KR19990024359A - Composite dielectric membrane - Google Patents

Abstract

A composite TiO ₂ / Ta ₂ O ₅ film formed for storage capacitors in three-dimensional cells for DRAM applications and formed by in-situ sequential CVD is introduced. A capacitor with an optional layer structure of Ta ₂ O ₅ / TiO ₂ / Ta ₂ O ₅ is per unit area when compared with a capacitor having a single layer structure of Ta ₂ O ₅ and a capacitor having a single layer structure of TiO ₂ . Similar leakage current density and higher capacity per unit area.

Description

COMPOSITE DIELECTRIC FILMS

FIELD OF THE INVENTION The present invention relates to composite dielectric films, and more particularly to composite Ta ₂ O ₅ / TiO ₂ / Ta formed by in-situ sequential chemical vapor deposition (CVD) methods and used for capacitors in DRAM. ₂ O ₅ Membrane.

As the minimum feature size of the ultra high density integrated circuits (VLSI) is reduced, introduction of a three-dimensional capacitor structure (eg, a stacked structure or a trench structure) is inevitable for highly DRAM devices. However, the higher the degree of integration of circuits, the more complex structures are required. To simplify the process, there is extensive research on high dielectrics that can prevent soft errors by providing sufficient storage charge without using complicated capacitor structures. In order for the high dielectric to be practical, it must have a satisfactory leakage current.

Tantalum pentaoxide (Ta ₂ O ₅ ) films with relatively high dielectric constants (20-25), good step coverage, and lower leakage current after post-deposition annealing treatment are the most It is one of the common dielectric films. The Ta ₂ O ₅ film is formed by CVD. Cross-sectional views of the structures of capacitors with a single film and a composite film are shown in FIG. A single Ta ₂ O ₅ film, denoted A, is formed on a phosphorus (P) doped polysilicon (n ⁺ poly-Si) bottom electrode. On top of the Ta ₂ O ₅ dielectric film, titanium nitride (TiN) and aluminum (Al) (not shown) top electrodes are formed by reactive sputtering.

Recently, interest in titanium dioxide (TiO ₂ ) is increasing because of high dielectric constants (30-100). Figure 1 shows the structure of a capacitor with a single TiO ₂ film, denoted I. Like the single Ta ₂ O ₅ dielectric film, the TiO ₂ dielectric film is formed on the lower n ⁺ poly-Si electrode, on which TiN and Al electrodes are formed.

The capacity per unit area of the single dielectric films described above is shown in graphical form in FIG. 4. Since the TiO ₂ film I has a much higher dielectric constant, the capacitance of the capacitor with the film I is much higher than that of the capacitor with the film A. However, referring to FIGS. 2A, 2B, 6A, and 6B, the leakage current of the film I is the largest and the leakage current of the film A is the smallest. The larger leakage current of film I is due to the lower energy band gap of the TiO ₂ film (3eV to 4eV for TiO ₂ and 4eV to 5eV for Ta ₂ O ₅ ) and the microstructure of the film. do. This will be described later. In addition, the breakdown voltage distribution is shown in FIG. Film A maintains a higher voltage than film I.

It is an object of the present invention to provide a dielectric film having a higher dielectric constant and thus a higher capacity.

Another object of the present invention is to provide a dielectric film having a satisfactory leakage current and a lower breakdown voltage.

1 is a cross-sectional view of various capacitors having a single dielectric film and a composite dielectric film;

2A and 2B show leakage current characteristics of a single film and a double film under positive polarity and negative polarity, respectively;

3 shows breakdown voltage distribution of a single film and a double film;

4 shows the capacity per unit area of a single membrane and a bilayer;

FIG. 5 is a view showing auger electron spectroscopy (AES) depth of an AIA composite membrane; FIG.

6A and 6B show leakage current characteristics of a single film and a double film under positive polarity and negative polarity, respectively;

7 shows the threshold voltage and capacitance per unit area as a function of a single film and a triple film;

8 is a view comparing A structure and AIA structure; And

9 shows lifetime extraction for A structures and AIA structures, that is, 50% cumulative failure of A structures and AIA structures as a function of applied electric field.

Explanation of symbols for the main parts of the drawings

A: Ta ₂ O ₅ film I: TiO ₂ film

AIA: Ta ₂ O ₅ / TiO ₂ / Ta ₂ O ₅ IAI: TiO ₂ / Ta ₂ O ₅ / TiO ₂

In order to achieve the above objects and advantages, and as the present invention aims at, a composite dielectric film having a polysilicon bottom electrode doped with phosphorus (P), according to the present invention, Is formed. Rapid thermal nitridation (RTN) is performed for about 60 seconds at a temperature of about 900 ° C. in an ammonia atmosphere for the phosphorus-doped polysilicon bottom electrode. On the phosphorus-doped polysilicon bottom electrode, the first tantalum pentaoxide from a mixture of pentaethoxyl tantalum and oxygen gas by low pressure chemical vapor deposition, tantalum pentaoxide) layer is formed. On the first tantalum pentaoxide layer, a titanium dioxide layer is formed from a mixture of tetra-isopropyl-tianate and oxygen gas by low pressure chemical vapor deposition. A second tantalum pentaoxide layer is formed on the titanium dioxide layer. After the formation of the composite dielectric film, rapid thermal nitrous oxide annealing is performed at a temperature of about 800 ° C. for about 60 seconds. Reactive sputtering forms titanium nitride and aluminum upper electrodes.

It is to be understood that the foregoing general description and the following detailed description are exemplary and are for illustrative purposes only and are not intended to limit the invention as claimed.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, there is shown a bilayer consisting of Ta ₂ O ₅ (A) and TiO ₂ (I) films sequentially formed on an n ⁺ poly-Si bottom electrode and labeled AI. In addition, in FIG. 1, another double film which consists of the film | membrane I and the film | membrane A formed in order on the said n ⁺ polysilicon lower electrode, and is represented by IA is shown. In this and the following examples, both of films I and A were subjected to a low-polymerization chemical vapor deposition process to tetra-isopropyl-titanate (Ti) as an O ₂ and source gas, for example Ti source. (OC ₃ H ₇ ) ₄ , TPT) and as a Ta precursor, is formed from a mixture of pentaethoxy tantalum (Ta (OC ₅ H ₅ ) ₅ ). In the case of TiO ₂ deposition, the Ti source is vaporized at about 60 ° C. and injected into a reactor chamber using argon (Ar) gas. In the case of Ta ₂ O ₅ deposition, the Ta source is vaporized at 100 ° C. and injected into the reactive chamber. The deposition temperatures of TiO ₂ and Ta ₂ O ₅ are 450 ° C. and 350 ° C., respectively. Prior to formation, the sample is subjected to a rapid thermal nitriding process (RTN) for about 60 seconds in an ammonia (NH ₃ ) atmosphere, at about 900 ° C. After deposition, the sample is subjected to rapid thermal nitrogen dioxide (N ₂ O) annealing at about 800 ° C. for about 60 seconds. For use as a MOS capacitor, titanium nitride (TiN) and Al top electrodes are formed by reactive sputtering on the film AI.

2A and 2B, representative results of leakage current characteristics of 10 nm single film and double film are shown. The effective electirc field is calculated from the thickness of SiO ₂ with a dielectric constant of 3.82 calculated by the applied voltage and the CV measurement at 100 kHz. For both polarities, the capacitor with membrane A shows the lowest leakage current, while the capacitor with membrane I shows the highest leakage current. Note here that under positive polarity the AI structure has a higher leakage current compared to the IA structure. This is due to the reaction between TiO ₂ and Ta ₂ O ₅ which occurs during the post-deposition annealing treatment in which metallic Ta (Ti) present in the Ta ₂ O ₅ (TiO ₂ ) film diffuses into the TiO ₂ (Ta ₂ O ₅ ) film. Seems to do. Due to the stronger affinity for metallic Ti than metallic Ta, Ta functions as interstitial in the TiO ₂ film resulting in an increase in leakage current. In this embodiment, since it is impossible to control the amount of Ti diffused in the Ta ₂ O ₅ film, a large amount of Ti results in a larger leakage current of the AI double layer compared to the Ta ₂ O ₅ single layer. . As shown in Figures 2A and 2B, the I and IA structures (in this structure, the top layer is a TiO ₂ film) have an inferior leakage current for negative bias rather than for positive bias. This is probably because the surface of the TiO ₂ film is rougher than the Ta ₂ O ₅ film. In the case of the I and IA structures, surface roughness takes precedence over the work function difference between TiN and n ⁺ polysilicon. These results demonstrate that the leakage current is always higher when electrons are injected from the TiO ₂ / electrode. This means that the TiO ₂ and the contacting electrode play an important role in determining the electrical properties of the composite film.

3 shows the breakdown voltage distribution shown. The Ta ₂ O ₅ layer has a higher breakdown voltage than the composite layer. Capacitors with TiO ₂ dielectric films have higher capacities than capacitors with Ta ₂ O ₅ films. Both capacities for IA and AI are higher than for Ta ₂ O ₅ monolayers. This suggests that the combination of the TiO ₂ film and the Ta ₂ O ₅ film is more advantageous for increasing capacity compared to the single layer Ta ₂ O ₅ film.

Despite the higher capacitive action as a double layer structure, AI and IA are not optimal structures for composite films considering leakage current characteristics.

Referring back to FIG. 1, the upper layer film AIA and the other triple layer film IAI are deposited on the n ⁺ polysilicon bottom electrode. The method of depositing the two films A and I is the same as in the first embodiment. Here too, TiN and Al are used as the upper electrode. 5 shows the AES depth profile of the AIA structure. From this result, formation of a multilayered structure can be confirmed.

6A and 6B show leakage current characteristics of I, AIA, IAI, and A structures having a thickness of 15 nm. Capacitors with an IAI structure show superior leakage current compared to capacitors with an I film, and have higher leakage currents than AIA structures. This fact means that the leakage current is further inferior when electrons are injected from the TiO ₂ / electrode. Instead, when electron injection from the Ta ₂ O ₅ / electrode is made, the capacitor with the AIA structure shows a smaller leakage current. Moreover, capacitors with A and AIA structures have similar leakage current characteristics for both polarities.

FIG. 7 shows the critical voltage required to induce a leakage current of 10 nA / cm 2 and the capacity per unit area as a function of structure. TiO ₂ has the highest capacity but the lowest threshold voltage. Ta ₂ O ₅ has the opposite result. Although the AIA structure has a slightly lower threshold voltage (V _crit ) compared to the A structure, it has a capacity of about 15% higher.

FIG. 8 shows the distribution of the critical electric fields of the A and AIA structures, respectively, at positive and negative voltages. Here, the critical electric field is defined in an electric field having a leakage current of 1 μA / cm 2. From these results, it can be seen that the distribution of the AIA structure and the distribution of the A structure are similar.

FIG. 9 shows the field dependence of time versus 50% cumulative failure under two voltage stress polarities for the A and AIA structures. From this result, it can be seen that the reliability of the composite film AIA is comparable to that of the Ta ₂ O ₅ single film.

Those skilled in the art will appreciate that there may be various embodiments of the invention within the spirit and scope of the invention disclosed herein. The specific specification and embodiments disclosed herein are to be considered only as examples, the true scope and spirit of the invention being indicated by the following claims

According to the present invention as described above, the capacitor having a selective layer structure of Ta ₂ O ₅ / TiO ₂ / Ta ₂ O ₅ has a single layer structure of TiO ₂ and a capacitor having a single layer structure of Ta ₂ O ₅ Compared with capacitors, it has similar leakage current density per unit area and higher capacity per unit area.

Claims (8)

n ⁺ polysilicon bottom electrode; A titanium dioxide layer on the n ⁺ polysilicon bottom electrode; A tantalum pentaoxide layer on the titanium dioxide layer; A composite dielectric film comprising an upper electrode over the tantalum pentaoxide layer. The method of claim 1, Wherein the n ⁺ polysilicon bottom electrode is a phosphorus-doped polysilicon bottom electrode formed using an ammonia atmosphere, about 900 ° C., and a rapid nitriding process for about 60 seconds. The method of claim 1, The titanium dioxide layer is formed from a mixture of tetra-isopyrophyll-titanate and oxygen gas at a deposition temperature of about 450 ° C. using a low pressure chemical vapor deposition process; In the low pressure chemical vapor deposition process, the tetra-isopropyl-titanium is vaporized at a temperature of about 60 ° C., and the composite dielectric film is injected with the vaporized tetra-isopropyl-titanium into a reaction chamber using argon (Ar) gas. . The method of claim 1, The titanium pentaoxide layer is formed from a mixture of pentaethoxy tantalum and oxygen gas at a deposition temperature of about 350 ° C. using a low pressure chemical vapor deposition process; In the low pressure chemical vapor deposition process, the pentaethoxy tantalum is vaporized at a temperature of about 100 ° C., and the vaporized pentaethoxy tantalum is injected into a reaction chamber using argon (Ar) gas. The method of claim 1, Wherein the top electrode is a reactive sputtered and deposited titanium nitride and aluminum electrode. A polysilicon lower electrode doped with phosphorus (P); A tantalum pentaoxide layer on the bottom electrode; A titanium dioxide layer on the tantalum pentaoxide layer; A composite dielectric film comprising titanium nitride and an aluminum top electrode over the titanium dioxide layer. A polysilicon lower electrode doped with phosphorus (P); A first titanium dioxide layer on the phosphorus-doped polysilicon bottom electrode; A tantalum pentaoxide layer on the first titanium dioxide layer; A second titanium dioxide layer on said tantalum pentaoxide layer; A composite dielectric film comprising titanium nitride and an aluminum top electrode over the second titanium dioxide layer. A polysilicon lower electrode doped with phosphorus (P); A first tantalum pentaoxide layer on the phosphorus-doped polysilicon bottom electrode; A titanium dioxide layer on said first tantalum pentaoxide layer; A second tantalum pentaoxide layer on the titanium dioxide layer; 12. A composite dielectric film comprising titanium nitride and an aluminum upper electrode over the second tantalum pentaoxide layer.