A method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film.

Abstract

The application discloses a method for detecting trace metal contaminants on a wafer surface with Si3N4 film, and belongs to the technical field of wafer quality detection. The method comprises the following steps: etching the surface of a wafer to be detected by using a mixed atomizing gas of HF and HNO3; the etching frequency is equal to or greater than the thickness of the Si3N4 film on the surface of the wafer to be detected / 150; during each etching process, the mixed atomizing gas is introduced at a speed of 1800-2200 sccm for 10-20 s; a scanning liquid for collecting metal ions is used to dissolve the metal on the wafer surface obtained through the above pretreatment, and the metal concentration in the dissolved liquid is tested. The above pretreatment method is simple in operation, short in time consumption, and can quickly and effectively remove the Si3N4 and SiO2 on the wafer surface, so that the wafer surface is not hydrophilic due to the residual Si3N4, and the scanning liquid for collecting metal ions is not adsorbed, so that the test result of the metal contaminants on the wafer surface can be obtained.

Description

Technical Field

[0001] This invention relates to the field of wafer quality inspection technology, and more specifically, to a method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film. Background Technology

[0002] VPD (Vacuum-Phase Etching) involves etching away SiO2 from the wafer surface using HF (vacuum-phase etching) gas, exposing hydrophobic Si to facilitate subsequent ion collection. However, when testing wafers with Si3N4 thin films grown on their surfaces, the HF etching rate is very slow, requiring several hours to etch a single wafer. Furthermore, this process may leave Si3N4 residue, which makes the wafer surface hydrophilic. This residue can cause the scanning solution used to collect metal ions to adhere to the wafer surface, preventing subsequent testing.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, so as to solve or improve the above-mentioned technical problems.

[0005] This invention can be implemented as follows: In a first aspect, the present invention provides a pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, comprising the following steps: etching the surface of the wafer to be tested using a mixed atomized gas of HF and HNO3 to remove Si3N4 and SiO2 from the surface of the wafer to be tested. The etching is performed n times, where n ≥ the thickness of the Si3N4 film on the surface of the wafer under test / 150; where the thickness of the Si3N4 film and 150 are both in Å; during each etching process, the introduction rate of the mixed atomized gas is 1800sccm~2200sccm, and the introduction time is 10s~20s.

[0006] In an optional embodiment, the mass ratio of HF to HNO3 in the mixed atomizing gas is 1:1 to 1:10.

[0007] In an optional implementation, during each etching process, the mixed atomized gas is introduced from the side of the vapor phase etching chamber of the detection device, and the gas in the vapor phase etching chamber is discharged from the top of the vapor phase etching chamber.

[0008] In an optional implementation, the location where the gas is discharged from the vapor phase etching chamber is coaxial with the center of the wafer under test.

[0009] In an optional embodiment, the gas in the vapor phase corrosion chamber is discharged from the top of the vapor phase corrosion chamber at a rate of 1800 sccm to 2200 sccm, and the discharge time is 10 s to 20 s.

[0010] In an optional implementation, before the first etching, an inert gas is first introduced into the vapor phase etching chamber, followed by a mixed atomized gas.

[0011] In an optional implementation, after the nth etching is completed, inert gas is continued to be introduced into the vapor phase etching chamber to remove the residual mixed atomized gas in the vapor phase etching chamber.

[0012] In an optional embodiment, the inert gas is introduced at a rate of 7800 sccm to 8200 sccm and for a duration of 15 to 25 seconds.

[0013] In an optional embodiment, the wafer obtained after etching is heated to promote the decomposition of H2SiF6; wherein the heating is performed at 40°C to 100°C for 5 min to 10 min.

[0014] Secondly, the present invention also provides a method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, comprising: dissolving the metal on the wafer surface obtained after the above pretreatment with a scanning solution for collecting metal ions to obtain a solution; and testing the metal concentration in the solution.

[0015] The beneficial effects of this invention include: This invention uses a mixed atomized gas of HF and HNO3 as the reactant gas to react with Si3N4 and SiO2 on the wafer surface. The reaction equations involved include: Si3N4 + 12HNO3 → 3SiO2 + 4N2O3 + 6H2O; SiO2 + 6HF → H2SiF6 + 2H2O. As can be seen from the above reaction equations, the reaction of HNO3 with Si3N4 accelerates the formation of SiO2, and the reaction of HF with SiO2 further promotes the continued reaction of HNO3 with Si3N4; the two processes mutually reinforce each other.

[0016] By setting the number of etching operations on the wafer surface using mixed atomized gas to n times, where n ≥ the thickness of the Si3N4 film on the wafer surface / 150; during each etching process, the flow rate of the mixed atomized gas is 1800 sccm~2200 sccm, and the flow time is 10 s~20 s; the above-mentioned number of etching operations, single etching time, and mixed atomized gas flow rate are coordinated to ensure that both Si3N4 and SiO2 on the wafer surface are fully etched at a faster speed and in a shorter time. This pretreatment of the wafer surface effectively removes Si3N4 and SiO2, preventing residual Si3N4 from becoming hydrophilic and adsorbing the scanning solution used to collect metal ions, thus hindering subsequent testing. Furthermore, this pretreatment process is simple to operate and quick.

[0017] By using a scanning solution to collect metal ions to dissolve the metal on the wafer surface obtained after the above pretreatment and testing the concentration of the dissolved metal, the test results of metal contaminants on the wafer surface can be obtained quickly and accurately. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film in this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film provided by the present invention will be described in detail below.

[0022] This invention provides a pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, comprising the following steps: etching the surface of the wafer to be tested using a mixed atomized gas of HF and HNO3 to remove Si3N4 and SiO2 from the surface of the wafer to be tested.

[0023] In the above pretreatment process, the mixed atomized gas is used as the reactant gas to react with Si3N4 and SiO2 on the wafer surface. The reaction equations involved include: Si3N4+12HNO3→3SiO2+4N2O3+6H2O; SiO2 + 6HF → H2SiF6 + 2H2O.

[0024] As can be seen from the above reaction equations, the reaction between HNO3 and Si3N4 accelerates the formation of SiO2, and the reaction between HF and SiO2 also facilitates the continued reaction between HNO3 and Si3N4, with the two promoting each other.

[0025] In existing technologies, only HF is used as the reactant gas. The reaction between HF and Si3N4 is divided into two steps, and the reaction equations involved include: Si3N4 + 6H2O → 3SiO2 + 4NH3; SiO2 + 6HF → H2SiF6 + 2H2O.

[0026] This shows that HF ​​only reacts with SiO2, and the hydrolysis reaction of Si3N4 to form SiO2 is extremely slow. Therefore, the etching rate of Si3N4 by HF is very low.

[0027] By comparison, the etching rate of Si3N4 using a mixed atomized gas of HF and HNO3 as the reactant gas can be about 7 times that of using only HF as the reactant gas.

[0028] In contrast, the method provided by this invention, which uses a mixed atomized gas of HF and HNO3 as the pretreatment gas, is simple to operate, has a short processing time, and can effectively remove Si3N4 and SiO2 from the wafer surface, thereby exposing the hydrophobic Si. This avoids the situation in conventional methods where residual Si3N4 causes the wafer surface to become hydrophilic, which in turn adsorbs the scanning liquid used to collect metal ions, making subsequent testing impossible.

[0029] In some alternative implementations, the mass ratio of HF to HNO3 in the mixed atomizing gas can be from 1:1 to 1:10, such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, or other values ​​within the range of 1:1 to 1:10.

[0030] If the mass of HNO3 in the mixed atomized gas is too small (e.g., the mass ratio of HF to HNO3 is 1:0.5), it is not conducive to the oxidation of Si3N4 by HNO3 to form SiO2; if the mass of HNO3 in the mixed atomized gas is too large (e.g., the mass ratio of HF to HNO3 is 1:12), it is not conducive to the etching of SiO2 by HF.

[0031] In this invention, the mixed atomized gas etches the wafer surface n times, where n ≥ the thickness of the Si3N4 film on the wafer surface / 150; where the thickness of the Si3N4 film and 150 are both in Å. When the thickness of the Si3N4 film on the wafer surface / 150 is an integer, n can be equal to the thickness of the Si3N4 film on the wafer surface / 150, or it can be an integer greater than the thickness of the Si3N4 film on the wafer surface / 150; when the thickness of the Si3N4 film on the wafer surface / 150 is not an integer, n is an integer greater than the thickness of the Si3N4 film on the wafer surface / 150.

[0032] By setting the number of etching cycles as described above, the Si3N4 on the wafer surface can be fully etched.

[0033] In some alternative implementations, the flow rate of the mixed atomized gas during each etching process can be 1800 sccm to 2200 sccm, such as 1800 sccm, 2000 sccm or 2200 sccm, or other values ​​within the range of 1800 sccm to 2200 sccm.

[0034] During each etching process, the time for introducing the mixed atomized gas can be 10s to 20s, such as 10s, 15s or 20s, or other values ​​within the range of 10s to 20s.

[0035] The combination of the above-mentioned mixed atomized gas velocity, single etching time and etching number can enable the Si3N4 and SiO2 on the wafer surface to be fully etched at a faster speed and in a shorter time.

[0036] In some alternative implementations, such as Figure 1 As shown, during each etching process, the mixed atomized gas is introduced from the side of the vapor phase etching chamber of the detection equipment, and the gas in the vapor phase etching chamber is discharged from the top of the vapor phase etching chamber.

[0037] Preferably, multiple mixing atomizing gas vents are opened on the side of the vapor phase corrosion chamber, and these vents are located at the same horizontal height. More preferably, the multiple vents are arranged at equal intervals. The mixing atomizing gas flow conditions corresponding to each vent are consistent, including the flow rate, start time, and end time.

[0038] In practice, HF and HNO3 can be atomized into atomized gas through an atomizer at a mass ratio of 1:1 to 1:10 and then enter the vapor phase corrosion chamber. The gas in the vapor phase corrosion chamber is discharged through the exhaust system at the top of the vapor phase corrosion chamber.

[0039] This can also be understood as each etching process being the interaction of the mixed atomized gas within the vapor phase corrosion chamber, and n etching cycles being n cycles of the mixed atomized gas. In a single etching process, the entry of the mixed atomized gas from the side into the vapor phase corrosion chamber and the subsequent discharge of the gas from the top within the chamber are considered one cycle.

[0040] In some preferred embodiments, the gas exiting the vapor chamber is coaxial with the exact center of the wafer under test. That is, the gas exiting the vapor chamber is located directly above the wafer.

[0041] In some optional embodiments, the gas in the vapor phase corrosion chamber can be discharged from the top of the vapor phase corrosion chamber at a rate of 1800 sccm to 2200 sccm, and the discharge time can be 10 s to 20 s.

[0042] It should be noted that this invention, by introducing the mixed atomized gas from the side of the vapor phase etching chamber of the testing equipment and discharging the gas from the top of the vapor phase etching chamber directly above the wafer, allows the mixed atomized gas to flow inward from the side of the vapor phase etching chamber towards the center and then upward from the top. This flow path facilitates sufficient etching of Si3N4 on both the edge and center of the wafer surface. Combined with the n etching steps provided by this invention, it further ensures a uniform and sufficient reaction between the mixed atomized gas and the Si3N4 on the wafer surface.

[0043] In some alternative embodiments, before the first etching, an inert gas is first introduced into the vapor phase etching chamber, followed by a mixed atomized gas. This is to remove other gases from the vapor phase etching chamber before the mixed atomized gas is introduced, thus maintaining an inert atmosphere within the vapor phase etching chamber.

[0044] In the above process, the inert gas introduction rate can be 7800 sccm~8200 sccm, such as 7800 sccm, 8000 sccm or 8200 sccm, or other values ​​within the range of 7800 sccm~8200 sccm, and the introduction time can be 15s~25s (such as 15s, 20s or 25s).

[0045] In some alternative implementations, after the nth etching is completed, inert gas is continued to be introduced into the vapor phase etching chamber to remove the residual mixed atomized gas in the vapor phase etching chamber.

[0046] Similarly, in the above process, the inert gas introduction rate can be 7800 sccm~8200 sccm, and the introduction time can be 15s~25s (such as 15s, 20s or 25s, etc.).

[0047] Furthermore, the etched wafer is heated to promote the decomposition of H2SiF6, a process that can be carried out, for example, in a drying chamber or drying equipment.

[0048] In some alternative embodiments, the heating temperature can be 40°C to 100°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, or other values ​​within the range of 40°C to 100°C.

[0049] The heating time can be 5 min to 10 min, such as 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, or other values ​​within the range of 5 min to 10 min.

[0050] The above heating treatment can promote the decomposition of H2SiF6; the higher the heating temperature, the faster the reaction.

[0051] Accordingly, the present invention also provides a method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, comprising: dissolving the metal on the wafer surface obtained after the above pretreatment with a scanning solution for collecting metal ions to obtain a solution; and testing the metal concentration in the solution.

[0052] By performing the above pretreatment on the wafer surface and then conducting the test, the test results of surface metal contaminants can be obtained quickly and accurately.

[0053] It should be noted that this invention does not impose excessive limitations on the process and conditions regarding how the scanning solution applies the metal solution to the wafer surface, or on the testing of the metal concentration in the solution; reference can be made to relevant prior art.

[0054] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0055] Example 1 This embodiment provides a pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, wherein the thickness of the Si3N4 thin film on the wafer surface is known to be 2000 Å.

[0056] The pretreatment method includes the following steps: using a mixed atomized gas of HF and HNO3 to etch the surface of the wafer to be tested in order to remove Si3N4 and SiO2 from the surface of the wafer to be tested.

[0057] In the above mixed atomized gas, the mass ratio of HF to HNO3 is 1:1, with HF concentration of 24.5% and HNO3 concentration of 24.5%. The number of times the mixed atomized gas etches the wafer surface is n = 2000 / 150 ≈ 13.3 (taken as 14 times).

[0058] Before the first etching, inert gas is first introduced into the vapor phase etching chamber, followed by mixed atomized gas. The inert gas is introduced at a rate of 8000 sccm for 20 seconds.

[0059] During each etching process, HF and HNO3 gases are mixed and atomized through an atomizer at the aforementioned mass ratio. This mixture is simultaneously introduced into the vapor phase etching chamber through two axially symmetrical vents on both sides. The gas inside the chamber is then exhausted from the top (directly above the wafer) via an exhaust system. The introduction velocity of the mixed atomized gas during each etching process is 2000 sccm, and the introduction time is 15 s. The gas is also exhausted from the top of the vapor phase etching chamber at a velocity of 2000 sccm over a time of 15 s.

[0060] After the final etching is completed, inert gas is continuously introduced into the vapor phase etching chamber at a rate of 8000 sccm for 20 seconds.

[0061] The etched wafer was heated at 70°C for 5 minutes in a drying chamber to promote the decomposition of H2SiF6.

[0062] Example 2 This embodiment provides a pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, wherein the thickness of the Si3N4 thin film on the wafer surface is known to be 2000 Å.

[0063] The pretreatment method includes the following steps: using a mixed atomized gas of HF and HNO3 to etch the surface of the wafer to be tested in order to remove Si3N4 and SiO2 from the surface of the wafer to be tested.

[0064] In the above mixed atomized gas, the mass ratio of HF to HNO3 is 1:5, with the concentration of HF being 8.2% and the concentration of HNO3 being 40.8%. The number of times the mixed atomized gas etches the wafer surface is n = 2000 / 150 ≈ 13.3 (taken as 14 times).

[0065] Before the first etching, inert gas (nitrogen) is introduced into the vapor phase etching chamber, followed by mixed atomized gas. The inert gas is introduced at a rate of 7800 sccm for 15 seconds.

[0066] During each etching process, HF and HNO3 gases are mixed and atomized through an atomizer at the aforementioned mass ratio. This mixture is simultaneously introduced into the vapor phase etching chamber through two axially symmetrical vents on both sides. The gas inside the chamber is then exhausted from the top (directly above the wafer) via an exhaust system. The introduction velocity of the mixed atomized gas during each etching process is 1800 sccm, and the introduction time is 20 s. The gas is also exhausted from the top of the vapor phase etching chamber at a velocity of 1800 sccm over a time of 20 s.

[0067] After the final etching is completed, inert gas (nitrogen) is continuously introduced into the vapor phase etching chamber at a rate of 7800 sccm for 25 seconds.

[0068] The etched wafer was heated at 40°C for 10 minutes in a drying chamber to promote the decomposition of H2SiF6.

[0069] Example 3 This embodiment provides a pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, wherein the thickness of the Si3N4 thin film on the wafer surface is known to be 2000 Å.

[0070] The pretreatment method includes the following steps: using a mixed atomized gas of HF and HNO3 to etch the surface of the wafer to be tested in order to remove Si3N4 and SiO2 from the surface of the wafer to be tested.

[0071] In the above mixed atomized gas, the mass ratio of HF to HNO3 is 1:10, with the concentration of HF being 4.5% and the concentration of HNO3 being 44.5%. The number of times the mixed atomized gas etches the wafer surface is n = 2000 / 150 ≈ 13.3 (taken as 14 times).

[0072] Before the first etching, inert gas is first introduced into the vapor phase etching chamber, followed by mixed atomized gas. The inert gas is introduced at a rate of 8200 sccm for 15 seconds.

[0073] During each etching process, HF and HNO3 gases are mixed and atomized through an atomizer at the aforementioned mass ratio. This mixture is simultaneously introduced into the vapor phase etching chamber through two axially symmetrical vents on both sides. The gas inside the chamber is then exhausted from the top (directly above the wafer) via an exhaust system. The introduction velocity of the mixed atomized gas during each etching process is 2200 sccm, and the introduction time is 10 s. The gas is also exhausted from the top of the vapor phase etching chamber at a velocity of 2200 sccm over a time of 10 s.

[0074] After the final etching is completed, inert gas is continuously introduced into the vapor phase etching chamber at a rate of 8200 sccm for 15 seconds.

[0075] The etched wafer was heated at 100°C for 5 minutes in a drying chamber to promote the decomposition of H2SiF6.

[0076] Comparative Example 1 The difference between this comparative example and Example 1 is that the reaction gas is only HF gas.

[0077] Comparative Example 2 The difference between this comparative example and Example 1 is that the reaction gas is only HNO3 gas.

[0078] Comparative Example 3 The difference between this comparative example and Example 1 is that the mass ratio of HF to HNO3 in the mixed atomized gas is 1:0.5.

[0079] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass ratio of HF to HNO3 in the mixed atomized gas is 1:12.

[0080] Comparative Example 5 The difference between this comparative example and Example 1 is that the number of cycles is 10.

[0081] Comparative Example 6 The difference between this comparative example and Example 1 is that both the mixed atomizing gas and the inert gas are introduced through one vent on the side of the vapor phase corrosion chamber, and the gas inside the vapor phase corrosion chamber is discharged through the other vent.

[0082] Test case The wafers obtained from Examples 1-3 and Comparative Examples 1-6 were subjected to Si3N4 thickness testing, and the results are shown in Table 1.

[0083] The thickness of Si3N4 was measured using XRF (X-Ray Fluorescence).

[0084] Table 1. Si3N4 Thickness

[0085] As can be seen from Table 1, the pretreatment method provided by the present invention can effectively remove Si3N4 and SiO2 from the wafer surface, avoiding the possibility that the residual Si3N4 will cause the wafer surface to become hydrophilic and thus adsorb the scanning liquid used to collect metal ions, making subsequent tests impossible.

[0086] In summary, the pretreatment method provided by this invention is simple to operate, time-saving, and can effectively remove Si3N4 and SiO2 from the wafer surface. This avoids the possibility that residual Si3N4 would cause the wafer surface to become hydrophilic, thus adsorbing the scanning solution used to collect metal ions and preventing subsequent testing. Testing the wafer after the above pretreatment can quickly and accurately obtain test results for metal contaminants on the wafer surface.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pretreatment method for detecting trace metal contaminants on the surface of a wafer with a Si3N4 thin film, characterized in that, Includes the following steps: The surface of the wafer to be tested was etched several times using a mixed atomized gas of HF and HNO3 to remove Si3N4 and SiO2 from the surface of the wafer to be tested. The etching is performed n times, where n ≥ the thickness of the Si3N4 thin film on the surface of the wafer under test / 150; where the thickness of the Si3N4 thin film and 150 are both in Å. During each etching process, the flow rate of the mixed atomized gas is 1800 sccm to 2200 sccm, and the flow time is 10 s to 20 s.

2. The pretreatment method according to claim 1, characterized in that, In the mixed atomized gas, the mass ratio of HF to HNO3 is 1:1 to 1:

10.

3. The pretreatment method according to claim 1 or 2, characterized in that, During each etching process, the mixed atomized gas is introduced from the side of the vapor phase etching chamber of the detection device, and the gas in the vapor phase etching chamber is discharged from the top of the vapor phase etching chamber.

4. The pretreatment method according to claim 3, characterized in that, The gas exiting from the vapor phase etching chamber is coaxial with the center of the wafer under test.

5. The pretreatment method according to claim 3, characterized in that, The gas in the vapor phase corrosion chamber exits from the top of the vapor phase corrosion chamber at a speed of 1800 sccm to 2200 sccm, and the exit time is 10 s to 20 s.

6. The pretreatment method according to claim 3, characterized in that, Before the first etching, an inert gas is first introduced into the vapor phase etching chamber, followed by the mixed atomized gas.

7. The pretreatment method according to claim 3, characterized in that, After the nth etching is completed, inert gas is continuously introduced into the vapor phase etching chamber to remove the residual mixed atomized gas in the vapor phase etching chamber.

8. The pretreatment method according to claim 6 or 7, characterized in that, The inert gas is introduced at a rate of 7800 sccm to 8200 sccm and for a duration of 15 to 25 seconds.

9. The pretreatment method according to claim 1, characterized in that, The etched wafer is heated to promote the decomposition of H2SiF6; the heating is carried out at 40℃~100℃ for 5min~10min.

10. A method for detecting trace metallic contaminants on the surface of a wafer with a Si3N4 thin film, characterized in that, Includes the following steps: The scanning solution used to collect metal ions is used to dissolve the metal on the wafer surface obtained by the pretreatment according to any one of claims 1 to 9 to obtain a solution. The metal concentration in the solution was tested.

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