Electron beam evaporation of gold thin films suitable for liftoff lift-off process

Abstract

The application discloses a kind of electronic beam evaporation gold film methods suitable for Liftoff stripping process, using the small crucible less than the standard crucible site of electronic beam evaporation equipment specification to carry out evaporation operation, the volume of the small crucible is 1 / 3-5 / 6 corresponding standard crucible volume.Small specification crucible is used, and the volume of the small specification crucible is small, and the heat capacity is low, the energy input by the electron beam can be quickly concentrated in the gold raw material in the crucible, so that the gold raw material can quickly reach the evaporation temperature and form a stable evaporation gas flow, and a high evaporation rate can be achieved at a lower electron beam evaporation power, so that the evaporation rate can be 10-20 times that of the existing process, greatly shortening the time required for evaporation, improving production efficiency, and significantly reducing the continuous heat input to the chip, reducing the influence on the performance of photoresist, facilitating subsequent photoresist stripping operation.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication technology, specifically relating to an electron beam evaporation method for depositing gold thin films suitable for the Liftoff lift-off process. Background Technology

[0002] In the Liftoff process, the evaporation preparation of gold films is one of the key steps. Currently, the evaporation rate of electron beam evaporation films is generally 1-2 nm / s, and can reach 3-5 nm / s. Preparing a 1 μm thick gold film often requires a long evaporation time of 20-30 minutes, resulting in low production efficiency and making it difficult to meet the needs of large-scale industrial production.

[0003] During prolonged vapor deposition, the continuous energy output of the electron beam causes the chip temperature to rise, exceeding 100°C, and in some devices with limited target-substrate distance, even exceeding 200°C. However, the photoresist used in the liftoff process is extremely temperature-sensitive. High temperatures can cause thermal deformation and cross-linking curing of the photoresist, thus destroying its original morphology. This not only affects the quality of the gold film and the dimensional morphology of the gold electrodes, but also makes it difficult to completely remove the photoresist in subsequent liftoff processes. Residual photoresist severely impacts the electrical, optical, and reliability properties of the device, significantly reducing product yield. Summary of the Invention

[0004] The purpose of this invention is to provide an electron beam evaporation method for gold thin film deposition suitable for Liftoff stripping process, so as to solve the problems of low deposition efficiency, high chip temperature and difficulty in ensuring product quality in existing methods.

[0005] This invention is achieved through the following technical solution: An electron beam evaporation method for gold thin film deposition suitable for Liftoff stripping process uses a small crucible smaller than the standard crucible of the electron beam evaporation equipment for the evaporation operation. The volume of the small crucible is 1 / 3 to 5 / 6 of the corresponding standard crucible volume.

[0006] In some embodiments of the present invention, when the evaporation rate reaches 20 nm / s, the corresponding electron beam evaporation power does not exceed 30%.

[0007] In some embodiments of the present invention, the small crucible is made of boron nitride, tungsten, or molybdenum.

[0008] In some embodiments of the present invention, the small crucible is made of graphite.

[0009] In some embodiments of the present invention, the vapor deposition operation employs a stepped vapor deposition method, including: First stage: Gradually increase the evaporation rate from 1 nm / s to the first evaporation rate, continue evaporation for a first set time, and the electron beam evaporation power corresponding to the first evaporation rate is 20%-30%; The second stage involves controlling the evaporation rate at the first evaporation rate and continuing to evaporate for a second set time until the desired thickness of the evaporated gold film is achieved, and the second set time is greater than the first set time.

[0010] In some embodiments of the present invention, the first evaporation rate is 20 nm / s.

[0011] In some embodiments of the present invention, the vapor deposition operation further includes a third stage in which the vapor deposition rate is reduced to 1-5 nm / s and the vapor deposition is continued for a third set time.

[0012] In some embodiments of the present invention, the flow rate of the cooling circulating water is controlled during the vapor deposition process so that the flow rate of the cooling circulating water is less than that when using a standard crucible.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention employs a small-sized crucible with a small volume and low heat capacity. The energy input from the electron beam can be quickly concentrated on the gold material inside the crucible, enabling the gold material to quickly reach the evaporation temperature and form a stable evaporation gas flow. It can achieve a high evaporation rate with a relatively low electron beam evaporation power, making the evaporation rate 10-20 times that of existing processes. This significantly shortens the evaporation time, improves production efficiency, and significantly reduces the continuous heat input to the chip, minimizing the impact on photoresist performance and facilitating subsequent photoresist stripping operations.

[0014] The present invention, combined with the stepped evaporation method, effectively ensures the uniformity of gold film thickness and surface roughness at high evaporation rates, thus well meeting the quality requirements of device processing for gold thin films.

[0015] The method of this invention can be widely applied to semiconductor chip manufacturing, microelectromechanical system device fabrication, optoelectronic device processing and other fields, and is especially suitable for the fabrication of precision electronic devices with high requirements for the integrity of photoresist morphology and low chip temperature tolerance. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0017] Currently, for electron beam evaporation of gold thin films, some methods aim to increase the evaporation rate by optimizing electron beam focusing parameters and adjusting vacuum levels. However, the increase in evaporation rate is relatively small and can easily lead to poor uniformity and increased surface roughness of the gold film. Additionally, some methods employ multi-source co-evaporation technology, but this requires complex and costly equipment and demands extremely high precision in process parameter control. For example, setting up a zoned heating device within a standard crucible to concentrate energy on localized gold materials, while simultaneously confining the electron beam with a magnetic field to improve energy utilization, can increase the evaporation rate to around 15 nm / s and control the chip temperature below 60°C. However, this method suffers from complex equipment modifications, high costs, and difficulty in adjusting magnetic field confinement parameters, resulting in poor versatility and economic efficiency.

[0018] This invention, by improving crucible specifications and electron beam evaporation power, combined with a specific evaporation method, can effectively solve the problems of low evaporation rate, high chip temperature, and poor evaporation quality, with minimal impact on photoresist, and can effectively improve film quality and processing efficiency.

[0019] In some embodiments of the present invention, unconventional crucibles are used, which can achieve high evaporation rates at low electron beam power, breaking through the upper limit of evaporation rates of conventional schemes. The evaporation time is greatly shortened, and the impact on chip temperature is small. The chip temperature can be controlled at a low temperature, avoiding the problem of high chip temperature caused by long-term evaporation.

[0020] Specifically, the method of the present invention uses a small crucible with a specification smaller than that of the standard crucible in the electron beam evaporation equipment. The volume of the small crucible is 1 / 3 to 5 / 6 of the volume of the standard crucible. Different electron beam evaporation equipment is usually equipped with standard crucibles of corresponding specifications. The size and volume of the standard crucibles configured in different electron beam evaporation equipment will be different.

[0021] Research has shown that the specifications of the crucible directly affect the electron beam evaporation power at the same evaporation rate. In existing electron beam evaporation equipment, when using a standard crucible, the electron beam evaporation power needs to reach 60%-70% to achieve a evaporation rate of 1 nm / s, which makes it impossible to achieve a higher evaporation rate.

[0022] In this invention, a small crucible smaller than the standard crucible size of an electron beam evaporation device is used. To achieve a deposition rate of 1 nm / s, the electron beam evaporation power is less than 10%. When the electron beam evaporation power is around 20%, the deposition rate can reach 20 nm / s.

[0023] Utilizing a small, high-temperature resistant crucible, its compact size and low heat capacity allow for rapid concentration of electron beam energy onto the gold material within the crucible. This enables the gold material to quickly reach its evaporation temperature and form a stable evaporation gas flow. Compared to standard crucibles, this method achieves a high deposition rate at a lower electron beam evaporation power, reaching rates 10-20 times higher than existing methods. For example, the deposition time for a 1µm thick gold film can be reduced to 3-5 minutes, significantly improving production efficiency and meeting the demands of industrial-scale mass production.

[0024] According to the heat conduction formula Q=cmΔT (where Q is heat, c is specific heat capacity, m is mass, and ΔT is temperature change), since the small crucible has a small volume, the mass of the gold material in the small crucible is much smaller than that in the standard crucible. Therefore, under the same evaporation power, less heat is required to heat the gold material, and the time required for vapor deposition is greatly reduced, which can significantly reduce the continuous heat input of the electron beam to the chip.

[0025] The small crucible is made of high-purity boron nitride, tungsten, and molybdenum to ensure high temperature resistance and prevent chemical reaction with gold.

[0026] Small crucibles can also be made of high-purity graphite. Graphite's high-temperature resistance and chemical stability can also meet the requirements of evaporation deposition, and its better thermal conductivity allows for a further increase in the heating rate of the gold raw material. Under the same evaporation power, the deposition rate can be further increased to 20 nm / s. However, after long-term use, trace amounts of carbon may be incorporated into the gold film from the graphite crucible. Therefore, high-temperature pretreatment of the crucible is necessary before use to reduce carbon contamination.

[0027] The small crucible is fixedly installed at the center of the crucible position in the electron beam evaporation equipment, and the stability of the installation of the small crucible is ensured to avoid affecting the uniformity of film formation due to positional displacement during the evaporation process.

[0028] To pre-treat the chip to be vapor-deposited, place the chip with the photoresist pattern onto the sample holder inside the evaporation chamber, ensuring the chip surface is clean and free of impurities. Close the evaporation chamber and evacuate to 1×10⁻⁶. -5 The following high vacuum environment is used to avoid the influence of air on the vapor deposition process.

[0029] The method of this invention controls the vapor deposition process and adopts a stepped vapor deposition method, including the following steps: The first stage involves gradually increasing the electron beam evaporation power, raising the deposition rate from 1 nm / s to 20 nm / s. The maximum required electron beam evaporation power is approximately 25%, and this process is continued for 10-20 seconds, forming a dense gold film of 50-100 nm thickness on the chip surface as the underlayer. The duration of this continuous deposition refers to the time required to gradually increase the deposition rate from 1 nm / s to 20 nm / s.

[0030] This stage uses a lower evaporation rate to ensure adhesion between the gold film and the chip substrate, while avoiding gold particle splashing caused by an initial high evaporation rate.

[0031] The second stage: stabilize the evaporation rate at 20 nm / s. Since the small crucible has a small heat capacity, the energy concentration efficiency is higher. At this time, the corresponding electron beam evaporation power does not exceed 30%. Continue evaporation for 35-45 seconds to make the gold film thickness reach 800-900 nm.

[0032] This stage is the main evaporation stage for the gold film.

[0033] The third stage involves reducing the evaporation rate to 1-5 nm / s, at which point the required electron beam evaporation power is less than 10%, and continuing evaporation for 10-20 seconds. In this stage, the evaporation rate is rapidly reduced from 20 nm / s to 1-5 nm / s. The continuous evaporation time here includes the time required for the evaporation rate to decrease to the target evaporation rate and the time spent evaporating at the target evaporation rate.

[0034] This stage is mainly used to trim the surface of the gold film to compensate for any minor unevenness or defects that may occur on the surface of the formed gold film in the second stage, so as to ensure the quality of the formed surface of the gold film.

[0035] Reduce the flow rate of cooling circulating water during the vapor deposition process, depending on the equipment specifications, to prevent the crucible temperature from dropping too quickly during the vapor deposition process.

[0036] After completing the above vapor deposition operation, the electron beam is turned off, the vacuum environment of the evaporation chamber is maintained, and the chip is removed after it cools naturally to room temperature and then proceeds to the subsequent stripping process.

[0037] By adopting a stepped evaporation method, a lower evaporation rate is used in the first stage to avoid instantaneous high temperatures caused by direct impact from high power. This allows the chip temperature to be controlled below 50°C throughout the evaporation process, which is far below the thermal deformation temperature of the photoresist. This avoids thermal damage to the photoresist, ensures the integrity of the original morphology of the photoresist and the normal progress of subsequent stripping operations, and significantly improves the yield of chip devices.

[0038] The evaporation process employs a three-stage stepped evaporation method, which effectively solves the problems of poor gold film uniformity and high roughness that may result from using a purely high evaporation rate. In the first stage, a low evaporation rate is used to form the underlayer, ensuring a tight bond between the gold film and the chip substrate and reducing initial film defects. In the second stage, a high evaporation rate is used, which, while ensuring evaporation efficiency, results in better directionality of gold atom deposition due to the more concentrated and stable evaporation gas flow from the small crucible. This ensures good gold film formation quality even at high evaporation rates. In the third stage, a low evaporation rate is used to smooth the gold film surface, resulting in a gold film thickness uniformity error of less than ±5% and a surface roughness Ra of less than 5 nm, which can well meet the quality requirements of devices for gold films.

[0039] The stepped evaporation method can be adjusted according to the target gold film thickness and chip characteristics. For example, for a 0.5µm thick gold film, a two-stage evaporation method can be used, with the maximum evaporation rate appropriately reduced. For example, if the maximum evaporation rate is set to 5nm / s, only the first and second stages are used. The entire evaporation process does not exceed 3 minutes, and the chip temperature does not exceed 50℃. This method can also ensure the quality of the gold film and the integrity of the photoresist.

[0040] The specific process and corresponding effects of the method of the present invention will be described in detail below with reference to specific embodiments and comparative examples. Example

[0041] In this embodiment, the Genesis Winner MEB-600 electron beam evaporation coating machine is used. The standard crucible specifications of the equipment are: upper outer diameter 34.3mm, lower outer diameter 27.9mm, and height 20mm. The chip to be evaporated is a silicon-based chip with photoresist pattern, and the thickness of the gold film evaporated on the chip is 1µm.

[0042] The steps of the electron beam evaporation method for gold thin films are as follows: S01. A small crucible is used, with a volume of 1 / 3 of that of a standard crucible, and the material of the small crucible is high-purity boron nitride. S02. Fix the small crucible at the center of the crucible position in the electron beam evaporation coating machine; S03. Pre-treat the chip to be vapor-deposited: Place the chip with the photoresist pattern on the sample holder inside the evaporation chamber, ensuring the chip surface is clean and free of impurities. Close the evaporation chamber and evacuate to 1×10⁻⁶. -5 The following high vacuum environments; S04. Evaporation process, including: S041. Gradually increase the evaporation rate from 1 nm / s to 20 nm / s and continue evaporation for 15 s; the corresponding electron beam evaporation power is less than 25%; S042. Stabilize the evaporation rate at 20 nm / s and continue evaporation for 45 s; the corresponding electron beam evaporation power is about 30%. S043. Reduce the evaporation rate to 1 nm / s and continue evaporation for 20 s. S05. Turn off the electron beam, maintain the vacuum environment of the evaporation chamber, and remove the chip after it has cooled to room temperature naturally.

[0043] In this embodiment, the evaporation time is 80s, the maximum chip temperature is 50℃, the gold film uniformity error is less than ±5%, and the gold film surface roughness is less than 5nm. Example

[0044] This embodiment uses the same coating machine and the same small crucible as in Embodiment 1. The difference from Embodiment 1 is that the parameters of the vapor deposition operation steps are adjusted. The specific operation steps of the vapor deposition operation are as follows: S041. Gradually increase the evaporation rate from 1 nm / s to 20 nm / s and continue evaporation for 20 s. S042. Stabilize the evaporation rate at 20 nm / s and continue evaporation for 35 s. S043. Reduce the evaporation rate to 5 nm / s and continue evaporation for 10 s. In this embodiment, the evaporation time is 65s, the maximum chip temperature is 50℃, the gold film uniformity error is less than ±5%, and the gold film surface roughness is less than 5nm.

[0045] Comparative Example 1 In the comparative example, the same coating machine as in Example 1 was used, and a conventional coating scheme was adopted. The evaporation rate was 1 nm / s, and the corresponding electron beam evaporation power reached 68%. The evaporation was carried out for 17 minutes, and the highest temperature of the chip reached 260°C. The photoresist on the chip showed visible delamination.

[0046] The comparison shows that the present invention has significant advantages in terms of evaporation rate and chip temperature control. The uniformity and surface roughness of the prepared gold film can reach the same quality as slow evaporation, with little impact on photoresist performance. The time of the entire evaporation operation is shortened from about 20 minutes to less than 5 minutes, and the photoresist stripping time is shortened from 2-3 hours to less than 1 hour.

[0047] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0048] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0049] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0050] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. An electron beam evaporation method for depositing gold thin films suitable for Liftoff lift-off processes, characterized in that, The vapor deposition operation is performed using a small crucible with a size smaller than that of the standard crucible in the electron beam evaporation equipment. The volume of the small crucible is 1 / 3 to 5 / 6 of the volume of the corresponding standard crucible.

2. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 1, characterized in that, When the evaporation rate reaches 20 nm / s, the corresponding electron beam evaporation power does not exceed 30%.

3. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 1, characterized in that, The small crucible is made of boron nitride, tungsten, and molybdenum.

4. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 1, characterized in that, The small crucible is made of graphite.

5. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 1, characterized in that, The vapor deposition operation employs a stepped vapor deposition method, including: First stage: Gradually increase the evaporation rate from 1 nm / s to the first evaporation rate, continue evaporation for a first set time, and the electron beam evaporation power corresponding to the first evaporation rate is 20%-30%; The second stage involves controlling the evaporation rate at the first evaporation rate and continuing to evaporate for a second set time until the desired thickness of the evaporated gold film is achieved, and the second set time is greater than the first set time.

6. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 5, characterized in that, The first evaporation rate is 20 nm / s.

7. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 5, characterized in that, The vapor deposition operation also includes a third stage, in which the vapor deposition rate is reduced to 1-5 nm / s and the vapor deposition is continued for a third set time.

8. The electron beam evaporation method for gold thin film deposition suitable for Liftoff lift-off process according to claim 1, characterized in that, During the vapor deposition process, the flow rate of the cooling circulating water is controlled to be lower than that when using a standard crucible.