Target material for reducing defects of photomask substrate and processing method thereof
By treating the target material with ion implantation, its hardness and uniformity are improved, which solves the problem of photomask substrate defects caused by unstable target discharge and achieves high-yield photomask manufacturing.
Patent Information
- Application Number
- CN202410567657.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-09
- Publication Date
- 2025-12-26
AI Technical Summary
During the manufacturing process of photomask substrates, the low discharge stability of the target material leads to particle defects during thin film deposition. In particular, when silicon-containing targets are used for film deposition, particles mixed into the film result in a high defect rate, affecting the miniaturization effect of the photomask pattern.
The target material is treated by ion implantation to achieve a Vickers hardness of over 1000 Hv. This process includes steps such as vacuuming, argon preheating, and nitrogen and hydrogen reaction to improve the mechanical properties and uniformity of the target material, avoid vacuum chamber contamination, and enhance discharge stability.
It reduced the defect rate of the photomask substrate, improved the product yield, and shortened the photomask manufacturing process.
Smart Images
Figure CN121204625A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and in particular to a target material for reducing defects in photomask substrates and a method for processing the same. Background Technology
[0002] In the manufacturing process of integrated circuits, photomasks are used for mass production. A thin film is formed on the photomask substrate by sputtering a target containing transition elements, and then a photomask pattern is formed on this film. However, targets have the problem of low discharge stability, easily generating particles during film deposition. These particles mixed into the film cause defects, especially when using silicon-containing targets, where the discharge becomes unstable, and particles easily mix with the film layer during photomask substrate deposition. As photomask patterns become increasingly refined, the tolerance for defects becomes extremely stringent, and the problem of increased defect rates caused by particles becomes more pronounced. Particles refer to fine particles with diameters of, for example, 0.3 μm to 2 μm or larger. When particles are mixed into the film layer, they detach from the film layer during post-deposition cleaning, forming pinholes or semi-pinhole defects. This defect leads to pattern gaps, known as white defects, during the patterning process. Summary of the Invention
[0003] The purpose of this invention is to provide a target material and a processing method for reducing defects in a photomask substrate. When the target material processed by this invention forms a thin film on the photomask substrate, the defect problem can be improved and the defect rate can be reduced.
[0004] To achieve the above objectives, the present invention provides the following technical solution:
[0005] A method for treating a target material to reduce defects in a photomask substrate involves treating the target material using an ion implantation method, resulting in a Vickers hardness of over 1000 Hv for the treated target material.
[0006] There are two ways to improve the mechanical strength of materials: one is to manufacture completely defect-free metal crystals, but with current technology, even metal thin films are difficult to achieve this; the other is to increase the defect density of the lattice in the material as much as possible, creating more obstacles to hinder the movement of dislocation bands in the metal material. When the defect density reaches a certain level, it becomes relatively difficult to add new defects, thus improving the strength of the material. This invention utilizes this principle, treating the target material using an ion implantation method, which can achieve a Vickers hardness of over 1000 Hv. Using this target material enables the fabrication of photomasks with high yield and significantly reduces the defect rate in semiconductor devices.
[0007] Taking nitrogen ion implantation as an example, the process includes the following steps:
[0008] S20, the vacuum chamber is evacuated to achieve the preset vacuum level.
[0009] S30, adjust the magnetic field current of the ECR microwave plasma source and the current of the microwave transmitter tube to ignite the inserted argon gas, then turn on the main power supply of the pulse voltage and set the pulse bias voltage, frequency and pulse width to use argon ions to bombard the target surface to remove surface contaminants and preheat the target surface.
[0010] S40. After the target surface temperature reaches the set preheating temperature, stop introducing argon gas and replace it with nitrogen and hydrogen gas, and maintain the target temperature at the set reaction temperature.
[0011] S50: After the set time is reached, wait for the target material temperature to drop to room temperature, then break the vacuum and remove the processed target material.
[0012] In a preferred embodiment, S10 is included before S20, in which the edge of the target material is ground into an arc shape without damaging the polished surface, cleaned and dried with nitrogen gas, and then S20 is performed.
[0013] If the target material has sharp corners or burrs, the high bias voltage during ion implantation will cause sharp discharges with the burrs, contaminating the vacuum cavity and thus preventing ion defects and pores in the target material. In the above solution, grinding the target material edge into a rounded shape can effectively prevent the vacuum cavity from being contaminated.
[0014] In a preferred embodiment, the vacuum chamber is evacuated in step S20 by: starting a mechanical pump to begin coarse evacuation, and after the vacuum level reaches a first preset value, continuing to evacuate the turbine molecular pump until a second preset value is reached.
[0015] In the above scheme, by combining coarse and fine evacuation, the efficiency of vacuuming can be improved, and the direction of gas movement can be avoided due to mutual collisions. This allows the plasma gas to move in the voltage direction, thereby improving the uniformity of the ion implantation target.
[0016] In S30, the flow rate of the introduced argon gas is controlled to be 18 SCCM~22 SCCM.
[0017] Excessive argon gas flow rate can affect the uniformity of the ion implantation target, while insufficient flow rate will prevent the cavity pressure from reaching the ideal state. In the above solution, by controlling the argon gas flow rate between 18 SCCM and 22 SCCM, both the uniformity of the ion implantation target and the required cavity pressure can be achieved.
[0018] In step S40, both nitrogen and hydrogen have a purity of 99.99% or higher. Using high-purity nitrogen and hydrogen in this method ensures the Vickers hardness of the treated target material.
[0019] In step S40, the reaction temperature is 300℃~700℃.
[0020] The higher the insertion temperature, the thicker the modified layer is formed, and the mechanical properties are improved, since the effect of heat diffusion is proportional to temperature. However, when the insertion temperature is too high, the corrosion resistance of the material will decrease with the formation of metal nitrides. In the above scheme, by controlling the reaction temperature to 300℃~700℃, both mechanical properties and corrosion resistance of the target material can be guaranteed.
[0021] The present invention also provides a target material treated by the aforementioned method for reducing defects in photomask substrates.
[0022] The beneficial effects of this invention are: the target material treated by the method of this invention can suppress the generation of defects even in reactive sputtering using gases with low discharge stability. When using a photomask substrate to manufacture a transfer photomask, a transfer photomask with fewer defects can be manufactured, improving product yield, and the defect correction process can be significantly shortened, thereby shortening the manufacturing process of the transfer photomask. Attached Figure Description
[0023] Figure 1 This is a flowchart of a method for processing a target material to reduce defects in a photomask substrate, as described in the embodiment. Detailed Implementation
[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0025] Please see Figure 1 This embodiment provides a method for processing a target material to reduce defects in a photomask substrate, including the following steps:
[0026] S10: Grind the edge of the target material into an arc shape without damaging the polished surface, clean it, and then dry it with nitrogen.
[0027] Specifically, using a polishing machine with 320-grit sandpaper, the edge of the target material is ground into an arc shape without damaging the polished surface. This prevents sharp discharges caused by high bias voltage and target morphology during ion implantation, which could contaminate the vacuum chamber and thus avoid ion defects and pores in the target material. After cleaning, the target is dried with nitrogen gas and then placed into the vacuum chamber.
[0028] It's easy to understand that if the target material itself is already arc-shaped, this step is unnecessary. Furthermore, the purpose of this step is to avoid contaminating the vacuum chamber; if the impact of vacuum chamber contamination is not considered, this step is also unnecessary.
[0029] S20, the vacuum chamber is evacuated to achieve the preset vacuum level.
[0030] This step employs a preferred method for vacuuming. Specifically: a mechanical pump is started to begin rough evacuation, and the vacuum level is maintained at 0.8 x 10⁻⁶. -2 ~1.2x10 -2 After torr, the turbine molecular pump continues to pump air up to 0.8 x 10⁻⁶. -6 ~1.2x10 -6 torr.
[0031] In this step, the initial coarse evacuation can quickly bring the vacuum level in the vacuum chamber to a certain value, thus improving the efficiency of vacuuming. After the coarse evacuation, the fine evacuation is performed to prevent the gas from changing its direction of movement due to mutual collisions, so that the plasma gas moves in the voltage direction, thereby improving the uniformity of the ion implantation target.
[0032] S30 involves placing the target material into a plasma source (i.e., plasma gas) within a vacuum chamber, and then bombarding the target surface with argon gas to remove surface contaminants and preheat the target surface.
[0033] More specifically, first, turn on the main power of the system, adjust the magnetic field current of the ECR microwave plasma source and the current of the microwave emitter tube to ignite the inserted argon gas. Turn on the main power of the pulse voltage and set the pulse bias, frequency, and pulse width to use argon bombardment to remove contaminants from the target surface and raise its temperature. The argon gas flow rate is controlled at 18 SCCM~22 SCCM to ensure stable argon gas flow, thereby improving the uniformity of ion implantation into the target and ensuring a chamber pressure of approximately 2.0 x 10⁻⁶. - 3 torr.
[0034] Experimental studies investigated surface modification of chromium, silicon wafers, and molybdenum-silicon targets via plasma-source ion implantation (PSII). Nitrogen plasma was generated by radio frequency (13.56 MHz) glow discharge and ECR microwave discharge. Substrate bias voltage and current during implantation were monitored using a high-voltage probe and current transformer. Ions were accelerated from the plasma by high-voltage pulses (typically -20 kV, 100 Hz, 50 μs) applied directly to the substrate. Surface and near-surface composition and structure were characterized using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and grazing-angle X-ray diffraction (GXRD). The results demonstrate that PSII achieves uniform ion implantation of three-dimensional targets without manipulating the target material.
[0035] S40. After the target surface temperature reaches the set preheating temperature, stop introducing argon gas and replace it with nitrogen and hydrogen gas, and maintain the target temperature at the set reaction temperature.
[0036] Specifically, after the target material is preheated to the specified process temperature, such as 150°C, the process gas is switched to a mixture of nitrogen and hydrogen, and the flow rates are controlled to be 56 SCCM and 14 SCCM (N:H=4:1), respectively. The pulse bias and frequency are also adjusted to keep the target material at 700°C.
[0037] The reaction temperature varies depending on the target material, but a typical insertion temperature range is 300℃ to 700℃. Higher insertion temperatures result in a thicker modified layer and improved mechanical properties, as heat diffusion is directly proportional to temperature. However, excessively high insertion temperatures decrease the material's corrosion resistance due to the formation of metal nitrides; for example, above 400℃, chromium targets will form CrN. Therefore, for targets made of conventional materials, an insertion temperature of 300℃ to 700℃ is recommended.
[0038] Since the thermal diffusion mechanism during high-temperature ion implantation is a crucial factor determining the thickness of the modified layer, five implantation temperatures were compared in this experiment: 300℃, 400℃, 460℃, 520℃, and 700℃. The longer the implantation time, the longer the specimen remains at high temperatures, allowing the implanted nitrogen ions to diffuse deeper, resulting in a thicker nitrogen-modified layer. Therefore, as long as no significant physical or chemical changes occur, the highest possible temperature can be used. Similarly, to increase depth, since the utilization rate of typical target materials is approximately 30%, taking a 5T (5mm) target as an example, the sheet-like target workpiece can be immersed in plasma, and a negative bias can be applied to the workpiece. This allows ions in the plasma to implant onto the workpiece surface in three dimensions, thus enabling large-area uniform surface modification even for workpieces with complex shapes, thereby saving significant time and energy.
[0039] In addition to temperature, the test examples also tested the differences in the thickness of the modified layer with various nitrogen-hydrogen ratios, such as N:H=1:3 (13sccm:37sccm), N:H=1:1 (28sccm:28sccm), N:H=1:2 (13sccm:26sccm), N:H=3:1 (37sccm:13sccm), N:H=4:1 (52sccm:13sccm), and N:H=5:1 (65sccm:13sccm). After the process was completed, a glow discharge spectrometer (GDS) was used to perform a depth analysis of nitrogen in the modified layer. The thickness of the modified layer was determined by the change in nitrogen concentration. The process parameters of each specimen and the thickness of the nitrogen modified layer formed were analyzed, and the hardness under different conditions was tested. The experimental results show that, regardless of the temperature, the highest hardness occurred in the test case with a nitrogen-to-hydrogen ratio of 4:1. Moreover, the nitrogen-to-hydrogen ratio is a key factor affecting nitrogen penetration into the bulk material. A higher nitrogen content helps nitrogen penetrate into the bulk material, resulting in an increased nitrogen concentration. The same implantation temperature means that after nitrogen ions are implanted on the surface of the specimen, their ability to diffuse inside the substrate is the same. Different nitrogen-to-hydrogen ratios represent different ion implantation capabilities.
[0040] S50: After the set time is reached, wait for the target material temperature to drop to room temperature, then break the vacuum and remove the processed target material.
[0041] Once the set time is reached, immediately shut off the pulse voltage, plasma source power supply, and hydrogen gas. After the target material temperature drops to room temperature, fill the vacuum chamber with gas to bring the pressure inside the vacuum chamber close to or the same as the ambient temperature, then remove the processed target material. Nitrogen gas can be turned off or on; if not turned off, nitrogen is used as the gas source to bring the pressure inside the vacuum chamber close to or the same as the ambient temperature, facilitating target material removal.
[0042] The higher the temperature, the shorter the processing time required. Although longer processing time results in better thickness and hardness, the benefits of too long a time are not significant. Therefore, a processing time of 600 to 1000 seconds is ideal, meaning the optimal process time setting is 600-1000 seconds.
[0043] Both nitrogen and hydrogen must be 99.99% or higher in purity to avoid affecting the Vickers hardness of the treated target material due to insufficient purity.
[0044] S60, a glow discharge spectrometer (GDS) was used to perform surface depth profile analysis on the modified specimen to determine the thickness of the modified layer. A Vickers hardness tester was used to test the hardness of the target material, with the load ranged from 1 kg to 50 kg. The ion-placed target material was first cleaned with alcohol, and an appropriate load of 10 kg was selected for the Vickers hardness tester.
[0045] Experimental results confirm that the Vickers hardness of the target material obtained after the S10-S50 treatment can reach over 1100 Hv. However, to ensure product yield, a more reasonable approach is to test the hardness using a hardness tester after the S50 treatment. Only targets that pass the test are used for subsequent photomask manufacturing. If any targets do not meet the hardness requirements, a secondary treatment using the above method can be performed.
[0046] It should be noted that, based on specific experimental examples, this embodiment only illustrates the process of treating the target material using nitrogen ion implantation. In practice, other ion implantation methods can also be used, such as Plasma source / immersion ion implantation (PSI / PI) and Metal vapor vacuum arcsource ion implantation (MEVVA). Using ion implantation to treat the target material can achieve a Vickers hardness of over 1000 Hv.
[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for processing a target material to reduce defects in a photomask substrate, characterized in that, The target material was treated using an ion implantation method, resulting in a Vickers hardness of over 1000 Hv.
2. The method for processing the target material for reducing defects in a photomask substrate according to claim 1, characterized in that, Includes the following steps: S20, the vacuum chamber is evacuated to achieve the preset vacuum level. S30, adjust the magnetic field current of the ECR microwave plasma source and the current of the microwave transmitter tube to ignite the inserted argon gas, then turn on the main power supply of the pulse voltage and set the pulse bias voltage, frequency and pulse width to use argon ions to bombard the target surface to remove surface contaminants and preheat the target surface. S40. After the target surface temperature reaches the set preheating temperature, stop introducing argon gas and replace it with nitrogen and hydrogen gas, and maintain the target temperature at the set reaction temperature. S50: After the set time is reached, wait for the target material temperature to drop to room temperature, then break the vacuum and remove the processed target material.
3. The method for processing the target material for reducing defects in a photomask substrate according to claim 2, characterized in that, Before S20, there is also S10, which grinds the edge of the target material into an arc shape without damaging the polished surface, cleans it, dries it with nitrogen, and then performs S20.
4. The method for processing the target material for reducing defects in a photomask substrate according to claim 2, characterized in that, The vacuum process in S20 includes: starting a mechanical pump to begin rough evacuation, and after the vacuum level reaches a first preset value, continuing to pump air with a turbine molecular pump until a second preset value is reached.
5. The method for processing the target material for reducing defects in a photomask substrate according to claim 2, characterized in that, In S30, the flow rate of the introduced argon gas is controlled to be 18 SCCM~22 SCCM.
6. The method for processing the target material for reducing defects in a photomask substrate according to claim 2, characterized in that, In S40, the purity of both nitrogen and hydrogen is 99.99% or higher.
7. The method for processing the target material for reducing defects in a photomask substrate according to claim 2, characterized in that, In S40, the ratio of nitrogen to hydrogen is 3:1 to 5:
1.
8. The method for processing the target material for reducing defects in a photomask substrate according to claim 6, characterized in that, In step S40, the reaction temperature is 300℃~700℃.
9. The method for processing the target material for reducing defects in a photomask substrate according to claim 2, characterized in that, The process includes S60 after S50, in which a hardness tester is used to test the hardness of the processed target material.
10. A target material treated by the method for reducing defects in a photomask substrate as described in any one of claims 1-9.