Preparation method of passive device

Abstract

The invention discloses a preparation method of a passive device, and belongs to the technical field of integrated circuits. The method comprises the following steps: growing an isolation layer on a silicon substrate; a bottom electrode is formed through dry etching, and the work function of the bottom electrode is gt; 4.7 eV; a functional layer NbOx thin film is deposited on the bottom electrode, and the work function of the NbOx thin film ranges from 3.3 eV to 4.0 eV by regulating and controlling the oxygen content in the NbOx thin film; forming a top electrode on the functional layer, wherein the work function of the top electrode is gt; 4.7 eV; the electric potential difference between the functional layer NbOx thin film and the bottom electrode and the electric potential difference between the functional layer NbOx thin film and the top electrode are kept between 1 eV and 1.8 eV. The energy band of the NbOx thin film is matched with the energy band of the top electrode and the energy band of the bottom electrode, and forming-free operation is achieved. The reliability problem caused by initialization of the gating device is solved, and the problem that in the prior art, large operation voltage is increased, and peripheral circuit design is complex is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor and CMOS hybrid integrated circuit, and in particular relates to a method for preparing a passive device having the function of not requiring activation operation. Background Art

[0002] With the rapid development of the intelligent era, the amount of data is growing, and the demand for memory is increasing. However, with the slowdown of Moore's Law, it is particularly important to study new memories. As one of the representatives of new memories, the RRAM array adopts a cross-gate architecture, in which each word line and bit line are vertically connected, so that the leakage current has a significant impact on the read operation. The double-terminal structure of the selector has excellent scalability and simple structure. Connecting the selector with RRAM to form a 1S1R structure will not bring additional area overhead and is considered to be the most promising integrated structure. The selector is divided into barrier type, physical phase type and ion type. Research on the ion type shows that although it has a higher switching ratio, it has problems with reliability and insufficient on-state current. The reliability of the barrier type is better than that of the ion type selector, but the switching ratio is usually inferior to that of the ion type selector. In contrast, the physical phase type has not only relatively high reliability, but also a large on-state current. Among them, the material preparation involved in the OTS type (Ovonic Threshold switching) in the physical phase type is more complicated. Among the physical phase types, vanadium oxide and niobium oxide are Mott insulators with higher switching ratio and on-state current. As transition metal oxides, they are friendly to CMOS back-end processes and are ideal materials for gate tubes.

[0003] Usually, a Mott gate tube needs to undergo a high voltage electrical activation initialization operation. Currently, the characteristics of IMT devices based on Mott materials are improved through process and device design, which helps to improve the switching characteristics to alleviate some of the fluctuation problems caused by initialization. However, it still cannot fundamentally solve the fluctuation and reliability problems caused by initialization. Summary of the invention

[0004] In view of the above-mentioned deficiencies, the present invention proposes a method for preparing a non-electrically activated gating tube device to solve the reliability problem caused by the initialization of the gating device and the problem that the large operating voltage increases the complexity of the peripheral circuit design.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing a passive device, the steps comprising:

[0007] 1) growing an isolation layer on a silicon substrate;

[0008] 2) depositing an adhesion layer and a first metal layer on the isolation layer in sequence, and then forming a photoresist having a first photolithography pattern; and forming a bottom electrode by dry etching, wherein the work function of the first metal layer is greater than 4.7 eV;

[0009] 3) depositing a functional layer NbOx film on the bottom electrode, and adjusting the oxygen content in the NbOx film, wherein the work function of the NbOx film is between 3.3 eV and 4.0 eV;

[0010] 4) forming a photoresist having a second photolithographic pattern on the functional layer, and depositing a second metal layer, wherein the work function of the second metal layer is greater than 4.7 eV, and etching the second metal layer to form a top electrode; achieving a potential difference between the functional layer NbOx film and the bottom electrode and the top electrode, respectively, maintained at 1 eV to 1.8 eV.

[0011] In the above step 1), the isolation layer is preferably silicon oxide SiO 2 Or SiNx, preferably the preparation process is chemical vapor deposition CVD, plasma enhanced chemical vapor deposition PECVD, or thermal oxidation process. The thickness of the isolation layer is 200nm-1000nm. It can be set according to the actual use conditions of the device.

[0012] In the above step 2), the adhesion layer is preferably made of metal Ti, and the preferred preparation process is physical vapor deposition PVD or magnetron sputtering, etc. The thickness of the adhesion layer is 10-30 nm.

[0013] In the above step 2) and step 4), the metal layer material is preferably one or more of high work function metals (work function>4.7) such as platinum Pt, gold Au, palladium Pd, ruthenium Ru, iridium Ir, and their alloys. The preferred preparation process is physical vapor deposition PVD or magnetron sputtering, ion beam sputtering, electron beam evaporation or thermal evaporation, and the thickness of the metal layer is 10-100nm.

[0014] The preparation process of the functional layer material in step 3) is physical vapor deposition PVD or atomic layer deposition ALD, etc., and the thickness of the functional layer is 20-500nm. It is treated with oxygen plasma to ensure the surface is clean, or the natural oxide layer on the surface is treated by reverse sputtering.

[0015] The beneficial effects of the present invention are as follows:

[0016] The NbOx film used in the present invention has different properties depending on its oxygen content. Niobium oxide with little oxygen has metallic conductivity, while niobium oxide rich in oxygen has high resistivity, and the work function increases with the degree of oxidation. When the oxide semiconductor NbOx contacts the metal, the difference between the work function of the metal and the work function of the oxide semiconductor determines the height of the Schottky barrier. This directly affects the transport properties of electrons from the metal to the semiconductor. The contact potential difference between the NbOx film and the metal electrode is regulated by adjusting the preparation process conditions of the NbOx film. The contact potential difference between the functional layer NbOx film and the bottom electrode and the top electrode is maintained at 1eV to 1.8eV, respectively, to achieve good rectification characteristics. Specifically, the present invention achieves forming-free operation by adjusting the oxygen content in the NbOx film so that the energy band of the NbOx film matches the energy band of the top electrode and the bottom electrode.

[0017] As used herein, hyphenated chemical composition notation indicates the elements contained in a particular compound or alloy and is intended to indicate all stoichiometries involving the indicated elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the NbOx gating tube according to an embodiment of the present invention.

[0019] Figure 2 FIG. 1 is a top view of a NbOx gating tube according to an embodiment of the present invention.

[0020] Figure 3 This is a process flow chart of the gate tube device of the present invention.

[0021] Figure 4 Schematic diagram of the DC characteristics of the NbOx gating tube at room temperature according to an embodiment of the present invention, wherein (a) is a forward cycle and (b) is a reverse cycle.

[0022] Figure 5 Schematic diagram of the window characteristics of the NbOx gating tube according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below with reference to specific embodiments and accompanying drawings.

[0024] The following examples take the Ti / Au / NbOx / Pd gate tube prepared by the present invention as an example. Figure 1As shown in the figure, an isolation layer is grown on a silicon substrate, and an adhesion layer of titanium and a first metal layer of gold are sequentially deposited by electron beam evaporation. The work function of the first metal layer is > 4.7 eV. Then, photolithography is performed, and a bottom electrode is formed by dry etching. A functional layer of niobium oxide NbOx thin film is grown by PVD, using a NbO2 target for sputtering, with Ar = 12 - 13.5 sccm and O = 0.5 - 2 sccm; and Ar + O = 14 sccm is satisfied. Keeping the sputtering pressure constant, the sputtering power is 80 - 150 W, and NbOx thin film with 2 < X < 2.5 is prepared, such that the work function is between 3.3 eV and 4.0 eV. And it is subjected to oxygen plasma treatment to ensure surface cleanliness. A bottom electrode lead-out hole is formed by photolithography and dry etching. A photoresist with a second photolithography pattern is formed on the functional layer, and a second metal layer of palladium is deposited. The work function of the second metal layer is > 4.7 eV. Finally, a top electrode is prepared by photolithography, sputtering, and etching. The structure of the device is a cross-shaped type, and the effective area of the device is determined by the overlapping area of the top and bottom electrodes, as Figure 2 shown. In the present invention, the effective area of the device is 50 nm × 50 nm - 500 um × 500 um.

[0025] The specific preparation method of the strobe tube in the embodiment of the present invention is as Figure 3 shown, and includes the following steps:

[0026] 1) A 300-nm-thick isolation layer SiO is grown on the prepared silicon substrate by thermal oxidation process 2 .

[0027] 2) On the isolation layer, 10 nm of Ti is sequentially deposited by electron beam evaporation as an adhesion layer and 50 nm of Au as the first metal layer, and then a photoresist with a first photolithography pattern is formed; after post-baking for 30 min, a bottom electrode is set by dry etching. The work function of Au is 5.1 eV.

[0028] 3) On the bottom electrode, using magnetron sputtering through a metal target NbO 2 , with Ar:O = 12.5:1.5 and a sputtering power of 90 W, a functional layer dielectric of 80 nm NbOx is deposited, and it is subjected to oxygen plasma treatment to ensure surface cleanliness, and reverse sputtering is used to remove the native oxide layer (oxygen-rich) to avoid affecting the contact potential difference with the top electrode. The functional layer NbOx is an n-type semiconductor. By adjusting the argon and oxygen flow rates and the sputtering pressure in the PVD process, its work function is about 3.3 eV, which is less than the work function of Au. When in contact with Au, a Schottky barrier will be formed, and electrons need to overcome a large energy barrier to cross the barrier, thereby enhancing the non-linear characteristics of the device.

[0029] 4) A 50nm top electrode metal layer Pd is deposited on the functional layer, and then a photoresist with a second photolithography pattern is formed, and the metal layer is subjected to reactive ion etching to form a second metal layer. The work function of Pd is 5.12eV, and the functional layer NbOx will form a Schottky barrier when in contact with Pd. Since the work functions of Au and Pd are close, Schottky barriers will be formed at both ends of the NbOx functional layer, so that the potential difference between the NbOx semiconductor functional layer film and the bottom electrode and the top electrode is maintained at 1eV to 1.8eV. This energy band design allows high current to be passed without forming a conductive wire, avoiding the initialization operation of a large voltage.

[0030] Figure 4 Schematic diagram of the forward and reverse cycle (DC characteristics at room temperature) of the Ti / Au / NbOx / Pd gate tube of the embodiment of the present invention. In the DC scanning test, the device does not need to undergo an initialization process, which is different from the threshold transition of the traditional IMT device. The different performances of the positive voltage and negative voltage curves in the trap filling restriction area are mainly due to the different difficulty of injecting electrons from different metal materials on both sides. The work function of palladium is larger than that of gold, so electrons on the gold side are easier to inject. Therefore, when operating at a negative voltage, palladium relatively restricts the injection of electrons, and the overall conductive mechanism is dominated by the electrode-restricted Schottky mechanism. On the positive voltage side, the electron injection is sufficient, and the current shows a square law until it reaches the trap-free restriction area. As the voltage increases, the current increases sharply. The reason for this sudden increase in current is partly because after the trap is filled, it enters the trap-free restriction area, resulting in more partial pressure applied to the dielectric layer, further reducing the effective barrier height, thereby triggering the FN tunneling effect.

[0031] In addition, the device has a rectification characteristic, which is more significant when the absolute value of the applied voltage is greater than 1V. It is worth noting that under forward bias, the device exhibits a volatile resistive switching phenomenon and shows a clear hysteresis curve. The erase and write test shows that the device can withstand at least 10E6 switching cycles. In fact, after stress testing, it was found that the device can withstand stress for a longer time. In addition, during the test, the fluctuations between device cycles were also small. These advantages are attributed to the elimination of the IMT initialization process, thereby avoiding the instability problem caused by initialization, which is more conducive to large-scale application.

[0032] Figure 5 This is a schematic diagram of the window characteristics of the NbOx gating tube according to an embodiment of the present invention. The window of the device is greater than 500 when the number of cycle operations exceeds 10E6, and the performance is stable, which can effectively suppress the problem of bypass current in the array.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. A person skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for preparing a passive device, comprising the steps of: 1) growing an isolation layer on a silicon substrate; 2) depositing an adhesion layer and a first metal layer on the isolation layer in sequence, then forming a photoresist having a first photolithography pattern, and forming a bottom electrode by dry etching, wherein the work function of the first metal layer is greater than 4.7 eV; 3) depositing a functional layer NbOx film on the bottom electrode, and adjusting the oxygen content in the NbOx film, wherein the work function of the NbOx film is between 3.3 eV and 4.0 eV; 4) forming a photoresist having a second photolithography pattern on the functional layer, and depositing a second metal layer, wherein the work function of the second metal layer is greater than 4.7 eV, etching the second metal layer to form a top electrode, so that the potential difference between the functional layer NbOx film and the bottom electrode and the top electrode is maintained at 1 eV to 1.8 eV.

2. The preparation method according to claim 1, characterized in that The preparation process of the deposited functional layer NbOx film in step 3) is physical vapor deposition PVD or atomic layer deposition ALD.

3. The preparation method according to claim 2, characterized in that: The deposited functional layer NbOx film in step 3) is prepared by physical vapor deposition PVD, specifically by sputtering NbO2 target, Ar = 12 ~ 13.5sccm, O = 0.5 ~ 2sccm; and satisfying Ar + O = 14sccm, keeping the sputtering pressure unchanged, and the sputtering power is 80 ~ 150W, to prepare the NbOx film, so that 2 <X<2.5。 4. The preparation method according to claim 1, characterized in that: In step 1), the isolation layer is made of silicon oxide SiO2 or SiNx, and its preparation process is chemical vapor deposition CVD, plasma enhanced chemical vapor deposition PECVD, or thermal oxidation process. The thickness of the isolation layer is 200nm-1000nm.

5. The preparation method according to claim 1, characterized in that: In step 2), the adhesion layer is made of metal Ti, and its preparation process is physical vapor deposition PVD or magnetron sputtering, and the thickness of the adhesion layer is 10-30nm.

6. The preparation method according to claim 1, characterized in that: The first metal layer or the second metal layer is selected from one or more of metal platinum Pt, metal gold Au, metal palladium Pd, metal ruthenium Ru or metal iridium Ir and alloys thereof.

7. The preparation method according to claim 1, characterized in that: The preparation process for depositing the first metal layer or the second metal layer is physical vapor deposition (PVD), magnetron sputtering, ion beam sputtering, electron beam evaporation or thermal evaporation, and the thickness of the first metal layer or the second metal layer is 10-100 nm.

8. The preparation method according to claim 1, characterized in that: The thickness of the functional layer NbOx film is 20-500nm.

9. The preparation method according to claim 1, characterized in that: In step 3), the functional layer NbOx film is treated with oxygen plasma to ensure the surface cleanliness, or the natural oxide layer on the surface is treated by reverse sputtering.

Images