JP3393399B2 - Ashing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an ashing method for removing a film formed on a surface of a substrate to be processed. 2. Description of the Related Art For example, in a semiconductor manufacturing process,
2. Description of the Related Art A process for removing a resist film formed on a surface of a substrate to be processed such as a semiconductor wafer (hereinafter, referred to as a “wafer”) is performed. In such a process, a wafer in a processing vessel is conventionally heated and processed. In a container, for example,
A so-called plasma ashing method is used in which O ₂ (oxygen gas) is introduced, and the resist film is ashed and removed by oxygen radicals generated when O ₂ is turned into plasma. At that time, it has been proposed to add H ₂ (hydrogen gas) to the O ₂ as appropriate. [0003] However, according to the conventional plasma ashing method, there is no problem in removing the ordinary resist film.
The resist film after ion implantation of (phosphorus), As (arsenic), B (boron), etc., has the following problems. First, when removing the resist film after such ion implantation, the conventional ashing method of converting oxygen gas into plasma has a very low removal rate and causes a decrease in throughput. Moreover, the resist film was not completely removed, and the resist film having a thickness of 0.1 to 0.2 μm remained without being removed. For example, in the case of a resist film after P ion implantation, about 3 × 10 4 P-C
Since a residue mainly composed of a (carbon) -O-based compound is present, if it remains as it is, it will hinder subsequent processing. On the other hand, in the conventional plasma ashing method,
The wafer is exposed to an oxygen radical atmosphere while being heated. This is because heating the wafer accelerates the reaction and improves the ashing rate. Incidentally, this type of resist film has a hard layer on the surface (hard layer) and a soft layer on the inner side (soft layer).
If the temperature of the wafer rises to some extent before the hard layer on the surface is removed, the inner soft layer expands excessively due to the heat, and the hard layer on the surface is A phenomenon is seen in which the components of the inner soft layer rupture and scatter and adhere to the wafer surface (so-called "pumping phenomenon"). The components scattered and adhered to the wafer surface may include the P—C—O-based compound, and in such a case, it is difficult to remove the components by ordinary plasma ashing. Therefore, conventionally, in order to remove such a residue, an SPM process or an APM process has been further performed.
The former is a process of immersing the wafer in a solution mainly composed of sulfuric acid and hydrogen peroxide solution, and the latter is a process of removing the residue on the wafer surface by immersing the wafer in a solution mainly composed of ammonia and hydrogen peroxide solution. However, these processes require a separate dedicated processing device and further involve washing, drying, and the like after the process, and as a result, high throughput cannot be expected. Further, there is a possibility that the film on the surface of the wafer is removed more than necessary and the underlying layer is etched. [0008] The present invention has been made in view of the above points, and has as its object the above-mentioned P (phosphorus),
The resist film after the ion implantation of As (arsenic), B (boron) or the like can be removed at a high rate by the plasma ashing method, and the ashing without leaving the above-mentioned residue. It is to provide a method. Another object of the present invention is to provide an ashing method capable of suppressing etching of a base. [0009] In order to achieve the above object, a mixed gas comprising a plurality of gases is turned into a plasma, and the processing target is heated while maintaining the inside of the processing vessel at a predetermined reduced pressure. the method of the present invention that ash the predetermined film on the substrate under the plasma atmosphere, the up target substrate exceeds a predetermined temperature, and at least F-based gas, O ₂
And a first mixed gas containing an FG gas in which N ₂ and H ₂ are mixed , and a ratio of the flow rate of the F-based gas to the flow rate of the FG gas is set as a predetermined flow ratio, and the surface of the film is formed. After the hard layer and / or sidewalls are removed and the temperature exceeds the predetermined temperature, the temperature of the substrate to be processed is further increased and the FG gas at the predetermined flow ratio is further increased.
Each step of performing an ashing process on a soft layer inside the hard layer using a second mixed gas in which the ratio of the F-based gas to the mixed gas is reduced , wherein the mixed gas corresponding to a predetermined temperature of the substrate to be processed is included. and selection of, before Symbol
By controlling the flow ratio of the mixed-gas, it is characterized by suppressing the etching of underlying the substrate to be treated. Here, the predetermined temperature means a temperature at which the above-described pumping phenomenon occurs on the surface of the substrate to be processed.
For example, the temperature of the resist film on the silicon wafer surface is about 110 ° C. to 130 ° C. Above all, 126
℃ is easy to occur. In this case, it is more preferable to set the flow rate of the F-based gas in the first mixed gas to be smaller than the total flow rate of N ₂ and H ₂ . Further, according to a preferred embodiment, the flow rate ratio of the F-based gas to N ₂ and H ₂ in the mixed gas is such that the flow rate of the F-based gas is not more than ３ of N ₂ + H _2. It is characterized by. In this case, 1/6 is more optimal. According to still another aspect, there is provided a method for ashing a predetermined film on a surface of a substrate to be processed, which is heated in a processing vessel, in a plasma atmosphere by converting a mixed gas comprising a plurality of gases into plasma. The first mixed gas is used until the outer layer of the film on the surface of the substrate to be removed is removed, and the second mixed gas is used after the outer layer is removed. The outer layer of the film here refers to, for example, an outer hard layer in the resist after the above-described ion implantation processing. According to still another embodiment, there is provided a method for ashing a predetermined film on a surface of a substrate to be processed, which is heated in a processing vessel, in a plasma atmosphere by converting a mixed gas comprising a plurality of gases into plasma. Using the first mixed gas until the outer layer of the film on the surface of the substrate is removed, setting the temperature of the substrate to be relatively low, and removing the outer layer Is characterized by using the second mixed gas and setting the temperature of the substrate to be processed to a relatively high temperature. Here, the boundary between the relative low temperature and the relative high temperature may be set, for example, to a temperature at which pumping occurs. In the present invention, it is set at 120 ° C. to 130 ° C., especially about 126 ° C. Are suitable. According to a further aspect of the present invention, the first gas mixture is a gas containing at least N ₂ and H ₂ ,
In another embodiment, the first mixed gas is a gas containing at least an F-based gas, N _2, and H ₂ , and a flow rate ratio of the F-based gas, N _2, and H ₂ in the first mixed gas. Are characterized by having a relationship of F-based gas <N ₂ + H ₂ . According to still another mode, the first mixed gas is a gas containing at least an F-based gas, O ₂ , N ₂ and H ₂ , and further, an F-based gas in the first mixed gas. And the flow rate ratio between N ₂ and H ₂ has a relationship of F-based gas <N ₂ + H ₂ . According to still another aspect, in the first mixed gas, the flow rate of the F-based gas is preferably equal to or less than 1/3 of N ₂ + H ₂ . The F-based gas used in the present invention refers to a fluorine-based gas (a gas containing F (fluorine)). For example, CF ₄ , NF ₃ , and CHF ₃ can be used. The following ratios of the flow rate of H ₂ to N ₂ in the gas containing N ₂ and H ₂ are preferable in terms of the handling rules for the gas, the ease of actual handling, and the safety.
That is, the flow rate ratio of H ₂ to N ₂ is (N ₂ + H ₂ )
Is desirably 3% or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an ashing apparatus 1 used to execute an ashing method according to the present embodiment. The inside of the processing container 2 made of oxidized aluminum is vertically divided by a light-transmitting plate 3 made of a material such as sapphire glass or quartz glass which has corrosion resistance to a fluorine-based gas. A plurality of halogen lamps 4 as heating means are annularly provided on a base 5 in a lower space partitioned by the light transmitting plate 3. The power supply 6 of the halogen lamp 4 is provided outside the processing container 2, and has a configuration in which heating of the substrate to be processed by the halogen lamp 4 can be controlled by adjusting the output of the power supply 6. If the base 5 is configured to be rotatable by an appropriate driving mechanism, more uniform heating is possible. An opening 3 a is formed at the center of the light transmitting plate 3, and an exhaust pipe 8 leading to an exhaust means 7 such as a vacuum pump installed outside the processing vessel 2 is formed in the opening 3 a. It is possible to exhaust the atmosphere in the upper space above the light transmitting plate 3 and set the inside of the upper space to a predetermined pressure reduction degree by operating the exhaust means 7. The halogen lamp 4 is provided with a reflector 9 so that heat from the halogen lamp 4 is efficiently transmitted to the space above the light transmitting plate 3. A plurality of support pins 10 made of quartz or the like are provided on the upper surface of the light transmitting plate 3 in an annular shape.
It is mounted on this support pin 10. A temperature sensor 11 for measuring the temperature of the wafer W is provided on one of the support pins 10 ′.
Is provided, and a temperature signal from the temperature sensor 11 is transmitted to a temperature detecting device 12 installed outside the processing vessel 2.
Is output to. Therefore, the temperature of the wafer W can be constantly detected by the temperature detecting device 12. A baffle body 13 is provided at an upper portion in the processing vessel 2.
Is provided. The baffle body 13 is made of a ceramic material coated with, for example, sapphire.
The baffle plates 13a and 13b are provided at the top and bottom, and each of the baffle plates 13a and 13b has a large number of discharge ports 1a.
4 are formed. With this configuration, the support pins 10
It is possible to uniformly supply gas to the upper wafer W. An opening 2b is formed at the center of the top plate 2a of the processing container 2 above the baffle plate 13a, and a supply pipe 21 is connected to the opening 2b. The supply pipe 21 is made of, for example, a quartz tube and a material resistant to fluorine-based gas, and is connected to a gas supply source via a main valve 22. In the ashing apparatus 1, four gas supply sources 23, 24, 25, and 26 are provided.
Different gases can be supplied. That is, N ₂ (nitrogen gas) from gas supply source 23, H ₂ (hydrogen gas) from gas supply source 24, O ₂ (oxygen gas) from gas supply source 25, and gas supply source 26 The CF ₄ gas is supplied to the supply pipe 21. These gas supply sources 23, 24, 25, 26
Are connected in parallel to the main valve 22,
Further, a valve 27 and a mass flow controller 28 as a flow control device are interposed in the supply paths between the gas supply sources 23, 24, 25, 26 and the main valve 22, respectively. 2
By the control of 8, it is possible to flow an arbitrary combination of mixed gases, and also to flow the supply pipe 21 at an arbitrary flow ratio. A chamber 31 is provided on the outer periphery of the supply pipe 21 between the opening 2b of the processing vessel 2 and the main valve 22. An antenna member (not shown) that generates a microwave in the chamber 31 by receiving a high-frequency supply from a high-frequency power supply 32 is disposed in the chamber 31. In the example of the ashing device 1, a high frequency of, for example, 24.5 MHz is supplied from the high frequency power supply 32. When the high frequency is supplied, the gas flowing in the supply pipe 21 passing through the chamber 31 is turned into plasma. Next, regarding the control system of the ashing device 1, at least the power supply 6, the exhaust means 7, the valve 27, and the mass flow controller 28 are controlled by the control device 33. Based on the signal, the power source 6, the exhaust means 7, the valve 2
7. It is configured to control each of the mass flow controllers 28. For example, control of the halogen lamp 4 for maintaining the wafer W at a predetermined temperature, gas supply sources 23 and 2
The combination of the gases from 4, 25 and 26 and the setting of the respective flow ratios to a predetermined flow ratio are controlled by the controller 33. The main part of the ashing apparatus 1 for performing the ashing method according to the present embodiment has the above-described configuration. Next, the ashing method according to the present embodiment will be described. In the present embodiment, a process for ashing a resist film on a silicon wafer after P ion implantation will be described as an example. First, the halogen lamp 4 is turned on in advance, and the atmosphere in the processing container 2 is raised to a predetermined temperature. Next, the wafer W is loaded into the processing container 2 from a loading / unloading port (not shown) such as a gate valve formed on a side portion of the processing container 2, placed on the support pins 10, and set by the halogen lamp 4. , For example, to 120 ° C. Next, a predetermined mixed gas is supplied to the supply pipe 21 from the processing gas supply source. In the present embodiment, first mixed gas of N ₂ and H ₂ as a mixed gas (hereinafter, referred to as "FG") ratio of the 300 sccm (N ₂ is 291sccm, H ₂ is 9 sccm: flow ratio of H ₂ in FG Is 3
%), O ₂ 2000 sccm, CF ₄ gas 50 sccc
m. The pressure in the processing vessel 2 at that time is
It was set to 1.5 Torr. As described above, a predetermined mixed gas is caused to flow through the supply pipe 21 and the high-frequency power supply 32 is operated to, for example,
This mixed gas is turned into plasma in the supply pipe 21 in the chamber 31 under the power of 0 W. Then, the plasma-converted mixed gas is uniformly supplied to the wafer W through the baffle body 13, and active species in the plasma-converted mixed gas, for example, oxygen radicals, fluorine radicals, and the like are transferred to the resist film on the wafer W. Ashing is removed. More specifically, for the hard layer in the resist film, F (fluorine) removes C of the P—C—O-based compound and H (hydrogen) replaces P of the P—O-based compound. Remove. In this embodiment, since the above-mentioned mixed gas of FG, O ₂ and CF ₄ gas is used as the mixed gas, a higher ashing rate than the conventional one can be realized. Incidentally, as a result of flowing for 60 seconds, a high ashing rate of 550 Å / min was obtained for the resist film on the silicon wafer after the P ion implantation. When the result is compared with the prior art, FIG.
It becomes like the graph shown in. The graph of FIG. 2 shows the same wafer temperature (120
C) and the same time (60 seconds), and shows the relationship between the gas type and the ashing rate when the ashing process is performed by changing only the gas type. However, regarding the gas flow rate, O ₂ + FG means that O ₂ is 2000 sccm and FG is 10
Is 00sccm, O ₂ + CF ₄ gas, O ₂ 200
At 0 sccm, CF ₄ is 150 sccm. According to this, the gas species is O ₂ + FG,
In the case of performing ashing using O ₂ + CF ₄ gas, a low ashing rate of 100 Å / min or less can be obtained for a resist film on a silicon wafer after P ion implantation. A high ashing rate of 550 Å / min is obtained with O ₂ + CF ₄ gas + FG which is a gas type. Therefore, it can be confirmed that the ashing rate is higher than the conventional one. By the way, the ashing process was performed on the resist film not subjected to the ion implantation process under the same conditions as those in the graph of FIG. 2, and the result shown in the graph of FIG. 3 was obtained. . According to this, O ₂ + C
In the case of F ₄ gas, an extremely high ashing rate of 7000 angstroms / minute is shown. However, if the ashing rate is abnormally high, SiO ₂ which is a silicon oxide film as a base is also etched. It is not practical. In this regard, in the case of O ₂ + CF ₄ gas + FG as the mixed gas according to the present embodiment, an easy-to-use ashing rate of about 1400 Å / min is shown. Therefore, from this characteristic, even if ions such as P ions are not implanted into the soft layer portion inside the hard layer of the resist film, if the ashing process is continued with the same gas type as it is, the underlying layer is cut off. It won't. Therefore, an extremely high-speed and appropriate ashing process can be performed as a whole on a resist film into which ions such as P ions have been implanted. Of course, after the hard layer is removed, the gas may be switched by the control device 33 and the O ₂ + FG gas may be turned into plasma to perform the ashing process. When the wafer W is further heated, for example,
If the temperature exceeds 26 ° C., the inside soft layer portion may expand and the pumping phenomenon described above may occur. Therefore, the wafer W is not removed until the hard layer portion is removed.
After the ashing is performed with O ₂ + CF ₄ gas + FG of the plasma gas mixture and the hard layer is removed while maintaining the temperature not to exceed 126 ° C., the temperature of the wafer W is heated to, for example, 300 ° C. Ashing,
The ashing rate of the soft layer portion can be improved, and an extremely high speed ashing process can be performed as a whole. The determination of the removal of the hard layer is made in advance by confirming the time until the removal using a dummy wafer.
In actual processing, time control based on the time may be performed. Further, since the wafer temperature during ashing changes after the hard layer is removed, the removal of the hard layer can be detected by constantly monitoring the wafer temperature. The oxide film (SiO ₂ ) shown in FIG.
Ion implantation polysilicon (D-Poly) on 51
For example, when an etching process is performed on a pattern line with respect to the pattern line 52, a sidewall 54, which is a carbon-based compound, may remain on the line 53 as shown in FIG. 4 and 5, reference numeral 55 denotes a resist film. If the next processing is carried out while leaving the side walls 54 as they are, the yield is immediately lowered, which is not preferable. Therefore, it is desired to remove the sidewalls 54 by some method. However, the conventional ashing method cannot remove the sidewalls 54. However, as in the above embodiment, O ₂ +
When the resist film 55 was ashed using CF ₄ gas and FG, the side wall 54 could be removed as shown in FIG. This is presumably because F (fluorine) removed carbon in the sidewall 54. Therefore, the ashing method according to the present embodiment can remove not only the resist film but also the sidewalls generated after the etching process, so that the yield can be improved as compared with the conventional method. Further, as described above, the ashing method according to the present embodiment can remove even the sidewalls.
The inventors changed the flow rate ratio between CF ₄ gas and FG in O ₂ + CF ₄ gas + FG to change the silicon oxide film (SiO ₂ ).
The etching characteristics (depth of etching) were examined. Other conditions at this time were the same as those in the above embodiment, and the flow rate of O ₂ was fixed at 2000 sccm. The ashing time was 13 minutes. As a result, first, when the FG is fixed at 300 sccm and the flow rate of the CF4 gas is increased every 50 sccm from 0 to 150 sccm, the wafer temperature becomes 2
In both cases of 70 ° C. and 140 ° C., the etching was hardly performed up to 50 sccm, but the etching started rapidly when it exceeded 50 sccm.
Therefore, if the ashing process is performed while the flow rate of the CF ₄ gas is suppressed to 1/6 or less of FG, the silicon oxide film (SiO ₂ ) as the base is not etched. On the other hand, when the flow rate of the CF ₄ gas is
When the flow rate of FG was changed while keeping the value of m, the result shown in the graph of FIG. 8 was obtained. If the FG is not mixed, the silicon oxide film (SiO ₂ ) is severely etched, but the etching is suppressed as the flow rate of the FG is increased. When the FG is around 150 sccm, the wafer temperature is either 270 ° C. or 140 ° C. Also, it can be confirmed that the etching characteristics are greatly reduced. Therefore, FG
Is confirmed that there is a suppression function etching with CF4 gas, in particular, 3 times the CF ₄ gas, if the flow rate of CF ₄ gas in other words performed suppressed by ashing to 1/3 or less of the FG, Silicon oxide film (SiO 2)
₂ ) Etching can be greatly suppressed. As described above, if ashing is performed in a plasma atmosphere using O ₂ + CF ₄ gas + FG gas, P
Ashing of the resist film after the ion implantation process can be performed at high speed, and the sidewalls can be removed. In addition, by appropriately changing the ratio of CF ₄ gas to FG, an underlying silicon oxide film (SiO ₂ )
Since the etching characteristics can be controlled, it is possible to perform an ashing process in which the underlying silicon oxide film (SiO ₂ ) is not etched while the high-speed ashing rate is secured. The FG used in the above embodiment, that is, N ₂
The mixture gas of H ₂ and H ₂ was a gas having a flow rate ratio of H ₂ occupying 3%, but is not limited to this ratio, and may be used by appropriately changing the flow rate ratio of H _2. Good. However,
In consideration of gas handling rules, actual handling easiness, and safety, it is easy to use a H ₂ flow rate ratio of 3% or less. According to the ashing method of the present invention, P
The resist film after ion implantation of (phosphorus), As (arsenic), B (boron) or the like can be removed by ashing at a high rate. In addition, at least four types of gas components including at least the F-based gas, O ₂ , N ₂ and H ₂ are selected as the mixed gas, and the ratio of the F-based gas to the mixed gas of (N ₂ and H ₂ ) is determined. By reducing the flow rate ratio, it is possible to remove the hard layer on the substrate surface and also remove the sidewalls, eliminating the conventional secondary processing such as removal of the residue due to the pumping phenomenon, thereby improving the ashing rate. And the suppression of etching can be balanced to improve the ashing processing ability. Further, in the second mixed gas, an F-based gas
By relatively reducing the ratio of FG gas to
Reducing the ratio of FG gas to F-based gas relatively
The etching characteristics of the underlying silicon oxide film
Can be controlled, so the high-speed ashing
The underlying silicon oxide film is etched while securing
Ashing process can be performed .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing an outline of a configuration of an ashing apparatus used for performing an ashing method according to an embodiment of the present invention. FIG. 2 is a graph showing a comparison of an ashing rate of a resist film after phosphorus ion implantation according to an embodiment of the present invention with another ashing method. FIG. 3 is a graph showing a comparison between an ashing method according to an embodiment of the present invention and an ashing rate for a resist film to which no ion implantation has been performed, according to another embodiment; FIG. 4 is an explanatory sectional view showing a state of a surface of a wafer before an etching process. FIG. 5 is an explanatory cross-sectional view showing a state of a surface of a wafer on which a sidewall is formed after completion of an etching process. FIG. 6 is an explanatory sectional view showing a state of the surface of the wafer after the ashing method according to the embodiment of the present invention is performed. FIG. 7 shows an ashing method according to an embodiment of the present invention, in which the flow rate of a mixed gas (FG) of N ₂ and H ₂ is fixed and the flow rate of a CF ₄ gas is changed, and etching of a silicon oxide film is performed. It is a graph which shows a characteristic. FIG. 8 shows an ashing method according to an embodiment of the present invention, in which the flow rate of CF ₄ gas is fixed and the flow rate of a mixed gas (FG) of N ₂ and H ₂ is changed to etch the silicon oxide film. It is a graph which shows a characteristic. DESCRIPTION OF SYMBOLS 1 Ashing device 2 Processing vessel 4 Halogen lamp 7 Exhaust means 8 Exhaust pipe 12 Temperature detector 13 Baffle body 21 Supply pipes 23, 24, 25, 26 Gas supply source 27 Valve 28 Mass flow controller 31 Chamber 32 High frequency power supply 33 Control device W Wafer

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroshi Araki 650 Mitsuzawa, Hosaka-cho, Nirasaki, Yamanashi Prefecture Tokyo Electron Kyushu K.K. Lectron Kyushu Co., Ltd. Process Technology Center (56) References JP-A-5-184977 (JP, A) JP-A-64-48418 (JP, A) JP-A-5-267246 (JP, A) 2-77125 (JP, A) JP-A-4-180652 (JP, A) JP-A-6-177088 (JP, A) JP-A-8-69896 (JP, A) JP-A-1-106433 (JP, A) A) Japanese Utility Model Hei 2-24535 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 G03F 7/42 H01L 21/027 H05H 1/46

Claims (1)

(57) [Claim 1] A gas mixture of a plurality of gases is turned into a plasma, and a predetermined film of a substrate to be processed is heated while maintaining the inside of the processing vessel at a predetermined pressure reduction degree. In the ashing method under a plasma atmosphere, at least until the substrate to be processed exceeds a predetermined temperature, an FG gas obtained by mixing at least an F-based gas , O ₂ , N ₂ and H ₂
And removing a hard layer and / or a side wall on the surface of the film by using a first mixed gas containing: a ratio of the flow rate of the F-based gas to the flow rate of the FG gas as a predetermined flow ratio; After the temperature exceeds the predetermined temperature, the temperature of the substrate to be processed is further increased and the FG gas at the predetermined flow ratio is further increased.
Each step of ashing processing the soft layer inside the hard layer using a second mixed gas in which the ratio of the F-based gas to the gas is reduced , wherein the mixing corresponding to a predetermined temperature of the substrate to be processed is performed. and selection of the gas, by controlling the flow rate ratio before Symbol mixed-gas, the ashing method which comprises suppressing the etching of underlying the substrate to be treated.