JP2791770B2 - Apparatus for forming functional deposited film by microwave plasma CVD - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a deposited film, particularly a functional film, on a substrate, particularly a semiconductor device, a photoreceptor device for electrophotography, a line sensor for image input, an imaging device, and light. The present invention relates to an apparatus for forming a functional deposition film such as an amorphous semiconductor film used for an electromotive device or the like. [Description of Prior Art] Conventionally, semiconductor devices, photoreceptor devices for electrophotography,
Line sensors for image input, imaging devices, photovoltaic devices, other various electronic elements, optical elements,
Amorphous silicon,
Specifically, for example, an amorphous material compensated by a hydrogen atom and / or a halogen atom (eg, fluorine, chlorine, etc.)
Deposited films of amorphous semiconductors such as silicon (hereinafter referred to as “a-Si (H, X)”) have been proposed, and some of them have been put to practical use. And such a deposited film is a plasma CVD method, that is,
It is known that a source gas is decomposed by direct current, high frequency, or microwave glow discharge, and is formed by a method of forming a thin deposited film on a substrate such as glass, quartz, a heat-resistant synthetic resin film, stainless steel, or aluminum. And various devices for that purpose have been proposed. By the way, a plasma CVD method by microwave glow discharge decomposition (hereinafter referred to as “MW-PCVD method”) has recently attracted attention even at an industrial level, and has been used for forming a deposited film by the MW-PCVD method. The device is typically of the device configuration shown in the schematic perspective view of FIG. 2-a. In FIG. 2-a, reference numeral 1 denotes an entire vacuum vessel, 2 denotes a microwave introduction window made of a dielectric material such as alumina ceramics or quartz glass, 3 denotes a waveguide, 4 denotes microwaves, and 5 denotes exhaust. A tube, 6 is a substrate for film formation, and 7 is a film formation chamber (plasma generation chamber). The deposition film formation in such a conventional deposition film forming apparatus is performed as follows. That is, the inside of the vacuum vessel 1 is evacuated through the exhaust pipe 5, and the base 6 is heated and held at a predetermined temperature by a heater (not shown) built in a holding table (not shown) of the base. I do. Next, if, for example, an amorphous silicon deposition film is to be formed via a source gas supply means (not shown), a silane gas (SiH ₄ ) and a hydrogen gas (H ₂ )
1 × 10 ⁻² Torr in the film forming chamber 7 of the vacuum vessel 1.
Supply while maintaining the following degree of vacuum. Next, from a microwave power supply (not shown), for example, 2.45 GH
z microwave 4 is isolator, power monitor,
It is introduced into the film forming chamber 7 through a stub tuner (not shown), the waveguide 3, and the microwave introduction window 2. Thus, plasma is generated in the film forming chamber 7, causing chemical interaction to form a deposited film on the surface of the base 6. FIG. 3-a is a schematic perspective view showing another example of an apparatus for forming a deposited film by the MW-PCVD method, and is a typical example of an apparatus basically using a cylindrical substrate. In FIG. 3-a, 1 is a cylindrical vacuum vessel, 2 is a circular microwave introduction window (made of quartz, alumina, ceramics, etc.), 3 is a microwave waveguide, and 4 is a microwave from a microwave power supply (not shown). 5, an exhaust pipe communicating with an exhaust device (not shown) via an exhaust valve (not shown); 6 ', a cylindrical substrate placed on a substrate holding cylinder; 7, a film forming chamber;
Denotes a basic heater built in the substrate holding cylinder, and 16 denotes a source gas discharge ring communicating with a source gas supply source (not shown). The formation of a deposited film on the cylindrical substrate 6 'by the apparatus shown in FIG. 3-a is performed in the same manner as in the case of the apparatus shown in FIG. 2-a. By the way, in such a conventional deposited film forming apparatus by the MW-PCVD method, since the plasma generated in the film forming chamber 7 is an ionizer composed of electrons and ion particles,
Acts as a kind of electrical conductor. In particular, the frequency 2.45GH
When the plasma is excited by the microwave power of z, the ion particles that can additionally follow the high-frequency vibration are:
Limited to those with low mass like electrons. Therefore, when considering the density of the generated plasma, it is sufficient to pay attention to the electron density. However, plasma generated under the conditions of a vacuum degree of 2 × 10 ⁻² Torr and a microwave power of 200 W has an electron temperature of about Te = 4 electron volts (hereinafter referred to as eV) and an electron density of ne = 10 ¹⁷ With a low-pressure discharge plasma of about m ^-3 , microwaves of 2.45 GHz are several tens of μm from the introduction window.
The light is reflected at the plasma interface at a distance of m, cannot enter the plasma, and the plasma density rapidly attenuates as the distance from the introduction window increases. For this reason, if a conventional apparatus as described above is used to form a desired amorphous silicon deposited film on a large-area substrate using microwave plasma, it is necessary to use a large-diameter microwave introduction window. When such a large-diameter microwave introduction window is installed in the apparatus, the scale of the apparatus is inevitably increased. Since the microwave introduction window also serves as one wall of the vacuum vessel 1, another problem relating to the strength of the apparatus is required. In addition to the necessity of paying particular attention to the design of the apparatus, there arises a problem that the efficiency of use of the raw material gas is reduced when the volume of the film forming chamber 7 is greatly increased and the desired Even if a film-formed product is obtained, it will be quite costly. [Object of the Invention] The object of the present invention is to overcome the problems in the conventional apparatus as described above and to provide a semiconductor device, a photoconductor device for electrophotography, a photovoltaic element, other various electronic elements, an optical element, and the like. It is an object of the present invention to provide an apparatus capable of forming a deposited film as an element member to be used stably at a high speed by an MW-PCVD method. Another object of the present invention is to adjust the resonance state of a microwave power introduction window of an apparatus for forming an a-Si: H: X film by MW-PCVD by the structure of a dielectric material used as the window material. It is an object of the present invention to provide a means suitable for efficiently applying the microwave energy to plasma. [Structure of the Invention] The inventor of the present invention has intensively studied to solve the above-mentioned problems in the conventional apparatus and achieve the object of the present invention.
As a result, the following findings were obtained. That is, in order to sufficiently self-excit a low-pressure discharge plasma (electron density ne = 10 ¹⁵ to 10 ¹⁷ m ³ ) which can be excited by a microwave, the shapes of the microwave introduction window and the film formation chamber are set to the microwave. It has been found that it is necessary to have a structure acting as a resonator. Further, when a space other than the space having the coaxial resonator structure, for example, a space such as an exhaust port has an opening through which microwaves can enter, the space also acts as a part of the microwave resonator, and particularly a high vacuum. It was also found that when there is an exhaust port or the like in the microwave propagation path in the atmosphere, the resonance condition is shifted. Based on these findings, the present invention has attempted an apparatus having the configuration shown in FIGS. 2-b and 3-b in order to solve the above-mentioned problems in the conventional apparatus. That is, a metal plate (punched metal) having a large number of through holes (1 mm to 3.58 cmφ) at the opening of the exhaust pipe 5 to the film formation chamber or a metal mesh netting (1 mm to 3.58 cm mesh size) is used. The microwave reflecting member 8 is installed so that the opening is apparently closed. On the other hand, when the microwave introduction window has a resonator structure, the microwave introduction window is designed as follows. That is, when the microwave introduction window is of the TE ₁₁₁ resonance mode and the resonance wavelength λ is 12.245 cm (resonance frequency 2.45 GHz), the size of the microwave introduction window is determined based on the known coaxial resonator theory. formula: (However, a represents the radius (cm) of the circular resonator window, d represents its thickness (cm), and represents its relative permittivity). For example, when alumina ceramics having a purity of 99.5% (dielectric constant = 10) is used for the microwave introduction window, the resonance condition is set by setting the radius a of the microwave introduction window to 9.5 cm and the thickness d to 1.95 cm. Can be satisfied.
Here, the length of 1.95 cm of the thickness d corresponds to half the wavelength of the microwave propagating in the alumina ceramics. Then, the resonance state of the microwave power introduction window in the apparatus shown in FIG. 2-b using alumina ceramics having a thickness of 2.0 cm was measured. The solid line in FIG. 2-c shows the measurement result of the resonance frequency characteristic. In the figure, the horizontal axis represents frequency (the unit is GHz), and the vertical axis represents the return loss (hereinafter referred to as RL for simplification; the unit is dB).
Represents Here, the return loss is the microwave input voltage · V _F (v)
If, from the reflection coefficient ρ = V _R / V _F where the which is the ratio of the reflected voltage · V _R (v), and the RL = -20log ₁₀ ρ. In the figure, the microwave power introduction window has the lowest reflection loss at about 2.48 GHz and is about -40 dB, and it has been found that microwaves of this frequency are transmitted efficiently. However, at a frequency of 2.45 GHz, it was about -5 dB, and was mostly reflected by alumina ceramics. By the way, it is said that the oscillation frequency range of the conventionally used 2.45 GHz microwave oscillator has a width of 2.45 GHz ± 30 MHz. However, in practice, the characteristics of the magnetron oscillation tube, as shown by the dashed line in Fig. 2-c, indicate that a sharp narrow-band oscillation with a width of 1 to 5 MHz is performed when the center frequency is 2.45 GHz. understood. The oscillation frequency characteristics are shown by broken lines in FIG. In other words, 2.45
When trying to transmit microwave power of GHz, 2-c
The hatched area surrounded by the solid line and the broken line in the figure is the transmission power. For example, if you input 1KW microwave power,
About 560 W is reflected from the alumina window, and only about 440 W can be fed into the reactor. As described above, when the reflection loss at the oscillation frequency is large, most of the microwave power is cut off by the introduction window, and there is a problem that the microwave power cannot be efficiently supplied to the reaction chamber. . Moreover, when the input power is small, there is a problem that it is difficult to start the discharge itself. Further, if the discharge is continued for a long time in a state where the reflected power is large, there is a problem that the alumina is heated to a high temperature by the microwave energy and is damaged. It is apparent from FIG. 2C that such an increase in the reflection loss at the microwave oscillation frequency is caused by a shift in the resonance frequency of the microwave introduction window. The reason that the actual resonance frequency deviates from the design value is
The processing accuracy of alumina, the processing accuracy of the metallic microwave shielding material on the outer peripheral portion of alumina, the surface resistance thereof, and the like are considered. In other words, for microwaves, alumina Acts as a transmission line having a size of For example, 0.5mm
Despite the dimensional error described above, it acts on microwaves in the same way as a change of 1.5 mm in the cavity, and shifts its resonance frequency on the order of MHz. Further, a surface current parallel to the electric field of the microwave flows on the metal surface as the shield member to generate a reflected wave.
For this reason, the generation state of the reflected wave is slightly different depending on the material of the metal, the surface oxidation, and the processing state, and the resonance frequency is shifted. Therefore, even if the microwave power introduction windows have the same shape and the same material, the resonance frequencies rarely coincide completely with each other, and the above-mentioned design formula can be satisfied only approximately. Moreover, since alumina ceramics cannot be easily processed and its shape cannot be adjusted to fine-tune the resonance frequency, effective means for accurately and easily tuning to the microwave oscillation frequency is needed. Is done. Based on these findings, further research was focused on adjusting the resonance state of the microwave power introduction window, and various changes were made to the structure of the microwave transparent dielectric material used for the microwave power introduction window. By doing so, we have found that the resonance state can be reversibly adjusted. For example, in a microwave power introduction window having a TE ₁₁₁ resonance mode circular resonator structure, a plurality of alumina thin plates having substantially the same radius are laminated in the microwave transmission direction (thickness direction of alumina) to increase the resonance frequency. It can be sequentially moved to the frequency side, and among the electromagnetic field modes on the plane, a plurality of small-diameter alumina blocks are placed at the most concentrated position of the electric flux lines, that is, at the center of the circle in the case of TE ₁₁ mode. By individually arranging or sequentially stacking, the resonance frequency can be sequentially shifted to the lower frequency side, and furthermore, by stacking the small-diameter blocks at the center of the circular alumina plate, without changing the resonance frequency, It has been found that only the return loss can be adjusted. Then, it was confirmed that the adjustment of these resonance frequencies can be performed reversibly and with good reproducibility. The present invention has been completed based on the findings and confirmed facts. Microwave plasma CV of the present invention
The apparatus for forming a functional deposited film by the D method uses a microwave permeable dielectric material as a microwave introduction window, and makes the shape resonate with the microwave oscillation frequency, and divides the dielectric. Alternatively, a resonance frequency characteristic and an electromagnetic field mode can be adjusted by using a structure in which another dielectric material chamber is appropriately arranged and combined therewith. The apparatus for forming a functional deposited film by the microwave plasma CVD method of the present invention includes the following two embodiments. (1) A film forming chamber having a substrate holding means therein, a source gas supply port connected to the source gas supply means, and an exhaust port connected to the exhaust means, and a microwave from a microwave power supply An apparatus for forming a functional thin film by a microwave plasma CVD method, wherein a microwave transmitting window that allows transmission of a microwave constitutes a part of a wall of the film forming chamber, wherein the microwave transmitting window has a microwave transmitting window. The formation of a functional deposition film by microwave plasma CVD, characterized in that it has a resonator structure formed from a conductive material and has a structure in which it is divided into multiple layers along the microwave transmission direction and laminated. apparatus. (2) a film forming chamber having a substrate holding means therein, a source gas supply port connected to the source gas supply means, and an exhaust port connected to the exhaust means, and a microwave from a microwave power supply; An apparatus for forming a functional thin film by a microwave plasma CVD method, wherein a microwave transmitting window allowing transmission of light is formed as a part of a wall of the film forming chamber, wherein the microwave transmitting window has a microwave transmitting property. It has a resonator structure formed of a substance, and a block made of a dielectric material is provided on the atmospheric side of the microwave transmitting window at a symmetrical position so as to intersect a line of electric force passing through the center of the microwave transmitting window. Microwave plasma CV, characterized by having multiple structures mounted on a plate
Apparatus for forming functional deposited film by D method. By the way, the present inventor examined the fact that the resonance frequency can be changed by combining the shapes of dielectric materials having a relative dielectric constant larger than 1.0 in this way. The conclusion is that there is a conscious adjustment of the world mode. Therefore, according to the basic principle of the present invention, the dielectric material stacked on the alumina disk has a relative dielectric constant of
What is necessary is just to be larger than 1.0, ie, what can change the electric field. For example, when quartz glass having a relative dielectric constant of 3.5 is used, in the case of the same shape and arrangement as alumina, the amount of shift of the resonance frequency becomes small, and finer adjustment can be performed. On the other hand, in the device of the present invention, the electromagnetic field mode after the dielectric can be intentionally changed depending on the arrangement state of the dielectric block. Therefore, the alumina block is stacked at the center of the disk. In a circular waveguide
The TE ₁₁ mode can be transformed into a coaxial line type TE ₁₁ mode to prevent local heating by dispersing the amount of heat generated by the dielectric material due to microwave energy, or to make the plasma density uniform in the reactor. Can be. Further, in the device of the present invention, when the dielectric windows are divided and laminated in the microwave transmission direction, electric charges are accumulated at the lamination interface, and a minute reflection is generated with respect to the microwave. However, it has also been found that this does not prevent microwave transmission, but rather produces multiple interference due to reflected waves, exerts an antireflection effect on microwaves, and produces a favorable result of reducing reflection loss. . Further, in the device of the present invention, the dielectrics to be divided and laminated do not need to be the same substance, and if substances having different relative dielectric constants are appropriately used in combination, as in the case of the broadband anti-reflection technology in the optical field, a wide band resonance A microwave power introduction window having frequency characteristics can also be created. Embodiment Hereinafter, the microwave introduction window in the apparatus of the present invention will be described in more detail with reference to the embodiment shown in FIG. 1, but the present invention is not limited thereto. FIG. 1 shows a method of adjusting a resonance condition of a microwave power introduction window in a deposition film forming apparatus using the MW-PCVD method of the present invention.
An example of a method of adjusting the introduction window of the conventional TE ₁₁₁ resonance mode will be described. FIG. 1-a shows the conventional alumina window 2 having a thickness of 1.0 c.
FIG. 1-b is a schematic cross-sectional view of a structure in which the side wall of the alumina plate 10 on the plasma side is formed in a tapered shape, and the frequency characteristics are shown in FIG. In FIG. 1-b, the broken line represents the characteristics of the conventional introduction window. As is clear from FIG. 1-b, the resonance frequency shifts to the lower frequency side. The amount of shift of the resonance frequency can be further shifted to a lower frequency side by increasing the taper angle θ. FIG. 1-c shows the alumina plate 9 shown in FIG. 1-a.
FIG. 1D is a schematic cross-sectional view of a window on which one alumina plate 11 having a thickness of 0.2 cm and a diameter ≦ 2a is placed, and FIG. 1-d shows a frequency characteristic thereof. In FIG. 1-d, the dashed line represents the characteristic (shown in FIG. 1-b) before the alumina plate having a thickness of 0.2 cm was placed. First
From the −d diagram, it was found that the resonance point moved to the high frequency side by about 30 MHz. FIG. 1-e shows that one alumina plate 12 having a thickness of 0.2 cm is further laminated on the window. The characteristics are shown in FIG. 1-f. The dashed line indicates the characteristics before lamination (when one alumina plate having a thickness of 0.2 cm). From FIG. 1-f, the resonance point is further
It turned out to move to the high frequency side about 30MHz. FIG. 1-g shows a rectangular TE in which the electric lines of force are concentrated at two points on the center line where the electric lines of force of the window shown in FIG. 1-c are concentrated, that is, at the center of the E plane in the case of the TE ₁₁ mode. Since only the ₀₁ mode was made circular, the two lines of symmetry at both ends on the line where the lines of electric force were straight in FIG. 2 shows a schematic perspective view of a window in which blocks 13 are arranged. In the figure, the broken line indicates the distribution of the electric field E (lines of electric force). The characteristics are shown in FIG. 1-h. In the figure, the broken lines represent the characteristics of the window shown in FIG. 1-c. As a result, it was found that the resonance frequency moved to a low frequency side of about 10 MHz. Although not shown, if a φ2.0 cm alumina block is further laminated on each of the φ2.0 cm alumina blocks 13 in the window shown in FIG. 1-g, the resonance point further moves by about 10 MHz to the low frequency side. I understood. Unlike FIG. 1-g, when the alumina block was arranged at a position where the magnetic field was concentrated (a position rotated by 90 ° in the circumferential direction with respect to the illustrated block), the frequency characteristics hardly changed. FIG. 1-i is a schematic perspective view of a window having a single alumina block 13 disposed at the center of the window of FIG. 1-c, the characteristics of which are shown in FIG. 1-j. The resonance point hardly changes,
Return loss is increased by about 10 dB. FIG. 1-k shows that five alumina blocks 13 are arranged at the center in the same manner.
As shown in FIG. 1, the return loss was further increased. Here, when the alumina block 13 is placed in the center of the window, the TE ₁₁₁ resonance mode of the circular window is deformed, and the coaxial line type T ₁₁₁ is deformed.
It approaches the _E111 resonance mode. The change in the electric field distribution at that time is shown in FIG. 4-b. FIG. 4-a shows a conventional circular TE.
₁₁ shows an electric field distribution of ₁₁₁ modes. When plasma is generated using the window shown in FIG. 4-a, the plasma intensity is high near the line where the lines of electric force where the electric field is concentrated form a straight line, and the window generates a large amount of heat. In the window shown in FIG. 4-b in which the blocks are arranged, the region where the electric field intensity is high is dispersed, so that the plasma intensity becomes almost uniform. Further, heat generation is also dispersed, so that window damage due to heating hardly occurs. As described above, by appropriately disposing the alumina plate and the alumina block, the resonance frequency characteristics and the electromagnetic field mode of the window can be freely adjusted. Example 1 In this example, when the microwave power introduction window was used for the plasma CVD apparatus of FIG. 2-b, the center frequency of the microwave oscillator used was 2.45 GHz.
The structure of the window used was that shown in FIG. 1-g. Then, a mixed gas of 500 sccm of silane gas and 200 sccm of hydrogen gas was introduced as a source gas, and 1 kW of microwave power of 2.45 GHz was supplied from a microwave current under a condition of a vacuum degree of 2 × 10 ⁻³ torr. During the discharge, the microwave power of 100 W was reflected. This is considered to be due to the plasma generated in the reaction chamber rather than the alumina window. The discharge was extremely stable, and the temperature of the alumina window hardly changed during the one-hour film formation. Further, when the deposited amorphous silicon film was examined, it was found that the deposition rate was about twice that in the case where the conventional microwave power introduction window was used. Moreover, the electrical properties of the film are not affected by high-speed deposition,
Hardly changed. In the above-described embodiment, the circular alumina window that resonates in the TE ₁₁ mode has been described. However, the location of the alumina plate and the alumina block is limited to the location that acts on the electric field of the window, and the distribution is changed. considering that by adjusting the resonance condition, not limited to the TE ₁₁ mode in the window resonant mode, a window other than the example window, for example it may be a circular TE ₀₁ mode window. However, in this case, since the electric field is concentrically distributed as shown in FIG. 5, the resonance frequency moves when the block is disposed at the center and the circumference. In Figure 6, of the method of adjusting the resonance condition in the circular alumina windows TE ₀₁ mode, an example of mounting a ring-shaped dielectric plate 14 to be used to move the resonance frequency to the low frequency side. The movement to the higher frequency side was performed by laminating the circular alumina plates 11 as in the case of the TE ₁₁ mode. [Summary of the effects of the invention] The device of the present invention is a simple operation of laminating a dielectric window and a dielectric block on a microwave introduction window,
The resonance frequency of the microwave introduction window can be freely moved, and by matching the oscillation frequency of the microwave power supply, it is possible to reduce the reflection loss of the microwave at the introduction window, and to reduce the microwave power. This enables efficient introduction into the reaction chamber. Thus, in the microwave plasma CVD apparatus using the microwave power introduction window of the present invention, it is possible to form an amorphous silicon film at a high speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A to 1L are cross-sectional and perspective schematic views of a microwave power introduction window of the present invention and diagrams showing their frequency characteristics, and FIGS. FIG. 2 is a diagram showing an example of a device for forming a deposited film by the MW-PCVD method and frequency characteristics of microwave power introduction windows thereof. Figures 3-a and b show conventional MW-PCV
It is a schematic perspective view which shows the other example of the formation apparatus of the deposited film by the D method. The 4-a diagram is the electric field distribution of the circular TE ₁₁ resonance mode, the 4-b diagram is the electric field distribution of the coaxial TE ₁₁ resonance mode. Figure 5 is a field distribution of the circular TE ₀₁ resonance mode, Fig. 6 is a schematic perspective view of microwave power introduction windows of the circular TE ₀₁ mode. In the figure, 1 ... reaction vessel, 2,9,10 ... microwave introduction window, 3 ...
Waveguide, 4 ... Microwave, 5 ... Exhaust pipe, 6 ... Base, 6 '... Cylindrical base, 7 ... Film forming chamber, 8 ... Microwave reflecting member, 11,12 ... Dielectric Body plate, 13: Dielectric block, 14: Dielectric ring, 15: Substrate heating heater built in the substrate holding cylinder, 16: Source gas discharge ring

Claims (1)

(57) [Claims] It has a substrate holding means inside, has a film formation chamber provided with a source gas supply port connected to the source gas supply means and an exhaust port connected with the exhaust means, and transmits microwaves from a microwave power supply. An apparatus for forming a functional thin film by a microwave plasma CVD method in which a microwave transmitting window to allow constitutes a part of a wall of the film forming chamber, wherein the microwave transmitting window is made of a microwave permeable material. An apparatus for forming a functional deposition film by a microwave plasma CVD method, having a resonator structure formed, and having a structure in which the resonator structure is divided into a plurality of pieces along a microwave transmission direction and laminated. 2. A functional deposited film formed by a microwave plasma CVD method according to claim 1, wherein the microwave transmitting window is made of the same or different microwave transmitting materials having a relative permittivity ε of greater than 1.0. Forming equipment. 3. It has a substrate holding means inside, has a film formation chamber provided with a source gas supply port connected to the source gas supply means and an exhaust port connected with the exhaust means, and transmits microwaves from a microwave power supply. An apparatus for forming a functional thin film by a microwave plasma CVD method in which a microwave transmitting window allows a part of a wall of the film forming chamber, wherein the microwave transmitting window is formed of a microwave transmitting material. And a plurality of blocks made of a dielectric material on the atmospheric side of the microwave transmitting window at symmetrical positions so as to intersect electric lines of force passing through the center of the microwave transmitting window. Microwave plasma CVD characterized by having a mounted structure
For forming a functional deposited film by the EB method. 4. The functional deposition by the microwave program CVD method according to claim (3), wherein the dielectric block is made of the same or different microwave transmitting materials having a relative dielectric constant (ε) of more than 0.1. Film forming equipment.