JP2004273991A - Semiconductor manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor manufacturing method by which a deposit can be removed within a minimum time and further, a semiconductor device with a stable quality can be obtained. <P>SOLUTION: In the semiconductor manufacturing method including repeating insertion of a wafer W into a chamber 1 of a CVD (chemical vapor deposition) treatment apparatus and filming treatment to form a film over a plurality of wafers W, a reduced gas is fed into the chamber 1 for every filming and conditioning treatment is applied into the chamber 1 with a plasma resulting from applying a high frequency power. Filming and conditioning treatment are alternately performed predetermined times, and cleaning treatment is then performed for removing the deposit that is stuck within the chamber 1 by the predetermined times of filming treatment, by plasma etching. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor by a chemical vapor deposition method in which a source gas is flowed into a chamber containing a semiconductor substrate to form a film.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a method of manufacturing a semiconductor device, a method of depositing a metal film on a semiconductor substrate by a chemical vapor deposition method, for example, a thermal CVD method has been used. In a film forming process by CVD, a semiconductor substrate such as a silicon wafer having a structure required as a semiconductor device formed by a previous process is inserted into a chamber of a CVD apparatus, and a source gas is supplied into the chamber. A film is formed by depositing a film material on a semiconductor substrate surface.
[0003]
In a film forming process by CVD, a source gas is supplied not only to a substrate on which a film is to be formed, but also to a chamber, particularly to a peripheral portion of a susceptor on which a semiconductor substrate is mounted or a substrate mounted on the susceptor. It is inevitable that a film forming substance is deposited on a gas nozzle or the like. In order to prevent the film forming characteristics on the substrate from being changed by the presence or absence of the deposit in the chamber, cleaning is performed to remove the deposit in the chamber each time one deposition is completed, and the inside of the chamber is removed. There is a method of maintaining a state in which no sediment exists as a steady state.
[0004]
Conversely, in order to prevent a change in film formation characteristics by setting a state in which deposits are present in the chamber in a steady state, before performing film formation on a semiconductor substrate for actual semiconductor device manufacturing, There is also a method of performing a dummy film formation for depositing a film forming substance in a chamber. The dummy film formation is usually performed by mounting a silicon wafer on a susceptor as a dummy, which does not have a structure necessary for a semiconductor device, that is, is not itself a semiconductor substrate for manufacturing a semiconductor device. Is done.
[0005]
The former method has the advantage that there is no need to prepare a dummy, the amount of dust generated due to peeling of the film-forming substance deposited in the chamber is kept low, and the yield of semiconductor devices to be produced can be kept high. As a cleaning method, for example, a method using plasma of a fluorine source gas has been proposed (for example, see Patent Document 1).
[0006]
[Patent Document 1]
U.S. Pat. No. 5,207,836 (ABSTRACT, page 5, lines 35-56)
[0007]
[Problems to be solved by the invention]
However, according to the method disclosed in Patent Document 1, film formation cannot be performed during cleaning. Therefore, there is a problem that the processing capacity of the CVD apparatus is reduced.
[0008]
On the other hand, in order to avoid the decrease in the processing capacity as described above, a method of repeatedly performing film formation a plurality of times and then cleaning the inside of the chamber in accordance with the accumulated thickness of the formed film may be considered. However, in this method, when the film formed immediately after the cleaning is compared with the film obtained immediately before the cleaning without performing the cleaning, the state inside the chamber at the time of the film formation is different. There is a problem that instability such as a difference in the thickness of the semiconductor occurs, and as a result, the quality of the manufactured semiconductor deteriorates.
[0009]
The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a semiconductor manufacturing method capable of removing a deposit in a minimum time, reducing a reduction in processing capacity, and obtaining a semiconductor device of stable quality.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor manufacturing method according to the present invention forms a film on a plurality of semiconductor substrates by repeating insertion of a semiconductor substrate into a chamber and film formation processing on the inserted semiconductor substrate. Forming a film on the semiconductor substrate by a chemical vapor deposition method using a fluoride gas as a raw material, and simultaneously depositing a deposit in the chamber, After repeating the insertion and film formation of the semiconductor substrate into the chamber a plurality of times, cleaning is performed by plasma etching to remove deposits adhering to the chamber during the plurality of iterations, and the plurality of times are performed. Conditioning in the chamber using a reducing gas plasma is performed between each repetition.
[0011]
The film formation is preferably a non-selective film formation of a tungsten film using a tungsten hexafluoride gas as a raw material.
[0012]
In the semiconductor manufacturing method, a film forming process on a plurality of next semiconductor substrates may be further repeatedly performed from a state in which the deposits in the chamber are removed by the cleaning.
[0013]
The reducing gas plasma is a plasma in which an atmosphere containing an inert gas in addition to the reducing gas at a first ratio with respect to the reducing gas is excited, and the cleaning includes etching containing fluorine. Deposits are removed by plasma etching using a gas, and subsequently, an atmosphere containing only the reducing gas, or the inert gas in addition to the reducing gas is added to a second ratio different from the first ratio. It is preferable to remove the fluorine remaining in the chamber by using plasma in which an atmosphere including the above is excited.
[0014]
It is preferable that the reducing gas plasma is a plasma in which a gas containing hydrogen is excited. Examples of the first ratio are 0.05 to 0.20 with respect to the reducing gas 1, and the second ratios are 0.10 to 0.40 with respect to the reducing gas 1. There is something.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, one embodiment of the present invention will be described. In the present embodiment, a case where a tungsten film for internal wiring of a semiconductor integrated circuit is formed will be described as an example. As a film forming method, a film forming process is performed on a plurality of silicon wafers (hereinafter, simply referred to as “wafers”) as semiconductor substrates sequentially loaded into the same film forming chamber.
[0016]
The processing apparatus usable in the semiconductor manufacturing method of the present invention includes a chamber (reaction chamber) for accommodating a wafer, a reaction gas such as a source gas such as a metal fluoride, an etching gas such as a fluorine compound, and a reducing gas such as hydrogen. The apparatus is not particularly limited as long as it has a reaction gas introduction system capable of introducing gases into the chamber and a plasma generation mechanism for generating plasma by applying high frequency (RF) power to these gases. For example, a CVD processing apparatus 10 as shown as a schematic sectional view in FIG. 1 is preferably used.
[0017]
Hereinafter, a schematic configuration of the CVD apparatus 10 will be described with reference to FIG. As shown in FIG. 1, in the CVD apparatus 10, an upper electrode 3 and a susceptor 4 are provided facing each other in a chamber (reaction chamber) 1 which is sealed from the outside air by a chamber wall 2. The susceptor 4 has a substrate mounting surface on which the wafer W is mounted on its upper surface. The susceptor 4 is heated to a predetermined temperature by a lamp heater 7 provided on the lower surface side. The susceptor 4 is also kept at the ground potential and functions as an electrode for generating plasma.
[0018]
The upper electrode 3 includes a shower nozzle on the lower surface facing the susceptor for uniformly supplying the reaction gas supplied from the pipe 6 into the chamber 1. The reaction gas supplied into the chamber 1 is exhausted at a controlled exhaust rate from an exhaust port 5 provided in the peripheral portion of the chamber 1, and a reaction gas atmosphere of a predetermined pressure is formed in the chamber 1. The upper electrode 3 also functions as an electrode to which high frequency (RF) power output from the high frequency power supply 8 is applied via the impedance matching circuit 9. In the chamber 1, a shadow ring 11 is provided, which is located on the outer peripheral portion of the susceptor 4 and covers the outer peripheral portion of the wafer W placed on the susceptor 4.
[0019]
When performing film formation by CVD, the wafer W is placed on the heated susceptor 4, the wafer W is heated to a predetermined temperature, and then a source gas is supplied from the shower nozzle of the upper electrode. At this time, the outer periphery of the wafer W is covered by the shadow ring 11, and an inert gas such as nitrogen is flown as a purge gas into the gap between the shadow ring 11 and the wafer W through a purge gas supply path (not shown). Is prevented from being formed on the outer periphery. When cleaning is performed, an etching gas is supplied from a shower nozzle and high-frequency power is applied to the upper electrode 3 to generate plasma of the etching gas in a space between the upper electrode 3 and the susceptor 4. At this time, the position of the susceptor 4 is lowered by an unillustrated vertical mechanism so as to widen the gap between the shadow ring and the lower portion of the shadow ring so that the portion of the lower surface of the shadow ring that contacts the outer peripheral portion of the wafer W during film formation is also cleaned.
[0020]
FIG. 2 is a flowchart of the semiconductor manufacturing method according to the present embodiment. As shown in FIG. 2, in the semiconductor manufacturing method according to the present embodiment, a cleaning process is performed after alternately performing a film forming process on the wafer W and a conditioning process using reducing gas plasma a plurality of times. That is, the wafer W is carried into the tungsten film forming chamber 1 of the CVD processing apparatus 10, and thereafter, a predetermined vacuum pressure, for example, about 1 × 10 ^-3 Evacuation is performed until the pressure reaches Pa, and thereafter, a film forming material gas is supplied into the chamber to perform a film forming process (step 1).
[0021]
Specifically, a tungsten film is formed on the wafer W. As film forming conditions, for example, tungsten hexafluoride (WF ₆ ) Gas and hydrogen (H ₂ ) Use gas. The flow rate of the source gas is typically, for example, about 60 sccm and about 90 sccm, respectively. Also, typically, for example, the film forming pressure is 90 torr (12 kPa), and the film forming temperature is 415 ° C. Note that monosilane may be used instead of hydrogen gas. After the film formation, the wafer W is unloaded from the chamber 1.
[0022]
Next, a reducing gas such as hydrogen gas and an inert gas such as N ₂ WF remaining in the chamber 1 by supplying gas and exciting the plasma ₆ A conditioning process is performed to remove incomplete reactants derived from gas from the chamber 1 (step 2). Specifically, this conditioning process is performed under the processing conditions of, for example, a hydrogen gas flow rate of 500 to 1500 sccm, a nitrogen gas flow rate of 40 to 100 sccm, a pressure of 0.6 to 1.8 torr (80 to 240 Pa), and an RF power of 100 to 200 W. Is preferred. Typically, the process is performed under the conditions of a hydrogen gas flow rate of 500 sccm, a nitrogen gas flow rate of 60 sccm, a pressure of 1.2 torr (160 Pa), and an RF of 150 W.
[0023]
In the present embodiment, hydrogen gas, which is also used as a source gas for tungsten film formation, is used as the reducing gas used in the conditioning process. As described above, by using the gas used for another purpose, it is not necessary to add a new gas pipe for performing the conditioning process. When a reducing gas other than hydrogen is used as a source gas for forming another type of film or for another purpose, the reducing gas is used for conditioning. Is also good.
[0024]
Further, examples of the inert gas used together with the reducing gas in the conditioning treatment according to the present invention include helium gas, neon gas, argon gas, and krypton gas in addition to the nitrogen gas. Among them, nitrogen gas is preferable.
[0025]
In the conditioning treatment according to the present invention, nitrogen gas (N ₂ The purpose of mixing (1) is to adjust the fluctuation of the film thickness to be formed and the uniformity of the film thickness of the film formed between the previously processed wafer and the subsequent wafer. That is, by changing the flow rate of the nitrogen gas, it is possible to suppress a change in the film thickness before and after and a change in the film thickness uniformity on the wafer surface.
[0026]
For example, in the conditioning process, the flow ratio of nitrogen gas and hydrogen gas, that is, the mixing ratio is N ₂ : H ₂ = 1: 6 to 1:20. When the mixture ratio of the nitrogen gas and the hydrogen gas is out of the above range, there is a possibility that the reproducibility of the film thickness during continuous film formation is deteriorated, or the uniformity of the film thickness in the wafer surface is deteriorated. .
[0027]
After the conditioning process, the second wafer is loaded into the chamber 1 and a tungsten film is formed under the same processing conditions as the first wafer (step 3). Hereinafter, similarly, the film forming process and the in-chamber conditioning process are alternately performed, and these processes are repeated a certain number of times (steps 4 to 7). After the last film forming process (Step 7), a cleaning process in the chamber corresponding to the accumulated film thickness is performed (Step 8). Specifically, for example, nitrogen trifluoride (NF ₃ ) A gas is supplied into the chamber 1 at a flow rate of 150 sccm, and while maintaining the inside of the chamber 1 at 0.6 torr (80 Pa), an RF power of 250 W is applied to form a plasma state. Then, the tungsten film deposited on the peripheral portion of the susceptor 4 and the lower surface (shower nozzle) of the upper electrode 3 is removed by etching.
[0028]
Subsequently, hydrogen and nitrogen are supplied at flow rates of, for example, 500 sccm and 100 sccm, respectively, and plasma is generated under the conditions of, for example, a pressure of 1.2 torr (160 Pa) and an RF power of 150 W to remove fluorine remaining in the chamber 1. I do. In the case where the film forming process is further continued, after the cleaning process is completed, the film forming process and the conditioning process are repeated a certain number of times.
[0029]
Here, the cleaning process is performed collectively after the film formation on a plurality of wafers W, and the cleaning process is performed on each wafer W in comparison with the case where the cleaning process is performed for each film formation on each wafer W as in the related art. It has been clarified that by performing the conditioning process during the film formation, the time required for processes other than the film formation can be reduced and the processing capability can be improved.
[0030]
According to the conventional method, after film formation on each wafer W, NF ₃ Plasma (NF) generated by applying RF power to a gas atmosphere ₃ Plasma (H) generated by etching a deposited film using plasma and applying RF power to a mixed gas atmosphere of hydrogen and nitrogen. ₂ Plasma) to remove residual fluorine. That is, for example, during the film forming process of four wafers W, the NF ₃ Plasma treatment and H ₂ The plasma treatment is performed four times.
[0031]
On the other hand, in the present embodiment, one NF is performed during the film forming process for the four wafers W. ₃ Plasma treatment and four times of H ₂ Plasma treatment (3 conditioning treatments and 1 NF ₃ H after plasma cleaning ₂ Plasma treatment). However, NF ₃ Since the amount of the W film to be etched in the chamber is four times that of the conventional method, the plasma processing needs to be performed four times as long as the conventional method. On the other hand, H ₂ It is considered that the time required for the plasma processing is actually different from that of the conventional method. However, in the related art, the time was as short as 10 seconds. Therefore, when only the time for actually generating and processing the plasma is compared, the present embodiment is the same as the conventional method.
[0032]
However, in reality, NF is required to perform the cleaning process. ₃ Before generating plasma, it is necessary to perform steps such as exhausting the inside of the chamber to remove the remaining source gas, supplying an etching gas, and stabilizing the pressure. The application of the RF power is not actually performed instantaneously, but is performed gradually over a predetermined discharge stabilization time. Furthermore, NF ₃ After the plasma is generated for a predetermined time to perform etching, H ₂ Before the plasma is generated, steps such as exhausting the inside of the chamber, supplying the reducing gas, stabilizing the pressure, stabilizing the discharge, and the like are necessary. The total time required for the auxiliary operation (setup) before and after the actual generation and processing of the plasma is shorter in the present embodiment than in the conventional method, and the processing capacity is smaller. Can be improved. In particular, NF ₃ After generating plasma, H ₂ In contrast to the conventional method requiring four setup steps during processing of four wafers W in the conventional method, only one setup step is required in the present embodiment, which reduces the total time. Is realized.
[0033]
For example, in the time table shown in FIG. 3, in the case where film formation processing is continuously performed on n wafers W per batch, the time required for one film formation processing is A (sec), and the time required for one cleaning step is one. Assuming that the required time is B (sec), the total required time of the conventional cleaning method shown in FIG. 3B is expressed by the following equation (I).
nx (A + B) (I)
FIG. 3B shows the case where n = 4.
[0034]
Here, the required time B of the cleaning step is NF ₃ Plasma etching and H ₂ It includes two processes of removing residual fluorine by plasma. In addition, the above-mentioned time includes not only the time for actual processing but also the time for auxiliary operations such as exhaustion of gas in the chamber, gas supply, pressure stabilization, discharge stabilization, gas exhaustion after processing, and the like. In addition, the required time B (sec) of the cleaning step is actually NF after stabilization. ₃ It consists of a time D (sec) during which plasma etching is performed and a time E (sec) during which other processing is performed. That is, B = D + E.
[0035]
On the other hand, in the cleaning method according to the present invention shown in FIG. 3A, the time E (sec) during which plasma etching is performed in order to remove the tungsten deposited in the chamber during the n-sheet deposition. Only n times are required. Therefore, the time required for the cleaning step after the deposition of n sheets is [D + n × E] (sec). Note that H ₂ Removal of residual fluorine by plasma is NF ₃ It is the same even if the etching time becomes longer. FIG. 3B shows the case where n = 4. As a result, the total required time of the cleaning method according to the present invention is represented by the following formula (II), where the required time of one conditioning step is C (sec).
(N-1) × (A + C) + A + D + nxE (II)
[0036]
When the difference Δt between the above formulas (I) and (II), that is, the increase in the processing capacity according to the present invention shown in FIG. 3A is obtained, it is expressed by the following formula (III).
Δt = n × (B−C−E) −D + C (sec) (III)
In the above formula (III), typical numerical values in the case of a film thickness of 400 nm as shown below, that is, A = 196 (sec), B = 120 (sec), C = 58 (sec), D = 90 ( sec) and E = 30 (sec), the following equation (IV) is obtained.
Δt = 32 (n−1) (IV)
From the result of the formula (IV), it can be seen that the larger the number n of the wafers W to be continuously processed per batch is, the larger the value of the time difference Δt required for processing is.
[0037]
For example, when n = 4, the value of Δt is 96 (sec). In this case, the total required time in the conventional method is 1264 (sec) from the above formula (I). Therefore, when four wafers W are continuously processed, 96/1264 × 100 ≒ 7.6%. Saves time. In other words, the processing capacity has increased by 7.6%. Furthermore, in the conditioning step according to the present invention, there is room for further reduction of 5 to 10 seconds, and the processing capacity can be further improved. In addition, as described below, by appropriately adjusting the condition of the conditioning process performed between the film forming processes, the variation in the film thickness between the film forming processes and the in-plane uniformity of the formed film are obtained. Can be avoided.
[0038]
The embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above-described embodiment, a description has been given of the case of single-wafer processing in which wafers are processed one by one. However, the present invention can be similarly applied to a case where two or more wafers are simultaneously formed.
[0039]
In the above-described embodiment, the CVD processing apparatus configured to heat the wafer W by heating the susceptor with the lamp heater is used. The present invention is not limited to this. However, when heating with a lamp heater, the entire susceptor and its surrounding components in a wide area are heated. For example, the wafer W of the susceptor is placed by a resistance heater embedded inside the susceptor. It is considered that the influence of the deposits in the chamber is stronger than when only the heating portion is heated. Therefore, when using a CVD processing apparatus configured to heat the susceptor with a lamp heater, it is particularly necessary to perform the conditioning processing of the present invention.
[0040]
In the above embodiment, after performing the film forming process on the wafer W, the conditioning process is performed after the wafer W is unloaded from the chamber. However, the tungsten film formed on the wafer W is H ₂ Since no damage is caused by the plasma, the conditioning process can be performed with the wafer W remaining in the chamber 1. However, when the processing is performed in the sequence of FIG. 3A and the conditioning processing is performed while the wafer W after film formation is left in the chamber 1, the conditioning processing is performed on the first to third wafers W. H for ₂ The fourth wafer W is exposed to the plasma and is not exposed. Such different processing for each wafer causes instability of the semiconductor device to be produced. In order to prevent this, the conditioning process is preferably performed after the wafer W is unloaded from the chamber 1.
[0041]
(Example)
Hereinafter, examples of the present invention will be described. In this embodiment, a tungsten film used as an internal wiring of a semiconductor integrated circuit is formed. As the film forming conditions, WF ₆ Gas flow rate, H ₂ Gas flow rates were 60 sccm and 90 sccm, respectively. The film forming pressure was 90 torr (12 kPa), the film forming temperature was 415 ° C., and the film forming time was 196 seconds.
[0042]
After unloading the wafer W, hydrogen as a reducing gas and N as an inert gas are introduced into the chamber 1. ₂ And WF remaining in the chamber by exciting the plasma ₆ A conditioning process was performed to eliminate incomplete reactants derived from the gas from the chamber. Specifically, the conditioning processing was performed under the processing conditions of a hydrogen flow rate of 500 sccm, a nitrogen flow rate of 60 sccm, a pressure of 1.2 torr (160 Pa), an RF power of 150 W, and a discharge time of 10 seconds.
[0043]
Thereafter, the second wafer W was loaded into the chamber 1, and a tungsten film was formed under the same processing conditions as the first wafer. Hereinafter, the film forming process and the in-chamber conditioning process are alternately performed under the same conditions according to the time table of the series of process steps shown in FIG. 3A, and after the fourth film forming process is completed. Then, a cleaning process in the chamber 1 was performed according to the accumulated film thickness. Specifically, NF ₃ The gas is passed through the chamber 1 at a flow rate of 150 sccm, and while maintaining the pressure in the chamber 1 at 0.6 torr (80 Pa), an RF power of 250 W is applied to form a plasma state. The deposited tungsten film was removed by etching for 120 seconds.
[0044]
Subsequently, hydrogen and nitrogen are supplied at flow rates of 500 sccm and 100 sccm, respectively, and a plasma is generated under the conditions of a pressure of 1.2 torr (160 Pa) and an RF power of 150 W to perform a post-treatment for removing fluorine remaining in the chamber 1. went. In this processing step, the time required from the start of film formation on the first wafer W to the completion of the last cleaning processing was 1168 seconds (19 minutes 28 seconds). The time required for the conditioning process during the film formation process on each wafer W was 58 seconds. The time required for the final cleaning process was 3 minutes and 30 seconds including post-processing.
[0045]
(Comparative example)
Instead of performing a conditioning process after each film forming process, NF ₃ The film forming process was performed on four wafers under the same conditions as in the above embodiment except that the cleaning process by plasma was performed each time, that is, according to the time table of the conventional series of processing steps illustrated in FIG. Was. In the comparative example, the time required from the start of film formation on the first wafer to the completion of the last cleaning process was 1264 seconds (21 minutes and 4 seconds). In this comparative example, the time required for the cleaning process performed after each film formation was 120 seconds (2 minutes) including the time for the auxiliary operation. From the results of the examples and the comparative examples, it was confirmed that the time required for the entire process can be reduced to 1 minute and 36 seconds in the case of forming a film on four wafers according to the present invention.
[0046]
(Comparative experiment 1)
Comparative experiments were performed to confirm the effects of the present invention. On the other hand, in the sample group (Run 1), the film formation was performed without performing the cleaning process and the conditioning process while performing the film formation four times with a constant film formation time using four wafers. In the other sample group (Run 2), when forming a film four times with a constant film formation time using four wafers, a conditioning process was performed each time the film formation process was completed once. The electrical resistance of the films (sheets) formed for both sample groups Run1 and Run2 was measured. The results are shown in the graph of FIG. In the upper graph in FIG. 4, the horizontal axis indicates the number of the wafer subjected to the film formation processing (the order of the film formation processing), and the left vertical axis indicates the electric resistance value of each wafer at a predetermined position.
[0047]
As shown by the results in the upper graph in FIG. 4, the electrical resistance values of the first wafer and the second wafer of the sample group (Run 1) that were not conditioned between the film formation processes were measured. There is a big difference. This result indicates that in the sample group (Run 1), there is a difference in the thickness of the formed film between the first wafer and the second wafer.
[0048]
On the other hand, in the sample group (Run 2) subjected to the conditioning process for each film forming process, the electric resistance value is substantially constant throughout the first to fourth samples. This result indicates that in the sample group (Run 2), the film thickness of each of the films formed from the first wafer to the fourth wafer is substantially constant.
[0049]
As shown in FIG. 3B, the apparatus shown in FIG. 1 typically removes a tungsten film deposited in a chamber every time a film is formed, and deposits remain in the chamber. This is an apparatus that stably forms a film on a plurality of wafers W by setting a non-existent state to a steady state. By applying the present invention to such an apparatus, the film formation of the first wafer W after cleaning is started in a state where the tungsten film does not exist in the chamber, whereas the second wafer W Subsequent wafers W are formed with the tungsten film present in the chamber.
[0050]
As described above, it is feared that the first wafer W and the subsequent wafers W have different conditions in the chamber at the start of film formation, which may cause variations in film formation characteristics such as film thickness. . Actually, in Run 1 in which the conditioning process was not performed between the film formations, the film thickness between the first wafer W and the subsequent wafers W, which is considered to be caused by the change in the state of the chamber. Was confirmed. On the other hand, in Run2 in which the conditioning process was performed during the film formation process, no change in the film thickness was observed, and stable film formation was possible.
[0051]
H ₂ In the conditioning process using plasma, the tungsten film deposited in the chamber cannot be removed, so that even if the conditioning process is performed, the first wafer W and the second and subsequent wafers W There is a difference between the presence or absence of the tungsten film in the chamber. Therefore, the result that the change in the film forming characteristics can be prevented by the conditioning process means that the tungsten film itself deposited in the chamber is formed at least within a thin film thickness range of about 4 films. It shows no significant effect on film properties.
[0052]
On the other hand, WF remaining in the chamber in an unreacted state ₆ Gas or WF ₆ For the removal of incomplete reactants remaining in the chamber in an incomplete reaction state derived from gas and not being tungsten, H ₂ It is considered that the conditioning treatment using plasma has an effect. WF ₆ Has a low vapor pressure and exhibits a liquid state at room temperature. Therefore, on the surface of the wafer W heated to 415 ° C., even if it does not remain in an unreacted or incompletely reacted state, the temperature of the upper electrode 3 or the chamber wall 2 is lower than that of the wafer. In the inner surface, etc., of the WF, only the inside of the chamber is evacuated after the film formation. ₆ Is considered to remain unreacted or in a large amount in an incompletely reacted state.
[0053]
In Run 1 in which the conditioning process between film formations is not performed, the WF remaining in the chamber ₆ Alternatively, it can be understood that the film formation characteristics on the second and subsequent wafers W are changed due to the incomplete reactant and the film thickness is changed. On the other hand, during film formation, H ₂ In Run 2 conditioned by plasma, the remaining WF ₆ Alternatively, it can be understood that the change in the film formation characteristics was prevented by removing the incomplete reactant or at least reducing the residual amount.
[0054]
As described above, even when a film forming process is performed on a plurality of wafers W using a CVD processing apparatus that makes a state in which no deposit is present in the chamber a steady state, the film formation on each of the wafers W is not performed. In the meantime, by performing conditioning processing in the chamber and removing the remaining source gas or incomplete reactants derived from the source gas from the chamber, the change in film formation characteristics due to the presence of deposits in the chamber is eliminated. It turns out that it can be prevented. Conversely, by performing the conditioning process between the film forming processes, it is possible to reduce the number of cleaning processes and improve the processing capability while preventing a change in film forming characteristics between wafers.
[0055]
As described above, as the number of films continuously formed with only the conditioning process interposed therebetween during the cleaning process increases, the higher productivity improvement effect can be obtained. However, the number of continuous films cannot be increased without limit. For example, when a tungsten film is formed by using the CVD processing apparatus shown in FIG. 1, if the continuous film formation is continued, the tungsten film is deposited on the outer periphery of the wafer W by depositing the tungsten film on the shadow ring. It was confirmed that the effect of prevention was reduced. If a tungsten film is formed on the outer peripheral portion of the wafer W, it is peeled off in a subsequent step, which causes generation of particles. For this reason, the number of wafers capable of continuously forming a film is practically 4 to 5 when the film thickness per film is 400 nm. Therefore, in the above embodiment, the cleaning process is performed after the continuous film formation of four sheets.
[0056]
The number of films that can be continuously formed depends on the type of film to be formed, the device configuration, the film thickness per film, and the like. Therefore, it is preferable to appropriately set the number for each process. However, in any case, continuous film formation cannot be continued without limitation. That is, in the present invention, in addition to performing the conditioning process for each film formation, a cleaning process is performed after the film formation process of a predetermined number of sheets or a predetermined integrated film thickness to remove deposits in the chamber. It is necessary to remove it.
[0057]
(Comparative experiment 2)
In Comparative Experiment 2, in order to clarify the factors that influence the film thickness variation between the film forming processes in the case where the film is repeatedly formed, the experiments were performed by changing various plasma generation conditions in the conditioning process. Specifically, RF power at the time of plasma generation, N ₂ Addition amount, H ₂ The flow rate and the processing time were changed, and the effects of these conditions on the film thickness variation during the film forming process were investigated. As a result, N ₂ It was found that experimental factors other than the addition amount did not significantly affect the film thickness variation.
[0058]
FIG. 5 shows the results. FIG. ₂ When the flow rate is constant at 1000 sccm, the N ₂ 6 is a graph showing the relationship between the amount of addition and the variation in film thickness when a continuous film forming process is performed. In FIG. 5, the horizontal axis represents N during the conditioning process. ₂ Shows the amount added. On the other hand, the vertical axis represents a constant film formation time of 196 seconds, that is, two films based on the film thickness formed on the first wafer when the film is formed under the condition of the target film thickness of 400 nm. This shows the difference in film thickness (variation in film thickness) from the wafer. In the figure, the region where the film thickness variation is “-” indicates that the film thickness on the second wafer is thinner than the film thickness on the first wafer. In the area of “+”, the opposite is shown.
[0059]
In FIG. 5, Ref. The reference numeral indicates the variation in film thickness when a continuous film formation is performed without performing the conditioning process, for reference. This indicates that when the conditioning process is not performed during the continuous film formation, a film thickness variation of about 30 nm occurs between wafers. On the other hand, when the conditioning process is performed during the film formation, it can be seen that the film thickness variation between wafers can be reduced. In particular, N ₂ When the addition amount is increased in the range of 0 to about 75 sccm, the variation in the film thickness gradually approaches 0 in the negative range, and N ₂ It becomes almost 0 when the added amount is about 75 sccm. And more than that N ₂ Conversely, when the addition amount is increased, the film thickness variation increases on the + side.
[0060]
From this result, N at the time of conditioning ₂ It can be seen that by optimizing the amount of addition, for example, in this case, by setting the range of about 60 to 80 sccm, the variation in the film thickness between wafers can be minimized. Product quality can be stabilized by minimizing variations in film thickness between wafers. As described above, the conditioning process of the present invention uses the WF remaining in the chamber. ₆ Gas and WF ₆ It has the effect of removing incomplete reactants derived from gas. In order to obtain this effect, mainly H ₂ It is considered that hydrogen radicals generated from the gas are effective. In contrast, N ₂ The gas is H ₂ It can be considered as having an auxiliary effect of adjusting the concentration of hydrogen radicals by diluting the gas and adjusting the degree of the residue removing effect. Or even N ₂ It is also conceivable that the irradiation of nitrogen ions generated from the gas has the effect of adjusting the surface state of the deposited tungsten film.
[0061]
On the other hand, as described above, even in the cleaning process performed after performing the film forming process on the four wafers W, the NF ₃ Following plasma etching, H ₂ Gas and N ₂ A process (hereinafter, referred to as a post-process) of the gas mixed with the plasma is performed. However, H in post-processing ₂ Gas and N ₂ The mixing ratio with the gas is H ₂ N for 500 sccm ₂ 100 sccm, and H in the above-mentioned conditioning process. ₂ , N ₂ The mixing ratio is different from the optimum range. This post-processing is NF ₃ It has an effect of removing fluorine generated by plasma decomposition of gas and remaining in various chemical states in the chamber. For this purpose, mainly H ₂ It is thought that hydrogen radicals generated from the gas have an effect.
[0062]
As described above, the conditioning process performed during the film formation process on the wafer includes the NF. ₃ By using a reaction gas composed of the same gas as the reaction gas used in the post-processing performed after the plasma etching processing, it is not necessary to add a new gas pipe for performing the conditioning processing. However, the conditioning process during the film forming process and the NF ₃ The state in the chamber before the processing is different from the processing after the plasma etching processing, and the purpose of the processing is different. Therefore, the conditions of each processing are, in particular, H ₂ , N ₂ Preferably, the mixing ratio is optimized for each. Rather, by performing the processing under different conditions, the film forming characteristics of the state where the tungsten film is removed from the chamber (first film) and the state where the tungsten film is deposited in the chamber (second and subsequent films) are made uniform. It is considered that the variation in film thickness can be minimized.
[0063]
More specifically, within the range confirmed experimentally, the H of the atmosphere used in the conditioning process during the film forming process is used. ₂ N for gas ₂ The mixing ratio of the gas is adjusted to H ₂ N for gas ₂ Good results, that is, minimization of film thickness variation between film forming processes were realized in a range where the gas mixture ratio was smaller than the gas mixing ratio.
[0064]
【The invention's effect】
According to the present invention, it is possible to provide a semiconductor manufacturing method capable of removing a deposit in a minimum processing time and obtaining a semiconductor device of stable quality.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a CVD processing apparatus according to the present invention.
FIG. 2 is a flowchart of a semiconductor manufacturing method of the present invention.
FIG. 3 is a time table of the semiconductor manufacturing method of the present invention and a comparative example.
FIG. 4 is a graph showing the relationship between the number of processed sheets and the electric resistance value of a film.
FIG. 5 shows N during conditioning processing. ₂ 5 is a graph showing the relationship between the flow rate of addition and the variation in film thickness.
[Explanation of symbols]
1 ... chamber
2… Chamber wall
3: Upper electrode
4: Susceptor
7 ... Lamp heater
8 High frequency power supply
9 ... Impedance matching circuit
W ... Wafer

Claims (4)

A semiconductor manufacturing method comprising forming a film on a plurality of semiconductor substrates by repeating insertion of a semiconductor substrate into a chamber and film formation processing on the inserted semiconductor substrate, the method comprising: Is formed by a chemical vapor deposition method using a fluoride gas as a raw material, and at the same time, deposits are deposited in the chamber, and the insertion and deposition of the semiconductor substrate into the chamber are repeated a plurality of times. Then, cleaning is performed to remove deposits adhered in the chamber during the plurality of repetitions by plasma etching, and during each of the plurality of repetitions, the reducing gas plasma is used. A method for manufacturing a semiconductor, wherein conditioning in a chamber is performed. 2. The semiconductor manufacturing method according to claim 1, wherein the film formation is a non-selective film formation of a tungsten film using a tungsten hexafluoride gas as a raw material. 3. The semiconductor manufacturing method according to claim 1, wherein a film forming process on a plurality of next semiconductor substrates is further repeated from a state in which the deposits in the chamber are removed by the cleaning. The reducing gas plasma is a plasma in which an atmosphere containing an inert gas in addition to the reducing gas at a first ratio with respect to the reducing gas is excited, and the cleaning includes etching containing fluorine. Deposits are removed by plasma etching using a gas, and subsequently, an atmosphere containing only the reducing gas, or the inert gas in addition to the reducing gas is added to a second ratio different from the first ratio. 4. The semiconductor manufacturing method according to claim 1, wherein the method is performed by removing fluorine remaining in the chamber using plasma excited in an atmosphere included in the method.

Images