JP2738809B2 - Plasma processing method - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] Field of the Invention The present invention Ri engaging <br/> plasma treatment how, in particular, using plasma generated by microwave discharge, a thin film on the sample surface The present invention relates to a plasma processing method suitable for generation . 2. Description of the Related Art Generally, a plasma processing apparatus utilizing plasma generated by a microwave discharge in a magnetic field includes an electron cyclotron resonance generating position generated by the magnetic field and the microwave in a discharge tube which is a part of a discharge space. And a magnetic flux density distribution that sharply decreases from the electron cyclotron resonance point toward the sample stage provided in the sample chamber.
For this reason, the plasma generated near the resonance point has a density of 1 to 4 while being transported from the discharge tube to the sample stage.
This was reduced by more than two orders of magnitude, and efficient plasma processing could not be performed. Although there is a conventional example in which the above-described resonance position is arranged in the sample chamber, most of the microwaves are absorbed at the resonance position in the discharge tube because of the arrangement of the mirror magnetic field having the resonance position in the discharge tube. In addition, the amount of plasma generated at the resonance position in the sample chamber was restricted. [0004] Even if plasma can be generated at a resonance position in the sample chamber, most of the plasma is generated in the direction of the discharge tube because the magnetic field gradient in the vicinity thereof is directed from the sample chamber to the discharge tube. The plasma is returned and the flow rate of plasma toward the sample stage is reduced as a whole, and efficient plasma processing cannot be performed. A description will be given below with reference to the drawings. FIG. 4 is a summary P of the 31st Semiconductor Integrated Circuit Technology Symposium held on December 3 and 1986.
49 to 54 "CVD using ECS plasma" (hereinafter referred to as "CVD using ECS plasma").
A microwave 4 is incident on a discharge tube 2 having a magnetic field coil 1 on the outside through a waveguide 3 from an entrance window 5, and an electron cyclotron in a magnetic field generated by the magnetic field coil 1 is shown. When the motion and the microwaves 4 resonate at the resonance position, resonance electrons collide and ionize the plasma gas 6 to generate plasma. Then, the sample 7 is connected to the discharge tube 2.
The generated plasma is pushed out using a magnetic field gradient in the direction of the sample chamber 9 provided with the sample stage 8 holding the sample. This apparatus excites or ionizes the material gas 10 newly introduced into the sample chamber 9 by the plasma or the plasma to plasma-treat the surface of the sample 7. FIG. 5 shows the magnetic flux density distribution from the microwave entrance window 5 to the sample table 8 in FIG. 4, and the vertical axis is the axial direction with the boundary between the discharge tube 2 and the sample chamber 9 being 0. The distance and the horizontal axis are the magnetic flux density. In the case of the conventional example A, the magnetic flux density causing electron cyclotron resonance corresponding to the frequency (2.45 GHz) of the incident microwave 4 is Be (875 gauss).
In FIG. 5, this position is located about 3 cm in the axial direction from the microwave entrance window 5. For this reason, only the region of 3 cm is effective for plasma generation from the propagation characteristics of microwaves in the plasma and the condition of resonance absorption of microwave energy, and the plasma generated in the region of approximately 3 cm is approximately 3 cm.
It is transported in the direction of the sample table 8 by ambipolar diffusion under the force of the magnetic field gradient between 5 cm. At this time, since the transport distance is long and the magnetic field is rapidly reduced, the density of the plasma transported to the surface of the sample 7 is smaller than the plasma density near the resonance position where the electron cyclotron resonance occurs. Tended to decrease. FIG. 6 is a summary P6 of the 31st Semiconductor Integrated Circuit Technology Symposium held on December 3 and 4, 1986.
1-66 "a-Si: H by ECR plasma CVD method"
FIG. 7 shows the magnetic flux density distribution of the “film” (hereinafter referred to as Conventional Example B). The difference from Conventional Example A is that the magnetic flux density distribution is large as a whole. In addition, the position of the magnetic flux density corresponding to the resonance position is still in the discharge tube 2, and the region where the magnetic flux density is higher than that and effective for the resonance absorption of the microwave is a maximum of 2. / 3. Further, since the magnetic flux density decreases rapidly in the direction of the sample stage 8, the density of the plasma generated in the vicinity of the resonance position becomes smaller than that of the sample 7 as in the conventional example A.
Tended to decrease due to loss while diffusing to the surface of. FIG. 8 shows JP-A-59-3018 (hereinafter referred to as Conventional Example C), and FIG. 9 shows the magnetic flux density distribution. The conventional example C shown in FIG. 1 employs a mirror magnetic field configuration which is often used as a plasma confinement method for the purpose of increasing the plasma density, and is used to increase the magnetic body density near the surface of the sample 7 in the sample chamber 9. A permanent magnet 13 is provided. In the conventional example C, the incident microwave 4
Is propagated in a magnetic flux density region (region (I) in FIG. 9) larger than the resonance position and is resonantly absorbed in the plasma near the first resonance position (a in FIG. 9). However, if the magnetic flux density further passes the resonance position and attempts to propagate in a magnetic flux density region (region (II) in FIG. 9) smaller than the resonance position, it becomes difficult for the plasma to propagate. The plasma generated in (b) in FIG. 9 receives a force in the direction of the discharge tube due to the magnetic field gradient.
The density of the plasma incident on the substrate has a tendency to decrease as in the conventional examples A and B, as compared with the plasma density near the first resonance position. As described above, in the above conventional method, no consideration is given to the position where the density of the plasma generated by the electron cyclotron resonance in the microwave and the magnetic field decreases due to the loss while being transported to the sample surface. . In the above prior art, the relationship between the plasma density distribution and the magnetic flux density distribution in the direction from the discharge tube to the sample table is not taken into consideration, and the vicinity of the electron cyclotron resonance generation position to the sample surface is not considered. Since the density of the plasma to be transported tends to decrease, there is a problem that the utilization efficiency of the plasma is low and a high-quality film cannot be obtained, and the processing speed is slow and efficient plasma processing cannot be performed. The present invention has been made in view of the above points,
And has as its object the use efficiency of the produced plasma with improved handling quality by significantly improved, to provide a plasma treatment how capable of faster processing speed. The above object is achieved by applying a magnetic field such that a magnetic field generated by a magnetic field generating means and an electron cyclotron resonance generating position generated by a microwave are located near a sample.
In addition , this is achieved by forming a thin film having an etch rate ratio indicating the denseness of the thin film formed on the surface of the sample, which is equal to or less than the inflection point of the etch rate ratio . In general, a microwave that propagates in a plasma and causes electron cyclotron resonance is a clockwise circularly polarized wave, and this wave has a magnetic flux smaller than a magnetic flux density necessary for causing the electron cyclotron resonance. In a dense plasma,
Cut off and cannot propagate. Therefore, in the present invention, the magnetic flux density at the microwave incident end of the vacuum vessel is made larger than the magnetic flux density at the electron cyclotron resonance position, and the magnetic flux density distribution shape gradually decreases from the magnetic field generating means to at least the position of the sample stage. age,
In addition, by positioning the electron cyclotron resonance position near the sample stage, a region where high-density plasma is generated in a magnetic flux density region higher than the resonance magnetic flux density can be extended to near the sample stage in a vacuum vessel. In addition, the distance by which the plasma is extruded by the magnetic field gradient and transported to the sample stage can be reduced to zero. With this, the distance between the resonance position and the sample table can be made sufficiently small with respect to the plasma density which rapidly decreases on the magnetic flux density side smaller than the resonance magnetic flux density, so that high-density plasma is transported to the sample surface. It becomes possible. The position of the electron cyclotron resonance generated by the magnetic field and the microwave by the magnetic field generating means is
A magnetic field is applied so as to be positioned near the sample, and an etch rate ratio indicating the denseness of a thin film formed on the surface of the sample
Can be realized by forming a thin film having an inflection point of the etch rate ratio or less . An embodiment of the plasma processing apparatus according to the present invention will be described below with reference to FIGS. 1, 2 and 3. FIGS. 1 and 2 show an example in which the present invention is applied to a plasma processing apparatus for performing a sample surface treatment (film formation) by magnetic field microwave discharge. FIG. 1 shows a structure, in which a microwave 4 is introduced through a waveguide 3 into a discharge tube 2 forming a vacuum vessel provided with a magnetic field coil 1 on the outside, and the plasma is introduced into the discharge tube 2. The plasma is generated by exciting or ionizing the gas 6 by electron cyclotron motion in the magnetic field generated by the magnetic field coil 1 and electron cyclotron resonance by the microwave 4. A gradient of a magnetic field generated by the magnetic field coil 1 in a direction toward a sample chamber 9 forming a vacuum vessel provided with a sample stage 8 holding a sample 7 to be processed, which is connected to the discharge tube 2, causes the plasma to be generated. And the material gas 10 newly introduced to the front surface of the sample 7 in the sample chamber 9 is excited by the plasma flow or transported to the surface of the sample 7 while being ionized, so that the surface of the sample 7 This is a plasma processing apparatus that generates a thin film having a composition of gas 6 and material gas 10. FIG. 2 shows the magnetic flux density distribution in the axial direction from the discharge tube 2 to the sample table 8 in this embodiment. The horizontal axis indicates the axial distance, and the vertical axis indicates the magnetic flux density. The present invention is characterized in that the distribution shapes shown in FIGS. 2 and 3 are used, and the curve shown in FIG.
FIG. 2 shows a magnetic flux density distribution shape when the electron cyclotron resonance generated magnetic field position is at the boundary point between the sample chamber 9 and the sample chamber 9. FIG. 2 shows an example of a known magnetic flux density distribution. In FIG. 1, the microwave (2.45 GHz) 4 introduced into the discharge tube 2 by the waveguide 3 has a magnetic flux density (Be = corresponding to the resonance position) in the magnetic flux density distribution shape of FIG. 875 gauss) is located near the sample table 8 in the sample chamber 9 (point a in FIG. 1).
Propagating in the magnetic flux density region equal to or higher than the magnetic flux density corresponding to the resonance position in the discharge tube 2 and entering the sample chamber 9 and approaching the resonance position, ionization and excitation by electron cyclotron resonance are activated, and the plasma is proportionally increased. The density also increases, and the plasma generation probability reaches a maximum value at the resonance position. But,
When the microwave tries to propagate in a plasma having a magnetic flux density smaller than the magnetic flux density (875 gauss in this embodiment) corresponding to the resonance position, the microwave rotates right-handed circularly polarized, causing the electron cyclotron resonance. Due to the nature of the wave, it is cut off and cannot be propagated, and the microwave that has not been resonantly absorbed in the plasma is reflected at this resonance position. For this reason, in the low magnetic flux density region on the sample stage 8 side from the resonance position, plasma is hardly generated, and the plasma reaching the surface of the sample 7 is accompanied by a magnetic field that gradually decreases from the resonance position toward the sample stage 8. The plasma transported by ambipolar diffusion and the material gas 10 introduced in the vicinity of the resonance position become atoms and molecules ionized and excited by the plasma flow. Therefore, the sample table 8 is moved from the resonance position.
The plasma density distribution in the direction shows a sharp decrease. But,
According to the present invention, the distance from the resonance position to the surface of the sample can be reduced to approximately 0, so that the surface position of the sample 7 can be arranged before the plasma density sharply decreases, and the electron near the surface of the sample 7 can be arranged. Without reducing the processing speed, which is almost proportional to the density, the ion density that gives an ion bombardment that has an effect on the compactness at the time of film formation can also be appropriately selected, and a thin film with good quality and a high processing speed can be produced. . FIG. 3 shows the thin film formed on the surface of the sample according to the present embodiment at an etch rate ratio indicating the tightness, and the lower part of the horizontal axis shows the magnetic flux density distribution shape shown in FIG.
), The discharge tube 2 and the sample chamber 9 corresponding to the upper stage on the horizontal axis.
The magnetic flux density at the discharge tube outlet, which is the boundary point, is shown as the magnetic flux density at the resonance position as Be, and the vertical axis shows the etch rate ratio in arbitrary units. It is clear from this figure that when the resonance position is pulled out into the sample chamber 9 and is located near the sample table 8 (in FIG. 3 and in FIG. 3), the etch rate ratio is small and the dense film This indicates that the ion bombardment effect at the time of film formation is sufficiently high because the plasma density near the sample surface is high. That is, in order to obtain a dense film, it is understood that the magnetic field should be applied so that the electron cyclotron resonance position is located below the inflection point of the etch rate ratio. According to the plasma processing method of the present invention described above, the position of electron cyclotron resonance generated by the magnetic field and the microwave by the magnetic field generating means is located near the sample.
Applying a magnetic field to location, the etch rate ratio that indicates the density of the thin film formed on the surface of the sample, the etch rate ratio
Since the thin film whose thickness is below the inflection point is formed, the distance between the high-density plasma generation position and the sample surface is reduced, and high-density plasma can be transported to the sample surface, so that the etch rate ratio is small. Since a dense film is generated, plasma processing with good film quality and a high processing speed can be performed, which is very effective for this type of plasma processing method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a magnetic field microwave discharge plasma processing apparatus showing one embodiment of the present invention. FIG. 2 is a characteristic diagram showing an axial magnetic flux density distribution in the apparatus of FIG. FIG. 3 is a characteristic diagram showing a relationship between an etch rate ratio and a magnetic flux density of a thin film formed by the apparatus of FIG. FIG. 4 is a sectional view showing a conventional plasma processing apparatus. FIG. 5 is a characteristic diagram showing an axial magnetic flux density distribution in the device of FIG. FIG. 6 is a sectional view showing a conventional plasma processing apparatus. FIG. 7 is a characteristic diagram showing an axial magnetic flux density distribution in the device of FIG. 6; FIG. 8 is a cross-sectional view showing a conventional plasma processing apparatus. FIG. 9 is a characteristic diagram showing an axial magnetic flux density distribution in the apparatus of FIG. [Description of Signs] 1 ... magnetic field coil, 2 ... discharge tube, 3 ... waveguide, 4 ... microwave, 5 ... incident window, 6 ... plasma gas, 7 ... sample, 8
... sample stage, 9 ... sample room, 10 ... material gas, 11a, 11b
... cooling water, 12 ... evacuation.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Tadashi Sonobe               3-1-1, Sachimachi, Hitachi-shi, Ibaraki Stock               Hitachi, Ltd. Hitachi Plant (72) Inventor Jun Chiba               3-1-1, Sachimachi, Hitachi-shi, Ibaraki Stock               Hitachi, Ltd. Hitachi Plant (72) Inventor Naohiro Kadoma               4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Co., Ltd.                 Hitachi, Ltd. (72) Inventor Yasuhiro Mochizuki               4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Co., Ltd.                 Hitachi, Ltd. (72) Inventor Shigeru Takahashi               4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Co., Ltd.                 Hitachi, Ltd. (72) Inventor Takuya Fukuda               4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Co., Ltd.                 Hitachi, Ltd.                (56) References JP-A-62-292443 (JP, A)

Claims (1)

(57) [Claims] A microwave and a discharge gas are introduced into a container provided with a magnetic field generating means, and the discharge gas introduced into the container is resonated with electron cyclotron motion in a magnetic field generated by the magnetic field generating means. generates a plasma by Ri励 force, or ionized by the, formation of a thin film to the newly excited the introduced material gas into the container, or ionized by the surface of the sample housed in the container by the plasma The electron cyclotron resonance generated by the magnetic field and the microwave by the magnetic field generating means is positioned near the sample.
A magnetic field is applied such that the etch rate ratio indicating the denseness of the thin film formed on the surface of the sample is equal to the etch rate.
A plasma processing method comprising forming a thin film having a ratio of not more than an inflection point .