JPH09223684A - Plasma processing equipment - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] The ashing rate commensurate with the oxygen supply amount cannot be obtained for a while immediately after the start of ashing, the ashing rate is lowered, and stable ashing treatment cannot be performed during that time. SOLUTION: The ashing device is provided with a plasma generation chamber 1.
1. An apparatus for introducing the oxygen radicals of the oxygen plasma P generated in 1 into the plasma processing chamber 13 below the ion trap 12 and ashing the semiconductor wafer W on the mounting table 14, and an aluminum oxide film layer on the surface of the ion trap 12. 1
2B is provided, and the aluminum oxide film layer 12 prevents the metal aluminum 12C therein from being oxidized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for plasma processing an object to be processed with oxygen plasma.

[0002]

2. Description of the Related Art As a conventional plasma processing apparatus of this type, for example, an etching apparatus and an ashing apparatus can be mentioned. The latter ashing device is, for example, a device for removing a mask made of an organic polymer material used when forming an integrated circuit on a semiconductor surface by ashing using oxygen plasma or the like. There are various types of ashing devices. In recent years, the ashing device tends to shift from a batch type to a single-wafer type in order to cope with a large number of small-lot production of semiconductor products and an increase in the size of an object to be processed such as a semiconductor wafer. As an example of the single-wafer ashing device, there is a down-flow type using an oxygen plasma.

The downflow type ashing device is
For example, the oxygen plasma generated in the upper plasma generation chamber is introduced into the lower plasma processing chamber, and the mask on the surface of the semiconductor wafer on the mounting table is removed in this plasma processing chamber. The plasma generation chamber and the plasma processing chamber are partitioned by a partition having a large number of passage holes generally called a trap plate, and the trap plate captures ions, so that only oxygen radicals necessary for plasma processing are passed through the passage hole to form a plasma. The mask is introduced into the processing chamber by a down flow, and the used mask remaining on the surface of the semiconductor wafer is efficiently ashed and removed by oxygen radicals. Also,
When the ashing is performed, the unmasked portion of the semiconductor wafer surface exposed to the plasma is damaged by the plasma. Therefore, after the ashing, for example, the semiconductor wafer surface is briefly exposed to an etching gas mainly containing a fluorocarbon gas. It is lightly etched (hereinafter referred to as "light etching").

By the way, the trap plate is made of high-purity aluminum having excellent conductivity in order to efficiently remove the ions in the plasma. The trap plate efficiently captures the ions generated in the plasma generation chamber, prevents the ions from entering the plasma processing chamber, and prevents damage to the semiconductor wafer due to ion bombardment and charging of the semiconductor wafer. I am doing it.

On the other hand, recently, various electric products such as personal computers and mobile phones have been developed, and the fields of use of semiconductor products are widespread, and the demand for semiconductor products is tight. In order to meet the demand, it is necessary to produce semiconductor products with higher quality and more efficiently. From such a point, it is extremely important to improve throughput in each processing step of semiconductor manufacturing.

[0006]

However, in the case of the conventional ashing apparatus, the ashing speed becomes higher than that immediately after the ashing starts and stable processing can be performed shortly after the ashing starts. Until then (the initial period of ashing), an ashing rate commensurate with the oxygen supply amount cannot be obtained, and there is a problem that the throughput is reduced accordingly. Although it is the initial period of ashing, the influence becomes larger as the diameter of the semiconductor wafer becomes larger and the degree of integration of the integrated circuit becomes higher.

The present invention has been made to solve the above problems, and provides a plasma processing apparatus capable of ensuring a plasma processing rate commensurate with the oxygen supply amount immediately after the start of plasma processing and increasing throughput. It is intended to be provided.

[0008]

As a result of various studies on the cause of the slow ashing speed immediately after the start of the ashing process, the present inventors have found that oxygen in the plasma generation chamber is kept from high-purity aluminum for a while immediately after the start of ashing. It was found that the ashing rate is slowed down because the amount of oxygen radicals that are consumed to oxidize the trap plate is suppressed, the amount of plasma generated is suppressed by the amount consumed, and the amount of oxygen radicals introduced into the plasma processing chamber decreases.

The present invention has been made based on the above findings, and the plasma processing apparatus according to claim 1 of the present invention comprises:
A plasma generation chamber that receives oxygen gas to generate oxygen plasma, a partition wall made of a conductive material that captures ion components in the oxygen plasma generated in this plasma generation chamber and allows oxygen radicals to pass through, and through this partition wall A plasma processing chamber connected to the plasma generation chamber, and a mounting table on which a target object to be plasma-processed by the oxygen radicals, which is disposed in the plasma processing chamber, is mounted. An oxide film of the conductive material is provided on the surface of the partition wall, and the conductive film inside is prevented from being oxidized by the oxide film.

A plasma processing apparatus according to a second aspect of the present invention is the plasma processing apparatus according to the first aspect, wherein the conductive material is aluminum.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the embodiments shown in FIGS. FIG. 1 is a view showing a cross section of an ashing device which is an embodiment of the plasma processing device of the present invention. The ashing device 10 of this embodiment is shown in FIG.
As shown in FIG. 3, it is composed of a plasma generation chamber 11 for generating oxygen plasma P, and a conductive material (for example, aluminum) that captures ion components in the oxygen plasma P generated in the plasma generation chamber 11 and allows oxygen radicals to pass through. A partition wall, that is, a trap plate 12, and a plasma processing chamber 13 connected to the plasma generation chamber 11 via the trap plate 12.
It is comprised including. In addition, the plasma processing chamber 13
Is provided with a mounting table 14 on which the semiconductor wafer W is mounted.
The photoresist film (not shown) made of an organic polymer substance on the surface of the semiconductor wafer W on the mounting table 14 is removed by ashing by the oxygen radicals introduced by the downflow from the plasma generation chamber 11 into the plasma processing chamber 13. I am doing it.

The plasma generating chamber 11 has a bowl-shaped portion 11A.
And a cylindrical portion 11B extending upward from the upper end of the spherical portion of the bowl-shaped portion 12A, and is made of, for example, quartz. A pair of upper and lower electrodes 16A and 16B are attached to the cylindrical portion 12B via a spacer 15 made of an insulating member. The upper electrode 16A is connected to a high frequency power supply 18 via a matching circuit 17, and the lower electrode 16B is grounded. Further, the gas supply pipe 19 is provided in the tubular portion 11B.
A gas supply source 20 is connected via the
An etching gas mainly consisting of oxygen gas or a fluorocarbon gas such as carbon tetrafluoride is supplied from zero. A flow rate adjuster 21 is arranged in the gas supply pipe 19, and the flow rate adjuster 21 adjusts the flow rate of the oxygen gas or the etching gas.

Further, the plasma processing chamber 13 connected to the plasma generating chamber 11 is formed in a flat cylindrical shape by, for example, aluminum whose surface is anodized. A transport path 22 for loading and unloading the semiconductor wafer W is connected to the side surface of the plasma processing chamber 13, and a gate valve 23 is attached to the loading / unloading port. Therefore, by opening the gate valve 23, the semiconductor wafer W is transferred from the transfer path 22 into the plasma processing chamber 13 under high vacuum.
After carrying in and ashing, the semiconductor wafer W is kept under high vacuum.
So that they can be carried out. Also, the plasma processing chamber 1
A vacuum exhaust device 25 is provided on the bottom surface of 3 through a vacuum exhaust pipe 24.
Are connected to each other, and the plasma generation chamber 11 and the plasma processing chamber 1 are connected.
The inside of 3 is evacuated to a predetermined degree of vacuum and the treated gas is discharged. Also, the plasma processing chamber 1
A mounting table 14 is arranged at the center of the bottom surface of the unit 3. In the center of the mounting table 14, for example, three elevating pins 14A are arranged so as to be able to ascend and descend, and the semiconductor wafer W is transferred while the three elevating pins 14A are raised, and after the semiconductor wafer W is received, it is raised and lowered. The pin 14A descends, and the semiconductor wafer W is passed through an electrostatic chuck (not shown) arranged on the surface of the mounting table 14.
Is electrostatically adsorbed on the mounting table 14.

By the way, the trap plate 12 constituting the essential part of the present invention is disposed between the plasma generation chamber 11 and the plasma processing chamber 12. This trap plate 12 is
As shown in FIGS. 1 and 2, a large number of passage holes 12A are formed so as to be evenly distributed, and the oxygen radicals generated in the plasma generation chamber 11 through the plurality of passage holes 12A are brought into the plasma processing chamber 13. It is introduced in a flow. The trap plate 12 is grounded.

On the surface of the trap plate 12, as shown exaggeratedly in FIG. 2, an aluminum oxide film layer 12B formed by oxidizing aluminum is formed, and the aluminum metal film 12 inside the aluminum oxide film layer 12B is formed.
The oxidation of C is prevented. That is, when the active oxygen in the oxygen plasma P is adsorbed by the trap plate 12 during ashing, oxygen atoms are generated in the aluminum oxide film layer 12B.
By this, diffusion to the inside is blocked, and oxygen adsorption on the surface of the trap plate 12 reaches a saturated state and is not adsorbed any more, preventing consumption of oxygen in the plasma generation chamber 11 and eventually stabilizing generation of oxygen radicals. The oxygen radicals can be supplied in a stable state without reducing the amount of oxygen radicals supplied to the plasma processing chamber 13. As a result of the oxygen atoms not diffusing inward, the aluminum metal 12C which is the base of the aluminum oxide film layer 12B
Can be prevented from being oxidized. The reason why the diffusion of oxygen atoms into the interior can be prevented in this way is that the crystal structure of the aluminum oxide film layer 12B formed by the oxidation treatment is much denser than that of the natural oxide film. It seems that

However, the adsorption of active oxygen to the trap plate 12 is unavoidable, and since the active oxygen is adsorbed to the trap plate 12 although it is slight immediately after the start of the treatment, the ashing rate is slightly lowered immediately after the start of ashing. Is recognized,
The amount of adsorption is negligible. Further, the thickness of the aluminum oxide film layer 12B may be formed so that oxygen atoms do not diffuse inside, and the thickness is preferably 300 to 10,000 angstroms. If the film thickness is less than 300 Å, diffusion of oxygen atoms may occur, and if the film thickness exceeds 10,000 Å, charges due to ions and charges are not preferable. Further, it has been found that when the aluminum oxide film layer 12B contains fluorine, the growth of the oxide film can be suppressed, which is more effective.

Incidentally, in considering the variation of the thickness of the aluminum oxide film layer and the adsorption behavior of oxygen, the thickness of the aluminum oxide film layer of the trap plate was measured by the XMA (?) Analysis method utilizing X-ray diffraction. And TDS
(Thermal desorption mass) analysis method was used to measure the number of molecules of gas such as oxygen gas adsorbed and desorbed in the aluminum oxide film layer. As a result, during light etching, the adsorbed oxygen during ashing is bonded to carbon in the etching gas by the plasma of an etching gas, for example, a fluorocarbon-based gas such as carbon tetrafluoride, as schematically shown in FIG. However, although carbon monoxide and the like are generated and consumed, the surface of the aluminum oxide film layer 12B is already in an oxygen saturated state and oxygen is not taken away, and the aluminum oxide film layer 12B hardly changes.

On the other hand, in the case of the conventional trap plate 12 'made of solid aluminum, a natural oxide film 12'B of aluminum is formed on the surface thereof as schematically shown in FIG. 3 (b). However, the natural oxide film layer is extremely thin, and the adsorbed oxygen atoms easily diffuse inside during ashing, and the oxygen atoms diffuse to the interface with the aluminum metal 12′C as indicated by the dashed arrow in the figure. Aluminum oxide film layer 1 by oxidizing aluminum metal 12'C at the interface
2′B gradually grows and the film thickness increases. Therefore, until the oxidation of the aluminum metal 12'C by the adsorbed oxygen is stopped, the oxygen atoms adsorbed on the surface of the trap plate 12'diffuse into the inside of the trap plate 12 ', and the oxygen on the surface is in an unsaturated state. Oxygen in the generation chamber 11 is gradually consumed, the amount of oxygen radicals generated is reduced by the amount of consumption, and the desired ashing rate corresponding to the amount of oxygen supplied cannot be obtained. However, if no further oxidation occurs, a stable ashing rate can be obtained. Therefore, a stable ashing speed can be obtained if a short time has passed immediately after the start of ashing. Further, as schematically shown in FIG. 3C, during light etching, oxygen atoms in the trap plate 12 ′ that are in the process of diffusion are consumed by carbon or the like which is a decomposition product in the plasma of the etching gas, and the light etching rate is increased. And the oxidation of the aluminum metal 12C is suppressed.

Next, the operation will be described. First, the inside of the plasma generation chamber 11 and the plasma processing chamber 13 is evacuated using the vacuum exhaust device 25 until a predetermined degree of vacuum is reached. After that, the gate valve 23 is opened, the semiconductor wafer W is loaded into the plasma processing chamber 13 from the transfer path 22 by using a transfer mechanism (not shown), and the semiconductor wafer W is mounted on the mounting table 14. Close. Next, the high frequency power supply 18 applies high frequency power to the electrode 16A via the matching circuit 17, and oxygen gas is supplied from the gas supply source 20. At this time, the gas supply amount is adjusted by the flow rate regulator 21.
Holds a predetermined gas flow rate.

When oxygen gas is supplied from the gas supply pipe 19 into the plasma generation chamber 11, the electrode 16A,
Oxygen plasma P is generated between 16B. At this time, since the vacuum exhaust device 25 is driven, the oxygen plasma P generated in the plasma generation chamber 11 flows downward as indicated by the arrow in FIG. At this time, the trap plate 12 is oxygen plasma P
Trap plate for trapping ions inside and trapping only oxygen radicals 1
The gas is passed through a large number of two through holes 12A into the plasma processing chamber 13. In the plasma processing chamber 13, oxygen radicals react with the organic polymer compound of the photoresist film of the semiconductor wafer W, and the photoresist film is removed by ashing. Gases such as carbon dioxide and water generated by ashing flow out from the vacuum exhaust pipe 24. After the ashing, the oxygen gas is switched to the etching gas, and the semiconductor wafer W is light-etched to remove the partial damage due to the ashing. After the series of processes is completed, the gate valve 23 is opened, the next semiconductor wafer W is replaced, and a new semiconductor wafer W is ashed.

By the way, during ashing, oxygen in the oxygen plasma P is adsorbed on the surface of the trap plate 12, but the aluminum oxide film layer 1 is formed on the surface of the trap plate 12.
Since 2B is applied, the adsorbed oxygen atoms are prevented from diffusing inward by the aluminum oxide film layer 12B, and the amount of adsorbed oxygen on the surface reaches a saturated state immediately, and there is no further adsorption, The amount of oxygen consumed in the oxygen plasma P other than that for ashing can be ignored, an ashing rate suitable for the supply amount of oxygen gas can be secured immediately after the start of ashing, and ashing should be performed with high throughput immediately after the start of ashing. You can Further, during light etching, a small amount of adsorbed oxygen adsorbed on the surface of the trap plate 12 is consumed by the etching gas, but not so much as to deprive the aluminum oxide film layer 12B.

[0022]

EXAMPLES Next, specific examples will be described with reference to FIGS. 4 is a table showing a comparison of changes in the thickness of the aluminum oxide film of the trap plate when ashing and light etching are performed using the trap plate shown in FIG. 2 and the conventional trap plate, and FIG. A table showing a comparison of changes in the ashing rate when ashing and light etching are repeated three times using the trap plate shown in FIG. 2 in Example 1, and FIG. 6 is a case where the new trap plate is aged. 6 is a table showing the results of analysis of adsorbed molecules adsorbed on the trap plate in order to investigate the cause of the slower ashing rate.

Example 1 In this example, an ashing apparatus equipped with a trap plate having a 500 Å aluminum oxide film on its surface was used, and a silicon wafer and a photoresist film were formed on the silicon wafer under the following conditions 1 to 3. The formed photoresist wafer was ashed, and the result is shown in FIG. In this example, under condition 1, ashing was performed 3 times with and without aging for 1 hour, and the variation of the ashing speed between them was observed. Under conditions 2 and 3, ashing or consistent processing was performed on 1 lot (L) to 3 L (75 sheets) of wafers, the processing was repeated 3 times, and changes in the ashing speed depending on the lot and the number of times of processing were observed. The results of these changes in ashing speed are shown in FIG. The ashing speed in FIG. 5 is an average value for each lot.

From the results showing the change of the aluminum oxide film in FIG. 4, the following facts were found. That is, in the case of condition 1,
The film thickness of the aluminum oxide film is slightly thicker than that when the plasma is not irradiated, but when the light etching under the conditions 2 and 3 is performed to perform the integrated processing, the film thickness of the aluminum oxide film is irradiated with the plasma. The aluminum oxide film layer is stable with almost no change as compared with the case where it is not.

Further, the following was found from the results showing the change in the ashing speed shown in FIG. That is, in the case of condition 1, a higher ashing speed was obtained when aging was performed than when aging was not performed. In order to investigate the cause of this, a trap plate which is not irradiated with plasma and a trap plate which is irradiated with plasma under the conditions 1 and 2 are sampled, and the adsorbed gas on the surface is analyzed by TDS. The result is shown in FIG. . According to the analysis results shown in FIG. 6, it was found that a large amount of water molecules were adsorbed in addition to oxygen molecules when the plasma was not irradiated, and the adsorbed water molecules were almost halved when the plasma was irradiated. . From this result, it is presumed that the adsorbed water molecules were desorbed from the trap plate by the plasma irradiation, and the ashing rate was increased. Further, according to the results shown in FIG. 5, even if the ashing process was repeated, the ashing speed hardly changed. When the light etching under the conditions 2 and 3 was performed to perform the consistent processing, the ashing rate was substantially constant regardless of the number of wafer lots, and a consistently high ashing rate was obtained immediately after the start of the ashing. It was also found that there was no difference in the ashing speed each time even if the treatment was repeated.

[Condition 1]: Only ashing with oxygen was performed under the following conditions. FIG. 3 shows changes in the ashing rate in the case of performing ashing without aging and in the case of performing ashing after aging for 1 hour. Object to be treated: Silicon wafer High frequency power: 700 W Degree of vacuum: 2 Torr Gas flow rate: 1500 sccm Treatment time: 5 hours [Condition 2]: Oxygen ashing and light etching were performed under the following conditions. Object to be treated: Silicon wafer ashing High frequency power: 700 W Vacuum degree: 2 Torr gas flow rate: 1500 sccm Processing time: 3 minutes Light etching High frequency power: 800 W Vacuum degree: 1 Torr gas flow rate: CF ₄ / O ₂ = 900 sccm / 100 sc
cm 2 Processing time: 10 seconds Total processing time: 5 hours [Condition 3]: Processing was performed under the same conditions as Condition 2 except that a photoresist wafer was used instead of the silicon wafer.

Example 2 In this example, an ashing device equipped with a trap plate having a 2030 angstrom aluminum oxide film on its surface was used, and the same treatment as in Example 1 was performed. The results are shown in FIG. . According to the results shown in FIG. 4, it was found that the same results as in Example 1 were obtained in this example.

Example 3 In this example, an ashing apparatus equipped with a trap plate having a 7050 angstrom aluminum oxide film on the surface was used and the same treatment as in Example 1 was performed. The results are shown in FIG. . According to the results shown in FIG. 4, it was found that the same results as in Example 1 were obtained in this example.

From the results of Examples 1 to 3, if the aluminum oxide film of the trap plate has a certain thickness (500 angstroms), a high ashing rate can be obtained immediately after the start of ashing regardless of the film thickness. It was found that stable ashing can be continued.

Comparative Example 1 In this comparative example, ashing was performed under conditions 1 to 3 using a trap plate made of pure aluminum, and the results are shown in FIGS. The following facts were found from the results showing the change in the aluminum oxide film in FIG. That is, in the case of condition 1, oxygen in the oxygen plasma is adsorbed on the surface of the trap plate and oxidation progresses, and the aluminum oxide film grows large. In other words, oxygen in the oxygen plasma is consumed for oxidizing the trap plate. Further, when the light etching under the conditions 2 and 3 is performed and the integrated treatment is performed, the growth of the aluminum oxide film is smaller than in the case of the condition 1, but the film thickness is significantly larger than those in Examples 1 to 3. It is growing and it consumes a lot of oxygen.

Further, the following was found from the results showing the change in the ashing speed shown in FIG. That is, in the case of condition 1, if ashing is performed without aging, oxygen is consumed for the oxidation of the trap plate as described above, and the ashing rate is significantly lower than in Examples 1 to 3. Also,
In order to obtain the ashing rate after aging for 1 hour in Examples 1 to 3, it is necessary to age for as long as 30 hours. In other words, the ashing rate corresponding to the oxygen gas supply amount cannot be obtained for 30 hours immediately after the ashing.

The present invention is not limited to the above-described embodiment, and it can be widely applied to an etching apparatus or the like as long as it is an apparatus for processing by using plasma of oxygen gas. The present invention is not limited to wafers and can be applied to LCD substrates and the like.

[0033]

According to the first and second aspects of the present invention, it is possible to secure a plasma processing rate commensurate with the oxygen supply amount immediately after the start of plasma processing, and it is possible to increase throughput. A plasma processing apparatus can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an ashing device which is an embodiment of a plasma processing device of the present invention.

FIG. 2 is an explanatory diagram for explaining a cross-sectional structure of a trap plate used in the ashing device shown in FIG.

FIG. 3 is an explanatory view showing the behavior of oxygen and fluorocarbon-based gas on the surface of the trap plate during the ashing process and the light etching, and FIG. 3 (a) shows the gas during the light etching on the surface of the trap plate of the present invention. FIG. 6B is a diagram showing the behavior, FIG. 6B is a diagram showing the behavior of oxygen gas during ashing on the surface of the conventional trap plate, and FIG. 7C is a diagram showing the behavior of gas during light etching on the surface of the trap plate. .

FIG. 4 is a table showing a comparison of changes in film thickness of an aluminum oxide film of the trap plate when ashing and light etching are performed using the trap plate shown in FIG. 2 and a conventional trap plate.

FIG. 5 is a table showing the results of analysis of adsorbed molecules adsorbed on the trap plate in order to investigate the reason why the ashing rate is slower than when the new trap plate is aged.

FIG. 6 is a table showing the results of analysis of adsorbed molecules adsorbed on the trap plate in order to investigate the reason why the ashing rate is slower than when the new trap plate is aged.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ashing apparatus (plasma processing apparatus) 11 Plasma generation chamber 12 Trap plate (partition wall) 12B Aluminum oxide film layer (oxide film) 12C Aluminum metal (conductive material) 13 Plasma processing chamber 14 Mounting table W Semiconductor wafer (processing target) P oxygen plasma

Claims (2)

[Claims] 1. A plasma generation chamber that receives oxygen gas to generate oxygen plasma, and a partition wall made of a conductive material that captures ionic components in the oxygen plasma generated in the plasma generation chamber and allows oxygen radicals to pass therethrough. A plasma provided with a plasma processing chamber connected to the plasma generation chamber via the partition wall, and a mounting table for mounting an object to be processed which is disposed in the plasma processing chamber and is plasma-processed by the oxygen radicals. In the processing apparatus, an oxide film of the conductive material is provided on the surface of the partition wall, and the conductive film inside is prevented from being oxidized by the oxide film. 2. The plasma processing apparatus according to claim 1, wherein the conductive material is aluminum.