A process for removing oxide from a wafer

Abstract

The application provides a wafer oxide removal process, and relates to the technical field of semiconductors.The wafer oxide removal process comprises the following steps: a removal step: etching and removing the oxide layer on the wafer surface by using an HF solution, wherein the volume ratio of HF to H2O in the HF solution is 1:50-1:100; and a treatment step: cleaning the wafer by using an SC1 solution, wherein the volume ratio of NH4OH to H2O2 to H2O in the SC1 solution is 1:1:5-1:2:45, and the temperature is 20-35 DEG C.In the process, the oxide layer is sequentially treated by the removal step and the treatment step, the concentration range of HF in the HF solution in the removal step is set to be relatively low, the treatment temperature range in the treatment step is set to be relatively low, and the concentration of H2O2 in the SC1 solution is greater than or equal to the concentration of NH4OH, so that the removal effect of the oxide layer is effectively improved, the quality of the wafer Si is ensured, the yield of subsequent processes is ensured, and the performance and reliability of the formed device are ensured.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more particularly to a process method for removing wafer oxides. Background Technology

[0002] Semiconductor cleaning machines are key equipment in the wafer manufacturing process, used to remove impurities such as particles, metal contaminants, organic matter, and natural oxide layers from the wafer surface to ensure the yield and reliability of subsequent processes. Among these, the removal of the oxide layer on the wafer surface is of paramount importance. In current mainstream semiconductor processes, the etching and cleaning of oxide layers (such as SiO2 or high-k dielectric layers) need to achieve high uniformity and selectivity at the nanoscale to avoid problems such as current leakage and threshold voltage drift.

[0003] In related technologies, a single chemical reagent (such as hydrofluoric acid) is usually used to etch and remove the oxide layer as a whole. However, this removal method introduces etching residue pollution and wafer damage, which leads to a decrease in the yield of subsequent processes. Although some processes use multiple chemical reagents to process the oxide layer in sequence, the coordination effect between the multiple processing steps is poor, so the removal effect of the oxide layer still needs to be improved. Summary of the Invention

[0004] The purpose of this invention is to provide a process for removing wafer oxides, thereby solving the technical problem of poor oxide layer removal effect in related technologies.

[0005] To address the above problems, the present invention provides a process for removing wafer oxides, comprising: Removal step: The oxide layer on the wafer surface is removed by etching with HF solution, wherein the volume ratio of HF to H2O in the HF solution is 1:50~1:100; Processing step: The wafer is cleaned with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:5~1:2:45, and the temperature is 20~35℃.

[0006] Optionally, in the removal step, the volume ratio of HF to H2O in the HF solution is 1:70 to 1:100, the mass percentage concentration of HF is 0.5% to 2%, and the temperature is 20 to 25°C.

[0007] Optionally, in the removal step, the volume ratio of HF to H2O in the HF solution is 1:75 to 1:95, the mass percentage concentration of HF is 0.5% to 1.5%, and the temperature is 20 to 22°C.

[0008] Optionally, in the removal step: When the thickness of the oxide layer is less than 5 nm, the volume ratio of HF to H2O in the HF solution is 1:95~1:100, and the etching time is 10~20 s; And / or, when the thickness of the oxide layer is greater than or equal to 5 nm and less than or equal to 50 nm, the volume ratio of HF to H2O in the HF solution is 1:60~1:95, and the etching time is 20~40 s; And / or, when the thickness of the oxide layer is greater than 50 nm, the volume ratio of HF to H2O in the HF solution is 1:50~1:60, and the etching time is 30~60 s.

[0009] Optionally, in the processing step, the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:10 to 1:2:40, and the temperature is 23 to 35°C.

[0010] Optionally, in the processing step, the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:2:20 to 1:2:30, and the temperature is 25 to 30°C.

[0011] Optionally, the removal step includes: Obtain the temperature and HF concentration of the HF solution; The heating power of the heating assembly on the HF solution is adjusted according to the temperature to ensure that the temperature difference between the HF solution and the target temperature is less than or equal to 0.5°C; and, Adjust the replenishment amounts of HF and DI according to the HF concentration to ensure that the deviation of the HF concentration from the target concentration is less than ±0.1%.

[0012] Optionally, the processing step includes: Obtain the temperature and pH value of the SC1 solution; The heating power of the heating assembly on the SC1 solution is adjusted according to the temperature to ensure that the temperature difference between the SC1 solution and the target temperature is less than or equal to 0.3°C; and, Adjust the replenishment amounts of NH4OH, H2O2, and H2O according to the pH value to ensure that the deviation between the volume ratio of NH4OH, H2O2, and H2O and the target volume ratio is less than ±0.3%.

[0013] Optionally, the process may include a pretreatment step before the removal step: cleaning the wafer with ozone water, wherein the volume concentration of O3 in the ozone water is 1~50 ppm and the temperature is 20~25℃.

[0014] Optionally, a first cleaning step is further included between the removal step and the processing step: cleaning the wafer with DICO2, wherein the CO2 concentration is 0.2~0.5 vol% And / or, the processing step is followed by a second cleaning step: cleaning the wafer with DICO2, wherein the CO2 concentration is 0.2~0.5 vol.

[0015] The process method provided by this invention employs a sequential combination of a removal step and a processing step to treat the oxide layer. By setting a low concentration range of HF in the HF solution during the removal step, the etching damage to the wafer is reduced while simultaneously removing the oxide layer. Furthermore, by setting a low processing temperature range in the processing step, and ensuring that the concentration of H2O2 in SC1 is greater than or equal to the concentration of NH4OH, the oxidation reaction of the wafer Si by H2O2 in the processing step becomes dominant. This improves the smoothing effect of the processing step on the wafer surface and enhances the repair and protection effect of the passivation layer. While achieving the dissolution and removal of fluorides by NH4OH, the etching damage to the exposed wafer surface by NH4OH is effectively reduced. The combined removal and processing steps ensure effective removal of the oxide layer and guarantee the smoothness, uniformity, contamination resistance, and oxidation resistance of the resulting wafer. This effectively improves the oxide layer removal effect, ensures the quality of the wafer Si, the yield of subsequent processes, and the performance and reliability of the formed devices. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of the present invention, the drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the first process of the method for removing wafer oxides provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the second process of the method for removing wafer oxides provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] Among the related technologies for cleaning wafers to remove their surface oxide layers, the removal effect of the oxide layer is poor, resulting in residual etching contamination on the wafer and severe etching damage, leading to low wafer quality and affecting the yield of subsequent wafer processes.

[0022] This invention provides a process for removing oxides from wafers. By combining removal and processing steps to remove the oxide layer, the effective removal of the oxide layer can be ensured, and the smoothness, uniformity, anti-contamination, and anti-oxidation properties of the wafer obtained after processing can be guaranteed. This effectively improves the removal effect of the oxide layer, ensures the quality of the wafer Si, the yield of subsequent processes, and the performance and reliability of the formed devices.

[0023] Figure 1 This is a schematic diagram of the first process flow of a method for removing wafer oxides according to an embodiment of the present invention. Figure 1 As shown, the process includes the following steps: S102 Removal Step: The oxide layer on the wafer surface is removed by etching with an HF solution, wherein the volume ratio of HF to H2O in the HF solution is 1:50~1:100.

[0024] A wafer with an oxide layer on its surface is immersed in an HF solution. HF reacts with the oxide layer to etch and remove it, while simultaneously generating fluorides. Taking SiO2 as an example, the reaction formula between HF and SiO2 is as follows: while etching away SiO2, residual H2SiF6 is generated. SiO2+6HF→H2SiF6+2H2O(1); In this HF solution, the volume ratio of HF to H2O is 1:50 to 1:100. HF has a low concentration range, within which the Gibbs free energy (ΔG) of the reaction between the oxide layer and HF is lower. While ensuring that the HF solution has a certain etching rate on the oxide layer, it can improve the etching selectivity of the HF solution for the oxide layer and the wafer Si. This allows the HF solution to quickly etch away the oxide layer while minimizing etching damage to the wafer Si, thereby achieving the etching removal of the oxide layer and ensuring the quality of the wafer Si.

[0025] Specifically, when the volume ratio of HF to H2O in the HF solution is 1:50 to 1:100, the etching rate ratio of the HF solution to the oxide layer and the wafer Si can be increased to 2000:1.

[0026] In this process, a high concentration of hydrofluoric acid can be diluted to obtain an HF solution with the target volume ratio, and the etching time can be 10~60s.

[0027] S104 processing step: The wafer is cleaned with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:5~1:2:45, and the temperature is 20~35℃.

[0028] After etching away the oxide layer on the wafer surface with HF solution, the wafer is removed from the HF solution and immersed in SC1 solution for 10-30 seconds. SC1 solution is a mixture of NH4OH, H2O2, and H2O. H2O2 can slightly oxidize the surface of the Si wafer, especially the rough edges, to form a thin and uniform SiO2 oxide layer. NH4OH can react with the oxide layer to gently remove it, and can also react with residual fluorides such as H2SiF6 and SiF4 from the removal step to remove them. Taking SiO2 as an example, the relevant reaction formulas are as follows: Si+2H2O2→SiO2+2H2O(2); SiO2+2NH4OH→Si(OH)4+2NH3↑(3); Si-F+2NH4OH→Si-OH+NH4F+H2O(4); H2SiF6+6NH4OH→6NH4F+SiO2+4H2O (5).

[0029] Based on the relevant reaction between the SC1 solution and the wafer, the processing step has at least the following three effects: Firstly, the processing step can perform edge smoothing and surface roughness modification on the wafer. The specific process is as follows: Based on reaction formula (3), NH4OH can react with the residual SiO2 oxide layer after the removal step to dissolve and remove it, thereby repairing the micro-roughness of the wafer surface after HF etching to a certain extent; Based on the combination of reaction formulas (2) and (3), H2O2 can oxidize the protrusions and sharp corners formed by the wafer Si after HF etching to form a thin SiO2 oxide layer. Then, NH4OH complexes with the thin SiO2 oxide layer and dissolves and removes it. In this way, the "oxidation-dissolution" cycle is repeated to gradually remove the protrusions and sharp corners; In this way, the wafer surface, especially its rough edges, tends to be smoothed, thereby reducing the edge angle of the oxide layer, improving the smoothness of the wafer surface, and improving the withstand voltage and reliability of subsequent devices.

[0030] Secondly, based on reaction formulas (4) and (5), the processing step can remove the residual fluoride from the removal step, thereby reducing the contamination and damage of the fluoride to the wafer Si.

[0031] Thirdly, after the above smoothing and cleaning processes, based on reaction formula (2), H2O2 can oxidize the exposed wafer Si surface to form a uniform and dense SiO2 thin oxide layer. On the one hand, the thin oxide layer can repair the damage defects caused by HF to the wafer Si in the removal step, thereby repairing the micro-roughness of the wafer surface. On the other hand, the thin oxide layer can serve as a passivation layer for the wafer Si to protect it, thereby reducing the re-oxidation or contamination of the wafer Si in subsequent processes.

[0032] In this embodiment of the invention, the processing temperature is set to a relatively low range of 20~35℃, so that the reaction ratio of H2O2 in the processing step is >80%. At the same time, the concentration of H2O2 in SC1 is set to be greater than or equal to the concentration of NH4OH. The combination of processing temperature and the concentration of each component ensures that the oxidation reaction of H2O2 on the wafer Si in the processing step dominates, thereby improving the smoothing effect of the processing step on the wafer surface and the repair and protection effect of the passivation layer on the wafer surface. While achieving the dissolution and protrusion of NH4OH and the removal of fluorides, the etching damage of NH4OH on the exposed surface of the wafer is effectively reduced, thereby effectively improving the removal effect of the oxide layer, ensuring the quality of the wafer Si, the yield of subsequent processes, and the performance and reliability of the formed device.

[0033] In summary, the process method provided in this embodiment of the invention employs a sequential combination of a removal step and a processing step to treat the oxide layer. By setting a low concentration range of HF in the HF solution during the removal step, the etching damage to the wafer is reduced while simultaneously removing the oxide layer. Furthermore, by setting a low processing temperature range in the processing step, and ensuring that the concentration of H2O2 in SC1 is greater than or equal to the concentration of NH4OH, the oxidation reaction of the wafer Si by H2O2 in the processing step becomes dominant, improving the smoothing effect of the processing step on the wafer surface and enhancing the repair and protection effect of the passivation layer on the wafer surface. This effectively reduces the etching damage to the exposed wafer surface caused by NH4OH while achieving the dissolution and removal of fluorides by NH4OH. The combined removal and processing steps ensure effective removal of the oxide layer and guarantee the smoothness, uniformity, contamination resistance, and oxidation resistance of the resulting wafer. This effectively improves the oxide layer removal effect, ensures the quality of the wafer Si, the yield of subsequent processes, and the performance and reliability of the formed devices.

[0034] In this embodiment of the invention, in the removal step S102, the volume ratio of HF to H2O in the HF solution is 1:70 to 1:100, specifically 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100; preferably, the volume ratio of HF to H2O is 1:75 to 1:95, specifically 1:75, 1:78, 1:81, 1:84, 1:87, 1:90, 1:93, or 1:95; more preferably, the volume ratio of HF to H2O is 1:80 to 1:90, specifically 1:80, 1:82, 1:84, 1:86, 1:88, or 1:90. By limiting the concentration range of HF in the HF solution to a low level, while ensuring that the HF solution has a certain etching rate on the oxide layer, the etching selectivity of the HF solution for the oxide layer and the wafer Si can be improved, thereby ensuring the etching removal of the oxide layer and reducing the etching damage to the wafer Si.

[0035] In this embodiment of the invention, in the removal step S102, the mass percentage concentration of HF is 0.5%~2.0%, specifically 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, 0.7%, 0.5%, and 0.7%; preferably, the mass percentage concentration of HF is 0.5%~1.5%; more preferably, the mass percentage concentration of HF is 0.7%~1.3%, specifically 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, and 1.3%; and even more preferably, the mass percentage concentration of HF is 0.8%~1.2%.

[0036] In this embodiment of the invention, in the removal step of step S102, the temperature is 20~25℃, specifically 20℃, 21℃, 23℃, 24℃, or 25℃; preferably, the temperature is 20~22℃; more preferably, the temperature is 20℃. When the HF solution is in this lower temperature range, combined with the lower concentration range of HF, the etching rate of the HF solution on the wafer Si can be limited, thereby improving the etching selectivity of the HF solution for the oxide layer and the wafer Si in the removal step.

[0037] In this embodiment of the invention, specifically for the removal of ultrathin oxide layers with a thickness < 5 nm, oxide layers with a thickness greater than or equal to 5 nm and less than or equal to 50 nm, and thick oxide layers with a thickness > 50 nm, the following process parameters are used in step S102: Specifically, when the oxide layer is an ultrathin oxide layer with a thickness of <5nm, the volume ratio of HF to H2O in the HF solution during the removal step is 1:95~1:100; preferably, the volume ratio of HF to H2O is 1:96~1:99; more preferably, the volume ratio of HF to H2O is 1:97~1:98. The etching time is 10~20s. Setting the concentration of HF in the HF solution to be relatively low improves the etching selectivity of HF for the ultrathin oxide layer and the wafer Si, allowing the etching of the ultrathin oxide layer to be completed in a shorter time and reducing etching damage to the wafer Si.

[0038] When the thickness of the oxide layer is greater than or equal to 5 nm and less than or equal to 50 nm, the volume ratio of HF to H2O in the HF solution is 1:60 to 1:95; preferably, the volume ratio of HF to H2O is 1:70 to 1:90; more preferably, the volume ratio of HF to H2O is 1:75 to 1:85. The etching time is 20 to 40 s.

[0039] When the oxide layer is a thick oxide layer with a thickness > 50 nm, the volume ratio of HF to H2O in the HF solution of the removal step is 1:50~1:60, and the etching time is 30~60 s. By setting the concentration of HF in the HF solution to be slightly higher, while ensuring that HF ​​has a high etching selectivity for the thick oxide layer and the wafer Si, and reducing the etching damage to the wafer Si, the etching rate and removal efficiency of HF for the thick oxide layer are improved, thereby improving the process efficiency.

[0040] In this embodiment of the invention, the removal step S102 can also be further improved by the following operations to ensure the volume ratio, concentration, and temperature of HF and H2O in the HF solution, specifically including the following operation steps: Obtain the temperature and concentration of the HF solution; adjust the heating power of the heating element to the HF solution according to the temperature so that the temperature difference between the HF solution and the target temperature is less than or equal to 0.5℃; adjust the replenishment amount of HF and DI according to the HF concentration so that the deviation of the HF concentration from the target concentration is less than ±0.1%.

[0041] Specifically, an isothermal bath can be used to contain the HF solution. A target temperature for the HF solution is set. During the process, a temperature sensor can be used to monitor the current temperature of the HF solution in real time, and the heating power of the heating components in the isothermal bath can be adjusted according to the measured current temperature to keep the current temperature of the HF solution within ±0.5℃ of the target temperature. By controlling the temperature stability, the etching rate variation caused by temperature fluctuations can be reduced. Simultaneously, an online conductivity meter with a sensitivity of ±0.05 wt% can be used to monitor the current concentration of HF in the HF solution in real time, and HF and DI can be dynamically supplemented according to the measured current concentration to maintain the deviation of the HF concentration from the target concentration within ±0.1%. By limiting the HF concentration, the selective etching stability of the HF solution on the oxide layer and wafer Si is ensured.

[0042] In this embodiment of the invention, in the processing step S104, the volume ratio of NH4OH, H2O2, and H2O in the SC1 solution is 1:1:10 to 1:2:40, and the temperature is 23 to 35°C; wherein, the specific volume ratio of NH4OH, H2O2, and H2O can be 1:1:10, 1:1:20, 1:1:30, 1:1:40, 1:2:10, 1:2:20, 1:2:30, or 1:2:40, and the specific temperature can be 23°C, 25°C, 27°C, 29°C, 31°C, 33°C, or 35°C. Preferably, the volume ratio of NH4OH, H2O2, and H2O is 1:2:20 to 1:2:30, and the temperature is 25 to 30°C; specifically, the volume ratio of NH4OH, H2O2, and H2O can be 1:2:20, 1:2:22, 1:2:24, 1:2:26, ​​1:2:28, or 1:2:30, and the temperature can be 25°C, 26°C, 27°C, 28°C, 29°C, or 30°C. More preferably, the volume ratio of NH4OH, H2O2, and H2O is 1:2:25 to 1:2:30, and the temperature is 25 to 28°C.

[0043] In this embodiment of the invention, in step S104, the volume ratio, concentration, and temperature of NH4OH, H2O2, and H2O in the SC1 solution can be ensured through the following operations: Obtain the temperature and pH value of the SC1 solution; adjust the heating power of the heating component to the SC1 solution according to the temperature so that the temperature difference between the SC1 solution and the target temperature is less than or equal to 0.3℃; adjust the replenishment amount of NH4OH, H2O2 and H2O according to the pH value so that the deviation of the volume ratio of NH4OH, H2O2 and H2O from the target volume ratio is less than ±0.3%.

[0044] Specifically, an SC1 solution can be placed in a constant temperature bath and multi-zone heating can be used to eliminate the temperature difference between the wafer edge and center. The target temperature of the SC1 solution can be set, and the current temperature of the SC1 solution can be detected in real time by a temperature sensor. The heating power of each heating component in the constant temperature bath can be adjusted according to the measured current temperature to keep the current temperature of the SC1 solution within the range of ±0.3℃ of the target temperature. By limiting the processing temperature, the processing stability of the SC1 solution on the wafer can be improved, and the repair and protection effect of H2O2 on the wafer can be ensured. Simultaneously, the current pH value of the SC1 solution can be detected in real time using a pH sensor with an accuracy of ±0.1. Based on the measured current pH value, the concentration and volume ratio of each component in the SC1 solution can be calculated, and NH4OH, H2O2, and H2O can be dynamically replenished accordingly to maintain the deviation between the volume ratio of NH4OH, H2O2, and H2O in SC1 and the target volume ratio within ±0.3%. By limiting the volume ratio and concentration of NH4OH, H2O2, and H2O in the SC1 solution, it is ensured that the SC1 solution performs edge smoothing and surface roughness modification on the wafer, removes residual fluoride from the removal step, repairs wafer Si damage defects, and protects the passivation layer of the wafer Si.

[0045] In both the removal and processing steps, the etch rate fluctuation of the oxide layer is controlled within ±5%.

[0046] In this embodiment of the invention, a pretreatment step is included before the removal step: cleaning the wafer with ozone water, wherein the volume concentration of O3 in the ozone water is 1~50 ppm, preferably 20~50 ppm, more preferably 30~40 ppm; the temperature is 20~25℃, preferably 22~25℃, more preferably 25℃. Before removing the oxide layer from the wafer, a pretreatment step is first performed to remove organic matter from the wafer surface, clean the surface, improve the wafer cleanliness, and enhance the effectiveness of the subsequent removal step in removing the oxide layer; at the same time, the pretreatment step can also oxidize the exposed wafer Si to form a dense and uniform oxide layer, improve the overall uniformity of the oxide layer on the wafer surface, protect the exposed areas of the wafer, and reduce the etching damage caused to the exposed areas of the wafer by the subsequent removal step; specifically as follows: When wafers are immersed in ozone water, the strong oxidizing properties of O3 can react with organic contaminants on the wafer surface, such as photoresist residue and grease, to dissolve and remove them. The reaction formula is as follows: C x H y +O3→CO2↑+ H2O + R•(6).

[0047] Meanwhile, O3 can decompose in water into •OH free radicals and atomic oxygen [O]. Both can come into contact with the exposed surface of the silicon wafer to undergo an oxidation reaction to form an oxide layer, as shown in the following reaction formula: Si + 2[O] → SiO2 (7); Si + 4•OH → SiO2+ 2H2O (8).

[0048] Specifically, ozone water can be produced by introducing O3 gas into deionized water using an ozone generator.

[0049] In this embodiment of the invention, a first cleaning step is included between the removal step and the processing step: the wafer is cleaned with CO2, wherein the concentration of CO2 is 0.2~0.5 vol%, preferably 0.3~0.5 vol%, and more preferably 0.4 vol%. After the removal step is completed, residual HF is rinsed with deionized water mixed with CO2 and residual fluoride is dissolved to reduce secondary contamination of the wafer by both.

[0050] In this process, adding CO2 to deionized water forms weakly acidic H2CO3. H2CO3 can react with residual fluoride to enhance the rinsing effect of the first cleaning step on the residues on the wafer. NH4F is used as an example of a residue. The reaction formula is as follows: NH4F + H2CO3 → NH4+ + F +HCO3 (9).

[0051] In this embodiment of the invention, a second cleaning step is included after the processing step: cleaning the wafer with CO2, wherein the concentration of CO2 is 0.2~0.5 vol%, preferably 0.3~0.5 vol%, more preferably 0.4 vol%. After the processing step, all residual chemicals on the wafer are rinsed with deionized water mixed with CO2 to reduce the contamination of residual chemicals on wafer quality and ensure wafer quality; the rinsing time can be 30~60 seconds.

[0052] After the second cleaning step is completed, the wafer can be removed, and nitrogen gas can be blown onto the rotating wafer surface to effectively dry it and avoid water marks remaining on the wafer surface. The nitrogen purging flow rate can be 100-200 L / min, preferably 120-180 L / min, and more preferably 140-160 L / min. The wafer rotation speed can be 1000-2000 rpm, preferably 1200-1800 rpm, and more preferably 1400-1600 rpm.

[0053] Figure 2 This is a schematic diagram of the first process flow of a method for removing wafer oxides according to an embodiment of the present invention. Figure 2 As shown, the process includes the following steps: S202 Pretreatment Step: The wafer is cleaned with ozone water, wherein the volume concentration of O3 in the ozone water is 1~50 ppm and the temperature is 20~25℃.

[0054] S204 Removal Step: The oxide layer on the wafer surface is removed by etching with an HF solution. The volume ratio of HF to H2O in the HF solution is 1:50 to 1:100, the mass percentage concentration of HF is 0.5% to 2%, and the temperature is 20 to 25°C.

[0055] S206 First cleaning step: The wafer is cleaned using DICO2, where the CO2 concentration is 0.2~0.5 vol.

[0056] S208 processing step: The wafer is cleaned with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:5~1:2:45, and the temperature is 20~35℃.

[0057] S210 Second Cleaning Step: The wafer is cleaned using DICO2, where the CO2 concentration is 0.2~0.5 vol.

[0058] S212 Drying Step: Nitrogen gas is blown onto the rotating wafer surface to effectively dry it.

[0059] The present invention will be further described in detail below with reference to the embodiments.

[0060] Example 1 Removal of a thin oxide layer with a thickness of 3 nm: Step 1, Pretreatment: Use ozone water to clean and remove organic matter from the wafer surface. The volume concentration of O3 in the ozone water is 30 ppm, and the temperature is 20℃.

[0061] Step 2, Removal step: A single-wafer cleaning machine and HF solution are used to etch and remove the 3nm thick oxide layer on the Si surface of the wafer. The volume ratio of HF to H2O in the HF solution is 1:100, the mass percentage concentration of HF is 0.5%, the temperature is 20℃, and the etching time is 15s.

[0062] Step 3, the first cleaning step: DICO2 is used to clean the residual HF on the wafer and dissolve H2SiF6 to reduce secondary contamination.

[0063] Step 4, Processing step: Immediately clean the wafer with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:10, the temperature is 25℃, and the processing time is 20s.

[0064] Step 5, perform the second cleaning step: rinse the wafer with DICO2, where the CO2 concentration is 0.2 vol%, and the rinsing time is 30 seconds, to remove all residual chemicals.

[0065] Step 6, Drying step: Nitrogen gas is blown onto the rotating wafer surface to effectively dry it, wherein the nitrogen purging flow rate is 100 L / min and the wafer rotation speed is 1200 rpm.

[0066] Example 2 Removal of a 100nm thick oxide layer in an STI isolation trench structure: Step 1, Pretreatment: Use ozone water to clean and remove organic matter from the wafer surface. The volume concentration of O3 in the ozone water is 30 ppm, and the temperature is 20℃.

[0067] Step 2, Removal step: Using a single-wafer cleaning machine and HF solution, the 100nm thick oxide layer on the surface of the STI isolation tank structure is etched and removed. The volume ratio of HF to H2O in the HF solution is 1:50, the mass percentage concentration of HF is 2%, the temperature is 25℃, and the etching time is 50s.

[0068] Step 3, the first cleaning step: DICO2 is used to clean the residual HF on the wafer and dissolve H2SiF6 to reduce secondary contamination.

[0069] Step 4, Processing step: Immediately clean the wafer with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:2:30, the temperature is 35℃, and the processing time is 30s.

[0070] Step 5, perform the second cleaning step: rinse the wafer with DICO2, where the CO2 concentration is 0.2 vol%, and the rinsing time is 50 seconds, to remove all residual chemicals.

[0071] Step 6, Drying step: Nitrogen gas is blown onto the rotating wafer surface to effectively dry it, wherein the nitrogen purging flow rate is 120 L / min and the wafer rotation speed is 1500 rpm.

[0072] Example 3 For the removal of oxide layer on the surface of trenches with a depth-to-width ratio of 5:1: Step 1, Pretreatment: Use ozone water to clean and remove organic matter from the wafer surface. The volume concentration of O3 in the ozone water is 30 ppm, and the temperature is 20℃.

[0073] Step 2, Removal step: Use a single-wafer cleaning machine and HF solution to etch and remove the oxide layer on the surface of the trench. The volume ratio of HF to H2O in the HF solution is 1:80, the mass percentage concentration of HF is 1%, the temperature is 22℃, and the etching time is 40s.

[0074] Step 3, the first cleaning step: DICO2 is used to clean the residual HF on the wafer and dissolve H2SiF6 to reduce secondary contamination.

[0075] Step 4, Processing step: Immediately clean the wafer with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:5, the temperature is 25℃, and the processing time is 25s.

[0076] Step 5, perform the second cleaning step: use DICO2 to rinse the residual chemicals on the wafer, wherein the concentration of CO2 is 0.2 vol%, and the rinsing time is 40 seconds, to remove all residual chemicals.

[0077] Step 6, Drying step: Nitrogen gas is blown onto the rotating wafer surface to effectively dry it, wherein the nitrogen purging flow rate is 160 L / min and the wafer rotation speed is 1600 rpm.

[0078] Through the process described in Examples 1-3 above, the oxide layer can be effectively removed, and a wafer with a high morphological accuracy and an ultra-thin passivation layer can be obtained, which can ensure the yield of subsequent processes and the performance and reliability of the fabricated device.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for removing wafer oxides, characterized in that, include: Removal step: The oxide layer on the wafer surface is removed by etching with HF solution, wherein the volume ratio of HF to H2O in the HF solution is 1:50~1:100; Processing step: The wafer is cleaned with SC1 solution, wherein the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:5~1:2:45, and the temperature is 20~35℃.

2. The process method according to claim 1, characterized in that, In the removal step, the volume ratio of HF to H2O in the HF solution is 1:70 to 1:100, the mass percentage concentration of HF is 0.5% to 2%, and the temperature is 20 to 25°C.

3. The process method according to claim 2, characterized in that, In the removal step, the volume ratio of HF to H2O in the HF solution is 1:75 to 1:95, the mass percentage concentration of HF is 0.5% to 1.5%, and the temperature is 20 to 22°C.

4. The process method according to claim 1, characterized in that, In the removal step: When the thickness of the oxide layer is less than 5 nm, the volume ratio of HF to H2O in the HF solution is 1:95~1:100, and the etching time is 10~20 s; And / or, when the thickness of the oxide layer is greater than or equal to 5 nm and less than or equal to 50 nm, the volume ratio of HF to H2O in the HF solution is 1:60~1:95, and the etching time is 20~40 s; And / or, when the thickness of the oxide layer is greater than 50 nm, the volume ratio of HF to H2O in the HF solution is 1:50~1:60, and the etching time is 30~60 s.

5. The process method according to any one of claims 1-4, characterized in that, In the processing step, the volume ratio of NH4OH, H2O2 and H2O in the SC1 solution is 1:1:10 to 1:2:40, and the temperature is 23 to 35°C.

6. The process method according to claim 5, characterized in that, In the aforementioned processing step, the volume ratio of NH4OH, H2O2, and H2O in the SC1 solution is 1:2:20 to 1:2:30, and the temperature is 25 to 30°C.

7. The process method according to any one of claims 1-4, characterized in that, The removal step includes: Obtain the temperature and HF concentration of the HF solution; The heating power of the heating assembly on the HF solution is adjusted according to the temperature to ensure that the temperature difference between the HF solution and the target temperature is less than or equal to 0.5°C; and, Adjust the replenishment amounts of HF and DI according to the HF concentration to ensure that the deviation of the HF concentration from the target concentration is less than ±0.1%.

8. The process method according to any one of claims 1-4, characterized in that, The processing step includes: Obtain the temperature and pH value of the SC1 solution; The heating power of the heating assembly on the SC1 solution is adjusted according to the temperature to ensure that the temperature difference between the SC1 solution and the target temperature is less than or equal to 0.3°C; and, Adjust the replenishment amounts of NH4OH, H2O2, and H2O according to the pH value to ensure that the deviation between the volume ratio of NH4OH, H2O2, and H2O and the target volume ratio is less than ±0.3%.

9. The process method according to any one of claims 1-4, characterized in that, The removal step is preceded by a pretreatment step: cleaning the wafer with ozone water, wherein the volume concentration of O3 in the ozone water is 1~50 ppm and the temperature is 20~25℃.

10. The process method according to any one of claims 1-4, characterized in that, Between the removal step and the processing step, a first cleaning step is included: cleaning the wafer with DICO2, wherein the CO2 concentration is 0.2~0.5 vol%. And / or, the processing step is followed by a second cleaning step: cleaning the wafer with DICO2, wherein the CO2 concentration is 0.2~0.5 vol.

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