Hafnium oxide-based ferroelectric film annealing process with low thermal budget and hafnium oxide-based ferroelectric film

Abstract

The invention provides a hafnium oxide-based ferroelectric film annealing process with a low thermal budget and a hafnium oxide-based ferroelectric film, and relates to the field of ferroelectric films, the hafnium oxide-based ferroelectric film is subjected to multiple low-temperature rapid annealing cycles, and the hafnium oxide-based ferroelectric film annealing process comprises the following steps: heating to an annealing temperature of 400 DEG C at a heating rate of 10-80K / s, keeping the temperature for 15-120s, and cooling at a cooling rate of not less than 10K / s, and after cooling to room temperature, carrying out next annealing cycle. The internal defect distribution of the thin film is changed through repeated rapid annealing circulation; and multiple times of rapid cooling are introduced, so that multiple times of enhanced stress is generated in the thin film, the hafnium oxide phase change potential barrier is cooperatively regulated and controlled, conversion from a non-ferroelectric high-temperature tetragonal phase to a ferroelectric orthogonal phase is promoted, and the requirement for the high annealing temperature is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ferroelectric thin films, in particular to a hafnium oxide-based ferroelectric thin film annealing process with low thermal budget and a hafnium oxide-based ferroelectric thin film. BACKGROUND

[0002] Ferroelectric random access memory (FRAM) is considered as one of the most promising technology routes due to its low power consumption, high speed writing, excellent data retention capability and good endurance. Although the ferroelectric memory technology based on perovskite materials has been relatively mature, with the continuous miniaturization of semiconductor process size and the continuous improvement of integration density, such materials exhibit significant attenuation of ferroelectricity when the thickness is less than 100 nm, have great difficulty in preparing three-dimensional structures, and have insufficient compatibility with CMOS technology, which leads to the stagnation of its commercialization process at the 130 nm node. New ferroelectric thin film materials based on HfO2 have gradually attracted attention. Such hafnium oxide-based ferroelectric materials can maintain stable ferroelectric properties even in an extremely thin state, have good data retention capability, are easy to realize three-dimensional stacking, and are highly compatible with CMOS technology, thereby successfully overcoming the technical obstacles faced by traditional perovskite materials.

[0003] Although hafnium oxide-based ferroelectric memory exhibits the above-mentioned advantages, there are still many challenges to realize large-scale application in 130 nm and more advanced processes. In the current widely used ferroelectric memory preparation process, the hafnium oxide-based ferroelectric thin film layer is usually prepared by sputtering or atomic layer deposition, etc. The hafnium oxide-based thin film in the initial state obtained by deposition is usually amorphous and does not have ferroelectric properties, and must rely on additional annealing to promote thin film crystallization and form a crystal phase with ferroelectricity. In order to obtain a high enough residual polarization strength and ensure a certain storage window, the annealing temperature usually needs to be maintained between 500°C and 700°C. However, this temperature range has exceeded the upper limit of 400°C allowed by the current back-end process, which seriously hinders the integrated application of ferroelectric memory in CMOS circuits.

[0004] In order to realize the reduction of the temperature required for the annealing of hafnium oxide-based ferroelectric thin films, the temperature of the annealing step can be reduced by optimizing the thin film deposition and the annealing step, and improving the ferroelectric polarization characteristics at low temperature annealing. The optimization of the thin film deposition method includes using ozone treatment of the lower electrode surface, preparing a multi-layer interface layer, thin film ion implantation, using plasma enhanced atomic layer deposition, etc. The optimization of the annealing step mainly includes increasing the annealing gas pressure, ultraviolet light irradiation assisted annealing, laser annealing, etc.

[0005] Although many studies have met the requirement of reducing the process temperature, there are still some limitations: 1. requiring complex thin film structure, increasing the difficulty of deposition, or introducing materials not commonly used in CMOS process; 2. requiring the introduction of additional processing technology, increasing the complexity of the preparation process; 3. the unconventional thin film deposition and heat treatment conditions put additional high demands on the equipment, and these special equipment make it difficult for these methods to be widely applied.

[0006] Therefore, there is still an urgent need for a low thermal budget method that can reduce the process temperature and achieve high-performance ferroelectric hafnium-based thin films while being simple and convenient. SUMMARY

[0007] The purpose of the present application is to provide a low thermal budget hafnium oxide-based ferroelectric thin film annealing process, which changes the internal defect distribution of the thin film through repeated rapid annealing cycles; multiple rapid cooling is introduced to generate multiple enhanced stresses inside the thin film, which cooperatively regulates the phase transition barrier of hafnium oxide, promotes the transition from the non-ferroelectric high-temperature tetragonal phase to the ferroelectric orthorhombic phase, and avoids the need for high annealing temperature.

[0008] Another purpose of the present application is to provide a hafnium oxide-based ferroelectric thin film, which is fully crystallized through rapid annealing cycle processing, with reduced oxygen vacancies and stress regulation conducive to the formation of ferroelectricity.

[0009] The present application solves the technical problems by adopting the following technical solutions.

[0010] On the one hand, the present application provides a low thermal budget hafnium oxide-based ferroelectric thin film annealing process, which adopts multiple low-temperature rapid annealing cycles for the hafnium oxide-based ferroelectric thin film, and each low-temperature rapid annealing includes the following steps: The temperature is raised to 400℃ at a rate of 10-80K / s, and the temperature is maintained for 15-120s. The cooling rate is not less than 10K / s, and the next annealing cycle is performed after cooling to room temperature.

[0011] In some embodiments of the present application, the hafnium oxide-based ferroelectric thin film includes TiN layers, HZO layers and TiN layers deposited in sequence, wherein the thickness of the TiN layer is 20-40nm, and the thickness of the HZO layer is 8-10nm.

[0012] In some embodiments of the present application, the temperature rising rate is 10-20K / s, and the cooling rate is 10-20K / s.

[0013] In some embodiments of the present application, the temperature rising rate is 13K / s, the holding time is 60s, and the cooling rate is 10K / s.

[0014] In another aspect, the embodiment of the present application provides a hafnium oxide-based ferroelectric thin film obtained after the annealing process.

[0015] Compared with the prior art, the embodiment of the present application has at least the following advantages or beneficial effects: The multiple rapid low-temperature annealing cycle process provided by the present application realizes a low-heat-budget hafnium oxide-based ferroelectric thin film annealing process, the highest temperature in the whole process does not exceed 400 DEG C, meets the highest temperature requirement of the back-end process, and solves the problem of high-temperature annealing at 500 DEG C-700 DEG C required by high-performance ferroelectric thin films. Compared with other existing low-heat-budget annealing processes, the present application does not need complex thin film structure design or introduction of non-standard CMOS process and special equipment, and has the advantages of simplicity, convenience, excellent thin film performance and easy large-scale application. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0017] Figure 1 The temperature and time relationship diagram of the annealing process of the embodiment of the present application; Figure 2 The cross-sectional schematic diagram of the hafnium oxide-based ferroelectric thin film of the embodiment 1 of the present application; Figure 3 The three-dimensional schematic diagram of the hafnium oxide-based ferroelectric thin film device of the embodiment 1 of the present application; Figure 4 The residual polarization strength comparison diagram of the hafnium oxide-based ferroelectric thin film of the embodiment and the comparative example of the present application; Figure 5 The electron microscope diagram of the hafnium oxide-based ferroelectric thin film of the embodiment 1 and the comparative example 1 of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0019] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to specific embodiments.

[0020] The embodiment of the present application provides a hafnium oxide-based ferroelectric thin film annealing process with low heat budget, a plurality of low-temperature rapid annealing cycles are adopted for the hafnium oxide-based ferroelectric thin film, wherein each single low-temperature rapid annealing comprises three stages of rapid heating, holding and rapid cooling, and the holding stage, that is, the highest temperature stage in the annealing process, is set to a temperature of not more than 400 DEG C; the single low-temperature rapid annealing comprises the following steps: The temperature is raised to the annealing temperature 400 DEG C at a temperature raising rate of 10-80 K / s, the temperature is held for 15-120 s, and then the temperature is cooled to room temperature at a cooling rate of not less than 10 K / s, and then the next annealing cycle is performed.

[0021] The key step of thin film crystallization is the rapid cooling stage, and the cooling rate needs to be controlled to be 10 K / s or above, so that the hafnium-based ferroelectric thin film can be rapidly reduced from the holding temperature to room temperature, The hafnium oxide-based ferroelectric thin film is composed of three parts, that is, the bottom TiN layer, the middle Zr element doped HfO2 (HZO) thin film layer showing ferroelectricity, and the top TiN layer, wherein the bottom and top TiN layers are deposited by using a sputtering method; the HZO thin film layer is deposited by using an atomic layer technology (ALD), the deposition temperature is controlled to be lower than 400 DEG C by alternately depositing HfO2 thin film and ZrO2 thin film and sequentially circulating. The hafnium oxide-based ferroelectric thin film comprises TiN layers, HZO layers and TiN layers deposited in sequence, wherein the thickness of the TiN layer is 20-40 nm, and the thickness of the HZO layer is 8-10 nm.

[0022] After the deposition of the three-part thin film is completed, the subsequent patterning process is used to form a memory device array, and the thin film crystallization is performed through the above-mentioned low-temperature rapid annealing cycle process, so that the hafnium oxide-based ferroelectric thin film device with excellent ferroelectric performance is obtained, and the whole process temperature of thin film deposition and annealing process is not more than 400 DEG C.

[0023] More preferably, the temperature raising rate is 10-20 K / s, and the cooling rate is 10-20 K / s.

[0024] More preferably, the temperature raising rate is 13 K / s, the holding time is 60 s, and the cooling rate is 10 K / s.

[0025] More preferably, the number of annealing cycles is not less than 3.

[0026] The annealing process provided by the present application changes the internal defect distribution of the thin film through repeated rapid annealing cycles, introduces multiple rapid cooling, and due to the difference in thermal expansion coefficient between the electrode material and the ferroelectric thin film, multiple enhanced stresses are generated in the thin film, which cooperatively regulates the hafnium oxide phase transition barrier, promotes the transition from the non-ferroelectric high-temperature tetragonal phase to the ferroelectric orthorhombic phase, and avoids the need for high annealing temperature.

[0027] The features and performance of the present application are described in further detail below in connection with examples.

[0028] Example 1 1. Preparation of hafnium oxide-based ferroelectric thin film: First, a first layer of bottom TiN electrode is deposited on the substrate; then, on the TiN electrode, atomic layer technology (ALD) is used for deposition, by alternately depositing HfO2 thin film and ZrO2 thin film and sequentially cycling, the deposition temperature is controlled at 250°C; in the third step, a top TiN electrode is deposited, and then a patterned metal top electrode is obtained by photolithography etching. The thickness of the TiN electrode is 20 nm, and the thickness of the HZO ferroelectric thin film layer is 10 nm. As shown in FIG. 1. Figure 2 and 3 .

[0029] 2. Annealing The capacitor device containing the hafnium oxide-based ferroelectric thin film is placed in a rapid annealing furnace, and annealing is performed by a low-temperature rapid annealing cycle method, and the holding temperature of each time in the rapid annealing cycle is controlled to be not more than 400°C. As shown in FIG. 2. Figure 1 .

[0030] Specifically, the heating rate is 13K / s, the annealing temperature is 400°C, the holding time is 60s, the cooling rate is 10K / s, and after each single annealing is completely cooled to room temperature, the next rapid annealing cycle is performed. A total of 10 cycles are performed.

[0031] The sample obtained in this example is tested for performance, and after three rapid annealing cycles, the highest residual polarization strength is achieved, and excellent ferroelectric performance is achieved.

[0032] Example 2 1. Preparation of hafnium oxide-based ferroelectric thin film: The preparation method is the same as that of Example 1, and the thickness of the TiN electrode layer is 40 nm, and the thickness of the HZO ferroelectric thin film layer is 8 nm.

[0033] 2. Annealing The annealing process is the same as that of Example 1.

[0034] Comparative Example 1 Based on the hafnium oxide-based ferroelectric thin film prepared in Example 1, a conventional low-temperature annealing process (single) is used, the heating rate is 13K / s, the annealing temperature is 400°C, the holding time is 30s, and the cooling rate is 10K / s.

[0035] Comparative Example 2 Based on the hafnium oxide-based ferroelectric thin film prepared in Example 1, a conventional low-temperature annealing process (single) is used, the heating rate is 13K / s, the annealing temperature is 550°C, the holding time is 30s, and the cooling rate is 10K / s.

[0036] Comparative Example 3 Based on the hafnium oxide-based ferroelectric thin film prepared in Example 1, a conventional low-temperature annealing process (single) was used, the heating rate was 13 K / s, the annealing temperature was 400℃, the holding time was 300 s, and the cooling rate was 10 K / s.

[0037] Experimental Example The remanent polarization of the hafnium oxide-based ferroelectric thin film after treatment in Example 1-2 and Comparative Example 1-3 was tested, and the results are shown in Figure 4 From Figure 4 , it can be concluded that, compared with Example 1, the HZO thin film after treatment in Comparative Example 1 did not produce enough ferroelectric phase, and the overall ferroelectric thin film showed paraelectric characteristics, no significant remanent polarization, and could not meet the application of ferroelectric memory devices; the hafnium oxide-based ferroelectric thin film after treatment in Comparative Example 2 used a high-temperature annealing process, and the polarization performance of the hafnium oxide-based ferroelectric thin film obtained was similar to that after low-temperature rapid annealing cycle, and no outstanding effect was obtained, and the high temperature conflicted with the back-end process temperature limit, and could not be compatible with the current CMOS process. It also shows that the low-temperature rapid annealing cycle process provided by the embodiment of the present application has similar remanent polarization to the hafnium oxide-based ferroelectric thin film treated by the conventional high-temperature annealing process, and can meet the related requirements. The hafnium oxide-based ferroelectric thin film obtained in Comparative Example 3 also has good ferroelectricity, but the remanent polarization value is slightly lower than that of the hafnium oxide-based ferroelectric thin film after treatment in Example 1.

[0038] High-resolution transmission electron microscopy was used to observe the hafnium oxide-based ferroelectric thin film after treatment in Example 1 and Comparative Example 1, as shown in Figure 5 , wherein Figure 5 (a) is an electron microscope image of the hafnium oxide-based ferroelectric thin film after treatment in Comparative Example 1, Figure 5 (b) is an electron microscope image of the hafnium oxide-based ferroelectric thin film after treatment in Example 1; from Figure 5 , it can be concluded that Figure 5 the film in (a) is not fully crystallized, has more oxygen defects, and the stress is in the out-of-plane direction. Figure 5 The film in (b) is fully crystallized, the oxygen vacancies are reduced, and the stress is adjusted to the in-plane direction which is conducive to the formation of ferroelectricity.

[0039] The above-described embodiments are part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without creative labor fall within the scope of protection of the present application.

Claims

1. A low thermal budget hafnium oxide-based ferroelectric thin film annealing process, characterized in that, The hafnium oxide-based ferroelectric thin film is subjected to multiple low-temperature rapid annealing cycles, including the following steps: The temperature is raised to the annealing temperature of 400℃ at a temperature raising rate of 10-80K / s, and the temperature is kept for 15-120s, and then the temperature is cooled to room temperature at a cooling rate of not less than 10K / s, and then the next annealing cycle is performed.

2. The low thermal budget hafnium oxide-based ferroelectric thin film annealing process of claim 1, wherein, The hafnium oxide-based ferroelectric thin film comprises TiN layers, HZO layers and TiN layers deposited in sequence, wherein the thickness of the TiN layer is 20-40nm, and the thickness of the HZO layer is 8-10nm.

3. The low thermal budget hafnium oxide-based ferroelectric thin film annealing process of claim 1, wherein, The temperature raising rate is 10-20K / s, and the cooling rate is 10-20K / s.

4. The low thermal budget hafnium oxide-based ferroelectric thin film anneal process of claim 3, wherein, The temperature raising rate is 13K / s, the temperature keeping time is 60s, and the cooling rate is 10K / s.

5. A hafnium oxide-based ferroelectric thin film, characterized by, The hafnium oxide-based ferroelectric thin film obtained after being treated by the annealing process according to any one of claims 1-4.

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