Plasma photoresist removing method for narrow-band-gap compound semiconductor material

Abstract

The invention provides a plasma photoresist removing method for a narrow-band-gap compound semiconductor material. The method comprises the following steps that a to-be-processed object is subjected to plasma cleaning, radio frequency power is output in a pulse mode, and the average radio frequency power in a pulse period ranges from 20 W to 200 W; wherein the to-be-processed object is made of a narrow-band-gap compound semiconductor material. According to the plasma photoresist removing method, the residual photoresist on the surface of the infrared detector chip can be effectively removed, the surface of the chip cannot be greatly damaged, and the plasma photoresist removing method is of great significance in improving the performance of the infrared detector.

Description

Technical Field

[0001] The invention relates to a plasma degumming method for narrow-bandgap compound semiconductor materials. Background Art

[0002] The degumming process is a very important process in the infrared detector processing process. After the photolithography process, we often need to face the removal of the primer after development or the removal of the denatured photoresist after the dry etching process. Whether the photoresist is removed cleanly and thoroughly in these links and whether there is any damage to the sample will directly affect the subsequent process and the performance of the device.

[0003] For a simple and economical plasma cleaning device, two flat electrodes are usually set in a sealed container to form an electric field, and a vacuum pump is used to achieve a certain vacuum degree. The reaction gas, such as oxygen, undergoes glow discharge under the signal of radio frequency voltage to generate a plasma field. The active groups in the plasma field reach the surface of the chip and react chemically with the photoresist to generate volatiles, thereby achieving the purpose of cleaning. After being accelerated by the electric field of the sheath layer, the cations in the oxygen plasma field bombard the chip surface with an energy of 0 to 20 eV, causing physical bombardment on the chip surface. Since most of the bond energies in the polymer are between 0 and 10 eV, the small-energy cations bombard the sample surface, which can break the original chemical bonds (C=C, C=H, C=O, C=N, Si-Si, Si-O, etc.) on the sample surface, thereby promoting chemical reactions. The large-energy ions cause certain damage to the chip surface, which will seriously affect the performance of the infrared detector.

[0004] Therefore, when using a flat-panel plasma cleaning device to perform a degumming process on infrared detector chips, how to control the energy of ions in the plasma so that the ions can promote the chemical reaction between active groups and residual glue without causing major damage to the chip surface is a problem that needs to be solved urgently. Summary of the invention

[0005] The technical problem solved by the present invention is to overcome the defects in the prior art that the residual glue cannot be effectively removed and the chip is easily damaged during the degumming process of the infrared detector chip, and provide a plasma degumming method for narrow bandgap compound semiconductor materials. The plasma degumming method of the present invention can effectively remove the residual glue on the surface of the infrared detector chip without causing major damage to the chip surface, which is of great significance to improving the performance of the infrared detector.

[0006] The plasma degumming method of the infrared detector of the present invention adopts a radio frequency power supply that can output radio frequency power in a pulsed manner. In this pulse form, the average power required to excite and maintain the plasma is much smaller than the plasma power required for continuous operation, so that the number of ions with excessive energy in the cleaning gas plasma is greatly reduced, so that the ions can promote the chemical reaction between the active groups and the residual glue, which not only meets the need to remove the residual glue on the surface of the detector, but also will not cause major damage to the surface of the chip, which is of great significance to improving the performance of the infrared detector.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] The present invention provides a plasma degumming method for narrow bandgap compound semiconductor materials, which comprises the following steps:

[0009] The object to be processed is subjected to plasma cleaning, and radio frequency power is output in a pulsed manner, with an average radio frequency power of 20W to 200W in one pulse cycle; wherein the material of the object to be processed is a narrow-bandgap compound semiconductor material.

[0010] In the present invention, the waveform of the pulse is preferably a rectangular wave and the low level is zero.

[0011] In the present invention, the narrow bandgap compound semiconductor material generally refers to a material with a bandgap lower than 3 eV.

[0012] In the present invention, the narrow bandgap compound semiconductor material is preferably HgCdTe material, InSb material, InAs / GaSb type II superlattice material or InGaAs material.

[0013] In the present invention, the object to be processed may be an infrared detector chip, preferably a HgCdTe infrared detector chip, an InSb infrared detector chip, an InAs / GaSb type II superlattice infrared detector chip or an InGaAs infrared detector chip.

[0014] In a preferred embodiment, the narrow bandgap compound semiconductor material is a 2-inch epitaxial material, and the structure of the epitaxial material is, from bottom to top, 350 μm thick semi-insulating InP, 1 μm thick n + InP buffer layer, 3μm thick In 0.53 Ga 0.47 As intrinsic absorption layer, 0.5μm thick n - Type InP.

[0015] In the present invention, the duty cycle of the pulse may be 5% to 50%, preferably 30% to 40%, for example 20%. The duty cycle generally refers to the proportion of the power-on time to the total time in a pulse cycle.

[0016] In the present invention, the average radio frequency power=the radio frequency power×the duty cycle of the pulse.

[0017] In the present invention, the average radio frequency power is preferably 10W to 150W, for example 80W.

[0018] In the present invention, the radio frequency power may be 200-400W, preferably 300-400W, for example 400W.

[0019] In the present invention, during the process of outputting radio frequency power in a pulsed manner, the pulse frequency may be 0.1 Hz to 10 kHz, preferably 10 kHz.

[0020] In the present invention, in the process of outputting the radio frequency power in a pulsed manner, the radio frequency frequency is preferably 0.1 MHz to 100 MHz, for example, 13.56 MHz.

[0021] In the present invention, the radio frequency is preferably 1000 to 10000 times, for example 1356 times, the pulse frequency.

[0022] In the present invention, during the plasma cleaning process, the process gas used may be conventional in the art, preferably O2, and more preferably may include one or more of H2, CH4 and NH3.

[0023] In the present invention, the plasma cleaning device may be conventional in the art, preferably a flat-plate plasma cleaning device, such as a plasma enhanced chemical vapor deposition device.

[0024] In the present invention, during the plasma cleaning process, the radio frequency power supply of the cleaning device can be conventional in the art, such as a radio frequency power supply of model mks AX7710MKS-01.

[0025] In the present invention, the gas flow rate of the plasma cleaning is preferably 1000-2000 sccm, for example, 1000 sccm.

[0026] In the present invention, the chamber pressure of the plasma cleaning is preferably 2-5T, for example 2.5T.

[0027] In the present invention, the plasma cleaning time is preferably 2 to 5 minutes, for example 5 minutes.

[0028] In a preferred embodiment, the process parameters of the plasma cleaning are: the RF power is 200-400 W, the pulse frequency is 0.1 Hz-10 kHz, the gas flow rate is 1000-2000 sccm, the chamber pressure is 2-5 T, and the cleaning time is 2-5 minutes.

[0029] In a more preferred embodiment, the process parameters of the plasma cleaning are: the RF power is 400 W, the average RF power is 80 W, the pulse frequency is 10 kHz, the gas flow rate is 1000 sccm, the chamber pressure is 2.5 T, and the cleaning time is 5 minutes.

[0030] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0031] The reagents and raw materials used in the present invention are commercially available.

[0032] The positive and progressive effects of the present invention are:

[0033] The plasma degumming method of the present invention can effectively remove the residual glue on the surface of the detector chip without causing serious damage to the chip surface, which is of great significance for improving the performance of the infrared detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of outputting radio frequency power in a pulsed manner according to the present invention.

[0035] Figure 2 The IV curves of the photosensitive chips prepared by using the wafers of the infrared detectors after plasma cleaning in Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0036] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0037] The information of the equipment used in the following examples and comparative examples is shown in Table 1:

[0038] Table 1

[0039]

[0040] The wafer of the infrared detector to be processed in the following embodiments and comparative examples is a 2-inch epitaxial material, and the material structure is 350 μm thick semi-insulating InP, 1 μm thick n + InP buffer layer, 3μm thick In 0.53 Ga 0.47 As intrinsic absorption layer, 0.5μm thick n - Type InP.

[0041] Preparation process of the infrared detector wafer to be processed:

[0042] 230nm Si3N4 diffusion mask is plated on the whole wafer → diffusion hole is exposed by photolithography → Si3N4 film at the diffusion hole is etched away → photoresist is removed by acetone and alcohol → Zn is diffused to prepare pn junction → Si3N4 film at n groove is exposed by photolithography for the second time → Si3N4 film is etched by SF6 and Ar + Etch the InP cap layer, corrode the InGaAs layer with tartaric acid → remove the photoresist with acetone and alcohol → perform the third photolithography to expose the Si3N4 diffusion mask → etch the exposed Si3N4 diffusion mask → remove the photoresist with acetone and alcohol to obtain the wafer of the infrared detector to be processed.

[0043] Example 1

[0044] Plasma enhanced chemical vapor deposition equipment was used, the RF power source was 13.56MHz mks AX7710MKS-01, and oxygen was used as the process gas. The process parameters during plasma cleaning were: RF power 400W, gas flow rate 1000sccm, and pressure 2.5T.

[0045] Preset the output mode of the power supply, such as Figure 1 As shown, the pulse signal is divided into two parts, high level and low level, in one cycle. The high level is "on", the RF power is output, the duration is t1, the low level is "off", the duration is t2, and the time average power is P 平均 =P RF ×t1 / (t1+t2), the RF power corresponding to the low level is 0.

[0046] The pulse frequency is set to 10kHz (i.e., the pulse period is 0.0001s), the duty cycle t1 / (t1+t2) is set to 20% (i.e., t1=0.00002s, t2=0.00008s), and the RF power P RF The power of the plasma field is 400W and the RF frequency is 13.56MHz, so the time average power of the plasma field is 80W. When the oxygen flow rate is 1000sccm, the chamber pressure remains stable when it reaches 2.5T. Turn on the RF power supply, the process gas is normally ignited when the pulse signal is "on", and the plasma field remains stable under the capacitive effect when the pulse signal is "off". After 5 minutes of cleaning, the RF power is turned off to complete the cleaning process. After the cleaning is completed, the residual glue has been cleaned.

[0047] Comparative Example 1

[0048] The difference compared with Example 1 is that a continuous radio frequency signal is used to clean the wafer of the infrared detector to be processed at 13.56 MHz and a radio frequency power of 400 W.

[0049] Effect Example

[0050] 1. Residual glue removal

[0051] Through observation under an electron microscope, it can be seen that the residual glue on the InP surface of the wafer of the infrared detector to be processed in Example 1 and Comparative Example 1 is cleaned completely.

[0052] 2. IV test

[0053] The wafers of the infrared detector prepared in Example 1 and Comparative Example 1, which had been cleaned with plasma to remove residual adhesive, were respectively made into photosensitive chips with a diameter of 1 mm, and the preparation was repeated 3 times for each, and IV test was performed. The specific preparation process is as follows: 230nm Si3N4 film is plated on the surface of the whole wafer → p-electrode alloy hole is exposed by photolithography → Au film is sputtered → Au film is peeled off by acetone and alcohol → p-electrode alloying → Si3N4 film at n-groove is exposed by photolithography → acetone and alcohol are used to remove photoresist → extended electrode / thickened electrode area is exposed by photolithography → preparation of photosensitive chip is completed.

[0054] The two groups of photosensitive chips prepared above were subjected to IV test. The test results are as follows: Figure 2 As shown. Figure 2 It can be seen that the photosensitive chip made of the infrared detector wafer cleaned by the pulsed radio frequency signal with a duty cycle of 20% in Example 1 has a dark current that is significantly smaller than that of the comparative example 1 (continuous radio frequency signal cleaning) under the same reverse bias voltage, which means that the use of a pulsed radio frequency signal with a duty cycle of 20% for cleaning residual glue causes less damage to the device surface.

[0055] Through the above analysis, it can be known that the process of cleaning residual glue using pulsed radio frequency signals of the present invention can achieve the effect of removing residual glue on the surface of the detector without causing major damage to the surface of the chip.

Claims

1. A plasma stripping method for narrow bandgap compound semiconductor materials, characterized in that: It includes the following steps: The object to be processed is subjected to plasma cleaning, and radio frequency power is output in a pulsed manner, with an average radio frequency power of 20W to 200W in one pulse cycle; wherein the material of the object to be processed is a narrow-bandgap compound semiconductor material.

2. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1, characterized in that: The narrow bandgap compound semiconductor material is HgCdTe material, InSb material, InAs / GaSb type II superlattice material or InGaAs material.

3. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1 or 2, characterized in that: The duty cycle of the pulse is 5% to 50%, preferably 30% to 40%, for example 20%.

4. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1 or 2, characterized in that: The average radio frequency power is 10W to 150W, for example 80W; And / or, the radio frequency power is 200-400W, preferably 300-400W, for example 400W.

5. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1 or 2, characterized in that: In the process of outputting the radio frequency power in a pulsed manner, the pulse frequency is 0.1 Hz to 10 kHz, preferably 10 kHz; And / or, during the process of outputting the radio frequency power in a pulsed manner, the radio frequency frequency is 0.1 MHz to 100 MHz, for example, 13.56 MHz.

6. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1 or 2, characterized in that: During the plasma cleaning process, the process gas used is O2, and preferably may also include one or more of H2, CH4 and NH3; And / or, the plasma cleaning device is a flat-plate plasma cleaning device, such as a plasma enhanced chemical vapor deposition device.

7. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1 or 2, characterized in that: During the plasma cleaning process, the model of the radio frequency power supply of the cleaning device is mks AX7710MKS-01.

8. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 1 or 2, characterized in that: The gas flow rate of the plasma cleaning is 1000-2000 sccm, for example 1000 sccm; And / or, the chamber pressure of the plasma cleaning is 2-5T, for example 2.5T; And / or, the plasma cleaning time is 2 to 5 minutes, for example 5 minutes.

9. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 8, characterized in that: The process parameters of the plasma cleaning are: the radio frequency power is 200-400W, the pulse frequency is 0.1Hz-10kHz, the gas flow rate is 1000-2000sccm, the chamber pressure is 2-5T, and the cleaning time is 2-5 minutes.

10. The plasma stripping method for narrow bandgap compound semiconductor materials according to claim 9, characterized in that: The process parameters of the plasma cleaning are: the RF power is 400 W, the average RF power is 80 W, the pulse frequency is 10 kHz, the gas flow rate is 1000 sccm, the chamber pressure is 2.5 T, and the cleaning time is 5 minutes.

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