JP3629391B2 - Oxide film forming method and oxide film forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming an oxide film such as a gate oxide film of a semiconductor device and an oxide film forming apparatus, and more particularly to a method for forming a gate oxide film of a thin film transistor (TFT) used in a liquid crystal display device and the gate oxide film thereof. The present invention relates to a forming apparatus.
[0002]
[Prior art]
A silicon oxide film, such as a gate oxide film, formed on a TFT or the like of an active liquid crystal display device is generally formed by plasma CVD (Chemical Vapor Deposition). An oxide or the like accumulates on the inner wall of the chamber used for forming the gate oxide film during the film formation, and contaminates the thin film transistor that is the stack. For this reason, for example, the cumulative oxide film thickness is 600 nm, and when the cumulative film thickness is reached, a self-cleaning method is used in which the inside of the chamber is cleaned with a gas such as a fluorine compound. After this self-cleaning, there is usually provided a step of trially forming an oxide film by chamber seasoning, which can be said to be a break-in operation immediately after cleaning. By this self-cleaning, a clean TFT without contamination is formed.
[0003]
[Problems to be solved by the invention]
However, when an oxide film is formed by plasma CVD after self-cleaning, there is a phenomenon that the thickness of the oxide film becomes abnormally thin even after self-seasoning. For example, since the thickness of the gate oxide film of the TFT is set to 75 nm, the self-cleaning is usually performed after the eighth and fifteenth (or sixteenth) film formation is completed with 20 sheets as one lot. carry out. FIG. 15 is a diagram showing the transition of the thickness of the gate oxide film when self-cleaning is performed after the eighth and fifteenth films are formed (the average value of this lot is standardized to 100%). Is displayed). In FIG. 15, the ninth and sixteenth films are abnormally thin. When self-cleaning is performed for each sheet in order to prevent such a large change in film thickness, the film thickness is always kept at a thin film thickness in FIG. However, since the total processing time of the chamber seasoning process and the self-cleaning is long, the film formation time of the oxide film becomes extremely long and cannot be applied to an actual manufacturing method.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide an oxide film forming method and an oxide film forming apparatus that prevent a film thickness variation by suppressing a decrease in the film thickness of the oxide film after self-cleaning and prevent a decrease in yield. There is.
[0005]
[Means for Solving the Problems]
The method for forming an oxide film according to claim 1 is provided with a chamber and a partition that can be freely opened and closed, and is provided with the chamber and the partial pressure of the inert gas is maintained at a positive pressure with respect to the chamber. An oxide film forming method for forming an oxide film by plasma CVD on an object to be stacked that has been transferred into the chamber using an apparatus having a transfer chamber, wherein the fluorine compound is removed while exhausting. After the self-cleaning step of self -cleaning the chamber using the gas containing , and after the self-cleaning step, the film formation trial time of the oxide film in the chamber seasoning is excluded from the time addition, and a predetermined film formation non-execution time is taken. and a oxide film forming step for forming a film of the oxide film after, within the predetermined deposition non-execution time, with respect to the object to be laminate, and said chamber, before Between the transfer chamber, and repeating several times back and forth operation of the forward and return accompanied by opening and closing of the partition wall.
[0006]
According to this method, since the concentration of each component in the gas used for self-cleaning is reduced by exhaust, the self-cleaning residual gas, particularly fluorine, affects the thickness of the oxide film formed by the plasma CVD method. The impact is reduced. As a result, it is possible to suppress a decrease in the thickness of the oxide film formed immediately after self-cleaning and to limit the variation in the thickness of the oxide film.
The inert gas sent to the transfer chamber is originally used to maintain a positive pressure with respect to the chamber so that no toxic gas flows from the chamber. When the stack is reciprocated while opening and closing the partition walls, the same effect as purging with an inert gas can be obtained, and the gas used for self-cleaning can be reduced. Therefore, it is possible to prevent a reduction in the thickness of the oxide film formed on several sheets immediately after self-cleaning.
[0007]
The oxide film forming method of the present invention is preferably applied to, for example, a gate oxide film of a semiconductor device where the thickness accuracy of the oxide film is important. In particular, a gate oxide film formed on a TFT of an active matrix type liquid crystal display device, which is an oxide film having a large area, is desirable. These oxide films are usually formed with high accuracy to a very thin thickness, for example, a thickness of 75 nm. Therefore, if the absolute value of the variation range of the thickness is large, the relative variation becomes very large, resulting in a gate oxide film that cannot be used practically, thereby reducing the yield. As described above, according to the present invention, it is possible to prevent a decrease in yield by providing a film non-execution time immediately after self-cleaning and implementing various methods for reducing the self-cleaning gas while exhausting. Become.
[0008]
According to a second aspect of the present invention, there is provided the oxide film forming method according to the first aspect, further comprising a mass analyzer capable of outputting the frequency of detection of the components in the chamber, and monitoring the frequency of detection of the gas components in the chamber. However, the end time of the film formation non-execution time is determined.
[0009]
Since the composition of the gas component in the chamber can be known online by the above method, it becomes possible to form an oxide film by plasma CVD after reliably reducing the gas used for self-cleaning. .
[0010]
According to a third aspect of the present invention, in the method for forming an oxide film according to the first or second aspect, a gas purge with an inert gas is performed within a film formation non-execution time.
[0011]
As a result, since the gas used for self-cleaning and the compound of the gas are driven out by the inert gas and decrease, the influence on the film thickness of the oxide film such as fluorine in the gas used for self-cleaning is reduced. As the inert gas, a gas such as nitrogen, oxygen, helium, or argon can be used.
[0012]
According to a fourth aspect of the present invention, in the method for forming an oxide film according to the first or second aspect, the intermittent purge is performed in which the inert gas is repeatedly turned on and off within the film formation non-execution time.
[0013]
By repeatedly turning on and off the inert gas purge, the gas adsorbed on the inner wall of the chamber can be effectively expelled, and the adverse effect of these gases during the formation of the oxide film can be limited.
[0014]
In the oxide film forming method of claim 5, in the oxide film forming method of claim 1 or 2, the plasma discharge is repeatedly turned on and off while performing the gas purge within the film formation non-execution time.
[0015]
By the above method, the gas adsorbed on the side wall of the chamber can be desorbed and exhausted. As a result, the gas used for self-cleaning can be reduced to a level that does not cause a problem, and it is possible to prevent a reduction in the thickness of several oxide films formed immediately after self-cleaning.
[0018]
The oxide film forming method according to claim 6 is a method of forming an oxide film by plasma CVD on an object to be stacked that has been transferred into a chamber to which a mass analyzer is attached. After the chamber was self-cleaned using a gas containing, in the detection frequency measurement by the mass analyzer, the detection frequency of the mass number 19 component decreased to a predetermined multiple of the detection frequency of the mass number 36 component Later, an oxide film is formed.
[0019]
In the above, the component having a mass number of 19 is fluorine. The component of mass number 36 is unknown, but it can be used as a reference concentration because the time variation is small. The predetermined multiple is, for example, preferably 50 times, 40 times to suppress a decrease in film thickness after self-cleaning, and 30 times to further suppress film thickness variation. Further, if the evacuation is continued, an inert gas purge, an intermittent plasma discharge while performing the inert gas purge, and the like can be performed. According to the above method, the thickness of the oxide film formed immediately after self-cleaning can be reduced to a level that does not cause a problem by etching the oxide film in the oxide film forming step to form silicon fluoride. Can be suppressed.
[0020]
An apparatus for forming an oxide film according to claim 7 is an apparatus used in a method for forming an oxide film on a transported stack, and a chamber for forming an oxide film on the stack, and a chamber A film forming means for forming an oxide film on the stack that has been transported inside, an exhaust means for exhausting from the chamber, and a chamber for specifying the mass number of the component in the chamber and outputting the detection frequency of the component A mass analyzer attached to the mass spectrometer, and a detection frequency of the component having a mass number of 19 output by the mass analyzer does not form an oxide film while exceeding a predetermined multiple of the detection frequency of the component having a mass number of 36, And control means for forming an oxide film after a predetermined multiple or less.
[0021]
With this configuration, since the film formation is not performed while the fluorine concentration is high, the phenomenon that the oxide film becomes abnormally thin can be avoided, and the yield can be improved. The predetermined multiple is desirably 50 times, 40 times to suppress a decrease in film thickness after self-cleaning, and 30 times to further suppress film thickness fluctuation.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0023]
(Embodiment 1)
The present embodiment is an oxide film forming method in which a gate oxide film of a TFT of an active matrix liquid crystal display device is formed and a film formation non-execution time is increased while exhausting. First, as shown in FIG. 1, on the surface of the glass substrate 1, as a base film 2, for example, a SiN film, a silicon oxide film, or a two-layer film made of a silicon oxide film and a SiN film is formed by plasma CVD to a thickness of about 200 nm. Form to thickness. Thereafter, as shown in FIG. 1, an amorphous silicon film 3 is formed to a thickness of 50 nm by a low pressure CVD method or a plasma CVD method, and then the amorphous silicon film is crystallized. As a crystallization method, for example, laser irradiation with an excimer laser can be used. Next, as shown in FIG. 2, the crystallized polysilicon film 3 is patterned into a channel shape. Next, as shown in FIG. 3, a gate oxide film 4 is formed on the polysilicon film to a thickness of 75 nm by plasma CVD.
[0024]
In the formation of the gate oxide film 4, self-cleaning using NF ₃ gas was performed every 8 sheets. After forming an oxide film in the chamber seasoning after self-cleaning, the pump exhaust state was set to 12 minutes. After that, the stack in the state shown in FIG. 2 was introduced into the film forming chamber, and the gate oxide film 4 was formed as shown in FIG.
[0025]
FIG. 4 is a diagram showing the thickness of each gate oxide film in a lot (19 sheets) according to the film formation order. In FIG. 4, the thickness of the gate oxide film of the prior art that does not take the film formation non-execution period is shown for comparison, but the variation in the thickness of the gate oxide film in the lot is -6% to + 4%. Is suppressed. In addition, by performing the exhaust for 4 minutes, the film thickness of the oxide film immediately after self-cleaning, which has been reduced to 11%, is suppressed to about -7%.
[0026]
After forming the gate oxide film, a gate electrode is formed by sputtering a metal film such as an Al alloy, Cr, or Ta, and patterning and etching are performed to form the gate electrode 8 as shown in FIG. Thereafter, source and drain regions 5 and 6 and a channel region 7 were formed by ion implantation, and an interlayer insulating film 9 was formed by plasma CVD as shown in FIG. Next, contact holes were opened in the interlayer insulating film 9 to form pad contacts 11 and 12, and then source and drain wiring films were formed and patterned into wiring shapes 13 and 14. Further, as shown in FIG. 7, a SiN film as the passivation film 15 was formed by plasma CVD.
[0027]
As is recognized in this embodiment, by reducing the film formation non-execution time to 12 minutes while evacuating, reduction of the oxide film thickness in the formation of several oxide films immediately after self-cleaning is greatly suppressed. . As a result, the yield in the TFT manufacturing process can be improved.
[0028]
(Embodiment 2)
As in the first embodiment, in the TFT gate oxide film forming process, self-cleaning using NF ₃ gas in the chamber was performed every time eight films were formed. Thereafter, in this embodiment, a nitrogen gas purge for 360 seconds and an oxygen gas purge for 720 seconds are performed with the chamber seasoning in between. FIG. 8 is a schematic configuration diagram of the oxide film forming apparatus used in the present embodiment. In the present embodiment, the mass analyzer 24 is attached to the chamber 23, and the film is formed while monitoring the detection frequency of the gas component in the chamber 23. Further, the control means 25 that enables film formation only when the detection frequency of fluorine having a mass number of 19 does not exceed 40 times the detection frequency of components having a mass number of 36 is provided with a mass analyzer 24 and a plasma CVD film formation means 22. Between. The oxide film is formed on a stack 21 in which a predetermined stack is stacked on a substrate, and the chamber is evacuated by an exhaust pump 26.
[0029]
FIG. 9 is a diagram showing the transition of the component detection frequency (the number of counts per unit time) in a conventional film forming method for comparison. As can be seen from FIG. 9, the conventional film formation non-execution time is 60 seconds after the chamber seasoning. FIG. 10 is a diagram showing the transition of the component detection frequency in the present embodiment. 9 and 10, the mass number 19 is fluorine gas, and the mass number 85 is silicon fluoride (SiF ₃ ). The components of mass numbers 33 and 36 are unknown. Since the component of the mass number 36 maintains a substantially constant value except during chamber seasoning, it can be used as a reference value for relative comparison. FIG. 11 is a diagram showing the thickness of the oxide film in each substrate No that is in the film formation order No. The average film thickness value of the lot is normalized and displayed as 100%. By purging with the nitrogen gas and oxygen gas described above, the fluctuation of the gate oxide film was suppressed very well, and the inter-substrate variation could be within the range of ± 3%. When the thicknesses of the gate oxide films of the substrates Nos. 7 to 12 in FIG. 11 and the detection frequencies of the components in FIGS. 9 and 10 are associated with each other, the fluorine detection frequency has a great influence on the thickness of the oxide film. I understand. After the self-cleaning, except for the chamber seasoning time, if the oxide detection film is formed after setting the fluorine detection frequency to 50 times or less the detection frequency of the mass number 36 component, the decrease in the film thickness is suppressed. be able to. More preferably, after the detection frequency of fluorine is set to 40 times or less, more preferably 30 times or less, the detection frequency of the component having a mass number of 36, an oxide film is formed. As a result, it becomes possible to produce a gate oxide film having a small film thickness variation as a whole. In addition, the ratio of the detection frequency of the component of mass number 19 and the component of mass number 36 can be considered as the molar ratio.
[0030]
(Embodiment 3)
Also in this embodiment, a TFT gate oxide film of a TFT panel used in a liquid crystal display device was produced. Except for changing the oxygen gas purge time, the same steps as in the first embodiment are used. In this embodiment, chamber seasoning is performed after self-cleaning, and the time of oxygen gas purging performed thereafter is changed from 360 seconds to 1080 seconds to form a gate oxide film. FIG. 12 shows the thickness of the gate oxide film of each substrate No in each lot. Further, FIG. 13 shows the difference between the maximum value and the minimum value of the gate oxide film in each lot, and it can be seen that the difference between the maximum value and the minimum value decreases as the purge time increases. In particular, it can be seen that when the gas purge time is extended from 600 seconds to 1080 seconds, the difference between the maximum value and the minimum value is greatly reduced. In particular, it can be seen that the above difference can be reduced to 10 nm or less by setting the gas purge time to 900 seconds or more. In addition, this gas purge time means the total of the two gas purge times, when performing two gas purges with a chamber seasoning in between.
[0031]
(Embodiment 4)
Also in this embodiment, a TFT gate oxide film of a TFT panel used in a liquid crystal display device was produced. When the first gate oxide film was formed immediately after self-cleaning, the film was reciprocated three times between the film formation chamber and the transfer chamber (transfer chamber). The time required for this round trip is about 10 minutes. Other steps are the same as those in the first embodiment. The film thickness of the gate oxide film of each substrate No is shown in FIG. The thickness of each gate oxide film in the present embodiment is within ± 3%. From this result, reciprocating between the film forming chamber and the transfer chamber is very effective in suppressing the film thickness variation of the gate oxide film in the lot by suppressing the decrease in the film thickness of the oxide film after self-cleaning. Can be confirmed.
[0032]
While the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.
[0033]
【The invention's effect】
By using the manufacturing method of the present invention, an oxide film such as a gate oxide film that requires highly accurate film thickness control can be formed using a plasma CVD method. This manufacturing method can be easily implemented using existing equipment, and the film formation time is extended only for 4 to 10 minutes only in the film formation immediately after self-cleaning, and the film formation is performed otherwise. The time will not be extended. As a result, it is possible to easily suppress the film thickness variation of the gate oxide film and the like, which can contribute to the improvement of the yield.
[Brief description of the drawings]
1 is a cross-sectional view of a stage in which a base film and an amorphous silicon film are formed over a glass substrate in Embodiment Mode 1. FIG.
FIG. 2 is a cross-sectional view of a stage where an amorphous silicon film is crystallized and patterned into a transistor with respect to the state of FIG.
3 is a cross-sectional view of a stage where a gate oxide film is formed in the state of FIG.
4 is a diagram showing a film thickness of a gate oxide film of a TFT according to the first embodiment in comparison with a conventional example with a lot average value being 100%. FIG.
5 is a cross-sectional view of a stage in which a gate electrode is formed in the state of FIG. 3 and the source region and the drain region are doped.
6 is a cross-sectional view at a stage where an interlayer insulating film is formed in the state of FIG. 5;
7 is a cross-sectional view at a stage where a source wiring and a drain wiring are formed in the state of FIG. 6 and a passivation film is formed. FIG.
8 is a schematic configuration diagram of an oxide film forming apparatus used in Embodiment 2. FIG.
FIG. 9 is a diagram showing a change in concentration of a gas component in a chamber in a conventional example.
FIG. 10 is a diagram showing a change in concentration of a gas component in a chamber in the second embodiment.
11 is a diagram showing the thickness of a gate oxide film of a TFT according to a second embodiment in comparison with a conventional example with a lot average value being 100%. FIG.
12 is a diagram showing the thickness of a gate oxide film of a TFT according to Embodiment 3 for each purge time with each lot average value being 100%. FIG.
13 is a diagram showing the influence of the gas purge time on the difference between the maximum value and the minimum value of the gate oxide film of each lot shown in FIG.
14 is a diagram showing the thickness of a gate oxide film of a TFT according to a fourth embodiment in comparison with a conventional example with a lot average value being 100%. FIG.
FIG. 15 is a diagram showing the thickness of a gate oxide film of a conventional TFT with a lot average value of 100%.
[Explanation of symbols]
1 glass substrate, 2 base film, 3 silicon film, 4 gate oxide film, 5, 6 source, drain region, 7 channel region, 8 gate electrode, 9 interlayer insulating film, 11, 12 pad contact, 13, 14 source wiring, Gate wiring, 15 passivation film, 21 stack, 22 plasma CVD apparatus, 23 chamber, 24 mass analyzer, 25 control means, 26 exhaust pump.

Claims (7)

Using a device having a chamber and a transfer chamber provided attached to the chamber and separated by an openable / closable partition wall in which the partial pressure of the inert gas is kept positive with respect to the chamber And an oxide film forming method for forming an oxide film by plasma CVD on an object to be stacked that has been transferred into the chamber,
A self-cleaning step of self -cleaning the chamber using a gas containing a fluorine compound while exhausting;
After the self-cleaning process, to the exclusion of deposition trial time of oxide film in chamber seasoning from the temporal addition, after taking a predetermined deposition non-execution time, the oxide film forming step for forming a film of the oxide film And
Within the predetermined film formation non-execution time, the reciprocating operation of moving back and forth between the chamber and the transfer chamber with opening and closing of the partition wall is repeated several times with respect to the stack. Film forming method. A mass analyzer capable of outputting a detection frequency of a component in the chamber is provided in the chamber, and the end time of the film formation non-execution time is determined while monitoring a detection frequency of a gas component in the chamber. Item 2. The method for forming an oxide film according to Item 1. The oxide film forming method according to claim 1, wherein a gas purge with an inert gas is performed within the film formation non-execution time. The oxide film forming method according to claim 1, wherein the inert gas purge is repeatedly turned on and off within the film formation non-execution time. The method for forming an oxide film according to claim 1, wherein the plasma discharge is repeatedly turned on and off while performing a gas purge within the film formation non-execution time. An oxide film forming method for forming an oxide film by plasma CVD on an object to be stacked that has been transferred into a chamber to which a mass analyzer is attached,
After self-cleaning the chamber using a gas containing a fluorine compound while exhausting, in the detection frequency measurement by the mass analyzer, the detection frequency of the mass number 19 component is the detection frequency of the mass number 36 component. A method of forming an oxide film, wherein the oxide film is formed after being lowered to a predetermined multiple or less. An oxide film forming apparatus used in a method of forming an oxide film on a laminate to be conveyed,
A chamber for forming an oxide film on the stack;
A film forming means for forming an oxide film on the object to be stacked that has been transferred into the chamber;
Exhaust means for exhausting from the chamber;
A mass analyzer attached to the chamber for identifying the mass number of the component in the chamber and outputting the detection frequency of the component;
While the detection frequency of the mass number 19 component output by the mass analyzer exceeds a predetermined multiple of the detection frequency of the mass number 36 component, the oxide film is not formed and becomes the predetermined multiple or less. And a control means for forming the oxide film.

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