CN102931070B - Silicon substrate isotropic wet etching process - Google Patents

Abstract

The invention provides a novel silicon substrate isotropic wet etching process. The process includes forming two sacrificial layers on the surfaces of silicon substrates by adding SiO2 and negative 450CP photo-resists, forming graphs needed to be machined through a surface micromachining photolithography technique, and using isotropic etching to obtain two-dimensional machined graphs with small depth-to-width ratios. According to the silicon substrate isotropic wet etching process, a certain quantity of acetic acids and water are added in a HF+HNO3 corrosion system selecting reasonable proportioning to serve as buffer agents to stabilize corrosion rates, and a corrosion solution is placed in an ice water mixture to control the reaction temperature to obtain a silicon corrosion system with an optimum corrosion rate, depth-to-width ratio and surface quality.

Description

A kind of silica-based isotropism wet-etching technology

Technical field

The present invention relates to semiconductor silicon material surface micro-fabrication and manufacturing technology field, particularly a kind of silica-based isotropism wet-etching technology.

Background technology

Current Micro-machining based on silicon can be divided into surperficial silica-based micro-processing technology (Surface Micromachining) and the silica-based micro-processing technology of body (Bulk Micromachining) two main flows.The Micro-machining based on silicon feature different from traditional machining always first arranges from whole system the design of operation, adopts top-down method for designing.Dark (thickness) that can accomplish due to the micro-machined motion of silicon face is very little with the ratio of width (lateral dimension), therefore is called as two dimension processing.

The wet etching course of general silicon is in corrosive liquid, first make material surface be oxidized, and then make one or more oxide dissolution by chemical reaction, this is actually electrochemical corrosion course.Electrochemical corrosion refers to the corrosion process that metal or semi-conducting material are suffered in electrolyte aqueous solution.Owing to being mixed with various reagent in same corrosive liquid, so above-mentioned two processes are carried out simultaneously.For isotropism chemistry corrosion influencing factor mainly contain some:

1) reagent is selected

The wet etching course of silicon is generally in corrosive liquid, first make material surface be oxidized, and then make one or more oxide dissolution by chemical reaction, this is actually electrochemical corrosion course.Owing to being mixed with various reagent in same corrosive liquid, so above-mentioned two processes are carried out simultaneously.Reagent for the corrosion of isotropism chemistry is a lot, comprises various salt (as CN base, NH ₄base etc.) and acid, HF+HNO ₃etching system can obtain high purity reagent, but needs in corrosion process to add buffer.CrO ₃there is metal ion to stain, limit its electronic device preparation in use.

2) impact of buffer

Buffer is generally weak acid or weak base, as NH ₄oH etc.In strong acid or strong base solution, add certain buffer just can play adjustment acidity (H ⁺concentration) and basicity (OH ^-) effect.At HNO ₃h in solution ⁺concentration is higher, because HNO ₃almost all ionize, but glacial acetic acid is that weak acid degree of ionization is less.Its ionization reaction formula is as follows:

At HNO ₃+ CH ₃in COOH solution, though should HNO be had ₃make H ⁺concentration is higher, but adds CH ₃after COOH, H ⁺with CHCOO ^-ionization generates CH ₃cOOH molecule.Because CH ₃the degree of ionization of COOH is little, so at HNO ₃+ CH ₃h in COOH solution ⁺concentration is lower, and this is the result being subject to buffer adjustment.

3) corrosion treatment temperature and impact that is ultrasonic or that stir

Corrosion treatment temperature is higher, and corrosion rate is faster.But wish that corrosion treatment temperature is lower to improve corrosion surface quality.The ultrasonic transmission speed can accelerating material, makes reactant be transported to the surface of solids in time and leave in time, is conducive to the carrying out reacted.When not stirring, material relies on diffusion to transmit, slowly, more unfavorable to reaction.Often at erosional surface bubbing in corrosion process, and hinder reaction to carry out, and make local overheating.Ultrasonic process can be adopted for this reason, accelerate gas evolution, to improve corrosion surface quality.

Summary of the invention

Technical problem to be solved by this invention is: selecting the HF+HNO of rational proportion ₃a certain amount of acetic acid is added and water stablizes corrosion rate as buffer in etching system, corrosive liquid is placed in mixture of ice and water and controls reaction temperature, thus the corrosion realized silicon, thus provide a kind of silica-based isotropism wet-etching technology of one with best corrosion rate, depth-to-width ratio and surface quality.

The technical scheme that technical solution problem of the present invention is taked is:

A kind of silica-based isotropism wet-etching technology, processing step is as follows:

The formation of a, sacrifice layer:

A.1, oxidation furnace is adopted to grow one deck SiO at silicon chip surface ₂, form ground floor sacrifice layer,

Process conditions:

Temperature: 1120 DEG C; Time: 10 '+85 '+10 '

SiO ₂thickness: 800 ± 50nm;

a.2, SiO is had in growth ₂the silicon chip of layer is coated with one deck negative photoresist, thus forms second layer sacrifice layer, process conditions:

Photoresist spinner rotating speed: 2000 turns/min,

Photoresist colloidality: negativity;

Photoresist thickness: 20000 ± 1000nm;

Photoresist viscosity: 450CP

The formation of b, figure:

Adopt photoetching process on second layer sacrifice layer, form required figure,

Etching condition: light intensity=1.4 ± 0.2mW/cm ²; Time for exposure=10 ± 2sec;

C, isotropic etch:

Under temperature 18 DEG C of conditions, the silicon chip forming required figure is immersed in corrosive liquid, etching time: 20min; Corrosion thickness: 2um;

Corrosive liquid composition described in step c and proportioning volume ratio are:

HNO ₃+HF+CH ₃COOH+ H ₂O ₂=16：10：4：1 (V/V)

Concentration is: HNO ₃68%(V/V), HF 48%(V/V), CH ₃cOOH 99.8%(V/V).

The mechanical performance that the present invention utilizes silicon fabulous, comprises intensity, hardness, thermal conductance and thermal expansion etc., obtains required two-dimentional graphics processing at its surface micro-fabrication.The present invention is selecting the HF+HNO of rational proportion ₃add a certain amount of acetic acid in etching system and water stablizes corrosion rate as buffer, corrosive liquid is placed in mixture of ice and water and controls reaction temperature, obtained the silicon etching system of best corrosion rate, depth-to-width ratio and surface quality by test.

Embodiment

Embodiment 1

1, the formation of sacrifice layer:

(1), silicon chip is put in oxidation furnace generate one deck 800SiO by high-temperature oxydation ₂, form ground floor sacrifice layer, oxidation furnace temperature: 1120 DEG C; Time: 10 '+85 '+10 ', SiO ₂thickness: 800nm;

(2), automatic glue application platform is adopted to have SiO in growth ₂the silicon chip of layer is coated with the negative photoresist that one deck viscosity is 450CP, forms second layer sacrifice layer, photoresist thickness: 20000nm;

2, the formation of figure:

Adopt negative-working photoresist technique, second layer sacrifice layer is formed required figure; Photoetching process condition: light intensity=1.6mW/cm ²; Time for exposure=10sec; Negative adhesiveness: 450CP.

3, isotropic etch

Preparation corrosive liquid: first measure 160mL HNO respectively with graduated cylinder ₃with 100mL HF, two kinds of solvents are fully mixed, then add 40mL glacial acetic acid (CH wherein respectively ₃and 10mL deionized water (H COOH) ₂o), abundant mixing is made it with plastic products stirring.Finally the corrosive liquid configured is placed in mixture of ice and water, makes it cooling at least 30 minutes.Use in order to corrosion.

Wherein: HNO ₃concentration is 68%(V/V); HF concentration is 48%(V/V); CH ₃cOOH concentration is 99.8%(V/V);

Under temperature 18 DEG C of conditions, the silicon chip forming required figure is immersed in corrosive liquid, etching time: 20min; Corrosion thickness: 2um.

Embodiment 2

1, the formation of sacrifice layer:

(1), silicon chip is put in oxidation furnace generate one deck 800SiO by high-temperature oxydation ₂, form ground floor sacrifice layer, oxidation furnace temperature: 1120 DEG C; Time: 10 '+85 '+10 ', SiO ₂thickness: 850nm;

(2), automatic glue application platform is adopted to have SiO in growth ₂the silicon chip of layer is coated with the negative photoresist that one deck viscosity is 450CP, forms second layer sacrifice layer, photoresist thickness: 21000nm;

2, the formation of figure:

Adopt negative-working photoresist technique, second layer sacrifice layer is formed required figure; Photoetching process condition: light intensity=1.4mW/cm ²; Time for exposure=10sec; Negative adhesiveness: 450CP.

3, isotropic etch

Preparation corrosive liquid: first measure 160mL HNO respectively with graduated cylinder ₃with 100mL HF, two kinds of solvents are fully mixed, then add 40mL glacial acetic acid (CH wherein respectively ₃and 10mL deionized water (H COOH) ₂o), abundant mixing is made it with plastic products stirring.Finally the corrosive liquid configured is placed in mixture of ice and water, makes it cooling at least 30 minutes.Use in order to corrosion.

Wherein: HNO ₃concentration is 68%(V/V); HF concentration is 48%(V/V); CH ₃cOOH concentration is 99.8%(V/V);

Under temperature 18 DEG C of conditions, the silicon chip forming required figure is immersed in corrosive liquid, etching time: 20min; Corrosion thickness: 2um.

Embodiment 3

1, the formation of sacrifice layer:

(1), silicon chip is put in oxidation furnace generate one deck 800SiO by high-temperature oxydation ₂, form ground floor sacrifice layer, oxidation furnace temperature: 1120 DEG C; Time: 10 '+85 '+10 ', SiO ₂thickness: 750nm;

(2), automatic glue application platform is adopted to have SiO in growth ₂the silicon chip of layer is coated with the negative photoresist that one deck viscosity is 450CP, forms second layer sacrifice layer, photoresist thickness: 19000nm;

2, the formation of figure:

Adopt negative-working photoresist technique, second layer sacrifice layer is formed required figure; Etching condition: light intensity=1. 2mW/cm ²; Time for exposure=8sec; Negative adhesiveness: 450CP.

3, isotropic etch

Preparation corrosive liquid: first measure 160mL HNO respectively with graduated cylinder ₃with 100mL HF, two kinds of solvents are fully mixed, then add 40mL glacial acetic acid (CH wherein respectively ₃and 10mL deionized water (H COOH) ₂o), abundant mixing is made it with plastic products stirring.Finally the corrosive liquid configured is placed in mixture of ice and water, makes it cooling at least 30 minutes.Use in order to corrosion.

Wherein: HNO ₃concentration is 68%(V/V); HF concentration is 48%(V/V); CH ₃cOOH concentration is 99.8%(V/V);

Under temperature 18 DEG C of conditions, the silicon chip forming required figure is immersed in corrosive liquid, etching time: 20min; Corrosion thickness: 2um; .

Claims (1)

1. a silica-based isotropism wet-etching technology, processing step is as follows:

The formation of a, sacrifice layer:

A.1, oxidation furnace is adopted to grow one deck SiO at silicon chip surface ₂, form ground floor sacrifice layer,

Process conditions:

Temperature: 1120 DEG C; Time: 10 '+85 '+10 '

SiO ₂thickness: 800 ± 50nm;

a.2, SiO is had in growth ₂the silicon chip of layer is coated with one deck negative photoresist, thus forms second layer sacrifice layer, process conditions:

Photoresist spinner rotating speed: 2000 turns/min,

Photoresist colloidality: negativity;

Photoresist thickness: 20000 ± 1000nm;

Photoresist viscosity: 450CP

The formation of b, figure:

Adopt photoetching process on second layer sacrifice layer, form required figure,

Etching condition: light intensity=1.4 ± 0.2mW/cm ²; Time for exposure=10 ± 2sec;

C, isotropic etch:

Under temperature 18 DEG C of conditions, the silicon chip forming required figure is immersed in corrosive liquid, etching time: 20min; Corrosion thickness: 2um;

Corrosive liquid composition described in above-mentioned steps c and proportioning volume ratio are:

HNO ₃：HF：CH ₃COOH：H ₂O ₂=16：10：4：1 (V/V)

Concentration is: HNO ₃68%(V/V), HF 48%(V/V), CH ₃cOOH 99.8%(V/V).