JP3206105B2 - Method for manufacturing dielectric element and semiconductor memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, for example, Applied Physics Letters
ters), Vol. 58, No. 11, pp. 1161-1163, 1991, used for large-capacity dynamic random access memory (DRAM) and nonvolatile memory using ferroelectric material. For the ferroelectric capacitor to be used, lead zirconate titanate (PZT) is used, and high-speed heat treatment using a lamp is performed as crystallization annealing.

[0003] Lamp heating conditions are, for example, 650 ° C, 1
0 sec, 100 ° C./sec.

[0004]

However, the remanent polarization density when using the conventional lamp heating is 10 μm / cm ^2.
When this ferroelectric capacitor is used as a large-capacity nonvolatile memory, it cannot be said to be a sufficient value in consideration of the retention characteristics of remanent polarization and film fatigue due to repetitive polarization reversal.

[0005] The retention characteristics and the film fatigue due to repetitive polarization reversal will be briefly described below.

[0006] Writing of information in a nonvolatile memory device using a ferroelectric substance is performed according to the direction of polarization of the ferroelectric film.

That is, the ferroelectric film has a capacitor structure sandwiched between upper and lower electrodes. For example, the ferroelectric film has a coercive electric field higher than the coercive electric field of the ferroelectric film so that the upper electrode has a positive potential with respect to the lower electrode. When a bias is applied, the polarization direction is downward, and when a bias is applied in the opposite direction to the above direction, the polarization direction is upward.

[0008] The direction of this polarization corresponds to information 0 and 1.

Therefore, the value of the remanent polarization density is 0 μm / cm.
^When it becomes ² , the information 0 and 1 cannot be determined, and memory destruction occurs.

[0010] The memory retention characteristic is whether or not the information held at the time of reading can be read out while the direction of polarization is held, for example, in the downward direction.

In general, the value of the remanent polarization decays with temperature and time, so that the stored information disappears.

On the other hand, when information is rewritten, the direction of the bias applied to the capacitor is changed. It is known that the value of the remanent polarization is attenuated even when the direction is repeated. .

The present invention is intended to solve such a conventional problem.
Even when a ferroelectric capacitor is used as a large-capacity non-volatile memory, the remanent polarization density is improved so that there is no practical problem, even when the retentive polarization retention characteristics and film fatigue due to repeated polarization reversal are taken into account. To provide a method for manufacturing a dielectric element.

[0014]

According to the present invention, there is provided a method for manufacturing a dielectric element, comprising the steps of (1) forming an amorphous dielectric film directly or via another layer on a semiconductor substrate; A step of forming a silicon oxide layer above the body film and a step of crystallizing the dielectric film with the silicon oxide layer provided above are provided in this order.

(2) The crystallization step is performed by irradiating ultraviolet rays. (3) The ultraviolet light is obtained by using a laser as an ultraviolet light source. (4) The laser is an excimer laser. (5) The wavelength of the excimer laser is a wavelength of an absorption band of the dielectric film.

(6) The excimer laser is irradiated in an oxygen atmosphere. (7) The excimer laser is composed of XeCl, ArCl, A
It is characterized in that any one of rF, KrCl, KrF, XeBr and XeF is used. (8) The ultraviolet light is obtained by using any one of a hydrogen discharge tube, a low-pressure and a high-pressure mercury lamp, and a Xe lamp as an ultraviolet light source.

Further, a semiconductor memory device of the present invention is characterized in that: (9) the semiconductor memory device is manufactured by using the method of manufacturing a dielectric element according to any one of the above (1) to (9). (10) a semiconductor substrate, an active element formed on the semiconductor substrate, and a dielectric film formed on the semiconductor substrate and having a crystalline structure of a perovskite crystalline dielectric film, The dielectric film has a degree of crystal orientation of 111.
It is characterized by showing orientation. (11) A semiconductor memory device manufactured by using the method for manufacturing a dielectric element according to any one of claims 1 to 8, wherein the degree of crystal orientation of the dielectric film is 111. Features.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a method for manufacturing a dielectric element according to the present invention will be described with reference to FIGS. 1 (a) to 1 (c).

As shown in FIG. 1A, a silicon substrate 10
A silicon dioxide film (SiO ₂ ) 1 as an interlayer insulating film
02, a lower electrode Pt 104 is formed via a titanium (Ti) film 103 as an adhesion layer, and Pb and Pb are formed thereon.
Amorphous dielectric film 105 containing Zr, Ti, and O as main components
The, for example PbO 10% containing excess Pb _1.1 (Zr _0.5
It is formed by a high frequency magnetron sputtering method using Ti _0.5 ) 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, and is a group that becomes PZT for short. is there.

The SiO ₂ 102 was formed by plasma-enhanced chemical vapor deposition of tetra-ethyl-ortho-silicate (TEOS), and its film thickness was set to 5000 °.

The Ti film 103 and the Pt 104 are formed by a direct current sputtering method.
000Å.

The thickness of the amorphous dielectric film 105 is 5000
Å

Next, as shown in FIG. 1B, for example, an excimer laser 106 of XeCl is irradiated to the dielectric film 105 perpendicularly to the silicon substrate.

The XeCl excimer laser emits ultraviolet light and has a wavelength of 308 nm.
In the absorption band of No. 5, the dielectric film 105 absorbs the excimer laser, heats up rapidly, and is crystallized by itself at that temperature.

The excimer laser was irradiated in an oxygen atmosphere at 500 mJ and 10 W at 20 Hz for 0.5 second.

As a result, a polycrystalline PZT 107 having a perovskite crystal structure is formed as shown in FIG.

At this time, the degree of crystal orientation of polycrystalline PZT 107 shows a strong (111) orientation, and the particle size of PZT is 20%.
It was about 0 °, and a very dense film was obtained.

The remanent polarization density was 20 μC / cm ² .

A second embodiment of the method for manufacturing a dielectric element according to the present invention will be described with reference to the sectional views of the manufacturing steps shown in FIG.

The difference from the first embodiment is that a silicon dioxide film (SiO ₂ ) 108 is formed as a cap layer on the amorphous dielectric film 105.

The thickness of SiO ₂ 108 is 500 °,
Some of the ultraviolet light is absorbed by SiO ₂ 108, but some is transmitted.

As described above, by providing the cap layer on the amorphous dielectric film 105, the evaporation of oxygen from the dielectric film 105 can be prevented. Can be used for crystallization.

In the above two embodiments, the X-ray source is X
Although the description has been made using the eCl excimer laser, ArCl,
ArF, KrCl, KrF, XeBr, XeCl, Xe
Of course, even if an excimer laser such as F is used, it falls within the absorption band of the dielectric film, which is of course good.

Further, ultraviolet rays such as a hydrogen discharge tube, low and high pressure mercury lamps, and Xe lamps may be used.

Also, as a method of forming an amorphous dielectric film, high-frequency magnetron sputtering has been described.
Of course, a sol-gel method may be used.

Further, although the angle at which the excimer laser 106 is implanted into the silicon substrate 101 is described as being vertical, any number of incident angles may be used as long as the angle is greater than 0 degrees and less than 90 degrees.

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, or lanthanum (La), calcium (Ca), niobium (Nb), neodymium (N
d), bismuth (Bi), antimony (Sb), tantalum (Ta) and the like may be doped.

In the above embodiment, the capacitor is formed on the silicon substrate. However, an active element such as a transistor may be formed on the silicon substrate.

In this case, by suppressing the penetration length of the ultraviolet rays to the extent of the amorphous dielectric film, it is possible to eliminate the adverse effect on the underlying active element.

[0041]

As described above, the method for manufacturing a dielectric element according to the present invention irradiates an amorphous dielectric with ultraviolet rays that can be absorbed by the dielectric and crystallizes the amorphous dielectric very rapidly. Crystallization can be performed, and the degree of orientation of specific crystal planes can be increased, the grain size can be reduced, and the film can be made denser, so that the remanent polarization of the ferroelectric can be increased and the characteristics of each crystal grain can be made uniform. It has the effect of reducing the coercive electric field and the saturation electric field, and has the effect of increasing the dielectric constant even in the case of a paraelectric substance. When integrated on a conventional semiconductor substrate, it can be said that the dielectric element can be integrated without adversely affecting the active element, and that crystallization can be performed at a higher speed than in the past, so that it can be manufactured in a short time. Has the effect.

[Brief description of the drawings]

FIG. 1 is a manufacturing process sectional view for explaining a first example of a method for manufacturing a dielectric element of the present invention.

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

[Explanation of symbols]

Reference Signs List 101 silicon substrate 102 SiO ₂ 103 Ti film 104 Pt lower electrode 105 amorphous dielectric film 106 excimer laser 107 polycrystalline PZT 108 SiO ₂

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification code FI H01L 27/04 27/105 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 27/108 H01L 21/268 H01L 21/324 H01L 21/822 H01L 21/8242 H01L 27/04 H01L 27/105

Claims (11)

(57) [Claims] A step of forming an amorphous dielectric film on a semiconductor substrate directly or via another layer; a step of forming a silicon oxide layer above the dielectric film; And a step of crystallizing the dielectric film in a state in which is provided above, in this order. 2. The method according to claim 1, wherein the crystallization step is performed by irradiating ultraviolet rays. 3. The method for manufacturing a dielectric element according to claim 2, wherein the ultraviolet light is obtained by using a laser as an ultraviolet light source. 4. The method according to claim 3, wherein the laser is an excimer laser. 5. The method according to claim 4, wherein the wavelength of the excimer laser is a wavelength of an absorption band of the dielectric film. 6. The method according to claim 4, wherein the excimer laser is irradiated in an oxygen atmosphere. 7. The excimer laser according to claim 1, wherein the excimer laser is XeCl, Ar
The method according to claim 4, wherein any one of Cl, ArF, KrCl, KrF, XeBr, and XeF is used. 8. The ultraviolet light, a hydrogen discharge tube as an ultraviolet light source,
3. The method according to claim 2, wherein one of a low-pressure and high-pressure mercury lamp and a Xe lamp is used. 9. A semiconductor memory device manufactured by using the method for manufacturing a dielectric element according to claim 1. Description: 10. A semiconductor substrate, an active element formed on the semiconductor substrate, a dielectric film formed on the semiconductor substrate and having a crystalline structure of a perovskite crystalline dielectric film,
Wherein the dielectric film has a degree of crystal orientation of 111. 11. A semiconductor memory device manufactured by using the method for manufacturing a dielectric element according to claim 1, wherein the degree of crystal orientation of the dielectric film is 111. A semiconductor memory device characterized by the above-mentioned.