JPH07228985A - Low temperature dry etching method and device therefor - Google Patents

Abstract

PURPOSE:To satisfy all of the characteristics of the side face of an oxide film on a substrate by controlling the dry etching conditions. CONSTITUTION:A waveguide sample 10 as an oxide film-coated substrate is sent from a spare chamber 2 to a reaction chamber 1-1, and the WSi film and photoresist are etched off to form a core pattern. The sample 10 is introduced into a reaction chamber 1-2 through the spare chamber 2, and the core layer is dry-etched at a low temp. based on the core pattern. As the optimum condition at this time, the substrate is controlled to <=-20 deg.C, the gaseous Ar flow rate is superimposed on the gaseous CHF3 flow rate by >=2 times in the gaseous etchant, and the total flow rate is controlled to >=60cc/min. The reaction chamber 1-2 is kept at : 2.66 Pa, and the power of a high-frequency power source 6-2 applied between the electrodes is controlled to >=450W. After etching, the sample is returned to the reaction chamber 1-1 to remove the WSi film on the core pattern, and finally the sample 10 is discharged into the atmosphere from one spare chamber 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low temperature dry etching method and apparatus for keeping a material to be etched at a low temperature and dry etching the surface of the material to be etched.

[0002]

2. Description of the Related Art Recently, as a method of dry-etching an oxide film or a metal film with good verticality, the temperature of the substrate to be etched is maintained and controlled at a low temperature of 0.degree. Therefore, a so-called low temperature dry etching technique, which suppresses the radical reaction on the side surface while maintaining the above, has been attracting attention.

FIG. 9 is a schematic block diagram of a low temperature dry etching apparatus by reactive ion etching used by the present inventor for study. This comprises a reaction chamber 1 for etching and a preliminary chamber 2 for inserting / removing a sample 10 as a substrate to be etched.

First, sample 1 composed of a quartz glass substrate
0 is conveyed to the preparatory chamber 2 via the sample insertion / extraction system 12. After that, the preliminary chamber 2 is evacuated by the exhaust system 4. On the other hand, in the reaction chamber 1, a high vacuum (1.33 × 10 3) is provided by the exhaust system 3 so as to receive the sample 10 from the preliminary chamber 2.
^{-1 to} 1.33 × 10 ^-2 Pa). In addition, the lower electrode 5-2 for mounting the sample 10 keeps the sample 10 at a low temperature of 0 ° C. or lower by causing a refrigerant to flow in the electrode as shown by arrows 9-1 and 9-2. There is.

Next, the auxiliary chamber 2 is set to a desired vacuum degree (1.33).
(Pa or less), the gate valve 11 as an airtight valve is opened to transfer the sample 10 from the preliminary chamber 2 onto the lower electrode 5-2 of the reaction chamber 1 and to place it on the lower electrode 5-2. Next, He is sprayed on the back surface of the sample 10 in the direction of the arrow of the He gas supply system 8 to accelerate the temperature reduction of the sample 10.

After that, the upper electrode 5-1 and the lower electrode 5-2.
High-frequency power source 6 is applied between and to generate plasma,
This is a method of performing etching while flowing an etching gas (CHF ₃ gas is used to etch the silica glass film in this case) in the plasma atmosphere. In this method, the quartz glass film is etched by using the WSi film patterned on the film as a mask.

[0007]

However, in this method, the temperature of the sample 10 (0 ° C to -40 ° C), the degree of vacuum in the reaction chamber (13.3 to 1.33 Pa), the flow rate of the etching gas of CHF ₃ ( 10 to 50 cc / min), the verticality of the film side surface etched by variously changing the power (300 to 500 W) of the high frequency power source 6, the roughness of the film side surface, the sub-trench, the etching rate and the etching selection ratio (= (oxide film etching As a result of evaluating (rate) / (etching rate of WSi film)), it was not possible to find conditions satisfying all the above evaluation items. That is, (1) In order to improve the verticality of the side surface of the film and reduce the roughness of the side surface, it is necessary to reduce the gas flow rate of CHF ₃ and maintain a high vacuum, but on the other hand, the etching rate decreases, It was found that large sub-trench occurred. On the contrary, it was found that if the flow rate of CHF ₃ is increased in order to increase the etching rate and reduce the size of the sub-trench, the verticality deteriorates and the side surface becomes rough.

(2) It is unavoidable that the WSi film is also etched by the CHF ₃ gas and its pattern width gradually narrows, but the etching selection ratio between the WSi film and the silica glass oxide film is not increased. It was found that the etching of the WSi film progressed rapidly and the width thereof became smaller, and accordingly, the pattern width of the silica glass oxide film became significantly smaller than the desired value.

(3) Further, it has been found that when the degree of vacuum is lowered, the etching rate is increased, but the verticality is deteriorated and the side surface is also roughened.

(4) Further, CHF ₃ gas is harmful, and when the amount thereof is large, not only does it harm the human body, but it also promotes the adhesion of reaction products to the reaction chamber and the exhaust system, thus improving the reproducibility of low temperature dry etching. It has also been found that it lowers and accelerates the deterioration of the device life.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to improve the verticality of the side surface of the material to be etched or the side surface of the oxide film, the roughness of the side surface of the film, the sub-trench, the etching rate and the selectivity. It is an object of the present invention to provide a low temperature dry etching method and an apparatus therefor capable of realizing the characteristics satisfying all of the above.

[0012]

First, in the first invention, the material to be etched inserted in the preliminary chamber is conveyed to the reaction chamber through an airtight valve, and the substrate is kept at a low temperature of 0 ° C. or lower in the reaction chamber. When the surface of the material to be etched is subjected to low temperature dry etching using a fluorine-based gas, the flow rate of the inert gas is overlapped with the flow rate of the fluorine-based gas by a factor of 2 or more to flow into the reaction chamber. The low-temperature dry etching method is characterized in that the etching is performed while maintaining the temperature.

A second invention is characterized in that, in the first invention, the material to be etched is a substrate with an oxide film, and the surface of the material to be etched subjected to low temperature dry etching is an oxide film of the substrate with an oxide film. This is a low temperature dry etching method.

A third aspect of the invention is that in the second aspect of the invention, the temperature of the substrate is kept at -20 ° C. or less and the total flow rate of the fluorine-based gas flow rate and the inert gas flow rate is set to 60 cc / min or more. It is a characteristic low temperature dry etching method.

A fourth aspect of the present invention is the same as the second and third aspects, wherein the oxide film is SiO ₂ or P is formed on SiO ₂ .
Ti, Ge, B, Ta, Er, Pr, Nd, Zn, S
This is a low-temperature dry etching method characterized in that at least one dopant such as n or N is added. The above oxide film is preferable, but SiON or SiO _x N _y H _z may be used instead.

A fifth invention is a low temperature dry etching method according to the fourth invention, wherein CHF ₃ is used as the fluorine-based gas.

A sixth invention is the same as the fifth invention, except that CH
F ₃ gas flow rate is 30 cc / min or more, total flow rate of inert gas and CHF ₃ gas is 60 cc / min or more, vacuum degree is 2.66 Pa or less, high frequency power for generating plasma is 450 W or more, substrate is A low temperature dry etching method is characterized in that the temperature is set to -20 ° C or lower.

A seventh invention is the low-temperature dry etching method according to the first to sixth inventions, wherein the inert gas is Ar gas.

An eighth aspect of the present invention is capable of supplying a preliminary chamber for inserting / removing a substrate with an oxide film, a fluorine-based gas and an inert gas, and at least twice the inert gas flow rate as the fluorine-based gas flow rate. At least one reaction chamber provided with an etching gas supply system capable of being superposed and supplied, and an exhaust system capable of evacuating the chamber to 2.66 Pa or less, a preliminary chamber and a reaction chamber. A gate valve to be connected, a pair of electrodes provided in the reaction chamber on which an oxide film-coated substrate is placed, a means for applying high-frequency power of 300 W or more between the pair of electrodes, and at least one reaction chamber Means for holding the substrate at 0 ° C. or lower, and means for inserting / removing the substrate into / from the spare chamber and transferring the substrate between the spare chamber and at least one reaction chamber through a gate valve. Also is cold dry etching apparatus capable of etching the oxide film on the substrate.

In a ninth aspect based on the eighth aspect, at least one of the remaining reaction chambers other than the reaction chamber for etching the oxide film is used to etch the metal film on the upper surface of the oxide film using a photoresist mask. This is a low temperature dry etching apparatus characterized by being used as a reaction chamber.

A tenth aspect of the present invention is the substrate having an oxide film according to the eighth and ninth aspects, wherein the substrate having a flat back surface is used as the substrate having an oxide film and the substrate having an oxide film is placed on one electrode in an airtightly sealed state. The low-temperature dry etching apparatus is characterized in that He gas is supplied to the back surface from outside the reaction chamber so that the back surface of the substrate is kept in a He gas atmosphere.

An eleventh aspect of the present invention is the eighth to tenth aspects of the invention, wherein the area of the exhaust system provided in the reaction chamber is larger than the area of the substrate with an oxide film so that the degree of vacuum is 2.66 Pa or less. This is a low temperature dry etching apparatus characterized by being realized.

[0023]

In the first and second aspects of the invention, the total flow rate of the etching gas as well as the fluorine-based gas is increased by causing the flow rate of the inert gas to overlap the flow rate of the fluorine-based gas at least twice. Is the way. Regarding the flow rate of the fluorine-based gas, in the etching evaluation item, the verticality, the smoothness of the side surface, the sub-trench, and the etching rate may conflict with each other.

That is, the increase of the fluorine-containing gas deteriorates the verticality and the smoothness of the side surface, but the sub-trench and the etching rate are improved. Therefore, by increasing the fluorine-based gas and the total flow rate in this manner, it is possible to achieve both verticality, side surface smoothness, sub-trench, and etching rate.

However, if the total flow rate is increased, the degree of vacuum will decrease. Therefore, in the present invention, the degree of vacuum is set to 2.66 Pa or less by using a pump capable of high speed and high vacuum exhaust. As a result, the verticality of the etched substrate surface or the side surface of the oxide film and the roughness of the side surface can be favorably maintained. This brings very good results particularly when the core pattern of the waveguide made of an oxide film formed on the substrate is processed into a substantially rectangular cross section by dry etching.

For example, when a waveguide type optical device having a wavelength selection function such as an optical demultiplexer, an optical multiplexer, an optical filter, an optical directional coupler, etc. is realized, the verticality of the side surface of the core is disturbed. However, the wavelength characteristics of the optical device (for example, the central wavelength or the degree of separation between two wavelengths) change. Further, the roughness of the side surface of the core causes not only the change of the wavelength characteristics but also the increase of the light propagation loss. Therefore, 90
It is extremely important to have good verticality to ° and to reduce side surface roughness.

On the other hand, in the present invention, since the flow rate of the fluorine-based gas is increased, the sub-trench is hardly generated and the etching rate is improved. Although the shape of the sub-trench will be described later, the occurrence thereof also deteriorates the wavelength characteristics of the optical device and causes an increase in loss. Further, the confinement of light in the core of the waveguide becomes non-uniform and polarization dependency is caused, which has been a major obstacle to the realization of the optical device having the wavelength selection function.
However, according to the present invention, since this can also be improved,
An extremely large effect can be obtained.

As described above, the increase of the fluorine-based gas deteriorates the verticality and the smoothness of the side surface, but in the present invention, the inert gas is superposed with the fluorine-based gas more than twice. Therefore, deterioration of the verticality and the smoothness of the side surface can be prevented.

Further, the increase of the fluorine-based gas causes a problem that the etching selection ratio with respect to the oxide film becomes small and the reduction amount of the core pattern width becomes large. However, when the inert gas is superposed on the fluorine-based gas. The selection ratio can be greatly improved.

According to the third aspect of the invention, the lower the substrate temperature is, the more easily reaction products are attached to the etched surface, and the sub-trench is generated. Therefore, the total flow rate of the fluorine-based gas flow rate and the inert gas flow rate is set to 60 cc / min or more to suppress the generation of the sub-trench.

It should be noted that, as in the case of the present invention, it is possible to perform etching while maintaining the substrate temperature during etching at -20 ° C. or lower.
For example, in the case of etching a substrate in which an electronic circuit element or an optical circuit element is formed in advance in the waveguide or on the upper surface, it is extremely effective to damage the above element. This is because the thickness of the core of the waveguide is usually as thick as 3 μm or more and several tens of μm, so that the dry etching time also takes a long time of 1 hour or more. If the substrate is exposed to a high temperature state (usually a high temperature of several hundreds of degrees Celsius if not cooled) for such a long time, not only will the element be damaged, but the core or buffer layer This is because the movement of the refractive index controlling dopant causes a change in the refractive index distribution and the movement of OH ⁻ , which causes the deterioration of the optical characteristics.

[0032] As in the fourth invention, the oxide film is etched, SiO ₂ is of course, P to SiO _2, T
i, Ge, B, Ta, Zn, Sn, Zr, Er, Pr,
If it is applied to a material to which at least one dopant such as Nd and N for controlling the refractive index, for controlling the thermal expansion coefficient, and for adding functionality is added, this can be easily etched. Moreover, as described above, since the process is a low temperature process, the diffusion of the dopant does not occur at all, and it is possible to prevent deterioration of desired optical characteristics during the process. This is extremely effective in realizing a highly accurate waveguide.

A metal film (eg, WSi, W, Ta, T) is used as a mask material for etching the oxide film.
Even if a metal film (i, Al, Ni, Cr, etc.) or a resist film is used, it is not exposed to high temperature during etching, so that the metal film or the resist film is not deteriorated and stable. It can be etched. As a result, it is possible to realize a core pattern having a very small reduction amount, and it is possible to manufacture an optical device having desired optical characteristics as designed.

According to the fifth aspect of the invention, CHF ₃ gas is preferable as the gas for etching the oxide film, but other than that, C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ , CF ₄ etc. It may be a fluorine-based gas, a gas in which at least one of the above gases is mixed, or a gas to which C ₂ H ₄ or the like is added.

According to the sixth aspect, the CHF ₃ gas flow rate, which is a process parameter, is 30 cc / min or more, the total amount of the inert gas flow rate and the CHF ₃ gas flow rate is 60 cc / min or more, and the degree of vacuum is 2. Since the optimum high frequency power of 66 Pa or less for generating plasma and 450 W or more for the substrate temperature and -20 ° C. or less for the substrate are satisfied, all of the etching evaluation items can be more satisfactorily satisfied.

According to the seventh invention, since the inert gas is Ar gas, all the etching evaluation items can be satisfied more stably. In particular, in terms of the reduction amount of the core pattern, as will be described in detail in the examples, the selection ratio can be increased by using Ar gas as compared with an inert gas such as He or N _2, so that the reduction amount can be reduced. There is an effect that there is little.

According to the eighth aspect of the present invention, the gas supply system capable of supplying the flow rate of the fluorine-based gas by superimposing the flow rate of the inert gas on the flow rate of the inert gas to the reaction chamber by a factor of 2 or more, and the pressure in the chamber to 2.66 Pa or less. It has an exhaust system capable of vacuum exhaust.
Further, in order to increase the etching rate, a high frequency power of 300 W or more is applied between the electrodes in the reaction chamber to keep the substrate in the reaction chamber at 0 ° C. or lower. Moreover, it is designed to be inserted / removed through the spare chamber, and the spare chamber and the reaction chamber are connected by an airtight gate valve to automatically convey between these chambers, so vertical It is possible to perform etching satisfying all the characteristics such as the smoothness of the side surface, the sub-trench, the reduction of the core width, and the etching rate.

According to the ninth invention, at least one of the remaining reaction chambers is used as a reaction chamber for etching the metal film on the upper surface of the oxide film, so that the metal film on the upper surface of the oxide film is continuously etched. The oxide film can be etched by using a gate valve, and since both chambers are connected via a gate valve, the substrate does not have to be taken out into the atmosphere, so pattern defects due to dust or impurities can be prevented. You can Also, since it does not go into the atmosphere, OH in the atmosphere
^- (Hydroxyl ion) does not adhere to the oxide film or diffuse into the oxide film, and a low-loss waveguide can be manufactured.

As in the tenth invention, a substrate having a flat back surface is used as the substrate with an oxide film, and the back surface of the substrate with an oxide film is hermetically sealed between the electrodes so that the back surface of the substrate is filled with He gas. When kept in the atmosphere, the He gas can keep the back surface of the substrate in the He atmosphere without leaking into the reaction chamber, and the substrate can be efficiently kept at a low temperature.

As in the eleventh aspect, when the area of the exhaust system of the reaction chamber is larger than the area of the substrate with an oxide film,
High speed and surely a vacuum degree of 2.66 Pa or less can be obtained.

[0041]

FIG. 1 shows a first embodiment of a low temperature dry etching apparatus by reactive ion etching according to the present invention. Here, as the material to be etched, a waveguide sample 1 which will be described in detail later is used.
0 (see FIG. 2A) was used.

This apparatus has two reaction chambers 1-1 and 1-2 for dry etching, exhaust systems 3-1 and 3-2 for evacuating each reaction chamber, and before transporting to each reaction chamber. A preliminary chamber 2 for creating a vacuum state is provided. further,
An exhaust system 4 for evacuating the inside of the auxiliary chamber 2, a cable valve 11-1 connecting the reaction chamber 1-1 and the auxiliary chamber 2 on one side, and a gate valve 11 connecting the reaction chamber 1-2 and the auxiliary chamber 2 on the other side.
-2, an etching gas (N
Gas supply system 14 for supplying F ₃ , CF _4, etc., and C for supplying etching gas CHF ₃ into the other reaction chamber 1-2.
An HF ₃ gas supply system 7 is provided.

In addition, the reaction chamber 1-2 is provided with an Ar gas supply system 21 for introducing the flow rate of the Ar gas which is more than double the flow rate of the CHF ₃ into the reaction chamber 1-2. There is. The introduction of this Ar gas is very effective in improving the verticality of the oxide film, reducing the side surface roughness, suppressing the occurrence of sub-trench, and reducing the reduction (blurring) of the oxide film (core) pattern width after etching. Is. Similar effects can be expected by using an inert gas such as He or N ₂ instead of Ar gas.

Furthermore, in the apparatus of FIG. 1, one reaction chamber 1
-1, a high frequency power source 6-1 applied between the upper electrode 13-1 installed in -1 and the lower electrode 13-2 on which the sample 10 is placed,
A high-frequency power source 6-2 applied between the upper electrode 5-1 installed in the other reaction chamber 1-2 and the lower electrode 5-2 on which the sample 10 is placed, and in each reaction chamber 1-1 and 1-2. Lower electrode 1
A coolant circulation system 9 is provided to flow the coolant in the directions indicated by arrows 9-1 to 9-2 in order to cool the sample 10 on 3-2 and 5-2 to a low temperature. As can be seen from the illustrated example, each of the reaction chambers of this example constitutes a parallel plate reactive ion etching apparatus. Of these, low temperature dry etching is performed in the reaction chambers 1-1 and 1-2 provided with the coolant circulation system 9.

Further, holes 13-21 and 5-21 for fitting the sample 10 are provided in the central portions of the lower electrodes 13-1 and 5-2 on which the sample 10 is placed in the reaction chambers 1-1 and 1-2, respectively. Back surface of sample 10 and lower electrode 13-1 or 5
An air-tight seal can be made between the -2 and -2. The lower electrodes 13-1 and 5-2 are provided with a He gas supply system 8 communicating with the hermetically sealed portion, and He gas can be blown to the back surface of the sample 10 to accelerate the temperature reduction of the sample 10. .

Further, the sample 10 is inserted into the preliminary chamber 2,
Sample insertion / sample extraction system 1 for taking out a sample from the spare chamber 2
2, and to prevent dew condensation, gas (N ₂ ,
A gas supply system 15 for introducing Ar, O ₂ , O, He, etc.), a spare chamber 2 and two reaction chambers 1 (not shown).
A transfer system for transferring the sample 10 between the first and second points is provided.
The transfer system and the sample insertion / removal system 12 constitute a conveying means. Next, a method of dry etching using this low temperature dry etching apparatus will be described with reference to FIG.

First, the sample inserted from the sample insertion / sample extraction system 12 in the preliminary chamber 2 will be described with reference to FIG. As the sample, a SiO ₂ substrate having a thickness of 1 mm and a diameter of 3 inches was used. The back surface of this substrate is processed flat. Instead of the SiO ₂ substrate, semiconductors such as Si, InP, GaAs, quartz-based and multi-component glass, LiNbO ₃ , LiTaO ₃
Alternatively, a dielectric material, a magnetic material, or the like may be used. This sample has a buffer layer 20, a core layer 19, and a WSi on the substrate 16 in this order.
The film 18 is formed, and the photoresist pattern 17 is patterned on the WSi film 18.

The buffer layer 20 is made of SiO ₂ and has a thickness of about 10 μm. An oxide film is used for the core layer 19. For example, SiO ₂ , TiO ₂ , GeO ₂ , P ₂ O ₅
A refractive index controlling additive such as 0. Films with a few wt% to a few dozen wt% added, or SiON, SiO _x N _y H _z
And so on. In this example, a film (thickness of about 8 μm) in which 1% by weight of TiO ₂ was added to SiO ₂ was used. WSi film 1
Since 8 serves as a mask material for etching the core layer 19, it has a thickness of about 1 μm. The photoresist pattern 17 is a mask material for patterning the WSi film 18 by dry etching, and its film thickness is selected to be 0.5 to 1 μm in view of the selection ratio.

Now, the sample 10 shown in FIG.
After being inserted into the preparatory chamber 2 shown in (1), N ₂ gas (or a gas such as Ar, He, O ₂ or the like) having a dew point of −60 ° C. or lower is introduced into the preparatory chamber 2 from the direction of the arrow of the gas supply system 15. While flowing (gas flow rate 100 cc / min), the inside of the preliminary chamber 2 is evacuated by the exhaust system 4 to dry. Along with this, the two reaction chambers 1-1 and 1-2 are also evacuated by the evacuation systems 3-1 and 3-2. After maintaining the vacuum degree in the preliminary chamber 2 and the reaction chambers 1-1 and 1-2 at 1.33 × 10 ⁻¹ Pa or less, one of the reaction chambers 1
Open the gate valve 11-1 connected to -1 and sample 10
Is transferred from the preliminary chamber 2 to the reaction chamber 1-1, and the lower electrode 13-
Place on top of 2. Then, the substrate is cooled to −40 ° C. by the coolant circulation system 9 and the He gas supply system 8. Next, the gate valve 11-1 is closed, NF ₃ gas is caused to flow at 20 cc / min from the direction of the arrow of the gas supply system 14, and the high frequency power source 6-1 (high frequency power source) is provided between the upper electrode 13-1 and the lower electrode 13-2. Two
0 W) was applied to generate plasma between the electrodes 13-1 and 13-2. The exhaust system 3-1 was set so that the degree of vacuum in the reaction chamber 1-1 at this time was 1.33 Pa. As a result, the etching of the WSi film 18 was completed in about 6 minutes.
A sample in this state is shown in FIG. The width of the etched WSi pattern was reduced by only 1% with respect to the width of the photoresist pattern. It is considered that this is because the photoresist was hardly damaged or etched because of the low temperature etching. In addition, the etched WSi side surface was also extremely smooth.

Next, the etching gas supplied from the gas supply system 14 was switched from NF ₃ gas to CF ₄ gas, and etching was similarly carried out in a plasma atmosphere to remove the photoresist pattern film on the surface (FIG. 2).
(C)).

Thereafter, the gas supply system 14 is closed to stop the supply of CF ₄ gas, the high frequency power source 6-1 is turned off, the gate valve 11-1 is opened, and the sample 10 is sent back into the auxiliary chamber 2 by the transfer system. It was Then, high vacuum evacuation was performed again while flowing N ₂ gas in the preliminary chamber 2 at 100 cc / min.

Next, the lower electrode 5 in the other reaction chamber 1-2
-2, a refrigerant is made to flow from the circulation system 9 as indicated by arrows 9-1 to 9-2, and the lower electrode 5-2 is also at a low temperature (-4 in this embodiment).
The temperature was controlled at 0 ° C. The reaction chamber 1 is equipped with a high-speed turbo molecular pump, and is evacuated to a high vacuum (1.33 × 10 ^-2 Pa or less) by an exhaust system 3-2 having a diameter area larger than that of the substrate.
The sample 10 was conveyed in -2.

That is, the gate valve 11-2 connected to the other reaction chamber 1-2 is opened, and the preliminary chamber 2 is moved to the reaction chamber 1-
The sample is conveyed onto the second lower electrode 5-2. Lower electrode 5-
After the sample 10 was placed on the sample 2, He gas was blown to the back surface of the sample 10 from the direction of the arrow at 5 cc / min to place the sample 10 in the He atmosphere with the He gas to accelerate the temperature reduction to −40 ° C. The sample 10 is clamped on the lower electrode 5-2 so that the He gas does not leak into the reaction chamber 1-2.
That is, the constant gas pressure of He is applied to the back surface of the sample 10.

In this way, the sample 10 was cooled to a desired low temperature (-
CHF ₃ gas is made to flow from the direction of the arrow of the gas supply system 7 while maintaining the temperature at 40 ° C.), and a high frequency power source 6-2 is applied between the upper electrode 5-1 and the lower electrode 5-2 to generate plasma. The low temperature dry etching of the core layer 19 was performed. This state is shown in FIG.

After completion of etching in the reaction chamber 1-2, the gas supply systems 7 and 21 are closed to stop CHF ₃ gas and Ar gas, the high frequency power source 6-2 is turned off, and the gate valve 11-
2 was opened, and the sample 10 was transferred into the preliminary chamber 2 which was evacuated while N ₂ gas was flowed at 100 cc / min. After transfer, gate valve 1 connected to one reaction chamber 1-1 again
1-1 was opened, and the sample 10 was placed from the preliminary chamber 2 onto the lower electrode 13-2 of the reaction chamber 1-1. And gas supply system 14
NF ₃ gas is caused to flow in the direction of the arrow, and high-frequency power (20 W) is applied between the upper electrode 13-1 and the lower electrode 13-2, while maintaining a vacuum degree of 1.33 Pa and WSi on the core pattern 19. The film 18 was removed by dry etching to obtain the structure shown in FIG.

Thereafter, the gas supply system 14 is closed to stop the NF ₃ gas, the high frequency power source 6-1 is turned off, and the gate valve 1
The sample No. 1-1 was opened and the sample 10 was conveyed into the preliminary chamber 2. Next, after vacuum evacuation while flowing N ₂ gas for a while, vacuum evacuation in the preliminary chamber 2 is stopped, and N ₂ gas is continuously introduced to fill the preliminary chamber 2 with N ₂ gas. The vacuum inside was released, and the sample 10 was taken out into the atmosphere.

Various experimental examples according to the above-mentioned process will be shown below. In addition to the examples according to the method of the present invention, this experimental example includes comparative examples according to the conventional method.

(Comparative Example 1) The vacuum degree was kept at 1.33 Pa,
The high frequency power (RF power) was set to 300 W and etching was performed for 90 minutes while flowing CHF ₃ gas at 10 cc / min. As a result, the verticality of the side surface of the etched core is shown in FIG.
As shown in (a), it was good. The side surface roughness was also good as shown in FIG. However, the etching rate was as low as 400 Å / min (hereinafter, A / min), and as shown in FIG. 5, the reaction product 24 adhered to the side surface 22 of the core, whereby the sub-trench 23 was generated. As described above, the sub-trench 23 increases scattering loss due to non-uniformity of the waveguide structure, and
It deteriorates wavelength characteristics and polarization characteristics. Further, the reduction amount of the core width is close to 10% of the WSi width, which is also a problem.

The side surface of the core shown in FIG.
It shows the case where the F ₃ gas is less than 10 cc / min.

(Comparative Example 2) The degree of vacuum was kept at 1.33 Pa,
High frequency power is 300W and CHF ₃ gas is 40cc / m
Etching was performed for 90 minutes while flowing in. as a result,
The perpendicularity of the side surface of the etched core became a shape of a taper as shown in FIG. That is, the verticality deteriorated. Further, its side surface was also roughened as shown in FIG. On the contrary, the etching rate increased to 500 A / min, and the sub-trench 23 as shown in FIG. 5 almost disappeared. Furthermore, the reduction amount of the core width was worse than in the first experiment.

(Comparative Example 3) The vacuum degree was kept at 2.66 Pa,
After that, etching was performed under the same conditions as in Comparative Example 1. As a result, the verticality and the roughness of the side surface deteriorated, and sub-trench also occurred. Instead, the etching rate increased about 1.2 times. Also in this case, the reduction amount of the core width was worse than in the first experiment.

(Comparative Example 4) The temperature of the sample was changed from -40 ° C to 0.
The etching was carried out under the same conditions as in Comparative Example 1 except that the temperature was changed to ° C. As a result, the verticality and the roughness of the side surface were deteriorated, but the sub-trench was reduced and the etching rate was increased. Also in this case, the reduction amount of the core width was further increased.

As described above, it was not possible to obtain the conditions satisfying all of the verticality, the side surface roughness, the sub-trench, the etching rate, and the accuracy of the core width. Therefore, a method of superposing Ar gas of the present invention on CHF ₃ gas was examined.

(Comparative Example 5) Under the conditions of Comparative Example 1, Ar gas flow rate was superposed at 10 cc / min and the core film was etched. As a result, the side surface of the core was etched to about 90 °,
There was little roughness on that side. However, the sub-trench still occurs. Furthermore, the etching rate was not improved. Next, the Ar gas flow rate was increased to 15 cc / min, and no change was observed. However, the reduction amount of the core width was 3% or less compared to the WSi width, and it was confirmed that the reduction amount of the core width was significantly reduced by superimposing Ar gas.

Example 1 The core film was etched under the conditions of Comparative Example 2 by superposing an Ar gas flow rate of 125 cc / min. As a result, the verticality and the smoothness of the side surface were extremely good, and sub trenches were hardly generated. Further, the etching rate can be as large as that of Comparative Example 2, and the reduction amount of the core width is also Comparative Example 5.
By the way, I was able to obtain the results that met all the initial goals. Further, as a result of conducting a similar experiment from this condition by gradually reducing the Ar gas flow rate, it was found that the Ar gas flow rate of 80 cc / min or more was effective.

Example 2 Under the conditions of Example 1, C
Change the HF ₃ gas flow rate from 40cc / min to 30cc / min,
Also, change the degree of vacuum from 1.33Pa to 1.995Pa,
The etching was performed for about 90 minutes. As a result, verticality,
The smoothness of the side surfaces was good, and sub trenches were hardly generated. The etching rate and the reduction amount of the core width were almost unchanged. Also in this case, it was found that an effective effect can be obtained when the Ar gas flow rate is 60 cc / min or more.

(Embodiment 3) Under the conditions of Embodiment 2, the high frequency power is changed from 300 W to 450 W, and similarly 90
As a result of performing the etching for 1 minute, the etching rate was improved to about 1000 A / min. The verticality, the smoothness of the side surface, the sub-trench, and the reduction amount of the core width were all good.

These are shown in Table 1. When the results of Table 1 are summarized and arranged, it is found that the relationship between process parameters and evaluation items is as shown in Table 2. Note that the selection ratio of WSi to the oxide film (= (etching rate of oxide film) /
(WSi etching rate) was a value of 15 or more, which was a sufficient value for etching the core film for the waveguide.

[0069]

[Table 1]

[0070]

[Table 2]

That is, since the CHF ₃ gas flow rate has a contradictory result between the verticality and the smoothness of the side surface, and the sub-trench and the etching rate, take an intermediate value, and ≧
The flow rate of Ar gas is set to 30 cc / min, and the flow rate of Ar gas is twice that of CHF ₃ and the total flow rate is 60 cc / min or more, thereby suppressing deterioration of verticality and side smoothness.

Since it is desirable that the degree of vacuum is as high as possible, the degree of vacuum is set to ≤2.66 Pa. Since the high frequency power does not directly affect the verticality, the side surface roughness, and the sub-trench and contributes to the etching rate, it is desirable to be as high as possible. The temperature is used to prevent damage to optical elements and electronic circuit elements formed on or in the waveguide, to improve verticality and smoothness of side surfaces, and to reduce the loss of the etched core pattern width. The lowest temperature possible (≦ −20 ° C.) is preferable. Note that FIG.
In the above, SiO _x N _y H formed by plasma CVD method as the core layer 19 using SiH ₄ , N ₂ O and N ₂ gas.
_{The z} film was etched in the same manner, but it was possible to obtain characteristics almost equivalent to the above results.

As in the present invention, A
The flow rate of the r gas is superposed twice or more, and the reaction chamber is set to 2.
In order to exhaust at a high speed of 66 Pa or less, the exhaust system 3-2 was exhausted by using a turbo molecular pump or a rotary pump having an exhaust rate of 500 l / sec or more. Exhaust system 3-2
A large-diameter exhaust pipe having a diameter of 6 inches was used as the exhaust pipe.
That is, the area of the substrate to be etched (2 inches in diameter ~
It is an indispensable condition to exhaust gas using an exhaust pipe having a diameter larger than 5 inches. This is also one of the features of the low temperature dry etching apparatus of this embodiment.

Next, description will be made on the experimental results of the optical multiplexer / demultiplexer having the waveguide structure, which was experimentally manufactured using the above-mentioned low temperature dry etching apparatus.

FIGS. 6A and 6B are schematic views of a waveguide type optical multiplexer / demultiplexer, wherein FIG. 6A is an overall plan view,
(B) shows the aa 'sectional view of (a), respectively. First, as shown in (a), the optical signals of wavelengths λ ₁ and λ ₂ that are incident on the input end of the optical multiplexer / demultiplexer as shown by arrow 26 propagate in the core 25-1 and reach the coupling region 29. Propagating while interfering between the core 25-1 and the core 25-2, the arrows 27-1 and 27-
2, the optical signals of wavelengths λ ₁ and λ ₂ are demultiplexed and output.

In this structure, in order to perform demultiplexing with low loss and to improve wavelength separation, as described above, the side surfaces of the cores 25-1 and 25-2 have good verticality, and The roughness should be small, the sub-trench should be small, and the width reduction of the cores 25-1 and 25-2 should be suppressed. The width and thickness W of the cores 25-1 and 25-2 are 8 μm, the interval S between the cores 25-1 and 25-2 is 5.5 μm, and the ratio between the core 25-1 (25-2) and the clad 28 is The demultiplexing characteristics of the prototyped optical multiplexer / demultiplexer were evaluated with a refractive index difference of 0.25%. The results are shown by the solid line (optical multiplexer / demultiplexer produced by the method of this example) and the dotted line (optical multiplexer / demultiplexer produced by the method of the comparative example) in FIG. 7. However, in design values, λ ₁ = 1.3 μm, λ ₂ = 1.
It was set to 55 μm.

In the method of this embodiment, there is almost no shift in the center wavelength to be demultiplexed, whereas in the method of the comparative example, there is a considerable shift in the center wavelength (about 0.12).
μm) occurred. The propagation loss of the method of this example was also small. This is also due to the side surface being roughened and the sub-trench being greatly reduced. Furthermore, the wavelengths λ ₁ and λ ₂
The isolation between and is 2 in the method of this embodiment.
It was found that the method of the comparative example could obtain isolation of only about 20 dB, while the value of 0 dB or more was obtained. As described above, it was found that the method of the present example also provided good results for the optical characteristics of the waveguide.

FIG. 8 shows a second embodiment in which the low temperature dry etching apparatus of the present invention is simplified. In the apparatus shown in FIG. 1, the reaction chamber 1-1 is omitted and only one reaction chamber capable of low temperature dry etching is used as the preliminary chamber 2.
This is a low temperature dry etching apparatus connected to the above, and performs the low temperature dry etching process of FIG.

The present invention is not limited to the above embodiment. First, the number of reaction chambers may be three, and further four or more.
That is, by providing one or two or more reaction chambers, the film to be etched can be a metal or oxide composed of a one-layer film, a two-layer film, a three-layer film, and a multilayer film,
Alternatively, it may be a composite film of metal and oxide. All of these reaction chambers are configured to be connected via a common auxiliary chamber.

Further, in the above Examples 1 to 3, Ar
The case where the gases are superposed has been described, but the verticality of the core when He or N ₂ gas is used instead of Ar gas,
Side smoothness, sub-trench, etching rate is Ar
It is almost the same as when using gas, and He or N
The selection ratio when ₂ gases were used was 10 or more, and the reduction amount of the core width was 5% or less of the WSi width, confirming that the object of the present invention can be sufficiently achieved.

Further, the dry etching apparatus is not limited to the parallel plate type reactive ion etching apparatus, and may be another dry etching apparatus. Also,
In the above-described embodiment, the low temperature dry etching is performed in the reaction chamber 1-1 that is one side for etching the WSi film or the like. Omit the cooling by 8,
Ordinary dry etching may be performed. Also, the sample is not limited to the above-mentioned embodiment, and a material to be etched such as for semiconductor IC can be used.

[0082]

【The invention's effect】

(1) According to the invention of claim 1, the verticality of the side surface of the etched material surface is maintained at about 90 °, and the side surface is not roughened and the sub-trench is hardly generated, and the etching rate is also high. It can be etched in a sufficiently large state. Further, the flow of the inert gas in a superimposed manner has an action of sufficiently diluting a harmful gas such as CHF ₃ gas, so that the harm to the human body can be reduced. Further, it has an effect of significantly reducing the adhesion of reaction products to the reaction chamber and the exhaust system, can enhance the reproducibility of low temperature dry etching, and can prevent the deterioration of the life of the apparatus. Further, by overlapping the inert gas, the width reduction amount of the etched oxide film can be suppressed to be small.

(2) According to the invention of claim 2, in addition to the effect of claim 1, when an optical element or an electronic circuit element is formed on or in the substrate to be etched, these It can be etched without damage. This makes it possible to easily realize desired optical characteristics (loss characteristics, wavelength characteristics, polarization characteristics, etc.) when a pattern such as a waveguide is formed by etching.

(3) According to the third aspect of the present invention, since the reaction product is less likely to adhere to the surface, it is possible to suppress the generation of sub-trench.

(4) According to the invention described in claim 4, it is possible to easily carry out etching without causing diffusion of the dopant, and it is possible to prevent deterioration of optical characteristics. (5) According to the invention described in claim 5, since the etching gas suitable for the oxide film is used, the etching can be favorably performed.

(6) According to the invention described in claim 6, since each process parameter for etching is set to an optimum value, it is possible to satisfy all of the various etching characteristics more satisfactorily.

(7) According to the invention described in claim 7, since the inert gas is Ar gas, etching can be performed more stably. In addition, in terms of reduction of the width of the etched oxide film, an excellent effect is obtained as compared with the case of using an inert gas such as He or N ₂ .

(8) According to the invention described in claim 8, since the apparatus is configured to obtain good process parameters, it is possible to carry out etching satisfying all etching characteristics.

(9) According to the invention described in claim 9, since the oxide film can be continuously etched after etching the metal film, work efficiency is good, and dust or unnecessary impurities are attached or mixed effectively. Can be prevented.

(10) According to the invention of claim 10,
The substrate can be efficiently kept at a low temperature without leaking He gas into the reaction chamber.

(11) According to the invention of claim 11,
The desired high degree of vacuum can be reliably obtained at high speed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for explaining a first embodiment of a low temperature dry etching apparatus of the present invention.

FIG. 2 is a manufacturing process diagram of a waveguide for explaining an embodiment of a low temperature dry etching method of the present invention.

FIG. 3 is an explanatory diagram showing verticality of an etching oxide film due to a difference in low temperature dry etching conditions.

FIG. 4 is an explanatory diagram showing side surface roughness of an etching oxide film due to a difference in low temperature dry etching conditions.

FIG. 5 is an explanatory diagram showing a state of generation of sub-trench of an etching oxide film by low temperature dry etching.

FIG. 6 is a schematic diagram of an optical multiplexer / demultiplexer having a waveguide structure, which is prototyped using the low temperature dry etching apparatus of this embodiment.

FIG. 7 is a comparative characteristic diagram between the example of the waveguide type optical multiplexer / demultiplexer shown in FIG. 6 and a conventional example.

FIG. 8 is a schematic configuration diagram of an apparatus for explaining a second embodiment of the low temperature dry etching apparatus of the present invention.

FIG. 9 is a schematic configuration diagram of a low temperature dry etching apparatus used for studying the present invention.

[Explanation of symbols]

1-1 Reaction Chamber 1-2 Reaction Chamber 2 Preliminary Chamber 3-1 Exhaust System 3-2 Exhaust System 4 Exhaust System 5-21 Hole 7 CHF ₃ Gas Supply System 8 He Gas Supply System 9 Refrigerant Circulation System 10 Sample 11-1 Gate valve 11-2 Gate valve 12 Sample insertion / extraction system 13-21 hole 14 Gas supply system 15 Gas supply system 21 Ar gas supply system

Claims (11)

[Claims] 1. A material to be etched inserted in a preparatory chamber is conveyed to a reaction chamber through an airtight valve, and the substrate is kept at a low temperature of 0 ° C. or lower in the reaction chamber so that the surface of the material to be etched is a fluorine-based gas. When performing low-temperature dry etching using, the flow rate of the inert gas is made to overlap the flow rate of the fluorine-based gas by a factor of 2 or more, the flow rate is made to flow in the reaction chamber, and the vacuum degree in the reaction chamber is kept at 2.66 Pa or less. A low temperature dry etching method characterized in that etching is performed. 2. The low temperature dry etching method according to claim 1, wherein the material to be etched is a substrate with an oxide film, and the surface of the material to be etched to be low temperature dry etched is an oxide film of the substrate with an oxide film. And a low temperature dry etching method. 3. The low-temperature dry etching method according to claim 2, wherein the temperature of the substrate is maintained at -20 ° C. or lower and the total flow rate of the fluorine-based gas and the inert gas is 60 cc / m 2.
A low temperature dry etching method characterized in that a flow rate of at least in is applied. 4. The low temperature dry etching method according to claim 2 or 3, wherein the oxide film is SiO ₂ , or SiO ₂ contains P, Ti, Ge, B, Ta, Er, Pr, N.
A low-temperature dry etching method, characterized in that at least one dopant such as d, Zn, Sn, N is added. 5. The low temperature dry etching method according to claim 4, wherein CHF ₃ is used as the fluorine-based gas. 6. The low-temperature dry etching method according to claim 5, wherein the CHF ₃ gas flow rate is 30 cc / min or more,
The total flow rate of inert gas and CHF ₃ gas is 60cc / min.
Flowing above, vacuum degree is 2.66Pa or less, high frequency power generating plasma is 450W or more, and substrate temperature is -2.
A low-temperature dry etching method characterized in that the temperature is 0 ° C. or lower. 7. The low temperature dry etching method according to claim 1, wherein the inert gas is Ar gas. 8. A preliminary chamber for inserting / removing a substrate with an oxide film, a fluorinated gas and an inert gas can be supplied, and the fluorinated gas flow is superposed at least twice as much as the inert gas flow. At least one reaction chamber provided with an etching gas supply system capable of performing vacuum exhaust and an exhaust system capable of evacuating the chamber to 2.66 Pa or less, and a gate connecting the preliminary chamber and the reaction chamber. A valve, a pair of electrodes provided in the reaction chamber on which an oxide film-coated substrate is placed, a means for applying high-frequency power of 300 W or more between the pair of electrodes, and at least one reaction chamber in the reaction chamber. A means for holding the substrate at 0 ° C. or lower, and a carrying means for inserting / removing the substrate into / from the preliminary chamber and transferring the substrate between the preliminary chamber and at least one reaction chamber through a gate valve, Even without cold dry etching apparatus capable of etching the oxide film of the substrate. 9. The low temperature dry etching apparatus according to claim 8, wherein at least one of the remaining reaction chambers is a reaction chamber for etching the metal film on the upper surface of the oxide film using a photoresist mask. Low temperature dry etching equipment. 10. The low-temperature dry etching apparatus according to claim 8, wherein the substrate with an oxide film has a flat back surface, and the oxide film is placed on the one electrode in a hermetically sealed state. A low temperature dry etching apparatus, characterized in that He gas is supplied to the back surface of the attached substrate from outside the reaction chamber so that the back surface of the substrate is kept in a He gas atmosphere. 11. The low-temperature dry etching apparatus according to claim 8, wherein the area of the exhaust system provided in the reaction chamber is larger than the area of the substrate with an oxide film and 2.66 Pa. A low temperature dry etching apparatus characterized in that the following vacuum degree is obtained.