CN117348345A - Gluing method for optimizing thickness of photoresist in center of wafer - Google Patents

Abstract

The invention discloses a photoresist coating method for optimizing the thickness of photoresist in the center of a wafer. According to the invention, an air injection step is added in the gluing process, so that the wafer center thickness is optimized, the photoresist thickness uniformity is controlled, and the probability of stacking photoresist in the middle of the wafer is reduced. The distance between the gas nozzle and the wafer surface and the gas pressure of the gas ejected from the gas nozzle determine the thickness variation of the wafer middle area in the gas ejection step. Reasonable air injection speed and air pressure, preventing the formation of a glue ripple effect and preventing the loss of the attached photoresist. The invention provides two photoresist homogenizing steps, which obviously improves the thickness uniformity of photoresist in the middle area and the peripheral area of the wafer and improves the reliability of subsequent photoetching and etching.

Description

Gluing method for optimizing thickness of photoresist in center of wafer

Technical Field

The invention belongs to the technical field of semiconductor manufacturing, and relates to a gluing method for optimizing the thickness of photoresist in the center of a wafer.

Background

In the photolithography process, spin coating is one of the important steps before exposure, and the process can be simplified into three stages:

1) And (3) glue dripping: when the wafer is stationary or rotating very slowly, the photoresist is dropped onto the center of the wafer surface. 2) High-speed rotation: the wafer is rotated rapidly to a higher speed and the photoresist is stretched across the wafer surface.

3) And (5) throwing off redundant glue: and (5) removing the redundant photoresist, and obtaining a more uniform photoresist covering layer on the wafer.

The center thickness of the photoresist is easily larger than the thickness of the outer ring because the center line speed is slower than the outer ring when the wafer rotates, and the photoresist is accumulated on the edge due to the surface tension of the wafer edge. When the photoresist viscosity is high, the film thickness may eventually show an uneven appearance, i.e. the center area is thick, and gradually becomes thinner outwards, and the edge is also thick, as shown in fig. 2.

Because the wafer edge processing steps follow in the process, a greater glue thickness at the edge can be effectively processed. However, as the viscosity of the photoresist increases, the photoresist in the middle of the wafer is slightly thicker than the periphery, which causes conditions such as uneven thickness of the whole photoresist, mismatching with the target film thickness, and the like, resulting in deviation from ideal conditions during subsequent exposure, and poor CD (critical dimension), LWR (line width roughness) and other appearances of the photoresist after photoetching, which affect the quality of photoetching.

In order to solve the above problems, the conventional method for adjusting the thickness and the form of the photoresist mainly comprises: the spray nozzle drop dosage, the switching frequency, the wafer rotation speed and the acceleration are controlled when the glue is coated, the baking temperature and time are controlled after the glue is coated, the cavity humidity is controlled, and the like. However, these methods can only solve the overall thickness of the photoresist, and cannot effectively solve the phenomenon of middle partial thickness caused by the increase of the viscosity of the photoresist.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a photoresist coating method for optimizing the thickness of photoresist at the center of a wafer, which optimizes the phenomena of photoresist accumulation and thick film thickness in the middle area of the wafer along with the increase of the viscosity of the photoresist by adding a step of central air pressure Jian Bao in the photoresist coating process, so that the photoresist covered on the surface of the wafer is more uniform. The gluing method can be used for improving the reliability of subsequent photoetching and etching under the condition that the viscosity of an advanced-size key layer or photoresist is high.

A glue coating method for optimizing photoresist thickness in a wafer center, comprising:

step S1: wafer pretreatment:

placing a wafer needing to be subjected to a gluing process on a rotary table, and pre-rotating by adopting any rotating speed; then cleaning the surface of the wafer;

step S2: dropwise adding photoresist;

according to the invention, after photoresist is dripped, the rotating speed is determined according to the photoresist adhesiveness, so that the photoresist can be rapidly unfolded; and (3) the photoresist is rapidly unfolded and then is decelerated, so that the photoresist in the central area tends to be flat.

Step S3: spin coating:

3-1 first time spin coating:

the wafer after the photoresist is dripped in the step S2 is increased in rotating speed to n1, and uniform photoresist is rotated at a constant speed, so that the thickness of the photoresist attached to the current wafer reaches T+delta; wherein T represents the target thickness of the photoresist, and delta represents the redundant thickness;

3-2 air pressure thinning:

moving a gas nozzle to the center above the wafer, wherein the distance d between the vertical position of the nozzle and the surface of the wafer is d, d is more than 0, and spraying gas which does not react with photoresist on the surface of the photoresist at the center of the wafer by using the gas nozzle;

according to the invention, the jet operation is adopted, based on the mechanical action of air pressure on the surface of the liquid film, the thickness of photoresist on the surface of the wafer (especially the thickness of the central area) is reduced by the air pressure, and the rotating speed of the wafer is reduced during jet, so that the film thickness change of the pressing area is relatively uniform, the formed depressions are diffused to the periphery, and the overall film thickness is uniform.

3-3 times spin coating:

restoring the rotation speed of the wafer to a target rotation speed n2 of the target photoresist thickness, and carrying out secondary photoresist homogenizing, wherein n2 is more than n1 and more than 1000rpm, so that the thickness of the photoresist attached on the current wafer is thinned to T; the secondary spin time is less than the spin time for the first time;

step S4: rinsing the edge and the back of the wafer;

step S5: and (5) post-treatment.

Preferably, the wafer surface is an advanced-sized AA layer or POLY layer.

Preferably, the pre-rotation duration in step S1 is 1S or less.

Preferably, the surface cleaning in the step S1 adopts a rotating speed of less than 50rpm, and the cleaning solvent is dripped for 2S-3S; and after the flushing is finished, the rotating speed is at least increased to 1000rpm and the cleaning solution is rotated for a duration of less than or equal to 0.5s, and the superfluous cleaning solvent is thrown away.

Preferably, the step S2 specifically includes: dropwise adding photoresist in the center of the upper surface of the wafer pretreated in the step S1, wherein the rotating speed of the photoresist adding process is kept at 1000rpm-2000rpm, and the dropwise adding time is controlled within 2S-3S; then, the rotation speed is reduced to 200rpm or less and kept to be 1s or less.

Preferably, the spin time for the first time in step S3 is 10S-20S, the secondary spin time is 5S-10S.

Preferably, the vertical position of the nozzle in step S3-2 is spaced from the wafer surface by a distance d of 0 < d.ltoreq.50 mm.

Preferably, in the step S3-2, the flow rate of the nozzle gas is controlled to be less than or equal to 500ml/S, the rotating speed of the air injection process is reduced to at least 500rpm, and the air injection time is controlled to be less than or equal to 1S.

Preferably, in step 3-1

Preferably, the gas that does not react with the photoresist in step 3-2 is nitrogen.

Preferably, the step S4 specifically includes: and (3) flushing the edge and the lower surface of the wafer after the photoresist is uniformly coated in the step (S3) by using ultra-pure water, treating photoresist accumulation at the edge, and keeping the rotation speed of 800rpm-1200rpm in the flushing process, wherein the wafer rotation flushing time is controlled to be 5S-10S.

Preferably, in step 3-2, the film thickness h of the air pressure reduction satisfies the following relationship:

wherein p is the pressure difference between the gas sprayed out and the outside, ρ is the photoresist density, v is the photoresist viscosity, and d is the distance from the nozzle to the photoresist surface.

Preferably, the step S5 specifically includes:

and the rotating table is at least increased to 2000rpm, and is kept to rotate at a constant speed for 5s-10s, so that superfluous ultra-pure water is thrown away, and the wafer is dried.

The beneficial effects of the invention are as follows:

according to the invention, an air injection step is added in the gluing process, so that the wafer center thickness is optimized, the photoresist thickness uniformity is controlled, and the probability of stacking photoresist in the middle of the wafer is reduced. The distance between the gas nozzle and the wafer surface and the gas pressure of the gas ejected from the gas nozzle determine the thickness variation of the wafer middle area in the gas ejection step. Reasonable air injection speed and air pressure, preventing the formation of a glue ripple effect and preventing the loss of the attached photoresist.

The invention provides two photoresist homogenizing steps, which obviously improves the thickness approaching consistency probability of the photoresist middle area and the surrounding area and improves the reliability of subsequent photoetching and etching.

Drawings

FIG. 1 is a flow chart of the process of the present invention;

fig. 2 is a graph showing the result of spin coating in the conventional process, wherein the film thickness eventually has a non-uniform appearance, i.e., the center area is thick, the thickness gradually becomes thinner outwards, and the edges are also thick.

Fig. 3 is a schematic diagram of 9 positions of film thickness measurements on a wafer after photoresist gumming.

Fig. 4 is a graph showing wafer speeds versus time for example 1 and comparative example 1.

Detailed Description

The invention will be further analyzed with reference to specific examples.

Example 1: glue coating method (at 23 ℃) for optimizing thickness of photoresist in center of wafer, see FIG. 1

Step S1: wafer pretreatment

A 12 inch wafer (the front layer comprisesSilicon nitride and->Hard mask layer) on a rotary table, pre-rotating at 2000rpm for 1s; then cleaning the surface of the wafer, keeping the rotating speed of 30rpm in the cleaning process, dripping a cleaning solvent for flushing for 3 seconds; after the flushing is finished, the rotating speed is at least increased to 1000rpm and the cleaning solution is rotated for 0.1s, and the superfluous cleaning solvent is thrown away;

step S2: drop-in photoresist

Dropwise adding 20732ml of photoresist AM into the center of the upper surface of the wafer pretreated in the step S1, wherein the adding process keeps the rotating speed 1850rpm, and the dropwise adding time is controlled within 2 seconds; then, the rotation speed is reduced to 100rpm and kept rotating for 1s;

step S3: rotary spin coater

3-1 primary rotation spin coater

The wafer after the photoresist is dripped in the step S2 is increased to 1200rpm, and the photoresist is uniformly rotated for 15S, so that the thickness of the photoresist attached on the current wafer reaches

(Angstroms) is the photoresist thickness unit,>

3-2 air pressure thinning

Moving into a gas nozzle to the center above the wafer, wherein the distance from the vertical position of the nozzle to the surface of the wafer is 50mm, spraying nitrogen to the surface of the photoresist at the center of the wafer by using the gas nozzle, controlling the flow rate of the gas of the nozzle to be less than or equal to 500ml/s, and reducing the rotating speed of the spraying process to 500rpm for 1s;

in the air pressure thinning process, the rotating speed of the wafer is reduced, so that the wafer rotates at a small rotating speed of 500rpm, bubbles and waves generated by too fast diffusion of a thinning area are prevented, and the air pressure with small air pressure is controlled to jet air in a short time, so that the thickness of the thinned wafer is prevented from being too large. After the air injection step, the rotating speed is increased again, so that the thickness of the photoresist reaches the target thickness.

Based on the mechanical action of air pressure on the surface of the liquid film, the film thickness h of air pressure thinning has the following relation with environmental parameters:

wherein p is the pressure difference between the gas sprayed out and the outside (the area of the nozzle can be increased to reduce pa), ρ is the photoresist density, v is the photoresist viscosity, and d is the distance from the nozzle to the photoresist surface. The thickness h of the pressed film is controlled to be smaller than 8% of the thickness of the primary uniform glue, and the thickness of the glue is prevented from being smaller than the final target thickness in the thinning process.

3-3 times spin coating:

recovering the rotation speed of the wafer to the target rotation speed 1479rpm of the target photoresist thickness to perform secondary photoresist homogenizing for 10s, so that the thickness of the photoresist attached on the current wafer is thinned to

The rotating speed of the wafer is adjusted from 1479rpm to 1200rpm (the rotating speed is adjusted downwards by 20% relative to the target rotating speed) during the primary spin coating, so that the thickness of the glue on the wafer subjected to the primary spin coating is larger than the target thickness by more than 3%, and the glue exceeds the range clamping range. After the central air pressure is thinned, the photoresist is evenly coated at the target rotating speed, the photoresist thickness is adjusted to the target thickness, and the whole thickness is more uniform.

Step S4: wafer edge and backside rinse

Rinsing the edge and the lower surface of the wafer after the photoresist is homogenized in the step S3 by using ultra-pure water, treating photoresist accumulation at the edge, keeping the rotation speed of 1000rpm in the rinsing process, and controlling the wafer rotation rinsing time to be 7S;

step S5: post-treatment

The rotating table is rotated at a speed of 2000rpm, and kept at a constant speed for 5s, so that superfluous ultra-pure water is thrown away, and the wafer is dried.

TABLE 1COT New Recope

Comparative example 1: traditional wafer center photoresist thickness gumming method (23 ℃ C.)

Step S1: wafer pretreatment

A 12 inch wafer (the front layer comprisesSilicon nitride and->Hard mask layer) is placed on a rotary table, and pre-rotation is carried out by adopting a rotating speed of 2000rpm for a duration of 1s; then cleaning the surface of the wafer, keeping the rotating speed of 30rpm in the cleaning process, dripping a cleaning solvent for flushing for 3 seconds; after the flushing is finished, the rotating speed is at least increased to 1000rpm and the cleaning solution is rotated for 0.1s, and the superfluous cleaning solvent is thrown away;

step S2: drop-in photoresist

Dropwise adding 20732ml of photoresist AM into the center of the upper surface of the wafer pretreated in the step S1, wherein the adding process keeps the rotating speed 1850rpm, and the dropwise adding time is controlled within 2 seconds; then, the rotation speed is reduced to 100rpm and kept rotating for 1s;

step S3: rotary spin coater

3-1 rotary spin coater

The wafer after the photoresist is dripped in the step S2 is increased to 1479rpm, and the photoresist is uniformly rotated for 25 seconds, so that the thickness of the photoresist attached on the current wafer reaches

Step S4: wafer edge and backside rinse

Rinsing the edge and the lower surface of the wafer after the photoresist is homogenized in the step S3 by using ultra-pure water, treating photoresist accumulation at the edge, keeping the rotation speed of 1000rpm in the rinsing process, and controlling the wafer rotation rinsing time to be 7S;

step S5: post-treatment

The rotating table is rotated at a speed of 2000rpm, and kept at a constant speed for 5s, so that superfluous ultra-pure water is thrown away, and the wafer is dried.

TABLE 2COT Old Recipe

RRC: reduced Resist Consumption organic solvent washing and photoresist lubrication

EBR: edge Back rim, back flushing

Resist: photoresist

Edge1,2: different positions at the edge of the wafer are used for flushing the edge to remove accumulated photoresist

9 points were taken on the wafers processed in example 1 and comparative example 1, film thickness data at 9 positions were measured (see fig. 3), and mean values and range ranges at 9 positions were calculated. The process targets are as follows: the mean clamping value is within +/-1% of the target glue thickness, and the range clamping range is 3%, wherein the range maximum range usually appears in the film thickness difference between the central point and the peripheral point. Example 1 by the air pressure center thinning process, the center point thickness to peripheral thickness gap will be significantly reduced. With a target thickness ofFor example, the conventional coating process of comparative example 1 was used, and the maximum difference between the film thicknesses of the center point and the peripheral point was +.>The actual gap is->In the case where the film thicknesses of the eight measurement points other than the center point are uniform, the maximum value of the uniformity (standard deviation sigma) is +.>While example 1 by using the center air pressure thinning process, the expected difference between the center point and the peripheral thickness is optimized to be greater than 50%, i.e. the range of range clamping can be reduced to 1.5%, and the actual film thickness difference between the center point and the peripheral point will be less than +.>The maximum value of the uniformity can be reduced to +.>The wafer speeds of example 1 and comparative example 1 are shown in fig. 4 as a function of time.

While the fundamental and principal features of the invention and advantages of the invention have been shown and described, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing exemplary embodiments, but may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Claims (10)

1. A glue spreading method for optimizing the thickness of photoresist in the center of a wafer is characterized by comprising the following steps:

step S1: wafer pretreatment:

placing a wafer needing to be subjected to a gluing process on a rotary table, and pre-rotating by adopting any rotating speed; then cleaning the surface of the wafer;

step S2: dropwise adding photoresist;

step S3: spin coating:

3-1 first time spin coating:

the wafer after the photoresist is dripped in the step S2 is increased in rotating speed to n1, and uniform photoresist is rotated at a constant speed, so that the thickness of the photoresist attached to the current wafer reaches T+delta; wherein T represents the target thickness of the photoresist, and delta represents the redundant thickness;

3-2 air pressure thinning:

moving a gas nozzle to the center above the wafer, wherein the distance d between the vertical position of the nozzle and the surface of the wafer is d, d is more than 0, and spraying gas which does not react with photoresist on the surface of the photoresist at the center of the wafer by using the gas nozzle;

3-3 times spin coating:

restoring the rotation speed of the wafer to a target rotation speed n2 of the target photoresist thickness, and carrying out secondary photoresist homogenizing, wherein n2 is more than n1 and more than 1000rpm, so that the thickness of the photoresist attached on the current wafer is thinned to T; the secondary spin time is less than the spin time for the first time;

step S4: rinsing the edge and the back of the wafer;

step S5: and (5) post-treatment.

2. The method according to claim 1, wherein step S2 is specifically: dropwise adding photoresist in the center of the upper surface of the wafer pretreated in the step S1, wherein the rotating speed of the photoresist adding process is kept at 1000rpm-2000rpm, and the dropwise adding time is controlled within 2S-3S; then, the rotation speed is reduced to 200rpm or less and kept to be 1s or less.

3. The method according to claim 1, wherein the primary spin time in step S3 is 10S-20S and the secondary spin time is 5S-10S.

4. The method of claim 1, wherein the vertical position of the nozzle in step S3-2 is spaced from the wafer surface by a distance d that satisfies 0 < d.ltoreq.50 mm.

5. The method according to claim 1, wherein the flow rate of the nozzle gas is controlled to be less than or equal to 500ml/S in the step S3-2, the rotating speed of the air injection process is reduced to at least 500rpm, and the air injection time is controlled to be less than or equal to 1S.

6. The method according to claim 1, wherein in step 3-1

7. The method of claim 1, wherein the gas that does not react with the photoresist in step 3-2 is nitrogen.

8. The method according to claim 1, wherein step S4 is specifically: and (3) flushing the edge and the lower surface of the wafer after the photoresist is uniformly coated in the step (S3) by using ultra-pure water, treating photoresist accumulation at the edge, and keeping the rotation speed of 800rpm-1200rpm in the flushing process, wherein the wafer rotation flushing time is controlled to be 5S-10S.

9. The method of claim 1, wherein the wafer surface is an advanced-sized AA layer or POLY layer.

10. The method according to claim 1, wherein in step 3-2, the air pressure thinned film thickness h satisfies the following relationship:

wherein p is the pressure difference between the gas sprayed out and the outside, ρ is the photoresist density, v is the photoresist viscosity, and d is the distance from the nozzle to the photoresist surface.