JP2004273764A - Method for forming tungsten film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a tungsten film capable of improving a throughput and having a good embedding property, for instance, regardless of small diameter for embedding. <P>SOLUTION: The method for forming the tungsten film on an object W to be processed in a processing chamber 22 comprises a step 79 for forming an initial tungsten film by alternately repeating a reducing gas supplying step for supplying a reducing gas and a tungsten gas supplying step for supplying the tungsten-contained gas; a step 84 for forming a passivation tungsten film by flowing the reducing gas into the processing vessel, increasing the flow of the tungsten-containing gas, and gradually increasing the pressure in the processing vessel; and a step 80 for forming the main tungsten film by continuously flowing the reducing gas and the tungsten containing gas. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a tungsten film on a surface of an object to be processed such as a semiconductor wafer, and more particularly, to an improved invention of a previous application (Japanese Patent Application No. 2002-234273) of the present applicant, in which a method for forming a passivation tungsten film The present invention relates to a method for forming a tungsten film with improved processes.
[0002]
[Prior art]
In general, in the manufacturing process of a semiconductor integrated circuit, W (tungsten) and WSi (tungsten) are used to form a wiring pattern on the surface of a semiconductor wafer as an object to be processed or to bury a recess between wirings or a contact recess. (Silicide), Ti (titanium), TiN (titanium nitride), TiSi (titanium silicide), Cu (copper), Ta ₂ O ₅ 2. Description of the Related Art A thin film is formed by depositing a metal or a metal compound such as (tantalum oxide). Of the various thin films described above, a tungsten film is frequently used because it has a low specific resistance and a low film forming temperature. To form this kind of tungsten film, WF is used as a source gas. ₆ A tungsten film is deposited by using (tungsten hexafluoride) and reducing it with hydrogen, silane, dichlorosilane, or the like.
[0003]
When the above-mentioned tungsten film is formed, a Ti film, a TiN film, or a laminated film of the both is used as a base film on the wafer surface for reasons such as improvement in adhesion and suppression of a reaction with a lower silicon layer. And the tungsten film is deposited on the barrier layer.
Here, in the case of embedding a concave portion or the like, hydrogen gas having a lower reducing property than silane is mainly used in order to improve the embedding property. ₆ The gas may attack the barrier layer and react with the barrier layer and fluorine to expand in volume, thereby generating a volcano projecting upward in a protruding manner or a void in the buried hole.
[0004]
This will be described with reference to FIG. FIG. 17 is a cross-sectional view showing a buried hole in which a volcano and voids are generated. A buried hole 2 such as a contact hole is provided on the surface of the semiconductor wafer W, and a barrier layer 4 made of, for example, a Ti / TiN film is formed in advance on the surface including the inner surface of the buried hole 2. And WF in this state ₆ Gas and H ₂ When the tungsten film 6 is deposited and buried by supplying the gas simultaneously, the WF ₆ The fluorine contained therein diffuses into the barrier layer, and in particular, the Ti in the surface barrier layer 4 reacts with the fluorine, so that the tungsten film 6 is deposited in a protruding manner from the vicinity of the buried hole 2 as a base and the tip of the protruding portion is formed. Volcano 8 is generated by the stress of the tungsten film 6 in the portion, and a void 10 is generated in the buried hole 2.
[0005]
Then, in order to prevent the generation of the volcano 8 and the like, first, instead of hydrogen gas, a silane having a stronger reducing power is used, and a nucleation layer of a tungsten film is formed with a small thickness, for example, about 300 to 500 °. Is formed, and then, starting from this nucleation layer, H ₂ Gas and WF ₆ A main tungsten film is deposited by gas, but in this case, the surface of the barrier layer 4 as a base film is nucleated by, for example, a surface on which an organic metal film is formed or an oxidized surface. In some cases, the layers could not be uniform.
Therefore, prior to the formation of the nucleation layer, only a silane alone is supplied for a predetermined time and a silane reaction intermediate (SiHx: x <4 ) Is adsorbed on the wafer surface, and the nucleation layer is grown from this as a starting point. FIG. 18 is a view showing a process when filling a buried hole with tungsten using such a method.
[0006]
First, as shown in FIG. 18 (A), a silane (SiH ₄ ) Is supplied alone, and the above SiH _x (FIG. 18 (A) and FIG. 18 (B)). Then, as described above, WF is performed for a predetermined time. ₆ Gas and SiH ₄ A gas is simultaneously supplied as shown in FIG. 18C, and a tungsten film is deposited starting from the reaction intermediate 12 to form a nucleation layer 14 (FIG. 18D).
Next, as shown in FIG. ₆ Gas and H ₂ By supplying the gas at the same time, the main tungsten film 16 is deposited as shown in FIG.
[0007]
[Problems to be solved by the invention]
Incidentally, the barrier layer 4 formed on the wafer surface may be formed using, for example, an organic compound source of Ti. In this case, the carbon component contained in the source gas is taken into the barrier layer 4, which causes the exposed surface of the barrier layer containing the carbon component to cause a reaction intermediate of SiHx even when the above-mentioned initiation process is performed. The adhesion of the body becomes uneven and the nucleation layer 14 is formed unevenly, and the step coverage of the nucleation layer 14 itself is deteriorated. As a result, the embedding property of the main tungsten film is poor, and voids and volcanoes are formed. Was a problem.
Further, if the ratio of the thickness of the nucleation layer 14 to the total thickness of the tungsten film including the main tungsten layer 16 is not so large, no problem occurs. When the ratio of the thickness of the nucleation layer 14 to the thickness of the nucleation layer 14 becomes so large that it cannot be ignored, voids of a size that cannot be ignored due to poor step coverage of the nucleation layer 14 occur. There was also a problem that it would.
[0008]
The problems described above have become particularly serious when the size of the buried hole is reduced to, for example, 0.2 μm or less due to the further miniaturization and thinning of the semiconductor production.
The present invention has been devised in view of the above problems and effectively solving the problems. An object of the present invention is to improve the throughput and improve the embedding property, for example, even if the diameter of the embedding hole is small, it is possible to suppress the occurrence of voids and the occurrence of volcano having a size that adversely affects the characteristics. An object of the present invention is to provide a method for forming a tungsten film having good characteristics.
[0009]
[Means for Solving the Problems]
In forming a tungsten film on a surface of an object to be processed in a processing chamber capable of being evacuated, a reducing gas supply step of supplying a reducing gas and a tungsten gas supplying a tungsten-containing gas are provided. An initial tungsten film forming step of forming an initial tungsten film by alternately and repeatedly performing a gas supply step and a purge step of evacuating while supplying an inert gas between the two steps. And a passivation tungsten film for forming a passivation tungsten film while gradually increasing the pressure in the processing container by simultaneously changing and increasing the flow rate of the tungsten-containing gas while flowing the reducing gas into the processing container. Forming step, the reducing gas and the tungsten-containing gas in the processing container. A tungsten film forming method characterized by having a main tungsten film forming step of forming a main tungsten film continues flowing.
As a result, the initial tungsten film as a nucleation layer with high film thickness uniformity was formed, the passivation tungsten film was formed more efficiently, and then the main tungsten film was deposited, so that the filling characteristics were particularly improved. For example, even if the diameter of the buried hole is small, it is possible to suppress the occurrence of voids and the occurrence of volcano that are large enough to adversely affect the characteristics. In addition, since the above-mentioned series of three steps are continuously performed in the same processing container, for example, an incubation period caused by changing the processing container is eliminated, and the throughput can be improved accordingly.
[0010]
In this case, for example, in the passivation tungsten film forming step, the temperature of the object to be processed is gradually increased.
Further, for example, the temperature of the object to be processed is substantially the same between the initial tungsten film forming step, the passivation tungsten film forming step, and the main tungsten film forming step. Have maintained.
In this way, by maintaining the process temperature between the respective steps substantially constant, it is not necessary to raise or lower the process temperature on the way, so that it is possible to further improve the throughput.
[0011]
Further, for example, the pressure in the processing container is 2666 Pa (20 Torr) or less in the initial tungsten film forming step and the passivation tungsten film forming step, and 2666 Pa (20 Torr) in the main tungsten film forming step. (20 Torr) or more.
[0012]
Further, for example, as defined in claim 5, the tungsten-containing gas is WF ₆ One of a gas and an organic tungsten source gas.
Further, for example, as defined in claim 6, the reducing gas is H ₂ Gas, silane (SiH ₄ ), Disilane (Si ₂ H ₆ ), Dichlorosilane (SiH ₂ Cl ₂ ), Diborane (B ₂ H ₆ ), Phosphine (PH ₃ ).
Further, for example, as defined in claim 7, the tungsten-containing gas is WF ₆ And the reducing gas is SiH in the initial tungsten film forming step. ₄ H gas in the passivation tungsten film forming step and the main tungsten film forming step. ₂ Gas.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for forming a tungsten film according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing a heat treatment apparatus for performing a method of forming a tungsten film according to the present invention, FIG. 2 is a view showing a supply mode of each gas, and FIG. FIG. 4 is an enlarged sectional view showing an example of a tungsten film deposited on the surface of a semiconductor wafer.
First, a heat treatment apparatus for carrying out the method of the present invention will be described. This heat treatment apparatus 20 has, for example, a processing container 22 made of aluminum having a substantially cylindrical cross section. A shower head 24 for selectively introducing, for example, various film-forming gases and carrier gases as flow-controlled processing gases into a ceiling portion of the processing container 22 through a sealing member 26 such as an O-ring. The film forming gas is injected toward the processing space S from a number of gas injection ports 28 provided on the lower surface. One or a plurality of diffusion plates 27 having a plurality of diffusion holes 25 are provided in the shower head 24 so as to promote the diffusion of the gas introduced therein. May be used.
[0014]
In the processing container 22, as an object to be processed, for example, three L-shaped holding members 32 (only two are shown in FIG. 1) are placed on a cylindrical reflector 30 standing upright from the bottom of the processing container. A mounting table 34 for mounting the semiconductor wafer W is provided.
Below the mounting table 34, a plurality of, for example, three L-shaped lifter pins 36 (only two are shown in the illustrated example) are provided so as to stand upward. The base of the lifter pins 36 is A vertically long insertion hole (not shown) formed in the reflector 30 is inserted and connected to the ring member 38 in common. Then, the ring member 38 is moved up and down by a push-up bar 40 provided through the bottom of the processing container, whereby the lifter pins 36 are inserted through the lifter pin holes 42 provided through the mounting table 34 so that the wafer W is moved. It can be lifted.
[0015]
A bellows 44 that can be extended and contracted to maintain the inside of the processing container 22 airtight is interposed at a penetrating portion of the container bottom of the push-up bar 40, and the lower end of the push-up bar 40 is connected to an actuator 46. .
An exhaust port 48 is provided at a peripheral edge of the bottom of the processing container 22, and an exhaust passage 50 connected to a vacuum pump (not shown) is connected to the exhaust port 48. It can be evacuated to a degree of vacuum. A gate valve 52 that is opened and closed when a wafer is loaded and unloaded is provided on a side wall of the processing container 22.
Although not shown, a vacuum gauge (Capamanometer) for measuring the pressure is provided in the processing container 22, and a pressure control valve (Auto Pressure Control Valve) for adjusting the pressure in the processing container 22 is provided in the exhaust passage 50. Have been.
[0016]
A transmission window 54 made of a heat ray transmitting material such as quartz is provided airtightly at the bottom of the processing container directly below the mounting table 34 via a sealing member 56 such as an O-ring. A box-shaped heating chamber 58 is provided so as to surround the heating chamber 58. In the heating chamber 58, for example, a plurality of heating lamps 60 are attached as heating means to a turntable 62 also serving as a reflecting mirror, and the turntable 62 is provided at the bottom of the heating chamber 58 via a rotation shaft. It is rotated by a motor 64. Therefore, the heat ray emitted from the heating lamp 60 passes through the transmission window 54 and irradiates the lower surface of the thin mounting table 34 to heat it, and further indirectly heats the wafer W on the mounting table 34. I am getting it. By using the heating lamp 60 in this manner, the rate of temperature rise of the wafer W can be extremely increased.
[0017]
Next, the method of the present invention performed using the apparatus configured as described above will be described.
First, the gate valve 52 provided on the side wall of the processing container 22 is opened, the wafer W is loaded into the processing container 22 by a transfer arm (not shown), and the lifter pins 36 are pushed up to transfer the wafer W to the lifter pins 36. Then, the lifter pins 36 are lowered by lowering the push-up bar 40, and the wafer W is mounted on the mounting table 34. On the surface of the wafer W, a barrier layer 4 such as a Ti / TiN film is already formed as a base film in the previous step including the inner surface of the buried hole 2 (see FIG. 18A).
[0018]
Next, a predetermined film forming gas, a carrier gas, or the like is supplied as a processing gas from the processing gas source (not shown) to the shower head unit 24 in a gas supply mode as described later in a predetermined amount, and the gas is supplied to the gas injection hole on the lower surface. 28 to supply it into the processing container 22 substantially evenly. At the same time, the inside of the processing container 22 is evacuated to a predetermined pressure by sucking and exhausting the internal atmosphere from the exhaust port 48, and while rotating the heating lamps 60 of the heating means located below the mounting table 34. Drives and emits thermal energy.
The radiated heat rays pass through the transmission window 54 and then irradiate the back surface of the mounting table 34 to heat it. Since the mounting table 34 is very thin, for example, about 1 mm as described above, the mounting table 34 is quickly heated. Therefore, the wafer W mounted thereon can be quickly heated to a predetermined temperature. The supplied film-forming gas causes a predetermined chemical reaction, and a thin film of a tungsten film is deposited and formed on the entire surface of the wafer.
[0019]
In the method of the present invention, the entire film forming process is formed by an initial tungsten film forming step 79, a passivation tungsten film forming step 84, and a main tungsten film forming step 80, as shown in FIG. Here, the supply mode of each gas throughout the film forming process will be specifically described with reference to FIG.
FIG. 2 shows three types of gas supply modes. In each mode, for example, Ar, N ₂ The gas is continuously supplied at a constant flow rate or at a variable flow rate as needed. Similarly, the inside of the processing container 22 is continuously evacuated during a series of steps.
Here, WF is used as the tungsten-containing gas. ₆ Gas and H as the reducing gas ₂ Gas or this H ₂ SiH with stronger reducing power than gas ₄ Gas is used. In addition, the steps of the initial tungsten film forming step, the passivation tungsten film forming step, and the main tungsten film forming step described below are continuously performed in the same processing container 22.
[0020]
First, the gas supply mode in the initial tungsten film forming step shown in FIG. 2A is, as shown in FIG. ₄ Gas supply step 70 for supplying gas and WF as a tungsten-containing gas ₆ The tungsten gas supply step 72 for supplying a gas is alternately repeated a plurality of times with a purge step 74 for evacuating while supplying a carrier gas as an inert gas interposed between these two steps. An initial tungsten film 76 (see FIG. 4) is formed. That is, SiH ₄ Gas supply and WF ₆ The initial tungsten film forming step is performed by alternately repeating the gas supply and interposing a purge step 74 between the repeated steps. The end of the initial tungsten film forming step is completed in the reducing gas supply step 70. Then, the inside of the processing vessel 22 is coated with SiH on the substrate (wafer) surface. ₄ By depositing SiHx with the gas, the film is easily formed effectively in the next passivation film forming step 84 and the main tungsten film forming step 80. This point is the same in FIGS. 2B to 2C.
[0021]
After the initial tungsten film 76 is formed in this manner, next, SiH is used as a reducing gas. ₄ H instead of gas ₂ Using a gas, a passivation tungsten film forming step 84 of forming a passivation tungsten film 82 (see FIG. 4), which is a feature of the present invention, is continuously performed. Note that, also in this case, an inert gas such as Ar, N ₂ Gas etc. are continuously flowing. In the passivation tungsten film forming step 84, the same gas type as that of the main tungsten film forming step 80, that is, WF ₆ Gas and H ₂ Gas and WF ₆ H before flowing gas ₂ The gas is flowed to maintain the flow rate constant, and then the flow rate of the tungsten-containing gas is changed so as to gradually increase, and at the same time, the pressure in the processing chamber 22 (process pressure) and the substrate temperature are increased. It is gradually rising (see FIG. 3). The period T5 of the passivation tungsten film forming step 84 is, for example, 3 to 90 seconds, and preferably 10 to 60 seconds. In this case, the pressure and the substrate temperature in the processing container 22 may be kept constant.
[0022]
Specifically, as shown in FIG. 3, after performing the short-time purging step 74 of the initial tungsten film forming step 79, the WF ₆ The gas is allowed to flow through the exhaust line without being introduced into the processing container 22, and for example, the mass flow meter is stabilized for about 1 to 30 seconds, preferably about 3 to 5 seconds, and WF ₆ Stabilize the gas flow. This WF ₆ WF after Δt seconds when the gas flow rate becomes stable ₆ The gas flows into the processing vessel 22 and the WF ₆ Gradually increase the gas flow.
Also H ₂ Gas supply is WF ₆ The gas is supplied into the processing container 22 at Δt seconds before the gas flow rate becomes stable. In this passivation tungsten film forming step, a passivation tungsten film is formed on the initial tungsten film.
WF as described above ₆ The reason for gradually increasing the flow rate of the gas from a small amount is to form a passivation film that is as thin as possible so that the WF in the main tungsten film forming step ₆ This is because the purpose is to suppress damage from gas and to reinforce the initial tungsten film of the protective film. Thus, the total film formation time can be shortened by shortening the film formation time in the initial tungsten film formation step 79, and the throughput can be improved.
[0023]
That is, the passivation tungsten film is formed by H ₂ A gas supply amount is supplied at a predetermined flow rate, and the WF is supplied as described above. ₆ The gas is gradually increased to the supply amount in the main tungsten film forming step 80 over a predetermined time, so that the WF ₆ To minimize (fluorine) damage, use WF ₆ It is necessary to reduce the gas supply. However, to get embedding, WF ₆ The gas needs to be more. To make this compatible, H ₂ Supply gas and after a while WF ₆ The supply of gas is started and the supply amount is gradually increased.
In FIG. 3, the process pressure in the passivation tungsten film forming step 79 is linearly increased in a pressure range of 13330 Pa or less, for example, preferably from 1000 Pa (7.5 Torr) to 10610 Pa (80 Torr). It is increased linearly in the temperature range from 300 ° C. to 450 ° C., for example preferably from 350 to 410 ° C. The processing time is preferably from 10 to 60 seconds, and more preferably from 20 to 40 seconds under the conditions of temperature rise and pressure rise. Further, when processing is performed at a constant temperature, the processing time may be 10 to 20 seconds because there is no change in the temperature of the substrate.
[0024]
Next, when the passivation tungsten film forming step 84 is completed, the WF ₆ Flow the gas flow, H ₂ The main tungsten film forming step 80 is continuously performed while reducing the flow rate of the gas and flowing the gas. Here, an inert gas such as Ar, N ₂ Gas etc. are continuously flowing. In this way, the main tungsten film forming step 84 is performed for a predetermined time, and the burying hole 2 is completely buried with the main tungsten film 78, for example. At this time, the process pressure and the process temperature are not substantially changed from the time when the passivation tungsten film forming step is completed, and are kept constant.
Here, in the initial tungsten film forming step, assuming that the period from one reducing gas supply step 70 to the next reducing gas supply step 70 is one cycle, three cycles are performed in the case of FIG. The number of cycles is not particularly limited.
[0025]
The period T1 of each reducing gas supply step 70 and the period T2 of each tungsten gas supply step 72 are each 0.5 to 30 seconds, preferably 1.5 to 10 seconds, and the period of the purge step 74. T3 is 0 to 30 seconds, preferably 0 to 10 seconds. In the purging step, only the evacuation may be performed. Preferably, the total pressure (Total Pressure) of the reducing gas, the tungsten-containing gas, and the inert gas is controlled to be constant through the reducing gas supply step 70, the tungsten gas supply step 72, and the purge step 74. This is because, by keeping the total pressure of the gas constant, the temperature of the wafer (object to be processed) and the adsorption amount of the gas to be coated can be kept constant. The total pressure of the gas is controlled by measuring the pressure in the processing vessel 22 with a vacuum gauge attached to the processing vessel 22 and adjusting a pressure regulating valve attached to the exhaust passage 50 so that the pressure becomes constant. It does by doing.
[0026]
Here, the time of the purge step 74 was evaluated, and the result will be described. FIG. 5 shows silane (SiH) in the processing vessel. ₄ 5A is a diagram showing a distribution state of the partial pressure. FIG. 5A shows a case where a diffusion plate 27 is provided in the shower head unit 24, and FIG. This is the case where no is provided. In the figure, the horizontal axis represents the distance from the center of the wafer in the radial direction. Here, SiH ₄ Immediately after stopping the supply of SiH, the residual SiH on the wafer when purging for several seconds (0 to 3 seconds) is performed. ₄ Is measured.
[0027]
As is clear from FIG. 5, when the dispersing plate is provided in the shower head portion (FIG. 5A), the partial pressure becomes low earlier, and in the case shown in FIG. By performing a purging process of about ₄ 1 × 10 ^-1 Pa can be reduced to about Pa. In the case shown in FIG. ₄ 1 × 10 ^-1 It turns out that it can be reduced to about Pa. It should be noted that a similar effect (an effect similar to that of the diffusion plate) can be obtained by making the gas injection port 28 of the shower head thinner.
Therefore, irrespective of the structure of the shower head, if the purge step is performed for at least about 3 seconds, the partial pressure of the residual silane can be reduced to zero and the influence of the gas phase reaction can be ignored.
[0028]
Returning to FIG. 2, the SiH ₄ Gas and WF ₆ The gas flow rates are relatively small to reduce their partial pressure ratio. Further, the process temperature is set to a low value, for example, 200 to 500 ° C., preferably 250 to 450 ° C. The thickness of one cycle of the initial tungsten film is 1 to 50 °, preferably 3 to 20 °.
The time of the main tungsten film forming step 80 depends on the film thickness to be formed. Here WF ₆ Gas flow rate, H ₂ The film formation rate is set high by increasing both the flow rate of the gas and slightly increasing the process pressure and the process temperature.
[0029]
As a result, the initial tungsten film 76 is deposited relatively uniformly and satisfactorily on the surface of the wafer W. This initial tungsten film 76 functions as the nucleation layer 14 in FIG. 18C, and therefore, the main tungsten film 78 can be deposited thereon with good burying properties.
In the passivation tungsten film forming step 84 which is a feature of the present invention, WF ₆ Since the passivation tungsten film 82 (see FIG. 4) is formed by gradually increasing the gas and gradually increasing the process pressure, the barrier property of the initial tungsten film 76 is reinforced. With this function, the initial tungsten film 76 can be made as thin as possible. Further, the effect of reducing the effect of the high resistance initial tungsten film 76 can be expected.
For this reason, the passivation tungsten film is formed by a so-called WF ₆ Functions as a passivation film or a barrier film with respect to the WF in forming the main tungsten film. ₆ In this case, damage to the Ti film due to the diffusion of F can be suppressed, and the filling characteristics can be further improved.
[0030]
That is, the film quality characteristics (barrier properties) of the passivation tungsten film 82 are improved, and for example, diffusion of fluorine atoms into the lower layer can be significantly suppressed.
Furthermore, the three steps of the initial tungsten film forming step 79, the passivation tungsten film forming step 84, and the main tungsten film forming step 82 can all be performed continuously in the same processing vessel 22, so that the transfer of the semiconductor wafer is performed. Since the time can be eliminated and the incubation period at the beginning of the main tungsten film forming step 80 can be eliminated, the throughput can be improved accordingly.
[0031]
The gas supply mode shown in FIG. 2 (B) is different from the gas supply mode shown in FIG. 2 (A) in the first reduction gas supply step 70A of the repeated reduction gas supply steps. The parameter consisting of the product of the partial pressure (Torr) and the supply time (sec) is set to be larger than the above-mentioned parameter (Torr · sec) of the other reducing gas supply step 70. Here, this SiH ₄ The parameter (Torr · sec) is increased by extending the period T4 of the first reducing gas supply step 70A without changing the gas flow rate, for example, by performing the period from 1 to 120 seconds, preferably from 15 to 90 seconds.
[0032]
Thus, the first SiH ₄ By performing only the gas supply process, for example, for a long time, the initiation process is performed on the surface of the wafer W as described above with reference to FIG. Certain reaction intermediates will attach. Therefore, the initial tungsten film 76 to be deposited thereon becomes easy to grow, abnormal growth is suppressed, and the film can be formed with uniform thickness. Here, each process condition in the gas supply mode of FIG. 2B will be described. 2A and 2C, the corresponding parts are under the same process conditions.
[0033]
Gas ratio, SiH in the first reducing gas supply step 70A ₄ / Carrier gas = 100 to 1000 sccm / 1000 to 10000 sccm, the process pressure is 20 to 100 Torr (2666 to 13330 Pa), and the process time T4 is 5 to 90 seconds. Regarding the process temperature at this time, the upper limit is 200 to 500 ° C., preferably 250 to 450 ° C. in consideration of avoiding generation of volcano and improvement of step coverage.
At this time, the SiH ₄ The parameter (Torr · sec) of the product of the gas partial pressure and the supply time is 10 to 300 (Torr · sec), preferably 30 to 200 (Torr · sec) in order to avoid generation of volcano.
[0034]
In the initial tungsten forming process, the gas ratio, SiH ₄ / Carrier gas = 50 to 500 sccm / 2000 to 12000 sccm, the period T1 is 1 to 15 seconds, the process pressure is 1 to 20 Torr (133.3 to 2666 Pa), the process temperature is 200 to 500 ° C., preferably 250 to 450 ° C. ° C. Under these processing conditions, SiHx is deposited.
The gas ratio in the tungsten gas supply step 72, WF ₆ / Carrier gas = 5 to 300 sccm / 200 to 12000 sccm, period T2 is 1 to 15 seconds, process pressure is 1 to 20 Torr (133.3 to 2666 Pa), process temperature is 200 to 500 ° C., preferably 250 to 450 ° C. ° C. Under this processing condition, a second tungsten film is formed. Thus, the initial tungsten film is formed by alternately repeating the supply of the reducing gas and the supply of the tungsten gas.
[0035]
Here, the reducing gas supply step 70 and the tungsten gas supply step 72 will be described in detail. FIG. 6 shows the relationship between the silane parameter (Torr · sec) at about 280 ° C. and the film thickness formed per cycle. When the parameter is 0.2 or more, the film thickness is substantially saturated. On the other hand, when the parameter is less than 0.2, the film thickness depends on the magnitude of the parameter. In order to form the initial tungsten film 76, various parameters can be set by setting the parameters to 0.1 to 10, preferably 0.2 to 5, as long as the film thickness that can be formed in one cycle is stabilized. The film thickness can be saturated and stabilized within the range of the process conditions.
[0036]
FIG. 7 shows the WF at approximately 280 ° C. ₆ Is a graph showing the relationship between the parameter (Torr · sec) and the film thickness formed per cycle. When the parameter is 0.04 or more, the film thickness is substantially saturated. If the value is too small, the film thickness depends on the size of the parameter. However, as described above, in order to stabilize the film thickness formed in one cycle, the parameter is set to 0.01 to 10, preferably 0.04 to Set to 5.
FIG. 8 is a graph showing the temperature dependence of the film thickness formed per gas supply cycle. Here, SiH ₄ And WF ₆ Are alternately supplied 90 times (90 cycles) to indicate the film thickness per cycle. The horizontal axis represents the actual wafer temperature.
[0037]
As is apparent from this graph, the W film is not deposited at a wafer temperature of 100 ° C. or lower, and the film formation rate of the W film gradually increases with the temperature up to 200 to 300 ° C., and thereafter increases to 300 ° C. or higher. It turns out that the film formation rate sharply increases as the temperature rises. Therefore, it is found that the wafer temperature (slightly lower than the process temperature) is preferably set to 100 ° C. or more from the viewpoint of the film thickness.
FIG. 9 shows WF ₆ 5 is a graph showing a relationship between a gas parameter (Torr · sec) and the number of generated volcanoes per cell. Here, one cell refers to an aggregate including about 50,000 contact holes. According to this graph, when the parameter is 0.5 or less, the generation of volcano is zero, but when the parameter is larger than 0.5, the number of generated volcano increases substantially proportionally. In WF ₆ The parameters of the gas are between 0.01 and 0.6, preferably between 0.04 and 0.5. In this case, the thickness of the initial tungsten film 76 for suppressing generation of volcano depends on the inner diameter of the buried hole 2, but is, for example, about 10 to 200 °, preferably about 20 to 150 °.
[0038]
Next, in the passivation tungsten film forming step 84, the gas ratio, WF ₆ / H ₂ / Carrier gas = 10-500 sccm / 500-6000 sccm / 2000-12000 sccm, the process pressure is changed from 1 Torr (133.3 Pa) to 100 Torr (13330 Pa) as described above, and the process temperature is 200-500 ° C. Preferably, the temperature is changed substantially linearly from 250 to 450 ° C., and in the case of FIG. 2, from 350 to 390 ° C., and the process time T5 is from 1 to 90 seconds, preferably from 3 to 60 seconds. In order to avoid the occurrence of volcano, passivation tungsten film is WF ₆ Functions as a passivation film or a barrier film with respect to the WF in forming the main tungsten film. ₆ The damage of the TiN film due to the diffusion of F can be suppressed, and the filling characteristics can be further improved.
[0039]
Although the thickness of the passivation tungsten film 82 depends on the inner diameter of the buried hole 2, damage to the underlying film in the main tungsten film forming step is improved, the burying property is improved, and the step coverage is more than a certain level. In order to obtain the above, it is good to set within the range of about 10 to 500 °, preferably about 200 to 400 °.
In the passivation tungsten film forming step 84, at least one of the process pressure and the process temperature is set to be substantially the same as in the initial tungsten film forming step in the previous step. Thereby, the transition between both steps can be performed smoothly and in a short time.
[0040]
In the main tungsten film forming step 80, the gas ratio, WF, and the like are set to obtain a certain level of step coverage and a film forming rate while improving the embedding property. ₆ / H ₂ / Carrier gas = 50 to 500 sccm / 500 to 6000 sccm / 2000 to 8000 sccm, the process pressure is 10 to 100 Torr (133.3 to 13330 Pa) as described above, and the process temperature is 300 to 500 ° C., preferably 350 to 500 ° C. 450 ° C. The main tungsten film is formed under these film forming conditions.
[0041]
In the above embodiment, hydrogen and silane were used as the reducing gas, but disilane (Si ₂ H ₆ ), Dichlorosilane (SiH ₂ Cl ₂ ), Diborane (B ₂ H ₆ ), Phosphine (PH ₃ ), Etc., and these may be appropriately combined. In this case, it is preferable to use a gas having a greater reducing power in the initial tungsten film forming step than in the main tungsten film forming step 80.
Further, the same reducing gas may be used in the initial tungsten film forming step, the passivation tungsten film forming step, and the main tungsten film forming step.
Also, here, SiH is used for the initial tungsten film forming process. ₄ Was used, but instead, H generated using plasma or ultraviolet light was used. ₂ Radicals (active species) may be used.
As the tungsten-containing gas, WF is used. ₆ The gas is not limited to gas, and an organic tungsten source gas may be used.
[0042]
Also, WF ₆ Regarding the partial pressure of the gas, the lower limit is about 0.4 Torr (53 Pa) in order to increase the step coverage to some extent, and the upper limit is 2. when the process pressure is 40 Torr or less in order to avoid generation of volcano. It is about 0 Torr (266 Pa). Furthermore, WF ₆ / H ₂ The gas ratio is 0.01 to 1 and preferably 0.1 to 0.5 for increasing the step coverage to some extent and avoiding volcano. In the main tungsten film forming step 80, WF ₆ When the process was performed by changing the flow rate of the gas and changing the process pressure, the throughput was improved as the gas amount was increased, but the improvement in the throughput almost stopped at around 70 to 80 Torr. Therefore, the process pressure is preferably about 70 Torr or more.
[0043]
FIG. 10 is a graph showing the temperature dependence of the resistance value of the tungsten film. In the figure, a shows a tungsten film formed by a conventional CVD method (process temperature: 400 ° C.), b shows a tungsten film formed by the method of the present invention at a process temperature of 280 ° C., Show the membrane.
As is apparent from this graph, the films b and c according to the method of the present invention have about 2 to 4 times higher resistance than the film a formed by the conventional CVD method. This is considered to be because the crystallite size of the films b and c formed by the present method is 2 to 4 times smaller than that of the conventional method. It can also be seen that the films b and c formed by the method of the present invention have higher resistance values as the films are formed at higher temperatures. This is probably because a film formed at a higher temperature contains a higher concentration of Si.
[0044]
Finally, the concentration of F (fluorine) diffused on the wafer surface was evaluated, and the evaluation result will be described.
FIG. 11 shows SiH as a reducing gas. ₄ , Si ₂ H ₆ , B ₂ H ₆ 5 is a graph showing an F concentration (diffusion amount) profile on a wafer surface using FIG. Here, a TiN film, a Ti film, and a SiO film are formed below the W film (tungsten film). ₂ A wafer on which films are sequentially formed is used.
As is apparent from this graph, the F concentration in the W film of the method of the present invention is 1 × 10 ¹⁷ atms / cc, and the F concentration in the W film by the conventional CVD method is 3 × 10 ¹⁷ Atms / cc, the diffusion amount of F in the W film of the present invention was suppressed to about 1/3, thereby confirming that the film had high barrier properties.
[0045]
<Mode of transition from passivation tungsten film forming step (also referred to as PA step) to main tungsten film forming step (also referred to as MA step)>
In the method of the present invention described above, the case of “with temperature change” and the case of “without temperature change” (constant temperature) were examined in the passivation tungsten film forming process. The process conditions at this time are as follows.
[With temperature change]
Process temperature: The temperature was raised from 350 ° C. at the beginning of the PA step to 390 ° C. at the MA step (see FIG. 3).
Process pressure: Increased from 7.5 Torr to 80 Torr.
・ Temperature rising time (boosting time): 30 seconds (to require a certain amount of time for temperature stabilization)
・ WF ₆ Gas flow rate: increased from 60 sccm to 350 sccm.
[0046]
[No temperature change]
Process temperature: maintained constant at 410 ° C. over the PA and MA steps.
・ Boosting time: 15 seconds
・ Process pressure, WF ₆ The gas flow rate is the same as in the case of "temperature change"
The initial tungsten film forming step and other process conditions are set to be the same.
As a result of the above evaluation, in the case of “no temperature change” in which the process temperature was increased in the PA step and maintained at 410 ° C., the throughput was high and good.
On the other hand, in the case of “there is a temperature change” in which the process temperature is gradually changed from 350 ° C. to 390 ° C. in the PA process, the embedding characteristics were favorable contrary to the above.
[0047]
Next, in the initial tungsten film forming step, SiH is used as a reducing gas. ₄ , Si ₂ H ₆ , B ₂ H ₆ The case where is used will be described.
By using the method of the present invention as shown in FIG. ₄ , Si ₂ H ₆ , B ₂ H ₆ The embedding is performed using the method described below, and the state of occurrence of voids in the embedding hole and the evaluation of the embedding characteristics are described below. At this time, the inner diameter of the embedding hole was 0.09 μm.
[0048]
The supply mode and process conditions of each gas in the initial tungsten film forming process used the flowchart shown in FIG. The flow rates of the silane, disilane, and diborane gases were set so as to be the same.
FIG. 12 shows the temperature dependence of the film formation rate per cycle. It was confirmed that the film formation rate of each gas increased as the temperature increased. It was also found that the film formation was started at a lower temperature in the order of disilane, diborane, and silane, and that the film formation rate per cycle increased in the order of disilane, diborane, and silane.
[0049]
Next, FIG. 13 shows the result of examining the film thickness dependence of the specific resistance and the surface roughness at a process temperature of 320 ° C. FIG. 13A shows the dependency of the specific resistance on the film thickness, and FIG. 13B shows the dependency of the surface roughness on the film thickness.
The specific resistance was found to be higher in the order of disilane, silane, and diborane. And, it was confirmed that the specific resistance was reduced as the film thickness was increased. In particular, disilane has a sharply lower specific resistance than the other two gases.
The surface roughness increases in the order of diborane, silane, and disilane, and the surface roughness increases as the film thickness increases. However, disilane shows a peculiar change, showing a projection-like characteristic in which the surface roughness suddenly increases and then rapidly decreases once the film thickness is around 80 °.
[0050]
Next, FIG. 14 shows the result of examining the concentrations of F, Si, and B in the film. FIG. 14A shows the F concentration, and FIG. 14B shows the Si and B concentrations. In FIG. 14, W indicates a tungsten film, and TiN indicates an underlying titanium nitride film. Although the boundary between the two films is actually unclear due to the fusion of the two materials, the illustrated example shows a section for the sake of convenience.
Regarding the F concentration shown in FIG. 14A, the amount of F diffused in the TiN film of the underlayer is found to be smallest for diborane and has high barrier properties.
As shown in FIG. 14B, the concentrations of Si and B in the W film are higher in the order of diborane, silane, and disilane, and are calculated to be about 10%, 1%, and 1% or less of B or Si, respectively. Contains. In particular, in the case of diborane, it was found that the amount of B contained in the film was high.
[0051]
Next, FIG. 15 shows the result of examining the crystallinity of tungsten in the film. In this study, an X-ray diffractometer was used. In the case of disilane, only α-W and β-W cubic tungsten were observed, and it was confirmed that the crystallinity was high.
On the other hand, in the case of silane and diborane, the diffraction line was broad, and the crystallinity was low. In particular, in the case of diborane, it was confirmed that the degree of the amorphous state was higher.
[0052]
Next, FIG. 16 shows the result of embedding a contact hole having a hole diameter of 0.09 μm and A / R = 12. FIG. 16 is a drawing-substitute photograph showing a buried state of a contact hole.
From FIG. 16, it was confirmed that diborane and silane had good embedding properties, but that disilane had voids, and that embedding properties were insufficient.
As a result, Si ₂ H ₆ In the case of the above, various characteristics such as a high film formation rate and a large crystallite size are the same as those of the conventional method using a reducing gas and WF. ₆ This is the same as the growth mode in which nuclei are formed like islands as in the case of simultaneous CVD of gas. It is considered that the phenomenon shown in FIG. 13 in which the specific resistance was reduced and the surface roughness was once increased and then reduced was caused by the growth of island-shaped nuclei, which became a continuous film. Since the formed nuclei grow preferentially, the film becomes non-uniform, which causes deterioration of the embedding property.
[0053]
On the other hand, B ₂ H ₆ In the case of (1), the resistance value is high and the embedding property is the best with no seam. This is explained by the fact that B is contained at a high concentration of about 10%, and as a result, the crystallite size is small or amorphous is mixed. Since the crystallite size is small, a uniform and dense film is formed. For this reason, the amount of F diffusion of the base TiN is the smallest, and it has high barrier properties.
In addition, SiH ₄ In the case of ₂ H ₆ And B ₂ H ₆ , But the film growth mode is B ₂ H ₆ As in the case of the above, the crystallite size becomes small and the film becomes dense. While ensuring a sufficient embedding property even in a miniaturized contact hole having a hole diameter of 0.09 μm and A / R = 12, ₂ H ₆ The resistance is lower than that of the above, and the adhesion of the film can be secured. Therefore, overall judgment is made based on the state of occurrence of voids in the buried holes and the burying characteristics. ₂ H ₆ , B ₂ H ₆ , SiH ₄ In this order, good results were obtained. Good filling characteristics can be obtained by using the hole diameter of the contact hole of 0.09 μm this time, and it is effective for the next generation of fine holes of 0.13 μm or less in the future.
In the present embodiment, a semiconductor wafer has been described as an example of an object to be processed. However, the present invention is not limited to this, and it is needless to say that the present invention can be applied to an LCD substrate, a glass substrate, and the like.
[0054]
【The invention's effect】
As described above, according to the method for forming a tungsten film of the present invention, the following excellent operational effects can be exhibited.
According to the present invention, an initial tungsten film is formed as a nucleation layer having high film thickness uniformity, a passivation tungsten film is formed more efficiently, and thereafter a main tungsten film is formed. Is deposited, so that the embedding characteristics can be particularly improved. For example, even if the diameter of the embedding hole is small, it is possible to suppress the generation of voids and the occurrence of volcano having a size that adversely affects the characteristics. In addition, since the above-described series of three steps are continuously performed in the same processing container, for example, an incubation period caused by changing the processing container is eliminated, and the throughput can be improved accordingly.
According to the third aspect of the present invention, by maintaining the process temperature between the steps substantially constant, there is no need to raise or lower the process temperature on the way, so that the throughput can be further improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram showing a heat treatment apparatus for performing a method of forming a tungsten film according to the present invention.
FIG. 2 is a diagram showing a supply mode of each gas.
FIG. 3 is a flowchart showing a relationship between an example of each gas flow rate and process conditions throughout the film forming process.
FIG. 4 is an enlarged sectional view showing an example of a tungsten film deposited on a surface of a semiconductor wafer.
FIG. 5 shows silane (SiH) in a processing vessel. ₄ FIG. 6 is a diagram showing a distribution state of partial pressures in FIG.
FIG. 6 is a graph showing a relationship between a silane parameter (Torr · sec) and a film thickness formed per cycle.
FIG. 7: WF ₆ Is a graph showing the relationship between the parameter (Torr · sec) and the film thickness formed per cycle.
FIG. 8 is a graph showing the temperature dependency of a film thickness formed per gas supply cycle.
FIG. 9: WF ₆ 5 is a graph showing a relationship between a gas parameter (Torr · sec) and the number of generated volcanoes per cell.
FIG. 10 is a graph showing the temperature dependence of the resistance value of a tungsten film.
FIG. 11 is a graph showing an F concentration (diffusion amount) profile on a wafer surface.
FIG. 12 is a diagram showing the temperature dependence of a film forming rate per cycle.
FIG. 13 is a diagram showing the film thickness dependence of specific resistance and surface roughness at a process temperature of 350 ° C.
FIG. 14 is a diagram showing the concentrations of F, Si, and B in a film.
FIG. 15 is a diagram showing an X-ray diffraction result when the crystallinity of tungsten in a film is examined.
FIG. 16 is a photograph as a substitute of a drawing, showing a buried state of a contact hole.
FIG. 17 is a cross-sectional view showing a buried hole in which a volcano and voids are generated.
FIG. 18 is a diagram showing an example of a process when filling a buried hole with tungsten.
[Explanation of symbols]
2 Embedding hole
4 Barrier layer
20 Heat treatment equipment
22 Processing container
24 shower head
60 heating lamp
70 Reducing gas supply process
72 Tungsten gas supply process
74 Purge process
76 Initial tungsten film
78 Main tungsten film
79 Initial tungsten film formation process
80 Main tungsten film formation process
82 Passivation tungsten film
84 Passivation Tungsten Film Forming Process
W Semiconductor wafer (workpiece)

Claims (7)

When forming a tungsten film on the surface of an object to be processed in a processing vessel made evacuable,
The reducing gas supply step of supplying the reducing gas and the tungsten gas supply step of supplying the tungsten-containing gas are alternately and repeatedly performed with a purge step of evacuating while supplying an inert gas between the two steps. An initial tungsten film forming step of forming an initial tungsten film as described above,
A passivation tungsten film forming step of forming a passivation tungsten film while gradually increasing the pressure in the processing container by simultaneously changing the flow rate of the tungsten-containing gas while increasing the flow rate while flowing the reducing gas into the processing container. When,
A main tungsten film forming step of forming a main tungsten film by continuously flowing the reducing gas and the tungsten-containing gas through the processing vessel;
A method of forming a tungsten film, comprising: 2. The tungsten film forming method according to claim 1, wherein in the passivation tungsten film forming step, the temperature of the object to be processed is gradually increased. 2. The temperature of the object to be processed is maintained substantially the same between the initial tungsten film forming step, the passivation tungsten film forming step, and the main tungsten film forming step. The method for forming a tungsten film as described above. The pressure in the processing chamber is 2666 Pa (20 Torr) or less in the initial tungsten film forming step and the passivation tungsten film forming step, and is 2666 Pa (20 Torr) or more in the main tungsten film forming step. Item 4. The method for forming a tungsten film according to any one of Items 1 to 3. The tungsten-containing gas, method of forming a tungsten film according to any one of claims 1 to 4, characterized in that any one of the WF ₆ gas and organic tungsten source gas. The reducing gas is one of H ₂ gas, silane (SiH ₄ ), disilane (Si ₂ H ₆ ), dichlorosilane (SiH ₂ Cl ₂ ), diborane (B ₂ H ₆ ), and phosphine (PH ₃ ). The method for forming a tungsten film according to any one of claims 1 to 5, comprising: The tungsten-containing gas is WF ₆ gas, the reducing gas is SiH ₄ gas in the initial tungsten film forming step, and H ₂ gas in the passivation tungsten film forming step and the main tungsten film forming step. The method for forming a tungsten film according to claim 1.

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