JP2832982B2 - Thin film formation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a thin film using a thermal chemical vapor deposition method (thermal CVD method).

(Prior art) In the chemical vapor deposition (CVD) method, a raw material is supplied as a gas,
This is a method of depositing a thin film by a gas phase or a chemical reaction on the substrate surface.

Conventionally, thin film formation methods using this CVD method include a thermal CVD method in which raw material gas molecules adhering to the substrate surface are thermally decomposed by heating the substrate and the required thin film is deposited, or adsorbed in the gas phase or on the substrate surface. Photo-CVD method to irradiate the source gas molecules with light to decompose photochemically or thermally and deposit them, and plasma CVD method to decompose and decompose the source gas molecules in the gas phase into plasma by discharge or microwaves and decompose by collision process, etc. It has been known. These CVD methods can form a wide variety of thin films at a relatively low temperature with little damage to a base, and are used in various situations as thin film forming means.

Until now, various thin films of dielectrics, semiconductors and metals have been formed using the CVD method. For example, as an example of forming a metal thin film using a thermal CVD method, molybdenum (Mo)
And Tundsten (W) thin film formed on a natural oxide film of silicon is described in the Journal of Electrochemical Societ
y) Reported by Kaplan et al. in Vol. 117, pages 693-700. According to this, carbonyl compounds such as molybdenum carbonyl (Mo (CO) ₆ ) and tungsten carbonyl (W (CO) ₆ ) are used as raw materials,
At about 500 ° C., thin films of Mo and W are formed at a deposition rate of about 20 ° / sec. In the thermal CVD method or the optical CVD method, a laser beam is focused on the substrate while scanning the focused laser beam, or by irradiating the substrate with an optical pattern obtained by transmitting a mask pattern. It is applied to a so-called laser direct writing method and a pattern transfer method for forming a fine pattern-shaped thin film on the substrate. An example of this is Applied Physics B, Vol.
On pages 66 to 66, there is an example in which a fine thin film pattern of Mo, W, or the like is drawn on a glass or sapphire substrate using a laser direct drawing method by Gilge et al. Among them, a carbonyl compound of W or Mo is used as a raw material, and an Ar laser (wavelength: 350 nm) is used as a laser light source.
Focus on a spot diameter of about m and irradiate the substrate with a film thickness of 1000
It is described that the thin film pattern of Å was drawn at a laser scan speed of about 1 μm / s.

(Problems to be Solved by the Invention) However, any of the above-mentioned methods in the CVD method has a problem that the deposition rate of the film is low and the productivity is low. For example, in the LSI manufacturing process,
Although it is often necessary to form a thin film having a thickness of about 1 μm, in a normal CVD process, as shown above, the deposition rate is about 1000 mm / min, which is several tens of minutes to form one thin film. Takes time. If such thin film formation is repeated many times, the total process time becomes several hours,
It is the main factor that lowers the throughput. For this reason, in the CVD process, many wafers are usually processed at one time in a single process.However, when the size of the apparatus is increased in order to cope with a recent or future increase in the diameter of the wafer. In addition, it is difficult to collectively process such a plurality of wafers in order to protect the uniformity of film formation, and it is necessary to improve the film formation speed itself in order to increase the throughput.

Also, in the thin film pattern formation using the laser direct writing method, the slow drawing speed narrows the application field of this method to the non-mass production field such as wiring correction of LSI, and the increase in the drawing speed is the mass production field of this method. Various researches have been conducted to expand the possibility of application to medical devices.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a thin film having a high deposition rate and an excellent productivity by eliminating such problems of the prior art.

(Means for Solving the Problem) The present invention relates to a thin film forming method for depositing a thin film on a substrate by heating the substrate installed in a gaseous atmosphere of a chemical causing a thermal decomposition reaction. The above temperature is set to be equal to or lower than the condensation temperature of the compound gas, the compound condensed on the substrate has a time width shorter than the time required for thermal desorption by heating the substrate, and the gas of the compound is Longer than the time required to cause re-condensation, pulse heating to a temperature equal to or higher than the decomposition temperature of the compound gas using a pulsed substrate heating means having a period shorter than 100 μms, A thin film is formed at a high speed by effectively utilizing the raw material molecules condensed on the substrate.

(Operation) The present invention provides a method of drawing a metal fine pattern thin film on an LSI substrate by a laser direct writing method, in which a pulsed laser light source is used as a light source, compared with a continuous (CW) laser light source. The present invention has been made based on new findings obtained from experimental facts by the inventor that the deposition rate of a film per unit time of laser irradiation is extremely high. This experiment and consideration of the results will be described.

In this experiment, W (CO) ₆ was used as a raw material, and a thin film of a fine pattern of W was directly drawn on a substrate by a thermal CVD reaction caused by local heating of the substrate by a focused laser beam. FIG. 2 shows a configuration diagram of the apparatus used in the experiment. Light emitted from the laser light source 1 is condensed by the lens 3 reflected by the mirror 2, and is irradiated through the window 4 onto the substrate 6 placed in the CVD cell 5. CVD source gas is solid W (CO)
Obtain the vapor by sublimating heated W (CO) _{6 6} installed and the gas supply system 7, which is guided to CVD cell 5 are diluted with Ar gas. The remaining gas after the reaction is exhausted by the exhaust unit 8. The XY stage 9 controls the drawing position of the wiring to be drawn and the scanning direction and speed of the drawing. As the laser light source 1, a second harmonic (532 nm) of a Q-switched Nd: YAG laser was used as a pulse light source, and a CW Ar laser light source (515 nm) was used as a CW light source.

Next, the operation in this configuration will be described. The substrate 6 is placed at a predetermined position in the CVD cell 5. Next, the exhaust unit 8 is operated to exhaust the air in the CVD cell 5. A from gas supply system 7
rW (CO) ₆ gas diluted with gas flows into the CVD cell 5,
Laser light is irradiated from the laser light source 1 to deposit W.
At the same time, the XY stage 9 is operated in the direction in which the wiring is formed, and a W film pattern is formed. When the formation of the thin film is completed, the emission of the laser beam and the gas supply are stopped, and a series of operations for forming the wiring is completed.

An example of the results thus obtained will be described below in the order of using a pulse laser light source and using a CW laser light source.

Experimental conditions when using a pulse laser light source are as follows. The repetition number of the irradiation laser light is 10 KHz, the pulse width is 100 ns, and the spot size on the substrate is 1 μm. C
W (CO) ₆ gas of VD raw material is obtained by heating the raw material container to 63 ° C., the vapor pressure is 1 torr, and the total gas pressure is 1 atm. The substrate temperature was set to 60 ° C., slightly lower than 63 ° C., which is the temperature at which W (CO) ₆ gas condensation occurs. Substrate temperature 63 ℃
Above that, it was difficult to form a thin film. XY
Stage scanning is 0.5 μm per step, scanning speed is 0.25
μm / s. When drawing is performed under these conditions, the thickness of the obtained W film increases as the peak power of the irradiation laser increases, but when the peak power reaches approximately 100 mW, the film thickness saturates at a value of approximately 3000 °, The line width was 1 μm. Further, it was confirmed that the film thickness was proportional to the reciprocal of the writing speed, and it was found that the film thickness was proportional to the product of the deposition amount per pulse and the number of irradiation pulses.

Next, for comparison, a fine pattern thin film of W was directly drawn on the same substrate using a CW laser light source. The experimental conditions were the same as those when the pulse laser light source was used, with the spot size of the irradiation laser light being 1 μm and other conditions. When writing is performed under these conditions, the thickness of the obtained W film increases as the power of the irradiation laser is increased, as in the case of using the pulse laser, but when the power reaches about 100 mW, the film thickness becomes 3000.
The saturation was achieved at a value of about Å, and the line width at that time was about 1 μm, which was about the same as that when a pulsed laser light source was used.

Comparing the deposition speed in the two cases with the deposition amount per one step (0.5 μm), the deposition amount per one step is the same as 0.5 μm × 1 μm × 3000 ° in both cases, In the case of drawing using a laser, a pulse width (100 ns) x the number of repetitions (10 kHz) x a dwell time of one step (2 s) = 2.0 ms. In the case of writing, the same amount of W thin film is deposited at the same irradiation time as the one-step stay time = 2 s. Therefore, when the amount of deposition per unit irradiation time is converted into that, the deposition is about 1000 times faster when the pulse laser is used than when the CW laser is used.

Next, consider why the deposition rate per unit irradiation time is faster when using a pulsed laser light source than when using a CW laser light source. Generally, in a chemical reaction,
The production rate of the product obtained by the reaction is determined by the rate of the chemical reaction and the rate of the raw material supply. When the reaction rate is smaller than the feed rate and the production rate of the reaction product is determined by the former, this reaction is said to be reaction-limited,
On the contrary, it is said that the supply is limited. In the thermal CVD reaction, while the substrate temperature is relatively low, the deposition rate increases with an increase in the substrate heating temperature, and the deposition rate is determined by the reaction rate. Is determined by the supply speed. Therefore, the upper limit of the deposition rate is determined by the value determined by the raw material supply rate, and the higher the raw material supply rate, the larger the upper limit of the obtained deposition rate.

The supply mechanism of the source molecules to the deposition reaction region in the thermal CVD method includes (a) supply from the gas phase, (b) supply by surface diffusion of the source molecules adsorbed outside the reaction region on the substrate,
(C) Supply from raw material molecules themselves adsorbed on the substrate reaction region before heating the substrate.
When heating the substrate regularly like normal thermal CVD,
The adsorbed molecule (c) itself seems to contribute to the deposition in the initial stage of the reaction, but once consumed, it no longer contributes to the deposition.

Therefore, when comparing the amount of deposition with the estimated amount of raw material supply from the gas phase for this experimental result, the amount of deposition using a CW laser is smaller than the amount of raw material supply from the gas phase, but the pulse laser is used. On the other hand, it was found that the amount of deposition in the case of being larger than that supplied from the gas phase. This means that in drawing using pulsed laser light, the supply of the raw material is effectively performed from a source other than the gas phase, and the supply from the surface adsorption phase occurs by the mechanism (b) or (c). It indicates that. The supply mechanism of (a) and (b) exists in common both when using a pulsed light source and when using a CW light source. If it is dominant compared to the supply itself, it seems that there is no difference between the case of the pulsed light source and the case of the CW light source, but the result is different, so when the pulsed light source is used, it is mainly It is concluded that the feed of the raw material occurs by the mechanism of (c) and the deposit is formed. From the same consideration, it is concluded that, when the CW laser light source is used, the material is mainly supplied from the gas phase (a) and the deposition is formed.

The reason why the supply from the adsorbed molecules in (c) is effectively performed when the pulse light source is used and the supply from the adsorbed molecules is not performed when the CW light source is used can be explained very simply. This is because when the substrate is heated constantly, such as when the substrate is heated using a CW light source, the adsorbed molecules in (c) contribute to the deposition in the initial stage of the reaction, as described above. However, once consumed, they no longer contribute to deposition. On the other hand, when heating the substrate in a pulsed manner, such as when heating the substrate using a pulsed light source, no deposition is performed between heating and heating, and the substrate is cooled, so that the substrate is cooled again. Source molecules can be adsorbed. Therefore, by heating the substrate in a pulsed manner, it is possible to make effective use of the adsorption phase on the substrate.

In this experiment, since the substrate temperature was lower than the condensation temperature, condensation of the raw material molecules occurred on the substrate.
Since the density of the condensed phase is much greater than the density of the gas phase,
If a deposition reaction occurs using this condensed phase as a source of source molecules, a much higher deposition rate can be obtained as compared to a thin film forming method using a source supply from a gas phase as in a normal thermal CVD reaction. The experimental fact that the use of a pulsed light source makes it difficult to form a thin film when the substrate temperature is raised above the condensation temperature supports the above conclusion.

From the findings obtained above, it is understood that there is a possibility that a high-speed thin film can be formed by condensing as much of the source molecules as possible on the substrate and heating the substrate in a pulsed manner.

Next, sufficient conditions are considered for the duration and cycle of the substrate heating, and the possibility of forming a high-speed thin film is considered.

When the substrate is heated, the number of molecules in the condensed phase decreases due to thermal desorption at the same time as the consumption of the raw material molecules in the deposition process. Accordingly, the condensed phase at least heating Continued heating time required t ₁ or more to heat withdrawal is no longer the material supply from the condensed phase, the raw material supply from the gas phase is to contribute. So when cutting the substrate heating at this time t _1, the substrate is cooled again condensed phase is formed. Assuming that the time required for the formation of the condensed phase is t ₂ , when the substrate is heated again at least at a time interval of t ₂ or more, the state returns to the same state as before the substrate heating, and the deposition is repeated. Therefore, by modulating the substrate heating so that the time width is smaller than t ₁ and the repetition period is larger than t ₂ , it is possible to always cause the deposition by the supply of the raw material from the condensed layer. . If the rate of heating switching is increased within the range where this condition is satisfied, the deposition is considered to be independent during each heating cycle, so that a large deposition rate can be obtained in proportion to the number of times of heating. . When the repetition period becomes about t ₂ or less, the recondensation of the source molecules on the substrate becomes insufficient, and the deposition rate is reduced due to the influence of the previous heating cycle.

Molecules in the condensed phase are linked by weak intermolecular forces, such as van der Waals forces. The concentration of molecules in the condensed phase is determined by the balance between the rate of condensation of molecules from the gas phase onto the substrate and the rate of desorption from the substrate to the gas phase. The condensation rate and the desorption rate have different values depending on the substrate temperature, and the concentration of the condensed phase has a constant value determined by the substrate temperature. When the substrate is rapidly raised from a low-temperature state in which condensation occurs to a high-temperature state in which normal deposition occurs (500 to 1000 ° C.) in the limit of the required time 0, the time required for molecules to desorb is an average in the high-temperature state. It is determined by the adsorption time, which is estimated to be about 1 μs or less, depending on the type of the raw material molecule. Therefore, if the time required to heat the substrate to the temperature at which deposition occurs is very small than ₁ μs, t ₁ is about ₁ μs, and if the time required for heating is larger than 1 μs, t ₁ is It is determined by the time required. When the substrate is rapidly lowered from the temperature at which deposition normally occurs to a low temperature at which condensation occurs at the limit of the required time 0, the time required for molecules to condense and the concentration of the condensed phase to be saturated is an average in the low temperature state. It is determined by the adsorption time, and this time is also estimated to be about 1 μs. Therefore, when the time required for the substrate to cool to a temperature at which condensation occurs is extremely smaller than 1 μs, t ₂ is about 1 μs, and the time required for cooling is 1 μs.
If it is larger than μs, t ₂ is determined by the time required for this cooling. Usually, the time required for heating and the time required for cooling are almost the same, so when using a substrate with good heat conduction and a small thermal time constant, or when forming a thin film of a fine pattern by laser direct drawing or pattern transfer. Since the time required for heating and cooling becomes shorter as the substrate heating area becomes smaller, high repetition is possible, and the present invention is effective.

In the experiment described above, the pulse period of the pulse laser light source was 1/10 KHz = 100 μs, and the total deposition rate (deposition amount per unit time, not deposition amount per unit irradiation) was CW laser light source. Was the same as when using. Under these experimental conditions, the time required for cooling the substrate is 1 μs or less, so that the number of repetitions of the pulsed light source can be further increased by about 100 times. Thus, when the CW laser is used based on the principle of the present invention, Thus, the total deposition rate can be improved.
From the above considerations, the change in the deposition rate when the number of repetitions was increased, assuming that the heating was performed steadily using a CW laser as 1, as shown in FIG. It is considered that the curve increases in proportion to the number of repetitions while it is small, but decreases when the number of repetitions exceeds a certain number of repetitions, and approaches 1 when the number of repetitions approaches about 1 MHz. In this case, the maximum is less than when using a CW laser under the same conditions.
A deposition rate about 100 times higher can be expected. Therefore, by using this method, it is possible to form a thin film at an extremely high speed as compared with a conventional thin film forming method of performing constant heating such as thermal CVD.

(Example) Next, an example related to the present invention will be described in detail with reference to the drawings. This embodiment is an example in which a thin film of a fine pattern of W is directly drawn on a substrate using W (CO) ₆ as a raw material and using a pulse laser light source as heating means for the substrate, similarly to the above experiment.

FIG. 1 is a configuration diagram of a thin film forming apparatus used in an embodiment according to the present invention. Light emitted from a semiconductor laser light source 1 (wavelength 0.83 nm) driven by a pulse power source 10 capable of arbitrarily changing the pulse width and the number of repetitions is condensed by a lens 3 reflected by a mirror 2 and passed through a window 4 to a CVD cell. 5
It is irradiated onto the substrate 6 placed inside. CVD source gas is
The gas supply system 7 in which solid W (CO) ₆ is installed is heated to W
This vapor is obtained by sublimating (CO) ₆ , which is diluted with Ar gas and led to the CVD cell 5. The remaining gas after the reaction is exhausted by the exhaust unit 8. The XY stage 9 controls the drawing position of the wiring to be drawn and the scanning direction and speed of the drawing.

Next, the operation in this configuration will be described. The substrate 6 is placed at a predetermined position in the CVD cell 5. Next, the exhaust unit 8 is operated to exhaust the air in the CVD cell 5. A W (CO) ₆ gas diluted with Ar gas is flowed into the CVD cell 5 by the gas supply system 7 and irradiated with laser light from the laser light source 1 to deposit W. At the same time, the XY stage 9 is operated in the direction of forming the wiring to form a W thin film pattern. When the formation of the thin film is completed, the emission of the laser beam and the gas supply are stopped, and a series of operations for forming the wiring is completed.

An example of the result obtained in this way will be described below. The CVD conditions are as follows. The peak power of the irradiation laser light is 100 mW, the pulse width is 100 ns, and the spot size on the substrate is 1 μs. W (CO) ₆ gas of CVD raw material is obtained by heating the raw material container to 63 ° C, and the vapor pressure is 1t
orr, gas total pressure is 1 atm. The substrate temperature was set at 60 ° C, slightly lower than the sublimation temperature of 63 ° C, and W (CO)
₆ condensed states were created. The reason for setting the substrate temperature to 60 ° C, which is slightly lower than the sublimation temperature of 63 ° C, is that if this substrate is extremely cooled, W (CO) ₆ crystals will precipitate directly on the substrate. It is to prevent. XY
The scanning of the stage is 0.5 μm per step.

Under these conditions, the laser repetition rate is set to (a) 10 KHz (period 1
(00μs), (b) 100KHz (period 10μs), (c) 200KHz
(Period 5 μs), (d) Drawing was performed while changing to 1 MHz (period 1 μs). As a result, the maximum scanning speed at which a W line having a film thickness of 5000 A or more can be drawn is 0.25 μm /
s, 2.5 μm / s for (b), 20 μm for (c)
/ s and 5 μm / s in the case of (d), and it was confirmed that drawing was possible at a scanning speed (in other words, a deposition speed) of about 80 times as compared with the case where CW laser light was used. It was also confirmed that there was an optimum number of repetitions for high-speed drawing.

The above embodiment describes an example in which a thin film is formed by a so-called laser direct drawing method in which a substrate is locally heated by irradiating a laser beam focused on the substrate and a fine thin film pattern is directly drawn by a thermal CVD reaction. However, as a method of heating the substrate, a pattern transfer method of heating the substrate in a pattern using a patterned laser beam or flash lamp beam, or irradiating the substrate with a laser beam or a powerful flash lamp to heat the entire surface of the substrate A method can be used. Further, based on the principle of the present invention, not only the method using light, but also a method for transiently heating the substrate, such as using pulse current heating or dielectric heating when the substrate is conductive. It goes without saying that it can be applied to all.

Further, in this embodiment, the raw material is W (CO)
₆ , an example of depositing a W thin film has been described. However, based on the principle of the present invention, the effect of the present invention is to form a thin film for depositing another thin film such as an insulator or a semiconductor thin film using another source gas. It goes without saying that it can be applied to all methods. For example, as raw materials, silane (SiH ₄ ), copper bishexafluoroacetylacetonate (Cu (hfac) ₂ ), dimethyl gold acetylacetonate (Me ₂ Au (acac)), dimethyl aluminum hydride (Me ₂ AlH), molybdenum carbonyl ( Mo
(CO) ₆ ) using amorphous Si, Cu, Au, Al,
Mo was deposited on Si or SiO ₂ or on SiN _x , but the effect of the present invention has been confirmed.

(Effects of the Invention) As described above, according to the method of the present invention, raw material molecules condensed on a substrate can be effectively used.
For this reason, a thin film can be formed on a substrate at a higher speed than the conventional CVD method, and productivity can be improved in an LSI manufacturing process or the like.

[Brief description of the drawings]

FIG. 1 is a block diagram of a thin film forming apparatus used in an embodiment according to the present invention, FIG. 2 is a block diagram of a conventional thin film forming apparatus, and FIG. 3 illustrates the dependence of the deposition rate of the thin film on the number of substrate heating repetitions. FIG. 1 laser light source 2 mirror 3 lens 4
... Window, 5 ... CVD cell, 6 ... Substrate, 7 ... Gas supply system, 8 ... Exhaust unit, 9 ... XY stage, 10 ...
... A pulse power supply for driving a semiconductor laser, 11... A curve showing the deposition rate when pulse-like heating is performed.

Claims (2)

(57) [Claims] In a thin film forming method for depositing a thin film on a substrate by heating a substrate placed in a gas atmosphere containing a compound causing a thermal decomposition reaction, the temperature of the substrate is reduced by condensation of the compound gas. Temperature or less, the compound condensed on the substrate has a time width shorter than the time required for thermal desorption by heating the substrate, and the time required for the compound gas to recondense on the substrate. Longer than 100μs
Using pulsed substrate heating means with a shorter period,
A method for forming a thin film, comprising heating a substrate in a pulsed manner to a temperature equal to or higher than the decomposition temperature of the compound gas. 2. The time width is 1 μs or less and the period is 1 μs.
2. The method for forming a thin film according to claim 1, wherein a pulse-like substrate heating means having a length of at least 100 μs is used.