JPH08124923A - Method and system for heat treating thin oxide film - Google Patents

Abstract

PURPOSE: To suppress leak current effectively without causing any damage on a thin oxide film by irradiating the thin oxide films with first and second lights emitted from first and second light sources having specified emission wavelengths thereby heat treating the thin oxide film in oxidizing atmosphere. CONSTITUTION: A thin oxide film is heat treated in oxidizing atmosphere. The thin oxide film is irradiated with a first light from first light source 1 having emission wavelength in the range of 130-170nm and a second light from a second light source 2 having emission wavelength in the range of 200-300nm and heat treated. For example, a deuterium lamp 1 is employed as a light source for exciting oxygen molecules to produce ozone and a low pressure mercury lamp 2 is employed as a light source for exciting the ozone to produce oxygen radicals. A sample 4 where Ta2 O5 is deposited on a silicon substrate is heat treated at 400 deg.C for 10min. in oxygen gas atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for an oxide thin film and a heat treatment apparatus used for the same, and more particularly, to effectively reduce a leak current without damaging the oxide thin film. The present invention relates to a heat treatment method for an oxide thin film and a heat treatment apparatus used for this heat treatment method.

[0002]

2. Description of the Related Art As a capacitive insulating film of a semiconductor memory device, a high dielectric constant Ta film is used in order to obtain a large capacity in a small area.
_{The use of a 2} O ₅ (tantalum pentoxide) film has been investigated. In this case, since the capacitive insulating film is intended to be formed on the electrode having a three-dimensional structure, it is necessary to use a method having excellent step coverage as a method for manufacturing the Ta ₂ O ₅ film. For this reason, the chemical vapor deposition method (CVD method) using the organic compound as the raw material is used.

However, Ta formed by this method
_{The 2} O ₅ film contains a large amount of impurity carbon and oxygen vacancies mixed from the raw material, and has a very large leak current. Therefore, heat treatment is performed after forming the Ta ₂ O ₅ film to remove the above-mentioned impurity carbon and oxygen vacancies. Is essential.

In order to remove impurity carbon and oxygen vacancies in the Ta ₂ O ₅ film, heat treatment in an oxidizing atmosphere is effective, and a heat treatment method using oxygen radicals having a strong oxidizing property has been studied. There is. For example, a method of activating oxygen with a low-pressure mercury lamp (UV-O ₂ annealing method) is disclosed in Japanese Patent Laid-Open No. 1-128531 and Extended Abstracts of Conference on Solid State Devices and Materials, 1987
219 pages (Extended Abstracts of Conference)
on Solid State Devides and Materials, p.219 (198
7)). Further, as another method, a method of activating ozone with a low-pressure mercury lamp (UV-O ₃ annealing method) is disclosed in JP-A-2-283022 and "Technical Technical Report".
Digest of Symposium on BLS Technology, 1989, p. 25 (Tech
nical Digest of Symposium on VLSI Technology, p.25
(1989)). Further, a method of activating oxygen with plasma (O ₂ plasma annealing method) is disclosed in JP-A-4-199828 and Extended Abstracts of Conference on Solid State Devices. and. Materials, 1993
862 pages (Extended Abstracts of Conference)
on Solid StateDevides and Materials, p.862 (199
3)).

[0005]

FIG. 2 shows the wavelength dependence of the optical absorption coefficient of oxygen molecules and ozone. As is clear from FIG. 2, oxygen molecules absorb light having a wavelength of 200 nm or less to become ozone, and ozone is 200 nm or more and 300 nm or more.
It absorbs light having a wavelength of nm or less to become oxygen radicals.

The low-pressure mercury lamp used in the UV-O ₂ annealing method emits light L ₁ having a peak at a wavelength of 254 nm and light L ₂ having a peak at a wavelength of 185 nm as shown in FIG. The light L ₁ having a peak at 254 nm can excite ozone up to oxygen radicals. However, as is clear with reference to FIG. 2, since the excitation of oxygen molecules is extremely low in the light L ₂ having a peak at a wavelength of 185 nm, the obtained ozone concentration is low, and as a result, sufficient oxygen radicals are supplied. However, the effect of repairing oxygen vacancies in the Ta ₂ O ₅ film and reducing the leak current becomes insufficient.

Therefore, oxygen molecules are excited into ozone in advance by plasma and transported to the heat treatment chamber, and the ozone is excited in the treatment chamber by a low pressure mercury lamp to generate oxygen radicals to treat the Ta ₂ O ₅ film. A method of doing so has been proposed (UV-O ₃ annealing method). A typical example of the apparatus used in this method is shown in FIG. But,
In order to sufficiently repair the oxygen deficiency, it is necessary to raise the processing temperature in the heat treatment chamber sufficiently, but since ozone is easily dissociated into oxygen molecules at 300 ° C. or higher,
If the substrate temperature during the heat treatment is increased to 300 ° C. or higher, ozone is dissociated and the leak current reduction effect is reduced.

On the other hand, Ta₂O_FiveAfter forming the film, oxygen
Method of heat treatment by exposing to Zuma (O ₂Plasma Annie
Le method) is also proposed. Of the equipment used in this method
A typical example is shown in FIG. This method is₂O_Fivefilm
Oxygen radicals are constantly generated on the surface of
Therefore, even if the substrate temperature is raised to 300 ° C or higher,
The dissociation of oxygen radicals₂O_FiveOxygen in the film
The leakage current due to the defect is effectively reduced.

However, according to this method, the Ta ₂ O ₅ film is damaged by the plasma, and a new cause of the leak current is generated. Therefore, there has been a strong demand for a heat treatment method and a heat treatment apparatus used therefor capable of effectively reducing the leak current of the Ta ₂ O ₅ film only by light and heat without using plasma.

An object of the present invention is to solve the above problems of the conventional heat treatment method and to effectively reduce the leak current without damaging the oxide thin film. And to provide a heat treatment apparatus for carrying out this heat treatment method.

[0011]

In order to achieve the above object, the present invention provides a first light source (for example, a deuterium lamp) that emits light having a wavelength capable of exciting oxygen into ozone, and ozone into oxygen radicals. The oxide thin film is irradiated with light using a second light source (for example, a low-pressure mercury lamp) that emits light having a wavelength that can be excited to generate oxygen radicals from oxygen.

[0012]

As shown in FIG. 3, the deuterium lamp is 160 n
It has a particularly large emission peak near m, and since oxygen molecules have a large light absorption coefficient in this wavelength region, they effectively absorb oxygen to generate ozone. Further, the generated ozone is excited into oxygen radicals by the light L ₁ having a wavelength of 254 nm generated from the low pressure mercury lamp. The deuterium lamp also has a wavelength of 200 nm to 300 nm.
However, since the emission intensity is about 5 orders of magnitude smaller than that of a low pressure mercury lamp, the deuterium lamp alone has a low effect of exciting ozone into oxygen radicals, and a low pressure mercury lamp is used as the second light source. However, the effect of ozone generation is far greater.

Therefore, even if ozone is dissociated and returns to oxygen molecules on the surface of the substrate heated to a temperature of 300 ° C. or higher, the excitation light from the deuterium lamp is always radiated and the returned oxygen is returned. Molecules are excited by ozone again to secure a sufficient amount of ozone, and this ozone is excited by oxygen radicals by the light L _{1 having} a wavelength of 245 nm from the low pressure mercury lamp to generate a sufficient amount of oxygen plasma. Is generated.

As a result, like the O ₂ plasma annealing method, the substrate temperature can be raised to 300 ° C. or higher,
In addition, since plasma is not used and heat treatment is performed only by light and heat, damage due to the plasma does not occur and a new factor that causes a leak current does not occur.

In the present invention, the higher the light intensity of the deuterium lamp and the lower pressure mercury lamp, the more preferable. If the light intensity of the above lamp is too small, it is difficult to obtain a sufficient effect, so the light intensity of the deuterium lamp is 10 ^-2 μW / cm 2.
^{2. It} is recommended that the low-pressure mercury lamp has an optical imaginary value of 1 mW / cm ² or more. The ratio of the light intensity of the low-pressure mercury lamp to the deuterium lamp can be set in the range of 1 to 10 ⁵ , and in the range of 1 to 10 ² , extremely preferable results can be obtained.

[0016]

【Example】

<Example 1> An example of a heat treatment apparatus used for carrying out the present invention is shown in FIG. Similar to the conventional heat treatment apparatus, a sample stage 3 provided with a heater (not shown) for heating the sample 4 is provided in the reaction vessel 19, and a line for supplying oxygen gas into the reaction vessel 19 and the above A line for exhausting the reaction container 19 is provided. By controlling the flow rate of oxygen with a mass flow controller (not shown) and installing different full scales in parallel, 10 cc
The controllable range is from m to 10 l / min. The exhaust system is equipped with a turbo molecular pump and a rotary pump, and the pressure is adjusted to 0.
The control is made within the range of about 1 Torr to 10 Torr. If the exhaust gas is allowed to flow through the exhaust duct without passing through the pump system, it is possible to perform the heat treatment under normal pressure.

A deuterium lamp 1 was provided as a light source for exciting oxygen molecules into ozone, and a low-pressure mercury lamp 2 was provided as a light source for exciting ozone into oxygen radicals. Since the deuterium lamp 1 has a small diameter, it is preferable to provide a plurality of deuterium lamps 1 in order to irradiate the entire surface of the sample (wafer) 4 with uniform brightness. In this example, eight were used. The number of deuterium lamps 1 to be used is preferably as large as possible in view of the uniformity of irradiation, but the sample 4 and the deuterium are appropriately selected depending on the type of the deuterium lamp 1 and the size and number of the samples 4. The distance between the lamp 1 and the low-pressure mercury lamp 2 depends on the brightness of the deuterium lamp 1 and the low-pressure mercury lamp 2 and the pressure of the atmosphere gas, but it should be approximately 20 cm or less in order to obtain sufficient oxygen radicals. preferable. However, if they are too close to each other, the uniformity of irradiation will be deteriorated. Therefore, it is preferable to avoid making the distance between the sample 4 and the deuterium lamp 1 and the low-pressure mercury lamp 2 too close. The shortest distance is the used lamp 1, 2
Are selected as appropriate depending on the type and number of the samples, the size and number of the samples 4, the pressure of the atmospheric gas, and the like.

In this embodiment, the single-wafer type apparatus for processing the samples 4 one by one is used. However, the size of the sample table 3 is set so that a plurality of samples 4 can be placed thereon, and the lamp is used. It is also possible to make a batch type device by increasing the number of the above so that all samples can be uniformly irradiated with light.

As shown in FIG. 6, n-type, specific resistance 0.0
Silicon substrate 6 with a low resistance of about 1 Ωcm (diameter 10 cm
And 15 cm) are soaked in a hydrofluoric acid solution diluted to about 1/10 for 1 minute to etch the surface, and after confirming water drainage, washing and drying are performed, and then the Ta ₂ O ₅ film 7 is chemically removed. It was formed by the vapor growth method. The chemical vapor deposition method is
Pentaethoxytantalum (heating the raw material container to 125 ° C,
Carrier gas: N ₂ , flow rate: 50 ccm) and oxygen (flow rate: 600 ccm) were introduced as reaction gases into the reaction vessel of the heat treatment apparatus, pressure was 0.2 Torr, and substrate temperature was 42.
The Ta ₂ O ₅ film 7 having a thickness of 9 nm was formed under the condition of 0 ° C.
Was formed. The flow rate of pentaethoxytantalum in this case was about a fraction of N ₂ used as the carrier gas.

Next, using the apparatus shown in FIG. 1, while irradiating eight deuterium lamps 1 and one low-pressure mercury lamp 2 at a distance of 20 cm between the sample 4 and the lamps 1 and 2, an oxygen gas atmosphere was emitted. Inside, heat treatment was performed at a temperature of 400 ° C. for 10 minutes. A W film 8 having a thickness of 100 nm was formed on the Ta ₂ O ₅ film 7 thus obtained, and unnecessary portions were removed by well-known photo etching to form an upper electrode for characteristic measurement having a side of 100 μm. .

For comparison, the Ta ₂ O ₅ film 7 formed by the above method was heat-treated according to the conventional heat treatment method (UV-O ₂ annealing method, UV-O ₃ annealing method and O ₂ plasma method). Similarly, the characteristic measuring upper electrode 8 was formed on each surface, and the voltage-current characteristics of both were measured. In the UV-O ₂ annealing method, oxygen gas was introduced into the heat treatment chamber, excitation was performed only by the low pressure hydrogen lamp, and the substrate temperature was 280 ° C. In the UV-O ₃ annealing method, oxygen molecules are excited into ozone in advance by microwave plasma, and then transported into the processing chamber, and excited only by the low pressure mercury lamp, and the substrate temperature is 28.
It was set to 0 ° C. In addition, the O ₂ plasma annealing method is performed in an oxygen atmosphere with a pressure of 10 Torr at a frequency of 13.
A high frequency power of 56 MHz was applied to form oxygen plasma, and the sample heated to 400 ° C. was exposed to the oxygen plasma. Among the heat treatment methods of the present example and the conventional heat treatment described above, U
In both the V-O ₂ annealing method and the UV-O ₃ annealing method, the pressure inside the reaction vessel was normal pressure, and the reaction time was 10 minutes including the O ₂ plasma annealing method.

The obtained results are shown in FIG. As apparent from FIG. 7, the Ta ₂ O ₅ film obtained in the present example, the leakage current density is smaller than that the Ta ₂ O ₅ film obtained by other heat treatment method, for the Ta ₂ O ₅ film The effect of reducing the leakage current density is greater than that of other conventional heat treatment methods. Further, FIG. 8 shows the T formed by this embodiment.
Dielectric breakdown voltage of a ₂ O ₅ film (judgment current density: 10 ^-8 A / c
the substrate temperature dependence of m ^2), is a graph comparing the results obtained with conventional UV over O ₃ annealing. As described above, in the case of the UV-O ₃ annealing method, the heat treatment temperature is 30.
Above 0 ° C, the leakage current reduction effect disappears,
In the case of the present invention, on the other hand, the withstand voltage is remarkably lowered, but even with the heat treatment temperature of 300 ° C. or higher, the withstand voltage monotonically increases and a high withstand voltage can be obtained even at a high temperature.
It was found that the optimum temperature is about 400 ° C. However,
If the temperature becomes excessively high, the growth of the silicon oxide film at the interface between the silicon substrate and the Ta ₂ O ₅ film may become remarkable, and the capacity may decrease, and the Ta ₂ O ₅ film may be crystallized to cause leakage. Therefore, it is better not to raise the heat treatment temperature excessively. For this reason, the heat treatment of the present invention is performed at 300 ° C.
It is preferable to carry out in the temperature range of ˜700 ° C.

In the present embodiment, the chemical vapor deposition method using pentaethoxy tantalum as a raw material was used as the method for forming the Ta ₂ O ₅ film. However, the raw material for Ta is not limited to the above pentaethoxy tantalum. TaCl ₅ , Ta (OC
H ₃ ) ₅ , Ta (N (CH ₃ ) ₂ ) _{5 and} other various Ta organic sources can be used, and a Ta target in an oxygen atmosphere (for example, O ₂ / Ar = 10%, 5 mTorr) can be used. The Ta ₂ O ₅ film may be formed by RF sputtering with an RF power of about 150 W. It was confirmed that the above-mentioned effects obtained by the present invention can be similarly obtained regardless of the method of forming the Ta ₂ O ₅ film. Also, Ta
Considering the diffusion length of oxygen radicals, the film thickness of the ₂ O ₅ film is
It is 20 nm or less, preferably 10 nm or less. However, if the film thickness is too small, unfavorable obstacles such as pinholes may occur, so in practice it should be avoided that the thickness is approximately 5 nm or less.

In the present embodiment, the silicon film is used as the lower electrode of the capacitor. However, not only the silicon film but also various metal materials such as W, and films made of those silicides can be used, and the same effect is obtained. was gotten. Further, although the Ta ₂ O ₅ film is used as the capacitor insulating film in this embodiment, Si, Ti, Zr, Hf, Y or Nb is used.
Oxide film, PbTiO ₃ film, Pb (Zr _X Ti _{1 over} X) O ₃
The same effect was obtained when a film made of a mixture of oxides such as a film, a SrTiO ₃ film, a Ba _x Sr _1-x TiO ₃ film, and a Bi-based layered ferroelectric compound thin film was used.

In this embodiment, a deuterium lamp and a low pressure mercury lamp were used as the excitation light source. However, not only deuterium lamps and low-pressure mercury lamps, but oxygen absorption coefficient of 10 cm ^-1 atm ^-1 or more, 130 nm
A combination of a first light source capable of emitting light having a wavelength of 170 nm or less and a second light source capable of emitting light having a wavelength of 200 nm or more and 300 nm or less and having an optical absorption coefficient of ozone of 10 cm ^-1 atm ^-1 or more The same effect can be obtained by using it. Further, for example, like synchrotron radiation, the above 130 nm or more and 170 nm or less and 200 n
A light source capable of emitting light having both wavelengths of m or more and 300 nm or less may be used.

<Embodiment 2> This embodiment is an example in which the heat treatment method according to the present invention is applied to the production of a dynamic random access memory (DRAM). A sectional view of the memory cell is shown in FIG. Here, the capacitance insulating film has a film thickness of 9n.
m Ta ₂ O ₅ film 9 formed on the polycrystalline silicon film 13 using the same chemical vapor deposition method as in Example 1 using pentaethoxytantalum as a raw material, and a deuterium lamp and a low pressure While irradiating with a mercury lamp, heat treatment was performed at 400 ° C. for 10 minutes in an oxygen atmosphere. The numbers of low-pressure mercury lamps and deuterium lamps used are 1 and 8, respectively.

The SiO ₂ equivalent thickness of the Ta ₂ O ₅ film 9 formed in this manner is 2.5 nm, the breakdown voltage is 2V (determination current density 10 ^-8 A / cm ^2), the Ta ₂ A semiconductor device having an O ₅ film 9 and having a sectional structure shown in FIG.
It was confirmed that it could operate as a RAM. Further, it goes without saying that the Ta ₂ O ₅ film 9 formed according to the present invention can be applied not only to DRAM but also to a capacitor part requiring a large capacity such as a communication LSI. Further, not only as a capacitive element but also when applied to the formation of a gate oxide film of a MOS transistor, an oxide film having a higher withstand voltage than the conventional method can be obtained.

In FIG. 9, symbol 10 is a Si substrate, 11 is a SiO ₂ film, 12 is a TiN film, 14 is an n ⁺ region (source / drain region), 15 is a polycrystalline silicon film (word line), 16 Is a PSG / SOG / PSG film, 17
Represents a WSi ₂ film, 18 represents a BPSG / HLD film, and all portions other than the Ta ₂ O ₅ film 9 were formed by a conventionally known method.

[0029]

As is apparent from the above description, according to the present invention, it becomes possible to manufacture a high dielectric constant oxide film having a high withstand voltage, and miniaturization and integration of various semiconductor devices such as DRAM. It is extremely useful for improving the density.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view showing an example of a heat treatment apparatus according to the present invention,

FIG. 2 is a diagram showing wavelength dependence of light absorption coefficients of oxygen and ozone,

FIG. 3 is a diagram showing emission spectra of a deuterium lamp and a low-pressure mercury lamp,

FIG. 4 is a diagram showing an example of a conventional heat treatment apparatus,

FIG. 5 is a diagram showing another example of a conventional heat treatment apparatus.

FIG. 6 is a view showing a structure of a sample used in the first embodiment,

FIG. 7: Voltage obtained by the present invention and conventional method-
Figure comparing current density characteristics,

FIG. 8 is a diagram comparing the heat treatment temperature dependence of the breakdown voltage in the present invention and the conventional method,

FIG. 9 is a cross-sectional view of a main part of a DRAM showing a second embodiment of the present invention.

[Explanation of symbols]

1 ... deuterium lamp, 2 ... low-pressure mercury lamp, 3 ... sample stand, 4 ... sample, 5 ... plasma generator, 6 ... silicon substrate, 7 ... Ta ₂ O ₅ film, 8 ... W film, 9 ... Ta ₂ O
₅ film, 10 ... Si substrate, 11 ... SiO ₂ film, 12 ...
TiN film, 13 ... Polycrystalline silicon film, 14 ... n ⁺ -S
i (source / drain region), 15 ... Polycrystalline silicon film (word line), 16 ... PSG / SOG / PSG film (interlayer insulating film), 17 ... WSi ₂ film (bit line), 18
... BPSG / HLD film (interlayer insulating film), 19 ... Reaction vessel.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical indication location H01L 21/8242 (72) Inventor Yuzuru Ohji 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Central Inside the research institute (72) Inventor Shinpei Iijima 1-280 Higashi Koikekubo, Kokubunji City, Tokyo Inside Hitachi Central Research Laboratory

Claims (12)

[Claims] 1. A method of heat-treating an oxide thin film in an oxidizing atmosphere, wherein the heat treatment is at least 130 n.
First light emitted from a first light source having an emission wavelength of m to 170 nm and at least 200 nm to 30
A heat treatment method for an oxide thin film, which is performed by irradiating the oxide thin film with second light emitted from a second light source having an emission wavelength of 0 nm or less. 2. The heat treatment method for an oxide thin film according to claim 1, wherein the first light source is a deuterium lamp and the second light source is a low pressure mercury lamp. 3. The heat treatment method for an oxide thin film according to claim 1, wherein the oxide thin film is a tantalum oxide film. 4. The heat treatment method for an oxide thin film according to claim 3, wherein the thickness of the tantalum oxide film is 20 nm or less and 5 nm or more. 5. The heat treatment method for an oxide thin film according to claim 1, wherein the heat treatment is performed at a temperature of 300 ° C. or higher and 700 ° C. or lower. 6. The oxide thin film comprises Si, Ta, Ti, Z
r, Hf, Y, Pb, Nb, Sr, Ba, La and B
The heat treatment method for an oxide thin film according to claim 1 or 2, which is at least one oxide selected from the group consisting of i or a mixture of the oxides. 7. A reaction vessel, a sample table arranged in the reaction vessel, means for introducing a predetermined gas into the reaction vessel, means for discharging gas from the reaction vessel, and the sample table. A means for heating the sample placed on the first surface, and a first having an emission wavelength of at least 130 nm and 170 nm.
And a second light source having an emission wavelength of at least 200 nm and 300 nm or less. 8. The heat treatment apparatus according to claim 7, wherein the first light source is a deuterium lamp, and the second light source is a low-pressure mercury lamp. 9. The distance between the first light source and the sample is 2
It is 0 cm or less, The claim 7 or 8 characterized by the above-mentioned.
The heat treatment apparatus according to. 10. The heat treatment apparatus according to claim 7, wherein the distance between the second light source and the sample is 20 cm or less. 11. A reaction vessel, a sample stage arranged in the reaction vessel, means for introducing a predetermined gas into the reaction vessel, means for discharging gas from the reaction vessel, and the sample stage. Means for heating the sample placed on, and at least 130 nm and 170 nm and at least 20 nm
A light source having an emission wavelength of 0 nm or more and 300 nm or less,
A heat treatment apparatus comprising at least a heat treatment apparatus. 12. The heat treatment apparatus according to claim 11, wherein the light source is synchrotron radiation light.