Rapid prototyping preparation method for GeTe-based phase change light modulator

Abstract

The invention discloses a rapid prototyping preparation method for a GeTe-based phase change light modulator. According to the invention, the GeTe material is used as the phase change layer and also used as the photoresist, and the patterning treatment of the phase change material layer is synchronously completed through the exposure and development treatment of the GeTe material, so that the technological process is simplified, and the traditional gluing and stripping steps are not needed; the steps of gluing, baking and the like of the photoresist layer are reduced, the damage of temperature accumulation of the whole device to the phase change layer is reduced, the precision of the whole structure is improved, and the polarization sensitivity is improved. Meanwhile, the preparation process is optimized by taking the GeTe material as the phase change layer and the photoetching layer, and high-precision pattern transfer with the minimum cd of 200nm is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microelectronic device manufacturing, and in particular to a rapid prototyping preparation method for a GeTe-based phase change optical modulator. BACKGROUND

[0002] The phase change optical modulator is based on the reversible conversion characteristics of the crystalline-amorphous state of the phase change material (PCM) under laser or electric pulse induction, accompanied by significant mutations in the refractive index, extinction coefficient and other optical parameters. It has the outstanding advantages of non-volatility (state retention without continuous power consumption), large refractive index contrast, fast response (nanosecond level), strong reconfigurability, etc., and has become the core candidate technology of the next generation of programmable photonic devices and high-density silicon photonics integrated systems.

[0003] The current mainstream preparation process of the phase change material (PCM) optical modulator mainly uses the "deposition-patterning-post-processing" multi-step process, in which the patterning link needs to realize pattern transfer through four key steps of gluing, photoresist development, etching and stripping. In the gluing stage, the surface of the substrate with a PCM thin film is pretreated to remove impurities and oxides, and then a continuous thin film of photoresist is formed on the substrate by spin coating in a clean environment. The photoresist needs to be pre-baked after gluing to remove the solvent in the photoresist by gentle heating, which not only reduces the risk of surface contamination, but also enhances the adhesion of the photoresist to the PCM thin film, reducing the peeling or falling off problem in the subsequent process. The photoresist development link uses a photoetching system to transfer the preset device pattern to the photoresist layer: the traditional process uses a patterned mask, and the photoresist is sensitized by ultraviolet light; the emerging maskless laser direct writing technology directly defines the pattern by scanning the focused laser beam, without the need for a physical mask, which can achieve higher precision pattern drawing. The light beam alignment and energy density need to be accurately controlled during exposure to ensure clear pattern edges, and the substrate is immersed in a developing solution during development to realize selective removal by taking advantage of the solubility difference between the light-sensitive and non-light-sensitive areas of the photoresist. The etching link uses plasma etching to remove the PCM thin film in the non-PCM pattern area that is not protected by the photoresist. In the stripping stage, the substrate is immersed in an organic solvent to remove the residual photoresist layer by taking advantage of the solvent's solubility to the photoresist. In the etching process, the etching time needs to be strictly controlled to prevent over-etching from damaging the optical waveguide in the non-pattern area, and under-etching from forming residues on the optical waveguide; in the stripping link, the immersion time and temperature need to be controlled to ensure that the redundant material is completely removed without damaging the target pattern and non-pattern area waveguide.

[0004] However, the existing conventional preparation process has a significant negative impact on the core performance of the phase change optical modulator, mainly in four key dimensions: 1. The thermal budget is out of control, which leads to the degradation of material performance. The cumulative heat effect of film deposition and glue baking process can induce element segregation and abnormal grain growth of GeTe and other chalcogenide materials, which destroys the stability of the reversible conversion between amorphous and crystalline states, reduces the modulation depth (the difference in light intensity between crystalline and amorphous states), and greatly shortens the cycle life. 2. The interface defect aggravates the optical loss. The photoresist residue and the plasma damage caused by dry etching can form a large number of deep level defects on the surface of the phase change material. These defects act as light absorption centers to increase the insertion loss at the communication wavelength (1550nm), and the chemical corrosion of the developing solution to the chalcogenide material can cause the sidewall roughness of the waveguide to rise, further enhancing the scattering loss. 3. The lack of structural precision worsens the polarization sensitivity. The multi-process overlay deviation leads to asymmetric waveguide cross-section, which makes the device polarization-dependent loss (PDL) too high to meet the polarization-insensitive application requirements, while uniform phase modulation requires high polarization sensitivity. 4. Process fluctuations amplify performance discreteness. Parameter drifts such as sputtering power fluctuations and developing time deviations can cause the refractive index contrast of batch devices to differ, which seriously affects the consistency of large-scale photonic integration, which is particularly disadvantageous for applications such as holographic imaging that require precise control of phase.

[0005] Therefore, developing a high-process-stability preparation method that can avoid multi-step thermal damage, reduce interface pollution, and improve structural consistency has become a key technical bottleneck that needs to be broken through in the field of photonic integration. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a rapid forming preparation method for GeTe-based phase change optical modulators. The method uses GeTe material as the phase change material and uses laser direct writing technology to directly pattern the GeTe phase change layer to obtain a PCM structure with a preset pattern. The preparation process of this method is simpler and does not require additional spin-on photoresist, reducing cross-sectional defects, improving structural precision, and reducing performance discreteness.

[0007] In order to achieve the purpose of the present application, the present application provides the following technical solutions: A rapid forming preparation method for GeTe-based phase change optical modulators, comprising the following steps: Step 1. Preparing a GeTe phase change material thin film layer on a prepared waveguide device; Step 2. Exposing the GeTe phase change material thin film layer to light using a laser direct writing system; Step 3. Dry or wet developing the exposed GeTe phase change material thin film layer to obtain a waveguide device with a patterned phase change layer; Step 4, integrating the waveguide device of the patterned phase change layer into the optical modulator device.

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

[0009] Further, in the physical vapor deposition method, a GeTe alloy with a purity of 99.99% or above is used as the target material, the vacuum degree is ≤5×10 -5 Pa, the flow rate of the sputtering gas Ar is 20-25 sccm, the sputtering gas pressure is 1.0-1.5 Pa, the sputtering power is 80-90 W, and a direct current bias of -20 to -50 V is applied.

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

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

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

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

[0014] Further, in step 3, when the GeTe phase change material thin film layer is subjected to dry development, Cl2 or Ar plasma can be used for etching.

[0015] Compared with the prior art, the present application has the following advantages: 1. Reduce interface defects and reduce optical loss. The existing process needs to use a separate photoresist for pattern preparation. In the use process of the photoresist, there are phenomena such as photoresist residue, plasma damage, and chemical corrosion of the developing solution, which can form deep level defects and increase the waveguide sidewall roughness, resulting in the increase of insertion loss and scattering loss. The present application uses GeTe material as the phase change layer and also as the photoresist. Through the exposure and development of GeTe material, the patterning process of the phase change material layer is completed synchronously, simplifying the process flow, eliminating the need for traditional coating and stripping steps, reducing photoresist residue from the source, and optimizing the interface quality. During the development process, the pattern transfer is completed using the "crystalline / amorphous solubility difference" of GeTe itself, which has little effect on the waveguide device, reduces the sidewall roughness, and reduces the scattering loss. In addition, the present application uses GeTe material as the phase change layer and also as the photoresist. Compared with the traditional process of coating both the photoresist layer and the phase change layer, the present application reduces the coating and baking steps of 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. Improve structural precision and improve polarization sensitivity. The multi-process overlay deviation of the existing process easily leads to asymmetric waveguide cross-section, which makes the polarization-dependent loss too high and cannot meet the polarization-insensitive requirement. The present application uses a one-step forming preparation method to ensure the structural consistency through a high-precision laser direct writing process. A femtosecond laser is used to achieve high-precision pattern transfer with a minimum cd of 200nm by controlling the laser spot radius to 350nm and controlling process parameters such as laser single pulse energy. At the same time, the single-step lithography process avoids multi-process overlay deviation, ensures the symmetry of the waveguide cross-section, greatly reduces the polarization-dependent loss, and meets the stringent requirements of uniform phase modulation for polarization insensitivity.

[0017] 3. Suppress process fluctuation and reduce performance dispersion. The parameter drift such as development time deviation of the existing process can amplify the difference in refractive index contrast between batch devices, affecting the consistency of large-scale integration. The one-step forming preparation method of the present application shortens the process manufacturing chain, reduces the superimposed risk of multi-link errors, and significantly improves the consistency of the refractive index contrast of batch devices. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference signs. In the drawings, the elements or parts are not necessarily drawn according to the actual proportions. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings from these drawings without creative labor.

[0019] Figure 1 Flow chart of the rapid prototyping method for GeTe-based phase change optical modulator provided by the embodiment of the present application.

[0020] Figure 2 Flow chart of the phase change optical modulator prepared by the existing process.

[0021] Figure 3 For the lithography contrast experiment under different laser wavelengths, the lines No. 27 and No. 28 in the figure correspond to 1050 nm wavelength, the line No. 26 corresponds to 525 nm wavelength, and the lines No. 25 and below correspond to 350 nm wavelength lithography pattern, the pattern period is 500 nm, and the number of lines in each group is 10.

[0022] Figure 4 For the lithography contrast experiment results of the same pattern under different laser single pulse energies when the laser wavelength is 350 nm. The single pulse energy decreases by steps of 0.5 μJ from right to left and from top to bottom, the maximum single pulse energy on the right top is 14 μJ, and the minimum single pulse energy on the left bottom is 4.5 μJ.

[0023] Figure 5 For Figure 4 The second line and the second column correspond to the enlarged SEM image of the single pulse energy of 10 μJ.

[0024] The reference signs are 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 DESCRIPTION

[0025] The embodiments of the technical scheme of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical scheme of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by those skilled in the art to which the present application belongs; the terms used herein are only for the purpose of describing the specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0026] In this paper, the suffixes such as "module", "component" or "unit" used to represent elements are only for the convenience of the description of the present application, and have no specific meaning in itself. Therefore, "module", "component" or "unit" can be used mixedly.

[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 the GeTe phase change material thin film layer can further comprise other methods such as evaporation, chemical vapor deposition, metal compound vapor deposition, etc.

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

[0034] In some embodiments, when the GeTe phase change material is exposed as a negative photoresist, the rapid solubility 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 a negative pattern is obtained by development.

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

[0036] Comparative Example 1 As shown in Figure 2 , the method for preparing a phase change optical modulator in the prior art is generally a Lift-off process. The general process can be divided into four steps: 1. PVD of the phase change material layer on the prepared SiN waveguide device and annealing treatment; 2. coating of photoresist on the phase change material layer, 3. photolithography and development on the specific region, 4. etching of the excess phase change material and removal of the photoresist mask by Lift-off, only leaving the phase change material in the patterned region, thereby obtaining a patterned phase change material layer and SiN waveguide device.

[0037] Compared with the prior art, the preparation method of the present application does not require the coating of additional photoresist, the preparation process is simpler, and the deviation caused by the multi-process overlay of the prior art is reduced, and the structural precision can be better controlled and improved.

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

[0039] Figure 3The contrast effect diagram of the same grating structure for different laser wavelengths is shown in the figure. The NO. 27 row and the NO. 28 row correspond to the 1050 nm wavelength, the NO. 26 row corresponds to the 525 nm wavelength, and the NO. 25 row and the rows below correspond to the 350 nm wavelength. The pattern period is 500 nm, and the number of lines in each group is 10. Figure 3 The middle engraved pattern is a line with a period of 500 nm. It can be clearly observed that when the laser wavelength is 1050 nm, the line width is greater than half of the period, about 300 nm; when the laser wavelength is 525 nm, the line width is close to half of the period, about 250 nm; and when the laser wavelength is 350 nm, the line width is less than half of the period, about 200 nm. Thus, it is verified that under the same experimental conditions, the line width CD of the line pattern photoetched under the three wavelengths of 1050 nm, 525 nm and 350 nm becomes thinner as the wavelength decreases. In the present application, the 350 nm wavelength is used for photoetching, and a high-resolution PCM pattern photoetching with a line width of 200 nm can be realized.

[0040] Comparative Example 3 The preparation method and process parameters of the present application are used in the present comparative example, and the only difference is that different single-pulse energy laser thermal photoetching process parameters are used for comparison test. Under the condition that the wavelength is 350 nm and other parameters are the same, Figure 4 The comparison test results of different single-pulse energy laser thermal photoetching.

[0041] Figure 4 In the figure, the single-pulse energy decreases by 0.5 μJ from right to left and from top to bottom, wherein the single-pulse energy in the upper right area is the largest, 14 μJ, and the single-pulse energy in the lower left area is the smallest, 4.5 μJ. The comparison test results show that when the single-pulse energy gradually decreases from 14 μJ, the photoetching resolution gradually increases, and the photoetched line width gradually decreases; and when the single-pulse energy is less than 7 μJ (corresponding to the fourth row), the photoetched line becomes blurred, and the clarity decreases. As shown in the figure, when the single-pulse energy is 10 μJ, the photoetched line width is 230 nm. Based on the above experimental results, the present application uses a single-pulse energy of 7-10 μJ for etching, and a high-resolution laser thermal photoetching with a photoetched line width of 200 nm can be realized. Figure 4 Figure 5

[0042] ​​The above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present 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: 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.

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. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 3, characterized in that, In the physical vapor deposition method, the deposition rate of GeTe phase change material is controlled at 20–40 nm / min.

5. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 1, characterized in that, 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.

6. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 1, characterized in that, 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.

7. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 1, characterized in that, 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.

8. The rapid prototyping method for GeTe-based phase-change optical modulators as described in claim 1, characterized in that, 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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