阅读说明：本技术 束流比例检测方法及检测设备 (Beam proportion detection method and detection equipment ) 是由 尚林涛 邢伟荣 周朋 刘铭 王经纬 于 2019-08-27 设计创作，主要内容包括：本发明公开了一种束流比例检测方法及检测设备。束流比例检测方法包括：检测第一束流的生长速率v<Sub>1</Sub>,检测第二束流的生长速率v<Sub>2</Sub>,计算第一束流与第二束流的有效吸附束流比例N,N＝v<Sub>1</Sub>/v<Sub>2</Sub>。采用本发明,可以精确的计算出分子束外延生长过程中第一束流与第二束流实际参与键合反应所吸附结合到样品表面上的有效吸附束流比例,从而在实际试验过程中,根据需求快速且准确的确定出合成符合一定化学计量比的化合物半导体材料的束流控制实验参数,进而可以减少实验的重复性和肓目性,提高实验效率和生产效率。(The invention discloses a beam proportion detection method and detection equipment. The beam current proportion detection method comprises the following steps: detecting the growth rate v of the first beam 1 Detecting the growth rate v of the second beam 2 Calculating the effective adsorption beam current ratio N, N-v of the first beam current and the second beam current 1 /v 2 . By adopting the method and the device, the effective adsorption beam ratio of the first beam and the second beam which actually participate in the bonding reaction and are adsorbed and combined on the surface of the sample in the molecular beam epitaxial growth process can be accurately calculated, so that the beam control experiment parameters of the compound semiconductor material which is synthesized to meet a certain stoichiometric ratio can be rapidly and accurately determined according to the requirements in the actual experiment process, the repeatability and the blind property of the experiment can be further reduced, and the experiment efficiency and the production efficiency can be improved.)

1. A beam current proportion detection method is characterized by comprising the following steps:

detecting the growth rate v of the first beam₁，

Detecting the growth rate v of the second beam₂，

Calculating the effective adsorption beam current ratio N, N-v of the first beam current and the second beam current₁/v₂。

2. The method of claim 1, wherein detecting the growth rate v of the first beam current₁The method comprises the following steps:

extending a first beam on a substrate;

in the first beam epitaxy process, detecting an intensity oscillation curve of the first beam by using a reflection type high-energy electron diffractometer RHEED;

calculating the growth rate v of the first beam according to formula 1₁，

v₁＝m/(T₂-T₁) Formula 1;

wherein, T₁A time T corresponding to a peak in the intensity oscillation curve of the first beam₂M is a time period [ T ] corresponding to another peak in the intensity oscillation curve of the first beam₁,T₂]The number of inner peaks.

3. The method of claim 2, wherein the extending the first beam over the substrate comprises:

continuously extending the second beam current on the substrate for a first time period t₁；

Continuously extending the second beam current for a second time period t₂Then, on the substrateContinuously extending the first beam flow for a third time period t₃；

Wherein, t₂+t₃≤t₁。

4. The method of claim 3, wherein t is₂Satisfies the following conditions: t is t₂> 0s, said t₃Satisfies the following conditions: t is t₃≥1s。

5. The method of claim 3, further comprising:

continuously extending the second beam current on the substrate for a first time period t₁Before, a substrate with a crystal orientation of 100 is selected, and the substrate is subjected to deoxidation treatment.

6. The method of claim 1, wherein the detecting the growth rate v of the second beam current₂The method comprises the following steps:

extending a second beam on the substrate;

in the second beam epitaxy process, detecting an intensity oscillation curve of the second beam by using a reflection type high-energy electron diffractometer RHEED;

calculating the growth rate v of the second beam according to formula 2₂，

v₂＝n/(T₄-T₃) Formula 2;

wherein, T₃A time T corresponding to a peak in the intensity oscillation curve of the second beam₄N is a time period [ T ] corresponding to another peak in the intensity oscillation curve of the second beam₃,T₄]The number of inner peaks.

7. The method of claim 6, wherein the extending the second beam current on the substrate comprises:

continuously extending the first beam stream on the substrate for a fourth time period t₄；

Continuing to extend the first beam stream for the fourth time period t₄Then, in the liningContinuously extending the second beam current for a fifth time period t on the bottom₅。

8. The method of claim 7, wherein t is₄Satisfies the following conditions: t is less than or equal to 6s₄Less than or equal to 20s, the t₅Satisfies the following conditions: t is t₅＞t₄。

9. The method of claim 1, wherein the first beam current is a group III beam current and the second beam current is a group V beam current.

10. A beam ratio detection apparatus, characterized by comprising: memory, processor and computer program stored on the memory and executable on the processor, which when executed by the processor implements the steps of the beam ratio detection method according to any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of molecular beam epitaxy, in particular to a beam proportion detection method and detection equipment.

Background

The key control parameters when the compound semiconductor material is grown by using the molecular beam epitaxy technology are growth temperature and beam ratio of material elements, wherein the growth of the semiconductor material can be in reasonable thermodynamic and kinetic growth modes by using the molecular beam epitaxy technology, and good crystallization quality is obtained; the latter is critical to the growth of high quality, properly stoichiometric semiconductor materials. Particularly, when binary III-V group compound semiconductor materials (such as InSb, GaSb and the like) which are relatively simple are grown, the method has certain practical significance for accurately correcting and controlling the V/III beam current ratio to grow high-quality III-V group semiconductor materials at a determined growth temperature and reducing the repeatability and blindness of experiments.

Disclosure of Invention

The embodiment of the invention provides a beam proportion detection method and detection equipment, which are used for solving the problem of low beam proportion detection precision in the prior art.

On one hand, the embodiment of the invention provides a beam proportion detection method, which comprises the following steps:

detecting the growth rate v of the first beam₁，

Detecting the growth rate v of the second beam₂，

Calculating the effective adsorption beam current ratio N, N-v of the first beam current and the second beam current₁/v₂。

According to some embodiments of the invention, the detecting a growth rate v of the first beam current₁The method comprises the following steps:

extending a first beam on a substrate;

in the first beam epitaxy process, detecting an intensity oscillation curve of the first beam by using a reflection type high-energy electron diffractometer RHEED;

calculating the growth rate v of the first beam according to formula 1₁，

v₁＝m/(T₂-T₁) Formula 1;

wherein, T₁A time T corresponding to a peak in the intensity oscillation curve of the first beam₂M is a time period [ T ] corresponding to another peak in the intensity oscillation curve of the first beam₁,T₂]The number of inner peaks.

Further, the extending the first beam stream on the substrate includes:

continuously extending the second beam current on the substrate for a first time period t₁；

Continuously extending the second beam current for a second time period t₂Then, continuously extending the first beam stream on the substrate for a third time period t₃；

Wherein, t₂+t₃≤t₁。

In some embodiments of the invention, the t is₂Satisfies the following conditions: t is t₂> 0s, said t₃Satisfies the following conditions: t is t₃≥1s。

In some embodiments of the invention, the method further comprises:

continuously extending the second beam current on the substrate for a first time period t₁Before, a substrate with a crystal orientation of 100 is selected, and the substrate is subjected to deoxidation treatment.

According to some embodiments of the invention, the detecting a growth rate v of the second beam current₂The method comprises the following steps:

extending a second beam on the substrate;

in the second beam epitaxy process, detecting an intensity oscillation curve of the second beam by using a reflection type high-energy electron diffractometer RHEED;

calculating the growth rate v of the second beam according to formula 2₂，

v₂＝n/(T₄-T₃) Formula 2;

wherein, T₃For intensity oscillation of the second beamTime, T, corresponding to a peak in the curve₄N is a time period [ T ] corresponding to another peak in the intensity oscillation curve of the second beam₃,T₄]The number of inner peaks.

Further, the extending a second beam current on the substrate includes:

continuously extending the first beam stream on the substrate for a fourth time period t₄；

Continuing to extend the first beam stream for the fourth time period t₄Then, continuously extending the second beam current for a fifth time period t on the substrate₅。

In some embodiments of the invention, the t is₄Satisfies the following conditions: t is less than or equal to 6s₄Less than or equal to 20s, the t₅Satisfies the following conditions: t is t₅＞t₄。

According to some embodiments of the invention, the first beam is a group III beam and the second beam is a group V beam.

On the other hand, an embodiment of the present invention further provides a beam ratio detection apparatus, including: a memory, a processor and a computer program stored on the memory and executable on the processor, the computer program, when executed by the processor, implementing the steps of the beam ratio detection method as described above.

By adopting the embodiment of the invention, the effective adsorption beam ratio of the first beam and the second beam which actually participate in the bonding reaction and are adsorbed and combined on the surface of the sample in the molecular beam epitaxial growth process can be accurately calculated, so that the beam control experiment parameters for synthesizing the compound semiconductor material which meets a certain stoichiometric ratio can be rapidly and accurately determined according to the requirements in the actual experiment process, the repeatability and the blind eye performance of the experiment can be further reduced, and the experiment efficiency and the production efficiency can be improved.

The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

FIG. 1 is a schematic flow chart of a beam current ratio detection method according to an embodiment of the present invention;

FIG. 2 is a schematic flow chart of a beam current ratio detection method according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of beam ratio detection equipment in the embodiment of the present invention.

FIG. 4 is a graph of the intensity oscillation of the group III beam detected by RHEED in an embodiment of the present invention;

fig. 5 is a graph of the intensity oscillation of the group V beam detected by RHEED in the embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

On one hand, an embodiment of the present invention provides a beam ratio detection method, as shown in fig. 1, where the detection method includes:

s101, detecting the growth rate v of the first beam₁，

S102, detecting the growth rate v of the second beam₂，

S103, calculating the effective adsorption beam current ratio N of the first beam current to the second beam current, wherein N is equal to v₁/v₂。

By adopting the embodiment of the invention, the effective adsorption beam ratio of the first beam and the second beam which actually participate in the bonding reaction and are adsorbed and combined on the surface of the sample in the molecular beam epitaxial growth process can be accurately calculated, so that the beam control experiment parameters for synthesizing the compound semiconductor material which meets a certain stoichiometric ratio can be rapidly and accurately determined according to the requirements in the actual experiment process, the repeatability and the blind eye performance of the experiment can be further reduced, and the experiment efficiency and the production efficiency can be improved.

On the basis of the above-described embodiment, various modified embodiments are further proposed, and it is to be noted herein that, in order to make the description brief, only the differences from the above-described embodiment are described in the various modified embodiments.

According to some embodiments of the invention, the detecting a growth rate v of the first beam current₁The method comprises the following steps:

extending a first beam on a substrate;

in the first beam epitaxy process, detecting an intensity oscillation curve of the first beam by using a reflection type high-energy electron diffractometer RHEED;

calculating the growth rate v of the first beam according to formula 1₁，

v₁＝m/(T₂-T₁) Formula 1;

wherein, T₁Is the time T corresponding to one wave peak in the intensity oscillation curve of the first beam₂M is a time period [ T ] corresponding to another peak in the intensity oscillation curve of the first beam₁,T₂]The number of inner peaks.

It should be explained that the reflection type high energy electron diffractometer RHEED is an important component on the molecular beam epitaxy equipment MBE, and it can be used to observe the cleanness, flatness and surface structure of the sample surface in situ during growth, and judge the sample surface growth condition by observing the RHEED diffraction image and RHEED oscillation curve. For example, an electron gun of the RHEED glazes a high-energy electron beam of 10-30 KeV to the surface of a sample at a very small glancing angle (1-2 degrees), the momentum component of the electron perpendicular to the surface of the sample is very small, and the electron is scattered by a coulomb field, so that the penetration depth of the electron beam is only 1-2 atomic layers, and the RHEED diffraction image on a fluorescent screen can completely reflect the structural information of the surface of the sample. The intensity information of the beam current of the first beam current participating in adsorption bonding can be obtained through the intensity oscillation of the diffraction spots.

The intensity oscillation curve may be an oscillation diagram in which the horizontal axis is a time axis and the vertical axis is the intensity of the first beam. The intensity oscillation curve of the first beam current may be a period curve graph, and in the intensity oscillation curve graph, a time period between every two adjacent peaks may represent one oscillation period. [ T ]₁,T₂]The number of inner peaks includes the number of peaks located within the time period T1 to T2 plus 1 peak at T1 and T2.

In addition, the peak is used to represent the period of the intensity oscillation curve in the present embodiment, and then, it is easy for those skilled in the art to think that the trough is used to represent the period of the intensity oscillation curve, that is, the growth rate v of the first beam is calculated according to the formula 3₁，

v₁＝a/(T₆-T₅) Formula 3;

wherein, T₅Is the time T corresponding to one wave trough in the intensity oscillation curve of the first beam₆A is the time corresponding to another wave trough in the intensity oscillation curve of the first beam, and a is the time period [ T₅,T₆]The number of the inner wave troughs.

Further, the extending the first beam stream on the substrate may specifically include:

continuously extending the second beam current on the substrate for a first time period t₁；

Continuously extending the second beam current for a second time period t₂Then, the first beam stream continues to be extended on the substrate for a third time period t₃；

Wherein, t₂+t₃≤t₁。

It will be appreciated that the second beam is first allowed to extend over the substrate for a period of time before the first beam is extended. Therefore, the second beam current can form a buffer layer on the substrate to cover the rough substrate surface, and the detection effect of the first beam current is improved. In addition, it should be noted that, during the epitaxy process of the first beam, the epitaxy process of the second beam is still maintained. The second beam current can form a protective effect on the first beam current.

In some embodiments of the invention, t₂Can satisfy the following conditions: t is t₂＞0s，t₃Can satisfy the following conditions: t is t₃The time is more than or equal to 1 s. E.g. t₂Can be 3s, 5s, 9s, 12s, t₃And can be 5s, 7s, 9s and 12 s.

In some embodiments of the present invention, the method may further include:

continuously extending the second beam current on the substrate for a first time period t₁Before that, a substrate having a crystal orientation of 100 was selected, and the substrate was subjected to a deoxidation treatment. Thereby, the detection accuracy can be improved.

According to some embodiments of the invention, the growth rate v of the second beam current is detected₂The method comprises the following steps:

extending a second beam on the substrate;

in the second beam epitaxy process, detecting an intensity oscillation curve of the second beam by using a reflection type high-energy electron diffractometer RHEED;

calculating the growth rate v of the second beam according to the formula 2₂，

v₂＝n/(T₄-T₃) Formula 2;

wherein, T₃Is the moment T corresponding to one wave peak in the intensity oscillation curve of the second beam₄Is the time corresponding to another peak in the intensity oscillation curve of the second beam, and n is the time period [ T₃,T₄]The number of inner peaks.

It should be explained that the reflection type high energy electron diffractometer RHEED is an important component on the molecular beam epitaxy equipment MBE, and it can be used to observe the cleanliness, flatness and surface structure of the sample surface in situ during growth, and determine the growth condition through the observed curve. For example, an electron gun of RRHEED glares 10-30 KeV high-energy electron beams to the surface of a sample at a very small glancing angle (1-2 degrees), the momentum component of electrons vertical to the surface of the sample is very small, and the electrons are scattered by a coulomb field, so the penetration depth of the electron beams is only 1-2 atomic layers, and the RHEED diffraction image on a fluorescent screen can completely reflect the structural information of the surface of the sample. And the intensity information of the beam current of the second beam current participating in adsorption bonding can be obtained through the intensity oscillation of the diffraction spots.

The intensity oscillation curve may be an oscillation diagram in which the horizontal axis is a time axis and the vertical axis is the intensity of the second beam. The intensity oscillation curve of the second beam may be a period curve graph, and in the intensity oscillation curve graph, a time period between every two adjacent peaks may represent one oscillation period. [ T ]₃,T₄]The number of inner peaks includes the number of peaks located within the time period T3 to T4 plus 1 peak at T3 and T4.

In addition, it should be noted that the peak is used to represent the period of the intensity oscillation curve in the present embodiment, and then, it is easy for those skilled in the art to think that the trough is used to represent the period of the intensity oscillation curve, that is, the growth rate v of the second beam is calculated according to equation 4₁，

v₁＝b/(T₈-T₇) Formula 4;

wherein, T₇Is the time T corresponding to one wave trough in the intensity oscillation curve of the second beam₈B is the time corresponding to another wave trough in the intensity oscillation curve of the second beam current, and b is the time period [ T₇,T₈]The number of the inner wave troughs.

Further, the extending the second beam current on the substrate may specifically include:

continuously extending the first beam stream on the substrate for a fourth time period t₄；

Continuously extending the first beam for a fourth time period t₄Then, extending the second beam continuously on the substrate for a fifth time period t₅；

In the second beam epitaxy process, detecting the growth rate v of the second beam by adopting in-situ on-line monitoring equipment₂。

It will be appreciated that after a period of time during which the first beam is being extended onto the substrate, the extension of the first beam is stopped and the extension of the second beam is simultaneously turned on. Thus, a few monolayers previously deposited by the first beam may provide a basal moat effect for oscillations of different intensities of the same number of monolayers induced by the second beam.

In addition, it should be noted that the second beam is deposited for a longer time than the first beam, and completely covers the single layer reserved by the first beam, i.e. t₅>t₄And then, the excessive second beam current simultaneously plays a role in protecting the surface structure of the sample. In some embodiments of the invention, t₄Satisfies the following conditions: t4 is more than or equal to 6s and less than or equal to 20s, t₅Satisfies the following conditions: t is t₅>t₄. E.g. t₄And may be 8s, 9s, 10s, 11s, 12s, or the like.

According to some embodiments of the invention, the first beam may be a group III beam and the second beam may be a group V beam. For example, the first beam may be an indium beam, an aluminum beam, or a gallium beam. The second beam can be a phosphorus beam, an arsenic beam or an antimony beam.

The beam ratio detection method according to an embodiment of the present invention is described in detail below in a specific embodiment with reference to fig. 2. It is to be understood that the following description is illustrative only and is not intended to be in any way limiting. All similar structures and similar variations thereof adopted by the invention are intended to fall within the scope of the invention.

As shown in fig. 2, a method for detecting a beam current ratio according to an embodiment of the present invention includes:

s201, selecting a substrate with the crystal orientation of 100, and preprocessing the substrate.

Pretreatment is understood here to mean a cleaning process, such as removal of surface residues of moisture and organic substances.

S202, placing the substrate into a growth chamber, and performing deoxidation treatment;

it should be noted that the growth chamber is maintained at a suitable growth temperature.

S203, continuing the epitaxial V-group beam flow on the substrate for a first time period t₁；

It can be understood that the group V beam stream transmitting device is turned on for the first time period t₁And the group V beam canSo as to form an epitaxial layer with a certain thickness on the substrate and protect the surface structure of the sample.

S204, continuing to extend the group V beam stream for a second time period t₂Thereafter, the epitaxial III-beam flow is continued for a third time period t on the substrate₃Wherein, t₂+t₃≤t₁；

It can be understood that the group V beam stream transmitting device is turned on for the second time period t₂Then, the emitting device of the III group beam current is opened and lasts for a third time period t₃During measurement of group III beam induced RHEED oscillations, which are performed under a relatively excessive amount of group V beam protection, the group V beam is also in an open state, and the oscillation rate is determined by the relatively small amount of group III beam induction.

S205, in the process of group III beam epitaxy, detecting an intensity oscillation curve of the group III beam by using RHEED (RHEED detection), as shown in FIG. 4, and calculating the growth rate v of the group III beam according to formula 1₁，

v₁＝m/(T₂-T₁) Formula 1;

wherein, T₁Is the time T corresponding to one wave peak in the intensity oscillation curve of the III group beam₂M is the time corresponding to another peak in the intensity oscillation curve of the III group beam current, and m is the time period [ T₁,T₂]The number of inner peaks.

It is understood that the second time period t is extended in the group V beam flow₂Then, the group III beam current emission device is turned on under the protection of the group V beam current and lasts for a third time period t₃To excite RHEED oscillations of a certain number (more than 5) of stable group III beams.

S206, continuing to extend the V-group beam flow for a first time period t₁Then, stopping the epitaxy of the V-group beam, and continuously extending the III-group beam on the substrate for a fourth time period t₄；

It will be appreciated that the emitting means of the group V beam are turned on for a first period t₁Then, the emitting device of the V group beam current is closed, and then the emitting device of the III group beam current is openedSetting and continuing for a fourth time period t₄。

S207, continuing to extend the III group beam flow for a fourth time period t₄Then, the epitaxial V-group beam flow is continued for a fifth time period t on the substrate₅；

It can be understood that the emitting device of the III-group beam current is switched on for the fourth time period t₄Then, the emitting device of the III group beam current is closed, and simultaneously the emitting device of the V group beam current is opened for a fifth time period t₅。

S208, in the epitaxial process of the group V beam, detecting the intensity oscillation curve of the group V beam by using RHEED (RHEED detection), as shown in FIG. 5, and calculating the growth rate V of the group V beam according to the formula 2₂，

v₂＝n/(T₄-T₃) Formula 2;

wherein, T₃Is the time corresponding to one wave peak in the intensity oscillation curve of the V-group beam current, T₄Is the time corresponding to another wave crest in the intensity oscillation curve of the V-group beam, and n is a time period [ T₃,T₄]The number of inner peaks.

S209, calculating the effective adsorption beam ratio N, N-V of the III group beam and the V group beam₁/v₂。

By adopting the embodiment of the invention, the effective adsorption beam current ratio of the III family beam current and the V family beam current in the molecular beam epitaxial growth process can be accurately calculated, so that the beam current control experiment parameters for synthesizing the compound semiconductor material which accords with a certain stoichiometric ratio can be rapidly and accurately determined according to the requirements in the actual experiment process, the repeatability and the blind eye performance of the experiment can be further reduced, and the experiment efficiency and the production efficiency can be improved.

For general III-V materials, the beam current should be controlled in the adjustment of the beam current source size so that the ratio of the effective adsorption beam current V/III of the III-V is between 1 and 1.5, namely 2/3< N <1, namely, the V group elements in the materials forming the III-V are slightly excessive to meet the formation condition of the stoichiometric ratio of the materials.

It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention, and those skilled in the art can make various modifications and changes. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

On the other hand, an embodiment of the present invention provides a beam ratio detection apparatus, as shown in fig. 3, including: a memory 1010, a processor 1020 and a computer program stored on the memory 1010 and executable on the processor 1020, the computer program realizing the following method steps when executed by the processor 1020:

s101, detecting the growth rate v of the first beam₁，

S102, detecting the growth rate v of the second beam₂，

S103, calculating the effective adsorption beam current ratio N of the first beam current to the second beam current, wherein N is equal to v₁/v₂。

By adopting the embodiment of the invention, the effective adsorption beam ratio of the first beam and the second beam which actually participate in the bonding reaction and are adsorbed and combined on the surface of the sample in the molecular beam epitaxial growth process can be accurately calculated, so that the beam control experiment parameters for synthesizing the compound semiconductor material which meets a certain stoichiometric ratio can be rapidly and accurately determined according to the requirements in the actual experiment process, the repeatability and the blind eye performance of the experiment can be further reduced, and the experiment efficiency and the production efficiency can be improved.

It should be noted that in the description of the present specification, reference to the description of the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples", etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.