A method for removing photoresist

Abstract

The application discloses a method for removing photoresist, which is formed in the process of manufacturing a shielding structure tip array field emission electron source, and the shielding structure of the shielding structure tip array field emission electron source is a multi-insulation layer sandwich structure of SiO2 / Si3N4 / SiO2. The method mainly comprises the following steps: step one, soaking the substrate with photoresist in a photoresist removing solution; step two, megasonic cleaning; and step three, oxygen plasma etching treatment. Based on the unique insulation layer structure of the shielding structure tip array field emission electron source, the cavity must be manufactured by relying on long-time dry etching, which not only causes carbonization of the photoresist, but also increases the adhesion and hardness of the photoresist on the edge of the gate hole. The traditional photoresist removing process cannot successfully remove the firm and carbonized photoresist. The application adopts different photoresist removing methods for different regions of the photoresist, effectively solves the problem, and also ensures the completeness and integrity of the lower layer material of the photoresist.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of vacuum electron technology. More particularly, it relates to a method for removing photoresist. BACKGROUND

[0002] Compared with the mature application of hot cathode in vacuum devices, field emission cold cathode electron source has the advantages of instant start, room temperature operation, large current density, easy miniaturization, etc., and has good application prospect in the field of vacuum devices, especially in the development of future terahertz vacuum devices. The tip array type field emission electron source is the earliest developed and the most mature developed and applied field emission electron source. For example, the Spindt cathode electron source manufactured by bidirectional deposition process. The basic structure of this field emission electron source is substrate / emission tip / insulating layer / gate. However, this structure cannot withstand high voltage and large current in testing. The reason is that the undesired electron emission follows the along-thread discharge along the insulating layer, and the destructive arc formed thereby causes the device to suddenly fail. The prior art believes that adding a shielding structure will help to block the along-thread discharge.

[0003] The shielding structure of multiple insulating layers usually adds a Si3N4 insulating layer in the traditional single SiO2 insulating layer to block the along-thread discharge. However, the SiO2 insulating layer and the Si3N4 insulating layer have different etching selectivity ratios for etching liquid. The wet etching liquid commonly used in experiments is a BOE buffer solution. The etching rate of Si3N4 in this solution is very slow, so the shielding structure of the insulating layer containing Si3N4 cannot rely on wet etching to make a cavity structure, and must rely on dry etching. Dry etching is generally fluorine-based gas, which reacts with the etched sample by generating fluorine radicals. Compared with the SiO2 insulating layer, the dry etching process of Si3N4 is also very slow. Therefore, in order to completely etch off the Si3N4 insulating layer, the etching time will be significantly increased, which leads to the carbonization of photoresist and the enhancement of the adhesion of photoresist to the substrate surface, especially in the array area. The existing method is difficult to remove the carbonized or firmly adhered photoresist, and the residual photoresist will directly affect the subsequent tip deposition process, resulting in the failure of the tip array field emission electron source.

[0004] At present, there are two methods for removing photoresist in the field of microfabrication of vacuum electron devices. The first method is wet photoresist removal, and the commonly used photoresist remover is N-methyl pyrrolidone (NMP) solution. In the traditional short etching process, the photoresist can be completely dissolved by treating with the solution for 20 minutes. The second method is dry etching, and the commonly used method is to bombard the substrate with oxygen plasma and react with the photoresist, thereby removing the photoresist. However, for the shield structure tip array field emission electron source, the photoresist cannot be removed simply by using NMP solution, and the result does not change with the extension of time. Secondly, due to the unique characteristics of the shielding structure, there will be a part of the suspended gate above the cavity. The specific heat at this position is small. When using dry plasma to remove the photoresist, small power cannot remove the photoresist in a large area, and large power will directly damage the gate under the photoresist, that is, dry photoresist removal is also not suitable for removing the photoresist formed in the process of preparing the shield structure tip array field emission electron source. At the same time, due to the unique structure and material characteristics of the electron source, H2SO4 and H2O2 solutions commonly used in semiconductor processes cannot be used to remove the photoresist, and HF solution cannot be used for cleaning.

[0005] Therefore, there is an urgent need to provide a method for removing photoresist based on a shield structure tip array field emission electron source. SUMMARY

[0006] The purpose of the present application is to provide a method for removing photoresist. This method can completely remove the firm and carbonized photoresist, and at the same time ensure the integrity and completeness of the material under the photoresist.

[0007] To achieve the above purpose, the present application provides a method for removing photoresist, which is formed in the process of preparing a shield structure tip array field emission electron source. The shielding structure of the shield structure tip array field emission electron source is a multi-insulating layer sandwich structure of SiO2 / Si3N4 / SiO2. The method comprises the following steps:

[0008] Step one: immerse the substrate with photoresist in a photoresist removal solution for soaking;

[0009] Step two: megasonic cleaning;

[0010] Step three: oxygen plasma etching treatment.

[0011] Further, in the above method, the total thickness of the multi-insulating layer sandwich structure of SiO2 / Si3N4 / SiO2 is 1 μm, wherein the thickness of the Si3N4 insulating layer is 180 nm-220 nm.

[0012] The thickness of the photoresist is 0.8 μm-1.2 μm.

[0013] The main component of the photoresist removal solution is N-methyl pyrrolidone (NMP).

[0014] The soaking time of the wafer with photoresist in the stripping solution is 8-12 hours.

[0015] The megasonic cleaning condition is that the frequency of megasonic is 1MHz, the power of megasonic is 400-500W, and the time of megasonic cleaning is 15-25 minutes.

[0016] The cleaning solution used in the megasonic cleaning is deionized water, and the resistivity of the deionized water is 18MΩ·cm.

[0017] The equipment used in the oxygen plasma etching treatment is an inductively coupled reactive ion etching machine, the inductive coupling system and the etching radio frequency system of the inductively coupled reactive ion etching machine are started at the same time, the radio frequency power of the inductive coupling system is 290-310W, and the radio frequency power of the etching radio frequency system is 190-210W.

[0018] The oxygen plasma etching treatment is carried out at a working pressure of 8-10Pa for 40-60s.

[0019] The step one or step three further comprises observing the state of the wafer under a scanning electron microscope.

[0020] The beneficial effects of the present application are as follows:

[0021] 1. Based on the insulating layer structure of the shielding structure tip array field emission electron source, the cavity must be made by relying on long time dry etching, which not only causes carbonization of the photoresist, but also causes the increase of the adhesion and hardness of the photoresist on the edge of the gate hole, and the traditional stripping process cannot remove the firm and carbonized photoresist. The photoresist removal method provided by the present application adopts different stripping processes for different areas of the photoresist, effectively solving the problem and ensuring the smooth progress of the processing technology.

[0022] 2. The photoresist removal method provided by the present application not only can completely remove the firm and carbonized photoresist, but also can ensure the integrity and perfection of the lower layer material of the photoresist. BRIEF DESCRIPTION OF DRAWINGS

[0023] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0024] Figure 1 The flow chart of the photoresist removal method of the present application is shown;

[0025] Figure 2 The macroscopic structure of the shielding structure tip array field emission electron source is shown,

[0026] Among them, the reference signs are:

[0027] A - Array gate hole region; F - Non-array metal thin film region;

[0028] Figure 3 The scanning electron microscope picture of the substrate after soaking in the stripping solution in step 1) of Example 1 is shown.

[0029] Figure 4 The scanning electron microscope picture of the substrate after the photoresist is completely removed in Example 1 is shown.

[0030] Figures 5a-5i A processing flow chart of a shielded sharp cone array field emission electron source is shown,

[0031] In the drawings, reference numerals:

[0032] 01 - Silicon substrate; 02 - SiO2 insulating layer; 03 - Si3N4 insulating layer; 04 - Mo metal layer; 05 - photoresist layer; 06 - Al2O3 sacrificial layer;

[0033] Figure 6 The scanning electron microscope picture of the damaged area of the gate in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with preferred embodiments and the accompanying drawings. Like components are denoted by the same reference numerals in the drawings. Those skilled in the art should understand that the specific descriptions below are illustrative rather than limiting, and should not limit the scope of protection of the present application.

[0035] The purity of all raw materials of the present application is not particularly limited, and the present application preferably uses analytical pure.

[0036] The source and abbreviation of all raw materials of the present application belong to the conventional source and abbreviation in the art, and are clear and explicit in the field of their relevant uses. Those skilled in the art can purchase or prepare by conventional methods according to the abbreviation and the corresponding use.

[0037] In order to illustrate the structure of the shielded sharp cone array field emission electron source and the particularity of the photoresist thereof, the present application exemplarily provides a preparation method of a shielded sharp cone array field emission electron source, which comprises the following steps:

[0038] 1) providing a layer structure substrate (such as Figure 5aThe substrate is sequentially from bottom to top: Si substrate 01, SiO2insulating layer 02 (400 nm), Si3N4insulating layer 03 (200 nm), SiO2insulating layer 02 (400 nm), Mo metal layer 04 (200 nm), photoresist layer 05, photoresist selected from S1800 series, spin coating thickness 0.8-1.2 μm (wherein, from bottom to top, SiO2insulating layer 02, Si3N4insulating layer 03 and SiO2insulating layer 02 together form a multi-insulating layer sandwich structure of SiO2 / Si3N4 / SiO2) ;

[0039] 2) After two times of photoetching, a square grid metal Mo layer with a side length of 2 mm is formed and a circular hole with an aperture of 1-1.2 μm is distributed in a region with a diameter of 0.6 mm in the center, with a spacing of 5 μm. After development, the photoresist is removed from above the circular hole, and the remaining area is covered with photoresist (as shown in Figure 5b ) ;

[0040] 3) SF6gas is selected to etch the Mo metal layer 04 to form a grid hole (as shown in Figure 5c ) ;

[0041] 4) The SiO2insulating layer 02 below the grid hole is etched away by using a BOE buffer solution (as shown in Figure 5d ) ;

[0042] 5) Due to the selective etching of Si3N4, the BOE buffer solution etches it extremely slowly, and must rely on fluorine-based gas for dry etching. CHF3is used to etch away the Si3N4insulating layer and most of the SiO2insulating layer 02 in the bottom layer (as shown in Figure 5e ) ;

[0043] 6) The SiO2insulating layer 02 in the bottom layer is continuously etched by using a BOE buffer solution to complete the rugged three-dimensional cavity structure (as shown in Figure 5f ) ;

[0044] 7) The photoresist is removed (as shown in Figure 5g ) ;

[0045] 8) The smooth grid hole surface after the photoresist is removed is used to stack the Al2O3sacrificial layer 06 and the sharp cone array by using a two-phase deposition process (as shown in Figure 5h ) ;

[0046] 9) After the Al2O3sacrificial layer 06 is peeled off, a shielded structure sharp cone array field emission electron source is obtained (as shown in Figure 5i ).

[0047] Among them, the array grid hole area (A) of the shielded structure sharp cone array field emission electron source prepared by the above method is located in the center of the 2x2 mm area, with a diameter of 0.6 mm, and the rest is a non-array metal film area (F) (as shown in Figure 2The array gate hole region (A) is distributed with gate hole array with aperture 1-1.2 μm, interval 5 μm, and each gate hole contains an insulating cavity with rugged side wall (as shown in Figure 5f The region is graphically dense, and the photoresist adhesion increases significantly and is partially carbonized (i.e. denatured photoresist) during the process of graphically etching, and it is difficult to remove the photoresist. In addition, the gate itself is suspended and fragile, and cannot rely on traditional high-power plasma to remove the photoresist. Moreover, the smooth and intact gate hole after removing the photoresist is a necessary condition for forming the array of sharp cones, and therefore, the smooth removal of the photoresist is extremely important.

[0048] The present application provides a method for removing photoresist, which is formed in the process of manufacturing the array of sharp cones of the field emission electron source with shielding structure, and the method comprises the following steps:

[0049] Step one: immerse the substrate with photoresist in the photoresist removing solution for soaking;

[0050] Step two: megasonic cleaning;

[0051] Step three: oxygen plasma etching treatment.

[0052] It should be noted that the present application adopts different methods for removing photoresist in different regions of the array of sharp cones of the field emission electron source with shielding structure, and the method mainly comprises three steps. Step one: immerse the substrate with denatured photoresist in the photoresist removing solution to remove the photoresist in the whole non-array metal film region (F) and part of the array gate hole region (A); Step two: use deionized water megasonic cleaning to remove the photoresist again and clean the insulating cavity; Step three: use low-power oxygen plasma for short time treatment to remove the remaining photoresist in the array gate hole region (A) (the photoresist removing process is shown in Figure 1

[0053] Specifically, in step one, the substrate is inverted in the photoresist removing solution for initial dissolution to prevent impurities from falling into the cavity. Since the photoresist is partially denatured, the dissolution time is longer than that of the traditional structure. The dissolution time of the present application is preferably 8-12 h. If the time is too short, the photoresist with dissolution ability cannot be fully dissolved, and if the time is too long, the photoresist that can be dissolved by the photoresist removing solution cannot be dissolved, and the subsequent process cannot be carried out. Therefore, the soaking time should not be too long. After the treatment of the photoresist removing solution, the photoresist in the non-array metal film region (F) can be removed well, and the photoresist in the array gate hole region (A) cannot be completely removed due to strong adhesion, but the adhesion is reduced after the soaking of the photoresist removing solution, and a small part of the photoresist in the edge region can also be dissolved.

[0054] ​Preferably, the main component of the stripping solution is N-methyl pyrrolidone; it can also be understood that the main active component of the stripping solution is N-methyl pyrrolidone; for example, analytical pure N-methyl pyrrolidone liquid.

[0055] In step two, megasonic cleaning is used to clean the substrate, and in order to prevent impurities from falling into the cavity, the substrate also needs to be inverted in the cleaning solution. In this step, a high frequency of 1MHz can form high-speed micro-jets to further remove the remaining photoresist on the substrate after soaking in the stripping solution. Although the photoresist cannot be dissolved in the stripping solution in the first step, its adhesion has been significantly reduced, so it can be removed by high-speed micro-jets. Megasonic cleaning can also clean the cavity. The preferred megasonic power is 400W-500W, and the megasonic cleaning time is 15min-25min.

[0056] Preferably, the cleaning solution used for megasonic cleaning is deionized water; the deionized water has a resistivity of 18MΩ·cm. The deionized water has less impurities and no corrosiveness, which can ensure the integrity and perfection of the gate hole structure.

[0057] In step three, a low-power oxygen plasma is selected to bombard the substrate for a very short time to completely remove the remaining photoresist. The main purpose of this step is to remove the stubborn photoresist remaining in the array gate hole area (A) that was not removed in the second step.

[0058] Preferably, the equipment used for oxygen plasma etching treatment is an inductively coupled reactive ion etching machine; the inductively coupled system and the etching radio frequency system of the inductively coupled reactive ion etching machine are turned on at the same time, the radio frequency power of the inductively coupled system is 290W-310W; the radio frequency power of the etching radio frequency system is 190W-210W. The inductively coupled system and the etching radio frequency system are turned on at the same time to quickly remove stubborn photoresist. If either system cannot remove stubborn photoresist in a short time, and the power of the above two systems is too low to remove the photoresist, or too high to damage the gate hole.

[0059] Preferably, the oxygen plasma etching treatment is carried out at a working pressure of 8Pa-10Pa for 40s-60s. Under this condition, the oxygen plasma can make the photoresist react to generate carbon monoxide and carbon dioxide, which are removed from the chamber, and at the same time, it will not cause strong bombardment to the gate and damage the gate.

[0060] Preferably, after step one and step three, the substrate state is observed under a scanning electron microscope to check the stripping condition.

[0061] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention and not for limiting the claims of the present invention.

[0062] The adhesive remover used in the following examples is an NMP solution, purchased from Jingxie High-Tech Electronic Materials Co., Ltd.

[0063] Example 1

[0064] A method for removing photoresist (1 μm) is provided, wherein the photoresist is formed during the fabrication of a shielded cone array field emission electron source, and the shielding structure is a multi-insulating layer sandwich structure of SiO2 / Si3N4 / SiO2. The thickness of the Si3N4 insulating layer is 200 nm. The method includes the following steps:

[0065] 1) The substrate with photoresist was inverted and immersed in an NMP solution for initial dissolution, which took 8 hours (resin removal results are shown below). Figure 3 (as shown);

[0066] 2) Clean the substrate with deionized water (resistivity 18 MΩ·cm) using megohmmic cleaning for 20 minutes (megohmmic frequency 1 MHz, power 400 W). To prevent impurities from falling into the cavity, the substrate also needs to be inverted in the deionized water, and then the substrate is dried by nitrogen purging.

[0067] 3) The substrate is processed using an inductively coupled reactive ion etching machine; wherein, the inductive coupling system of the inductively coupled oxygen plasma and the etching radio frequency system are turned on simultaneously, with their powers set to 300W and 200W respectively, the pressure controlled at 9Pa, and the time controlled at 50s.

[0068] Result: The photoresist was completely removed, and the gate aperture was clean and intact after photoresist removal (e.g., Figure 4 (As shown).

[0069] Depend on Figure 3 It can be seen that the photoresist in the array gate hole area cannot be completely removed after soaking in the resist remover solution due to its strong adhesion.

[0070] Comparative Example 1

[0071] A method for removing photoresist is provided, which is the same as in Example 1, except that in step 3), the power of the inductive coupling system and the etching radio frequency system of the inductively coupled reactive ion etching machine is set to 400W and 300W respectively, the pressure is controlled at 9Pa, and the time is controlled at 50s.

[0072] Results: The photoresist was completely removed, but the gate via was damaged after the photoresist was removed (SEM image of the damaged area of ​​the gate is shown below). Figure 6 (As shown).

[0073] Comparative Example 2

[0074] A photoresist removal method was provided, which was the same as Example 1, except that in step 3), the power of the inductance coupling system and the etching radio frequency system of the inductance coupling reaction ion etching machine were set to 300 W and 200 W, respectively, the pressure was controlled to 9 Pa, and the time was 100 s.

[0075] Result: The photoresist was completely removed, but the gate hole was partially damaged after the photoresist was removed.

[0076] Comparative Example 3

[0077] A photoresist removal method was provided, which was the same as Example 1, except that in step 3), the power of the inductance coupling system and the etching radio frequency system of the inductance coupling reaction ion etching machine were set to 300 W and 200 W, respectively, the pressure was controlled to 9 Pa, and the time was 30 s.

[0078] Result: The photoresist was not completely removed.

[0079] Comparative Example 4

[0080] A photoresist removal method was provided, which was the same as Example 1, except that step 2) was not performed.

[0081] Result: The photoresist was not completely removed.

[0082] Comparative Example 5

[0083] A photoresist removal method was provided, which was the same as Example 1, except that step 1) was not performed.

[0084] Result: The photoresist was not completely removed.

[0085] Comparative Example 6

[0086] A photoresist removal method was provided, which was the same as Example 1, except that step 3) was not performed.

[0087] Result: The photoresist was not completely removed.

[0088] Comparative Example 7

[0089] A photoresist removal method was provided, which was the same as Example 1, except that the thickness of the Si3N4 insulating layer was 250 nm.

[0090] Result: The photoresist was not completely removed.

[0091] Obviously, the above embodiments of the present application are merely exemplary for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and here, all the implementation modes cannot be exhausted, and any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A method for removing photoresist formed in the process of making a shield structure tip array field emission electron source, the shield structure of the shield structure tip array field emission electron source being a multi-insulating layer sandwich structure of SiO2 / Si3N4 / SiO2, the array gate hole area of the shield structure tip array field emission electron source being located in the center of a 2x2 mm area with a diameter of 0.6 mm, the rest being a non-array metal film area, the array gate hole area being distributed with an array of gate holes with an aperture of 1-1.2 μm, a spacing of 5 μm, each gate hole containing an insulating cavity with rugged sidewalls below, a portion of the array gate being suspended above the insulating cavity, the thickness of the array gate being 200 nm, characterized in that, The method comprises the following steps: Step one: immerse the substrate with photoresist in a stripping solution for soaking, wherein the substrate is inverted in the stripping solution, and the soaking time is 8-12 hours; Step two: megasonic cleaning, wherein the megasonic cleaning is performed under the following conditions: the frequency of the megasonic is 1 MHz, the power of the megasonic is 400 W-500 W, and the megasonic cleaning time is 15 min-25 min; Step three: oxygen plasma etching treatment, wherein the oxygen plasma etching treatment is performed by using an inductively coupled reactive ion etching machine, the inductively coupled system and the etching radio frequency system of the inductively coupled reactive ion etching machine are simultaneously started, the radio frequency power of the inductively coupled system is 290 W-310 W, the radio frequency power of the etching radio frequency system is 190 W-210 W, and the oxygen plasma etching treatment is performed under a working pressure of 8 Pa-10 Pa for 40 s-60 s.

2. The method of claim 1, wherein, The total thickness of the SiO2 / Si3N4 / SiO2 multi-insulation layer sandwich structure is 1 μm, and the thickness of the Si3N4 insulation layer is 180 nm-220 nm.

3. The method of claim 1, wherein, The thickness of the photoresist is 0.8 μm-1.2 μm.

4. The method of claim 1, wherein, The main component of the stripping solution is N-methyl pyrrolidone.

5. The method of claim 1, wherein, The cleaning solution used in the megasonic cleaning is deionized water, and the resistivity of the deionized water is 18 MΩ·cm.

6. The method of claim 1, wherein, After step one and step three, the substrate state is observed by using a scanning electron microscope.

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