A method for preparing a nitride ferroelectric semiconductor for controlling nucleation of ferroelectric domains
Patent Information
- Application Number
- CN202611242980.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-17
- Publication Date
- 2026-10-30
AI Technical Summary
[0005]针对现有氮化物铁电半导体薄膜在极化翻转过程中存在铁电畴成核位置随机、翻转行为难以精确调控等问题，本发明提出了一种控制铁电畴成核的氮化物铁电半导体制备方法，有效控制铁电畴的成核位置和拓展范围
[0032]本发明通过在具有较低矫顽电场的成核诱导层中构建局部分布的低矫顽场岛状结构和在具有较高矫顽电场的铁电主体层中定义铁电功能区和边界调控区，实现了对铁电畴起始成核位置与后续扩展终点的协同调控，能够有效改善现有氮化物铁电半导体薄膜中铁电畴成核随机性较强、翻转路径及扩展范围难以限定的问题。其中，低矫顽场岛状结构在外加电场作用下更易优先发生极化翻转，并通过与其下方高矫顽场的铁电主体层之间的近邻耦合作用，在界面附近产生局域电场和弹性场，降低其下方及邻近高矫顽场的铁电主体层的极化翻转势垒，从而诱导铁电畴优先在预定区域成核，有利于提高极化翻转行为的一致性、可重复性和可设计性；经光热转换层辅助的短脉冲光照处理形成的边界调控区为晶体结构失序化的区域，该区域铁电性受到抑制或破坏，能够对相邻铁电功能区进行有效分隔，并限制铁电畴的横向扩展范围，从而抑制相邻铁电单元之间的翻转串扰，增强不同铁电单元之间的独立性。此外，本发明通过低矫顽场岛状结构与高矫顽场铁电主体层的协同设计，有利于降低高矫顽场的铁电工作区域的极化翻转势垒，进而降低器件工作电压和能耗，并减轻高电场作用下的介质击穿风险。由此制备得到的控制铁电畴成核的氮化物铁电半导体结构可应用于铁电存储单元、可重构电子器件、压电器件、声学器件及相关集成氮化物铁电器件中，具有良好的应用前景。
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Abstract
Description
Technical Field
[0001] This invention relates to nitride ferroelectric semiconductor growth technology, and more specifically to a method for preparing nitride ferroelectric semiconductors by controlling the nucleation of ferroelectric domains. Background Technology
[0002] In recent years, nitride ferroelectric materials, represented by scandium aluminum nitride (ScAlN), have attracted widespread attention due to their combination of ferroelectric, piezoelectric, and semiconductor properties. These materials typically possess advantages such as strong spontaneous polarization, high Curie temperature, tunable bandgap, and good compatibility with nitride processing systems, making them promising candidates for applications in electronic devices, ferroelectric memory, optoelectronic devices, and acoustic devices.
[0003] Currently, nitride ferroelectric semiconductor thin films still face some limitations in practical applications. On the one hand, these materials typically possess high coercive electric fields, requiring a large external electric field for polarization reversal. This can easily lead to higher device operating voltages, further increasing the risk of breakdown, increasing energy consumption, and reducing device reliability. On the other hand, during polarization reversal in existing nitride ferroelectric semiconductor thin films, the nucleation sites of ferroelectric domains are often affected by random defects, local stress distribution, electrode edge field enhancement, and material inhomogeneity, exhibiting strong randomness and resulting in poor consistency and repeatability of the reversal behavior. Furthermore, once polarization reversal occurs, its subsequent expansion range and termination boundary usually lack effective constraints, making it difficult to design and control the reversal path and region.
[0004] Therefore, developing a nitride ferroelectric semiconductor fabrication method that enables controllable ferroelectric domain nucleation sites and further limits the ferroelectric domain expansion range is of great significance for reducing operating voltage, improving switching consistency, enhancing polarization control capability, and expanding its application in ferroelectric memory and other fields. Summary of the Invention
[0005] To address the problems of random ferroelectric domain nucleation sites and difficulty in precisely controlling the reversal behavior during the polarization reversal process of existing nitride ferroelectric semiconductor thin films, this invention proposes a method for preparing nitride ferroelectric semiconductors that controls ferroelectric domain nucleation, effectively controlling the nucleation sites and expansion range of ferroelectric domains.
[0006] The method for preparing nitride ferroelectric semiconductors with controlled ferroelectric domain nucleation of the present invention includes the following steps:
[0007] 1) Growing the bottom electrode on the substrate;
[0008] 2) Two layers of nitride ferroelectric material with different coercive fields are sequentially formed on the bottom electrode. The lower nitride ferroelectric material has a higher coercive field as the main ferroelectric layer, while the upper nitride ferroelectric material has a lower coercive field as the nucleation induction layer.
[0009] 3) A first patterned mask comprising multiple patterned units is formed on the surface of the nucleation-inducing layer to divide the ferroelectric main body layer into multiple ferroelectric functional regions and boundary control regions; part of the surface of the nucleation-inducing layer is covered by the first patterned mask, and part is exposed without being covered by the first patterned mask.
[0010] 4) A photothermal conversion layer is deposited on the surface of the nucleation-inducing layer on which the first patterned mask is formed, so that the photothermal conversion layer is in direct contact with the nucleation-inducing layer on the exposed surface not covered by the first patterned mask;
[0011] 5) With the first patterned mask as protection, the photothermal conversion layer is subjected to multiple short-pulse light irradiation treatments. The photothermal conversion layer absorbs the light energy of the short-pulse light irradiation, generating transient heating and thermal expansion. The photothermal conversion layer transfers heat and thermal stress downward to the ferroelectric host layer in the region not covered by the first patterned mask. The multiple short-pulse light irradiation treatments cause the crystal structure of the region of the ferroelectric host layer not covered by the first patterned mask to become disordered, and the ferroelectricity is suppressed or destroyed, forming a boundary control region, which is used to separate adjacent ferroelectric functional regions and limit the lateral expansion range of ferroelectric domains. The region of the ferroelectric host layer covered by multiple patterned units of the first patterned mask is protected by the first patterned mask, retaining ferroelectricity and forming multiple ferroelectric functional regions.
[0012] By removing the first patterned mask and the photothermal conversion layer, a ferroelectric main body layer with defined ferroelectric functional regions and boundary control regions is obtained;
[0013] 6) A second patterned mask is formed on the surface of the nucleation-inducing layer to define the formation of multiple low coercive field island structures in the nucleation-inducing layer; each low coercive field island structure defined by the second patterned mask is located in the central region of the corresponding ferroelectric functional region, serving as an inducing structure for preferential nucleation of ferroelectric domains.
[0014] 7) Using the second patterned mask as protection, the nucleation induction layer not protected by the second patterned mask is etched, thereby retaining a locally distributed low coercive field island structure in the central region of the ferroelectric functional region surface, that is, the low coercive field island structure covers the central region of the ferroelectric functional region surface.
[0015] By removing the second patterning mask, a nitride ferroelectric semiconductor structure with a low coercive field island structure on the surface of the central region of the ferroelectric functional region of the ferroelectric host layer is obtained.
[0016] 8) A top electrode is grown on the ferroelectric functional region with a low coercivity island structure. The top electrode covers the low coercivity island structure and the exposed surface of the ferroelectric functional region. The top electrode and the bottom electrode together constitute the electrode structure.
[0017] 9) The low coercive field island structure and ferroelectric functional region are pre-polarized by electrode structure so that their polarization direction is consistent with the preset polarization direction. At this time, the ferroelectric domains in the ferroelectric functional region have a polarization direction consistent with the preset polarization direction, and are in an approximately single-domain state.
[0018] An external electric field with a direction opposite to the preset polarization direction is applied through the electrode structure. Under the action of the electric field, the low coercivity island structure undergoes polarization reversal before the ferroelectric host layer with a high coercivity field. After polarization reversal, the low coercivity island structure generates a local electric field and elastic field near the interface between itself and the ferroelectric host layer below it through the proximity coupling effect. This reduces the polarization reversal barrier in the corresponding region of the ferroelectric host layer, inducing the reverse polarized ferroelectric domains to preferentially nucleate in the region below the low coercivity island structure. Subsequently, the polarized ferroelectric domains extend downward along the film thickness direction from near the interface and further extend laterally to the surrounding area. When the reverse polarized ferroelectric domains extend to the boundary control region, the boundary control region blocks and restricts the further expansion of the reverse polarized ferroelectric domains, thereby limiting the polarization reversal range to the interior of the corresponding ferroelectric functional region.
[0019] In step 1), the substrate is made of a material suitable for the growth or deposition of nitride ferroelectric semiconductor thin films, such as a gallium nitride template (GaN template), an aluminum nitride template (AlN template), or sapphire (GaN template). The substrate is either silicon carbide (SiC) or silicon (Si). The bottom electrode material is N-type gallium nitride (n-GaN), titanium nitride (TiN), molybdenum (Mo), or platinum (Pt), with a thickness of 50 nm to 300 nm. The bottom electrode is grown using molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), reactive magnetron sputtering, or atomic layer deposition (ALD).
[0020] In step 2), the two layers of nitride ferroelectric material are formed sequentially using molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), reactive magnetron sputtering, or atomic layer deposition (ALD). The difference in coercive electric field between the two nitride ferroelectric material layers is achieved through differences in composition, doping, stress, or defects; the difference in coercive electric field is 0.5 MV / cm to 5 MV / cm. The thickness of the ferroelectric host layer is 50 nm to 1000 nm; the thickness of the nucleation-induced layer is 0.1 to 0.2 times the thickness of the ferroelectric host layer.
[0021] After the nucleation-induced layer is grown, the surface of the nucleation-induced layer is cleaned to remove particles, adsorbates and organic residues from the film surface. Cleaning can be done by organic solvent cleaning, deionized water cleaning, ultrasonic-assisted cleaning or a combination thereof to obtain a clean film surface.
[0022] In step 3), the first patterned mask is used to define the range of the ferroelectric functional region and the boundary control region in the ferroelectric host layer. The first patterned mask includes multiple patterned units distributed in an array. The first patterned mask is either a photoresist mask or a hard mask; wherein, the photoresist mask is formed by spin-coating photoresist, pre-baking, exposure, and development, and the hard mask is... , or One of them. The region of the ferroelectric main body layer covered by the first patterned mask is defined as the ferroelectric functional region. The surface shape of the patterned unit is consistent with the cross-sectional shape of the ferroelectric functional region. The surface shape can be circular, elliptical, square or polygonal, and the lateral dimension is 100 nm to 50 μm. Multiple ferroelectric functional regions can be distributed in a periodic array or a non-periodic array. The region between adjacent ferroelectric functional regions that is not covered by the first patterned mask forms a boundary control region.
[0023] In step 4), the photothermal conversion layer is used to absorb the light energy provided by subsequent short-pulse irradiation, generating transient temperature rise and thermal expansion. The photothermal conversion layer is made of one or more materials selected from metal materials, metal nitride materials, and carbon-based materials; it is formed by magnetron sputtering, electron beam evaporation, thermal evaporation, or atomic layer deposition, with a thickness of 10 nm to 200 nm. The photothermal conversion layer is preferably made of materials with high light absorption rate and photothermal conversion efficiency at the short-pulse irradiation wavelength, such as metal materials like nickel (Ni), titanium (Ti), and tungsten (W) and metal nitride materials like titanium nitride (TiN), to generate the required transient temperature rise; at the same time, the selected material has a different coefficient of thermal expansion with the material of the nucleation-inducing layer to generate thermal stress under interface constraints, and should have thermal stability capable of withstanding short-pulse irradiation treatment and chemical stability with the nucleation-inducing layer material.
[0024] In step 5), the short pulses are generated using a pulsed laser or a pulsed high-intensity light source. The photothermal conversion layer located in the area not covered by the first patterned mask is in direct contact with the nucleation-inducing layer. After absorbing light energy, it undergoes transient heating and thermal expansion. Due to the thermal expansion mismatch between the photothermal conversion layer and the nucleation-inducing layer, and the interface constraint that generates thermal stress, the heat and thermal stress are transferred downwards to the ferroelectric host layer, generating a localized transient thermal field and thermal stress field in the ferroelectric host layer below it. After the short pulse illumination ends, the heat is rapidly dissipated through the nitride ferroelectric semiconductor thin film and the substrate, causing the localized thermal field and thermal stress field to decay rapidly. The time interval between adjacent pulses is greater than the characteristic thermal relaxation time of the ferroelectric host layer, thus forming multiple rapid heating-cooling thermal cycles that are separated from each other. Under the action of transient temperature gradient, thermal expansion mismatch, and thermal stress cycle, the crystal structure of the corresponding region of the ferroelectric host layer becomes locally disordered, and the ferroelectricity is suppressed or destroyed, forming a boundary control region. The photothermal conversion layer on the first patterned mask is isolated from the nucleation induction layer. The first patterned mask can reduce the transfer of heat and stress to the masked area, thereby maintaining high crystal order and ferroelectricity in the area of the ferroelectric main layer that is masked by multiple patterned units of the first patterned mask, forming ferroelectric functional regions. Each patterned unit corresponds to one ferroelectric functional region, and multiple ferroelectric functional regions are distributed in an array, consistent with the distribution of the first patterned mask. Adjacent ferroelectric functional regions are separated by boundary control regions. The wavelength of the short pulse illumination is selected according to the light absorption characteristics of the photothermal conversion layer. Adjusting the wavelength of the short pulse makes the photothermal conversion layer have the strongest light absorption capability. The pulse width is adjusted according to the required transient heating rate. The smaller the pulse width, the greater the transient heating rate. The energy density and pulse number are adjusted according to the required degree and depth of crystal structure disorder. Increasing the energy density and pulse number can enhance the degree and depth of crystal structure disorder. Adjusting the energy density and pulse number can suppress or destroy the ferroelectricity of the crystal. The depth of crystal structure disorder is close to the total thickness of the nucleation induction layer and the ferroelectric main layer.
[0025] The first patterned mask and photothermal conversion layer are removed using one or more of the following methods in combination: lift-off, organic solvent cleaning, plasma resist removal, wet etching, and dry etching. When the first patterned mask is a photoresist mask, it is first removed using organic solvent or plasma resist removal, and then the photothermal conversion layer on the surface of the first patterned mask is removed by lift-off. The photothermal conversion layer is then removed using a wet etching or dry etching method suitable for its material. When the first patterned mask is a hard mask, the appropriate wet etching, dry etching, or a combination of removal processes is selected based on the materials of the hard mask and the photothermal conversion layer. During the removal process, the removal conditions are controlled to avoid significant damage to the nucleation-inducing layer and the ferroelectric host layer.
[0026] In step 6), a second patterned mask is used to define the low coercivity island structure to be retained in the nucleation induction layer. The second patterned mask includes multiple patterned units distributed in an array, the array arrangement being consistent with the distribution of the first patterned mask and the ferroelectric functional region. Each patterned unit of the second patterned mask is located on a corresponding ferroelectric functional region, and its surface shape is smaller than the cross-sectional shape of the ferroelectric functional region. The low coercivity island structure will serve as the induction structure for preferential nucleation of ferroelectric domains in the ferroelectric host layer. The second patterned mask is a photoresist mask or a hard mask, and can be formed by photolithography, electron beam lithography, nanoimprinting, or other patterning methods. The masking area of the second patterned mask faces the central region of the ferroelectric functional region. The second patterned mask defines the low coercivity island structure, and the shape of the patterned unit in the planar direction can be circular, elliptical, square, or polygonal, with a lateral dimension 0.05 to 0.2 times the lateral dimension of the corresponding ferroelectric functional region.
[0027] In step 7), using the second patterned mask as protection, the nucleation-inducing layer not covered by the second patterned mask is etched to remove the portion of the nucleation-inducing layer nitride ferroelectric material not protected by the second patterned mask, resulting in a low-coercivity island structure defined by the second patterned mask. The etching employs one or more combinations of reactive ion etching, inductively coupled plasma etching, ion beam etching, and wet etching. The low-coercivity island structure retains the low coercivity electric field characteristic of the nucleation-inducing layer nitride ferroelectric material and forms a localized coupling interface with the underlying ferroelectric host layer. Each ferroelectric functional region and its corresponding low-coercivity island structure constitute a ferroelectric unit.
[0028] The second patterned mask is removed using one or more of the following methods: organic solvent removal, plasma resist removal, wet etching, and dry etching. When the second patterned mask is a photoresist mask, it is removed using organic solvent cleaning or plasma resist removal; when the second patterned mask is a hard mask, it is removed using wet etching or dry etching methods adapted to the hard mask material.
[0029] In step 8), a top electrode pattern is first formed on the ferroelectric host layer with a low coercivity island structure, and then the top electrode is grown. The top electrode pattern corresponds to the ferroelectric functional region, so that the subsequently formed top electrode covers the surface of the low coercivity island structure and the exposed ferroelectric functional region around it, and no top electrode is formed on the surface of the boundary control region. The top electrode is made of titanium (Ti), platinum (Pt), molybdenum (Mo), tungsten (W), gold (Au), or titanium nitride (TiN), with a thickness of 50 nm to 200 nm. The top electrode is grown by electron beam evaporation, magnetron sputtering, or atomic layer deposition (ALD).
[0030] In step 9), an external electric field is applied to the low coercivity island structure and the ferroelectric functional region through an electrode structure for pre-polarization treatment. The pre-polarization electric field strength is 3 MV / cm to 10 MV / cm. An external electric field with a direction opposite to the preset polarization direction is applied, and the electric field strength that causes polarization reversal is 1 MV / cm to 5 MV / cm. Under the action of the external electric field, the low coercivity island structure preferentially undergoes polarization reversal. Through the proximity coupling between it and the high coercivity ferroelectric main body layer below it, a local electric field and elastic field are generated near the interface between the two, reducing the polarization reversal barrier of the adjacent high coercivity region. This induces ferroelectric domains in the ferroelectric main body layer to preferentially nucleate in the region below the low coercivity island structure and expand to the surrounding area.
[0031] Advantages of this invention:
[0032] This invention achieves coordinated control over the initiation nucleation location and subsequent expansion endpoint of ferroelectric domains by constructing locally distributed low-coercivity island structures in a nucleation induction layer with a low coercivity electric field and defining ferroelectric functional regions and boundary control regions in a ferroelectric host layer with a high coercivity electric field. This effectively improves the problems of strong randomness in ferroelectric domain nucleation and difficulty in limiting the flipping path and expansion range in existing nitride ferroelectric semiconductor thin films. The low-coercivity island structure is more prone to polarization reversal under an applied electric field. Through proximity coupling with the high-coercivity ferroelectric host layer below it, a local electric and elastic field is generated near the interface, reducing the polarization reversal barrier of the high-coercivity ferroelectric host layer below and adjacent to it. This induces ferroelectric domains to preferentially nucleate in a predetermined region, improving the consistency, repeatability, and designability of polarization reversal behavior. The boundary control region formed by short-pulse light treatment assisted by the photothermal conversion layer is a region of crystal structure disorder. Ferroelectricity in this region is suppressed or destroyed, effectively separating adjacent ferroelectric functional regions and limiting the lateral expansion range of ferroelectric domains. This suppresses reversal crosstalk between adjacent ferroelectric units and enhances the independence between different ferroelectric units. Furthermore, the synergistic design of the low-coercivity island structure and the high-coercivity ferroelectric host layer helps reduce the polarization reversal barrier in the high-coercivity ferroelectric operating region, thereby reducing device operating voltage and energy consumption, and mitigating the risk of dielectric breakdown under high electric fields. The resulting nitride ferroelectric semiconductor structure with controlled ferroelectric domain nucleation can be applied to ferroelectric memory cells, reconfigurable electronic devices, piezoelectric devices, acoustic devices, and related integrated nitride ferroelectric devices, showing promising application prospects. Attached Figure Description
[0033] Figure 1 This is a cross-sectional view of the bottom electrode, ferroelectric host layer, and nucleation induction layer obtained according to an embodiment of the method for preparing nitride ferroelectric semiconductors with controlled ferroelectric domain nucleation according to the present invention.
[0034] Figure 2 A schematic diagram of short-pulse light irradiation for an embodiment of the method for preparing nitride ferroelectric semiconductors with controlled ferroelectric domain nucleation according to the present invention;
[0035] Figure 3 This is a schematic diagram showing the division of ferroelectric functional regions and boundary control regions in a ferroelectric host layer according to an embodiment of the method for preparing nitride ferroelectric semiconductors for controlling ferroelectric domain nucleation according to the present invention.
[0036] Figure 4 This is a schematic diagram illustrating the formation of a second patterned mask according to an embodiment of the method for preparing a nitride ferroelectric semiconductor with controlled ferroelectric domain nucleation according to the present invention;
[0037] Figure 5 A cross-sectional view of a low coercive field island structure obtained in an embodiment of the method for preparing nitride ferroelectric semiconductors with controlled ferroelectric domain nucleation according to the present invention;
[0038] Figure 6 This is a cross-sectional view of the structure after forming the top electrode, according to an embodiment of the method for preparing a nitride ferroelectric semiconductor with controlled ferroelectric domain nucleation according to the present invention.
[0039] Figure 7 This is a schematic diagram of an embodiment of the method for preparing nitride ferroelectric semiconductors by controlling the nucleation of ferroelectric domains according to the present invention, in which an external electric field is applied to achieve polarization reversal, wherein (a) to (f) are schematic diagrams of the polarization reversal process. Detailed Implementation
[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0041] The method for preparing nitride ferroelectric semiconductors with controlled ferroelectric domain nucleation in this embodiment includes the following steps:
[0042] 1) Using a gallium nitride template as substrate 1, the substrate is first heated to 300℃ for pre-degassing, and then heated to 500℃ for heat treatment. On the substrate, N-type gallium nitride with a thickness of 100nm is grown as bottom electrode 2 using molecular beam epitaxy.
[0043] 2) Low-Sc composition ScAlN and high-Sc composition ScAlN are sequentially grown on the bottom electrode 2 using molecular beam epitaxy. In the ScAlN material system, generally, the higher the molar fraction of Sc, the lower the corresponding ferroelectric coercive field. Therefore, the coercive field of high-Sc composition ScAlN is lower than that of low-Sc composition ScAlN, making the high-Sc composition ScAlN layer more prone to preferential polarization reversal under the subsequent applied electric field. The lower-Sc composition ScAlN layer has a higher coercive field as the ferroelectric host layer 3, and the upper-Sc composition ScAlN layer has a lower coercive field as the nucleation induction layer 4. Figure 1 As shown.
[0044] The low-Sc-content ScAlN has a Sc molar fraction of 0.20, a thickness of 100 nm, and a coercive electric field of 4.2 MV / cm; the high-Sc-content ScAlN has a Sc molar fraction of 0.35, a thickness of 20 nm, and a coercive electric field of 3.4 MV / cm. The difference in coercive electric field between the two nitride ferroelectric materials is 0.8 MV / cm. The growth temperature is 600℃, the nitrogen flow rate of the plasma nitrogen source is 1.2 sccm, and the plasma source operating power is 400 W.
[0045] The mixture was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water, and then dried with nitrogen gas to remove particles, adsorbents, and organic residues.
[0046] 3) Photoresist is spin-coated onto the surface of the nucleation-inducing layer. After pre-baking, exposure, and development, a first patterned mask 5 is formed, which is used to divide the ferroelectric main layer into multiple ferroelectric functional regions and boundary control regions. The areas covered by the first patterned mask correspond to the subsequent ferroelectric functional regions, and the areas not covered by the first patterned mask correspond to the subsequent boundary control regions. The first patterned mask has multiple patterned units distributed in a two-dimensional periodic array to define the cross-sectional shape of the ferroelectric functional regions of the ferroelectric main layer. The surface shape of the patterned units is circular with a diameter of 20 μm, and the lateral dimension of the boundary control regions formed between adjacent ferroelectric functional regions is 5 μm.
[0047] 4) Ni is deposited on the surface of the nucleation-inducing layer on which the first patterned mask is formed to form a photothermal conversion layer 6 by magnetron sputtering; the photothermal conversion layer 6 has a thickness of 30 nm and covers the first patterned mask 5 and a portion of the exposed nucleation-inducing layer not covered by the first patterned mask 5; wherein, the photothermal conversion layer 6 on the exposed surface is in direct contact with the nucleation-inducing layer, while the photothermal conversion layer 6 on the first patterned mask 5 is isolated from the nucleation-inducing layer through the first patterned mask 5.
[0048] 5) The photothermal conversion layer is subjected to multiple short-pulse light irradiation treatments using a nanosecond pulsed laser, such as... Figure 2As shown, a pulsed laser with a wavelength of 532 nm and a pulse width of 10 ns was used. The laser repetition frequency was 10 Hz, and the incident energy density was 0.12 J / cm². Each irradiated area received 5 short laser pulses, and the laser spot diameter was 1 mm. The treatment was carried out under nitrogen atmosphere and room temperature conditions. The photothermal conversion layer absorbed the light energy of the short pulse irradiation, resulting in transient heating and thermal expansion, which was constrained by the interface. The photothermal conversion layer in the uncovered area transferred heat and thermal stress downward to the ferroelectric host layer. After the short pulse irradiation ended, the heat was rapidly dissipated through the nitride ferroelectric semiconductor thin film and the substrate, causing the local thermal field and thermal stress field to decay rapidly. The time interval between adjacent pulses was greater than the characteristic thermal relaxation time of the thin film structure, thus forming multiple rapid heating-cooling thermal cycles that were separated from each other. Under the influence of transient temperature gradient, thermal expansion mismatch, and thermal stress cycle, multiple short-pulse light irradiation treatments cause the crystal structure of the ferroelectric main layer region not covered by the first patterned mask to become disordered, and the ferroelectricity is suppressed or destroyed, forming boundary control region II, which is used to separate adjacent ferroelectric functional regions and limit the lateral expansion range of ferroelectric domains. The region of the ferroelectric main layer covered by the first patterned mask is protected by the first patterned mask and retains ferroelectricity as ferroelectric functional region I. Multiple ferroelectric functional regions are distributed in a two-dimensional periodic array, consistent with the distribution of the first patterned mask.
[0049] First, the first patterned mask is removed using an organic solvent, and then the photothermal conversion layer is removed by stripping. The photothermal conversion layer, which is in direct contact with the core-induced layer, is removed by etching. This yields a ferroelectric host layer defined with ferroelectric functional region I and boundary control region II, as shown below. Figure 3 As shown.
[0050] 6) Photoresist is spin-coated again onto the surface of the nucleation-inducing layer. After pre-baking, exposure, and development, a second patterned mask 7 is formed, comprising multiple patterned units distributed in a two-dimensional periodic array, consistent with the distribution of the ferroelectric functional regions and the first patterned mask. The patterned units of the second patterned mask are smaller than the cross-sectional shape of the ferroelectric functional regions and are located on the surface of the central region of the corresponding ferroelectric functional regions, such as... Figure 4 As shown, multiple low coercive field island structures are formed by defining the nucleation induction layer; each low coercive field island structure defined by the second patterned mask is located in the central region of the corresponding ferroelectric functional region I, serving as an induction structure for preferential nucleation of ferroelectric domains; the island structures are arranged in a two-dimensional array with a diameter of 2 μm.
[0051] 7) Using the second patterned mask as protection, the nucleation induction layer not protected by the second patterned mask is etched by inductively coupled plasma etching, thereby retaining locally distributed low coercive field island structures 8 in the central region of the ferroelectric functional region surface, that is, the low coercive field island structures 8 cover part of the surface of the ferroelectric functional region.
[0052] The second patterned mask was removed using an organic solvent, and a low-coercivity island structure 8 was formed on the surface of the central region of the ferroelectric functional area of the ferroelectric host layer, resulting in a nitride ferroelectric semiconductor structure, such as... Figure 5 As shown.
[0053] 8) A top electrode pattern is formed on the ferroelectric host layer with a low coercivity island structure by photolithography. The top electrode pattern corresponds to the ferroelectric functional region. A 50nm thick Ti electrode is formed by electron beam evaporation as the top electrode 9. The top electrode 9 covers the surface of the low coercivity island structure and the exposed ferroelectric functional region, such as... Figure 6 As shown, the top electrode 9 and the bottom electrode 2 together constitute the electrode structure.
[0054] 9) Pre-polarization treatment is performed by applying an external electric field to the low coercivity island structure and the ferroelectric functional region through an electrode structure. The electric field strength is 5 MV / cm, so that the polarization direction of the low coercivity island structure and the ferroelectric functional region is consistent with the preset polarization direction. In this embodiment, the preset polarization direction is downward. At this time, the ferroelectric domains in the ferroelectric functional region have a polarization direction consistent with the preset polarization direction, such as... Figure 7 As shown in (a), it is in an approximately single-domain state.
[0055] An external electric field with an intensity of 3.5 MV / cm is applied through the electrode structure, with the direction opposite to the preset polarization direction, i.e., upward. Figure 7 As shown in (b), under the influence of an electric field, the low-coercivity island structure undergoes polarization reversal before the ferroelectric host layer with a higher coercivity field. After polarization reversal, the low-coercivity island structure generates a local electric and elastic field near the interface with the underlying ferroelectric host layer through proximity coupling, reducing the polarization reversal barrier in the corresponding region of the ferroelectric host layer. This induces the reverse-polarized ferroelectric domains to preferentially nucleate in the region below the low-coercivity island structure, such as... Figure 7 As shown in (c); subsequently, the reverse-polarized ferroelectric domains extend downwards from near the interface along the film thickness direction, as... Figure 7 As shown in (d), and further extends laterally in all directions, as Figure 7 As shown in (e), when the reverse-polarized ferroelectric domains extend into the boundary control region, the boundary control region acts as a barrier and limit to the further expansion of the reverse-polarized ferroelectric domains, thereby confining the polarization reversal range within the corresponding ferroelectric functional region, such as... Figure 7 As shown in (f).
[0056] This invention forms a localized crystal structure disorder region within a predetermined boundary area to restrict the expansion boundary of ferroelectric domains, thereby reducing the randomness of ferroelectric domain nucleation, improving the consistency, repeatability, and designability of polarization reversal behavior, and helping to reduce the energy barrier required for local polarization reversal, device operating voltage, and energy consumption, while mitigating the risk of dielectric breakdown under high electric fields. The resulting nitride ferroelectric semiconductor structure with controlled ferroelectric domain nucleation can be applied to ferroelectric memory cells, reconfigurable electronic devices, piezoelectric devices, acoustic devices, and related integrated nitride ferroelectric devices.
[0057] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.
Claims
1. A method for preparing a nitride ferroelectric semiconductor with controlled ferroelectric domain nucleation, characterized in that, The preparation method includes the following steps: 1) Growing the bottom electrode on the substrate; 2) A nitride ferroelectric material with a high coercive electric field is sequentially formed on the bottom electrode as the ferroelectric host layer, and a nitride ferroelectric material with a low coercive electric field is formed as the nucleation induction layer. 3) A first patterned mask comprising multiple patterned units is formed on the surface of the nucleation-inducing layer; 4) Deposit a photothermal conversion layer on the surface of the nucleation-inducing layer on which the first patterned mask is formed; 5) The photothermal conversion layer is subjected to multiple short-pulse light irradiation treatments. The photothermal conversion layer absorbs the light energy of the short-pulse light irradiation to generate transient heating and thermal expansion, and transfers the heat and thermal stress downward to the region of the ferroelectric main body layer not covered by the first patterned mask. The ferroelectricity is suppressed or destroyed, forming a boundary control region. The region of the ferroelectric main body layer covered by the first patterned mask retains the ferroelectricity, forming multiple ferroelectric functional regions. Remove the first patterned mask and photothermal conversion layer; 6) A second patterned mask is formed on the surface of the nucleation-inducing layer; 7) Etch the nucleation-inducing layer to form a corresponding low-coercivity island structure on the surface of the central region of each ferroelectric functional region; Remove the second patterning mask; 8) Growing the top electrode on a ferroelectric functional region with a low coercive field island structure; 9) Perform pre-polarization treatment to give the ferroelectric domains in the ferroelectric functional region a polarization direction consistent with the preset polarization direction; When an external electric field is applied in the opposite direction to the preset polarization direction, the low coercivity island structure first undergoes polarization reversal, and the ferroelectric domains that induce reverse polarization preferentially nucleate in the region below the low coercivity island structure. The polarization-reversed ferroelectric domains extend downward along the film thickness direction and further extend laterally to the surrounding area. The boundary control region limits the polarization reversal range to the interior of the corresponding ferroelectric functional region.
2. The preparation method according to claim 1, characterized in that, In step 1), the substrate is a gallium nitride template, an aluminum nitride template, a sapphire substrate, a silicon carbide substrate, or a silicon substrate; the bottom electrode is made of N-type gallium nitride, titanium nitride, molybdenum, or platinum, with a thickness of 50 nm to 300 nm, and the bottom electrode is grown by molecular beam epitaxy, metal-organic chemical vapor deposition, reactive magnetron sputtering, or atomic layer deposition.
3. The preparation method according to claim 1, characterized in that, In step 2), different coercive electric fields are created between the two layers of nitride ferroelectric materials through differences in composition, doping, stress, or defects.
4. The preparation method according to claim 1, characterized in that, In step 2), the thickness of the ferroelectric host layer is 50 nm to 1000 nm; the thickness of the nucleation induction layer is 0.1 to 0.2 times the thickness of the ferroelectric host layer.
5. The preparation method according to claim 1, characterized in that, In step 3), the multiple patterned units of the first patterned mask are distributed in an array, and the surface shape of the patterned units is circular, elliptical, square or polygonal, with a lateral dimension of 100 nm to 50 μm.
6. The preparation method according to claim 1, characterized in that, In step 4), the photothermal conversion layer is made of one or more of metallic materials, metal nitride materials and carbon-based materials; it is formed by magnetron sputtering, electron beam evaporation, thermal evaporation or atomic layer deposition, and has a thickness of 10 nm to 200 nm.
7. The preparation method according to claim 1, characterized in that, In step 5), the short pulses are generated using a pulsed laser or a pulsed high-intensity light source.
8. The preparation method according to claim 5, characterized in that, In step 6), the second patterned mask includes multiple patterned units distributed in an array, consistent with the distribution of the first patterned mask and the ferroelectric functional region; the surface shape of the patterned units of the second patterned mask is circular, elliptical, square or polygonal, and the lateral dimension is 0.05 to 0.2 times the lateral dimension of the corresponding patterned unit of the first patterned mask.
9. The preparation method according to claim 1, characterized in that, In step 8), the top electrode is made of titanium, platinum, molybdenum, tungsten, gold or titanium nitride, with a thickness of 50 nm to 200 nm, and the top electrode is grown by electron beam evaporation, magnetron sputtering or atomic layer deposition.
10. The preparation method according to claim 1, characterized in that, In step 9), the electric field strength for pre-polarization treatment is 3 MV / cm to 10 MV / cm; the electric field strength for polarization reversal is 1 MV / cm to 5 MV / cm.