JP3138892B2 - Method and apparatus for forming thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for forming a thin film.

[0002]

2. Description of the Related Art Along with the high integration of semiconductor devices, many developments and high performances have been attempted in both process and equipment technologies, and various improvements have been made to one wiring technology. I have. Taking the contact hole of a MOS transistor as an example, as shown in FIG. 10, the contact hole size is reduced or the p-type (or p-type) formed in the n-type (or p-type) Si (silicon) film 1 is formed. Since the (n-type) diffusion layer 11 tends to be shallower with miniaturization, the metal wiring 12 buried in the contact hole, for example, a metal film 12 of W (tungsten) or Al (aluminum) and the diffusion layer 11 TiN
(Titanium nitride) film 13
It is intended to facilitate electrical connection between a metal and a semiconductor in a semiconductor device. In addition, blanket CVD (chemi
When a W film is grown by a cal vapor deposition method, SiO ₂ which is an interlayer insulating film is used.
The TiN film 13 formed on the surface of the film 14
It also plays the role of an adhesion layer that adheres to the O ₂ film.

[0003] Here, T is applied between the metal film 12 and the diffusion layer 11.
The reason why the iN film 13 is interposed is as follows. Since Al and W form an alloy with Si (silicon), mutual diffusion occurs between the diffusion layer 11 and the contact hole size is reduced or the diffusion layer 11 is shallow. In this case, the influence of the interdiffusion may increase, and the MOS may not operate. Therefore, TiN which does not cause the interdiffusion is interposed as a barrier layer.

Conventionally, a method of forming a TiN film is to arrange a target made of Ti and a semiconductor wafer to be processed in a N ₂ (nitrogen) gas atmosphere in an atmosphere of Ar (argon).
The Ti particles are knocked out by colliding ions with the target and sputtering, and the Ti particles are collided with N ₂ gas to form, for example, about 1000 Å of Ti.
An N film is formed on the wafer surface. In practice, however, a TiSi _x (silicide of titanium) film having a thickness of, for example, about several hundred angstroms is formed between the diffusion layer 11 and a good ohmic contact, although not shown.

[0005]

In the case of a contact hole in a DRAM, the line width of the contact hole is about 0.8 μm when the capacity of the DRAM is 4M.
At 16M, it becomes very fine, about 0.5 μm, and at 64M
Is further reduced to 0.35 μm and 0.25 μm at 256M. In order to fill the contact holes, sputtering can be sufficiently performed if the line width is about 0.8 μm, but if the line width is as fine as about 0.5 μm, the film cannot be isotropically formed. In a 16M DRAM, for example, W is buried by a blanket CVD method.

However, it is difficult to employ a CVD method as a method for forming a TiN film for the following reasons. That is, when a TiN film is formed by a CVD method, a compound of Ti and Cl (chlorine) must be used as a source gas.
₄ (Titanium tetrachloride) gas and NH ₃ (ammonia) gas are introduced into a vacuum chamber, and a TiN film is formed by a gas phase reaction at a temperature of 400 to 750 ° C.
l is taken in.

When analyzed by an X-ray analyzer, the Cl concentration in the TiN film is considerably high, for example, 0.1 to several atoms.
c% (1 × 10 ²⁰ atoms / cc to 1 × 10 ²¹ atom
ms / cc), and when the Cl concentration is high, T
Cl in the iN film penetrates into a metal film such as W or Al, and the metal film is corroded, resulting in disconnection. This has been confirmed by acceleration experiments.

The Cl concentration becomes higher as the process temperature becomes lower. For example, in the case of a device having a multilayer wiring structure using Al, when filling contact holes in the second and subsequent layers, the first layer of Al is not dissolved. Therefore, the process temperature must be set to 450 ° C. or less. In this case, the Cl concentration becomes high and the progress of corrosion of the metal film is accelerated.

Furthermore, ammonium chloride (NH ₄ Cl) produced as a by-product by the gas phase reaction adheres and deposits on the inner wall of the reaction chamber and becomes a source of particles, and this NH ₄ Cl is removed. Difficult cleaning work is required because it is difficult.

On the other hand, when a TiN film is formed by a sputtering method, Cl is not mixed into the film, and the sputtering method is currently used. However, as described above, if the line width of the contact hole becomes fine, it becomes difficult to form an isotropic film. Therefore, efforts have been made to arrange a collimator above the wafer and to take out the vertical component of the scattered particles from the target. However, when the capacity of the DRAM is 16M, problems such as in-plane uniformity of film thickness, film peeling, and decrease in throughput have become apparent, and the limit of the sputtering method has been reached. And 64
Sputtering can no longer be used for DRAMs larger than M and the CVD method has to be relied on. However, the incorporation of Cl into the TiN film is a barrier, and the transition to next-generation devices is hampered. It has become difficult.

In producing a TiN film by a CVD method using a TiCl ₄ gas and an NH ₃ gas, Japanese Patent Application Laid-Open No. 3-64473 discloses that the internal surfaces of a CVD reactor are heated to a temperature of 250 to 300 ° C. There is a description that the surface can be kept free of deposits and particles by heating, but in this method, as is clear from the characteristic diagram shown in FIG. Cl contamination cannot be avoided.

The present invention has been made under such circumstances, and an object of the present invention is to remove Cl in a thin film formed by CVD, thereby obtaining a CVD thin film having a small amount of Cl mixed therein. To provide a method for forming a thin film.

Still another object of the present invention is to provide a thin film forming apparatus capable of removing Cl in a thin film formed by CVD and removing a reaction by-product adhered to a wall surface of a reaction chamber. It is in.

[0014]

According to a first aspect of the present invention, there is provided a process for forming a thin film on a substrate to be processed by a gas phase reaction using a raw material gas comprising a compound containing a thin film component and Cl, Heat-treating the substrate on which is formed in a vacuum atmosphere to remove Cl in the thin film.

According to a second aspect of the present invention, a TiN film is formed on a substrate to be processed by a gas phase reaction using a source gas composed of a compound containing Ti and Cl and a source gas composed of an N ₂ gas or a compound containing N. The method includes a step of forming, and a step of heat-treating the substrate on which the TiN film is formed in this step in a vacuum atmosphere to remove Cl in the TiN film.

According to a third aspect of the present invention, a tungsten silicide is formed on a substrate to be processed by a gas phase reaction using a source gas composed of a compound containing W and F and a source gas containing Si and Cl.
A step of forming a side film and a tungsten film in this step.
Removing the Cl in the tungsten silicide film substrate to be processed which Risaido film is formed by heat treatment in a vacuum atmosphere, characterized in that it comprises a.

According to a fourth aspect of the present invention, there is provided a thin film forming apparatus wherein a thin film is formed on a substrate to be processed by a gas phase reaction using a raw material gas comprising a compound containing a thin film component and Cl, and a Cl compound is by-produced. A heating means for removing by-products adhering to the inside of the reaction chamber and Cl in the thin film in a vacuum atmosphere is provided.

[0018]

When a CVD thin film is formed using a source gas composed of a thin film component and a compound containing Cl, Cl is mixed into the thin film. For example, a TiN film is formed by reacting a TiCl ₄ gas and an NH ₃ gas, or a WSi ₂ (tungsten silicide) is formed by reacting a WF ₆ (tungsten hexafluoride) gas with a SiH ₂ Cl ₂ (dichlorosilane) gas. When a film is formed, Cl is mixed into the thin film as an impurity. This Cl may be in the form of certain compounds, for example NH ₄ Cl
The sublimation temperature of the Cl compound is reduced by exposing the thin film to a vacuum atmosphere, and thus the Cl compound is released from the thin film by the heat treatment, Cl concentration becomes low.

For example, when a TiN film is formed on a substrate to be processed by reacting a TiCl ₄ gas with an NH ₃ gas, NH ₄ Cl by-produced by this reaction adheres and deposits on the wall surface of the reaction chamber and the film is formed. Adsorbs on the surface and crystal interface. The presence of NH ₄ Cl in this case has been confirmed by analysis with TDS, Fourier transform infrared spectrophotometer, and the like. In this case, by heating the reaction chamber by the heating means in the reaction chamber, NH ₄ Cl is released from the wall surface of the reaction chamber or the like, and the reaction chamber is washed.

[0020]

FIG. 1 is a diagram showing an example of an apparatus used in an embodiment of the present invention. In FIG. 1, reference numeral 2 denotes a reaction chamber having a hermetic seal structure for performing CVD, and a heater for holding a semiconductor wafer 3 as a substrate to be processed and heating the semiconductor wafer 3 to a predetermined temperature is provided at the bottom in the reaction chamber 2. A wafer holding table 21 provided with 20 is provided. In the upper part of the reaction chamber 2,
A source gas supply unit 4 for supplying a source gas into the reaction chamber 2 is disposed to face the wafer holding table 21. The source gas supply unit 4 includes, for example, TiCl _{4 as a} source gas.
The distal end of the first gas supply pipe 41 for supplying gas is branched into a plurality of parts, and the distal end of the second gas supply pipe 42 for supplying, for example, NH ₃ gas as a raw material gas is branched into a plurality. These branch pipes are connected to a number of gas injection holes 44 of the gas injection plate 43 so that TiCl ₄ gas and NH ₃ gas are separately supplied into the reaction chamber 2 through the gas injection holes 44. It is configured. The first gas supply pipe 4
A liquid source 41a of TiCl ₄ covered with a heater 40 is connected to the base end of the first gas supply pipe 4 and a second gas supply pipe 4
An NH ₃ gas source 42 a is connected to the base end of the gas supply pipe 2, and the outer peripheral surface of the gas supply pipe 41 is covered with a heater (not shown).

An exhaust pipe 22 is provided at the bottom of the reaction chamber 2.
Is connected, and the reaction chamber 2 can be maintained at a predetermined degree of vacuum by a vacuum pump (not shown).

Adjacent to the reaction chamber 2, a post-processing chamber 5 having an airtight seal structure for performing post-processing on the wafer 3 on which a thin film is formed by CVD in the reaction chamber 2 is provided. A wafer holding table 51 is provided at the bottom of the post-processing chamber 5, and an exhaust pipe 52 connected to a vacuum pump (not shown) is connected to the bottom of the post-processing chamber 5.

In the upper part of the post-processing chamber 5, there is provided an infrared heater 6 for heating the wafer 3 on the wafer holding table 51 provided with a high melting point metal filament such as W, Ta (tantalum) or Mo (molybdenum). Is provided. G1 and G2 are gate valves for hermetically sealing the reaction chamber 2 and the post-processing chamber 5 to, for example, a load lock chamber (not shown), and G3 is an air-tight valve between the reaction chamber 2 and the post-processing chamber 5. This is a gate valve for sealing.

Next, the operation of the above embodiment will be described. First, the wafer 3 to be processed, which is carried into the reaction chamber 2, will be described with reference to FIG.
In the above, a p-type (or n-type) diffusion layer 71 is formed in a surface layer portion of an n-type (or p-type) Si substrate 7, and an upper portion of the diffusion layer 71 is opened on the surface of the Si substrate 7. An insulating film 72 is formed.

Then, the wafer 3 is introduced into the reaction chamber 2 by a transfer means (not shown) through the gate valve G1 and is mounted on the wafer holding table 21, and the wafer 3 is heated to, for example, 400 to 450 ° C. by the heater 20. Heat.
On the other hand, TiCl ₄ is introduced into the reaction chamber 2 through the source gas supply unit _4.
Gas and NH ₃ gas at 10 SCCM and 100 SCC respectively
M is introduced at a flow rate of M and exhausted by a vacuum pump (not shown) through an exhaust pipe 22 so that
The degree of vacuum is maintained at × 10 ⁻³ Torr to tens of Torr.
In such a CVD process, the TiC shown in the equation (1) is used.
TiN is generated by a gas phase reaction between the l ₄ gas and the NH ₃ gas, and is attached and deposited on the surface of the wafer 3, for example, as shown in FIG.
As shown by a chain line, a TiN film 73 having a thickness of about 1000 Å is formed.

6TiCl ₄ + 8NH ₃ → 6TiN + 24HCl + N ₂ (1) Thereafter, the wafer 3 in the reaction chamber 2 is post-processed by the transfer means (not shown) through the unloading port 23 with the same pressure in the reaction chamber 2 and the post-processing chamber 5. The wafer is conveyed onto the wafer holding table 51 in the chamber 5 and then evacuated through an exhaust pipe 52 by a vacuum pump (not shown), so that the inside of the post-processing chamber 5 is, for example, 1 × 10 ^-9 To
rr, and then the wafer 3 (shown by a dashed line) is heated by the infrared heater 6 to, for example, 50 to 450 ° C.
For a few seconds to several minutes.

Here, as described in the section "Problems to be Solved by the Invention", Cl is mixed in the TiN film 73 formed by the CVD in the reaction chamber 2 at a high concentration. This Cl is the HCl is a reaction product of TiCl ₄ and NH _3, and NH ₃ as a raw material gas reacts NH
₄ Cl (ammonium chloride) is produced and the NH ₄ C
It is presumed that they are taken into the TiN film 73 in the form of l.

The sublimation point of this NH ₄ Cl under normal pressure is 33
7.8 ° C., for example, in a vacuum atmosphere of 1 × 10 ⁻⁹ Torr, the temperature is considerably low. Therefore, by heating the wafer 3 to a temperature equal to or higher than the sublimation temperature of NH ₄ Cl in this state, FIG. )), NH ₄ Cl is converted to NH ₃
And HCl, which are considered to be released from the TiN film 72. Therefore, by performing the above-described post-processing on the wafer 3 in the post-processing chamber 5, the Cl concentration in the TiN film 73 is reduced, for example, by one digit.

Next, an experiment performed to confirm the effect of the present invention will be described. The apparatus used in the experiment is a sample stage 81 made of quartz glass in a sample chamber 8 as shown in FIG.
And a mass spectrometer 85 provided with a quartz rod 83 for guiding infrared light from the infrared generator 82 to the sample stage 81, and further connected to an exhaust pipe 84 and having a mass spectrometer 85a.
Is connected to the sample chamber 8.

First, a sample 80 was prepared in which a TiN film having a thickness of about 600 Å was formed on a silicon substrate in advance by the above-mentioned CVD method. However, as for the conditions for forming the TiN film, the flow rates of the TiCl ₄ gas and the NH ₃ gas are 10 sccm and 100 sccm, respectively, the film forming pressure is 100 mTorr, and the film forming temperature is 610 ° C. Also T
The Cl concentration in the iN film was previously determined by an X-ray microanalyzer and found to be 3.61 atomic%.

Then, the sample 80 is introduced into the sample chamber 8, the inside of the sample chamber 8 is maintained at a vacuum of 3 × 10 ⁻⁹ Torr, and the infrared rays from the infrared ray generator 82 are passed through the quartz rod 83 and the sample table. By irradiating the sample 80, the temperature of the sample 80 was increased from 50 ° C. to 900 ° C. at a rate of 1 ° C./sec, and mass analysis was performed by the mass spectrometer 85. The results shown in FIGS. was gotten. Thereafter, when the Cl concentration in the TiN film of the sample 80 was examined with an X-ray microanalyzer, the detection limit (0.1 atom) was obtained.
ic%).

FIGS. 4 and 5 are graphs in which the horizontal axis represents the temperature of the sample stage 81, and the vertical axis represents the number (relative amount) and mass number of molecules. FIGS. 4 (1) and (2) are graphs. NH ₂ and NH respectively
₃ in which the amount of released change, FIG. 5 (1), (2) are each H ³⁵ C
1 shows changes in the amount of H ³⁷ Cl released. As can be seen from this graph, the release amounts of NH ₂ , NH ₃ , H ³⁵ Cl, and H ³⁷ Cl all increased as the temperature rose from 50 ° C.,
It shows a high peak value around 90 ° C., and then decreases and fluctuates at a small value.

As described above, at a temperature around 90 ° C., NH ₂ , N ₂
Although H ₃ , H ³⁵ Cl and H ³⁷ Cl are often detected,
These are NH ₄ which is a reaction product of TiCl ₄ and NH _3.
It is considered to be a decomposition product by sublimation of Cl. Therefore, it is presumed that a large amount of Cl mixed on the surface of the TiN film and the crystal interface exists in the form of NH ₄ Cl crystals. As a result, NH ₄ Cl is decomposed by heat treatment in a vacuum atmosphere and released from the TiN film, It is considered that this reduces the Cl concentration in the TiN film from 3.61% to 0.1 atomic% or less, for example, one digit or more.

It is said that if the Cl concentration is less than a few atomic%, there is no risk of corrosion of the metal wiring.
The present inventor also knows this from the results of the accelerated test.
Therefore, by heating the TiN film with an infrared heater in a vacuum atmosphere, a part of the contained Cl is removed and the Cl concentration is reduced, whereby the corrosion of the metal wiring in the device can be suppressed. Service life is obtained. As a result, the Ti
Since the N film can be formed by the CVD method instead of the sputtering method, it is possible to cope with the miniaturization of the contact hole, which is effective for the next generation device. This can contribute to the realization of the above-mentioned large capacity.

As can be seen from the absorption spectrum shown in FIG. 6, NH ₄ Cl has a property of absorbing infrared rays having wavelengths of 3.20 μm and 7.15 μm. The infrared light intensity is high, while the transmittance of quartz light is 3.4 μm as shown in FIG.
It is presumed that NH ₄ Cl was decomposed efficiently by infrared rays having a wavelength of about 3.2 μm because the temperature rapidly decreased from around m.

Here, in the present invention, as shown in FIG. 8, three infrared heaters 6 serving as heating means are arranged in parallel in the reaction chamber 2, for example, near the left and right side walls in the reaction chamber 2. After the TiN film 73 is formed on the surface of the wafer 3, the introduction of the TiCl ₄ gas and the NH ₃ gas into the reaction chamber 2 is stopped, and the reaction is performed by further exhausting the gas through the exhaust pipe 22 by the vacuum pump 22 a. The inside of the chamber 2 is, for example, 1 × 10 ⁻⁶ Torr.
, And then the infrared heater 6 is turned on, and the infrared ray from the infrared heater
The heat treatment may be performed at 0 to 450 ° C. for several seconds to several minutes.

Here, "Problem to be solved by the present invention"
As described in the above section, the inner wall surface in the reaction chamber 2 is made of Ti.
NH ₄ C, a by-product of the gas phase reaction between Cl ₄ and NH ₃
l is deposited and T formed by CVD.
Cl is mixed into the iN film 63 at a high concentration.

As described above, the sublimation point of this NH ₄ Cl at a normal temperature is considerably low in a vacuum atmosphere of, for example, 1 × 10 ⁻⁶ Torr. As shown in FIG. 2B and FIG. 9, NH ₄ Cl adhered and deposited on the inner wall surface of the reaction chamber 2 by heating with infrared rays from the infrared heater 6.
Considered deposits 24 together with desorbed decomposed into HCl and NH _3, NH ₄ Cl in the TiN film 73 of the wafer 3 is released from the TiN film 73 was decomposed into HCl and NH ₄ similarly Can be Actually reacting TiCl ₄ gas and NH ₃ gas to adhere NH ₄ Cl to the inner wall of the reaction chamber 2,
Thereafter, when the above-described post-treatment was performed, the NH ₄ Cl film was almost completely removed from the inner wall surface of the reaction chamber 2.

According to this embodiment, NH ₄ Cl deposited on the inner wall surface of the reaction chamber 2 is decomposed and separated from the inner wall surface, so that the inside of the reaction chamber 2 is cleaned. 2 can be made maintenance-free, and NH ₄ Cl in the TiN film 73 is decomposed and released from the TiN film 73, so that a CVD thin film with a small amount of chlorine mixed in can be obtained.

In the above, according to the present invention, in addition to the structure shown in the above-described embodiment, for example, the upper surface of the post-processing chamber or the reaction chamber is constituted by a quartz glass window, and the quartz glass window is formed from outside the post-processing chamber or the reaction chamber. A configuration may be adopted in which infrared rays are taken in via the substrate and irradiated on the surface of the substrate to be processed.

The heating means for heating the TiN film is not limited to an infrared heater. The degree of vacuum at the time of heat treatment is 10 ⁻³ Torr to 10 ⁻⁹ Torr.
Torr is desirable, and more desirably 10 ⁻⁶ Torr or more.
10 ⁻⁹ Torr.

In the above embodiment, the case where the TiN film formed by the thermal CVD method is subjected to the heat treatment has been described.
It may be formed by reacting Cl and N ₂ .

Further, the thin film to be subjected to the heat treatment according to the present invention is not limited to the TiN film, but may be formed by a gas phase reaction using a raw material gas comprising a thin film component and a compound containing Cl. (Fluorine) and a source gas composed of a compound containing, for example, WF ₆ (tungsten hexafluoride) gas and a source gas containing Si and Cl, for example, SiH ₂ Cl ₂
It may be a WSi ₂ (tungsten silicide) film formed by a gas phase reaction using a (dichlorosilane) gas. The WSi ₂ thin film plays a role of a low resistance layer between the metal wiring and the silicon film like the TiN film,
l is mixed, and such a thin film is subjected to a heat treatment in a vacuum atmosphere so that the WSi
₂ can remove Cl taken in the film to reduce the contained Cl concentration, and the Al laminated on the WSi ₂ film
Corrosion of metal wiring such as a film can be suppressed.

[0044]

According to the first to third aspects of the present invention, the Cl concentration in the thin film formed by the CVD method and containing Cl as an impurity can be reduced, and therefore, the corrosion of the metal wiring in the device is suppressed. And the adverse effects of Cl can be reduced. According to the fourth aspect of the present invention, a thin film containing a small amount of chlorine can be obtained, and the reaction chamber can be easily cleaned.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view showing an example of an apparatus for performing a method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of a semiconductor wafer surface.

FIG. 3 is a schematic configuration diagram showing an experimental device for confirming the effect of the present invention.

FIG. 4 is a characteristic diagram showing a result of mass spectrometry in an experiment using the apparatus of FIG. 3;

FIG. 5 is a characteristic diagram showing a result of mass spectrometry in an experiment using the apparatus of FIG. 3;

FIG. 6 is a characteristic diagram showing light absorption characteristics of NH ₄ Cl.

FIG. 7 is a characteristic diagram showing light transmission characteristics of quartz.

FIG. 8 is a schematic transparent perspective view showing an example of an apparatus used in an embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a state of a semiconductor wafer surface and a reaction chamber wall.

FIG. 10 is an explanatory diagram showing an example of the structure of a contact hole.

[Explanation of symbols]

Reference Signs List 2 reaction chamber 3 semiconductor wafer 4 source gas supply unit 41a liquid source of TiCl ₄ 42a gas source of NH ₃ 5 post-processing chamber 6 infrared heater 73 TiN film

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takayuki Oba 1015 Kamidadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-3-243769 (JP, A) JP-A-3-129737 (JP, A) JP-A-3-64473 (JP, A) JP-A-5-3171 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/285 C23C 16 / 46 H01L 21/205

Claims (4)

(57) [Claims] 1. A step of forming a thin film on a substrate to be processed by a gas phase reaction using a source gas composed of a compound containing a thin film component and Cl, and placing the substrate on which the thin film has been formed in this step in a vacuum atmosphere. Removing the Cl in the thin film by heat-treating the thin film. 2. A step of forming a TiN film on a substrate to be processed by a gas phase reaction using a source gas composed of a compound containing Ti and Cl and a source gas composed of an N ₂ gas or a compound containing N. Heating the substrate to be processed on which the TiN film is formed in this step in a vacuum atmosphere to remove Cl in the TiN film. 3. A W and the raw material gas of a compound containing F, and forming a tungsten silicide film on a substrate to be processed by a vapor phase reaction using a raw material gas containing Si and Cl, tungsten in this process the tungsten substrate to be processed which silicide film is formed is heated in a vacuum atmosphere
A step of removing Cl in the silicide film. 4. A thin film forming apparatus in which a thin film is formed on a substrate to be processed by a gas phase reaction using a source gas composed of a thin film component and a compound containing Cl, and a Cl compound is by-produced. A thin-film forming apparatus provided with a heating means for removing the by-product and Cl in the thin film in a vacuum atmosphere.