JP2001181827A - Method for depositing glass film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the method for depositing a glass film by which the refractive index and thickness are made the same over the whole of the glass film. SOLUTION: In the method for depositing a glass film by which a silicon dioxide glass film essentially consisting of silicon dioxide and containing germanium dioxide of several % to 30% is deposited on a substrate by using a sputtering method, a target used for the sputtering method is composed of silicon dioxide and germanium dioxide, and its density is controlled to 70% or more of the solid body having the same composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a method for forming a glass film. In particular, the present invention relates to an improvement in a method of forming a glass film in which a silicon dioxide glass film containing silicon dioxide as a main component and containing several to 30% germanium dioxide is formed on a substrate by using a sputtering method. More particularly, it relates to improvements in which the formed glass film has the same refractive index and thickness throughout the glass film.

[0002]

2. Description of the Related Art Light has long been used as a communication signal medium. Since the optical signal transmission line used for transmitting the optical signal used in the optical communication includes an optical fiber and an optical signal circuit device such as a lens, a mirror, a prism, and an optical switch, such an optical signal is transmitted. Various optical switches are indispensable for configuring a signal circuit. This is for responding to a request for switching communication paths, etc., in order to avoid a failure or to temporarily increase communication traffic. Some optical signal circuit devices such as optical switches use a glass film formed on a substrate such as silicon by using a semiconductor device manufacturing technique as an optical waveguide. Such semiconductor device manufacturing techniques include a deposition method for depositing silicon dioxide or the like, a patterning method such as a photolithography method including an etching method for removing a deposited film of silicon dioxide or the like only from a selected region, and the like. However, it is well known that this semiconductor device manufacturing technique is suitable for mass production.

As an example of such an optical switch, a so-called 2 × 2 switch element using the principle of a Mach-Zehnder interferometer is known. The 2 × 2 switch element is an optical signal circuit element constituting a four-terminal network having two signal input ports and two signal output ports, and converts a signal input to each signal input port into two signal input ports. It has a function of selectively outputting to any of the output ports, which will be described below with reference to the drawings.

FIG. 3 is a plan view of a 2 × 2 switching element, FIG. 4 is a sectional view taken along the line AA, and FIG.
It is sectional drawing. In the figure, 1 is a substrate made of silicon or the like, 2 is a lower cladding layer made of a silicon dioxide film or the like, and 3 is a glass film made of silicon dioxide or the like having a larger refractive index than the lower cladding layer 2 and having an optical confinement effect. Reference numeral 4 denotes an upper cladding layer made of a silicon dioxide film or the like having a smaller refractive index than that of the optical waveguide, 5 denotes a heater made of a conductive layer, and 6 and 7 denote terminals of the heater 5. Here, 8 and 9 are two signal input ports, and 10 is two signal output ports.

A signal input to one signal input port 8 branches and flows into two optical waveguides 14 and 15 at a node 12 (first directional coupler 12).
(The second directional coupler 13). At this time, one of the signal output ports 10 or 11 is selected according to the phase relationship between the two optical signals to be joined, and is not output to the other signal output port 11 or 10. Here, when a current is passed through the heater 5 to heat it, the refractive index of the corresponding optical waveguide (15 in the figure) increases, and the speed of light flowing through this optical waveguide (15 in the figure) decreases. Then, when the optical signals merge in the second directional coupler 13, the phase relationship is inverted, and the signal output port 11 or 10 opposite to the previously selected signal output port is selected,
The signal is output only from the selected signal output port 11 or 10. In this manner, the signal input to any of the signal input ports is output only from the selected signal output port. Note that a case where a signal input to the signal input port 8 is output to the signal output port 10 is called a bar state, and a case where a signal input to the signal input port 8 is output to the signal output port 11 is a cross state. Call. However, the above describes the ideal state,
In reality, for a variety of reasons, a light signal of low intensity
It is also output from signal output ports that are not selected. The ratio between the intensity of the optical signal output from the unselected signal output port and the intensity of the optical signal output from the selected signal output port is referred to as “extinction ratio”.

In order to reduce the "extinction ratio", 2
It is necessary that the two optical waveguides of the × 2 switch element have the same optical characteristics as each other, and the refractive index and the thickness of the glass film forming the optical waveguide are the same as those of the glass film. In the area, they need to be the same. In particular, as described above, instruments for optical signal circuits such as optical switches, such as 2 × 2 switch elements, are generally manufactured using semiconductor device manufacturing technology. Is generally formed on a single wafer, and the refractive index and the thickness of the glass film constituting the optical waveguide need to be the same in all regions on the wafer.

[0007] By the way, a sintered body target and a molten target are known as targets used in the sputtering method. However, the sintered body target has a higher efficiency of sputtering the target, and the sputtered particles have a higher efficiency. Therefore, a sintered target is often used because it has an advantage such as a small size. The sintered body target is made into a powder of the target material, a powder binder is added thereto, a solvent is mixed and kneaded to produce a green sheet, and then the green sheet is produced by firing. The solvent volatilizes, and the binder also burns, leaving a number of small cavities. Therefore, the density of the sintered target is lower than the density of the solid target having the same composition. This is because there are numerous microscopic cavities inside. In this specification, the ratio of the density (mass per volume) of a sintered body target to the density (mass per volume) of a solid body target having the same composition is defined as “volume density”. , The density of the solid target is 100
%, The ratio between the density of the sintered body target and the density of the solid body target is defined as the volume density of the sintered body target.

[0008]

However, when a sintered target is used, the spatial distribution of sputtered fine particles may not always be uniform. for that reason,
There is a disadvantage that the refractive index and the thickness of the deposited film (the glass film in this specification) are likely to be non-uniform depending on the region. As described above, this disadvantage is a serious disadvantage that is hard to overlook when the deposited film (glass film in the present specification) is used for manufacturing an optical signal circuit device such as an optical switch.

An object of the present invention is to form a silicon dioxide-based glass film containing silicon as a main component and containing several to 30% of germanium dioxide on a substrate, and to form a glass film having a refractive index, a thickness and a refractive index. Is to provide an improved method for manufacturing a glass film so that the same can be used throughout the glass film.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to form a silicon dioxide glass film containing silicon dioxide as a main component and containing several to 30% germanium dioxide on a substrate by using a sputtering method. The target used for the sputtering method is a composition of silicon dioxide and germanium dioxide (generally, a composition of silicon dioxide and germanium dioxide containing 3% or more of germanium dioxide), and the volume density is determined by the composition of the composition. This is achieved by setting the volume density determined from the above to 100% and setting it to 70% or more (reducing the hollow portion in the target). In other words, in forming a silicon dioxide glass film containing silicon dioxide as a main component and containing several to 30% germanium dioxide on a substrate, a target used for the sputtering method is a composition of silicon dioxide and germanium dioxide. (Generally,
A composition of silicon dioxide and germanium dioxide containing at least 3% of germanium dioxide) and a density of
This is achieved by making the density of the solid body having the composition 70% or more. When the multiple sputtering method is used, this requirement is not always necessary for a target not containing germanium dioxide.

In this method for forming a glass film, it is effective to make the spatial distribution of the sputtered fine particles sufficiently large to make the spatial distribution uniform, and specifically, to reduce the size of the target. It is effective that the size of the glass film to be formed is 1.5 times or more.

Further, the use of a multiple sputtering method using two or more targets makes it possible to use different targets (for example, one target is a target of a composition of silicon dioxide and germanium dioxide). However, the other target can be a silicon dioxide only target, etc.)
It is easier to achieve the object of the present invention. In this case, if the power supplied to each target is controlled independently, it is easier to achieve the object of the present invention.

[0013]

The operation of the present invention is as follows. (1) Increasing the volume density of the target, for example, setting the density (density of the solid body) determined by its composition to 100% and setting the density of the target to 70% or more of the density of the solid body, in other words, This means reducing the cavities in the target. Then, the target becomes denser, the distance between the silicon dioxide particles and the germanium dioxide particles is shortened, the spatial distribution of the sputtered particles becomes uniform, and the refractive index and thickness of the formed glass film are reduced. Is effective for making the same over the entire glass film. (2) When the volume density of the target is small, irregularities are formed on the surface of the target, but when the volume density of the target is large, irregularities are not formed on the surface of the target. (3) If the volume density of the target is large, the mechanical strength is improved and the electric resistivity is reduced. Therefore, the overheating of the target is suppressed, and the temperature rise of the target due to the ion bombardment is also suppressed. (4) If fine irregularities are present on the surface of the target, cracks are present, or defects are present, the refractive index and thickness of the formed glass film become the same over the entire glass film. Although it is known to be difficult, such a phenomenon is suppressed by increasing the volume density of the target. (5) If the volume density of the target is increased, when the vacuum chamber is opened for mounting the target or the wafer, moisture and gas, etc., are less likely to adhere to the surface of the target or the wafer, and the stability of sputtering is increased. Is improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for manufacturing a glass film according to the present invention will be described with reference to the drawings. For convenience, a method of manufacturing a 2 × 2 switch element will be described as an example, and a method of manufacturing a 2 × 2 switch element using the method of manufacturing a glass film according to the present invention will be described.

(1) Description of Sputtering Apparatus See FIG. 6 A multi-sputtering apparatus using two mutually different targets will be used. The multi-sputtering apparatus will be described. The figure shows a schematic configuration of a multi-sputtering apparatus using two mutually different targets. In the figure, reference numeral 3 denotes a wafer supporting drum for attaching a wafer to a side surface thereof, which is rotatably provided at the center of the vacuum vessel 25. Reference numerals 26 and 27 denote valves, 28 denotes an outer periphery of the vacuum vessel, 22 denotes a 4-inch wafer having a diameter of 10 cm attached to a side surface of the wafer supporting drum 21,
In the figure, three sheets are shown. Reference numeral 23 denotes a first target (a target of a composition of silicon dioxide and germanium dioxide in the present specification), and reference numeral 24 denotes a second target (a target of only silicon dioxide in the present specification). To run a sputter,
One terminal (often grounded) of the mutually different high frequency power supplies 29 and 30 is connected to the wafer supporting drum 21 via a slip ring or the like, and further connected to the wafer via this. And the other terminal are connected to the first target 23 and the second target 24, respectively. In this way, a high-frequency voltage is applied between the target and the wafer to supply sputtering power.

(2) Relationship between Sputtering Power and Composition of Deposited Material (Glass Film in the Present Specification) A high frequency voltage applied between a target and a wafer is controlled via a wafer supporting drum. If the sputtering power is controlled in this manner, the composition of the substance to be deposited (a glass film in this specification) can be adjusted. Therefore, in forming the glass film according to the present invention, the high-frequency voltage applied between the target and the wafer is controlled to control the sputtering power, and the refractive index of the glass film forming the optical waveguide is set to the upper and lower cladding layers. Can be larger than the refractive index of silicon dioxide.

(3) Size of Target It is clear that the size of the target should be sufficiently larger than the size of the wafer in order to make the spatial distribution of the sputter particles uniform. In order to determine whether the size should be larger than the size of the first target, the first target was a composition of silicon dioxide and germanium dioxide containing 10 mol% germanium dioxide, and the second target was used. Is silicon dioxide, its size is 20cm in length and 1 in width
0 cm, the volume density of the first target is 84%,
The step of forming a glass film was performed a plurality of times. And the result shown in FIG. 7 was obtained. The horizontal axis in FIG. 7 is the vertical distance from the center of the substrate when the length of the target in the vertical direction is 200, and the vertical axis is the film thickness at the center of the substrate of 100.
Is the relative film thickness. This figure shows that the film thickness variation is 4% or less in the range of about 67% or less of the size of the target. Since the film thickness sharply decreases in the region of 80% or more of the size of the target, it is determined that the size of the target is desirably 1.5 times or more the region where the deposit is to be deposited.

(4) 2 × 2 as an example of an optical signal circuit device formed using the method for forming a glass film according to the present invention.
Manufacturing Process of Optical Switch Device FIG. 3, FIG. 4 and FIG. 5 are referred to again. FIG. 3 is a plan view of the 2 × 2 switch device, FIG. 4 is a sectional view taken along the line AA, and FIG. FIG.
Using a sputter method, a silicon dioxide film 2 is formed on a silicon substrate 1 to a thickness of 30 μm. This silicon dioxide film 2 functions as a lower cladding layer. The glass film 3 according to the present invention is formed using the above-described sputtering apparatus (the apparatus described with reference to FIG. 6). At this time,
For the target, use a sintered target.
This sintering target is manufactured using the method described above. For the first target, a sintered body of a composition of silicon dioxide and germanium dioxide containing 10 mol% germanium dioxide is used, and for the second target, a sintered body of silicon dioxide is used. The first target is 10 cm wide, and the volume density of the first target is 84%. That is, the density of the first target is set to 84% of the density of the first target assuming that the density of the completely solid body having the composition is 100%. That is, the volume density of the first target is set to be 70% or more, where the volume density of the completely solid body having the composition is 100%. The volume density of the sintering target can be controlled by controlling the firing step. The size of the target is set to be at least 1.5 times the size of the wafer, and the sputtering power is controlled so that the refractive index difference between the glass film 3 and the upper and lower clad layers 2 and 4 is smaller than that of the upper and lower clad layers 2 and 4. Increase by 0.75%. The optical waveguide 3 having the illustrated pattern is completed using a photolithography method. Silicon dioxide film 4 using CVD method
Is formed to a thickness of 30 μm. This silicon dioxide film 4
Functions as an upper cladding layer. A conductor film 5 is formed on the silicon dioxide film 4, and the heater 5 having the illustrated pattern is completed by using photolithography.
Here, 6 and 7 are terminals of the heater 5, 8.9 are two signal input ports, and 10 and 11 are two signal output ports. Reference numeral 12 denotes a first node (first directional coupler 12), reference numerals 14 and 15 denote two optical waveguides, and reference numeral 13 denotes a second node (second directional coupler 13).
It is. The operation is as described above with reference to the drawings.

(5) Confirming the effect of the method for producing a glass film according to the present invention (confirming the relationship between the volume density of the target and the phase difference of the optical waveguide formed of the formed glass film) The first target is 10 mol % Of germanium dioxide containing a composition of silicon dioxide and germanium dioxide, the composition is constant, the sintering conditions are changed, and a plurality of samples with volume densities varying from 50% to 94% are manufactured. Using this, a sintered body of silicon dioxide was used as the second target, and the glass film 3 according to the present invention was formed using the above-described sputtering apparatus (the apparatus described with reference to FIG. 6). . Here, the relative refractive index difference was set to 0.75%. A phase error analysis method using a symmetric Mach-Zehnder interferometer circuit (Takashi Goh, Senichi Suzuki and Akio Sugita: Jo
urnal of Lightwave Technology, Vol. 15, pp. 2107-2
113, "Estimation of waveguide phase error in silic
a-based waveguides ") were used to obtain the results shown in FIG. 1 (target volume density and standard deviation of phase error per unit length). As is apparent from FIG. When it becomes larger, the standard deviation of the phase error per 1 mm of the length is remarkably reduced, and a good characteristic is exhibited as the optical waveguide.

(5) Confirmation of Characteristics of 2 × 2 Optical Switch Element Produced Using Method for Producing Glass Film According to the Present Invention The above-mentioned “extinction ratio” is used as an index indicating the characteristic of a 2 × 2 optical switch element. Is used. Here, the “extinction ratio” is
As described above, the ratio between the output signal intensity from the output signal terminal from which the output signal should be output and the output signal intensity from the output signal terminal from which the output signal should not be output. The plurality of 2 manufactured for the effect confirmation test (confirmation test of the relationship between the volume density of the target and the phase difference of the optical waveguide formed of the glass film to be formed) of the method for producing a glass film according to the present invention described above.
The “extinction ratio” was measured for the × 2 optical switch element, and the result is shown in FIG. As is apparent from the figure, when the volume density of the target is larger than 70%, the "extinction ratio"
Is remarkably reduced, and it can be seen that good characteristics are exhibited as a 2 × 2 optical switch element.

Although the above description has been made by taking a 2 × 2 optical switch element as an example, an optical signal circuit device manufactured by using the glass film manufacturing method according to the present invention is a 2 × 2 optical switch element. It is not limited to. It is suitable for use in the manufacture of all kinds of optical signal circuit equipment that requires characteristics in which the film thickness and the refractive index are uniform in all regions. Further, it is known to add diphosphorus pentoxide / diboron trioxide / titanium dioxide when producing a silicon dioxide glass film composed of a composition of silicon dioxide and germanium dioxide. Even when such an additive is added, it has been experimentally confirmed that the method for producing a glass film according to the present invention is suitable.

[0022]

As described above, in the method of manufacturing a glass film according to the present invention, a film of silicon dioxide glass containing silicon dioxide as a main component and containing several to 30% germanium dioxide by using a sputtering method. Is formed on a substrate, a target used for the sputtering method is a composition of silicon dioxide and germanium dioxide (generally, a composition of silicon dioxide and germanium dioxide containing at least 3% of germanium dioxide), and its volume is It is known that the density is set to 70% or more assuming that the volume density determined by the composition of the composition is 100% (the density of the target is set to 70% or more of the density of the solid body having the composition). More preferably, the size of the target is 1.5 times or more the size of the glass film to be formed. In addition, the use of a multiple sputtering method using two or more targets is included. In addition, when using the multiple sputtering method, the power supplied to each target is Cavities in the target are reduced, the target becomes denser, the distance between silicon dioxide particles and germanium dioxide particles is reduced, and the spatial distribution of sputtered particles is uniform. And the refractive index and thickness of the formed glass film become the same over the entire glass film. further,
When the volume density of the target is large, irregularities are not formed on the surface of the target, the mechanical strength is improved, the electrical resistivity is reduced, the overheating of the target is suppressed, and the temperature of the target is increased due to ion bombardment The surface of the target does not have fine irregularities, cracks, or defects, and the refractive index and thickness of the formed glass film are the same over the entire glass film. It becomes easy to become. In addition, when the vacuum chamber is opened for mounting a target or a wafer, moisture, gas and the like hardly adhere to the surface of the target or the wafer, and the stability of sputtering is improved.

[Brief description of the drawings]

FIG. 1 shows the result of confirming the effect of the method of manufacturing a glass film according to the present invention (the standard deviation of the phase error per unit length of an optical waveguide made of a glass film to be formed).

FIG. 2 shows the result of confirming the characteristics (extinction ratio) of a 2 × 2 optical switch element manufactured using the method for manufacturing a glass film according to the present invention.

FIG. 3 is a plan view of a 2 × 2 optical switch element.

FIG. 4 is a side view of the 2 × 2 optical switch element (AA in FIG. 6);
Cross section)

FIG. 5 is a side view of a 2 × 2 optical switch element (BB in FIG. 6);
Cross section)

FIG. 6 is a schematic configuration diagram of a multiple sputtering apparatus.

FIG. 7 shows the relationship between the size of a target used in the method of manufacturing a glass film according to the present invention and the thickness of the formed glass film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower cladding layer, such as a silicon dioxide film 3 Glass film according to the present invention 4 Upper cladding layer, such as a silicon dioxide film 5 Heater 6.7 Heater terminal 8.9 Signal input port 10.11 Signal output port 12 First Directional coupler 13 second directional coupler 14/15 optical waveguide 21 wafer supporting drum 22 wafer 23/24 first / second target 25 vacuum vessel 26/27 valve 28 vacuum pump 29/30 high frequency power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C23C 14/34 C23C 14/34 U H01L 21/316 Y G02B 6/12 M H01L 21/316 N ( 72) Inventor Atsushi Murasawa 20-1 Sakuragaoka-cho, Shibuya-ku, Tokyo F-term in NTT Electronics Corporation (reference) 2H047 KA03 NA02 PA04 QA04 RA08 TA41 2K002 AB05 BA13 CA15 DA08 FA07 HA11 4K029 AA06 BA43 BA46 BC07 BD12 CA05 DC05 DC12 DC22 EA01 EA09 5F058 BA20 BC05 BF12 BJ01 BJ10 5F103 AA08 DD27 DD30 GG03 HH03 LL20 RR05

Claims (5)

[Claims] 2. A method according to claim 1, wherein the main component is silicon dioxide.
In a method of forming a glass film by forming a silicon dioxide glass film containing 0% germanium dioxide on a substrate by using a sputtering method, the targets used in the sputtering method are silicon dioxide and germanium dioxide. Wherein the volume density is 70% of the volume density determined by the composition of the composition.
A method for forming a glass film, characterized by the above. 2. A method according to claim 1, wherein the main component is silicon dioxide.
In a method of forming a glass film by forming a silicon dioxide glass film containing 0% germanium dioxide on a substrate by using a sputtering method, the targets used in the sputtering method are silicon dioxide and germanium dioxide. Wherein the density is 70% or more of the density of the solid body having the composition of the composition. 3. The size of the target used in the sputtering method is 1.times. The size of the formed glass film.
3. The method for forming a glass film according to claim 1, wherein the ratio is at least 5 times. 4. The method for forming a glass film according to claim 2, wherein the sputtering method is a multiple sputtering method using two or more targets. 5. The voltage applied to a target used in the multiple sputtering method can be controlled independently for each target, and the power supplied to the target can be controlled for each target. 5. The method of forming a glass film according to claim 4, wherein the method can be controlled independently of the above.