JPH07263572A - Manufacture of semiconductor memory device and semiconductor memory device and application system using it - Google Patents

Abstract

PURPOSE:To realize the high integration of a semiconductor memory device and to miniaturize the system to which the semiconductor memory device is applied by making an electrode containing metal titanium into a semiconductor substrate and forming an insulating film in the surface of the electrode with plasma oxidation applied to the electrode. CONSTITUTION:A thermal oxide film 2 is formed on a semiconductor substrate 1 at first. Next, a metal titanium thin film 3 is formed for a lower electrode by a sputtering method. Further, an insulating film 4 is formed with the surface of the metal titanium thin film 3 oxidized by a plasma oxidation method. Finally, a metal thin film is formed for an upper electrode 5 by an evaporation method and a capacitor is completed. Thus, since metal titanium is oxidized by oxygen plasma which is high density and high reactive, an insulating film containing oxide titanium of high dielectric constant can be made at a low temperature as compared with the other oxidation method such as thermal oxidation method. Thereby, the fining of of a capacitor can be performed with sufficient capacity being secured for alpha-ray resistance.

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 semiconductor memory device to which a high dielectric constant insulator is applied, a semiconductor memory device and its application system.

[0002]

2. Description of the Related Art In order to reduce the size and increase the speed of a computer, the dynamic random access memory (hereinafter abbreviated as DRAM) which is a storage element of the computer is highly integrated. The basic circuit of the DRAM memory cell unit currently used is composed of a MOS transistor and a capacitor. This circuit stores 1 bit of data depending on the amount of charge stored in the capacitor. This capacitor must store a charge of 100 fC or more in order to prevent an error (soft error) due to the charge generated by α rays. Therefore, for example, when the circuit operates at a voltage of ± 1.5 V, the capacitance of the capacitor needs to be 60 fF or more.

In order to highly integrate the DRAM, it is necessary to miniaturize the size of the capacitor of the memory cell while ensuring the capacitance of the capacitor as described above.

The prior art which makes this possible is the eighth
There is a method of using a material having a large relative permittivity (ε _r ) as an insulating film of a capacitor, as described in Proceedings of the 32nd Ferroelectric Application Conference, pp.3-29. Materials having a large relative dielectric constant include SrTiO ₃ (ε _r ≈200 to 300) and Pb.
There is Zr _1-x Ti _x O ₃ (ε _r ≈1000). These substances are silicon dioxide (ε _r
It has a large relative dielectric constant of about 50 to 250 times that of ≈4).

[0005]

The thin films of SrTiO ₃ and PbZr _1-x Ti _x O ₃ described above have a good crystallinity and a high dielectric constant equivalent to those of bulk materials. It is necessary to make the substrate temperature higher than 500 ° C. in an oxygen atmosphere. At this time, the surface of aluminum (hereinafter referred to as Al) or polycrystalline silicon, which is the lower electrode of the capacitor, is oxidized to form aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) or silicon dioxide (hereinafter referred to as SiO ₂ ). To be done. The relative permittivities of Al ₂ O ₃ and SiO ₂ are about 9 and about 4, respectively. That is, the relative permittivity of these oxides is SrTiO ₃ or PbZr _1-x T
It is much smaller than i _x O ₃ . As a result, the insulating film of the capacitor is a high-dielectric-constant film and a low-dielectric-constant film connected in series, so that the capacitance of the capacitor is reduced.

As a method for preventing such electrode oxidation,
There is a method using a noble metal electrode such as platinum. But,
In a multi-element oxide insulating film such as SrTiO ₃ or PbZr _1-x Ti _x O _3, there is a problem that a low dielectric constant phase is generated due to composition shift. For example, sputtering method or C
When the PbZr _1-x Ti _x O ₃ film is formed by the VD (Chemical Vapor Deposition) method, Pb in the insulating film easily diffuses into the Pt electrode, so Pb is deficient in the insulating film. Therefore, Zr
O ₂ precipitates. The dielectric constant of ZrO ₂ is 10 or less, and P
It is smaller than the dielectric constant of bZr _1-x Ti _x O ₃ . Further, when Si of the substrate diffuses in the electrode and reaches the surface of the electrode, SiO ₂ is formed here. Therefore, even if a precious metal electrode is used,
The capacitance of the capacitor decreases.

An object of the present invention is to solve the above problems and to highly integrate a semiconductor memory device.

Another object of the present invention is to downsize and speed up a system to which a semiconductor memory device is applied.

[0009]

A first feature of the present invention for achieving the above object is a method of manufacturing a semiconductor memory device having the following steps.

(A) A step of forming an electrode containing metallic titanium, which will be an electrode of a capacitor, on a semiconductor substrate.

(B) A step of plasma-oxidizing the electrode formed in the step (a) to form an insulating film of a capacitor on the surface of the electrode.

(C) A step of forming another electrode of the capacitor on the surface of the insulating film formed in the step (C).

A second feature of the present invention is that a semiconductor substrate is provided with an electrode containing metallic titanium as one electrode of a capacitor, and an insulating film containing titanium oxide having crystals of a rutile structure is used as an insulating film of the capacitor. Is provided in the semiconductor memory device.

A third feature of the present invention is an application system having the semiconductor memory device of the present invention.

[0015]

According to the first feature of the present invention, since titanium metal is oxidized by the oxygen plasma having high density and high reactivity, it has a high dielectric constant at a lower temperature than other oxidation methods such as thermal oxidation. An insulating film containing titanium oxide (hereinafter referred to as TiO ₂ ) can be manufactured. Therefore, as compared with other oxidation methods such as thermal oxidation, oxidation of the lower electrode and S from the semiconductor substrate are performed.
The diffusion of i, etc. is unlikely to occur. Further, since TiO ₂ is chemically and thermodynamically stable, it is hard to deteriorate due to the influence of the process after forming the insulating film. Furthermore, TiO
_{Since No. 2} has a simple binary chemical composition, composition deviation is unlikely to occur. Therefore, a low dielectric constant film or a high dielectric constant insulating film containing no low dielectric constant phase can be obtained. As a result, it is possible to miniaturize the capacitor while ensuring a sufficient capacitance for the α-ray resistance, so that the semiconductor memory device can be highly integrated. Further, according to the second feature of the present invention, TiO ₂ having a rutile structure crystal has a high dielectric constant and is a substance which hardly causes compositional deviation.
Therefore, since the capacitor can be miniaturized, the semiconductor memory device can be highly integrated. Further, since the present TiO ₂ is chemically and thermodynamically stable, the insulating film is unlikely to be defective. Therefore, a highly integrated and large capacity semiconductor memory device can be obtained with a high yield.

Further, according to the third feature of the present invention, a large-capacity semiconductor memory device highly integrated according to the present invention can constitute an inexpensive and large-capacity storage device, and a memory card, a microprocessor, a computer. It is possible to downsize the system such as.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 shows a method of manufacturing a semiconductor memory device according to an embodiment of the present invention. However, this figure shows
4 illustrates a method of manufacturing a capacitor unit. a) First, the thermal oxide film 2 having a film thickness of about 100 nm is formed on the Si substrate 1. b) Next, a metal titanium (Ti) thin film 3 having a thickness of about 500 nm is formed as a lower electrode by a sputtering method. c) Further, the surface of the metal Ti thin film 3 is oxidized by the plasma oxidation method to form the TiO ₂ insulating film 4 having a film thickness of about 100 nm. d) Finally, gold (Au) is used as the upper electrode 5 by a vapor deposition method.
A thin film is formed to a thickness of about 50 nm to complete a capacitor. When the Ti thin film is formed by the sputtering method, metallic Ti is used as a target, argon is used as the sputtering gas, the sputtering gas pressure is 1 Pa, and the substrate temperature is 30.
The film is formed under the condition of 0 ° C. In addition to the sputtering method, a chemical vapor deposition (CVD) method can be used for producing the Ti thin film. In this case, titanium tetrachloride (TiCl
₄ ) is plasma decomposed in a hydrogen (H ₂ ) atmosphere to form a Ti thin film.

FIG. 2 shows an ECR (electron cyclotron resonance) plasma processing apparatus used for plasma oxidation of a Ti thin film. The Si substrate 100 is set on the substrate susceptor 102 having a built-in substrate heater. The microwave waveguide 1 is provided in the vacuum container 101 through a microwave introduction window 106 made of quartz.
08 is connected. Then, through this waveguide, from a microwave generator (not shown) at 2.45 GHz
The microwave electric field is introduced into the vacuum container 101. The vacuum container 101 is connected to the substrate loading load lock chamber 104 via a gate valve 109. And from here S
The i substrate is carried into the vacuum container 101. Oxygen gas is introduced into the vacuum container 101 through the reactive gas inlet 105 for plasma oxidation. A magnetic field coil 103 is installed around the vacuum container 101. Each magnetic field coil is controlled so that the direction of magnetic force lines on the Si substrate 100 is perpendicular to the substrate.

Using this ECR plasma processing apparatus, Ti
When oxidizing the thin film, the vacuum vessel 101 is evacuated to about 1 × 10 ⁻⁶ Torr, and then oxygen gas at a flow rate of 100 ml / min is introduced into the vacuum vessel 101 to set the pressure to 0.1 Pa. When microwaves are introduced into the vacuum chamber 101, electron cyclotron resonance occurs due to the electric field of the microwaves and the magnetic field (875 Gauss) generated by the magnetic field coil. As a result, the oxygen gas in the vacuum container becomes a plasma state. The Ti thin film is oxidized by such excited oxygen and oxygen ions. Therefore, the reaction between Ti and oxygen occurs more strongly than in ordinary thermal oxidation, so that the substrate temperature during oxidation can be reduced.

FIG. 3 shows the X-ray diffraction pattern of the TiO ₂ film examined by the present inventors when the microwave power was 600 W. At a substrate temperature of 180 ° C., the diffraction peak is only for the lower electrode, Ti. Therefore,
At this substrate temperature, the structure of the TiO ₂ film is amorphous. When the substrate temperature is increased to 280 ° C., (11) of TiO ₂ having a rutile structure is formed at an X-ray diffraction angle 2θ = 27.6 °.
A diffraction peak from the (0) plane appears. That is, a TiO ₂ crystal having a rutile structure is growing. When the substrate temperature is further increased, the X-ray diffraction angle 2θ = 27.55 to 27.75 °
In this range, a strong diffraction peak appears from the TiO ₂ (110) plane of the rutile structure. Then, as the temperature rises, the diffraction intensity increases. This is because when the substrate temperature is increased, T
It shows that the crystallinity of iO ₂ is improved.

FIG. 4 shows the substrate temperature and Ti when the microwave power was 600 W, which was studied by the present inventors.
The relationship of the relative permittivity of the O ₂ film is shown. As shown in FIG. 3, at the substrate temperature of 280 ° C., the relative dielectric constant suddenly increases corresponding to the start of the appearance of the diffraction peak of TiO ₂ having a rutile structure.
And, when the substrate temperature is 400 ° C. or higher, it exceeds 100. However, at 500 ° C. or higher, the relative dielectric constant tends to be saturated or decreased. Regarding the crystallinity, as shown in FIG. 3, the higher the substrate temperature is, the better. However, Ti directly on the Si substrate
When the lower electrode is formed, Si and T are heated at about 500 ° C or higher.
i reacts to generate titanium silicide (TiSi).
Thus, when the lower electrode becomes TiSi, SiO ₂ becomes T
It is formed between the iO ₂ insulating film and the capacitance of the iO ₂ insulating film.

As described above, the substrate temperature is set to 280 to 500.
By performing plasma oxidation in the range of ℃, it is possible to produce a rutile structure TiO ₂ having a high dielectric constant without causing a decrease in capacitance due to silicide.

FIG. 5 shows the relationship between the Ti oxide film thickness and the substrate temperature. As shown in this figure, when the oxidation temperature is increased, the oxidation rate becomes faster. Therefore, the higher the temperature, the more difficult it becomes to control the film thickness. Therefore, Pt, which is difficult to oxidize, is used as the lower electrode. By oxidizing the Ti / Pt laminated film in which Ti is formed on Pt, the upper Ti is completely oxidized to TiO ₂ , but the lower Pt remains as an electrode without being oxidized. Therefore, even if the oxidation rate is increased, the lower electrode of the capacitor will not be lost and ohmic contact with other elements will not be lost. This makes it possible to prevent a decrease in yield due to defective electrodes. Not only Pt but also a noble metal such as Au, Pt, Pd, Ir, Re can be used as the electrode.

FIG. 6 shows the relationship between the Ti film thickness before plasma oxidation and the TiO ₂ film thickness formed by plasma oxidation. Since the film thickness is doubled by the oxidation, the Ti film formed at the thickness of the Ti film initially formed is generated by the plasma oxidation.
The film thickness of O ₂ can be controlled. That is, (A)
The lower electrode is formed of a laminated film of Ti and Pt, the thickness of the Ti is set to half the predetermined insulating film thickness, and (B) Ti is entirely oxidized. The accuracy of can be increased.

The film may peel after the plasma oxidation. This is because distortion occurs due to volume expansion due to oxidation. This can be prevented by dividing the Ti metal film into fine patterns before oxidation. As a result, the contact area between the metal Ti film and TiO ₂ is reduced, so that the oxidative stress is relaxed and peeling does not occur.

(Embodiment 2) FIG. 7 shows a sectional view of a DRAM in which a TiO ₂ film is applied to the insulating film of a capacitor. In this figure, 201 is a p-type Si substrate, 202 is an n-type doped layer that constitutes the source of a MOS transistor, and 203 is the other.
Is an n-type doped layer constituting a drain, 204 is a gate electrode, 206 is a storage node electrode, 207 is an insulating film of a capacitor, 208 is a plate electrode, 209 is a Si oxide film, 2
Reference numeral 10 is a gate insulating film, 211 is an interlayer insulating film, and 205 is a bit line. In this DRAM manufacturing method, first, a source 202 and a drain 203, a gate insulating film 210, a gate electrode 204, and an S that form a MOS transistor are formed on a substrate.
After forming the i oxide film 209, a Ti / Pt laminated film is formed on the upper surface of the Si oxide film 209 by a sputtering method or a CVD method, and then patterned. In this laminated film, Pt contacts the n-type doped layer of the source 202. Here, as in the previous embodiment, instead of Pt, A
Noble metals such as u, Pt, Pd, Ir and Re can be used as electrodes. After forming the laminated electrode in this way, a TiO ₂ insulating film to be the insulating film 207 of the capacitor is formed by plasma oxidation as in the previous embodiment. Further, Pt is formed as the plate electrode 208 by the sputtering method, and the interlayer insulating film 211 and the bit line 205 are formed, whereby the DRAM cell is completed.

In this embodiment, the insulating film of the capacitor is TiO ₂ containing crystals of the rutile structure. As a result, since the insulating film has a high dielectric constant, it is possible to miniaturize the dimensions of the capacitor while ensuring a sufficient capacitance for α-ray resistance. Moreover, since this insulating film is thermodynamically and chemically stable, defects do not easily occur in this insulating film. Therefore, according to the present embodiment, the highly integrated and high yield DRA
M can be realized.

FIG. 8 is a block diagram of the DRAM of the present invention.
The memory cell is composed of one MOS transistor 1101 and a capacitor 1102. Then, this memory cell has 1
Stores bit data.

The gate electrode of the MOS transistor is connected to the word line 1103, and the word line is connected to the decoder driver of the peripheral circuit. The drain electrode of the MOS transistor is connected to the bit line 1104, and this bit line is further connected to the sense amplifier 1105, the read circuit 1106, and the read circuit 1106.
It is connected to a peripheral circuit such as the writing circuit 1107. Also, the source electrode of the MOS transistor is connected to one electrode of the capacitor, and the other electrode of the capacitor is connected to the plate line common to each bit.

In the conventional DRAM cell, SiO ₂ is used for the insulating film of the capacitor. However, since SiO ₂ has a small dielectric constant of 4, it is difficult to secure a sufficient capacity when the cell area is reduced for high integration. On the other hand, in the DRAM cell of the present invention, a sufficient capacitance can be obtained by using TiO ₂ having a high dielectric constant for the insulating film. Therefore, a large-capacity DRAM having a high degree of integration can be constructed.

(Embodiment 3) FIG. 9 shows the DRAM cell of the present invention used in a logic element (microprocessor), memory element (DRAM), semiconductor disk substrate, and semiconductor memory card. The block diagram of a computer system is shown.

Since the DRAM cell of the present invention is small and has a large capacity, the entire system is miniaturized. Furthermore, since a large amount of information can be read and written at high speed, the processing capacity of the entire system is improved.

[0034]

According to the present invention, a capacitor having a large electrostatic capacity can be easily manufactured. When the capacitor of the present invention is applied to a DRAM, a highly integrated and large capacity DRAM can be realized.

[Brief description of drawings]

FIG. 1 is a method of manufacturing a semiconductor memory device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an ECR plasma processing apparatus.

FIG. 3 is a thin film X-ray diffraction pattern of a titanium oxide thin film.

FIG. 4 is a diagram showing the relationship between the relative dielectric constant of a titanium oxide thin film and the substrate temperature.

FIG. 5 is a diagram showing the relationship between the film thickness of titanium oxide produced by plasma oxidation of a Ti thin film and the substrate temperature.

FIG. 6 is a diagram showing the relationship between the film thickness of a metal Ti thin film before plasma oxidation and the film thickness of a titanium oxide thin film after plasma oxidation.

FIG. 7 is a cross-sectional view of a dynamic random access memory cell embodying the present invention.

FIG. 8 is a configuration diagram of a dynamic random access memory embodying the present invention.

FIG. 9 is a configuration diagram of a computer system embodying the present invention.

[Explanation of symbols]

1 ... Si substrate, 2 ... Thermal oxide film, 3 ... Metal Ti thin film, 4 ...
TiO ₂ insulating film, 5 ... Au upper electrode, 100 ... Substrate, 1
01 ... Vacuum container, 102 ... Substrate susceptor, 103 ... Magnetic field coil, 104 ... Load lock chamber, 105 ... Reactive gas inlet, 106 ... Microwave inlet window, 108 ... Microwave waveguide, 109 ... Gate valve, 201 ... P Type Si substrate,
202 ... Source, 203 ... Drain, 204 ... Gate electrode, 205 ... Bit line, 206 ... Storage node electrode, 207
... Capacitor insulating film, 208 ... Plate electrode, 209
... Si oxide film, 210 ... Gate insulating film, 211 ... Interlayer insulating film, 1101 ... MOS transistor, 1102 ... Capacitor 1103 ... Word line, 1104 ... Bit line, 1
105 ... Sense amplifier, 1106 ... Read-out circuit, 11
07 ... Writing circuit.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/822

Claims (11)

[Claims] 1. A method of manufacturing a semiconductor memory device, comprising the steps of forming an electrode containing metal titanium on a semiconductor substrate, and forming an insulating film on the surface of the electrode by plasma-oxidizing the electrode. And a step of forming another electrode on the surface of the insulating film, the method of manufacturing a semiconductor memory device. 2. The method of manufacturing a semiconductor memory device according to claim 1, wherein the plasma oxidation is performed at a temperature of 280 ° C. or higher and 500 ° C. or lower. 3. The method of manufacturing a semiconductor memory device according to claim 1, wherein the electrode containing metal titanium is a laminated electrode of metal titanium and a noble metal. Method. 4. The method of manufacturing a semiconductor memory device according to claim 1, wherein the film thickness of the metal titanium is half the thickness of the insulating film. Method for manufacturing semiconductor memory device. 5. A semiconductor memory device having a capacitor, comprising: a semiconductor substrate; one electrode of the capacitor, which is provided on the semiconductor substrate, contains titanium metal; and titanium oxide having crystals of a rutile structure. An insulating film and the other electrode of the capacitor provided on the surface of the insulating film,
A semiconductor memory device comprising: 6. A semiconductor memory device having a capacitor, a semiconductor substrate, one electrode of a capacitor containing metal titanium, which is provided on the semiconductor substrate, and a surface of the one electrode, and an X-ray diffraction intensity. Is 2
An insulating film of a capacitor having a diffraction peak at a diffraction angle in the range of 7.55 to 27.75 °, and the other electrode of the capacitor provided on the surface of this insulating film,
A semiconductor memory device comprising: 7. A semiconductor memory device having a capacitor, a semiconductor substrate, one electrode of a capacitor containing metal titanium, which is provided on the semiconductor substrate, titanium oxide, and having a relative dielectric constant of 100 or more. , The insulating film of the capacitor, and the other electrode of the capacitor provided on the surface of this insulating film,
A semiconductor memory device comprising: 8. A semiconductor memory card comprising the semiconductor memory device according to claim 5. 9. A semiconductor disk device comprising the semiconductor memory device according to claim 5. Description: 10. A semiconductor memory device according to any one of claims 5 to 7, characterized by comprising:
Microprocessor. 11. A semiconductor memory device according to any one of claims 5 to 7, a semiconductor memory card according to claim 8, a semiconductor disk device according to claim 9, and a semiconductor memory device according to claim 10. A computer having any of the microprocessors described in.