JP3721760B2 - Induction plasma ashing processing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma ashing apparatus effective in the manufacture of semiconductor devices, liquid crystal display substrates, and the like.
[0002]
[Prior art]
As semiconductor devices become highly integrated, semiconductor wafers have larger diameters, and liquid crystal displays have a larger area, the demands on these processing equipment are becoming stricter, reducing equipment costs, improving throughput, and processing. Correspondence to the increase in area of objects and cleanliness are important issues.
[0003]
In a plasma etching processing apparatus, a thin film on a wafer on which a photoresist with a circuit pattern is previously baked as a mask is used to etch a pattern with ions or radicals in plasma of chlorine or fluorine gas. After the etching process, an ashing process, which is a step of removing the remaining photoresist by ashing with active oxygen radicals generated by oxygen plasma, is performed. In the ashing process, since the generation rate of oxygen radicals depends on the electric field strength, conventionally, a high-frequency capacitively coupled plasma source and a microwave plasma source that generate a strong electric field have been often used. Since these plasma sources generate an electric field of several tens to several hundreds V / m at the ion sheath portion of the plasma or the microwave introduction portion by a high frequency power source or a microwave source, radicals can be efficiently generated. On the other hand, the electric field in the azimuth direction generated by the high frequency inductively coupled plasma source along the antenna is about 5 V / m, and the generation rate of oxygen radicals is smaller than other plasma sources. Under the same pressure, the generation rate of oxygen radicals and oxygen positive ions increases as the electric field strength increases, but the dependency on the electric field strength differs, so the ratio between the oxygen radical generation rate and the oxygen ion generation rate. Is larger as the electric field strength in the plasma is smaller. In the high frequency inductively coupled plasma source, although the oxygen radical generation rate is lower than that of microwaves, etc., the number of ions is small, so there is less risk of charge-up damage, and the plasma source can be placed relatively close to the wafer. However, since the necessity for an ion decay structure is small, a structure with little loss of oxygen radicals is possible as a result.
[0004]
[Problems to be solved by the invention]
In the inductively coupled plasma ashing apparatus, the plasma source can be installed relatively close to the wafer by taking advantage of the small number of ions. Further, it is not necessary to isolate the plasma with a perforated plate for ion attenuation. On the other hand, the ashing rate distribution on the wafer is strongly affected by the plasma generation distribution and flow distribution. Therefore, when using a large-diameter wafer as used in recent years, the ashing rate distribution can be made uniform. It was difficult.
[0005]
An object of the present invention is to overcome the problem of ashing rate uniformity, which is a problem of the conventional induction plasma ashing apparatus as described above, on a workpiece having a large diameter of 300 mm and a semiconductor wafer.
[0006]
[Means for Solving the Problems]
The above objective is to optimize the distribution of radicals at the wafer position by using a high frequency inductively coupled plasma source as the plasma source and setting the discharge tube inner diameter, radical transport distance, stage diameter, etc. within a certain range of dimensions. It is realized by. Oxygen radicals generated by the induction antenna are transported to the position of the wafer located below by the flow of oxygen gas introduced from above, but at this time, oxygen radicals diffuse while having a specific diffusion coefficient, In addition, on the surface of the discharge tube, it is transported by the gas flow while being lost with a specific extinction coefficient. Therefore, by properly balancing the flow rate, diffusion, and loss on the discharge tube surface of the oxygen gas, which is the mother gas, a uniform and high ashing rate can be obtained within the wafer surface, and the low characteristic of induction plasma is low. Damage ashing is possible.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is not limited to the field of semiconductor device manufacturing, but can also be applied to liquid crystal display manufacturing and ashing of other objects to be processed. Here, plasma for manufacturing semiconductor devices is used. An embodiment will be described by taking an ashing processing apparatus as an example.
[0008]
FIG. 1 is a sectional view showing the structure of the ashing device of the present invention. The processing chamber 1 in the figure is an aluminum vacuum container, for example, and is connected to a vacuum exhaust means 2. A stage 4 for placing the semiconductor wafer 3 is installed in the processing chamber 1. The wafer loaded into the processing chamber from the transfer system 5 for loading and unloading the semiconductor wafer 3 as the object to be processed is carried and held on the stage by the push rod 6. The substantially disk-shaped stage 4 includes temperature adjusting means 7 such as a heater inside.
[0009]
On the other hand, an approximately cylindrical discharge tube 8 made of an insulator such as alumina or quartz is installed on the upper portion of the processing chamber 1 through a vacuum seal such as an O-ring. A coil-shaped antenna 9 is installed so as to surround the discharge tube. A high frequency power supply 11 is connected to the antenna 9 via an impedance matching unit 10. The frequency of the high-frequency power supply is not particularly limited, but is generally several hundred kHz to several tens of MHz, and the commercial frequency of 13.56 MHz is relatively practical. When high frequency power is applied to the antenna 9, first, electrons are directly accelerated by the electric field generated by the antenna to start discharging, and when the power is further increased, an induced magnetic field is generated by the current flowing through the antenna. To prevent this, an azimuthal electric field is generated in the plasma near the antenna in the discharge tube, electrons are accelerated, and plasma is generated.
[0010]
The upper part of the discharge tube is sealed with an O-ring seal by a flange 13 having a gas supply port 12 for ashing treatment. The gas is introduced into the discharge tube from a number of small holes provided in the flange. The introduced gas flows inside the discharge tube, crosses the plasma generation unit 14 and reaches the stage unit. If gas is introduced only from the center part of the flange, a flow velocity distribution with a high center remains to a considerably lower position. Therefore, it is necessary to blow out the gas from the entire surface in the form of a shower or to introduce the gas from the outer peripheral portion of the flange. Even if the outer peripheral flow rate is high at the blowout position, the gas flow receives resistance at the surface of the discharge tube, so the flow velocity distribution is almost the same as that blown from the entire surface on the downstream side, so it is introduced from the entire surface. The flow velocity distribution is not so different from that of the case.
[0011]
A perforated plate 15 is installed below the discharge tube for the purpose of reducing charged particles incident on the wafer and finely adjusting the distribution of the ashing rate on the wafer, if necessary. In the case where distribution and charge-up damage are not a problem, the perforated plate 15 may not be particularly installed.
[0012]
In the high-frequency inductively coupled plasma ashing processing apparatus configured as described above, in order to realize uniform plasma ashing processing on a semiconductor wafer, it is necessary to make the density distribution of oxygen radicals transported on the wafer uniform. It has been confirmed that the distribution of the ashing rate on the wafer substantially matches the supply distribution of oxygen radicals. As described above, oxygen radicals are generated in the form of a ring by the induction antenna in the vicinity of the induction antenna (in the case of a plurality of antenna turns, at an approximately middle position of all the turns). 2 and 3, a plasma generation unit 14 is generated in the vicinity of the antenna 9. FIG. 2 shows the distribution of the oxygen radical generation rate in the discharge tube. The generated oxygen radicals are transported to the wafer located below by the flow of oxygen gas introduced from the upper part. At this time, the oxygen radicals are diffused with an inherent diffusion coefficient, and the discharge tube At the surface, it is transported by the gas stream while being lost with its own extinction coefficient. Therefore, the distribution of the density of oxygen radicals carried on the wafer is determined by the balance between the flow rate of oxygen gas, which is the mother gas, diffusion, and loss on the discharge tube surface. FIG. 3 shows an example of the distribution of oxygen radical density obtained as a balance between these in the discharge tube.
[0013]
Therefore, in order to obtain a uniform ashing rate on the wafer, the geometric dimension of the discharge part is particularly important. 4A and 4B show main dimensions that affect the oxygen radical distribution. Of these, the most dominant for the oxygen radical distribution at the wafer position is the inner diameter A of the discharge tube and the transport distance B from the main discharge position. The effects of dimensions C, D, and E in the figure will be described later. We have determined the dimensions of the discharge part to obtain a uniform ashing rate from ashing experiments and oxygen radical distribution calculations. FIG. 5 is a diagram showing a range satisfying an ashing rate of 3 microns / min ± 10% under a predetermined oxygen flow rate and high-frequency power condition when the horizontal axis is the discharge tube inner diameter A and the vertical axis is the transport distance B. It is. In the high frequency induction plasma apparatus, the pressure range generally used is about 80-200 Pa. In FIG. 5, it can be seen that the range in which sufficient performance can be obtained for a specific condition is a specific size range with respect to the wafer size. With respect to this range, when B is large, the distribution is medium-high, and when B is small, the distribution is M-type reflecting the radical generation distribution at the discharge position, and the uniformity is off by 10%. End up. Further, when A is small, the height is medium and when it is A, the absolute value of the rate is lowered while it is shifted to the outside height, and also falls outside the range of 3 microns / min ± 10%. In addition, for example, when the pressure is changed from 200 Pa to 80 Pa, the diffusion is improved. Therefore, the range of the ashing rate of 3 μm / min ± 10% is shifted to the lower right in the figure, and the radical generation amount is reduced by lowering the pressure. It falls and the range becomes narrow. The range in which a sufficient ashing rate and uniformity can be obtained under practical pressure, flow rate, and power conditions is indicated by a solid line. The inner diameter A of the discharge tube is 95% to 125% of the wafer diameter, and the transport distance B Is from 30% to 120%.
[0014]
The relationship between the inner diameter A and the transport distance B has been described above. The stage outer diameter C, the dimension D between the stage and the chamber, and the chamber inner diameter E also affect the ashing rate distribution.
[0015]
That is, unless the structure is such that oxygen radicals carried from above are confined to some extent at the wafer position, there arises a problem that the overall rate is lowered.
[0016]
First, regarding the stage dimension C, if C is close to 100% with respect to the wafer dimension, oxygen radicals will flow down, and the wafer outer peripheral rate will decrease. Therefore, it is desirable that the stage outer diameter C is at least 103% or more with respect to the wafer diameter.
[0017]
Next, consider the distance D between the stage and the chamber upper surface. First, it goes without saying that in order to restrict the gas flow by the dimension D, A <C is necessary as shown in FIG. The distance D must be secured to some extent in order to carry in and out the wafer. However, when the distance D is increased in a structure with a large EA, oxygen radicals escape to that portion. Therefore, it is better to make D as small as possible within a range where the flow rate and pressure can be secured. . As shown in FIG. 6, when the ring-shaped member 16 is inserted instead of reducing the dimension D, the distance between the structure and the stage is considered to be equivalent to D. become. Also, in this case, if the gas flow is sufficiently constricted in this ring (if the conductance of this portion is sufficiently small and dominant), neither the stage nor the chamber is necessarily circular. The value of D is preferably 25 mm or less, but since at least about 10 mm is required for delivery of the wafer, the actual value of D is about 10 to 25 mm unless the stage 2 is driven in the vertical direction. It is.
[0018]
Regarding the chamber inner diameter E, if D is sufficiently small and the gas flow between the stage and the stage is sufficiently restricted, there is no problem even if it is large. However, if A ≧ C or if D cannot be made very small due to the problem of the conveyance space, it is necessary to make the dimension of E relatively close to the wafer diameter and C, and to restrict the gas flow at that part. is there. Therefore, E is desirably a size in the range of 102 to 120% with respect to the wafer diameter and the stage diameter C.
[0019]
In any case, the absolute value of the ashing rate, especially when the oxygen radicals are focused on the wafer by reducing D or E-C within a range in which the oxygen gas flow rate can be secured under the ashing pressure condition, The ashing rate at the outer periphery of the wafer can be increased.
[0020]
In the description so far, a straight tube has been described as a discharge tube, but there is no particular change in a discharge tube having a non-uniform tube diameter, for example, a tapered discharge tube. At this time, if the taper is too tight, as shown in FIG. 7, the gas flow velocity distribution is accelerated only in the center portion. Therefore, depending on the pressure and flow rate conditions, the usable taper angle is at most about θ = 30 ° with respect to the central axis of the tube. The above-described dimensional relationship of A, B or C, D, E is established in the range of θ <30 °. Examples of usable taper tubes are shown in FIGS. When a taper tube is used, the average tube inner diameter A ′ can be used as the inner diameter A, so that it can be replaced with the inner diameter and the transport distance of the straight pipe described so far. When the curved surface (R) is used instead of the taper, as shown in FIG. 10, the angle θ may be considered by connecting a range that substantially has a curve.
[0021]
As described above, the embodiment of the present invention has been described by taking a plasma ashing apparatus for manufacturing a semiconductor device as an example. However, the present invention is not limited to processing of a semiconductor device, but also processing of a liquid crystal display substrate and ashing of other objects to be processed. Applicable to all processes.
[0022]
【The invention's effect】
According to the plasma ashing processing apparatus of the present invention, by adopting a high frequency induction plasma source and optimizing the flow of oxygen radicals, even with a large area to be processed, low charge-up damage, high speed and uniform Plasma ashing can be performed, and the throughput of the apparatus is improved. As a result, the quality of the manufactured semiconductor device is also improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a graph showing a distribution of oxygen radical generation rates.
FIG. 3 is a graph showing a distribution of oxygen radical density.
FIG. 4 is a diagram showing dimensions of a discharge portion that affects the rate distribution.
FIG. 5 is a view for explaining a rate uniform dimension range;
FIG. 6 is a view showing a flow velocity distribution in a tapered tube having a tight angle.
FIG. 7 is a view showing an embodiment of a tapered discharge tube.
FIG. 8 is a diagram showing a first embodiment of a discharge tube.
FIG. 9 is a view showing a second embodiment of the discharge tube.
FIG. 10 is a view showing a third embodiment of the discharge tube.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Processing chamber, 2 ... Vacuum exhaust means, 3 ... Semiconductor wafer, 4 ... Stage, 5 ... Transfer system, 6 ... Push rod, 7 ... Temperature control means, 8 ... Discharge tube, 9 ... Antenna, 10 ... Impedance matching device DESCRIPTION OF SYMBOLS 11 ... High frequency power supply, 12 ... Gas supply port, 13 ... Flange, 14 ... Plasma production | generation part, 15 ... Perforated plate, 16 ... Ring-shaped member.

Claims (2)

A flange having a gas inlet is connected to one end of a discharge tube around which an induction antenna for plasma generation is arranged, and the other end is connected to a processing chamber in which a stage for placing an object to be processed is installed. In an induction plasma ashing apparatus for processing an object to be processed in the processing chamber ,
The inner diameter of the discharge tube is 95 to 125% of the outer diameter of the workpiece; and
The inner diameter of the structure defining the processing chamber inner diameter or the processing space in the processing chamber is configured to be 102 to 120% of the diameter of the workpiece and the stage, and
The distance from the main discharge part in the discharge tube to the object to be processed is constituted by 30% to 120% of the diameter of the object to be processed, and
The outer diameter of the stage is configured to be 103% or more of the outer diameter of the workpiece, and is configured to be larger than the inner diameter dimension of the discharge tube ; and
The gas introduction port is composed of a plurality of small holes provided in the flange, and the distribution of the small holes is arranged in a substantially ring shape on the outer peripheral portion of the flange, and gas is introduced from the gas introduction port.
An inductive plasma ashing apparatus characterized in that an object having an outer diameter of 300 mm is processed by oxygen radicals generated at a predetermined pressure in Pa . The induction plasma ashing processing apparatus according to claim 1,
An inductive plasma ashing apparatus characterized in that a substantial distance between the stage and the upper surface in the chamber or other structure is equal over the entire circumference and is 10 to 25 mm .

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