JP3397275B2 - Method of forming trench - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a trench for forming an element isolation region, a capacitive element, etc. in manufacturing a semiconductor device.

[0002]

2. Description of the Related Art Before etching a Si substrate to form a trench, a SiO ₂ film and a photoresist were sequentially formed on the Si substrate and a photoresist processed into an inverted pattern of the trench to be formed was used as a mask. Then, the SiO ₂ film was etched to remove the photoresist, and then the Si substrate was etched using the SiO ₂ film as a mask.

However, in this method, for example, in order to form a device isolation region having a flat surface, a SiO ₂ film is deposited after the trench is formed and the trench is filled, and this Si is formed.
Even if chemical mechanical polishing is applied to the O ₂ film to flatten the surface, the SiO ₂ film formed on the Si substrate is the same as that filling the trench, so that the SiO ₂ film on the Si substrate is formed. _{The two} films did not serve as a stopper for chemical mechanical polishing, and the surface of the Si substrate could be etched.

Therefore, there has been proposed a method of forming a trench in consideration of a stopper when performing chemical mechanical polishing,
3 and 4 show one conventional example. In this conventional example, as shown in FIG. 3A, a SiO ₂ film 12 for buffering and adhesion, a Si ₃ N ₄ film 13 and a polycrystalline S are formed on a Si substrate 11.
The i film 14 is sequentially formed, and the photoresist 15 is processed on the polycrystalline Si film 14 to have a reverse pattern of the trench to be formed.

Next, as shown in FIG. 3B, the polycrystalline Si film 14 is etched using the photoresist 15 as a mask, and further, as shown in FIG. 3C, the photoresist 15 is etched.
Then, the Si ₃ N ₄ film 13 and the SiO ₂ film 12 are etched using the polycrystalline Si film 14 as a mask to form an opening 16 having a pattern of a trench to be formed.

Next, as shown in FIG. 4A, the Si substrate 11 is etched using the photoresist 15, the polycrystalline Si film 14 and the Si ₃ N ₄ film 13 as a mask to form a trench 17, and As shown in FIG. 4B, the photoresist 15 is removed by ashing.

In one conventional example as described above, the polycrystalline Si film 14 is formed by chemical mechanical polishing of the SiO ₂ film (not shown) deposited to fill the trench 17 after the trench 17 is formed. The surface of the Si substrate 11 serves as a stopper, and the Si ₃ N ₄ film 13 also serves as a stopper in a portion where the thickness of the polycrystalline Si film 14 is thin due to the nonuniformity of the thickness of the polycrystalline Si film 14. Are never etched.

[0008]

However, in the above-mentioned conventional example, since the fluorocarbon gas is used for etching the Si ₃ N ₄ film 13 and the SiO ₂ film 12 in the step of FIG. The fluorocarbon polymer 18 adheres to the side wall of the.

As a result, as shown in FIG. 4 (a), the fluorocarbon polymer 18 also serves as a mask during the etching for forming the trench 17, and as is clear from FIG. 4 (b), the polycrystalline Si film is formed. 14 and the Si ₃ N ₄ film 13 are processed according to the designed size, a dimensional conversion difference occurs in the trench 17, and it is difficult to manufacture a semiconductor device precisely processed based on the designed size. .

If the photoresist 15 is removed by ashing after forming the opening 16 in the step of FIG. 3C, the fluorocarbon polymer 18 is also removed at the same time. However, if the photoresist 15 is removed at this point to expose the polycrystalline Si film 14, the etching selection ratio between the polycrystalline Si film 14 and the Si substrate 11 is small.
When the trench 17 is formed in the step (a), the polycrystalline S
The i film 14 is also etched so that the polycrystalline Si film 14 does not serve as a stopper during the subsequent chemical mechanical polishing.

If the photoresist 15 is formed directly on the Si ₃ N ₄ film 13, the opening 16 is formed in the step of FIG. 3C.
Even if the photoresist 15 is removed by ashing after the formation of Si, the Si ₃ N ₄ film 13 is not easily etched even when the trench 17 is formed in the step of FIG. However, when the thick Si ₃ N ₄ film 13 is formed, the Si substrate 1
Since the stress for 1 becomes large, Si ₃ N ₄ with a large film thickness
Since the film 13 cannot be formed, the deep trench 17
Cannot be formed.

[0012]

According to a first aspect of the present invention, there is provided a method of forming a trench, comprising: a Si ₃ N ₄ film and polycrystalline Si on the Si ₃ N ₄ film.
Product consisting of a film and a photoresist on this polycrystalline Si film
Forming a layer film on a Si substrate as a mask layer , forming an opening of a pattern of a trench to be formed in the mask layer, and removing a polymer adhering to the side wall of the opening by forming the opening And a step of forming the trench by etching the Si substrate using the mask layer from which the polymer has been removed as a mask.

A method for forming a trench according to claim 2 is the method for forming a trench according to claim 1, wherein the photoresist is used.
While leaving the
It is characterized that you removed.

A method of forming a trench according to a third aspect is the method of forming a trench according to the second aspect, wherein the static electricity removing plasma is used.
The oxygen plasma is used to remove residual charges and
The feature is that the removal of the mer is performed at the same time .

In the method for forming a trench according to the present invention, the polymer adhering to the side wall of the opening is removed by forming an opening in the mask layer, and the Si substrate is etched using the mask layer from which the polymer has been removed as a mask to form the trench. Therefore, the polymer attached to the sidewall of the opening of the mask layer does not serve as a mask during etching for forming the trench.

Moreover, on the Si ₃ N ₄ film and this Si ₃ N ₄ film,
Since the laminated film composed of the polycrystalline Si film and the photoresist on the polycrystalline Si film is formed as the mask layer, the trench is later filled with the SiO ₂ film to etch the surface of the Si substrate.
Surface of Si substrate by chemical mechanical polishing without etching
Can be flattened and the stress on the Si substrate
It is possible to form deep trenches without increasing
Wear.

Further, if the polymer is removed by oxygen plasma, the oxygen plasma is also used for removing the photoresist, so that it is not necessary to use a new device for removing the polymer. Moreover, although included a photoresist mask layer, the photoresist be removed polymers are allowed to remain, the photoresist also serves as a mask during the etching of trench formation.

Oxygen plasma is used as the static elimination plasma.
To remove residual charge and polymer simultaneously.
For example, it is necessary to perform a new process to remove the polymer.
Absent.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION First and second specific examples of the present invention will be described below with reference to FIGS. 1 and 2
The 1st example is shown. In this first specific example, FIG.
As shown in (a), the SiO ₂ film 22 having a film thickness of 5 nm and having a film thickness of 1 nm is provided on the Si substrate 21 for buffering and adhesion.
The Si ₃ N ₄ film 23 having a thickness of 00 nm and the polycrystalline Si film 24 having a thickness of 200 nm are sequentially formed by a low pressure CVD apparatus.

Then, the chemically amplified photoresist 25 is used.
Is applied on the polycrystalline Si film 24, and the photoresist 25 is applied to the inversion pattern of the trench to be formed by exposure by the excimer laser reduction projection exposure apparatus and subsequent development.
To process.

Next, as shown in FIG. 1B, the photoresist 25 is used as a mask and an ECR type etching apparatus is used to etch a natural oxide film (not shown) and polycrystalline Si film 24 on the surface of the polycrystalline Si film 24. The film 24 is etched under the following conditions.

Etching conditions for natural oxide film Cl ₂ / O ₂ 75/2 ml / min Microwave filament current 250 mA (2.45 GHz) Pressure 0.4 Pa High frequency power 80 W (800 kHz) Magnetic field 87.5 mT (875 G) Etching time 10 seconds

Etching conditions for the polycrystalline Si film 24 Cl ₂ / O ₂ 75/4 ml / min Microwave filament current 250 mA (2.45 GHz) Pressure 0.4 Pa High frequency power 60 W (800 kHz) Magnetic field strength 87.5 mT (875 G) Etching Time 70 seconds

Next, as shown in FIG. 1C, the Si ₃ N ₄ film 23 and the SiO ₂ film 22 are formed as follows by using the photoresist 25 and the polycrystalline Si film 24 as a mask by a magnetron type etching apparatus. The etching is performed under the conditions to form the opening 26 having the pattern of the trench to be formed.

Etching conditions of Si ₃ N ₄ film 23 and SiO ₂ film 22 C ₄ F ₈ / O ₂ / Ar 5/4/100 ml / min Pressure 2.7 Pa High frequency power 400 W (13.56 MHz) Magnetic field strength 12 mT (120 G ) Etching time 150 seconds

Also in this first embodiment, as shown in FIG. 1C, the fluorocarbon polymer 2 is formed on the side wall of the opening 26 by etching the Si ₃ N ₄ film 23 and the SiO ₂ film 22.
8 is attached. Therefore, in the first specific example,
Oxygen plasma treatment under the following conditions is performed by an ashing device to remove the fluorocarbon polymer 28 while leaving the photoresist 25 as shown in FIG.

Removal condition of fluorocarbon polymer 28 O ₂ 2 l / min Pressure 250 Pa Substrate heating temperature 120 ° C. Microwave power 800 W (2.45 GHz) Ashing time 5 seconds

Next, as shown in FIG. 2B, the photoresist 25, the polycrystalline Si film 24, and the Si ₃ N ₄ film 23 are used as a mask, and the surface of the Si substrate 21 is naturally etched by an ECR type etching apparatus. Oxide film (not shown) and Si substrate 21
Is etched under the following conditions to form the trench 27. After that, as shown in FIG. 2C, the photoresist 25 is removed by an ashing device.

Etching conditions for natural oxide film Cl ₂ / O ₂ 75/2 ml / min Microwave filament current 250 mA (2.45 GHz) Pressure 0.4 Pa High frequency power 70 W (800 kHz) Magnetic field 87.5 mT (875 G) Etching time 5 seconds

Etching conditions of Si substrate 21 HBr / O ₂ 120/2 ml / min Microwave filament current 250 mA (2.45 GHz) Pressure 0.5 Pa High frequency power 70 W (800 kHz) Magnetic field strength 87.5 mT (875 G) Etching time 120 seconds

Next, a second specific example will be described. In the second specific example, the Si ₃ N ₄ film 23 and the SiO ₂ film 22 are etched under the following conditions by an etching device in which an electrostatic attraction device is mounted on the electrode on which the Si substrate 21 is installed, and then the Oxygen plasma is used as the static elimination plasma for eliminating the residual charges of the electroadsorption device, and the residual charges and the fluorocarbon polymer 28 are removed at the same time. The steps other than these are the same as those of the above-described first specific example.

Etching conditions of Si ₃ N ₄ film 23 and SiO ₂ film 22 C ₄ F ₈ / O ₂ / Ar 5/4/100 ml / min Pressure 2.7 Pa High frequency power 400 W (13.56 MHz) Magnetic field strength 12 mT (120 G ) Etching time 150 seconds Electrostatic adsorption voltage -1000V

The removal conditions for residual charge and fluorocarbon polymer 28 O ₂ 100 ml / min pressure 2.7Pa RF power 300W magnetic field strength 12 mT (120G) processing time 20 seconds electrostatic attraction voltage off

[0034]

According to the method of forming a trench of the present invention,
After that, the trench is filled with a SiO ₂ film and the surface of the Si substrate is etched.
The surface of the Si substrate can be chemically and mechanically polished without etching.
The surface can be flattened and the response to the Si substrate is
It is possible to form deep trenches without increasing force.
Even though it is possible, the polymer attached to the side wall of the opening of the mask layer does not serve as a mask during the etching for forming the trench. It is possible to manufacture a semiconductor device processed into the above.

Further, if the polymer is removed by oxygen plasma, it is not necessary to use a new device for removing the polymer, so that it is possible to form a trench in which the dimensional conversion difference is suppressed without increasing the cost. it can. Shi
Duck, although included a photoresist mask layer, since the photoresist also serves as a mask during etching for trench formation, it is possible to form the deep trenches.

Oxygen plasma is used as the static elimination plasma.
To remove residual charge and polymer simultaneously.
For example, it is necessary to perform a new process to remove the polymer.
There is no difference in the size conversion without increasing the cost.
A suppressed trench can be formed.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a first half of a first embodiment of the present invention in process order.

FIG. 2 is a side sectional view showing the latter half of the first specific example in the order of steps.

FIG. 3 is a side sectional view showing the first half of a conventional example of the present invention in process order.

FIG. 4 is a side sectional view showing the latter half of a conventional example in the order of steps.

[Explanation of symbols]

23 Si ₃ N ₄ Film 24 Polycrystalline Si Film 25 Photoresist 26 Opening 27 Trench 28 Fluorocarbon Polymer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/822 H01L 21/8242

Claims (3)

(57) [Claims] 1. A Si ₃ N ₄ film and a polycrystal on the Si ₃ N ₄ film.
It consists of a Si film and a photoresist on this polycrystalline Si film.
Forming a laminated film as a mask layer on a Si substrate, forming an opening of a trench pattern to be formed in the mask layer, and removing the polymer adhering to the side wall of the opening by forming the opening. A method for forming a trench, comprising: a step; and a step of etching the Si substrate using the mask layer from which the polymer has been removed as a mask to form the trench. Wherein while leaving the photoresist, forming method of claim 1, wherein the trenches and removing the polymer by an oxygen plasma. 3. The oxygen plasma is used as static elimination plasma.
To remove the residual charge and the polymer simultaneously.
3. Forming the trench according to claim 2, wherein
Method.