JP5044307B2 - Thin film formation method - Google Patents

Description

  The present invention relates to a method for forming a thin film, and more particularly to a method for forming a thin film by firing fine metal particles to form a metal thin film.

  With the recent high integration and high speed of LSI in the semiconductor industry, the miniaturization and multi-layering of the wiring of the semiconductor substrate has progressed, and the problem of signal delay due to inter-wiring capacitance and wiring resistance has arisen due to the narrowing of the wiring pitch.

  In order to avoid this, it is necessary to use a wiring material having a low resistivity and an interlayer insulating film having a low dielectric constant. As a wiring material, instead of a conventional Al alloy or the like, the resistivity is low and electromigration ( EM) resistant metal thin films are starting to be put into practical use.

There are many general methods for forming a metal thin film. For example, sputtering, CVD, plating, etc. are widely used. In addition, as a technique for forming a wiring with a metal thin film, a so-called damascene method in which a metal thin film is deposited on a substrate surface on which fine holes such as wiring grooves, via holes, and contact holes are formed, and then subjected to CMP (Chemical-mechanical polishing) treatment. Has been developed.
However, the above-described conventional method for forming a metal thin film has the following problems.

In the case of the sputtering method, the step coverage is generally limited. Even if it is used together with the reflow method, there is a restriction that the reflow temperature is lowered due to the compatibility with the low dielectric constant film. It is difficult to promote. There is also a problem that the process cost is high.
In the case of the CVD method, there are problems that the raw material cost is high, the film forming speed is low, and the process cost is high.
In the case of the plating method, in particular, when a copper thin film is grown by the plating method, it is necessary to provide a copper thin film as a so-called seed layer on the barrier layer, and there is a problem such as residual plating solution in the void. is there.

As described above, none of the above film forming methods is satisfactory as a method for forming a metal thin film, and in any of these film forming methods, when filling a hole or groove having a high aspect ratio, a wiring trench is formed. Satisfactory embedding performance to the above has not been obtained.
There are prior arts that attempt to solve the above problems by using a metal ultrafine particle dispersion. However, when metal fine particles are used, if the heat treatment is insufficient, the resistance value increases, and conversely, the heat treatment is excessive. However, there is a problem that the grain growth is too advanced and the wire breaks or loses the metallic luster and whitens.
JP 2001-254185 A

  An object of the present invention is to solve the above-described problems of the prior art and provide a technique for forming a high-quality metal thin film using a metal ultrafine particle dispersion.

In order to solve the above problems, the present invention applies a dispersion liquid in which fine metal particles coated with an organic substance are dispersed in a dispersion solvent to the surface of a film formation target, and bakes the film formation target in a heating tank. a thin film forming method for forming a metal thin film, the time of firing, the introduction article al air into the heating tank, instrument in the heating signal to the heating chamber corresponding to the CO gas pressure in the tank Is a method of forming a thin film in which the time when the absolute value of the rate of change in the intensity of the signal becomes smaller than a reference is determined as the end point of the firing.
Further, according to the present invention, the measuring instrument includes a quadrupole mass spectrometer and a plurality of differential exhaust chambers connected in series, and the differential exhaust chamber at one end of the series connection is the heating tank. The differential exhaust chamber at the other end is connected to the quadrupole mass spectrometer,
A thin film forming method for outputting the signal from the quadrupole mass spectrometer .

Since it is possible to accurately detect when the organic dispersant is removed, the organic dispersant remains, or conversely, heating is continued after removal of the organic dispersant to grow the particle size of the metal thin film. There is no such thing as
Therefore, it is possible to obtain a metal thin film excellent in conductivity and reflectance at a low process cost.

  First, helium is introduced into the vacuum chamber of the vapor deposition apparatus, Cu vapor is generated while introducing α-terpineol vapor in a helium atmosphere at a pressure of 0.5 Torr, and the generated Cu vapor is brought into contact with α-terpineol. Then, CU ultrafine particles of 0.1 μm or less with α-terpineol attached are cooled and recovered.

  α-Terpineol was replaced with an organic dispersant composed of octanoic acid and 2-ethylhexylamine to obtain fine metal particles whose surface was covered with an organic dispersant, and then dispersed in toluene. obtain.

  A dispersion liquid in which metal fine particles having a particle diameter of 0.1 μm or less are dispersed is dropped on the film formation target (substrate) 13, and a layer of the dispersion is formed on the film formation target (substrate) 13 by spin coating or the like. After forming, it is dried in a drying furnace to form a deposited layer of metal fine particles, and is carried into the heating tank 11 of the baking apparatus 10 of FIG.

  A heating device 12 and an air supply device 15 are provided in the heating tank 11, and the film formation target (substrate) 13 is heated by the heating device 12 while introducing air into the heating tank 11 by the air supply device 15. When the temperature of the metal fine particle deposition layer is raised, the solvent contained in the metal fine particle deposition layer volatilizes and evaporates, then the organic dispersant burns, and when the organic dispersant is removed, the metal fine particles are heated. Underneath, a metal thin film is formed.

  A partial pressure measuring device 20 is connected to the heating tank 11, and when the film formation target 13 is heated in the heating tank 11, the CO gas pressure inside the heating tank 11 is measured by the partial pressure measuring device 20, The point in time when the organic dispersant is removed is detected.

The method for measuring the CO gas pressure will be described. The partial pressure measuring instrument 20 has a quadrupole mass spectrometer 22. In the quadrupole mass spectrometer 22, the gas pressure in the atmosphere to be measured is Although it can be measured for each type of gas, the operating pressure of the quadrupole mass spectrometer 22 is one-tenth (10 ^-8 ) of atmospheric pressure, and the inside of the heating tank 11 is atmospheric pressure. The internal atmosphere of the direct heating tank 11 cannot be measured directly.

The partial pressure measuring instrument 20 is connected to a decompression device 17 having a plurality (three in this case) of differential exhaust chambers 21 _{1 to} 21 ₃ connected in series, and to each of the differential exhaust chambers 21 _{1 to} 21 ₃ . and evacuation device 18 is provided, of the differential pumping chamber 21 ₁ to 21 ₃ which are connected in series, a differential exhaust chamber 21 ₁ of the one end of which is connected to the heating tank 11, the other end of the differential pumping chamber 21 ₃ is connected to a quadrupole mass spectrometer 22.

When the evacuation device 18 is operated and the differential evacuation chambers 21 _{1 to} 21 ₃ are evacuated, the pressure in the differential evacuation chamber 21 ₁ close to the heating tank 11 is high, and the one closer to the quadrupole mass spectrometer 22 The pressure in the differential exhaust chamber 21 ₃ becomes lower.

As described above, when the differential exhaust chambers 21 _{1 to} 21 ₃ are provided and the differential exhaust chambers 21 _{1 to} 21 ₃ are evacuated, the differential to which the quadrupole mass spectrometer 22 is connected is provided. The pressure in the exhaust chamber 21 ₃ becomes a pressure at which the quadrupole mass spectrometer 22 can operate, and the inside of the heating tank 11 can be measured via the differential exhaust chambers 21 _{1 to} 21 ₃ .

  When the deposition layer of the metal fine particles is heated and the combustion of the organic dispersant is started by oxygen in the internal atmosphere of the heating tank 11, carbon monoxide, carbon dioxide, and water are generated from the dispersant, and are converted into gas and heated. Is released inside.

With the quadrupole mass spectrometer 22, carbon monoxide (CO: molecular weight 28) in the gas in the differential exhaust chamber 21 ₃ is continuously measured from the start of heating, and the pressure value of the CO gas is determined. Since the CO gas pressure in the differential exhaust chamber 21 ₃ is proportional to the CO gas pressure in the heating tank 11, the partial pressure measuring device 20 determines the value of the CO gas pressure in the heating tank 11. I can know.
Since CO gas is generated by the combustion of the dispersant, the CO gas pressure in the heating tank 11 decreases as the combustion proceeds, and as a result, the value of the measured CO gas pressure also decreases.

  When the organic dispersant covering the metal fine particles is removed by combustion, the CO gas generation stops and the CO gas is not supplied into the heating tank 11. The atmosphere is supplied to the heating tank 11 together with the exhaust by the vacuum exhaust device 18, and when CO gas generation is stopped, the CO pressure in the heating tank 11 becomes equal to the CO pressure contained in the atmosphere.

When the CO pressure in the heating tank 11 becomes a constant value, the value of the CO partial pressure detected by the partial pressure measuring device 20 also becomes a constant value. Accordingly, when it is detected that the decrease in the CO pressure has been completed, it is determined that the removal of the organic dispersant covering the metal fine particles has been completed, and the film formation target 13 is taken out of the heating tank 11 and the baking process is completed. To do.
A decrease in CO pressure or a constant CO pressure can be detected by a change in the intensity of the CO signal output from the measuring instrument.

  For example, if the intensity of the CO signal indicating the CO pressure measured by the partial pressure measuring instrument 20 at the measurement time t is I, the sign A is a proportionality constant, and the CO pressure change rate D is D = A × dI / dt. When the absolute value of the rate of change D falls below a predetermined value, it can be determined that the CO pressure change has stopped and the organic dispersant has been removed.

Further, assuming that the intensity of the CO signal at different adjacent measurement times t ₁ and t ₂ is I ₁ and I ₂ , it changes as D = A × {(I ₁ −I ₂ ) / (t ₁ −t ₂ )}. The rate can be determined.
As described above, since the time when the organic dispersant is removed can be accurately detected, it is possible to prevent the metal fine particles from being excessively heated in the state where the organic dispersant is removed.

  The film formation target (substrate) 13 from which the organic dispersant has been removed and the metal thin film has been formed can be taken out of the heating bath 11 and processed in the subsequent process.

Ag fine particles were used as the metal fine particles, and octanoic acid having 8 carbon atoms and 2-ethylhexylamine having 8 carbon atoms were adhered as dispersing agents.
The metal fine particles were dispersed in toluene at a metal concentration of 40 wt% to prepare a dispersion. The Ag nanoparticles used here were those produced by a gas evaporation method.

Next, the glass substrate was set on a spin coater, and while being rotated, the dispersion was dropped from above, and the surface of the glass substrate was covered with the dispersion.
Viewpoint time after dropping the rotation speed of the glass substrate, the film thickness of the dry燥後was adjusted to 0.2 [mu] m.

  The glass substrate in this state is carried into the heating tank 11 of the baking apparatus 10, the atmosphere is introduced into the heating tank 11 by the air supply apparatus 15, and the glass substrate is 220 ° C. by the heating apparatus while being evacuated by the vacuum exhaust apparatus 18. The metal film was baked while measuring the pressure of carbon monoxide in the heating tank 11 with a quadrupole mass spectrometer 22 (Sepion 2 manufactured by ULVAC, Inc.) to form a metal thin film made of an Ag thin film. .

The relationship between the intensity of the output signal of the quadrupole mass spectrometer 22 and the heating time is shown in FIG. The horizontal axis represents the heating time, and the vertical axis represents the intensity of the CO signal indicating the CO gas pressure.
Since the organic dispersant that coats the Ag fine particles reacts with oxygen to become carbon monoxide and is removed, the sintering of the Ag particles proceeds, so the intensity of the CO signal decreases as the heating time elapses. As described above, when the decrease in the intensity of the CO signal is completed and the intensity of the CO gas pressure becomes a constant value, the organic dispersant covering the Ag fine particles is burned and removed. It means that.

In the graph of FIG. 2, it is considered that the reduction in the intensity of the CO signal was completed in about 70 minutes, and the removal of the organic dispersant was completed in the vicinity of 70 minutes.
Next, the glass substrates were baked at different heating times while measuring the pressure of carbon monoxide, and the specific resistance and specular reflectance were measured. The measurement results of the heating time and the specific resistance and specular reflectance of the obtained metal thin film are shown in Table 1 below.

  From the results shown in Table 1, when heating for 120 minutes, the specific resistance increases and the reflectivity decreases. This is because the heating time is excessively long, so that grains grow and the characteristics of the metal thin film deteriorate. It is thought that.

In addition, in the said Example, although octanoic acid and 2-ethylhexylamine were used as an organic dispersing agent and both were made to adhere, any one may be made to adhere. The organic dispersant of the present invention is not limited to octanoic acid and 2-ethylhexylamine, and may be other dispersants as long as they are made of an organic substance and burned with oxygen.
In the above-described embodiment, firing was performed at 220 ° C., but when an Ag metal thin film is formed from Ag fine particles, the heating temperature can be in the range of 150 ° C. to 300 ° C.

An example of a baking apparatus that can be used in the method of the present invention Graph showing the relationship between heating time and CO signal intensity

Explanation of symbols

11 ... Heating tank 13 ... Target for film formation

Claims (2)

A thin film forming method of applying a dispersion liquid in which metal fine particles coated with an organic substance are dispersed in a dispersion solvent to the surface of a film formation target, and firing the film formation target in a heating tank to form a metal thin film. ,
During the firing, while the atmosphere is introduced into the heating tank, a signal corresponding to the CO gas pressure in the heating tank is measured with a measuring instrument in a state where the pressure in the heating tank is atmospheric pressure , A thin film forming method in which the time when the absolute value of the rate of change in strength becomes smaller than a reference is determined as the end point of the firing. The measuring instrument has a quadrupole mass spectrometer and a plurality of differential exhaust chambers connected in series,
The differential exhaust chamber at one end of the series connection is connected to the heating tank, and the differential exhaust chamber at the other end is connected to the quadrupole mass spectrometer.
The thin film forming method according to claim 1, wherein the signal is output from the quadrupole mass spectrometer .

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