JP4624207B2 - Film forming method and film forming apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for forming a silicon oxide film used as, for example, an interlayer insulating film.

  In a MOSFET transistor, a gate electrode is formed on a gate insulating film between a source region and a drain region, and a current flowing between the source and drain regions is controlled by the gate electrode. As the gate electrode, a metal gate electrode is becoming mainstream in order to reduce the resistance. As shown in FIG. 6, the present inventors have made a polysilicon layer 10 and a tungsten nitride (WN) layer. 11 and the tungsten (W) layer 12 are examined from the lower side in this order. In the figure, reference numeral 18 denotes a gate insulating film.

  By the way, in the MOSFET transistor, after forming the gate electrodes 1A and 1B, the interlayer insulating film 13 is formed between the gate electrodes 1A and 1B. With the recent miniaturization and high integration of devices, these gate electrodes are formed. The aspect ratio of the recess 14 between 1A and 1B is as large as 4 or more, for example. As the interlayer insulating film 13 for embedding the recess 14 between the gate electrodes 1A and 1B having such a high aspect ratio, a BPSG film has been widely used. This BPSG film is a silicate glass film doped with boron (B) and phosphorus (P).

  However, the BPSG film 13 has a film forming temperature of about 600 ° C., but it needs to be processed at a high temperature of about 850 ° C. in order to melt and fill the recess 14 between the gate electrodes 1A and 1B. When the metal gate electrodes 1A and 1B are exposed to a high temperature during this process, there is a problem that the overall resistance of the formed MOSFET transistor increases.

  For this reason, in the gate electrodes 1A and 1B, since the resistance of the WN layer 11 is large, the WN layer 11 cannot be made so thick. For this reason, the WN layer 11 must be made as thin as about 5 nm. If the gate electrodes 1A and 1B are thin, the W of the WN layer 11 reacts with the polysilicon layer 10 when the gate electrodes 1A and 1B are exposed to a high temperature, so that it is assumed that WSi having a high resistance is generated. .

  Therefore, in order to form the interlayer insulating film 13 at a lower temperature, instead of the BPSG film, an organic silane-based gas such as TEOS (tetraethylorthosilicate) gas and an aminosilane-based gas such as a Vista butylaminosilane gas are used as a raw material gas. However, the film forming temperature in this process is 680 ° C., and the temperature is not sufficiently lowered. The SiO2 film formed by the method has a problem that voids such as the void 15 shown in FIG. 7A and the seam 16 shown in FIG. In FIG. 7, reference numeral 17 denotes a silicon substrate.

  For this reason, this CVD process decomposes TEOS gas in the gas phase and embeds SiO2 in the recess 14 between the gate electrodes 1A and 1B. For example, as shown in FIG. Since the decomposition product 18 of the TEOS gas generated in the gas phase is deposited on the gate electrodes 1A and 1B so as to be deposited, as shown in FIG. 8B, the upper surfaces of the gate electrodes 1A and 1B, or between them, However, it is difficult to adhere to the side surfaces of the gate electrodes 1A and 1B. Therefore, as shown in FIGS. 8B and 8C, the thickness of the upper surface of the two gate electrodes 1A and 1B is large and the thickness of the side surface is small. This is presumably because the void 15 is formed between the two gate electrodes 1A and 1B as shown in FIG.

  Even if the SiO2 film is embedded without forming the void 15 in the recess 14 between the gate electrodes 1A and 1B, the source electrode and drain of the recess 14 embedded with the SiO2 film are formed after the formation of the SiO2 film. When a through hole called a contact hole is formed in the upper part of the electrode and the bottom surface of the hole is washed with hydrofluoric acid (HF), the hydrofluoric acid used in this step oozes out from the contact hole. As a result, the SiO2 film is etched in the vicinity of the central portion of the recess 14 by the hydrofluoric acid, and a void called a seam 16 is formed.

  Here, in the CVD process using the TEOS gas, SiO2 formation and desorption of impurities such as alcohol occur at the same time to form SiO2, but the SiO2 film has a concave portion between the gate electrodes 1A and 1B as described above. 14 is embedded sequentially from both sides of the recess 14 (on the side walls of the gate electrodes 1A and 1B) toward the center of the recess 14, so that the last embedding instant is formed from both sides of the recess 14. The wall of the SiO2 film is closed from both sides, and impurities are difficult to escape. For this reason, since this portion is in a state containing an impurity and is brittle, the hydrofluoric acid is likely to attack, and as a result, it is considered that the seam 16 is formed by etching with hydrofluoric acid.

  Here, as a method for forming an interlayer insulating film, a CVD process is performed at a pressure of less than 2.66 kPa (20 Torr) and a temperature of 300 ° C. or more and less than 500 ° C. using TEOS gas and O 3 (ozone) gas as source gases. Using a technology (Patent Document 1), a TEOS gas, an ozone-containing oxygen gas (O3-containing O2 gas), and a gas that generates H2O in combination with O2, such as H2O2 gas, a pressure of 1.33 Pa (10 Torr) is used. There are various patent documents such as a technique (Patent Document 2) for performing a plasma CVD process under a process condition of a temperature of 200 ° C.

  However, the technique of Patent Document 1 performs the CVD process by decomposing TEOS in the gas phase as described in the document 1 that the TEOS-containing gas and the O 3 -containing gas easily react in the gas phase. Therefore, in the end, the film formation proceeds by the mechanism shown in FIG. 8 and the gap between the high aspect ratio gate electrodes 1A and 1B having an aspect ratio of 4 or more is embedded without forming the void 15 or the seam 16. It is insufficient.

  The technique of Patent Document 2 is plasma CVD, in which TEOS gas, O3-containing O2 gas, and H2 O2 gas are decomposed by plasma. Even in this case, TEOS is eventually decomposed in the gas phase to form a film. For this reason, film formation proceeds by the mechanism shown in FIG. 8, which is insufficient for embedding between the high aspect ratio gate electrodes 1A and 1B without forming the void 15 or the seam 16.

  Therefore, the interlayer insulating film 13 in the layer in which the gate electrodes 1A and 1B of the multilayer wiring structure of the integrated circuit are formed is formed at a low temperature of, for example, 500 ° C. or lower in order to suppress adverse effects on the gate electrodes 1A and 1B. The coverage is good so that the recess 14 having a high aspect ratio between the gate electrodes 1A and 1B can be filled without any gaps, and is sufficiently resistant to a chemical solution containing fluorine (F) such as hydrofluoric acid. The development of an interlayer insulating film that satisfies this requirement is required.

Japanese Patent No. 3254294 JP-A-6-168930

  The present invention has been made under such circumstances, and an object of the present invention is to provide a technique capable of forming a silicon oxide film with good coverage at a low film formation temperature.

For this reason, the film forming method of the present invention is a method of forming a silicon oxide film on a target object by using a vapor of an organic silicon source in a reduced pressure atmosphere and a heated atmosphere in a processing container in which the target object is placed. In
The inside of the processing vessel is heated to a temperature lower than the decomposition temperature of the vapor of the organic silicon source and to generate hydroxyl active species and oxygen active species by oxygen gas and hydrogen gas ,
The organic silicon source supplied into the processing vessel is decomposed by hydroxyl active species and oxygen active species generated by the oxygen gas and hydrogen gas supplied into the processing vessel, and silicon dioxide is oxidized on the object to be processed. A film is formed.
The organic silicon source is selected from, for example, tetraethylorthosilicate gas and binary aminosilane gas .

  Further, the object to be processed is formed, for example, with a plurality of gate electrodes, and the silicon oxide film is used as an interlayer insulating film formed on the gate electrodes so as to embed between the gate electrodes, for example. it can.

Further, the film forming apparatus of the present invention includes a processing container in which an object to be processed is placed,
Pressure adjusting means for setting the inside of the processing vessel to a reduced pressure atmosphere;
Heating means for heating the inside of the processing vessel;
A film forming gas supply path for supplying vapor of the organic silicon source into the processing container;
An oxidizing gas supply path for supplying oxygen gas into the processing vessel;
A reducing gas supply path for supplying hydrogen gas into the processing vessel;
Flow rate adjusting means provided in the film forming gas supply path, the oxidizing gas supply path, and the reducing gas supply path, respectively, for adjusting the flow rates of the vapor , oxygen gas, and hydrogen gas of the organic silicon source. When,
A control unit for controlling the pressure adjusting means, the heating means, and the flow rate adjusting means,
The control unit sets the inside of the processing container to a reduced pressure atmosphere and heats it at a temperature lower than the decomposition temperature of the vapor of the organic silicon source to thereby generate hydroxyl active species and oxygen activity generated by oxygen gas and hydrogen gas. The pressure adjusting means, the heating means, and the flow rate adjusting means are controlled so as to form a silicon oxide film on the object to be processed using a seed.

According to the present invention, a vapor of organic silicon source, and oxygen gas, a hydrogen gas, by heating at a temperature lower than the decomposition temperature of the vapor of the organic silicon source under a reduced pressure atmosphere, an oxygen gas Since the silicon oxide film is formed using hydroxyl active species and oxygen active species generated by hydrogen gas , the silicon oxide film is formed at a deposition temperature lower than the vapor decomposition temperature of the organic silicon source. be able to.

At this time, the silicon oxide film adsorbs the organic silicon source vapor on the object to be processed without decomposing, and then the organic silicon source vapor adsorbed on the object by the hydroxyl active species and oxygen active species. It is presumed that the silicon oxide film is formed by decomposing, and the silicon oxide film thus formed has good coverage. Further, since the film is formed by radical oxidation, the film quality is strong, and the silicon oxide film thus formed has a high resistance to a chemical solution containing fluorine.

  Therefore, for example, when such a silicon oxide film is used as an interlayer insulating film of a layer in which a plurality of gate electrodes are formed, the filling characteristics between two adjacent gate electrodes are good. Further, since the processing is performed at a low temperature that does not decompose the film forming gas, even if the gate electrode contains a metal, it is possible to suppress an adverse effect that occurs when the gate electrode is exposed to a high temperature.

A silicon dioxide film (SiO2 film) which is a silicon oxide film formed by the method of the present invention is used as an interlayer insulating film of a layer in which a metal gate electrode of a multilayer wiring structure of an integrated circuit is formed, for example. Here, a structure of a layer in which a gate electrode is formed in a MOSFET transistor having a metal gate electrode will be briefly described with reference to FIG. In this MOSFET transistor, an N well 21 and a P well 22 are formed on a P type Si substrate 20, and P ⁺ type source / drain regions 21 a and 21 b are formed in the vicinity of the surface of the N well 21. Is provided with a gate electrode 3A. Near the surface of the P-well 22, N ⁺ type source / drain regions 22a and 22b are formed, and a gate electrode 3B is provided thereon.

In the figure, reference numeral 23 denotes an SiO 2 film, 24a and 25a denote source electrodes connected to the P ⁺ -type source region 21a and N ⁺ -type source region 22a, respectively, and 24b and 25b denote P ⁺ -type drain regions 21b and N ^{+, respectively.} A drain electrode connected to the drain region 22b of the mold, and the source electrodes 24a and 25a and the drain electrodes 24b and 25b are made of, for example, aluminum (Al). In the figure, reference numeral 26 denotes a field SiO 2 film formed between the N well 21 and the P well 22.

  Both the gate electrodes 3A and 3B are formed by laminating a polysilicon layer 31, a WN layer 32, and a W layer 33 in this order from the lower side, and side spacers 34 are formed on the side walls of the gate electrodes 3A and 3B. ing. The polysilicon layer 31 of the gate electrodes 3A and 3B is formed to a thickness of 60 nm, the WN layer 32 is formed to a thickness of 5 nm, and the W layer 33 is formed to a thickness of about 40 nm. A recess 35 is formed between the gate electrodes 3A and 3B. The width is set to about 60 nm, for example, and the height of each of the gate electrodes 3A and 3B is set to about 250 nm, for example, so that the aspect ratio of the recess 35 between the gate electrodes 3A and 3B becomes 4 or more.

An interlayer insulating film 4 made of, for example, a SiO2 film formed by the method of the present invention is buried between the gate electrodes 3A and 3B, and the interlayer insulating film 4 is set to have a thickness of about 65 nm, for example. . In the figure, 37 is a through hole called a via hole formed so as to be in contact with the upper surfaces of the gate electrodes 3A and 3B, 38 is a P ⁺ type source electrode 24a, an N ⁺ type source electrode 25a, and a P ⁺ type drain electrode. 24b is a through hole called a contact hole formed so as to be in contact with the upper surface of the N ⁺ -type drain electrode 24b.

  Next, an example of a film forming apparatus for carrying out the film forming method of the present invention will be described with reference to FIG. In FIG. 2, 5 is a reaction vessel that forms a processing vessel formed of, for example, quartz in a vertical cylindrical shape, and the lower end of the reaction vessel 5 is opened as a furnace port, The flange 52 is integrally formed. Below the reaction vessel 5, a lid 53 made of, for example, quartz that contacts the lower surface of the flange 52 and hermetically closes the opening 51 is provided so as to be opened and closed in a vertical direction by a boat elevator (not shown). A rotating shaft 54 is provided through the center of the lid 53, and a wafer boat 55, which is a workpiece holder, is mounted on the upper end of the lid.

  The wafer boat 55 includes three or more, for example, four support columns 56, and a plurality of, for example, 125 semiconductor wafers (hereinafter referred to as "wafers") W can be held in a shelf shape. A groove (slot) is formed in the support column 56. However, among the 125 wafer W holding regions, a plurality of dummy wafers are held at the upper and lower ends, and the product wafer is held in the region between them. A motor M that forms a drive unit for rotating the rotary shaft 54 is provided below the rotary shaft 54, so that the wafer boat 55 is rotated by the motor M. A heat retaining unit 57 is provided on the lid 53 so as to surround the rotating shaft 54.

  An L-shaped injector 61 for supplying gas to the wafer W in the reaction vessel 5 is inserted into the flange 52 at the bottom of the reaction vessel 5. A gas supply pipe 62, which is a gas supply path, is connected to the base end side of the injector 61, and the other end side of the gas supply pipe 62 is connected to flow rate adjusting valves V1, V2, and V3 that respectively constitute flow rate adjusting means. A film forming gas supply source 63, an oxidizing gas such as oxygen (O 2) gas supply source 64, and a reducing gas such as hydrogen (H 2) gas supply source 65 are connected to the gas supply pipe 62 and the injector 61. The gas required for film formation can be supplied into the reaction vessel 5 via Here, the gas supply unit 6 includes the gas supply pipe 62, the film forming gas supply source 63, the oxygen gas supply source 64, the hydrogen gas supply source 65, and the flow rate adjusting valves V1, V2, and V3. Further, the downstream side of the film forming gas supply source 63 of the gas supply unit 6 is the film forming gas supply path, the downstream side of the oxygen gas supply source 64 of the gas supply unit 6 is the oxidizing gas supply path, and the hydrogen gas supply source 65 of the gas supply unit 6. The downstream side of each corresponds to a reducing gas supply path.

As the film forming gas, an organic silicon source vapor, for example, TEOS gas, BTBAS (Bistal aminosilane) gas, or the like, or an inorganic silicon source vapor, for example, monosilane gas, chlorosilane gas, hexachlorodisilane (HCD) gas, or the like is used. be able to. Furthermore, as the oxidizing gas, in addition to oxygen gas, one or more gases selected from the group consisting of N ₂ O gas, NO gas, and NO ₂ gas can be used, and the reducing gas can be hydrogen gas or the like. In addition, one or more gases selected from the group consisting of NH ₃ gas, CH ₄ gas, and HCl gas can be used.

  Further, an exhaust port 7 for exhausting the inside of the reaction vessel 5 is formed above the reaction vessel 5. Connected to the exhaust port 7 is an exhaust pipe 73 having a vacuum pump 71 and a pressure adjusting means 72 that constitute a vacuum exhaust means capable of evacuating the reaction vessel 5 to a desired degree of vacuum. Around the reaction vessel 5, a heating furnace 75 provided with a heater 74 that is a heating means for heating the inside of the reaction vessel 5 is provided. As the heater 74, it is preferable to use a carbon wire or the like that is free from contamination and has excellent temperature rise and fall characteristics.

  Further, this film forming apparatus includes a control unit 100 including a computer. This control unit 100 has a function of starting a processing program, reading out description items of a process recipe in a memory (not shown), and controlling processing conditions based on the recipe, and includes a heater 74, a pressure adjusting unit 72, and a gas. A control signal for controlling each of the supply units 6 is output.

  Next, an example of a film formation method performed using the above-described film formation apparatus will be described. First, a predetermined number of semiconductor wafers W to be processed, such as wafers W on which gate electrodes 3A and 3B, source electrodes 24a and 25a, and drain electrodes 24b and 25b are formed on a P-type Si substrate 20 as shown in FIG. For example, the boat elevator (not shown) is raised (loaded) into the reaction vessel 5 held by the wafer boat 55 and maintained at a temperature of about 100 ° C., for example.

  Subsequently, after the wafer boat 55 is loaded and the lower end opening 51 of the reaction vessel 5 is closed by the lid 53, the temperature in the reaction vessel 5 is decomposed at a rate of temperature increase of, for example, 200 ° C./minute. The temperature is raised to a temperature lower than the temperature, for example, about 500 ° C., and the inside of the reaction vessel 5 is evacuated to a degree of vacuum of about 266 Pa (2 Torr) by the vacuum pump 71 through the exhaust port 7.

  Here, the temperature lower than the decomposition temperature of the TEOS gas means a temperature at which the TEOS gas is not decomposed in the reduced pressure atmosphere and active species are generated by the oxygen gas and the hydrogen gas. For example, the temperature of the TEOS gas at 266 Pa is The decomposition temperature is about 550 ° C., for example, and oxygen gas and hydrogen gas generate active species such as hydroxyl active species and oxygen active species under a reduced pressure of, for example, 1.33 kPa (10 Torr) or less. It means a temperature of not lower than ℃ and lower than 550 ° C.

  Regarding the flow rates of TEOS gas, oxygen gas and hydrogen gas, the flow rate ratio of TEOS gas, oxygen gas and hydrogen gas is preferably about 0.1 to 0.2: 2: 1. .33 kPa (10 Torr) or less is preferable.

  Then, after stabilizing the temperature in the reaction vessel 5 at, for example, 500 ° C., for example, a TEOS gas from the film forming gas supply source 63 has a predetermined flow rate, for example, 150 sccm, and an oxygen gas from the oxygen gas supply source 64 has a predetermined flow rate, for example, 2000 sccm, hydrogen Hydrogen gas is supplied from the gas supply source 65 into the reaction vessel 5 at a predetermined flow rate, for example, 1000 sccm, and the inside of the reaction vessel 5 is adjusted to a reduced pressure atmosphere of, for example, 266 Pa (2 Torr) by the pressure adjusting means 72 to perform the film forming process 10. Do about minutes. In this way, in the reaction vessel 5, as will be described later, a SiO2 film is formed so as to embed between the gate electrodes 3A and 3B on the wafer W.

  During the series of steps, the wafer boat 55 is rotated by the motor M. Thus, after forming a SiO2 film with a predetermined thickness of, for example, 50 nm on the gate electrodes 3A and 3B, the supply of the film forming gas into the reaction vessel 5 is stopped. Further, the supply of N2 gas from a nitrogen gas source (not shown) is started and purged to return the pressure in the reaction vessel 5 to atmospheric pressure, and the temperature in the reaction vessel 5 is lowered to a set temperature of, for example, 200 ° C. Then, the wafer boat 55 is unloaded from the reaction vessel 5. Here, a series of steps for forming the SiO2 film performed in this film forming apparatus controls the heater 74, the pressure adjusting means 72, the gas supply unit 6 and the like based on the process recipe stored in the control unit 100. It is done.

  The unloaded wafer W is then formed with via holes 37 and contact holes 38, and the bottom surfaces of these holes 37 and 38 are washed with hydrofluoric acid. TiN is embedded to manufacture a MOSFET transistor that is a semiconductor device.

  In this method, the TEOS gas that is a film forming gas is adsorbed on the solid surface to be formed without being decomposed, and active species that decompose TEOS on the solid surface are generated, and the solid surface is generated by the active species. It was made as a result of finding a condition capable of decomposing TEOS adsorbed on the surface.

  That is, since the SiO2 film is formed by heating at a temperature lower than the decomposition temperature of the TEOS gas under a reduced pressure atmosphere using TEOS gas, oxygen gas, and hydrogen gas, the gate of the wafer W will be described later. The TEOS gas is adsorbed on the electrodes 3A and 3B without being decomposed, and then the gate is activated by the hydroxyl active species (OH *) and oxygen active species (O *) which are active species generated by oxygen gas and hydrogen gas. The TEOS adsorbed on the electrodes 3A and 3B is decomposed to form an interlayer insulating film 4 made of a SiO2 film.

  For this reason, the SiO2 film can be formed at a low temperature of 500 ° C. or lower, which is a temperature lower than the decomposition temperature of the TEOS gas, and the coverage is good. The SiO2 film can be embedded without forming the film. Further, since the film forming process is performed at a temperature of 500 ° C. or less as described above, for example, the metal gate electrodes 3A and 3B formed by laminating the polysilicon layer 31, the WN layer 32, and the W layer 33 are formed. Even in the case of the included transistor, the interlayer insulating film 4 is embedded between the gate electrodes 3A and 3B while suppressing the adverse effect of, for example, increasing the resistance caused by exposing the gate electrode to a high temperature of 600 ° C. or higher. Can do.

  Further, in the film forming process of the present invention, it is presumed that the SiO2 film is formed by radical oxidation in which TEOS is decomposed on the solid surface by hydroxyl active species and oxygen active species. Therefore, the CVD process is performed using TEOS gas. The film quality is stronger than that of the SiO2 film formed in (1). For this reason, even when the bottom surfaces of the via hole 37 and the contact hole 38 are washed with hydrofluoric acid in a later process, the resistance to hydrofluoric acid is large, so that permeation of hydrofluoric acid into the recess 35 can be prevented, and seam is generated. Can be suppressed.

  Next, the background of the present invention will be described. First, the present inventors examined a mechanism by which voids are formed when a SiO2 film is embedded in a recess between gate electrodes having an aspect ratio of 4 or more by a conventional CVD process using TEOS gas and O2 gas. As a result, as described in the background art section, the TEOS gas is decomposed in the gas phase, and this decomposed product adheres to the gate electrode and the recess, so that the decomposed product is deposited on the upper surface of the gate electrode. Although it adheres easily, it is hard to adhere to a side wall, Therefore It was guessed that a void might be easy to be formed in the center part of a recessed part.

  Therefore, the present inventor attaches the TEOS gas to the gate electrodes 3A and 3B on the wafer W without decomposing them, and if the TEOS is decomposed after being attached to the gate electrodes 3A and 3B, the gate electrodes 3A, 3B, Since TEOS adheres to the top surface and side walls of 3B and the bottom surface of the recess 35 with a uniform thickness, a SiO2 film can be formed with a uniform thickness on the top surface and side walls of the gate electrodes 3A and 3B and the bottom surface of the recess 35. We thought that the formation of voids could be suppressed, and decided to examine the feasibility of this method.

  Therefore, first, in order to adsorb the TEOS gas to the gate electrodes 3A, 3B and the like without decomposing, the temperature of the film forming process is set to a temperature at which the TEOS gas is not decomposed in the reduced pressure atmosphere of the reaction vessel 5, A gas that generates radical species that decompose TEOS attached to the surfaces of the gate electrodes 3A and 3B at the surface of the gate electrodes 3A and 3B at this temperature was selected by performing various experiments. As a result, by adding TEOS gas as a film forming gas and adding oxygen gas and hydrogen gas, as will be apparent from an experimental example described later, the gate electrodes 3A and 3B are formed on the top surface and side walls and the bottom surface of the recess 35. It has been found that a SiO2 film can be formed with a uniform thickness.

  Regarding the mechanism by which the SiO2 film is formed by TEOS, oxygen gas, and hydrogen gas in this way, TEOS gas does not decompose at 500 ° C. under a reduced pressure of 266 Pa. Therefore, at this temperature, as shown in FIG. It is supplied as it is without being decomposed into a solid surface such as 3A or 3B. For this reason, the TEOS gas decomposes in the gas phase, and the decomposition product is larger and heavier than when the decomposition product is supplied to the solid surface. Therefore, the undecomposed TEOS gas is not supplied so as to accumulate. Thus, the TEOS 41 is adsorbed with a uniform thickness on the top and side walls of the gate electrodes 3A and 3B and the bottom surface of the recess 35.

  On the other hand, oxygen gas and hydrogen gas, for example, as shown in FIG. 3B, in a reduced pressure atmosphere of 500 ° C. and 266 Pa, oxygen and hydrogen burn on the solid surfaces of the gate electrodes 3A, 3B, etc. Of active species. Of these active species, it is considered that TEOS adsorbed on the solid surface is decomposed and converted into SiO 2 by hydroxyl active species (OH *) and oxygen active species (O *). When the SiO2 film 42 is formed with a uniform thickness on the top and side walls of the gate electrodes 3A and 3B and the bottom surface of the recess 35 as described above, the top surfaces of the gate electrodes 3A and 3B are formed as shown in FIG. And the SiO2 film 42 is formed with the same thickness on the side surfaces. Therefore, no SiO2 film is formed in the recess 35 between the two gate electrodes 3A and 3B so as to protrude from the upper surface of the gate electrodes 3A and 3B, and gradually inward from both side surfaces of the recess 35. Since the SiO2 film is formed, it is presumed that the SiO2 film 42 can be embedded in the recess 35 without forming a void as shown in FIG.

  Further, as described above, the SiO2 film of the present invention is formed by radical oxidation by reaction of radical species generated on a solid such as the wafer W and TEOS, so that the film quality of the formed SiO2 film is strong. The resistance to chemicals containing fluorine is considered high.

  On the other hand, in the process of forming a SiO2 film by CVD using TEOS gas and O2 gas, or in the process of forming SiO2 by CVD using TEOS gas and O radical, the TEOS gas is vaporized as described above. Voids are formed because the film is deposited so that it decomposes and accumulates in the phase. Also, in the process of forming SiO2 by plasma CVD using TEOS gas, O3-containing O2 gas, and H2O2 gas, TEOS, O3, O2, and H2O2 are decomposed by plasma, and as a result, TEOS gas as described above. It is inferred that the film is decomposed and deposited in the gas phase. Further, since H2O2 gas is decomposed using plasma, it is considered that O radicals and H radicals are generated without generating OH radicals.

  In the above example, the interlayer insulating film is taken as an example, but an insulating film other than the interlayer insulating film may be used.

  Next, experimental examples performed to confirm the effects of the present invention will be described.

<Experimental example 1>
Example 1
Using the above-mentioned apparatus, TEOS gas, hydrogen gas, and oxygen gas are supplied to the reaction vessel 5 at the flow rates of 150 sccm, 1000 sccm, and 2000 sccm, respectively, the film forming temperature is 500 ° C., and the pressure is 266 Pa (2.0 Torr). ), An SiO 2 film having a thickness of 30 nm is formed so as to fill a recess having an aspect ratio of 2.5, and then wetted with an etching solution containing 50 wt% HF and H 2 O for 1 minute. Etching was performed, and the etching rate at that time was measured. Here, the composition of the etching solution was 50 wt% HF / H2O = 1/399.

(Comparative Example 1)
Using an apparatus similar to that in Example 1, a SiO2 film having a thickness of 50 nm is formed by a conventional CVD process so as to fill the concave portion having the aspect ratio of 2.5. Wet etching was performed under the same conditions as above, and the etching rate at that time was measured. The film formation conditions here were a TEOS gas flow rate of 190 sccm, a film formation temperature of 680 ° C., and a pressure of 53 Pa.

  The result is shown in FIG. As a result, the etching rate by the etching solution containing HF is higher in the SiO2 film (Example 1) formed by the process of the present invention than in the SiO2 film (Comparative Example 1) formed by the conventional CVD method. It was confirmed that the etching rate of the SiO2 film of Example 1 was almost half that of the SiO2 film of Comparative Example 1. Here, the low etching rate indicates that the film quality is strong and the resistance to the etching solution containing fluorine is high.

  As a result, the process of the present invention is performed at a film formation temperature of 500 ° C., which is lower than the film formation temperature of the conventional CVD process (Comparative Example 1), but more than the SiO 2 film obtained by the conventional CVD process. It is recognized that the film quality is strong and the resistance to hydrofluoric acid is high. Further, it is understood that since the resistance to hydrofluoric acid is high, the generation of seams formed by the permeation of hydrofluoric acid into the SiO2 film can be suppressed.

<Experimental example 2>
(Example 2)
Using the above-described apparatus, TEOS gas, hydrogen gas, and oxygen gas are supplied to the reaction vessel at the flow rates of 150 sccm, 1000 sccm, and 2000 sccm, respectively, the film forming temperature is 500 ° C., and the pressure is 266 Pa (2.0 Torr). After forming a SiO2 film so as to fill a recess having an aspect ratio of 2.4, a polysilicon film having a thickness of 100 nm is formed on the SiO2 film, and a fault between the SiO2 film and the polysilicon film is formed. The photograph was taken with an SEM (electron microscope). The reason why the polysilicon film is formed on the SiO2 film is to take a tomographic photograph of the SiO2 film.

  A trace of the tomographic image of this SiO2 film is shown in FIG. In FIG. 5, 81 is a silicon substrate, 82 and 83 are gate electrodes formed on the silicon substrate, 84 is a recess formed between the gate electrodes, and the aspect ratio of the recess 84 is 2.4. In the figure, reference numeral 85 denotes a SiO2 film, and 86 denotes a polysilicon film.

  Then, when the thickness of the formed SiO2 film 85 was measured for the upper part a of the gate electrode 82, the side wall part b, and the bottom part c of the recess 84, the thickness of the SiO2 film was the upper part a: 34 nm, and the side wall part. b: 35 nm, bottom c: 34 nm, that is, b / a = 1.029, c / a = 1.0. By the method of the present invention, the SiO2 film is formed on the top and side walls of the gate electrode 82 and the bottom of the recess 84. It can be seen that can be formed with a substantially uniform thickness.

(Comparative Example 3)
Using an apparatus similar to that in Example 1, a SiO2 film is formed using TEOS gas and O3 gas so as to fill the recess 84 having the aspect ratio of 2.4 shown in FIG. In addition, a tomographic photograph of this SiO2 film was taken. The film formation conditions in this example were a TEOS gas flow rate of 190 sccm, an O3 gas flow rate of 200 sccm, a film formation temperature of 500 ° C., and a pressure of 266 Pa.

  Based on the tomographic image, when the thickness of the formed SiO2 film was measured for the upper part a of the gate electrode 82, the side wall part b, and the bottom part c of the recess 84, b / a = 1.05, c / a = 0.95.

(Comparative Example 4)
Using an apparatus similar to that in Example 1, a SiO2 film is formed using TEOS gas and O3 gas so as to fill the recess 84 having the aspect ratio of 2.4 shown in FIG. In addition, a tomographic photograph of this SiO2 film was taken. The film formation conditions in this example were set to a TEOS gas flow rate of 190 sccm, an O3 gas flow rate of 200 sccm, a film formation temperature of 550 ° C., and a pressure of 133 Pa.

  Based on the tomographic image, the thickness of the formed SiO2 film was measured for the upper part a of the gate electrode 82, the side wall part b, and the bottom part c of the concave part 84. As a result, b / a = 1.0, c / a = 0.93.

(Comparative Example 5)
Using the same apparatus as in the first embodiment, a SiO2 film is formed using TEOS gas and O2 gas so as to fill the recess 84 having the aspect ratio of 2.4 shown in FIG. In addition, a tomographic photograph of this SiO2 film was taken. The film forming conditions in this example were TEOS gas flow rate 130 sccm, O 2 gas flow rate 100 sccm, film forming temperature 600 ° C., and pressure 266 Pa.

  Based on the tomographic image, when the thickness of the formed SiO2 film was measured for the upper part a of the gate electrode, the side wall part b, and the bottom part c of the recess 84, b / a = 1.0 and c / a = 0. 97.

  Here, in Experimental Example 2, the embedding characteristic of the SiO2 film in the recess 84 having a high aspect ratio is indirectly evaluated. As a result of this experiment, the SiO2 film (Example 2) formed by the process of the present invention has a lower film formation temperature than Comparative Examples 3 and 4, but the SiO2 film is formed on the upper portion of the gate electrode 82, the side wall portion, It will be understood that the recess 84 can be formed uniformly at the bottom.

  Thus, the thickness of the SiO2 film on the top surfaces of the gate electrodes 82 and 83, the thickness of the SiO2 film on the side surfaces of the gate electrodes 82 and 83, and the thickness of the SiO2 film on the bottom surface of the recess 84 are substantially the same. Since the film is gradually formed in the same manner on the upper surface and the side surface of the gate electrode 82 as described above, the SiO2 film is not formed so as to protrude from the upper surface of the gate electrode 82, so that voids are not easily formed. It suggests.

  In addition, as for the formation mechanism of the SiO2 film formed by the process of the present invention, the film is formed by the decomposition of the TEOS gas in the gas phase and the decomposition product falling on the gate electrode. It is different from the type.

  Furthermore, this experiment shows that in Comparative Example 5, the SiO2 film can be uniformly formed on the top of the gate electrode, the side wall, and the bottom of the recess, almost the same as in Example 2. It is understood that when the height is increased, the SiO2 film tends to be easily formed uniformly on the top of the gate electrode, the side wall, and the bottom of the recess.

  From the above experiment, by using TEOS gas, oxygen gas, and hydrogen gas and heating at a temperature lower than the decomposition temperature of TEOS gas in a reduced pressure atmosphere as in the film forming method of the present invention, for example, 500 ° C. It can be seen that even at the following low temperatures, it is possible to form a SiO2 film that has good coverage with respect to a high aspect ratio recess and good resistance to fluorine-containing gas.

It is sectional drawing which shows the structure of the MOSFET transistor in which the silicon oxide film of this invention is used. 1 is a longitudinal sectional view showing a film forming apparatus for performing a film forming method of the present invention. It is process drawing for demonstrating the effect | action of the film-forming method of this invention. It is a characteristic view which shows the etching rate which is an experimental result conducted in order to confirm the effect of the film-forming method of this invention. It is a trace figure of the tomographic photograph of the SiO2 film formed by the film-forming method of the present invention. It is sectional drawing for demonstrating metal gate electrodes. It is sectional drawing for demonstrating the void and seam formed in the SiO2 film | membrane formed into a film by the CVD process using the conventional TEOS gas. It is process drawing for demonstrating the effect | action of the CVD process using the conventional TEOS gas.

Explanation of symbols

W Semiconductor wafer 20 P type Si substrate 21a P ⁺ type source region 21b P ⁺ type drain region 22a N ⁺ type source region 21b N ⁺ type drain region 24a P ⁺ type source electrode 24b P ⁺ type drain electrode 25a N ⁺ type source electrode 25b N ⁺ type drain electrodes 3A and 3B Gate electrode 31 Polysilicon layer 32 WN layer 33 W layer 37 Via hole 38 Contact hole 5 Reaction vessel 55 Wafer boat 6 Gas supply part 62 Gas supply pipe 63 Film formation gas supply source 64 Oxygen gas supply Source 65 Hydrogen gas supply source 71 Vacuum pump 74 Heater 75 Heating furnace

Claims (4)

In a method of forming a silicon oxide film on a target object by using a vapor of an organic silicon source in a reduced pressure atmosphere and a heated atmosphere inside a processing container in which the target object is placed,
The inside of the processing vessel is heated to a temperature lower than the decomposition temperature of the vapor of the organic silicon source and to generate hydroxyl active species and oxygen active species by oxygen gas and hydrogen gas ,
The organic silicon source supplied into the processing vessel is decomposed by hydroxyl active species and oxygen active species generated by the oxygen gas and hydrogen gas supplied into the processing vessel, and silicon dioxide is oxidized on the object to be processed. A film forming method comprising forming a film. 2. The film forming method according to claim 1 , wherein the organic silicon source is selected from tetraethyl orthosilicate and binary aminosilane. The object to be processed is formed with a plurality of gate electrodes, and the silicon oxide film according to claim 1 is an interlayer insulating film formed on the gate electrodes so as to be embedded between the gate electrodes. the film forming method according to claim 1 or 2, characterized in. A processing container in which an object to be processed is placed;
Pressure adjusting means for setting the inside of the processing vessel to a reduced pressure atmosphere;
Heating means for heating the inside of the processing vessel;
A film forming gas supply path for supplying vapor of the organic silicon source into the processing container;
An oxidizing gas supply path for supplying oxygen gas into the processing vessel;
A reducing gas supply path for supplying hydrogen gas into the processing vessel;
Flow rate adjusting means provided in the film forming gas supply path, the oxidizing gas supply path, and the reducing gas supply path, respectively, for adjusting the flow rates of the vapor , oxygen gas, and hydrogen gas of the organic silicon source. When,
A control unit for controlling the pressure adjusting means, the heating means, and the flow rate adjusting means,
The control unit sets the inside of the processing container to a reduced pressure atmosphere and heats it at a temperature lower than the decomposition temperature of the vapor of the organic silicon source to thereby generate hydroxyl active species and oxygen activity generated by oxygen gas and hydrogen gas. A film forming apparatus, wherein the pressure adjusting means, the heating means, and the flow rate adjusting means are controlled so as to form a silicon oxide film on the object to be processed using a seed.

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