Test method for determining optimal cooling rate of low-temperature temporary bonding of EMC wafer and glass wafer

Abstract

The invention discloses a test method for determining the optimal cooling rate of low-temperature temporary bonding of an EMC wafer and a glass wafer. The test method comprises the following steps: vacuumizing the vacuum degree in a bonding cavity to 5 * 10 <-3 > Pa; raising the temperature of the upper heating plate and the lower heating plate to 200 DEG C and maintaining the temperature for 3 minutes; applying a pressure of 5000N into the bonding cavity, filling nitrogen to maintain the pressure for 15 minutes, and then performing pressure relief operation; cooling the upper and lower heating plates from 200 DEG C to 80 DEG C at a preset cooling rate; detecting the bonding quality at the bonding interface of the wafer; and the cooling rate is adjusted for multiple times, and the optimal cooling rate of low-temperature temporary bonding is determined by combining the bonding quality and the production duration at the wafer bonding interface corresponding to different cooling rates. According to the invention, the problem of how to consider both the production efficiency and the bonding quality in the temporary bonding process of the EMC and the glass is solved, and the suitable cooling rate range of the EMC and the glass bonding wafer is determined.

Description

Technical Field

[0001] The invention belongs to the field of low-temperature temporary bonding of wafers, and in particular relates to an experimental method for determining an optimal cooling rate for low-temperature temporary bonding of an EMC wafer and a glass wafer. Background Art

[0002] Fan-out wafer-level packaging (FOWLP) is an advanced integrated circuit packaging technology that breaks through the limitations on the number of I / O pins. It increases the area of ​​a single package by reconfiguring the wafer / wafer. Advanced wafer-level packaging processes are then applied to complete multi-layer rewiring and bumping. After dicing and separation, the resulting package is capable of interconnecting with external electrical devices [1-3]. Compared to traditional packaging based on wire bonding technology, fan-out packaging offers significant advantages in terms of package volume, product performance, packaging cost, and packaging efficiency. Currently, there are two main types of fan-out packaging: one based on epoxy molding compound (EMC) and the other based on silicon-based materials. Fan-out packaging based on temporary bonding of EMC and glass is prone to fragmentation during the post-bonding cooling phase due to the significant difference in thermal expansion coefficients between the EMC wafer and the glass wafer. In actual production, the cooling rate is accelerated to improve production efficiency. However, a rapid cooling rate, for materials with significantly different thermal expansion coefficients, such as EMC and glass substrates, presents a significant challenge: the conflict between fragmentation and production efficiency. How to optimize cooling rate and improve production efficiency is a real problem that semiconductor manufacturers need to solve.

[0003] The invention with publication number CN103094099A discloses a method for annealing wafers after bonding, comprising the following steps: step one, heating the bonded wafer from room temperature to 300°C at a heating rate of less than 15°C / min; step two, keeping the wafer after step one at 300°C for more than 1 hour; step three, cooling the wafer after step two to room temperature at a cooling rate of less than 20°C / min. During the annealing process, this invention slowly heats up and cools down at a lower rate, and basically does not require any changes to the existing equipment. The entire annealing process only requires one heating and one cooling. The control is simple and the operation is convenient. This simplifies the existing annealing process and effectively avoids wafer breakage caused by excessively fast heating and cooling rates, thereby increasing production capacity. However, this invention does not solve the problem of screening the optimal cooling rate, and the equipment is not operating in the optimal state.

[0004] In addition, in the present invention, factors such as the vacuum degree, bonding temperature, and bonding pressure in the bonding chamber also have a significant impact on the integrity rate of temporary wafer bonding. First, the vacuum degree in the bonding chamber is related to the number of impurities that may exist in the chamber during the wafer bonding process. When the vacuum degree in the chamber is low, air is easily retained at the bonding interface. These air bubbles will form after bonding. The presence of bubbles will reduce the bonding strength and may cause local detachment of the bonding layer during subsequent processing. Secondly, the uniformity of the bonding pressure directly affects the size of the gap between the wafer and the substrate. These gaps will affect the bonding quality at the temporary bonding interface of the wafer. Finally, a suitable bonding temperature can accelerate the molecular movement of the bonding material, enhance its diffusion and interweaving, and help improve the bonding strength. Its uniformity can ensure that the bonding material interacts uniformly with the wafer and substrate in the entire area, achieving uniform bonding.

[0005] Therefore, how to eliminate the influence of other influencing factors and design a wafer bonding test method based on EMC and glass temporary bonding fan-out packaging to determine the post-wafer bonding cooling rate that can meet high production efficiency and bonding quality is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] The present invention discloses an experimental method for determining the optimal cooling rate for low-temperature temporary bonding of an EMC wafer and a glass wafer, which solves the problem of how to strike a balance between production efficiency and bonding quality during the temporary bonding process of EMC and glass, determines the appropriate cooling rate range for EMC and glass bonded wafers, and emphasizes that controlling the cooling rate of the upper and lower heating plates during the cooling stage is crucial, which is of great significance for bonding wafers with thermal mismatch and lattice mismatch, and effectively strikes a balance between production efficiency and bonding yield.

[0007] The present invention discloses a test method for determining an optimal cooling rate for low-temperature temporary bonding of an EMC wafer and a glass wafer, the test method comprising the following steps:

[0008] S1, the vacuum degree in the bonding chamber is reduced to 5×10 -3 Pa; raise the temperature of the upper and lower heating plates to 200°C and maintain the temperature for 3 minutes;

[0009] S2, applying a pressure of 5000N to the bonding chamber and filling it with nitrogen to maintain the pressure for 15 minutes before releasing the pressure;

[0010] S3, cooling the upper and lower heating plates from 200°C to 80°C at a preset cooling rate; testing the bonding quality at the wafer bonding interface;

[0011] S4, adjusting the cooling rate multiple times, and repeating steps S1 to S3 after each adjustment of the cooling rate;

[0012] S5, combining the bonding quality at the wafer bonding interface corresponding to different cooling rates and the production time to determine the optimal cooling rate for low-temperature temporary bonding.

[0013] The bonding chamber meets the processing conditions of 8-inch wafer temporary bonding, eutectic bonding, and thermal compression bonding.

[0014] The cooling rates were set to natural cooling, 5°C / min, 1.13°C / min, and 3°C / min, respectively.

[0015] Step S5 further comprises:

[0016] The bonding quality at the wafer bonding interface is detected and determined based on the bonding surface integrity rate at different cooling rates;

[0017] Determine the rationality of the wafer bonding cooling rate based on the bonding quality, and narrow the range of the optimal cooling rate for wafer temporary bonding;

[0018] In the range of the optimal cooling rate for temporary wafer bonding, calculate the weighted sum of production time and bonding quality using the following formula:

[0019] Q=0.7*X BQ +0.3*X PT (1)

[0020] Where Q represents the cooling quality factor; XBQ represents the bonding quality factor; XPT represents the production aging factor; the solution formula for the production aging factor XPT is as follows:

[0021] X PT =e -λt (2)

[0022] In the formula, λ represents the time decay coefficient, and t represents the production time;

[0023] According to the calculated Q value, one of the cooling rates is selected as the optimal cooling rate.

[0024] The beneficial effects of the present invention are:

[0025] First, the present invention provides an experimental method for determining the optimal cooling rate for low-temperature temporary bonding of EMC wafers and glass wafers. Multiple wafer bonding tests are set up, and specific process steps are set up in the tests to control influencing factors other than the cooling rate, analyze the bonding quality of the wafers at various cooling rates, and thus determine a cooling rate suitable for production.

[0026] Secondly, the test method for determining the optimal cooling rate of the low-temperature temporary bonding of the EMC wafer and the glass wafer fully considers the influencing factors in the production process, including the vacuum degree in the bonding cavity, the bonding temperature and the bonding pressure, and sets specific process steps to control the influencing factors except the cooling rate; on this basis, the bonding quality at the wafer bonding interface is detected and determined according to the actual bonding effect and specific technical indexes such as the wafer bonding interface intact rate; and then the rationality of the wafer bonding cooling rate is determined according to the bonding quality, so as to narrow the range interval of the optimal wafer temporary bonding cooling rate, and the optimal cooling rate can be screened out only through several tests.

[0027] Thirdly, the test method for determining the optimal cooling rate of the low-temperature temporary bonding of the EMC wafer and the glass wafer solves the problem of how to balance the production efficiency and the bonding quality in the EMC and glass temporary bonding process, determines the suitable cooling rate range of the EMC and glass bonded wafer, and emphasizes that the cooling rate of the upper and lower heating plates in the cooling stage is crucial, which is of great significance for the wafer bonding of thermal mismatch and lattice mismatch, and effectively balances the production efficiency and the bonding yield. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The flow chart of the test method for determining the optimal cooling rate of the low-temperature temporary bonding of the EMC wafer and the glass wafer is shown. DETAILED DESCRIPTION

[0029] The following examples can make the professional technical personnel more fully understand the present application, but do not limit the present application in any way.

[0030] The present application discloses a test method for determining the optimal cooling rate of the low-temperature temporary bonding of the EMC wafer and the glass wafer, comprising:

[0031] S1, the vacuum degree in the bonding cavity is extracted to 5x10 -3 Pa; the temperature of the upper and lower heating plates is increased to 200℃ and maintained at this temperature for 3 minutes;

[0032] S2, a pressure of 5000N is applied to the bonding cavity, and nitrogen is filled to maintain the pressure for 15 minutes and then the pressure is released;

[0033] S3, the upper and lower heating plates are cooled from 200℃ to 80℃ at a preset cooling rate; the bonding quality at the wafer bonding interface is detected;

[0034] S4, the cooling rate is adjusted for multiple times, and steps S1 to S3 are repeated after each adjustment of the cooling rate;

[0035] S5, combining the bonding quality at the wafer bonding interface corresponding to different cooling rates and the production time to determine the optimal cooling rate for low-temperature temporary bonding.

[0036] The test platform selected in the embodiment of the present invention meets the production requirements of temporary bonding, eutectic bonding, and hot pressing bonding of 8-inch wafers, and the upper and lower heaters can be heated and cooled independently. In this embodiment, a total of four groups of control experiments are set up, and other influencing factors and process steps except the cooling rate are kept consistent between the groups. The cooling rates of the four groups of control experiments are set to natural cooling, 5°C / minute, 1.13°C / minute, and 3°C / minute, respectively. Except for the natural cooling group, the cooling rates of the upper and lower heating plates in the other three groups of control experiments are controlled to remain consistent to ensure the temperature uniformity in the bonding cavity during the cooling stage.

[0037] After the four sets of tests are completed, the bonding quality at the wafer bonding interface is detected and determined based on the actual bonding results of the four sets of tests, using specific technical indicators such as the bonding surface integrity rate; the rationality of the wafer bonding cooling rate is then determined based on the bonding quality, in order to narrow the range of the optimal cooling rate for wafer temporary bonding. Production efficiency is evaluated based on production time, and the optimal cooling rate for low-temperature temporary bonding is screened within the range by combining production efficiency and the bonding quality at the wafer bonding interface. Specifically:

[0038] The bonding quality at the wafer bonding interface is detected and determined based on the bonding surface integrity rate at different cooling rates;

[0039] Determine the rationality of the wafer bonding cooling rate based on the bonding quality, and narrow the range of the optimal cooling rate for wafer temporary bonding;

[0040] In the range of the optimal cooling rate for temporary wafer bonding, calculate the weighted sum of production time and bonding quality using the following formula:

[0041] Q=0.7*X BQ +0.3*X PT 1)

[0042] Where, Q: cooling quality factor. The higher the value, the more suitable the cooling rate is for production.

[0043] XBQ: bonding quality factor;

[0044] XPT: production time factor;

[0045] Among them, the solution formula of production aging factor XPT is as follows:

[0046] X PT =e -λt 2)

[0047] Where, λ: time attenuation coefficient;

[0048] t: production time [s];

[0049] According to the calculated Q value, one of the cooling rates is selected as the optimal cooling rate.

[0050] In this invention, factors affecting bonding include the vacuum level within the bonding chamber, bonding temperature, and bonding pressure. To this end, the invention employs the following specific process steps: evacuating the bonding chamber to a vacuum level of 5 × 10⁻³Pa; raising the temperature to 200°C and maintaining that temperature for 3 minutes; applying a pressure of 5000N and then filling with nitrogen to maintain the pressure for 15 minutes; and finally releasing the pressure. This ensures a vacuum level of 5 × 10⁻³Pa, a bonding temperature of 200°C, and a bonding pressure of 5000N within the bonding chamber, minimizing the impact of these factors on the cooling rate.

[0051] In summary, the present invention solves the problem of how to strike a balance between production efficiency and bonding quality during the temporary bonding process of EMC and glass, determines the appropriate cooling rate range for EMC and glass bonded wafers, and emphasizes that it is crucial to control the cooling rate of the upper and lower heating plates during the cooling stage. This is of great significance for the bonding of wafers with thermal mismatch and lattice mismatch, and is directly related to production efficiency and bonding yield.

[0052] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A test method for determining the optimal cooling rate for low-temperature temporary bonding of an EMC wafer to a glass wafer, characterized in that: The test method comprises the following steps: S1, the vacuum degree in the bonding chamber is reduced to 5×10 -3 Pa; raise the temperature of the upper and lower heating plates to 200°C and maintain the temperature for 3 minutes; S2, applying a pressure of 5000N to the bonding chamber and filling it with nitrogen to maintain the pressure for 15 minutes before releasing the pressure; S3, cooling the upper and lower heating plates from 200°C to 80°C at a preset cooling rate; testing the bonding quality at the wafer bonding interface; S4, adjusting the cooling rate multiple times, and repeating steps S1 to S3 after each adjustment of the cooling rate; S5, combining the bonding quality at the wafer bonding interface corresponding to different cooling rates and the production time to determine the optimal cooling rate for low-temperature temporary bonding.

2. The test method for determining the optimal cooling rate for low-temperature temporary bonding of an EMC wafer and a glass wafer according to claim 1, characterized in that: The bonding chamber meets the processing conditions of 8-inch wafer temporary bonding, eutectic bonding, and thermal compression bonding.

3. The test method for determining the optimal cooling rate for low-temperature temporary bonding of an EMC wafer to a glass wafer according to claim 1, characterized in that: The cooling rates were set to natural cooling, 5°C / min, 1.13°C / min, and 3°C / min, respectively.

4. The test method for determining the optimal cooling rate for low-temperature temporary bonding of an EMC wafer to a glass wafer according to claim 1, characterized in that: Step S5 further comprises: The bonding quality at the wafer bonding interface is detected and determined based on the bonding surface integrity rate at different cooling rates; Determine the rationality of the wafer bonding cooling rate based on the bonding quality, and narrow the range of the optimal cooling rate for wafer temporary bonding; In the range of the optimal cooling rate for temporary wafer bonding, calculate the weighted sum of production time and bonding quality using the following formula: Q=0.7*X BQ +0.3*X PT 1) Where Q represents the cooling quality factor; XBQ represents the bonding quality factor; XPT represents the production aging factor; the solution formula for the production aging factor XPT is as follows: X PT =and -λt 2) In the formula, λ represents the time decay coefficient, and t represents the production time; According to the calculated Q value, one of the cooling rates is selected as the optimal cooling rate.

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