JP2683692B2 - Plasma gas phase reaction method - Google Patents

Description

The present invention provides a method for forming a flat or substantially flat high-quality insulating film on a surface to be formed by a pressure reducing plate by plasma chemical vapor reaction. Is.

The present invention includes a step of forming an insulating coating by an anisotropic plasma CVD method by a method such as disposing a substrate on the cathode side, and an isotropic plasma etching method such as disposing a substrate on the anode side. In combination, a method for forming a film on a surface having a concavo-convex surface and forming the upper surface to be flat or substantially flat (a shape in which the height difference between the top and bottom is small or smoothly continuous) Is provided.

[B] Conventional technology Recently, the area of wiring in an IC chip has been increasing with the high integration and large scale of LSI.

For this reason, it is becoming more and more important to make the wiring multi-layered and to reduce the pattern and the wiring width.

The horizontal dimensions of patterns such as wiring and connection holes are miniaturized according to scaling rules, while the vertical dimensions such as the thickness of electrode wiring and insulating film are wiring resistance, stray capacitance, withstand voltage, migration resistance, etc. It is necessary to meet the specifications of the device of (3), and it is not easy to miniaturize it in the horizontal direction.

Further, since the patterns of the wirings and the connection holes are formed by etching with strong anisotropy for miniaturization, the end surface shape of the LSI pattern becomes steep.

Moreover, since the wiring is multi-layered, the unevenness on the upper surface of the LSI chip is naturally severe. Such unevenness on the upper surface of the LSI chip leads to a decrease in reliability such as a decrease in pattern processing accuracy and a disconnection of wiring.

As a means for solving such a problem, a technique for flattening the upper surface of the interlayer insulating film is emphasized.

A thermal CVD method is widely known as a method for forming this interlayer insulating film as a thin film forming technology by a conventional chemical vapor phase reaction (hereinafter referred to as CVD) method. This thermal CVD method adds thermal energy to the reaction gas for film formation introduced into the reaction chamber,
The gas was decomposed or activated to form a film. In this case, since the energy supply for the reaction is only heat, the temperature is also high, and it is performed in the range of 500 to 800 ° C.

For this reason, it is impossible to fabricate a semiconductor device that is vulnerable to high temperatures, and a technology for forming a film at a low temperature, which is promising as a next-generation LSI device, has been required.

As a method of forming a film at a lower temperature, plasma
A CVD method (a gas-phase film forming method using plasma is hereinafter referred to as a plasma CVD method) is known. In this case, high frequency power is applied to the reactive gas introduced into the reaction chamber from the outside to decompose and activate the reactive gas, and a film is formed on the heated substrate. In this case, the substrate having the formation surface is disposed on the anode side, and the heating temperature of the substrate is 20.
In the range of 0 to 450 ° C., the density of the material for film formation was increased. The reason for disposing the substrate on the anode side is to eliminate plasma damage to the underlying material. Furthermore, the basic idea of this film formation is the isotropic CVD method for performing isotropic deposition. For this reason, when forming a film in the recess, cusps (nests) are likely to occur at the corners of the bottom, and it is impossible to improve the step coverage in the case of multilayer wiring.

On the other hand, recently, there is an optical CVD method as a technique for preventing damage to the underlayer. In this method, light energy is applied to a reactive gas to decompose and activate it to form a film on a substrate, which does not require high temperature as in the thermal CVD method, and plasma CVD Although it is an ideal film forming method that does not physically damage the underlying material like the method, it has a drawback that the film forming rate is as slow as 1/10 to 1/50 of the plasma CVD method.

On the other hand, a plasma etching method is known as a manufacturing process of a semiconductor integrated circuit. In this method, a substrate is arranged on the cathode side, and anisotropic plasma etching is performed using self bias. By this anisotropic etching, a concave portion in a predetermined area is made sharp.

[C] The purpose of the present invention The present invention is completely different from these conventionally known techniques. In plasma CVD, the so-called anisotropic plasma CVD method, which is formed with anisotropy (the present invention is For the sake of clarity, we will use the tentative name). Further, isotropic plasma etching is basically performed by performing plasma etching with isotropy, and this is basically repeated at least once.

The present invention solves these conventional problems, and an object thereof is to form an insulating film having an upper surface without a steep step, particularly an interlayer insulating film.

(Configuration of the present invention)

In the present invention, anisotropic deposition is performed by the plasma CVD method. Then, of course, a film is also formed on the convex portion of the formation surface having an uneven surface, but it has been found that a particularly dense film can be formed especially on the bottom portion of the concave portion, and using this characteristic, an insulating film having a flat upper surface is formed. Is to make. The present invention is a film formation by this anisotropic plasma CVD method,
By repeating isotropic plasma etching, which is the reverse of the conventional anisotropic plasma etching (also called reactive ion etching RIE), the same reaction system (same reaction furnace or multiple multi-chamber continuous reaction furnaces) ), The upper surface is not flat or smooth, and a substantially flat coating is not produced.

According to the present invention, an insulating film such as a silicon oxide film using a photochemical vapor reaction is formed on a substrate to reduce plasma damage, and then a predetermined film thickness (for example, 0.5 to 3 μm) is obtained by an anisotropic plasma CVD method.
After forming the silicon oxide film up to m), isotropic plasma etching treatment (hereinafter referred to as etch back treatment) is performed in the same reaction system.

Further, if necessary, these steps are repeated to form an insulating film having an upper surface with no steep uneven steps, that is, an insulating film having a flat or substantially flat upper surface.

The present invention treats the anisotropic plasma CVD method and the isotropic plasma etching as isothermal or approximately isothermal (a temperature difference within ± 50 ° C. of each other), and eliminates the waiting time between one step and the next step. To improve its productivity.
Furthermore, the present invention has found that, as a preferable example thereof, both anisotropic plasma CVD and isotropic etching can be performed without external heating at room temperature (there is self-heating by plasma), and the anisotropic at room temperature It was discovered by the plasma CVD method that it has enough practical properties for an interlayer insulating film and a buried field insulating film.

An experimental example will be shown below to show a method for producing the silicon oxide film shown in the present invention.

Example 1 FIG. 2 shows a schematic view of an insulating film forming apparatus used in this experiment.

In the figure, a pair of electrodes (2), (8) are provided in the reaction chamber (1), both of which are insulated from the ground level. A substrate (3) having a surface to be formed is arranged on one side thereof. Furthermore, the reaction chamber (1) has an ultraviolet light source chamber (4) for photo CVD, and a plurality of ultraviolet light sources (6) are installed in this chamber.
The pressure of the ultraviolet light source chamber (4) is adjusted to be substantially equal to the pressure of the reaction chamber (1). The film-forming substrate (3) is installed in the reaction chamber (1) with the film-forming surface facing downward by the substrate support (2) that is also insulated from the reaction container and also serves as a heater for heating the substrate. ing. In this equipment, the deposition up method is adopted so that dust such as flakes generated during film formation does not adhere to the substrate.

From the plasma processing power supply (9) to the matching coil (1
High frequency energy goes through a pair of electrodes (2), (8)
It is connected to. And ground one and use it as an anode,
The ground (12) is selected by the switch (11) so that the other is the negatively biased cathode of 100-500V.

When anisotropic CVD is to be performed, the electrode (8) is grounded and is on the anode side, and the electrode (2) with the substrate is on the cathode side.

In anisotropic CVD, the reactive gas is directional because it is accelerated in the electrolytic direction by a bias voltage. Then, when the surface collides with the surface to be formed by this acceleration, this kinetic energy is also added thereto, and a dense film can be formed. Due to this directional property, the film thickness of the formed film is thick on the surface perpendicular to the bias electric field and parallel to the bias electric field (side surface).
Is formed thin. In particular, since the sufficiently accelerated reactive gas reaches the bottom of the recess as well, a dense film can be formed even at the bottom, and the generation of cusps and the like can be prevented.

On the other hand, when performing isotropic plasma etching, the electrode (2) is grounded so that the substrate is on the anode side without self-bias and the electrode (8) is on the cathode side.

That is, isotropic etching is a method in which a reactive gas is uniformly impinged on the surface to be etched without being accelerated by an electric field, and a plasma reaction is caused on the surface. For this reason, more radicals collide with the convex portions and are easily etched, and radicals are less likely to reach the concave portions, and thus are less likely to be etched. Isotropic etching is to perform etching without applying a bias having the directionality of this radical.

In the anisotropic CVD method, among the reactive gases, the silicide gas and the oxide gas are mixed in the pipe, introduced into the reaction chamber through the gas nozzle (7), and mixed near the substrate (3). There is. The unnecessary gas is exhausted from (13).

In the photochemical gas phase reaction, a direct excitation method was adopted in which the ultraviolet light emitted from the ultraviolet light source (6) was applied to the reactive gas through the quartz transmission window (5).

Furthermore, an anisotropic plasma is formed on the transparent window (5).
A mesh electrode (8) for CVD and isotropic plasma etching is placed. A high frequency power can be applied to the mesh electrode (8) by a power source (9) between the mesh electrode (8) and the substrate support electrode (2). Although not shown in the drawing, the electrode (2) and the substrate support electrode (2) are optionally used to promote anisotropic plasma CVD.
AC bias voltage (eg 50KHz, peak voltage ± 350
V, it is effective to apply DC bias of −100 to −500V to the substrate side.

Using this device, the reaction pressure is 0.01 to 0.3 torr on the substrate having irregularities as shown in FIG. 1 (A), the substrate temperature is room temperature (room temperature ± 50 ° C. or less), input high frequency power 13.56 MHz, 100 W to 5 W
A silicon oxide film was formed by changing the ratio of monosilane and nitrous oxide as a reactive gas under the condition of 00W.

The following reactions can be considered from the refractive index and infrared absorption of the silicon oxide film in the SiH ₄ / N ₂ O ratio of 0.005 to 0.5.

SiH ₄ + 2N ₂ O → SiO ₂ + 2N ₂ + 2H ₂ By such anisotropic plasma CVD, Fig. 1 (A)
An insulating film such as a silicon oxide film is formed on a substrate having a formation surface (30-1) having an uneven shape as shown in FIG. In FIG. 1 (A), the convex portion (2) and the narrow concave portion (2
1) Make a wide recess (22). A silicon oxide film (30-1) having an average film thickness of 8000 Å was formed on these upper surfaces by an anisotropic plasma CVD method. Then, the upper surface of the protrusion (2
4) On the bottom surfaces (22) and (26) of the recess, a film was formed with a thickness of 1.0μ. The side surface (25) could only be formed to a thickness of 0.2μ.

This process condition is SiH ₄ / N ₂ O = 1/2, high frequency output 300
W, 13.56 MHz, and the substrate was placed on the Casotto side. At this time, the bias was −350V. The substrate temperature was room temperature. Despite the film formation at room temperature, the specific resistance is 5 × 10 ¹⁷
Ωcm, and withstand voltage was 8 × 10 ⁶ V / cm (voltage at which current of 1 μA / cm ² or more flows). In this case, the plasma pressure was as high as 0.05 torr and the film formation rate was as high as 0.1 to 1 μ / min.

The convex portion (23) of the substrate (3) had a shape in which the space of the concave portion (21) was 0.8 μm narrow and the width of the wide concave portion (22) was 2 μm. The uneven shape could be uniformly covered.

The thickness of the upper surface / thickness of the side surface can be set to 2 to 20 and generally 3 or more.

 Next, this insulating film was subjected to isotropic etching.

As shown in FIG. 1 (A), after forming a thick silicon oxide film covering the surface of the uneven substrate, the reactive gas in the reaction chamber is exhausted and removed, and an organic halide gas such as CF ₄ which is an etching gas is used. , CF ₃ H or NF ₃ , SF _6, etc. are introduced into the reaction chamber, the pressure is adjusted to 0.1 torr, and high frequency power is applied between the mesh electrode (8) and the substrate support electrode (2) to achieve isotropic A discharge was generated to cause a characteristic plasma etching, and the formed coating film (30-1) was etched to eliminate the steep uneven portion. Then, as shown in FIG. 1 (B), the recesses (28) are not so much etched, and a part or all of the silicon oxide film (24) on the projections can be mainly etched. Therefore, the insulating film could be deliberately embedded in the recess.

Performing this process, etching in the recess is 0 to 0.2 μm
And etching the insulating film on the convex portion to a thickness of about 0.2 to 0.5 μm (etching ratio 2 to 10 for example 3
As shown in FIG. 1B, which was obtained as described above, the steep portion of the uneven step was removed. Thus, the interlayer insulating film (30-2) without a steep step can be formed in the same apparatus and the same reaction chamber.

This step was repeated again because the thickness of the coating on the protrusions was too thin in this figure and the top surface was not yet sufficiently flattened. That is, as shown in FIG. 1 (C), an insulating film (30-3) is laminated on these by an anisotropic CVD method as in FIG. 1 (A). An insulating film (31) was obtained. Further, thereafter, as shown in FIG. 1 (D), isotropic plasma etching was performed as in the step of FIG. 1 (B). And the insulating film (30-4) was obtained.
Then, the insulating film on the convex portion (28 ') and the insulating film on the concave portion (2
6 ') and 6') could be smoothly connected to each other at this boundary (25 '). This smoothly continuous upper surface is extremely important for producing other fine electric wirings with the same line width on the upper surface.

Further, by repeating these as required, a silicon oxide film (30-5) having a flat upper surface could be formed as shown in FIG. 1 (E).

Further, at the time of the etching treatment, the coating can be simultaneously removed on the inner wall of the reaction chamber and the transmitted light window (5), and it is not necessary to stop the operation of the apparatus for cleaning, which leads to the improvement of productivity.

In addition, in this example, the anisotropic plasma CVD method and the isotropic plasma etching method were used together for the production of the silicon oxide film. However, when the film is formed by the anisotropic plasma CVD, the substrate having an uneven surface is formed. To prevent plasma damage of the
Obviously, it is possible to cover all of them by the CVD method and then use the embodiment of the present invention.

Example 2 This example outlines a film forming apparatus having another structure.

In FIG. 3, FIG. 3 (A) is a vertical sectional view taken along the line AA ′, and FIG. 3 (B) is seen from above.

It has a substrate loading / unloading chamber (47) and a buffer chamber (46) in front of it. A region (41) is a reaction chamber for performing optical CVD, a region (42) is a reaction chamber for performing anisotropic plasma CVD, a region (43) is a reaction chamber for performing anisotropic etching, and a region (44). ) Is a space for performing isotropic plasma CVD, or (45) is a space for performing isotropic plasma etching. Each reaction chamber has a gate valve (51), (5
Substrates (3-1), (3-2), (3) which are partitioned by 2), (53), (54), (55), and (56), and which have a surface to be formed in each reaction chamber at the same time. -3), (3-4),
(3-5) is processed. During this process, the film-formed substrate (3-6) is taken out between the load / unload chamber (47) and the buffer chamber (46), and a substrate having a new uneven surface not yet formed ( Insert it from (47) to (46). In each of the reaction chambers, as shown in Example 1, a predetermined anisotropic plasma CVD and isotropic plasma etching treatment were performed, and then all the reaction chambers were evacuated. And after making each reaction chamber an equal pressure, the gate valves of (51) ... (56) are simultaneously opened. Further, all the substrates were transferred to the adjacent reaction chamber as shown by the arrow, that is, the substrate (3-1) was at the position (3-2),
The board (3-2) is located at the position (3-3), and the board (3-3) is
Is moved to the position (3-4), the substrate (3-4) is moved to the position (3-5), and the substrate (3-5) is moved to the position (3-6). The substrate is removed as described above.

As shown in FIG. 3 (A), in order to perform anisotropic plasma CVD, the substrate side is the cathode side as shown in the reaction chambers (42) and (44). To perform isotropic etching, the substrate side is the anode side as shown in the reaction chambers (43) and (45).

Thus, as shown in FIG. 1, an insulating film having a flat or substantially flat surface could be formed on the uneven surface.

If a multi-chamber configuration is used as shown in FIG.
It was possible to obtain about 3 times the throughput as compared with the case where only one reaction chamber shown in the figure was used.

Furthermore, in FIG. 3, reaction chambers (41), (42), (4
Since 4) is mainly only film formation, anisotropic plasma CVD,
By shifting the isotropic plasma etching one by one, the inner wall of the reaction chamber can be automatically cleaned.

As shown in FIG. 3, the substrate was isothermal in all reaction chambers, and in particular, in this embodiment, the room temperature was within ± 50 ° C. Then, even though plasma CVD has been used so far, film formation has been 3 times.
00 ~ 400 ℃, etching is at room temperature, so 3 for each reaction chamber
There was a temperature difference of over 00 ° C, and much waiting time was required for raising and lowering the temperature. However, as shown in the present invention, it was discovered that the film formed by anisotropic plasma CVD made at room temperature was denser and harder than expected.
Since both isotropic etching and room temperature can be performed at room temperature, it is possible to fabricate a multi-chamber structure device that can be mass-produced as well as improving productivity.

Of course, the number of chambers may be increased if necessary. Further, due to the relocation, not all of them are carried out at the same time, but a device may be provided in which a buffer space is once provided between the reaction chambers.

In the above embodiments, the silicon oxide film is disclosed as the insulating film, but other insulating films, silicon nitride film, PSG (phosphorus glass), BSG (boron glass), and alumina film are also applicable.

Furthermore, not only monosilane but also other polysilanes (SinH _{2n + 2} ), dimethylsilane, tetramethylsilane, and other organosilicon compounds (SiHn (C
Organosilicon oxygenates such as H ₄ ) _4-n ) or tetraethoxysilane (TEOS) can also be used if desired.

[E] Effect As described above, the present invention is completely opposite to the “isotropic” plasma CVD and the “anisotropic” plasma etching that have been conventionally used. By the plasma etching, it was possible to form an insulating film having a flat or substantially flat upper surface on a substrate having an uneven surface. And since the plasma CVD method can be performed at room temperature or a temperature close to it, the productivity could be more than three times that of the previous one.

In addition, the gasp that is likely to be generated in the recess was also removed.

According to the method of the present invention, it is possible to fabricate an interlayer insulating film having no steep uneven steps such as VLSI and a buried field insulating film in the same reaction chamber of the same device, and it is possible to reduce the manufacturing cost of the device. .

In addition, the etching of the reaction chamber wall and the transmitted light window can be performed simultaneously during the etch-back process.

[Brief description of the drawings]

FIG. 1 shows a step of producing an interlayer insulating film of the present invention. 2 and 3 show schematic views of the apparatus used in the present invention.

Claims (4)

(57) [Claims] 1. A step of forming an insulating film on a surface of a substrate having uneven steps by an anisotropic plasma CVD method, and an isotropic plasma etching method for mainly removing the insulating film on the convex portion. And the step of performing at least once. 2. The plasma gas phase reaction according to claim 1, wherein the anisotropic plasma CVD method and the isotropic plasma etching are performed within a range of 0 ° C. to 70 ° C. Method. 3. The method according to claim 1, wherein the substrate is disposed on the cathode side when performing the anisotropic plasma CVD method, and the substrate is placed on the anode side when performing the isotropic plasma etching method. A plasma gas phase reaction method, characterized in that 4. The plasma vapor phase reaction method according to claim 2, wherein the anisotropic plasma CVD method and the isotropic plasma etching are performed at a substantially equal temperature.