JPH04349623A - Vapor growth apparatus - Google Patents

Abstract

PURPOSE:To suppress substantially the opportunity of thin film contamination caused by reactive gas introduced into a horizontal reaction tube type vapor growth apparatus in which a thin film is built up on the surface of a substrate by a method wherein the bottom surface of a reaction container through which the introduced reactive gas composed of a plurality of compound gases is made to flow horizontally is positioned on the same plane as the substrate mounting surface of a susceptor and the susceptor is heated while the reactive gas is made to flow. CONSTITUTION:A gas mixing means 5 which has a gas mixing part whose gas flow path cross section is composed of a squeezing plate and a diffusion space and a rectifying part which forms the flow of the gas flowing out of the gas mixing part into a streamline flow is directly connected to the reactive gas inlet of the body of a reaction container. By mixing a plurality of compound gases immediately before the reaction container 14, even a very little quantity of a reaction product produced by the thermal decomposition of the compound is not contained in the reactive gas introduced into the reaction container 14. Moreover, a film having a uniform thickness and uniform quality can be formed by providing the gas mixing part and the rectifying part.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is mainly aimed at a metal organic chemical vapor deposition (MOCVD) apparatus for growing a compound semiconductor film such as GaAs on a substrate, and the present invention is mainly directed to a metal organic chemical vapor deposition (MOCVD) apparatus for growing a compound semiconductor film such as GaAs on a substrate. The bottom surface of the reaction vessel through which the reaction gas consisting of multiple compound gases flows horizontally is formed on the same plane as the substrate mounting surface of the susceptor on which the substrate to be deposited is placed horizontally, and the susceptor is heated while the reaction gas is flowing. The present invention relates to a vapor phase growth apparatus for growing a thin film on the surface of a substrate to be film-formed.

0002

[Prior Art] A reaction gas consisting of multiple compound gases is
Vapor phase growth equipment, in which a thin film having a predetermined composition is grown on the substrate by flowing the flow parallel to the heated substrate and causing thermal decomposition on the substrate and depositing the thermal decomposition products on the substrate, has a large structure. There are two types: barrel type and horizontal reaction tube type. In the barrel type, as shown in FIG. 5, the susceptor 31 on which the substrate 1 is mounted is formed in a barrel shape, and this is arranged coaxially with the reaction container 32 in a bell-shaped reaction container 32, and the susceptor 31 is aligned with the central axis of the reaction container 32. The susceptor 31 and the substrate 1 are heated while being rotated, and a thin film is grown on the surface of the substrate 1 while introducing a reaction gas from the gas inlet 32a of the reaction vessel 32.

On the other hand, in the horizontal reaction tube type, as shown in FIG. 8, in the reaction vessel 3, the introduced reaction gas flows horizontally.
A thin film having a predetermined composition is grown by depositing thermal decomposition products of a reaction gas on the surface of a substrate 1 that is placed horizontally on a disk-shaped or square plate-shaped susceptor 2 and heated together with the susceptor 2. be. The substrate 1 may be rotated about its vertical axis in order to make the thickness and quality of the thin film uniform.

[0004] The vapor phase growth apparatus targeted by the present invention is
The latter is a horizontal reaction tube type, and the bottom surface of the reaction container 3 is formed on the same plane as the substrate mounting surface of the susceptor 2, and the reaction gas introduced into the reaction container 3 spreads over the surface of the substrate 1. It passes in a flowing state, and as it passes, it is thermally decomposed by the heat of the substrate 1 and susceptor 2, and decomposition products are deposited on the surface of the substrate 1.

[0005]

[Problems to be Solved by the Invention] In order to clarify the problems in the horizontal reaction tube type vapor phase growth apparatus configured as described above, first, we will first discuss the problems in the barrel type vapor growth apparatus and their problems. The disclosed means for point resolution will now be described.

In a barrel-type vapor phase growth apparatus, the reaction gas that has flowed at a certain speed through a relatively thin gas introduction pipe flows into a wide space that rapidly expands from the gas introduction port, so the reaction vessel is shaped like a bell. The flow stagnates at the shoulder area. Therefore, when switching the type of reaction gas and growing a thin film with a different composition on top of the previous thin film, the previous reaction gas that was stagnant in the stagnation mixes with the new reaction gas, causing the previous reaction gas to grow. A layer having a composition intermediate between the two thin films is formed between the thin film and the new thin film, causing a problem that the composition of the film does not switch sharply.

[0007] In order to solve this problem,
In Publication No. 0431, as shown in FIG. 6, a rectifying rib is provided between the dome-shaped cap 34 on the upstream side of the barrel-shaped susceptor 31 and the shoulder portion of the bell-shaped reaction vessel 32, and the gas flow direction of the rib and the gas flow direction are adjusted. The cross section in the direction perpendicular to the gas flow is similar to the cross section of a convex lens that is convex on both sides, and by changing the thickness of this rib in the direction perpendicular to the gas flow, the gas is transferred to the intermediate part between the barrel-shaped susceptor and the reaction vessel. The gas flow, which was turbulent on the upstream side of the ribs, is reduced by changing the thickness of the ribs in the direction of the gas flow. When passing through the substrate, the flow becomes laminar, so that the flow passes over the substrate surface in a laminar state.

Furthermore, in Japanese Patent Application Laid-Open No. 2-278717, as shown in FIG.
It is partitioned by a diffuser 36 with a large area and formed with uniformly distributed pores, the reaction gas is temporarily stored in the space upstream of the diffuser 36, and the reaction gas is uniformly flowed out from the diffuser 36 at a low speed. In addition to reducing stagnation in the shoulder part of the reaction vessel 32, an inner pipe 37 is provided between the susceptor 31 and the reaction vessel 32, so that when the type of reaction gas is switched, stagnation in the shoulder part of the reaction vessel 32 is reduced. The previously reacted reaction gas is made to flow outside the inner tube 37, so that the composition of the thin film is abruptly switched.

On the other hand, the present invention is directed to a horizontal reaction tube type in which the bottom surface of the reaction vessel is in the same plane as the substrate mounting surface of the susceptor so that the reaction gas passes over the substrate surface in a laminar flow state. Naturally, in a vapor phase growth apparatus, care must be taken to avoid swirling in the gas flow passing over the substrate surface.
The entire reaction vessel is constructed in such a way that no stagnation occurs throughout the entire space within the reaction vessel. That is, as shown in FIG. 8, the reaction gas flowing from the reaction gas inlet 3a of the reaction container 3 placed horizontally gradually expands in the reaction container portion upstream from the susceptor 2, where the flow path cross section gradually widens. As it expands, it enters a reaction vessel portion with a constant cross section of the flow path, and in this portion the entire flow becomes a flow parallel to the substrate 1 and passes through the substrate 1. Since the reaction gas gradually spreads on the upstream side of the reaction vessel 3, stagnation does not occur near the transition to the downstream reaction vessel portion where the cross section of the flow path is constant, and the top surface of the susceptor 2 and the bottom surface of the reaction vessel 3 are the same. Since it is in a plane, the reactant gas passes through the susceptor location in a laminar, vortex-free flow state. Therefore, when the type of reaction gas is changed, the composition of the thin film on the substrate changes abruptly.

By the way, in any of the above-mentioned conventional vapor phase growth apparatuses, a plurality of compound gases constituting the reaction gas are mixed in a separate mixer before being introduced into the reaction vessel. was introduced into the reaction vessel via piping. The liquid organic metal (alkylated product of group III element), which is one of the compound gases used when forming a compound semiconductor film, is gasified by bubbling of hydrogen carrier gas, and the hydrogen of group V element is formed at a predetermined vapor pressure. It is kept at a temperature of several tens of degrees Celsius in a reservoir so that it can be mixed with chemical compounds, and then sent to a mixer through a short pipe. and,
After being mixed with a hydride of a group V element in a mixer, it is heated midway through the piping to maintain a predetermined vapor pressure when it passes through the piping and reaches the reaction vessel. For this reason, a reaction similar to that on the substrate occurs inside the piping, albeit in an extremely small amount, and thermal decomposition products that have accumulated on the inner wall of the piping during long-term use peel off, causing particle contamination to the thin film on the substrate. There is a risk that it may result. Furthermore, this phenomenon may be accelerated due to an abnormality in the piping heating system.

An object of the present invention is to provide a vapor phase growth apparatus in which a thin film on a substrate is not contaminated by a reaction gas introduced into a reaction vessel.

0012

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a vapor phase growth apparatus targeted by the present invention, in which a reaction gas consisting of a plurality of introduced compound gases flows horizontally. The bottom surface of the reaction vessel is formed on the same plane as the substrate mounting surface of the susceptor on which the substrate to be film-formed is placed horizontally, and a thin film is formed on the surface of the substrate to be film-formed by heating the susceptor while flowing a reaction gas. A vapor phase growth apparatus for growth is installed at the reaction gas inlet of the reaction vessel body, and includes a diaphragm plate having a diaphragm hole that narrows the flow path cross section of the inflowing gas, and a diffusion space that diffuses the gas that has passed through the diaphragm hole of the diaphragm plate. It has one or more stages of gas mixing parts in the direction of gas flow, and a rectifying part that makes the gas flowing out from the most downstream gas mixing part into a laminar flow on the downstream side of the most downstream gas mixing part. The equipment shall be directly connected to the gas mixing means provided.

[0013] Furthermore, the gas mixing means includes a pipe and one or more throttles disposed in one or more stages spaced apart in the axial direction of the pipe on the upstream side of the pipe. It consists of a plate and a pyramidal body such as a triangular pyramid, which is located downstream of the most downstream aperture plate in the pipe and whose bottom face faces the aperture plate at a distance. A rectifying section is formed between each other and/or between the aperture plate and the bottom surface of the cone, and makes the gas flowing out from the most downstream gas mixing section into a laminar flow. It is preferable that the structure be formed by the slope of the shaped body and the inner wall surface of the pipe.

Furthermore, in the gas mixing means having this configuration, the number of throttle plates disposed on the upstream side of the pipe is one, and the total cross-sectional area of the throttle holes of the throttle plate is set to be equal to the total cross-sectional area of the flow path upstream of the throttle hole. It is even more preferable to use a gas mixing means having a cross-sectional area of 1/10 or less.

[0015] In addition, the gas mixing means having the above structure may be formed by forming the pipe, the aperture plate, and the conical body as parts of an integrally molded product made of quartz glass, or by forming the pipe, the aperture plate, and the conical body as parts of an integrally molded product made of quartz glass. It is preferable that the body is formed integrally with metal and inserted into a pipe made of quartz glass.

[0016]

[Function] By making the vapor phase growth apparatus such that the gas mixing means is directly connected to the reaction gas inlet of the reaction vessel, there is no piping from the gas mixing means to the reaction vessel, and the reaction in the reaction vessel is improved. There is no generation of reaction products due to thermal decomposition of the compound gas until immediately before the gas inlet, and the chance of particle contamination of the thin film formed on the substrate is significantly reduced. In addition, when the multiple compound gases introduced into the gas mixing means are ejected from the small aperture of the aperture plate into the diffusion space behind the aperture plate, they rapidly diffuse in all directions and mix with each other, resulting in effective gas mixing. It is possible to form a film with a uniform composition on the surface of the substrate.

However, on the other hand, in the gas within the diffusion space,
A large number of vortices formed during the mixing process are included, and if these are directly introduced into the reaction vessel, it is not preferable in terms of obtaining a thin film of stable quality. Therefore, if a rectifier is arranged downstream of the most downstream gas mixing part and the gas flowing out from the most downstream gas mixing part is sent into the reaction vessel as a laminar flow without vortices, it is possible to The gas laminarization function of the piping from the mixer to the reaction vessel (the function of the piping causing eddy energy to be lost due to its long path) can be taken over by the rectifying section of the gas mixing means.

Therefore, the specific structure of the gas mixing means based on this principle of construction consists of a pipe and one or more gas mixtures arranged in one or more stages at intervals in the axial direction of the pipe on the upstream side of the pipe. The structure consists of a diaphragm plate and a pyramidal body such as a triangular pyramid, which is located downstream of the most downstream diaphragm plate in the pipe and whose bottom face faces the diaphragm plate at a distance. A space is formed between the diaphragm plates and/or between the diaphragm plate and the bottom of the cone. If it is formed by the slope of the cone on the downstream side and the inner wall surface of the pipe, the reaction gas that has generated a vortex in the diffusion space will flow from the narrow ring-shaped flow path between the periphery of the bottom of the cone and the pipe. Since the cross section of the flow path gradually expands toward the reaction vessel, the reaction gas, which has most of the vortices eliminated by passing through the ring-shaped sandwiched flow path, eliminates the remaining vortices along its flow path and does not contain any vortices. It flows into the reaction vessel in a laminar flow state.

In the specific structure of the gas mixing means described above, the number of throttle plates disposed on the upstream side of the pipe is one, and the total cross-sectional area of the throttle holes in the throttle plate is equal to the flow upstream of the throttle holes. If it is 1/10 or less of the cross-sectional area of the path, a plurality of compound gases can be mixed sufficiently uniformly for practical purposes, as explained in the Examples section. Therefore, depending on the required flow rate of the reaction gas,
The gas mixing means can be formed into a simple structure without forming the gas mixing section in multiple stages.

In the vapor phase growth apparatus, in order to form a film as uniform in thickness and quality as possible, it is necessary to equalize and optimize the substrate temperature, rotate the substrate around its axis, and optimize the reaction gas flow rate. However, if these conditions are not changed after these conditions have been determined, it is desirable that each member of the device be constructed as simply and inexpensively as possible. The gas mixing means can also be manufactured at low cost using a mold if the pipe, aperture plate, and cone are each formed as parts of an integrally molded product made of quartz glass.

[0021] Furthermore, if the aperture plate and the conical body are integrally formed using metal and used as a gas mixing means that is inserted into a pipe made of quartz glass, the aperture hole can be adjusted to accommodate changes in various film forming conditions. It is possible to easily change the diameter and number of cones, or the size of the bottom surface of the cone.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the structure of a vapor phase growth apparatus according to the present invention. The reaction container 14 includes an outer container 16 and an inner container 15.
The outer container 16 is an airtight container, and the inner container 15 is a reactant gas inlet 1.
The inner container portion 15A has a rectangular flow path cross section, with a fan-shaped width that spreads in the flow direction from the side of No. 4, and a ceiling surface that is gently sloped.
and an inner container portion 15B having a constant rectangular flow passage cross section in the direction of flow. maintains its mounting position by its own weight even while the device is in operation. The top surface of the bottom of the inner container 15 is in the same plane as the substrate placement surface of the susceptor 2 on which the substrate 1 is placed, and the susceptor 2 is attached to the top surface of the heater 8 and the drive motor 12
As a result, it is rotated together with the heater 8 via the gear 11.

A gas mixing means 5 according to the present invention is connected to the reaction gas inlet 14a of the reaction vessel 14, and to this gas mixing means 5, hydrogen is gasified by hydrogen carrier gas from respective storage tanks (not shown). An alkylated product of a group element (here Ga(CH3)3) and a hydride of a group V element (here AsH3) are supplied through respective conduits. These compound gases are mixed by the gas mixing means 5 and introduced into the inner container 15 in a laminar flow state, flow in the inner container 15 in the direction of the solid arrow in a laminar flow state, and are discharged from the exhaust port 7 of the exhaust flange 4. It is discharged.

During film formation, the susceptor 2 is rotated by the drive motor 12 while being heated by the heater 8, and the gas mixing means 5
The compound gas that has been mixed and rectified into a laminar flow is introduced into the inner container 15, and hydrogen gas, nitrogen gas, or an inert gas is introduced between the outer container 16 and the inner container 15 as a sweep gas. This prevents the reaction gas flowing through the inner container from leaking to the outside of the inner container. The reaction gas is in the inner container 15
It passes through the substrate surface in a laminar state without creating stagnation or vortices, and as it passes through, it is heated and thermally decomposed, and the thermal decomposition products are deposited on the substrate to form a thin film with a predetermined composition. .

FIG. 2 shows a first embodiment of the gas mixing means structure according to the present invention. In this embodiment, the gas mixing means is formed as an integrally molded product made of quartz glass, and on the upstream side within the pipe portion (hereinafter referred to as pipe) 51, there are
One diaphragm plate 52 having a diaphragm hole in the center is formed, and on the downstream side of the diaphragm plate 52, a conical conical body 53 is supported inside the pipe 51 via a rib. The diameter of the throttle hole of the throttle plate 52 is such that the cross-sectional area is 1 of the flow path cross-sectional area on the upstream side of the throttle hole.
/10 or less, and the aperture plate 52
A diffusion space is formed between the downstream surface of the conical body 53 and the bottom surface of the conical body 53, in which the reaction gas squeezed by the throttle hole rapidly diffuses in all directions.

When the plurality of mixed gases that have flowed into the gas mixing means 5 are spouted into the diffusion space after the cross section of the flow path is narrowed by the throttle hole of the throttle plate 52, they are rapidly diffused in all directions and mixed uniformly. Ru. The mixed compound gas enters a narrow ring-shaped gap between the bottom periphery of the cone-shaped body 53 and the inner wall surface of the pipe 51, and from this ring-shaped gap, the vortices generated in the diffusion space are mostly eliminated. It flows out, gradually widens the cross section of the flow path between the slope of the cone 53 and the inner wall surface of the pipe 51, and reacts in a laminar flow state without vortices while eliminating vortices that could not be completely eliminated along the flow path. Flows into the container.

FIG. 3 shows a second gas mixing means according to the present invention.
An example is shown below. In this embodiment, the aperture plate 52 and the conical body 53 are integrally formed of stainless steel and inserted into a pipe 51 made of quartz glass. The throttle plate 52 is formed as a cylinder with a throttle hole formed in the bottom surface, and a plurality of throttle holes are formed in the bottom surface such that the total cross-sectional area thereof is 1/10 or less of the flow path cross-sectional area of the cylinder portion. ing.

In FIG. 4, when the gas mixing means has one throttle plate, the total cross-sectional area of the throttle hole is set to be 1/10 or more of the cross-sectional area of the flow path upstream from the throttle hole, and the substrate is mounted on a 2-inch diameter substrate. An example of film thickness distribution when forming a thin film without rotating the
An example of the film thickness distribution of a thin film when the thickness is 1/10 or less is shown. Figure (a) shows the former case, in which the film thickness is not symmetrical in the direction perpendicular to the flow, and the film thickness distribution is such that it is thick in one direction and rapidly decreases in the opposite direction. On the other hand, in the latter case, as shown in FIG. The influence of the ratio on the mixing degree appears in the form of film thickness distribution.

[0029]

[Effects of the Invention] In the present invention, since the vapor phase growth apparatus is constructed as described above, the following effects can be obtained.

In the apparatus of claim 1, the gas mixing means for mixing a plurality of compound gases is directly connected to the reaction gas inlet of the reaction vessel main body of the apparatus, and the compound gas is supplied from each storage tank to each short pipe. Because they are introduced into the gas mixing means independently from each other through No reaction products are produced, the chance of particle contamination of the substrate due to their peeling is significantly reduced, and the quality of the thin film formed is highly uniform. In addition, the conventional piping from the gas mixing means to the reaction vessel and its heating or warming device are omitted, reducing the cost of the entire apparatus including the compound gas storage tank.

Furthermore, the gas mixing section of the gas mixing means is composed of a throttle plate having a throttle hole that throttles the flow path cross section of the gas flowing in, and a diffusion space that diffuses the gas that has passed through the throttle hole. Since the gases are mixed effectively and the uniformly mixed gas is made into a laminar flow in the downstream rectifier, the gas mixing means according to the structure of the present invention has a film thickness,
Enables film formation with uniform film quality.

In the apparatus of the second aspect, the gas mixing means is formed in a simple structure, and the cost effectiveness of the first aspect is maintained without being diminished.

In the apparatus of claim 3, the gas mixing means is formed with the simplest structure based on the structure of claim 2, and the cost-retaining effect of claim 2 is reinforced.

In the apparatus of the fourth aspect, the gas mixing means is formed at a low cost, and in the case of an apparatus in which the film forming conditions such as the gas flow rate do not change, there is an effect that the apparatus can be constructed at a lower cost, although it is small.

In the apparatus of claim 5, the diameter and number of the throttle holes of the gas mixing means can be easily changed, and in the case of an apparatus in which film forming conditions such as gas flow rate are changed, the entire film forming conditions can be changed more quickly. It has the effect of making you do it.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the configuration of a vapor phase growth apparatus according to the present invention, in which (a) is a plan sectional view, and (b) is a side partial sectional view.

FIG. 2 is a vertical sectional view showing a first embodiment of the gas mixing means configuration according to the present invention.

FIG. 3 is a longitudinal sectional view showing a second embodiment of the gas mixing means configuration according to the present invention.

FIG. 4 is a diagram showing, in the form of film thickness distribution, the difference in gas mixing degree depending on the total cross-sectional area of the throttle hole when there is only one throttle plate constituting the gas mixing means according to the present invention; In a), the total cross-sectional area of the throttle hole is 1/1 of the cross-sectional area of the flow path upstream from the throttle hole.
A film thickness distribution diagram showing an example when the value is 10, and (b) a film thickness distribution diagram showing an example when the value is 1/10 or less.

[Figure 5
] Diagram of the configuration principle of a vapor phase growth apparatus for growing a compound semiconductor film on a substrate, which is different from the type targeted by the present invention.

[Figure 6
] Schematic diagram showing the device configuration for solving problems in the type of vapor phase growth device shown in FIG.

FIG. 7 is a schematic diagram showing another device configuration for solving the problems in the vapor phase growth device of the type shown in FIG.

[Figure 8] Diagram of the configuration principle of a vapor phase growth apparatus targeted by the present invention

[Explanation of symbols]

1 Substrate (substrate to be film-formed) 2 Susceptor 5 Gas mixing means 14 Reaction container 15 Inner container 15A Inner container part 15B Inner container part 16 Outer container 51 Pipe 52 Aperture plate 53 Cone

Claims (5)

[Claims] 1. The bottom surface of the reaction vessel through which the introduced reaction gas consisting of a plurality of compound gases flows horizontally is formed on the same plane as the substrate mounting surface of a susceptor on which the substrate to be film-formed is horizontally mounted, In a vapor phase growth apparatus that grows a thin film on the surface of a substrate to be film-formed by heating a susceptor while flowing a reaction gas, a restriction hole is provided in the reaction gas inlet of the reaction vessel body to narrow down the flow path cross section of the gas flowing into the reaction vessel body. A gas mixing section consisting of a diaphragm plate having a diaphragm plate and a diffusion space for diffusing the gas that has passed through the diaphragm hole in the diaphragm plate is provided in one or multiple stages in the direction of the gas flow, and the most downstream gas mixing section is located downstream of the gas mixing section on the most downstream side. A vapor phase growth apparatus, characterized in that a gas mixing means is directly connected to a gas mixing means including a rectifying section that converts gas flowing out from a downstream gas mixing section into a laminar flow. 2. In the vapor phase growth apparatus according to claim 1, the gas mixing means is disposed in the pipe and in one or multiple stages at intervals in the axial direction of the pipe on the upstream side of the pipe. Consisting of one or more throttle plates and a cone-shaped body such as a triangular pyramid located downstream of the most downstream throttle plate in the pipe and whose bottom face faces the throttle plate at a distance, the gas A diffusion space is formed between the diaphragm plates and/or between the diaphragm plate and the bottom surface of the cone, and a rectifying part that makes the gas flowing out from the most downstream gas mixing part into a laminar flow is formed in the cone. A vapor phase growth apparatus characterized in that the slope is formed by a slope of a pyramid on the downstream side of the bottom of the pipe and an inner wall surface of the pipe. 3. The vapor phase growth apparatus according to claim 2, wherein the number of aperture plates disposed on the upstream side of the pipe of the gas mixing means is one, and the total cross-sectional area of the aperture holes of the aperture plate. of,
A vapor phase growth apparatus characterized in that the cross-sectional area of the flow path on the upstream side of the throttle hole is 1/10 or less. 4. In the vapor phase growth apparatus according to claim 2 or 3, the gas mixing means consisting of a pipe, a diaphragm plate, and a cone-shaped body includes a pipe, a diaphragm plate, and a cone-shaped body, respectively. A vapor phase growth apparatus characterized in that it is formed as a part of an integrally molded product made of quartz glass. 5. In the vapor phase growth apparatus according to claim 2 or 3, the gas mixing means including the pipe, the aperture plate, and the cone-shaped body is characterized in that the aperture plate and the cone-shaped body are made of metal. A vapor phase growth apparatus characterized in that the apparatus is formed integrally with a quartz glass pipe and inserted into a pipe made of quartz glass.