阅读说明：本技术 一种提高vcsel氧化孔径均匀性的方法 (Method for improving VCSEL (vertical cavity surface emitting laser) oxidation aperture uniformity ) 是由 杨首朕 姚林松 陈丽祥 黄川� 王亮 于 2021-08-05 设计创作，主要内容包括：本发明涉及半导体技术领域,公开了一种提高VCSEL氧化孔径均匀性的方法,具体为：将VCSEL刻蚀的台面结构设计为花瓣型,且沟道宽度设计为10-25um；再将VCSEL置于氧化炉内,然后对氧化炉快速升温至VCSEL的氧化温度以下,并恒温25-35min,在升温和恒温时向氧化炉内通入氮气和水汽的混合气体；对氧化炉以10-20℃/min的升温速率升温至氧化所需温度,直至氧化完毕；最后对氧化炉降温,使氧化炉快速降温至180-220℃,然后自然冷却至室温。本发明能够提高VCSEL氧化孔径均匀性。(The invention relates to the technical field of semiconductors, and discloses a method for improving the uniformity of VCSEL (vertical cavity surface emitting laser) oxide aperture, which comprises the following steps: designing a VCSEL etched mesa structure into a petal type, and designing the width of a channel to be 10-25 um; then placing the VCSEL into an oxidation furnace, rapidly heating the oxidation furnace to below the oxidation temperature of the VCSEL, keeping the temperature for 25-35min, and introducing mixed gas of nitrogen and water vapor into the oxidation furnace during heating and keeping the temperature; heating the oxidation furnace to the temperature required by oxidation at the heating rate of 10-20 ℃/min until the oxidation is finished; and finally, cooling the oxidation furnace to ensure that the temperature of the oxidation furnace is quickly reduced to 180-220 ℃, and then naturally cooling to the room temperature. The invention can improve the uniformity of the oxide aperture of the VCSEL.)

1. A method for improving the uniformity of the oxide aperture of a VCSEL (vertical cavity surface emitting laser) is characterized in that: the mesa structure etched by the VCSEL is designed to be a petal type, and the width of a channel is designed to be 10-25 um.

2. A method according to claim 1, wherein the method comprises the steps of: the VCSEL etched table-board structure is designed to be a six-petal type.

3. A method according to claim 2, wherein the method comprises the steps of: in oxidation of VCSELs, the method comprises the following steps:

s1, placing the VCSEL into an oxidation furnace, rapidly heating the oxidation furnace to be below the oxidation temperature of the VCSEL, keeping the temperature for 25-35min, and introducing mixed gas of nitrogen and water vapor into the oxidation furnace during heating and keeping the temperature;

s2, heating the oxidation furnace to the temperature required by oxidation at the heating rate of 10-20 ℃/min until the oxidation is finished;

s3, cooling the oxidation furnace to quickly cool the oxidation furnace to 180-220 ℃, and then naturally cooling to room temperature.

4. A method according to claim 3, wherein the method comprises the steps of: the temperature increase rate in step S1 is 20 ℃/min.

5. A method according to claim 3, wherein the method comprises the steps of: the temperature rise temperature in the step S1 is 200-300 ℃.

6. A method according to claim 3, wherein the method comprises the steps of: in the step S1, the flow rate of nitrogen gas and water vapor introduced is 3L/min, and the water vapor is 2L/min.

7. A method for improving the uniformity of an oxide aperture of a VCSEL according to any of claims 3 to 6, wherein: the temperature rise temperature in the step S2 is 300-500 ℃.

8. A method for improving the uniformity of an oxide aperture of a VCSEL according to any of claims 3 to 6, wherein: in the step S3, the temperature in the oxidation furnace is decreased to 180-220 ℃ within 2-3 min.

9. A method according to claim 3, wherein the method comprises the steps of: before step S1, nitrogen gas of 10-20L/min is introduced into the oxidation furnace to clean the inner cavity of the furnace.

Technical Field

The invention relates to the technical field of semiconductors, in particular to a method for improving uniformity of VCSEL (vertical cavity surface emitting laser) oxide aperture.

Background

A Vertical Cavity Surface Emitting Laser (VCSEL) is a semiconductor laser whose laser light is emitted perpendicularly to the top surface. The structure is P-type and N-type Bragg reflectors and a resonant cavity sandwiched between the P-type and N-type Bragg reflectors. Both the P-type and N-type bragg mirrors are composed of multiple layers of epitaxial wafers to achieve 99% reflectivity.

The structure of a VCSEL generally comprises an N limiting layer, a gallium arsenide substrate, a buffer layer, an N-DBR layer, a P-DBR layer and the like from bottom to top; during preparation, the VCSEL is etched to the N-DBR position through an etching technology to expose an oxide layer, then the oxide layer is oxidized through an oxidation process, and an unoxidized circular photoelectric limiting hole (namely an oxidation hole) is left for realizing laser emission; tens of thousands of oxide holes are usually formed on a wafer, and the uniformity of the oxide holes is crucial to the luminescence performance of the laser.

Most of the current oxidation methods are wet oxidation processes, wherein nitrogen passes through a heated bubble bath bottle to carry out oxidation by taking out water vapor. However, the mesa structure etched by the current oxidation process is generally in a circular truncated cone shape, as shown in fig. 1, the mesa channel is circular, although the graph is simple and convenient and is mainly suitable for 6-inch wafers, the graph is not beneficial to the circulation of water vapor and the timely discharge of oxidation products, and the current use results show that the uniformity of the designed oxidation aperture is only about 10%, and the requirement of the industry on the increasing and increasing height cannot be well met.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a method for improving the uniformity of the oxide aperture of a VCSEL, in which the etched mesa structure of the VCSEL is designed to be petal-shaped, so as to increase the channel width and improve the uniformity of the oxide aperture of the VCSEL.

The invention solves the technical problems by the following technical means:

a method for improving the uniformity of the oxidation aperture of a VCSEL (vertical cavity surface emitting laser) is characterized in that a VCSEL etched mesa structure is designed to be a petal type, and the width of a channel is designed to be 10-25 um.

The principle of the scheme is as follows: the channel width of the general design is 1-6um, and the channel width is designed to be 10-25um in the scheme; the increase of the width of the channel is beneficial to the inflow of more water vapor when the oxidation process is carried out, and sufficient water vapor is beneficial to the oxidation; experiments prove that the wider the channel is, the oxidation rate is slightly slowed down, but the oxidation rate required by the scheme can be always ensured to be in a proper interval, and the oxidation rate is slightly slower than the conventional oxidation rate, so that the oxidation rate is adjusted without adjusting the oxidation temperature or the oxidation layer material, the oxidation rate is reduced, the precise control of the oxidation depth is realized by controlling the oxidation time, and the shape of an oxidation hole can be well adjusted.

On the basis of the design of the width of the channel, the scheme also designs the traditional circular Mesa (Mesa structure) channel into a petal type, so that pressure difference is formed in the channel on the edge of a small petal and a wide large channel, when oxidation reaction is carried out, the generated product is favorably diffused and flows out from the small petal channels, the distribution of water vapor is not greatly influenced, and the aim of improving the uniformity of the oxidation aperture is fulfilled.

Further, the VCSEL etched table-board structure is designed to be a six-petal type. The six-petal patterned edges are symmetrically distributed, so that the uniformity of the VCSEL oxidation aperture is improved more easily.

Further, when the VCSEL is oxidized, the method comprises the following steps:

s1, placing the VCSEL into an oxidation furnace, rapidly heating the oxidation furnace to be below the oxidation temperature of the VCSEL, keeping the temperature for 25-35min, and introducing mixed gas of nitrogen and water vapor into the oxidation furnace during heating and keeping the temperature;

s2, heating the oxidation furnace to the temperature required by oxidation at the heating rate of 10-20 ℃/min until the oxidation is finished;

s3, cooling the oxidation furnace to quickly cool the oxidation furnace to 180-220 ℃, and then naturally cooling to room temperature.

In the VCSEL oxidation process, water vapor is not introduced until the temperature reaches the oxidation temperature any more, but is introduced in the heating process, the temperature can be kept constant for a period of time after the temperature is raised, so that the cavity is filled with the water vapor, and then the temperature is rapidly raised to the temperature for final oxidation at the heating rate of 10-20 ℃/min, so that the temperature can be prevented from being raised too slowly, and the rapid heating can avoid the non-uniformity of the oxidation aperture caused by the fact that the oxidation rate is changed all the time. After the oxidation is accomplished, in the cooling process, this scheme no longer adopts natural cooling or slow refrigerated mode, but rapid cooling, and the purpose is the oxidation reaction that reduces the cooling in-process and probably takes place to the influence of oxidation aperture homogeneity.

Further, the temperature increase rate in step S1 is 20 ℃/min. Such a fast temperature rise rate can avoid the non-uniformity of the oxide pore diameter caused by the constant change of the oxidation rate.

Further, the temperature rise temperature in the step S1 is 200-300 ℃. The temperature can lead the oxidation furnace to be filled with water vapor before the oxidation of the VCSEL occurs.

Further, in the step S1, the flow rate of nitrogen gas and water vapor introduced is 3L/min, and the flow rate of water vapor is 2L/min.

Further, the temperature rise temperature in the step S2 is 300-500 ℃. Different oxidation temperatures are required according to the chip requirements, but are basically in the temperature range of 300-.

Further, in the step S3, the temperature in the oxidation furnace is decreased to 180-220 ℃ within a period of 2-3 min. This scheme no longer adopts natural cooling or slow refrigerated mode, but rapid cooling, and the oxidation that probably takes place among the so quick cooling purpose reduces the cooling process to avoid the oxidation reaction that probably takes place to the influence of oxidation aperture homogeneity.

Further, before step S1, nitrogen gas of 10-20L/min is introduced into the oxidation furnace to clean the furnace inner cavity. Therefore, the cleanliness of the oxidation furnace can be ensured.

The invention has the beneficial effects that:

1. the VCSEL etched mesa structure is designed into a petal shape, pressure difference is formed between the channels at the edges of small petals and the wide large channels, and when oxidation reaction is carried out, generated products can diffuse and flow out from the small petal channels, so that the distribution of water vapor is not greatly influenced, and the aim of improving the uniformity of the oxidation aperture is fulfilled.

2. The design of the invention enlarges the width of the channel, the design of the table-board is convenient for the inflow of water vapor and the timely discharge of products during wet oxidation, and the increase of the width of the channel also allows more water vapor to flow in the oxidation process, thus better improving the uniformity of the oxidation aperture.

3. In the oxidation process of the VCSEL, the water vapor is not introduced until the temperature reaches the oxidation temperature, but is introduced in the temperature rising process, the temperature is kept constant for a period of time, the water vapor is filled in the cavity, and then the temperature is quickly raised to the temperature for final oxidation, so that the nonuniform oxidation aperture caused by too slow temperature rise and the constantly changed oxidation rate can be prevented, and the uniformity of the oxidation aperture of the VCSEL is improved.

4. After the VCSEL is oxidized, the temperature is quickly reduced in the temperature reduction process instead of a natural cooling or slow cooling mode, the temperature is reduced within 2-3min, and the influence of oxidation reaction possibly generated in the temperature reduction process on the uniformity of the oxidation aperture can be reduced.

Drawings

FIG. 1 is a schematic diagram of a current prior art VCSEL etched mesa design;

FIG. 2 is a schematic diagram of the mesa structure design for VCSEL etching of the present invention.

Wherein, 1, mesa structure channel.

Detailed Description

The invention will be described in detail below with reference to the accompanying drawings, in which the following examples each use a 6 "wafer:

examples 1,

The method for improving the uniformity of the oxide aperture of the VCSEL comprises the following steps:

s1, introducing nitrogen gas of 10L/min into the oxidation furnace in a standby state to purge the cavity and keep the cleanliness of the cavity;

s2, designing a VCSEL etched mesa structure into a six-petal type as shown in figure 2, and designing the width of a channel to be 10 um;

s3, starting to heat the oxidation furnace to 200 ℃ at a heating rate of 20 ℃/min, keeping the temperature constant for 25min, and introducing water vapor into the furnace when the temperature starts to rise, wherein the water vapor is nitrogen and carries the water vapor to enter the oxidation furnace, the nitrogen is 3L/min, the water vapor is 2L/min, the total flow is 5L/min, and the furnace is filled with a water vapor environment;

s4, rapidly heating to 300 ℃ required by oxidation at a heating rate of 10 ℃/min for oxidation until the oxidation is finished;

and S5, after the oxidation process is finished, rapidly reducing the oxidation temperature to 180 ℃ within 2min by using a method of blowing cold air outside the furnace by using an air blower, and then taking out the wafer when the temperature of the wafer is reduced to room temperature, and measuring the oxidation aperture.

Examples 2,

The method for improving the uniformity of the oxide aperture of the VCSEL comprises the following steps:

s1, introducing 15L/min nitrogen into the oxidation furnace in a standby state to purge the cavity and keep the cleanliness of the cavity;

s2, designing a VCSEL etched mesa structure into a six-petal type as shown in figure 2, and designing the width of a channel to be 17 um;

s3, starting to heat the oxidation furnace to 250 ℃ at a heating rate of 20 ℃/min, keeping the temperature constant for 30min, and introducing water vapor into the furnace when the temperature starts to rise, wherein the water vapor is nitrogen and carries the water vapor to enter the oxidation furnace, the nitrogen is 3L/min, the water vapor is 2L/min, the total flow is 5L/min, and the furnace is filled with a water vapor environment;

s4, rapidly heating to 400 ℃ required by oxidation at a heating rate of 15 ℃/min for oxidation until the oxidation is finished;

and S5, after the oxidation process is finished, rapidly reducing the oxidation temperature to 200 ℃ within 2.5min by using a method of blowing cold air outside the furnace by using an air blower, and then taking out the wafer when the temperature of the wafer is reduced to room temperature, and measuring the oxidation aperture.

Examples 3,

The method for improving the uniformity of the oxide aperture of the VCSEL comprises the following steps:

s1, introducing 20L/min nitrogen into the oxidation furnace in a standby state to purge the cavity and keep the cleanliness of the cavity;

s2, designing a VCSEL etched mesa structure into a six-petal type as shown in figure 2, and designing the width of a channel to be 25 um;

s3, starting to heat the oxidation furnace to 300 ℃ at a heating rate of 20 ℃/min, keeping the temperature constant for 35min, and introducing water vapor into the furnace when the temperature starts to rise, wherein the water vapor is nitrogen and carries the water vapor to enter the oxidation furnace, the nitrogen is 3L/min, the water vapor is 2L/min, the total flow is 5L/min, and the furnace is filled with a water vapor environment;

s4, rapidly heating to the temperature 500 ℃ required by oxidation at the heating rate of 20 ℃/min for oxidation until the oxidation is finished;

and S5, after the oxidation process is finished, rapidly reducing the oxidation temperature to 220 ℃ within 3min by using a method of blowing cold air outside the furnace by using an air blower, and then taking out the wafer when the temperature of the wafer is reduced to room temperature, and measuring the oxidation aperture.

Examples 4,

This embodiment is different from embodiment 2 in that the embodiment still uses a circular mesa structure as shown in fig. 1, and the channel width is 4 um.

Examples 5,

This example is compared with example 2, except that in this example, after the temperature reached the oxidation temperature, water vapor was introduced.

Examples 6,

This example is different from example 2 in that natural cooling is directly adopted after the oxidation is completed, so that the wafer temperature is reduced to room temperature.

The oxidized wafers obtained from the above-mentioned examples 1 to 6 were measured for the pore size and the oxidation rate, and the final results are shown in the following table:

as can be seen from the comparison of the results of the examples 1-3 with the results of the prior oxidation process, the uniformity of the VCSEL oxidation aperture can be obviously improved by adopting the oxidation method of the invention; the oxidation carried out by the method of example 2 has better uniformity of the oxidation aperture and smaller standard deviation; since the oxidation rates at different temperatures will vary, example 3 has the highest temperature and the oxidation rate is the highest.

As can be seen from a comparison of example 2 with examples 4-6, the oxidation rate for each example is essentially consistent, always in the range of 0.6-0.7 um/min.

As can be seen from the comparison of the results of example 2 and example 4, the etched mesa structure of the VCSEL is designed into a six-petal symmetrical petal type, and the channel width is designed to be 10-25um, so that the uniformity of the oxidation aperture of the VCSEL can be obviously improved.

As can be seen from the comparison of the results of example 2 and example 5, the temperature is raised by introducing water vapor, which can improve the uniformity of the oxide aperture of the VCSEL.

As can be seen from the comparison of the results of example 2 and example 6, the VCSEL oxide aperture uniformity can be improved by rapidly cooling to below the oxidation temperature and then naturally cooling.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims. The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.