A rapid prototyping preparation method for a GeTe-based phase change light modulator

Abstract

The application discloses a kind of fast forming preparation methods for GeTe-based phase change optical modulator.The present application uses GeTe material as phase change layer, and also uses it as photoresist, through the exposure and development treatment of GeTe material, the patterning treatment of phase change material layer is completed synchronously, which simplifies the process flow, without the traditional glue coating, stripping step;Reduce the glue coating baking and other steps of photoresist layer, reduce the damage of temperature accumulation of overall device to phase change layer, and improve the overall structure precision, improve the polarization sensitivity.At the same time, for the optimization of preparation process of GeTe material as phase change layer and photoetching layer, high-precision pattern transfer with minimum cd of 200nm is realized.

Description

Technical Field

[0001] This invention relates to the technical field of microelectronic device manufacturing, specifically to a rapid prototyping method for GeTe-based phase-change optical modulators. Background Technology

[0002] Phase-change optical modulators are based on the reversible crystalline-amorphous conversion characteristics of phase change materials (PCMs) under laser or electric pulse induction. Accompanied by significant abrupt changes in optical parameters such as refractive index and extinction coefficient, they have outstanding advantages such as non-volatility (state maintenance without continuous energy consumption), large refractive index contrast, fast response (nanosecond level), and strong reconfigurability, making them a core candidate technology for next-generation programmable photonic devices and high-density silicon photonic integrated systems.

[0003] The current mainstream fabrication process for phase change material (PCM) optical modulators mainly follows a multi-step process of "deposition-patterning-post-processing". The patterning step requires four key steps to achieve pattern transfer: photoresist coating, photolithography and development, etching, and lift-off. In the photoresist coating stage, the substrate surface with the deposited PCM film is first pretreated to remove impurities and oxides. Then, in a clean environment, photoresist is spin-coated to uniformly cover the substrate and form a continuous film. After photoresist coating, a pre-baking treatment is required. The solvent in the photoresist is removed by gentle heating, which reduces the risk of surface contamination and enhances the adhesion between the photoresist and the PCM film, reducing the risk of peeling or detachment in subsequent processes. The photolithography and development stage uses a photolithography system to transfer the pre-set device pattern to the photoresist layer. Traditional processes use patterned masks, and the photoresist is exposed to ultraviolet light. Emerging maskless laser direct writing technology directly defines the pattern by scanning with a focused laser beam, eliminating the need for a physical mask and enabling higher precision pattern drawing. During exposure, precise control of beam alignment and energy density is required to ensure clear pattern edges. During development, the exposed substrate is immersed in a developing solution, utilizing the difference in solubility between photosensitive and non-photosensitive areas of the photoresist for selective removal. The etching stage uses plasma etching to remove the PCM film from non-PCM patterned areas that are not protected by photoresist. In the stripping stage, the substrate is immersed in an organic solvent, utilizing the solvent's dissolving effect on the photoresist to remove residual photoresist layers. During etching, the etching time must be strictly controlled to prevent over-etching from damaging the optical waveguide in non-patterned areas, and under-etching from leaving residue on the optical waveguide. During stripping, the immersion time and temperature must be controlled to ensure thorough removal of redundant material without damaging the target pattern or non-patterned waveguide areas.

[0004] However, existing conventional fabrication processes have a significant negative impact on the core performance of phase-change optical modulators, mainly in four key dimensions: 1. Uncontrolled thermal budget leads to material performance degradation. The cumulative thermal effects of processes such as thin film deposition and coating baking induce elemental segregation and abnormal grain growth in chalcogenide materials such as GeTe, disrupting the reversible conversion stability between amorphous and crystalline states, resulting in a decrease in modulation depth (the difference in light intensity between crystalline and amorphous states) and a significant reduction in cycle life. 2. Interface defects exacerbate optical losses. Photoresist residue and plasma damage caused by dry etching form a large number of deep-level defects on the surface of phase-change materials. These defects act as light absorption centers, increasing insertion loss in the communication band (1550nm). At the same time, the chemical corrosion of chalcogenide materials by the developer leads to an increase in the roughness of the waveguide sidewalls, further enhancing scattering loss. 3. Insufficient structural precision worsens polarization sensitivity. Overlay deviations in multiple processes lead to asymmetry in the waveguide cross-section, resulting in excessively high polarization-dependent loss (PDL) of the device, which cannot meet the requirements of polarization-insensitive applications. Uniform phase modulation, on the other hand, requires extremely high polarization sensitivity. 4. Process fluctuations amplify performance dispersion. Parameter drifts such as sputtering power fluctuations and development time deviations can lead to increased differences in refractive index contrast between batches of devices, which seriously affects the consistency of large-scale photonic integration. This is particularly detrimental to applications such as holographic imaging that require precise phase control.

[0005] Therefore, developing a high-process stability fabrication method that can avoid multi-step thermal damage, reduce interface contamination, and improve structural consistency has become a key technological bottleneck that urgently needs to be overcome in the field of photonic integration. Summary of the Invention

[0006] The technical problem this invention aims to solve is to provide a rapid prototyping method for GeTe-based phase-change optical modulators. This method uses GeTe material as the phase-change material and employs laser direct writing technology to directly pattern the GeTe phase-change layer, obtaining a pre-defined PCM structure. This method simplifies the fabrication process, eliminates the need for additional spin-coating photoresist, reduces cross-sectional defects, improves structural accuracy, and lowers performance dispersion.

[0007] To achieve the objectives of this invention, the following technical solutions are provided: A rapid prototyping method for GeTe-based phase-change optical modulators includes the following steps: Step 1: Fabricate a GeTe phase change material thin film layer on the prepared waveguide device; Step 2: Expose the GeTe phase change material thin film layer using a laser direct writing system; Step 3: Dry or wet development of the exposed GeTe phase change material thin film to obtain a waveguide device with a patterned phase change layer. Step 4: Integrate the waveguide device with the patterned phase change layer into the optical modulator device.

[0008] Furthermore, in step 1, a GeTe phase change material thin film layer is prepared on the waveguide device using physical vapor deposition.

[0009] Furthermore, the physical vapor deposition method uses a GeTe alloy with a purity of 99.99% or higher as the target material, and the vacuum degree is ≤5×10⁻⁶. -5 The sputtering gas flow rate of Ar is 20–25 sccm, the sputtering pressure is 1.0–1.5 Pa, the sputtering power is 80–90 W, and a DC bias voltage of -20 to -50 V is applied.

[0010] Furthermore, the deposition rate of the GeTe phase change material in the physical vapor deposition method is controlled at 20–40 nm / min.

[0011] Furthermore, in step 2, the process control parameters for laser direct writing are as follows: a femtosecond laser with a wavelength of 350nm is used, the pulse width is 150-300fs, the repetition frequency is 50-100kHz, the laser spot radius is about 350±20nm, and the laser single pulse energy is controlled at 7~10μJ.

[0012] Furthermore, in step 3, when the GeTe phase change material is exposed as a positive photoresist, an acidic or alkaline solution can be used as a developer to develop the GeTe phase change material thin film layer to obtain a positive pattern.

[0013] Furthermore, in step 3, when the GeTe phase change material is exposed as a negative photoresist, an alkaline oxidation solution can be used as a developer to develop the GeTe phase change material thin film layer to obtain a negative pattern.

[0014] Furthermore, in step 3, when the GeTe phase change material thin film layer is subjected to dry development treatment, it can be etched using Cl2 or Ar plasma.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Reduce interface defects and lower optical losses. Existing processes require separate photoresist for pattern preparation. During photoresist use, issues such as photoresist residue, plasma damage, and chemical corrosion from the developer arise, leading to deep-level defects and increased waveguide sidewall roughness, resulting in increased insertion and scattering losses. This invention uses GeTe material as both the phase change layer and the photoresist. Through exposure and development of the GeTe material, the patterning of the phase change material layer is completed simultaneously, simplifying the process flow. Traditional coating and stripping steps are eliminated, reducing photoresist residue from the source and optimizing interface quality. During development, the pattern transfer is achieved using GeTe's inherent "crystalline / amorphous dissolution difference," minimizing impact on waveguide devices, reducing sidewall roughness, and decreasing scattering losses. In addition, this invention uses GeTe material as both a phase change layer and a photoresist. Compared with the traditional process of coating both a photoresist layer and a phase change layer, this invention reduces the steps of coating and baking the photoresist layer, thereby reducing the damage to the phase change layer caused by the temperature accumulation of the overall device and indirectly maintaining the stability of the phase change material layer.

[0016] 2. Improved structural precision and reduced polarization sensitivity. Existing processes often suffer from multi-step overlay errors, leading to asymmetry in the waveguide cross-section and excessively high polarization-dependent losses, failing to meet the requirements for polarization insensitivity. This invention utilizes a one-step fabrication method with high-precision laser direct writing to ensure structural consistency. Employing a femtosecond laser, under controlled conditions of a 350nm laser spot radius, high-precision pattern transfer with a minimum cd of 200nm can be achieved by controlling process parameters such as laser single-pulse energy. Simultaneously, the single-step lithography process avoids multi-step overlay errors, ensuring waveguide cross-section symmetry, significantly reducing polarization-dependent losses, and meeting the stringent requirement of uniform phase modulation for polarization insensitivity.

[0017] 3. Suppress process fluctuations and reduce performance dispersion. Parameter drift in existing processes, such as development time deviations, amplifies the differences in refractive index contrast between batches of devices, affecting the consistency of large-scale integration. The one-step molding method of this invention shortens the manufacturing chain, reduces the risk of cumulative errors from multiple stages, and significantly improves the consistency of refractive index contrast between batches of devices. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0019] Figure 1 This is a flowchart illustrating a rapid prototyping method for fabricating GeTe-based phase-change optical modulators, as provided in an embodiment of the present invention.

[0020] Figure 2 A flowchart for fabricating a phase-change optical modulator using existing processes.

[0021] Figure 3 For the photolithography comparison experiment under different laser wavelengths, rows NO.27 and NO.28 correspond to a wavelength of 1050nm, row NO.26 corresponds to a wavelength of 525nm, and rows NO.25 and below correspond to photolithography patterns with a wavelength of 350nm. The pattern period is 500nm, and the number of lines in each group is 10.

[0022] Figure 4 This presents the comparative experimental results of lithographically depicting the same pattern at different laser single-pulse energies with a laser wavelength of 350 nm. The single-pulse energy decreases sequentially from right to left and from top to bottom in increments of 0.5 μJ, with the maximum single-pulse energy at the top right being 14 μJ and the minimum single-pulse energy at the bottom left being 4.5 μJ.

[0023] Figure 5 for Figure 4 The second row and second column correspond to the magnified SEM image with a single pulse energy of 10 μJ.

[0024] The attached figures are labeled as follows: 1-1 is GeTe phase change material, 1-2 is SiN waveguide, 1-3 is SiO2 layer, 1-4 is Si substrate, 2-1 is phase change material, 2-2 is SiN waveguide device, 2-3 is SiO2 material layer, 2-4 is Si substrate layer, and 2-5 is photoresist layer. Detailed Implementation

[0025] The embodiments of the technical solution of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of this application, and are therefore merely examples and should not be used to limit the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and the foregoing description of the accompanying drawings are intended to cover non-exclusive inclusion.

[0026] In this document, suffixes such as "module," "part," or "unit" used to denote elements are used only for the purpose of illustrative purposes and have no specific meaning in themselves. Therefore, "module," "part," or "unit" may be used interchangeably.

[0027] In this specification, certain embodiments may be disclosed in a range-bound format. It should be understood that this "range-bound" description is merely for convenience and brevity and should not be construed as a rigid limitation on the disclosed range. Therefore, the description of a range should be considered as specifically disclosing all possible subranges and the individual numerical values ​​within that range. For example, the description of the range "1-6" should be considered as specifically disclosing subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. This rule applies regardless of the breadth of the range.

[0028] Example like Figure 1 As shown in the figure, this application discloses a rapid prototyping method for GeTe-based phase-change optical modulators, including the following steps: Step 1: A GeTe phase change material thin film is prepared on the cleaned SiN waveguide device using physical vapor deposition (PVD). The specific process parameters for depositing GeTe PVD on the SiN waveguide device are: using a GeTe alloy with a purity of 99.99% or higher as the target material, and a vacuum degree ≤ 5 × 10⁻⁶. -5 The sputtering gas Ar flow rate is 20–25 sccm, the sputtering pressure is 1.0–1.5 Pa, the sputtering power is 80–90 W, and a DC bias voltage of -20 to -50 V is applied.

[0029] Step 2 involves exposing the GeTe phase change material thin film using a laser direct writing system. The process control parameters for laser direct writing are as follows: a 350nm femtosecond laser with a pulse width of 150-300 fs, a repetition rate of 50-100kHz, a laser spot radius of approximately 350nm, and a single-pulse laser energy controlled at 7-10μJ. By controlling these parameters, the peak energy density at the laser focal point can be precisely matched to the upper limit of the GeTe phase change threshold. The high photon energy of 3.5eV in the violet band is efficiently coupled with the 0.7-0.8eV bandgap of GeTe, effectively compressing the thermal diffusion range and thus improving lithography accuracy.

[0030] Step 3: The exposed GeTe phase change material thin film layer is subjected to dry or wet development to obtain a waveguide device with a patterned phase change layer.

[0031] Step 4: Integrate the waveguide device with the patterned phase change layer into the optical modulator device to obtain an optoelectronic optical modulator device based on phase change material.

[0032] In some embodiments, the method for preparing GeTe phase change material thin films may also include other methods such as evaporation, chemical vapor deposition, and metal compound vapor deposition.

[0033] In some embodiments, when GeTe phase change material is exposed as a positive photoresist, the high solubility of the crystalline region in acidic solutions (such as 5% HNO3) or alkaline solutions (such as 0.1 mol / L TMAH) can be utilized to develop the GeTe phase change material thin film layer and obtain a positive pattern.

[0034] In some embodiments, when GeTe phase change material is exposed as a negative photoresist, the rapid dissolution characteristics of the amorphous state in an alkaline oxidizing solution (0.5 mol / L NaOH + 3% H2O2) can be utilized to develop the GeTe phase change material thin film layer, and the development retains the crystalline pattern to obtain a negative pattern.

[0035] In some embodiments, when the GeTe phase change material thin film layer is subjected to dry development, etching can be performed using Cl2 or Ar plasma. By utilizing the different etching rates of Cl2 or Ar plasma for amorphous and crystalline states, combined with the selective induced phase transition of the GeTe phase change material thin film layer by laser in step 2, nanoscale precision pattern transfer can be achieved.

[0036] Comparative Example 1 like Figure 2 As shown, the existing method for fabricating phase-change optical modulators generally uses a lift-off process. The general process can be summarized in four steps: 1. Applying a PVD phase-change material layer to the prepared SiN waveguide device and annealing it; 2. Coating the phase-change material layer with photoresist; 3. Photolithography and development of specific areas; 4. Etching away excess phase-change material and removing the photoresist mask, leaving only the phase-change material in the patterned area, thus obtaining a patterned phase-change material layer and a SiN waveguide device.

[0037] Compared with existing processes, the preparation method of the present invention does not require the coating of additional photoresist, the preparation process is simpler, and the deviation caused by the multi-step overlay of existing processes is reduced, so the structural accuracy can be better controlled and improved.

[0038] Comparative Example 2 This comparative example uses the same preparation method and process parameters as the previous example, the only difference being that different laser wavelengths are used to perform photolithography on the same grating structure. The laser wavelengths used are 1050nm and 525nm.

[0039] Figure 3This image shows a comparison of the photolithography results of the same grating structure using different laser wavelengths. Rows 27 and 28 correspond to a wavelength of 1050 nm, row 26 corresponds to a wavelength of 525 nm, and rows 25 and below correspond to photolithography patterns at a wavelength of 350 nm. The pattern period is 500 nm, and each group has 10 lines. Figure 3 The etched pattern consists of lines with a period of 500 nm. It can be clearly observed that: at a laser wavelength of 1050 nm, the line width is greater than half the period, approximately 300 nm; at a laser wavelength of 525 nm, the line width is close to half the period, approximately 250 nm; and at a laser wavelength of 350 nm, the line width is less than half the period, approximately 200 nm. This verifies that, under the same experimental conditions, the line width (CD) of the etched patterns at wavelengths of 1050 nm, 525 nm, and 350 nm decreases as the wavelength decreases. In this invention, a 350 nm wavelength is used for lithography, enabling the lithography of high-resolution PCM patterns of 200 nm.

[0040] Comparative Example 3 This comparative example uses the same preparation method and process parameters as the previous example, the only difference being the use of laser thermolithography process parameters with different single-pulse energies for comparison. Under the condition that the wavelength is 350nm and all other parameters are the same,... Figure 4 The results show the comparative test results of laser thermolithography with different single-pulse energies.

[0041] Figure 4 In the experiment, the single-pulse energy decreases sequentially from right to left and from top to bottom in 0.5 μJ increments. The highest single-pulse energy (14 μJ) is found in the upper right region, while the lowest (4.5 μJ) is found in the lower left region. Comparative results show that as the single-pulse energy gradually decreases from 14 μJ, the lithographic resolution gradually improves, while the lithographic linewidth gradually decreases; however, when the single-pulse energy is less than 7 μJ (corresponding to...), the lithographic resolution decreases. Figure 4 (Fourth line) The lithographic lines become blurry, and the sharpness decreases. For example... Figure 5 As shown, the lithographic linewidth is 230 nm when the single-pulse energy is 10 μJ. Based on the above experimental results, this invention uses a single-pulse energy of 7~10 μJ for etching, which can achieve high-resolution laser thermolithography with a lithographic linewidth as low as 200 nm.

[0042] The above embodiments are merely illustrative of the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A rapid prototyping method for GeTe-based phase-change optical modulators, characterized in that, Includes the following steps: Step 1: Fabricate a GeTe phase change material thin film layer on the prepared waveguide device; Step 2: Exposure the GeTe phase change material thin film layer using a laser direct writing system. The process control parameters for laser direct writing are as follows: a femtosecond laser with a wavelength of 350nm, a pulse width of 150-300fs, a repetition frequency of 50-100kHz, a laser spot radius of approximately 350±20nm, and a laser single pulse energy controlled at 7~10μJ. Step 3: Dry or wet development of the exposed GeTe phase change material thin film to obtain a waveguide device with a patterned phase change layer. Step 4: Integrate the waveguide device with the patterned phase change layer into the optical modulator device.

2. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 1, characterized in that, In step 1, a GeTe phase change material thin film layer is prepared on the waveguide device using physical vapor deposition.

3. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 2, characterized in that, The physical vapor deposition method uses a GeTe alloy with a purity of 99.99% or higher as the target material, and the vacuum degree is ≤5×10⁻⁶. -5 The sputtering gas flow rate of Ar is 20–25 sccm, the sputtering pressure is 1.0–1.5 Pa, the sputtering power is 80–90 W, and a DC bias voltage of -20 to -50 V is applied.

4. A rapid prototyping fabrication method for a GeTe-based phase change optical modulator according to claim 3, wherein, In the physical vapor deposition method, the deposition rate of GeTe phase change material is controlled at 20–40 nm / min.

5. The method of claim 1, wherein the GeTe-based phase change optical modulator is prepared by a rapid prototyping method. In step 3, when the GeTe phase change material is exposed as a positive photoresist, an acidic or alkaline solution can be used as a developer to develop the GeTe phase change material thin film layer to obtain a positive pattern.

6. The method of claim 1, wherein the GeTe-based phase change optical modulator is prepared by a rapid prototyping method. In step 3, when the GeTe phase change material is exposed as a negative photoresist, an alkaline oxidation solution can be used as a developer to develop the GeTe phase change material thin film layer to obtain a negative pattern.

7. The method of claim 1, wherein the GeTe-based phase change optical modulator is prepared by a rapid prototyping method. In step 3, when the GeTe phase change material thin film layer is subjected to dry development, it can be etched using Cl2 or Ar plasma.

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