Wafer aging test method

Abstract

The invention provides a wafer aging test method, and relates to the technical field of wafer test. The first protective gas is introduced into the aging test cavity of the aging test device, so that air in the aging test cavity can be emptied, and the first protective gas with the temperature higher than the target aging test temperature is continuously blown into the aging test cavity, namely, the surface of the wafer to be tested can be blown; condensation and deposition of pollutants on the surface of the to-be-tested wafer can be avoided under the condition that the to-be-tested wafer cannot be prevented from being in contact with various gaseous pollutants, so that discoloration of the back gold surface of the to-be-tested wafer is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer testing, and in particular to a wafer aging testing method. Background Art

[0002] Semiconductor wafers or chips are often screened during the manufacturing process by undergoing burn-in testing. During burn-in testing, the wafers or chips are subjected to specific temperature, atmosphere, current, or voltage conditions for a specific period of time. However, after burn-in testing, the backing metal of the wafers or chips, especially silver-plated ones, is prone to discoloration. Some may exhibit an overall grayish-white, hazy discoloration, while others may develop circular or long streaks corresponding to the holes or grooves at the backing metal contact interface. This discoloration not only affects the appearance but also raises concerns about the conductivity of the discolored areas. Because the backing metal of the wafer or chip needs to conduct electricity, it is necessary to minimize such discoloration. However, no relevant technical documentation or processes have been found to explain the causes of backing metal discoloration or how to eliminate it. Summary of the Invention

[0003] The purpose of the present invention is to provide a wafer aging test method to solve the technical problem in the prior art that the back gold surface of the wafer is prone to discoloration during the aging test process.

[0004] In particular, the present invention provides a wafer aging test method, comprising:

[0005] Placing the wafer to be tested in the aging test chamber of the aging test device;

[0006] Continuously introducing a first protective gas into the burn-in test chamber, wherein the first protective gas has a moisture content of no more than 1%, a purity of no less than 99.999%, and a temperature higher than a target burn-in test temperature of the wafer to be tested;

[0007] When the pressure of the first protective gas introduced into the aging test chamber reaches a target pressure threshold, a test electrical signal is applied to the wafer to be tested to perform a wafer aging test at the target pressure threshold.

[0008] Optionally, before continuously introducing the first protective gas into the aging test chamber, the wafer aging test method further includes:

[0009] The first protective gas is preheated, wherein the temperature of the preheated first protective gas is higher than the target aging test temperature of the wafer to be tested, and the temperature of the preheated first protective gas is not lower than a first preset temperature.

[0010] Optionally, the first preset temperature is any value in the range of 90°C to 110°C.

[0011] Optionally, the first protective gas is nitrogen, carbon dioxide or any inert gas.

[0012] Optionally, before continuously introducing the first protective gas into the aging test chamber, the wafer aging test method further includes:

[0013] The aging test device is heated and baked, and the moisture content in the aging test chamber is maintained at no more than 1%.

[0014] Optionally, the aging test device is baked, and a baking temperature is not lower than a target aging test temperature of the wafer to be tested and not lower than a second preset temperature.

[0015] Optionally, the target air pressure threshold range is 1 atm to 1.3 atm.

[0016] Optionally, if the aging test chamber is connected to the outside, the first protective gas is continuously blown in during the aging test.

[0017] Optionally, the aging test equipment is provided with a protective gas inlet and a protective gas outlet respectively connected to the aging test chamber, the protective gas inlet is connected to the first protective gas providing device, and the protective gas outlet is connected to the outside;

[0018] During the aging test, the air pressure at the shielding gas inlet is greater than the air pressure at the shielding gas outlet.

[0019] Optionally, the wafer aging test method also includes: after completing the wafer aging test, stopping the introduction of the first protective gas and introducing the second protective gas, the moisture content of the second protective gas does not exceed 1%, the purity is not less than 99.999%, and the temperature is any value between 15°C and 30°C; the second protective gas is nitrogen, carbon dioxide or any one of the inert gases.

[0020] According to the solution of the present invention, by introducing the first protective gas into the aging test chamber of the aging test device, the air in the aging test chamber can be evacuated, and the first protective gas with a temperature higher than the target aging test temperature is continuously blown into the aging test chamber, which is equivalent to blowing the surface of the wafer to be tested. When it is inevitable that the wafer to be tested is exposed to various gaseous pollutants, the pollutants can be prevented from condensing and depositing on the surface of the wafer to be tested, thereby greatly reducing the discoloration of the back gold surface of the wafer to be tested.

[0021] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0023] Figure 1 is a schematic flow chart of a wafer aging test method according to one embodiment of the present invention;

[0024] Figure 2 is a schematic flow chart of a wafer aging test method according to another embodiment of the present invention;

[0025] Figure 3 is a schematic structural diagram of a aging test chamber according to one embodiment of the present invention;

[0026] Figure 4 is a schematic comparison diagram of the wafer to be tested before and after the aging test without adopting the wafer aging test method of this embodiment;

[0027] Figure 5 3 is a schematic comparison diagram of the wafer to be tested before and after the aging test using the wafer aging test method of this embodiment.

[0028] Reference numerals:

[0029] 10-shielding gas inlet, 20-aging test chamber, 30-shielding gas outlet. DETAILED DESCRIPTION

[0030] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0031] However, after the aging test, the back gold of the wafer, especially the silver-plated back gold, will have a higher probability of discoloration. Some will show grayish white or foggy overall discoloration, and some will form circular spots or long stripes of corresponding shapes at the interface where the back gold contacts, along with the holes or grooves on the interface. This phenomenon of back gold discoloration not only affects the appearance, but also makes people doubt whether the conductivity of the discolored area has changed. In the production process of wafer thinning, production defects will cause the back gold surface to show some strip-shaped or tear-shaped different-color areas, but this situation is different from the back gold discoloration. The back gold surface of the wafer proposed by the present invention does not have any hidden production defects itself, but is a discoloration problem found in normal products after aging and heating.

[0032] The applicant of the present invention has found that the main reason for the discoloration of the back gold surface of the wafer is pollution from the environment. Part of the pollution source is water vapor and trace substances that can be dissolved in water in the ambient gas, as well as pollutants such as dust attached to water vapor, which turn into water and adhere to the back gold surface of the wafer. After the back gold surface is heated, the water molecules evaporate, and the water-soluble substances turn into small solid particles and adhere to the back gold surface. Another part of the pollution source comes from the device materials that form the aging test environment. Some materials, such as PCB boards, air pipes, rubber sealing rings, and even the wafer surface itself, release water vapor and volatiles of various components during the heating process. When these gaseous pollutants come into contact with the back gold surface, if they are cooled, they will condense and deposit on the back gold surface of the wafer. The deposition of pollutants reduces the reflectivity of the back gold surface, presenting large gray-white fog or patches, similar to the formation of water stains. The present invention aims to achieve the purpose of eliminating or significantly reducing the discoloration of the back gold of the wafer by formulating specific environmental conditions and methods for formulating environmental conditions, under the premise of meeting the wafer aging test conditions.

[0033] Figure 1 FIG. 1 is a schematic flow chart of a wafer aging test method according to an embodiment of the present invention. Figure 1 As shown, in this embodiment, the wafer aging test method includes:

[0034] Step S100, placing a wafer to be tested in an aging test chamber of an aging test device, wherein the wafer to be tested has a gold back surface;

[0035] Step S200 , continuously introducing a first protective gas into the burn-in test chamber, wherein the moisture content of the first protective gas does not exceed 1%, the purity is not less than 99.999%, and the temperature is higher than the target burn-in test temperature of the wafer to be tested;

[0036] In step S300 , when the pressure of the first protective gas in the burn-in test chamber reaches a target pressure threshold, a test electrical signal is applied to the wafer to be tested to perform a wafer burn-in test at the target pressure threshold. Here, the target pressure threshold is greater than zero.

[0037] According to the solution of the present invention, by introducing the first protective gas into the aging test chamber of the aging test device, the air in the aging test chamber can be evacuated, and the first protective gas with a temperature higher than the target aging test temperature is continuously blown into the aging test chamber, which is equivalent to blowing the surface of the wafer to be tested. When it is inevitable that the wafer to be tested is exposed to various gaseous pollutants, the pollutants can be prevented from condensing and depositing on the surface of the wafer to be tested, thereby greatly reducing the discoloration of the back gold surface of the wafer to be tested.

[0038] In some embodiments, the target pressure threshold range is 1 atm to 1.3 atm, for example, 1 atm, 1.1 atm, 1.2 atm, or 1.3 atm. In other embodiments, the target pressure threshold can also be determined according to specific design requirements.

[0039] Figure 2 FIG. 1 is a schematic flow chart of a wafer aging test method according to another embodiment of the present invention. Figure 2 As shown, in some embodiments, before step S200, the wafer aging test method further includes:

[0040] In step S110, the first protective gas is preheated to a temperature higher than the target burn-in test temperature of the wafer to be tested and not lower than a first preset temperature. The target burn-in test temperature of the wafer to be tested can be determined based on specific design requirements.

[0041] This embodiment preheats the first protective gas in advance and then introduces the preheated first protective gas into the aging test chamber, which can prevent contaminants from condensing and settling on the surface of the wafer to be tested, and greatly reduces the discoloration of the back gold surface of the wafer to be tested.

[0042] In some embodiments, the first preset temperature is any value between 90°C and 110°C, such as 90°C, 95°C, 100°C, 105°C, or 110°C. In a preferred embodiment, the first preset temperature is 100°C. Generally, the preset temperature of the first protective gas only needs to be slightly higher than the target aging temperature of the wafer to be tested. In other embodiments, the first preset temperature can also be determined based on specific design requirements.

[0043] In some embodiments, the first protective gas is nitrogen, carbon dioxide, or any one of the inert gases. For example, the protective gases currently used in wafer aging tests are high-purity nitrogen and sulfur hexafluoride. Here, a high-purity and dry protective gas must be used. If it is a homemade protective gas, a drying and filtration step must be included, and the moisture content pressure dew point of the protective gas should be lower than -70°C. For the test chamber 20 with airtightness requirements, the blowing time of the first protective gas is determined according to the volume of the aging test chamber. The air in the aging test chamber is emptied as much as possible. The first protective gas must fill the aging test chamber where the wafer to be tested is located to isolate the air from contacting the surface of the wafer to be tested. In other words, the preset time is set according to the volume of the aging test chamber. The larger the volume, the longer the preset time, and the smaller the volume, the shorter the preset time. If the aging test device is an open structure, it is necessary to continuously blow the first protective gas into the aging test chamber to form an air curtain to protect the wafer to be tested.

[0044] In step S110, the first protective gas can be preheated using specific gas preheating equipment, such as a gas electric heater or other related similar special equipment. The gas electric heater can heat any gas, and the hot gas generated is dry and moisture-free, non-conductive, non-flammable, non-explosive, non-chemically corrosive, pollution-free, safe and reliable, and the heated space heats up quickly and controllably, and the temperature control is precise.

[0045] In some embodiments, before step S200, the wafer aging test method further includes:

[0046] Step S120: heat and bake the aging test device, and keep the moisture content in the aging test chamber no more than 1%. It should be noted that there is no order relationship between step S110 and step S120, and they can be performed simultaneously or in steps.

[0047] It can be understood that during the aging test process, the aging test device that accommodates or contacts the wafer to be tested, especially the aging test device with airtightness requirements, must be heated and baked before use and kept dry.

[0048] In some embodiments, the aging test device is baked, and the baking temperature is not lower than the target aging test temperature of the wafer to be tested and not lower than the second preset temperature.

[0049] Here, the second preset temperature is any value in the range of 90° C. to 110° C., for example, 90° C., 100° C., or 110° C. In a preferred embodiment, the second preset temperature is 100° C. In addition, the aging test device that has been cooled for more than 6 hours must be heated and baked. During the baking process, the first protective gas needs to be introduced multiple times to blow through the aging test chamber and airway of the aging test device.

[0050] In some embodiments, if the burn-in test chamber is connected to the outside, the first protective gas is continuously blown in during the burn-in test, thereby ensuring the test environment of the wafer to be tested during the burn-in test.

[0051] In some embodiments, if the aging test chamber is sealed, that is, not connected to the outside world, it is necessary to maintain the aging test chamber at a target air pressure threshold during the aging test. Here, it is necessary to maintain the air pressure of the input first protective gas greater than the air pressure at the protective gas outlet of the aging test chamber. The air pressure of the input first protective gas needs to be slightly higher than the air pressure at the protective gas outlet. For example, if the protective gas outlet is at indoor atmospheric pressure, the air pressure of the input first protective gas should be slightly greater than the indoor atmospheric pressure, so as to ensure that the aging test chamber is at a positive pressure relative to the outside of the aging test chamber.

[0052] Figure 3 FIG. 1 is a schematic structural diagram of an aging test chamber 20 according to an embodiment of the present invention. Figure 3As shown, in some embodiments, the aging test apparatus is provided with a shielding gas inlet 10 and a shielding gas outlet 30, each of which is connected to the aging test chamber 20. The shielding gas inlet is connected to the first shielding gas supply device, and the shielding gas outlet 30 is connected to the outside. During the aging test, the air pressure of the shielding gas inlet is greater than the air pressure of the shielding gas outlet 30.

[0053] In some embodiments, the air passage between the preheated first protective gas from the first protective gas supply device to the aging test chamber 20 should be as short as possible to prevent the temperature of the first protective gas from decreasing. The relative positions of the protective gas inlet 10 and the protective gas outlet 30 of the aging test chamber 20 to be protected by the gas should be designed in accordance with the following principles:

[0054] First, the shielding gas inlet 10 and the shielding gas outlet 30 should be placed at the two ends of the aging test chamber 20, and the airflow dead angle formed by obstructions in the aging test chamber 20 should be minimized;

[0055] Second: multiple protective gas inlets 10 are provided;

[0056] Third: When the aging test chamber 20 is at a high height, the height difference between the shielding gas inlet 10 and the shielding gas outlet 30 is considered according to the density difference between the first shielding gas and the original gas in the aging test chamber 20;

[0057] Fourth: all measures that are conducive to filling the aging test chamber 20 with the first protective gas and exhausting the original gas in the aging test chamber 20.

[0058] See also Figure 3 The aging test equipment has three shielding gas inlets 10 and one shielding gas outlet 30. The three shielding gas inlets 10 are located on the same side of the aging test chamber 20 and are spaced apart. The shielding gas outlet 30 is located on the other side of the aging test chamber 20. In other embodiments, the number of shielding gas inlets 10 and shielding gas outlets 30 can also be selected according to specific design requirements.

[0059] In some embodiments, the gas preheating device is connected to the first protective gas providing device for preheating the first protective gas. In addition, the gas preheating device not only has a preheating function, but also has a dehumidification function, so that the temperature and humidity of the first protective gas meet the set requirements.

[0060] In some embodiments, the wafer aging test method further includes: after completing the wafer aging test, stopping the introduction of the first protective gas and introducing the second protective gas.

[0061] Here, the second shielding gas has a moisture content of no more than 1%, a purity of no less than 99.999%, and a temperature of any value between 15° C. and 30° C., for example, 15° C., 20° C., 25° C., or 30° C. The second shielding gas is nitrogen, carbon dioxide, or any inert gas.

[0062] In this embodiment, all actions related to loading and unloading the wafers to be tested must be performed in a clean room environment. The humidity of the air in the clean room should be kept as low as possible, provided that it can be controlled. In other words, the environment must be kept clean and low in humidity. The fixtures and pipes involved in the burn-in test must be kept clean and dry.

[0063] Figure 4 is a schematic comparison diagram of the wafer to be tested before and after the aging test without using the wafer aging test method of this embodiment, Figure 5 This is a schematic comparison diagram of the aging test of the wafer before and after the aging test using the wafer aging test method of this embodiment. After testing, it was found that the left picture is the back gold surface of the wafer before aging heating, and the right picture is the back gold surface of the wafer after aging heating. The right picture shows that the back gold surface of the wafer has a grayish-white foggy overall discoloration. Using the wafer aging test method of this embodiment, the back gold surface of the wafer before and after aging heating, such as Figure 5 As shown in the figure, the left image shows the wafer's backside gold surface before aging and heating, and the right image shows the wafer's backside gold surface after aging and heating. The right image shows that the discoloration of the wafer's backside gold surface has been greatly reduced, and visual inspection shows almost no change. Since the environment cannot be absolutely clean, the air and protective gas cannot be absolutely dry, and the fixture and pipes cannot be absolutely dry and volatile-free, discoloration of the backside gold surface of the wafer under test is difficult to eliminate, but it can be greatly suppressed and reduced.

[0064] At this point, those skilled in the art will recognize that, although a number of exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications consistent with the principles of the present invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A wafer aging test method, characterized in that: include: Placing the wafer to be tested in the aging test chamber of the aging test device; Continuously introducing a first protective gas into the burn-in test chamber, wherein the first protective gas has a moisture content of no more than 1%, a purity of no less than 99.999%, and a temperature higher than a target burn-in test temperature of the wafer to be tested; When the pressure of the first protective gas introduced into the aging test chamber reaches a target pressure threshold, a test electrical signal is applied to the wafer to be tested to perform a wafer aging test at the target pressure threshold.

2. The wafer aging test method according to claim 1, characterized in that: Before continuously introducing the first protective gas into the aging test chamber, the wafer aging test method further includes: The first protective gas is preheated, wherein the temperature of the preheated first protective gas is higher than the target aging test temperature of the wafer to be tested, and the temperature of the preheated first protective gas is not lower than a first preset temperature.

3. The wafer aging test method according to claim 2, characterized in that: The first preset temperature is any value between 90°C and 110°C.

4. The wafer aging test method according to claim 1, wherein: The first protective gas is nitrogen, carbon dioxide or any inert gas.

5. The wafer aging test method according to any one of claims 1 to 4, characterized in that: Before continuously introducing the first protective gas into the aging test chamber, the wafer aging test method further includes: The aging test device is heated and baked, and the moisture content in the aging test chamber is maintained at no more than 1%.

6. The wafer aging test method according to claim 5, characterized in that: The aging test device is baked, and the baking temperature is not lower than the target aging test temperature of the wafer to be tested and not lower than a second preset temperature.

7. The wafer aging test method according to claim 1, characterized in that: The target air pressure threshold range is 1 atm to 1.3 atm.

8. The wafer aging test method according to claim 7, characterized in that: If the aging test chamber is connected to the outside, the first protective gas is continuously blown in during the aging test.

9. The wafer aging test method according to claim 8, characterized in that: The aging test equipment is provided with a protective gas inlet and a protective gas outlet respectively connected to the aging test chamber, the protective gas inlet is connected to the first protective gas supply device, and the protective gas outlet is connected to the outside; During the aging test, the air pressure at the shielding gas inlet is greater than the air pressure at the shielding gas outlet.

10. The wafer aging test method according to claim 1, wherein: The wafer aging test method also includes: after completing the wafer aging test, stopping the introduction of the first protective gas and introducing a second protective gas, wherein the moisture content of the second protective gas does not exceed 1%, the purity is not less than 99.999%, and the temperature is any value between 15°C and 30°C; the second protective gas is one of nitrogen, carbon dioxide or any inert gas.

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