A method for improving pattern resolution and uniformity in laser thermal mask lithography process

Abstract

The application provides a method for improving the resolution and uniformity of a photoetching pattern in a laser thermal mask photoetching process. The application uses a laser thermal mask photoetching technology to perform pre-exposure on a chalcogenide inorganic phase-change film. The resolution of an exposed pattern is improved by precisely controlling the initial temperature of the film sample. An infrared temperature sensor is used to monitor the temperature of an exposure area in real time during the exposure process, and a temperature feedback system is used to precisely control the temperature of a moving table to improve the uniformity of the exposed pattern. The temperature of the sample is controlled before exposure to keep it at a preset temperature, and the temperature is precisely controlled in real time during the exposure process to stabilize the temperature of the exposure area within a fluctuation range. Compared with the prior art, the application compensates for the defects of the light-thermal field control accuracy during the exposure process, improves the resolution and uniformity of the writing, and the higher initial temperature makes the crystallization degree of the crystallization area of the phase-change material higher, which is beneficial to subsequent development and other processes.

Description

Technical Field

[0001] This invention relates to the field of laser thermal lithography, and in particular to a method for improving the pattern resolution and uniformity of laser thermal lithography processes. Background Technology

[0002] In the field of photolithography, photolithography is mainly divided into two categories based on the type of photoresist used: optical photoresist and thermal photoresist. However, optical photoresist is mostly organic photoresist, and its macromolecular structure is gradually becoming unsuitable for the increasingly stringent roughness requirements. On the other hand, thermal photoresist is mostly inorganic material. When the temperature exceeds the threshold, the physical properties of the material change, so it is not limited by the optical diffraction limit. This allows the writing resolution to be only a fraction of the spot size or even a dozen times smaller. It also has advantages such as simple process steps and wide-band response, and has broad application prospects in the chip manufacturing industry.

[0003] Today, due to the high demands on integrated circuit processing speed, the resolution requirements for photolithography processes are also increasing. Although hot-strip lithography has the advantage of not being limited by the diffraction limit, further improving exposure resolution is fraught with difficulties due to the effects of heat accumulation and diffusion. Currently, the modulation precision of laser power and pulse width during exposure is insufficient, limited by the control precision of the exposure equipment in hot-strip lithography processes, thus restricting the control precision of the photothermal field. Therefore, developing new hot-strip lithography processes and proposing new exposure strategies are particularly important for the development of hot-strip lithography technology. Summary of the Invention

[0004] This invention addresses the problem of insufficient exposure resolution and uniformity in hot-mold lithography by proposing a novel and effective hot-mold lithography method to improve writing resolution and crystallization degree in the crystallized region. Based on existing hot-mold lithography exposure processes, the method modifies the exposure strategy by adding new temperature control techniques during exposure to achieve more flexible and precise temperature field control than simple laser exposure, thereby improving resolution and crystallization degree. It also offers advantages such as simple process and reduced cost.

[0005] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0006] A method for improving the resolution and uniformity of patterns in a hot-molded photolithography process, the method comprising the following steps:

[0007] S1. The substrate material is ultrasonically cleaned in a water bath for 10-30 minutes in sequence with acetone, anhydrous ethanol and ultrapure water. The water bath temperature for ultrasonic cleaning is 28-60℃. Then it is dried with high-pressure nitrogen gas with a purity of more than 99.9%.

[0008] S2. To prepare an inorganic phase change thin film with a thickness error of less than 5%, a 30–50 nm thick thermal stencil photoresist layer is deposited on the substrate using high-vacuum magnetron sputtering. This stencil is then rotated at a certain angle to deposit another 30–50 nm thick thermal stencil photoresist layer. The rotation angle is determined based on the relative position of the sample to be coated and the target material. The base vacuum of the high-vacuum magnetron sputtering system is controlled at 5 × 10⁻⁶. -4 Below Pa, the sputtering power is 160-200W, the working gas is argon, and the gas flow rate is 60-90 sccm;

[0009] S3. Place the coated sample onto the displacement stage of the maskless laser thermal lithography system and control the stage temperature to reach the preset temperature, which is 25-160℃. This preset temperature is related to the crystallization threshold temperature of the inorganic phase change film and the temperature rise after the laser interacts with the film sample at the corresponding power.

[0010] S4. Use an infrared temperature sensor to observe the sample surface temperature in real time. Once the temperature of the sample after coating is consistent with the temperature of the displacement stage, start the exposure operation.

[0011] S5. The coated sample is exposed using a maskless laser thermal lithography system. The infrared temperature sensor is used to monitor the center temperature of the exposed area on the sample surface in real time. The laser power is controlled so that the temperature of the exposed center of the coated sample exceeds the crystallization threshold temperature of the inorganic phase change thin film by 10-30°C. During the exposure process, a temperature control feedback system consisting of an infrared temperature sensor, a displacement stage heating plate, and a temperature control module in the maskless laser thermal lithography system is used to keep the temperature difference between the exposure center of the sample and the expected exposure center temperature less than 1%.

[0012] S6. Selective wet etching is performed on the exposed sample using a developer. Due to the different dissolution rates of amorphous and crystalline structures in the developer, an etching ratio is generated, forming an inorganic thermal photoresist thin film pattern layer with micro-nano patterned structure.

[0013] Preferably, the substrate material in step S1 is a silicon dioxide sample.

[0014] Preferably, in step S2, the hot-mold photoresist is a sulfide-based inorganic phase change material film AgInSbTe, and the rotation angle is 90 degrees, 180 degrees, or 270 degrees.

[0015] Preferably, the heating plate on the moving platform in step S3 is made of copper.

[0016] In step S4, keeping the sample temperature consistent with the displacement stage temperature means that the temperature difference between the sample center and the displacement stage setting temperature is less than 1%, and the temperature difference between the sample edge and the sample center is also less than 1%.

[0017] Preferably, in step S5, the exposure uses a wavelength of 405nm, the laser spot center temperature is 185-210℃, the exposure power is related to the substrate heating temperature, and is 0.7mW at 45-50℃ or 0.6mW at 65-70℃, the laser pulse is 25ns, and the sample exposure center temperature fluctuation range is less than 1%.

[0018] Preferably, in step S6, the developing solution is a 17% ammonium sulfide aqueous solution, the developing time is 3-5 minutes, and the developing temperature is 20-28°C.

[0019] Compared with the prior art, the technical effects of the present invention are as follows:

[0020] 1. By controlling the sample temperature before exposure, the defects in the precision of photothermal field control during exposure are compensated, thereby improving the writing resolution;

[0021] 2. A new temperature control method was added during the exposure process, which solved the problem that the sample surface temperature was solely determined by the laser power, and improved the uniformity of the exposure pattern;

[0022] 3. Higher initial temperatures result in a higher degree of crystallization in the crystallization region of the phase change material, which is beneficial for subsequent processes such as development. Attached Figure Description

[0023] Figure 1 This invention provides a schematic diagram of a process for improving pattern resolution and uniformity based on laser thermal lithography technology.

[0024] Figure 2 This invention provides a process flow diagram for improving pattern resolution and uniformity based on laser thermal lithography technology;

[0025] Figure 3 Comparison diagram of the effects of the process of this invention and existing traditional processes;

[0026] (a) The highest resolution that can be achieved by traditional laser thermal lithography is 141 nm;

[0027] (b) The optimized process achieves a resolution of 112nm and a high degree of crystallization;

[0028] (c) Traditional laser thermal lithography process has a maximum resolution of 149nm for linear exposure and a linear roughness of 15.25nm.

[0029] (d) After process optimization, the linear exposure resolution is 127nm and the linear roughness is 10.9nm. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments and accompanying drawings, but these should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1:

[0032] like Figure 1 , Figure 2 and Figure 3 As shown in a and 3b, a method for improving the resolution and uniformity of patterns in a hot-molded photolithography process includes the following steps:

[0033] S1. The SiO2 substrate with a diameter of 30 mm was ultrasonically cleaned in a water bath for 30 min in sequence with acetone, anhydrous ethanol and ultrapure water, while controlling the water bath temperature at 40℃. Then it was dried with high-pressure nitrogen gas with a purity of 99.9%.

[0034] S2. To prepare a uniform inorganic phase transition thin film, a 30 nm thick AgInSbTe hot-mode photoresist layer was first deposited on a cleaned SiO2 substrate using high-vacuum magnetron sputtering technology for 44 s. Then, the sample was rotated 90 degrees and another 40 nm thick AgInSbTe hot-mode photoresist layer was deposited for 55 s. The base vacuum of the high-vacuum magnetron sputtering system was controlled at 5 × 10⁻⁶. -4 The sputtering power is 200W, the working gas is Ar, the gas flow rate is 90sccm, and the turntable speed is 5r / min. The two-step coating process increases the uniformity of film thickness compared with the traditional coating process.

[0035] S3. Precisely control the initial temperature of the thin film sample to make the uniformity of subsequent crystallization higher. Place the coated sample on the displacement stage of the maskless laser thermal lithography system, turn on the heating switch of the heating plate on the displacement stage, set the heating temperature of the heating plate of the displacement stage to 70°C in the temperature control module of the maskless laser thermal lithography system, and use an infrared temperature sensor to observe whether the temperature of the displacement stage has reached the preset value.

[0036] S4. Use an infrared temperature sensor to observe the sample surface temperature in real time. The infrared sensor feeds the temperature back to the exposure system in real time. Wait for the temperature of the coated sample to be consistent with the preset value of the displacement stage (with a difference of less than 1%) before starting the exposure operation. At the same time, the infrared temperature sensor keeps detecting the sample surface temperature in real time.

[0037] S5. Laser thermolithography exposure is performed on a SiO2 substrate with a 405nm wavelength laser beam deposited with AgInSbTe chalcogenide phase change material film. The coarse adjustment motor is used to adjust the distance between the objective lens and the sample surface so that it is near the focal plane of the objective lens. The step of the coarse adjustment motor is set to 32 pulses (250ns), and the FES value of the focal plane position feedback is -0.08. The red light tracking module is turned on, and the piezoelectric ceramic position is adjusted to the center so that it can track the focal plane to the maximum extent during the exposure process. The stage is moved to the position to be exposed, and the stage moving speed is set to 1mm / s, and the return speed is 10mm / s. m, axis changing speed 0.1mm / s, temperature control system turned on, infrared temperature sensor keeps real-time detection of sample surface temperature and feeds back to temperature controller, set sample exposure center temperature 200℃, temperature control feedback system composed of heating plate, infrared detector, and temperature control module of maskless laser thermal lithography system automatically adjusts the temperature of heating plate of displacement stage to keep sample exposure center temperature at 198~202℃ (fluctuation range 1%), set mirror rotation speed 3000 faces / s, laser power 0.6mW, laser pulse width 25ns, laser period 250ns, duty cycle 1:10;

[0038] S6. Selective wet etching of the exposed phase change film was performed using a 17.5% ammonium sulfide concentrate as the developer, with a development temperature of 23°C and a development time of 5 min.

[0039] Traditional laser thermal lithography, under room temperature conditions, with a laser power of 0.9mW and a pulse width of 25ns, can achieve a maximum exposure resolution of 141nm. When the power is further reduced, the temperature will not reach the crystallization threshold temperature, and crystallization will not occur. The optimized process in this embodiment can achieve a maximum exposure resolution of 112nm and a high degree of crystallization, which improves both resolution and degree of crystallization compared with the traditional process.

[0040] Example 2:

[0041] like Figure 1 , Figure 2 and Figure 3 As shown in c and 3d, the difference from Example 1 is:

[0042] S3. Place the coated sample onto the displacement stage of the maskless laser thermal lithography system, turn on the heating switch of the heating plate on the displacement stage, set the heating temperature of the heating plate on the displacement stage to 35℃ in the temperature control module of the maskless laser thermal lithography system, and use an infrared temperature sensor to observe whether the temperature of the displacement stage has reached the preset value.

[0043] S5. Use a 405nm laser beam to perform laser thermolithography exposure on a SiO2 substrate with a deposited AgInSbTe chalcogenide phase change material film. Control the coarse adjustment motor to adjust the distance between the objective lens and the sample surface so that it is near the focal plane of the objective lens. The step of the coarse adjustment motor is set to 32 pulses (250ns), and the FES value of the focal plane position feedback is -0.08. Turn on the red light tracking module and adjust the position of the piezoelectric ceramic to be in the middle so that it can track the focal plane to the maximum extent during the exposure. Move the stage to the position to be exposed, and set the stage moving speed to 1mm / s and the return speed to 10mm / m. The axis changing speed is 0.1 mm / s. The temperature control system is turned on to maintain the infrared temperature sensor's real-time detection of the sample surface temperature and feedback to the temperature controller. The sample exposure center temperature is set to 200℃. The temperature control feedback system, composed of the heating plate, infrared detector, and temperature control module of the maskless laser thermal lithography system, automatically adjusts the temperature of the displacement stage heating plate to keep the sample exposure center temperature between 198 and 202℃ (fluctuation range of 1%). The mirror rotation speed is set to 3000 faces / s, the laser power to 0.7 mW, the laser pulse width to 25 ns, the laser period to 25 ns, and the duty cycle to 1:1, i.e., continuous light.

[0044] Traditional laser thermal lithography, under room temperature conditions, with a laser power of 0.8mW, a pulse width of 25ns, and an exposure speed of 0.5m / s, can achieve a maximum resolution of 149nm and a line roughness of 15.25nm while ensuring uniformity. In this embodiment, the optimized process results in an average line width of 127nm and a line roughness of 10.9nm, which not only improves the resolution but also the uniformity compared to the traditional process.

Claims

1. A method for improving the resolution and uniformity of patterns in a thermal lithography process, characterized in that, Includes the following steps: S1. After cleaning the substrate material, dry it with high-pressure nitrogen gas with a purity of over 99.9%; S2. An inorganic phase change thin film layer with a thickness of 60-100 nm is formed on the substrate material by two-step deposition using high vacuum magnetron sputtering technology; S3. Place the coated sample onto the displacement stage of the maskless laser thermal lithography system, and use the temperature control module in the maskless laser thermal lithography system to control the temperature of the displacement stage to reach the preset temperature of 25-160℃. S4. Use an infrared temperature sensor to observe the sample surface temperature in real time. Once the temperature of the sample after coating is consistent with the temperature of the heating plate on the displacement stage, start the exposure operation. S5. The coated sample is exposed using a maskless laser thermal lithography system. The infrared temperature sensor is used to monitor the center temperature of the exposed area on the sample surface in real time. The laser power is controlled so that the center temperature of the coated sample exceeds the crystallization threshold temperature of the inorganic phase change thin film by 10-30℃, i.e., the expected center temperature. During the exposure process, a temperature control feedback system consisting of an infrared temperature sensor, a displacement stage heating plate, and a temperature control module in the maskless laser thermal lithography system is used to keep the difference between the center temperature of the sample exposure and the expected center temperature less than 1%. S6. Selective wet etching is performed on the exposed sample using a developer to form an inorganic thermal photoresist thin film pattern layer with micro-nano patterned structure.

2. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, The substrate material in step S1 is a silicon dioxide sample.

3. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, The cleaning in step S1 includes ultrasonic cleaning in a water bath for 10-30 minutes with acetone, anhydrous ethanol, and ultrapure water, with the water bath temperature for ultrasonic cleaning being 28-60℃.

4. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, In step S2, a two-step deposition process using high-vacuum magnetron sputtering is employed to form an inorganic phase change thin film layer with a thickness of 60–100 nm on the substrate material. Specifically: A 30–50 nm thick thermal stencil photoresist layer is deposited on a substrate using high-vacuum magnetron sputtering. The substrate is then rotated at a certain angle to deposit another 30–50 nm thick thermal stencil photoresist layer. The rotation angle is determined based on the relative position of the sample to be coated and the target material. The base vacuum of the high-vacuum magnetron sputtering system is controlled at 5 × 10⁻⁶. -4 Below Pa, the sputtering power is 160-200W, the working gas is argon, and the gas flow rate is 60-90 sccm.

5. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 4, characterized in that, The thermal photoresist in step S2 is a sulfur-based inorganic phase change material thin film AgInSbTe.

6. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, The heating plate of the displacement stage in step S3 is made of copper.

7. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, In step S4, the sample temperature is kept consistent with the displacement stage temperature, that is, the temperature difference between the sample center and the displacement stage set temperature is less than 1%, and the temperature difference between the sample edge and the sample center is also less than 1%.

8. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, In step S5, the laser wavelength used for exposure is 405nm, the center temperature of the laser spot is 185-210℃, the exposure power is related to the temperature rise of the sample after coating, and is 0.7mW at 45-50℃ or 0.6mW at 65-70℃, with a laser pulse of 25ns.

9. The method for improving the resolution and uniformity of patterns in a hot-molded photolithography process according to claim 1, characterized in that, In step S6, the developing solution is a 17% ammonium sulfide aqueous solution, the developing time is 3-5 minutes, and the developing temperature is 20-28°C.

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