A method for removing humidity from a wafer cassette

Abstract

The application relates to the field of semiconductor wafer manufacturing, and discloses a method for removing humidity of a wafer box. The method mainly utilizes a vacuum drying principle. While a vacuum system is used to perform vacuumization, the wafer box to be dried is continuously heated, so that the moisture in the wafer box diffuses to the surface through a pressure difference or a concentration difference. The water molecules obtain sufficient kinetic energy on the surface of the wafer box, escape to the low-pressure air in the vacuum chamber after overcoming the attraction between the molecules, and are removed by a vacuum pump. In this way, the water vapor on the surface of the wafer box can be quickly and cleanly removed without consuming a large amount of gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor wafer manufacturing, and in particular to a method for removing humidity from a wafer box. BACKGROUND

[0002] In a semiconductor wafer factory, wafer boxes are used for wafer product circulation and shipment. For example, in a 12-inch wafer factory, after each process, the wafer product needs to be stored in a dry FOUP (front opening unified pod) to ensure that the product on the line will not be affected by humidity and the surface quality will not be affected. The product that needs to be shipped is stored in a FOSB (front opening shipping box), which has a more stringent requirement for humidity. When the humidity in the wafer box is not removed enough, it will cause the surface micro-roughness of the wafer product to change, which will have an adverse effect on the subsequent high-end chip manufacturing, and even cause the product to be scrapped.

[0003] The current mainstream wafer box cleaning and drying method mainly uses heated air or nitrogen to blow dry the water vapor on the surface of the wafer box, or uses heat radiation to dry or a large flow of air to carry away the water vapor on the surface of the wafer box. These methods basically require a long time of continuous operation of nearly 1 hour, which consumes a lot of energy, and the water vapor in the corners of the wafer box is not easy to remove completely, which may cause risks in subsequent product storage. SUMMARY

[0004] The present application provides a method for removing humidity from a wafer box to solve the problem of high energy consumption, long time consumption, and incomplete removal of the existing wafer box humidity removal method.

[0005] To achieve the above-mentioned purpose, the basic scheme of the present application provides a method for removing humidity from a wafer box, comprising the following steps:

[0006] S1: Cleanly package the wafer box and place it in a cleaning position;

[0007] S2: Open the wafer box, then use ultrapure water with a temperature of 40-60°C and a flow rate of 5-10 L / min to flush for 1-4 min, while continuously providing an exhaust of 600-1000 pa;

[0008] S3: Use clean CDA with a temperature of 60-90°C and a flow rate of 2500-3500 L / min to dry the wafer box for 8-15 min, while continuously providing an exhaust of 600-1000 pa;

[0009] S4: Place the wafer box in a vacuum chamber and close the vacuum chamber door;

[0010] S5: Start the vacuum system, and pump the vacuum chamber to make the inside of the vacuum chamber drop from one standard atmosphere to 500-1500 pa, and continuously heat the air in the chamber using the heating device in the chamber to keep the temperature of the air in the chamber at 90-120°C;

[0011] S6: Slowly inject clean nitrogen into the vacuum chamber after the vacuum pumping and heating stage is over, to make the inside of the vacuum chamber return to one standard atmosphere, and then take out the wafer box and assemble it completely.

[0012] The principle and beneficial effects of the basic scheme are that the present application mainly uses the principle of vacuum drying. The boiling point of water is 100°C at one standard atmosphere, and can be reduced to 80°C, 60°C, 40°C or even lower under vacuum negative pressure. The water in the wafer box is continuously heated while being pumped by the vacuum system, so that the water in the wafer box diffuses to the surface through the pressure difference or concentration difference. The water molecules obtain enough kinetic energy on the surface of the wafer box, escape to the low-pressure air in the vacuum chamber after overcoming the intermolecular attraction, and are removed by the vacuum system. Thus, the water vapor on the surface of the wafer box can be quickly removed without consuming a large amount of gas.

[0013] After the wafer box is removed by the method, the surface of the wafer box is not contaminated, the internal humidity of the wafer box after cleaning is reduced to 7%, and the internal humidity is stable at about 32% after 3h, which shows that the cleaned wafer box can ensure that the product surface is not affected by moisture. After the clean silicon wafer is packaged and transported for 24h, the number of particles greater than 37nm on the surface of each silicon wafer is increased by less than 3, which shows that the cleaned wafer box can load the current advanced process substrate silicon wafer without being contaminated. After the wafer box loaded with silicon products is opened after 2 years, the result of retesting shows that the surface roughness change value of the silicon wafer is less than 0.005ppm, the number of particles greater than 37nm is increased by less than 3, and the content of all elements on the surface of the metal is less than 0.5E9 atoms / cm 2 , which shows that the wafer box cleaned by the method can meet the requirements of the advanced process of the semiconductor substrate silicon wafer.

[0014] Optionally, the wafer box in S1 is a Shinku FOUP, Shinku FOSB, Miraial FOSB, Entergris FOSB, 3S FOSB for 12-inch silicon wafers, or Shinku A1, Shinku A3, Shinku A5, and Yingtege Ultrapak wafer box for 8-inch silicon wafers.

[0015] The method has a wide range of applications, and can be used for mainstream wafer boxes for temporary storage and shipment products and can meet the requirements of the respective wafer boxes.

[0016] Optionally, the vacuum cavity is pumped for 2-4 minutes in S5.

[0017] The vacuum pressure can be reduced quickly, so that the wafer box can be dried quickly, and the whole process time can be controlled to ensure the production efficiency.

[0018] Optionally, the heating device in S5 is a ceramic sheet heater, and the heating time is 2-4 minutes.

[0019] The ceramic sheet heater is used for heating, so that no gas overflow occurs, and the wafer box can be baked quickly through ceramic radiation heating. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A flowchart of the method for removing humidity from a wafer box is shown in the figure.

[0021] Figure 2 The internal humidity change of FOSB in Example 1 is shown in the figure.

[0022] Figure 3 The result graph of the increase of particles greater than 37nm on the surface of the silicon wafer in Example 1 is shown in the figure.

[0023] Figure 4 The result graph of the product surface metal level in Example 1 is shown in the figure.

[0024] Figure 5 The result graph of the product surface Haze change value in Example 1 is shown in the figure.

[0025] Figure 6 The internal humidity change of FOSB in Example 2 is shown in the figure.

[0026] Figure 7 The result graph of the increase of particles greater than 37nm on the surface of the silicon wafer in Example 2 is shown in the figure.

[0027] Figure 8 The result graph of the product surface metal level in Example 2 is shown in the figure.

[0028] Figure 9 The result graph of the product surface Haze change value in Example 2 is shown in the figure.

[0029] Figure 10 The internal humidity change of FOSB in Example 3 is shown in the figure.

[0030] Figure 11 The result graph of the increase of particles greater than 37nm on the surface of the silicon wafer in Example 3 is shown in the figure.

[0031] Figure 12 The result graph of the product surface metal level in Example 3 is shown in the figure.

[0032] Figure 13 Graph of results for product surface haze change value in Example 3;

[0033] Figure 14 Graph of FOSB internal moisture change in Comparative Example 1;

[0034] Figure 15 Graph of results for increase in particles greater than 37 nm on the wafer surface in Comparative Example 1;

[0035] Figure 16 Graph of results for product surface metal level in Comparative Example 1;

[0036] Figure 17 Graph of results for product surface haze change value in Comparative Example 1;

[0037] Figure 18 Graph of FOSB internal moisture change in Comparative Example 2;

[0038] Figure 19 Graph of results for increase in particles greater than 37 nm on the wafer surface in Comparative Example 2;

[0039] Figure 20 Graph of results for product surface metal level in Comparative Example 2;

[0040] Figure 21 Graph of results for product surface haze change value in Comparative Example 2;

[0041] Figure 22 Graph of FOSB internal moisture change in Comparative Example 3;

[0042] Figure 23 Graph of results for increase in particles greater than 37 nm on the wafer surface in Comparative Example 3;

[0043] Figure 24 Graph of results for product surface metal level in Comparative Example 3;

[0044] Figure 25 Graph of results for product surface haze change value in Comparative Example 3. Embodiments

[0045] The following is further explained in detail by way of specific embodiments:

[0046] A method of removing moisture from a wafer cassette, comprising the steps of:

[0047] S1: The wafer box is packaged and removed cleanly and placed in a position to be cleaned; the wafer box is a 12-inch silicon wafer used by Shinku FOUP, Shinku FOSB, Miraial FOSB, Entergris FOSB, 3S FOSB, or an 8-inch silicon wafer used by Shinku A1, Shinku A3, Shinku A5, and Ampacet Ultrapak wafer box;

[0048] S2: The wafer box is opened, and then ultra-pure water with a temperature of 40-60°C and a flow rate of 5-10 L / min is used to flush for 1-4 min, while continuously providing an exhaust of 600-1000 pa;

[0049] S3: Clean CDA (i.e., dry compressed air) with a temperature of 60-90°C and a flow rate of 2500-3500 L / min is used to dry the wafer box for 8-15 min, while continuously providing an exhaust of 600-1000 pa;

[0050] S4: The wafer box is placed in the vacuum chamber, and the vacuum chamber door is closed;

[0051] S5: The vacuum system is started, and the vacuum chamber is pumped for 2-4 min, so that the internal pressure of the vacuum chamber is reduced from one standard atmosphere to 500-1500 pa, while the heating device in the vacuum chamber is continuously used to heat the air in the chamber, so that the temperature of the air in the vacuum chamber is maintained at 90-120°C. The heating device is a ceramic sheet heater, and the heating time is 2-4 min;

[0052] S6: After the vacuum pumping and heating stage is completed, clean nitrogen is slowly injected into the vacuum chamber, so that the internal pressure of the vacuum chamber returns to one standard atmosphere, and then the wafer box is taken out and assembled completely.

[0053] The vacuum chamber is arranged after the clean CDA, and the specific structure of the vacuum chamber includes a cubic cavity, a vacuum port, a vacuum degree sensor, a temperature sensor, a ceramic heating sheet, a side cylinder door opening and closing structure, a position sensor arranged at the door contact cavity position, a high-temperature-resistant sealing strip, a FOSB / FOUP fixing buckle arranged on the side door, and a ceramic sheet heater used as the heating principle. This method of heating does not produce gas overflow, and the wafer box can be quickly baked through ceramic radiation heating. The specific structure of the vacuum chamber is relatively common and known, and the present application will not be described again. Example

[0054] The wafer box of FOSB of Shinku Rika was selected as the object of removing humidity, and the wafer box was rinsed with ultrapure water at a temperature of 50°C and a flow rate of 8 L / min for 3 min, while 800 pa of exhaust air was continuously supplied; the wafer box was dried with clean CDA at a temperature of 70°C and a flow rate of 3000 L / min for 10 min, while 800 pa of exhaust air was continuously supplied. Then the wafer box was placed in the vacuum chamber, the vacuum system was started, the air pressure in the vacuum chamber was reduced from one standard atmosphere (about 100000 pa) to 600 pa, and the ceramic sheet heater was started to keep the air temperature in the vacuum chamber at 90°C for 3 min. After the vacuum and heating were completed, clean nitrogen was slowly injected into the vacuum chamber to restore the air pressure in the vacuum chamber to one standard atmosphere, and then the wafer box was taken out and assembled completely.

[0055] The wafer box dried by the method of the present embodiment was observed, and no contamination was found on the surface. After being placed for 3 hours, the internal humidity was less than 32%, as shown in the attached Figure 2 After the clean silicon wafer was packaged and transported for 24 hours, the increase in particles greater than 37 nm on the surface of the silicon wafer was measured, and the result was less than 3, as shown in the attached Figure 3 The surface metal level of the product was measured, and the result was less than 0.5E9 atoms / cm2, as shown in the attached Figure 4 The change in Haze value on the surface of the product was measured, and the difference in Haze value before and after the product was packaged was less than 0.005 ppm, as shown in the attached Figure 5 The wafer box cleaned by the method of the present embodiment can meet the requirements of advanced processes for semiconductor substrate silicon wafers. Embodiment

[0056] The difference between the present embodiment and embodiment 1 is that in the present embodiment, the air pressure in the vacuum chamber is reduced to 1000 pa, and the air temperature in the vacuum chamber is heated to 100°C.

[0057] The wafer box dried by the method of the present embodiment was observed, and no contamination was found on the surface. After being placed for 3 hours, the internal humidity was less than 32%, as shown in the attached Figure 6 After the clean silicon wafer was packaged and transported for 24 hours, the increase in particles greater than 37 nm on the surface of the silicon wafer was measured, and the result was less than 3, as shown in the attached Figure 7 The surface metal level of the silicon wafer was measured, and the result was less than 0.5E9 atoms / cm2, as shown in the attached Figure 8 The change in Haze value on the surface of the product was measured, and the difference in Haze value before and after the product was packaged was less than 0.005 ppm, as shown in the attached Figure 9 The wafer box cleaned by the method of the present embodiment can meet the requirements of advanced processes for semiconductor substrate silicon wafers. Embodiment

[0058] The difference between this embodiment and embodiment 1 is that, in this embodiment, the air pressure of the vacuum cavity is reduced to 1500 pa, and the temperature in the vacuum cavity is heated to 120℃.

[0059] After the wafer box dried by this embodiment is used, no contamination is found on the surface, and after 3 hours of placement, the internal humidity result is shown in the following table 1. Figure 10 The increase value of the particles greater than 37 nm on the surface of the silicon wafer is measured after the clean silicon wafer is loaded and packaged for 24 hours of transportation, and the result is shown in the following table 2. Figure 11 The metal level on the surface of the silicon wafer is measured, and the result is shown in the following table 3. Figure 12 The Haze change value of the product surface is measured, and the result is shown in the following table 4. Figure 13 The Haze difference before and after the product is loaded is less than 0.005 ppm, which shows that the wafer box cleaned by this embodiment can meet the advanced process of the semiconductor substrate silicon wafer.

[0060] The difference between comparative example 1 and embodiment 1 is that, in this comparative example, the air pressure of the vacuum cavity is reduced to 2500 pa, and the temperature in the vacuum cavity is heated to 95℃.

[0061] After the wafer box dried by this comparative example is used, no contamination is found on the surface, and after 3 hours of placement, the internal humidity result is shown in the following table 5. Figure 14 The increase value of the particles greater than 37 nm on the surface of the silicon wafer is measured after the clean silicon wafer is loaded and packaged for 24 hours of transportation, and the result is shown in the following table 6. Figure 15 The metal level on the surface of the silicon wafer is measured, and the result is shown in the following table 7. Figure 16 The Haze change value of the product surface is measured, and the result is shown in the following table 8. Figure 17 The Haze difference before and after the product is loaded is more than 0.005 ppm, which shows that the wafer box cleaned by this comparative example cannot meet the advanced process of the semiconductor substrate silicon wafer.

[0062] The difference between comparative example 2 and embodiment 1 is that, in this comparative example, the temperature in the vacuum cavity is heated to 30℃, and the air pressure of the vacuum cavity is reduced to 1000 pa.

[0063] After the wafer box dried by this comparative example is used, no contamination is found on the surface, and after 3 hours of placement, the internal humidity result is shown in the following table 9. Figure 18 The increase value of the particles greater than 37 nm on the surface of the silicon wafer is measured after the clean silicon wafer is loaded and packaged for 24 hours of transportation, and the result is shown in the following table 10. Figure 19 The metal level on the surface of the silicon wafer is measured, and the result is shown in the following table 11. Figure 20The results are more than 0.5E9 atoms / cm2, the Haze change value of the product surface is measured, and the results are shown in the following table 1: Figure 21 The Haze difference before and after loading is more than 0.005ppm before the product is loaded, which indicates that the wafer box cleaned by the method of the comparative example cannot meet the advanced process of the semiconductor substrate silicon wafer.

[0064] The difference between Comparative Example 3 and Example 1 is that there is no vacuum and pressure reduction heating step in the comparative example, and the wafer box needs to be placed in a nitrogen cabinet for further drying after cleaning and drying. The drying time is 24h, and then the product is taken out and assembled.

[0065] The wafer box dried by the comparative example is observed, and no contamination is found on the surface. After 3 hours of placement, the internal humidity results are shown in the following table 1: Figure 22 The results are less than 32%, the silicon wafer is packaged and transported for 24h, the increase value of the particles on the surface of the silicon wafer is measured, and the results are shown in the following table 1: Figure 23 The increase value is more than 3, the metal level on the surface of the silicon wafer is measured, and the results are shown in the following table 1: Figure 24 The results are less than 0.5E9 atoms / cm2, the Haze change value of the product surface is measured, and the results are shown in the following table 1: Figure 25 The results are less than 0.005ppm, which indicates that the wafer box dried by the comparative example cannot meet the advanced process of the semiconductor substrate silicon wafer, and the nitrogen consumption is large, the cycle is too long, and the economic benefit is poor.

[0066] From Examples 1-3 and Comparative Examples 1-3, it can be seen that:

[0067] After the wafer surface is cleaned according to the method provided by the present application in Examples 1-3, the particle, metal data and surface Haze of the wafer surface are tested, and the test results meet the acceptance standard. The internal humidity change of the FOSB also meets the acceptance standard. In Comparative Examples 1-2, the particle, metal and Haze on the wafer surface are tested after the pressure or temperature in the vacuum cavity is changed, and the internal humidity of the wafer box is also abnormal.

[0068] It is found from Comparative Example 1 that when the vacuum degree in the vacuum cavity is changed to exceed the conditions protected by the patent, the particle and surface Haze on the wafer surface cannot meet the acceptance standard, and the internal humidity of the FOSB also cannot meet the acceptance standard.

[0069] It is found from Comparative Example 2 that when the heating temperature in the vacuum cavity is changed to exceed the conditions protected by the patent, the particle, metal and surface Haze on the wafer surface cannot meet the acceptance standard.

[0070] It is found by Comparative Example 3 that when using the conventional drying method, due to the long drying wafer box time, particles inside can fall into the wafer box, resulting in unqualified wafer test surface particles.

[0071] The above only describes the embodiments of the present application, and the well-known specific structures and characteristics in the scheme are not described in detail. It should be pointed out that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, which will not affect the effect and practicality of the patent. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A method for removing humidity from a wafer cassette, comprising: The method comprises the following steps: S1: removing the wafer box packaging and placing it in a position to be cleaned; S2: opening the wafer box and then using ultrapure water with a temperature of 40-60°C and a flow rate of 5-10 L / min to flush the wafer box for 1-4 min while continuously providing an exhaust of 600-1000 pa; S3: using clean CDA with a temperature of 60-90°C and a flow rate of 2500-3500 L / min to dry the wafer box for 8-15 min while continuously providing an exhaust of 600-1000 pa; S4: placing the wafer box in a vacuum chamber and closing the door of the vacuum chamber; S5: starting the vacuum system, pumping the vacuum chamber, and reducing the internal pressure of the vacuum chamber from one standard atmosphere to 500-1500 pa while continuously heating the air in the vacuum chamber using a heating device in the vacuum chamber to maintain the temperature of the air in the vacuum chamber at 90-120°C; the heating device is a ceramic sheet heater, and the heating time is 2-4 min; S6: after the vacuum pumping and heating stage is completed, slowly injecting clean nitrogen into the vacuum chamber to restore the internal pressure of the vacuum chamber to one standard atmosphere, then taking out the wafer box and assembling it completely; After the wafer box is processed through the above steps, the internal humidity of the wafer box is less than 32% after being placed for 3 h, the increase in particles greater than 37 nm on the surface of the silicon wafer is less than 3 after the clean silicon wafer is packaged and transported for 24 h, the metal level on the surface of the silicon wafer is less than 0.5E9 atoms / cm2, and the change in the Haze value on the surface of the product is less than 0.005 ppm, which can meet the requirements of advanced processes for semiconductor substrate silicon wafers.

2. The method of claim 1, wherein: The wafer box in S1 is a Shinku FOUP, a Shinku FOSB, a Miraial FOSB, an Entergris FOSB, a 3S FOSB for 12-inch silicon wafers, or a Shinku A1, a Shinku A3, a Shinku A5, or a Koyo Ultrapak wafer box for 8-inch silicon wafers. ​ 3. The method of claim 1, wherein: In S5, the vacuum chamber pumping time is 2-4 min.

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