JP3261735B2 - Method for manufacturing dielectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a manufacturing method of a ferroelectric capacitor mainly used for a dynamic random access memory (DRAM) or a nonvolatile memory.

[0002]

2. Description of the Related Art Conventionally, as a structure of a dielectric element, for example, an extended abstract of the 19
91 International Conference on Solid State Devices and Materials (Extended Abstracts of the
e 1991 International Conf
erence on Solid State Dev
ices and Materials), 1991,
As described in the paragraphs 195 to 197, a large capacity dynamic random access memory (DRA) is used.
M) and ferroelectric capacitors used for nonvolatile memories using ferroelectrics include lead zirconate titanate (PZT).
Alternatively, P doped with lanthanum (La)
The use of LZT was being considered.

[0003] As a method of manufacturing a dielectric element, conventionally,
For example, Extended Abstracts of the 1991 International Conference on Solid State Devices and Materials (Extended Abstracts of Materials)
the 1991 InternationalCon
reference on Solid State De
(Vices and Materials) 1991
As described in paragraphs 204 to 206, PLZT in which lead zirconate titanate (PZT) is doped with lanthanum (La) was formed by a sol-gel method.

In this case, as a raw material for PZT, lead acetate [Pb (CH ₃ COO) ₂ .3H ₂ O], zirconium tetra-en-basoxide [Zr (OC
₄ H ₉ ) ₄ ], titanium tetra eye propoxide [Ti (OC ₃ H ₇ ) ₄ ], and further as a raw material of La,
Lanthanum acetate [La (CH ₃ COO) ₂・
1.5H ₂ O] was used, and after mixing them at an appropriate molar ratio, spin-coating was performed on a silicon substrate on which a platinum film had been formed, calcination and annealing were performed to obtain a ferroelectric thin film. .

As another example of a method for manufacturing a dielectric element, for example, Journal of Applied Physics is used.
cs) As described in 736 to 741 in 1986, PLZT is formed on a sapphire substrate by a high-frequency magnetron sputtering method using a target obtained by sintering each raw material at an appropriate molar ratio. Thus, a crystalline thin film was obtained during sputtering.

[0006]

However, the conventional dielectric element is a PZT or PLZT as a ferroelectric capacitor.
Even in the case of using the memory, there is a limit in the holding characteristic of the memory, which has a practical problem.

That is, a polycrystalline ferroelectric is an aggregate of several crystal grains, and each crystal grain is also a set of domains oriented in various directions.

Each domain has spontaneous polarization.

Even when no electric field is applied to the ferroelectric capacitor from the outside, these spontaneous polarizations generate an internal electric field, so that mobile ions existing in the crystal grains or at the grain boundaries are not affected by the internal electric field. Will move.

[0010] Ferroelectric characteristics such as remanent polarization and dielectric characteristics such as dielectric constant corresponding to the memory of the nonvolatile memory are deteriorated, and when used as a nonvolatile memory or a DRAM, the actual use is guaranteed. There was a problem that a memory retention life of 10 years could not be obtained at 70 ° C.

Therefore, the dielectric element of the present invention is intended to solve such a conventional problem, and an object of the invention is to dope the mobile ions by doping phosphorus (P) as an impurity. Ring to prevent deterioration of ferroelectric properties such as remanent polarization and dielectric properties such as dielectric constant,
Non-volatile memory with excellent memory retention characteristics or DR
To provide AM.

Further, the conventional method of manufacturing a dielectric element has the following problems whether the sol-gel method or the sputtering method is used.

Even in the case of PZT which is not doped with La, since the vapor pressure of Pb is higher than that of other constituent elements, the molar ratio of Pb depends on the annealing conditions and the like. Deviate greatly.

In addition, in order to obtain optimum conditions such as dielectric constant and leak current by adding La, a large number of sol-gel raw materials or sputtering materials can be obtained by changing the molar ratio of Pb and La.
A target must be prepared, and the concentration of impurities and the profile in the depth direction, and PZ as a main component
It was very difficult to control the T composition at the same time.

Therefore, a method of manufacturing a dielectric element according to the present invention is to solve such a conventional problem.
The purpose is to control the impurity concentration easily by controlling the main component of the dielectric and the impurity independently, and it is also possible to control the doping profile.
It is possible to optimize the characteristics of the dielectric element such as the dielectric constant, the leak current, the remanent polarization, etc., and to greatly reduce the work for obtaining the optimum conditions.

[0016]

According to the present invention, there is provided a method of manufacturing a dielectric element, comprising the steps of (1) forming an amorphous dielectric film directly or through another layer on a semiconductor substrate; Doping the dielectric film with any one of neodymium (Nd), bismuth (Bi), niobium (Nb), and tantalum (Ta) by any one of a method, an ion implantation method, and an ion doping method; Crystallizing the dielectric film doped with the impurity after the step of doping the impurity. (2) forming an amorphous dielectric film directly or via another layer on the semiconductor substrate, crystallizing the amorphous dielectric film, and crystallizing the dielectric film After the step, neodymium (Nd), bismuth (Bi), niobium (N) is deposited on the crystallized dielectric film by any one of a thermal diffusion method, an ion implantation method, and an ion doping method.
b) doping any one of tantalum (Ta) impurities.

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the dielectric element of the present invention will be described with reference to the sectional structural view of FIG.

FIG. 1 is a sectional view showing a structure in which a ferroelectric capacitor is integrated on a semiconductor substrate on which active elements are actually formed.

Reference numeral 101 denotes a silicon substrate; 102, a diffusion layer formed by ion implantation and heat treatment; 103, a gate oxide film made of a silicon dioxide film (SiO ₂ );
4 is polycrystalline silicon and tungsten silicide (WS
The gate electrode formed according to i), which forms the main part of the field effect transistor.

The ferroelectric capacitor includes a platinum (Pt) lower electrode 105, a polycrystalline phosphorus (P) -doped PZT 106, and a platinum (Pt) upper electrode 107.

Below the lower electrode 105, a titanium (Ti) film 108 is formed as an adhesion layer.

Silicon dioxide films (SiO ₂ ) 109 and 110 are formed to separate the transistor and the capacitor, and the upper electrode 107 and the diffusion layer 102 are connected by an aluminum wiring 111.

The thickness of the P-doped PZT 106 is 5000 °
And the size was 2 μm square.

As in this embodiment, by using PZT doped with P as the ferroelectric capacitor portion, an accelerated test of the memory retention characteristics is performed at a high temperature, and the
With respect to the initial residual polarization density of 15 μC / cm ² when the V voltage was applied, the residual polarization density of 10 μC / cm ² after 10 years at the actual use guarantee temperature of 70 ° C. was extrapolated.

In the above embodiment, PZT was used as the P-doped ferroelectric film, but PbTiO ₃ , K
Oxide ferroelectrics having other perovskite crystal structures such as NbO ₃ and Pb (MnNb) O ₃ may be used, or lanthanum (La), neodymium (Nd), bismuth (Bi), niobium (Nb), Antimony (S
b), P may be doped into an oxide dielectric using tantalum (Ta) or the like as a dopant.

A first embodiment of the method for manufacturing a dielectric element according to the present invention will be described with reference to the manufacturing process sectional views of FIGS.

As shown in FIG. 2A, the silicon substrate 20
A silicon dioxide film (SiO ₂ ) 2 as an interlayer insulating film on 1
02, a Pt 204 as a lower electrode is formed via a Ti film 203 as an adhesion layer, and Pb, Zr, T
An amorphous dielectric film 205 containing i and O as main components is made of Pb _1.1 (Zr _0.5 T
i _0.5 ) Formed by a high frequency magnetron sputtering method using O _3.1 as a target.

This amorphous dielectric film is formed of polycrystalline lead zirconate titanate Pb (Zr _0.5 Ti _0.5 ) O ₃ , which exhibits ferroelectric properties by crystallization annealing described later. is there.

The SiO ₂ 202 was formed by plasma-enhanced chemical vapor deposition of tetra-ethyl-ortho-silicate (TEOS).

The Ti film 203 and the Pt 204 are formed by a direct current sputtering method.
000Å.

The thickness of the amorphous dielectric film 205 is set to 5000
Å

Next, as shown in FIG. 2B, impurity phosphorus (P) 2 is added to the amorphous dielectric film 205 by ion implantation.
06 is implanted perpendicularly to the silicon substrate 201.

The accelerating voltage is 40 KeV and the implantation concentration is 5
× 10 ¹⁴ / cm ² .

When driven under these conditions, most of P206
Is implanted into the amorphous dielectric film 205 and the underlying Si
It does not reach O ₂ 202.

After the implantation of P, the amorphous dielectric film 20 is formed.
5 is performed for crystallization annealing.

Annealing was performed in an oxygen atmosphere at a temperature of 600 ° C. for one hour.

By this heat treatment, a polycrystalline PZT 207 having a perovskite crystal structure with a thickness of 5000 ° was obtained (FIG. 2C).

Then, a film having a thickness of 2000 was used as the upper electrode.
Å, after deposition of gold (Au) having a size of 100 μm square, the remanent polarization density was measured to be 15 μC / cm ^2.
μC / cm ² was obtained.

Next, a description will be given of a second embodiment of the method for manufacturing a dielectric element according to the present invention with reference to FIGS.

As shown in FIG. 3A, the silicon substrate 20
A silicon dioxide film (SiO ₂ ) 2 as an interlayer insulating film on 1
02, a Pt 204 as a lower electrode is formed via a Ti film 203 as an adhesion layer, and Pb, Zr, T
i, amorphous dielectric film 205, for example, a PbO 10% containing excess Pb _1.1 mainly composed of O (Zr _0.5 Ti _0.5)
The O _{3 .1} formed by high-frequency magnetron sputtering using a target.

This amorphous dielectric film is formed of polycrystalline lead zirconate titanate Pb (Zr _0.5 Ti _0.5 ) O ₃ , which exhibits ferroelectric properties by crystallization annealing described later, and is a group that becomes PZT for short. is there.

The SiO ₂ 202 was formed by plasma-enhanced chemical vapor deposition of tetra-ethyl-ortho-silicate (TEOS), and its film thickness was 5000 °.

The Ti film 203 and the Pt 204 are formed by a direct current sputtering method, and their thickness is 200
000Å.

The thickness of the amorphous dielectric film 205 is set to 5000
Å

Subsequently, as shown in FIG. 3B, the amorphous dielectric film 205 is crystallized by annealing at 600 ° C. for 1 hour in an oxygen atmosphere to form a polycrystalline PZT20.
7 is formed.

Next, as shown in FIG. 3C, the amorphous dielectric film 205 is doped with impurity phosphorus (P) 2 by ion implantation.
06 is implanted perpendicularly to the silicon substrate 201.

The accelerating voltage is 40 KeV and the implantation concentration is 1
× 10 ¹⁴ / cm ² .

When driven under these conditions, most of P206
Is implanted into polycrystalline PZT 207 and the underlying SiO 2
Do not reach ₂ 202.

Then, a film having a thickness of 2000
Å, after deposition of gold (Au) having a size of 100 μm square, the remanent polarization density was measured to be 15 μC / cm ^2.
μC / cm ² was obtained.

In the second embodiment, the polycrystalline PZT20
As a forming method of 7, a crystallization annealing process is performed after forming an amorphous dielectric film once, but by increasing the substrate temperature at the time of sputtering to about 600 ° C. to 700 ° C. It is also possible to create PZT.

Also, by using chemical vapor deposition (CVD), it is possible to form crystalline PZT at the time of deposition.

In the above two embodiments, high frequency magnetron sputtering was used as a method for forming an amorphous dielectric film, but a sol-gel method may of course be used.

Also, although the description has been made assuming that the implantation angle of P206 into the silicon substrate 201 is vertical, it is larger than 0 degree,
Any number of incident angles may be used as long as the angle is smaller than 90 degrees.

Although the ion doping method using P ⁺ has been described as a doping method of P, a thermal diffusion method using POCl ₃ may be used, or PH ₃ which is a source gas of P may be used. Of course, an ion doping method in which all the decomposed cations such as P ⁺ and H ⁺ are implanted may be used.

In an embodiment of the method for manufacturing a dielectric element,
As described above, P was used as an impurity, but La, calcium (C
a), niobium (Nb), neodymium (Nd), bismuth (Bi), antimony (Sb), tantalum (T
An impurity such as a) may be doped.

Although PZT has been described as the ferroelectric film, PbTiO ₃ , KNbO ₃ , Pb (MnNb)
Oxide ferroelectrics having another perovskite crystal structure such as O ₃ may be used.

In the above two embodiments, the capacitor was formed on the silicon substrate. However, as shown in FIG.
An active element such as a transistor may be formed on a silicon substrate.

[0065]

As described above, the dielectric element of the present invention is a DRAM or a non-volatile memory having the above-mentioned dielectric capacitor by doping P as an impurity in a dielectric as a gettering agent for mobile ions. Under the actual use guarantee conditions, there is an effect that the memory retention characteristics can be remarkably improved to 10 years or more.

According to the method of manufacturing a dielectric element of the present invention, the impurity concentration can be easily controlled and the doping profile can be controlled by independently controlling the main component of the dielectric and the impurity as described above. Thus, the characteristics of the dielectric element such as the dielectric constant, the leak current, the remanent polarization, etc. can be optimized, and furthermore, there is an effect that the work can be greatly shortened to obtain the optimum conditions.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a dielectric element of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process for explaining a first embodiment of the method for manufacturing a dielectric element according to the present invention.

FIG. 3 is a manufacturing process sectional view for explaining a second embodiment of the method for manufacturing a dielectric element of the present invention.

[Explanation of symbols]

Reference Signs List 101 silicon substrate 102 diffusion layer 103 SiO ₂ gate film 104 gate electrode 105 platinum lower electrode 106 P-doped PZT 107 platinum upper electrode 108 Ti film 109 SiO ₂ 110 SiO ₂ 111 aluminum wiring 201 silicon substrate 202 SiO ₂ 203 Ti film 204 platinum lower Electrode 205 Amorphous dielectric film 206 Phosphorus (P) 207 Polycrystalline PZT

Continuation of the front page (56) References JP-A-3-106064 (JP, A) JP-A-4-80959 (JP, A) JP-A-2-1154 (JP, A) JP-A 64-82557 (JP) , A) JP-A-64-84656 (JP, A) JP-A-4-177765 (JP, A) Kiyoshi Okazaki, "Fourth Edition Ceramic Dielectric Engineering (Supplementary Seminar on Ferroelectric Physics)", Japan , Gakudonsha, June 1, 1992, pp. 335-336 Kiyoshi Okazaki, "Fourth Edition Ceramic Dielectric Engineering (Supplementary Exercise in Ferroelectric Physics)", Japan, Gakudensha, June 1992. January 1, pp. 549-552 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/8242 H01L 21/822 H01L 27/04 H01L 27/105 H01L 27/108

Claims (2)

(57) [Claims] A step of forming an amorphous dielectric film on a semiconductor substrate directly or through another layer; and forming the amorphous dielectric film by a thermal diffusion method, an ion implantation method, or an ion doping method. Neodymium (Nd), bismuth (Bi), niobium (Nb), tantalum (T
a) doping with any of the impurities of a), and crystallizing the dielectric film doped with the impurities after the doping of the impurities. Method. 2. A step of forming an amorphous dielectric film directly or via another layer on a semiconductor substrate; a step of crystallizing the amorphous dielectric film; After the crystallization step, neodymium (Nd), bismuth (Bi), niobium (Nb), tantalum (Ta) is applied to the crystallized dielectric film by any one of a thermal diffusion method, an ion implantation method, and an ion doping method. Doping with any one of the above-mentioned impurities).