer that has not been wet-etched after the metal interconnection layer is formed and before the passivation layer is formed, or a wafer that has not been wet-etched and cleaned for the photoresist remaining on the wafer surface after the metal interconnection layer and the passivation layer are formed.
[0038] In the process of forming the copper-aluminum alloy, or in the subsequent process of forming the passivation layer covering the metal interconnection layer, the copper-aluminum alloy layer will undergo etching or annealing processes, and the above process will inevitably cause the copper in the copper-aluminum alloy layer to precipitate. However, after the wafer has undergone many processes, such as after etching the passivation layer, some photoresist will generally remain on its surface. Subsequently, the wafer needs to be cleaned with a wet etching solution. If there is copper precipitation on the surface of the wafer, there will be an internal discharge reaction between copper and aluminum in the wet etching solution, resulting in pit 001 defects on the surface of the wafer, such as Figure 2 As shown. The pit defect will affect the subsequent wafer needle test and packaging wire bonding, which is not conducive to the subsequent testing and packaging of the wafer. This embodiment uses steps S2 to S4 to effectively detect and remove whether there is copper precipitation on the wafer surface, so as to avoid the pit defect from affecting the subsequent device testing and packaging.
[0039] S2: converting the copper precipitated on the surface of the wafer into copper ions;
[0040] Specifically, if there is precipitated copper on the surface of the wafer, the copper can be converted into copper ions, and the copper ions are subsequently precipitated to determine whether there is copper precipitation on the surface of the wafer and to remove the precipitated copper. Alternatively, the copper precipitated on the surface of the wafer can be converted into copper ions by electrochemical or chemical methods. In addition, in this process, it should be ensured that no damage is caused to other structures on the wafer.
[0041] In one example of this embodiment, the copper precipitated on the surface of the wafer is converted into copper ions by electrochemical means. Figure 4, provide an electrochemical work platform 100, an electrolytic cell 200, a wafer 300 to be tested, and an inert metal 400, and inject an electrolyte into the electrolytic cell 200. In the present embodiment, the inert metal 400 may be platinum, and of course, may also be other inert metals that can participate in electrochemical reactions. The wafer 300 to be tested and the inert metal 400 are placed in the electrolytic cell 200 with an electrolyte, and the wafer 300 and the inert metal 400 are respectively connected to the electrochemical work platform 100. Subsequently, the wafer 300 is used as an anode and the inert metal 400 is used as a cathode to control the voltage in the electrochemical work platform 100 to electrochemically polish the wafer 300. In order to avoid damage to the wafer 300 or the passivation layer formed on the wafer 300 by the electrolyte during this process, the electrolyte selects a weak acid solution or a weak acid salt solution. For example, the electrolyte may be one or more of a phosphoric acid solution, a sodium hydrogen phosphate solution, and a sodium phosphate solution. In this embodiment, a phosphoric acid solution with a mass percentage of 15% is used as the electrolyte. The pH of the electrolyte is weakly acidic, and the weakly acidic electrolyte will not have any effect on the passivation layer or the oxide layer on the wafer. In order to be able to well control the copper precipitation on the aluminum surface to be converted into copper ions without affecting the copper component in the copper-aluminum alloy, this embodiment controls the application of an AC voltage of 1v to 10v between the anode and the cathode, and controls the current density to be between 0.5A / dm 2 ~5A / dm 2 Due to the principle that copper is oxidized preferentially over aluminum in electrochemistry, this potential setting can effectively remove copper precipitation on the aluminum surface without damaging the aluminum metal. For example, the current density is controlled to be 1A / dm 2 , while ensuring the electrochemical polishing effect, the process can well avoid damage to the aluminum on the wafer. Optionally, the above-mentioned electrochemical method includes but is not limited to various electrochemical methods such as anodization, electrochemical oxidation and electrochemical corrosion. Since the present embodiment converts copper into copper ions by applying voltage and controlling the current density, the reaction process is more controllable and the removal efficiency of copper precipitation is higher.
[0042] In another example of the present embodiment, the copper precipitated on the surface of the wafer is converted into copper ions by chemical means. For example, a weak acid solution can be sprayed on the surface of the wafer, and oxygen can be introduced at the same time. In this environment, the copper precipitated on the surface of the wafer is oxidized to copper ions in an acidic environment, and then the copper ions are precipitated by a precipitant that reacts with the copper ions to form a precipitate. This method uses a weak acid solution and oxygen to convert copper into copper ions. The weak acid will not damage the wafer, but its chemical reaction process is slow and the process is more uncontrollable than the electrochemical method.
[0043] S3: using a precipitant to convert copper ions into a colored copper-containing precipitate;
[0044] After the precipitated copper is converted into copper ions in step S2, in order to clearly determine whether there is precipitated copper on the surface of the wafer, a precipitant can be used to convert the copper ions into a colored copper-containing precipitate. Based on the obvious color change, it is determined that there is precipitated copper on the surface of the wafer.
[0045] Specifically, in the example of converting the precipitated copper into copper ions by electrochemical means, citric acid is added as a precipitant to the electrolyte of the reaction, and the citric acid reacts with the copper ions in the electrolyte to generate a blue copper citrate complex, and the solution slowly turns light blue, and gradually turns blue as the reaction proceeds, and the reaction is stopped when the color of the solution does not change much. Finally, the approximate amount of copper precipitation is obtained based on the amount of copper citrate precipitate obtained. Optionally, the added precipitant is citric acid with a mass percentage of 2%. In this process, since the copper citrate precipitate is directly formed in the electrolyte, the step of cleaning the wafer after removing the copper can be avoided, simplifying the preparation process.
[0046] In the example of converting the precipitated copper into copper ions by chemical means, citric acid can be sprayed on the surface of the wafer so that the citric acid and the copper ions generate a blue copper citrate precipitate. In this process, the aluminum metal and the oxide of the passivation layer will not react with the citric acid, thereby avoiding wafer damage. In this embodiment, the concentration of the citric acid solution is between 5wt% and 10wt%. In addition, in order to simplify the operating steps, the weak acid solution used in converting copper into copper ions can be selected as citric acid, so that the citric acid can be used as a precipitant at the same time to avoid the introduction of other acids that have a negative impact on the wafer. Of course, the method of converting copper into copper ions and forming a precipitate by chemical means is not limited to this. In other embodiments, a mixture of ammonia solution and hydrogen peroxide can be sprayed on the surface of the wafer to be tested. In this process, if copper is precipitated, the precipitated copper will react with the mixed solution of hydrogen peroxide and ammonia water to form a copper ammonia complex. After the wafer is dried, it can be directly detected by a defect detection machine to see if a colored precipitate is generated, in order to determine if copper has precipitated. The wafer can then be directly cleaned with ultrapure water to remove the copper ammonia complex, in order to achieve the purpose of removing copper precipitation.
[0047] After step S3, the method further includes: judging whether copper is precipitated on the surface of the wafer according to whether colored precipitates are generated.
[0048] Specifically, after the step of converting copper ions into colored copper-containing precipitates using a precipitant, it is possible to determine whether copper is precipitated on the surface of the wafer by observing whether colored precipitates are generated. For example, in the example of converting precipitated copper into copper ions using an electrochemical method, it is possible to determine whether copper is precipitated on the surface of the wafer by observing changes in the electrolyte. In the example of converting precipitated copper into copper ions using a chemical method, it is possible to determine whether copper is precipitated by scanning the defect detection machine to observe the color change on the surface of the wafer.
[0049] Therefore, this embodiment can effectively judge whether there is copper precipitation on the surface of the wafer through the color development reaction of the precipitate, which is simple to operate and low in cost. Moreover, even for patterned wafers, as long as there is a color change, it can effectively detect whether there is copper precipitation. Due to the proper method adopted, this embodiment will not damage the structure of the wafer surface. In the above two methods, the method of removing copper precipitation by electrochemical means can directly judge whether there is copper precipitation by observing the color change of the electrolyte, and then the judgment of the copper precipitation is more intuitive, without the aid of a defect detection machine, and then this method has a simpler process and lower cost.
[0050] After steps S1 to S3, the wafer surface treatment method of this embodiment also includes: if a colored precipitate is generated, the precipitate is removed. Specifically, after step S3, in the example of converting copper into copper ions by electrochemical means, if there is a colored precipitate on the surface of the wafer, the time of electrochemical polishing can be controlled to completely convert the copper precipitate on the surface of the wafer into copper ions. In this process, citric acid can be used as an indicator. When the color in the electrolyte no longer changes, the electrochemical polishing reaction is stopped, and it is confirmed that the copper precipitate on the surface of the wafer has been completely removed. Compared with the method of removing copper precipitate by chemical means, this example can be used for batch removal of copper precipitate on the wafer, and the copper precipitate removal is more complete and more efficient, and it can cause no damage to the wafer surface. The generated copper citrate can also be directly left in the electrolyte, without the need to clean the wafer, and the operation is simpler.
[0051] In the example of converting copper into copper ions by chemical means, the wafer sprayed with citric acid is dried, and the dark blue particles on the surface of the wafer can be directly detected by the defect detection machine due to the color development reaction. If there are colored precipitates on the surface of the wafer, the amount of citric acid solution sprayed and the amount of oxygen introduced can be increased until no blue precipitates are generated on the surface of the wafer, and it is determined that the copper precipitation on the surface of the wafer has been completely converted to form a copper citrate complex, and finally the copper citrate precipitate on the surface of the wafer is cleaned to remove the copper precipitation. For example, the wafer can be placed in ultrapure water for cleaning to remove the copper citrate precipitate. Therefore, this example can effectively determine whether there is copper precipitation on the surface of the wafer, but because the copper precipitation is removed by spraying a weak acid solution, the chemical reaction rate is slow, and there may be incomplete removal of copper precipitation or low removal efficiency.
[0052] Example 2
[0053] The present embodiment provides a semiconductor device, which includes a wafer, or the semiconductor device is formed by cutting a wafer. The semiconductor device includes a semiconductor substrate, at least one transistor, a metal interconnection layer and a passivation layer. Among them, at least one transistor is formed in the semiconductor substrate or above the semiconductor substrate. The metal interconnection layer is formed above the at least one transistor and electrically connects the at least one transistor. The passivation layer is formed above the metal interconnection layer and at least a portion of the metal interconnection layer is exposed. The transistor can be a CMOS device, a logic device, etc., and the metal interconnection layer is a copper-aluminum alloy layer. The wafer is obtained by processing the wafer surface processing method in Example 1.
[0054] Since the semiconductor device of this embodiment is obtained by using the wafer surface processing method in Embodiment 1, no pit defects will appear on the metal interconnection layer during the preparation process, the preparation yield is high, and the testing and packaging of the device will not be affected.
[0055] In summary, the wafer surface treatment method of the present invention is simple to operate and low in cost, and can remove copper precipitation on the wafer surface in batches, thereby improving production efficiency. The electrochemical or chemical method used to detect and remove copper precipitation also has a good detection and removal effect for patterned wafers. The color reaction of the precipitate can be used to indicate whether the copper precipitation is completely removed, and the aluminum metal layer on the wafer surface will not be damaged, thereby avoiding the influence of copper precipitation on subsequent wafer needle testing and packaging, and improving the detection yield and efficiency.
[0056] The semiconductor device in the present invention is formed by using a wafer surface processing method and also has the above-mentioned technical effects.
[0057] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.
Claims
1. A method for processing a wafer surface, characterized in that: include: Providing a wafer, on which a metal interconnection layer is formed, wherein the metal interconnection layer contains copper; Converting copper precipitated on the surface of the wafer into copper ions; A precipitant is used to convert the copper ions into a colored copper-containing precipitate.
2. The processing method according to claim 1, characterized in that: The wafer is provided without undergoing a wet etching step after forming the metal interconnection layer.
3. The processing method according to claim 1, characterized in that: The step of converting the copper precipitated on the surface of the wafer into copper ions comprises: The copper precipitated on the surface of the metal interconnection layer of the wafer is converted into copper ions by electrochemical treatment.
4. The processing method according to claim 3, characterized in that: The step of converting the copper precipitated on the surface of the wafer into copper ions by electrochemical treatment includes: placing the wafer in an electrolyte; The wafer is used as an anode and an inert metal is used as a cathode to perform electrochemical polishing on the wafer to convert copper on the surface of the wafer into copper ions.
5. The processing method according to claim 4, characterized in that: The electrolyte is a weak acid solution or a weak acid salt solution.
6. The processing method according to claim 4, characterized in that: The step of electrochemically polishing the wafer includes: Apply an AC voltage of 1V to 10V between the anode and the cathode, and control the current density to be between 0.5A / dm 2 ~5A / dm 2 between.
7. The processing method according to claim 4, characterized in that: The step of converting the copper ions into a colored copper precipitate using a precipitant comprises: Citric acid is added to the electrolyte as a precipitant, and the citric acid reacts with the copper ions to generate a blue copper citrate precipitate.
8. The processing method according to claim 1, characterized in that: The step of converting the copper precipitated on the surface of the wafer into copper ions comprises: The copper precipitated on the surface of the wafer is converted into copper ions by chemical treatment.
9. The processing method according to claim 8, characterized in that: The step of converting the copper precipitated on the surface of the wafer into copper ions by chemical treatment includes: A weak acid solution is sprayed on the surface of the wafer, and oxygen is introduced at the same time, so that the copper precipitated on the surface of the wafer is oxidized into copper ions in an acidic environment.
10. The processing method according to claim 9, characterized in that: The step of converting the copper ions into a colored precipitate using a precipitant comprises: Spraying citric acid on the surface of the wafer, the citric acid and the copper ions generate blue copper citrate precipitate.
11. The processing method according to claim 9, characterized in that: The acidic solution is a citric acid solution, and the citric acid solution is also used as the precipitant.
12. The processing method according to claim 1, characterized in that: After the step of converting the copper ions into a colored copper-containing precipitate using a precipitant, the method further comprises: Whether copper is precipitated on the surface of the wafer is determined based on whether colored precipitates are generated.
13. The processing method according to claim 1, characterized in that: After the step of converting the copper ions into a colored copper-containing precipitate using a precipitant, the method further comprises: The copper-containing precipitate is removed.
14. A semiconductor device, characterized in that: The semiconductor device is obtained by the wafer surface processing method according to any one of claims 1 to 13, and the semiconductor device comprises: Semiconductor substrate; at least one transistor formed in or above the semiconductor substrate; a metal interconnect layer formed above the at least one transistor and electrically connected to the at least one transistor; A passivation layer is formed on the metal interconnection layer and exposes at least a portion of the metal interconnection layer.