RU2077751C1 - Process of manufacture of modified layers of silicon dioxide (variants) - Google Patents

Abstract

FIELD: semiconductor technology manufacture of solid gas sensors of sulfur dioxide. SUBSTANCE: modified layers of silicon dioxide are produced under isothermal conditions in presence of vapors of organic compounds carrying amino groups. Layers can be formed and modified simultaneously at temperature 120-200 C under total pressure 0.5-1.0 mm Hg from gas jet containing monosilane and oxygen with ratio of concentrations from 1.0 to 0.4 under partial pressure 0.3-0.7 mm Hg of monosilane. Another variant of manufacture of modified layers of silicon dioxide consists in that layers are formed from gas phase carrying monosilane and oxygen with ratio of concentrations from 0.6 to 0.4 under partial pressure 0.5-0.7 mm Hg of monosilane at temperature 70-120 C and total pressure 0.8-1.0 mm Hg and modification is carried out by annealing at 150-200 C in presence of vapors of organic compounds. EFFECT: enhanced efficiency of process. 5 cl, 2 dwg

Description

The invention relates to a technology for producing semiconductor devices and can be used in the manufacture of solid-state gas sensors for sulfur dioxide (SO ₂ ).

Known methods for modifying the surface of silicas (porous silica glasses, aerosils, polycrystalline SiO ₂ powders) with organic compounds containing various functional groups that provide specific adsorption of certain gases, including sulfur dioxide SO ₂ . Modification is usually carried out from solutions, sometimes for modifiers with a low boiling point, modification in a gaseous medium is used. Modified silicas are widely used in chromatography, catalysis, etc. [one]
The above methods are not applicable to obtain thin modified layers used in semiconductor devices.

A known method of producing modified layers of silicates with selective adsorption ability with respect to sulfur dioxide (SO ₂ ). These layers are used in sensitive elements of capacitive-type solid-state sensors [2]
The layers are prepared by hydrolysis and subsequent coprecipitation (by sol-gel technology) of alkoxysilanes containing tertiary amines and hydrophobic propyl groups (e.g., (C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ N (C ₂ H ₅ ) ₂ and (C ₂ H ₅ O) ₃ Si (CH ₂ ) ₂ CH ₃ )
In the resulting silicate layers, the modifier is bonded to the (SiO ₂ ) Si – C bond matrix. The adsorption capacity of SO ₂ is due to the fact that tertiary amines form a coordination compound with SO ₂ . The reversibility of this reaction provides reversible adsorption of SO ₂ . Adsorption of SO ₂ changes the dielectric properties of the modified silicate layers. These changes can be detected by changes in the capacitance and conductivity of a planar capacitor on which a modified layer is applied.

The specified method has the following disadvantages:
1. The method is not combined with microelectronics technology and excludes mass reproducible processing of plates.

 2. The method does not allow you to control the composition and properties of the layers during the synthesis. The layers are heterogeneous in thickness.

. В качестве модификаторов использовались алкоксисиланы, содержащие различные функциональные группы. Обработка проводилась в парах модификатора при давлении 0,5-1 мм рт.ст. в изотермических условиях в диапазоне температур от 80 до 190^oC в зависимости от типа модификатора. Длительность обработки составляла ≈12 часов. Толщина модифицированного слоя получалась равной 5-10

.A known method of producing ultrathin modified alkoxysilanes SO ₂ layers on the surface of silicon wafers [3]
For modification, a film of natural silicon oxide 10–20 thick was used

. Alkoxysilanes containing various functional groups were used as modifiers. Processing was carried out in modifier vapors at a pressure of 0.5-1 mm Hg. in isothermal conditions in the temperature range from 80 to 190 ^o C depending on the type of modifier. The processing time was ≈12 hours. The thickness of the modified layer was 5-10

.

 The specified method has the following disadvantages.

 1. The process proceeds under these conditions very slowly. One cycle is ≈12 hours.

 2. The limitation on the thickness of the obtained layers within the monolayer makes them unsuitable for use as sensitive elements of solid-state sensors. This is due to the fact that the concentration of absorption centers and, accordingly, the adsorption capacity of such layers, even at the highest possible degree of modification, is too small.

An object of the invention is the synthesis of modified SiO ₂ layers by gas phase deposition, which has no thickness limitations of at least ≈2 microns and allows the synthesis to be carried out in a controlled manner and to obtain layers with the required porosity and content of Si-OH and Si-H groups. These properties determine the possibility and success of the modification.

The technical problem is achieved by the fact that in the method of producing modified layers of silicon dioxide under isothermal conditions in the presence of vapors of organic compounds containing amino groups, the deposition of the layers is carried out at a temperature of 120-200 ^o C, pressures of 0.5-1 mm RT.article in relation to the concentration of oxygen and monosilane 0.4-1, the partial pressure of monosilane 0.3-0.7 mm RT. Art. and the partial pressure of the modifier (for example, diethylaminopropyltriethoxysilane) 2 • 10 ^-3 -5 • 10 ^-3 mm Hg

In addition, the task is achieved by the fact that in the method of producing modified layers of silicon dioxide under isothermal conditions in the presence of vapors of organic compounds containing amino groups, the deposition of the layers is carried out at a temperature of 70-120 ^o C, pressures of 0.8-1 mm Hg in relation to the concentration of oxygen and monosilane 0.4-0.6, the partial pressure of monosilane 0.5-0.7 mm RT. Art. followed by annealing in vapor modifier, for example triethanolamine at a temperature of 150-200 ^o C.

или

В первом варианте способа получения модифицированных слоев диоксида кремния режимы процесса обусловлены следующим.The essence of the invention lies in the fact that it was found that embedding modifier molecules (organic compounds containing tertiary amino groups) in the matrix of SiO ₂ layers is obtained by vapor deposition from the oxidation reaction of oxygen monosilane. The discovered possibility of modification is due to the fact that the layers obtained by the indicated method have a high concentration of chemically active Si-OH and Si-H groups (≈5 • 10 ²¹ cm ^-3 ), reacting with modifiers according to the following scheme

or

In the first embodiment of the method for producing modified layers of silicon dioxide, the process conditions are due to the following.

At synthesis temperatures above 200 ^° C., the degree of layer modification decreases, which manifests itself in a decrease in their adsorption capacity with respect to SO ₂ . At temperatures below 120 ^o C, the quality of the layers sharply decreases, their defectiveness increases, which manifests itself in an increase in the etching rate by 2-3 times.

 The restriction on the total pressure in the reactor (0.5-1 mm Hg) and the partial pressure of monosilane (0.3-0.7 mm Hg) is caused by the fact that beyond the limits of the indicated intervals the layer uniformity in thickness deposition zone.

At a ratio of O ₂ / SiH ₄ > 1, in the presence of modifier vapors, the layers do not grow; at 0 ₂ / SiH ₄ <0.4, the quality of the obtained layers deteriorates.

When the partial pressure of the modifier P _m > 5 • 10 ^-3 mm RT.article layer growth stops, pressure drop below 2 • 10 ^-3 mm Hg leads to a sharp decrease in the degree of modification.

 In the second version of the method for producing modified layers of silicon dioxide, the process conditions are due to the following.

At synthesis temperatures above 120 ^o C, the concentration in the layers of impurity Si-OH and Si-H groups sharply decreases, which allows modification. At temperatures below 70 ^o stops the growth of SiO ₂ layers, a powdery silicon dioxide is formed.

мм рт.ст. наряду с ростом слоя происходит образование SiO₂ в газовой фазе, что приводит к ухудшению качества слоев. При давлениях ниже 0,8 мм рт.ст. и

мм рт. ст. скорости осаждения падают практически до нуля.At pressures in the reactor above 1 mm Hg and

mmHg. Along with layer growth, SiO ₂ is formed in the gas phase, which leads to a deterioration in the quality of the layers. At pressures below 0.8 mmHg and

mmHg Art. deposition rates drop to almost zero.

At ratios O ₂ / SiH ₄ > 0.6, film growth is not observed; at O ₂ / SiH ₄ <0.4, the quality of the resulting layers deteriorates.

Annealing of the layers of modifier vapors at T> 200 ^° C leads to a partial resinification of the modifier and sintering of the layers, which greatly reduces their adsorption capacity with respect to SO ₂ . At annealing temperatures below 150 ^o C, the rate of modification is sharply reduced.

 Examples of specific performance of the method.

The layer was deposited in a cylindrical quartz reactor heated by a resistance furnace. The substrates were located on a dural boat, which divided the reactor into two parts. This ensures the ratio of surface to volume in the deposition zone (S / V) ≈3 cm ^-1 .

 1. Modification during growth.

 Example 1

The synthesis temperature of 200 ^o C.

 The pressure in the reactor is 0.5 mm Hg.

 The partial pressure of monosilane 0.3 mm RT.article

The ratio of O ₂ / SiH ₄ = 1.

Partial pressure modifier (DEAPTES) ≈5 • 10 ^-3 mm Hg

.Synthesis Time 10 min
Layer Thickness 4000

.

 Example 2

The synthesis temperature of 150 ^o C
The pressure in the reactor 0.6 mm RT.article

Monosilane partial pressure 0.43
The ratio of O ₂ / SiH ₄ = 0.4.

Partial pressure modifier (DEAPTES) ≈3.5 • 10 ^-3 mm Hg

 Synthesis time 5 min.

.Layer Thickness 3000

.

Example 3
The synthesis temperature of 120 ^o C.

 The pressure in the reactor is 1 mmHg.

 The partial pressure of monosilane is 0.7.

The ratio of O ₂ / SiH ₄ = 0.4.

Partial pressure modifier (DEAPTES) ≈2 • 10 ^-3 mm Hg

 Synthesis time 5 min.

.Layer Thickness 2000

.

 II. Processing in modifier pairs.

 Example 4

The synthesis temperature of 70 ^o C.

 The pressure in the reactor is 1 mmHg.

 The partial pressure of monosilane 0.7 m Hg

The ratio of O ₂ / SiH ₄ = 0.4.

 The synthesis time is 2.5 hours.

.Layer Thickness 4500

.

The annealing temperature in the vapor modifier 180 ^o C.

 Example 5

The synthesis temperature of 100 ^o C.

 The pressure in the reactor of 0.88 mm RT.article

 The partial pressure of monosilane is 0.55 mm Hg.

The ratio of O ₂ / SiH ₄ = 0.6.

 Synthesis time 90 min.

 Layer thickness 1 μm.

The annealing temperature in the vapor modifier 150 ^o C.

 Example 6

The synthesis temperature of 120 ^o C.

 The pressure in the reactor is 0.8 mm Hg.

 The partial pressure of monosilane is 0.5 mm Hg.

.The ratio of O ₂ / SiH ₄ = 0.6
Synthesis Time 60 min
Layer Thickness 9000

.

The annealing temperature in the vapor modifier 200 ^o C.

 The modification effect was established by the IR spectra of the layers, and the method of multiple disturbed total internal reflection (MNVPO) was used.

In fig. 1 shows the characteristics of the IR transmission spectra of SiO ₂ layers deposited on a germanium substrate in the range from 1400 to 4000 cm ^-1 .

a) The spectrum of the unmodified film synthesized at 100 ^o C. The absorption bands in the region of 2200-2300 cm ^-1 correspond to stretching vibrations of the Si-H bond, in the range of 3300-3700 cm ^-1 stretching vibrations of the hydroxyl groups of Si-OH and water.

This type of spectrum is typical for layers obtained in the temperature range 70-120 ^o C.

b) The characteristic spectrum of the film modified in pairs of amino alcohols (in this case, triethanolamine). Comparison with spectrum (a) shows that upon modification
the absorption band corresponding to Si – H vibrations almost completely disappears in the region of 2200–2300 cm ^–1 ;
the intensity of oscillations in the region of 3300-3700 cm ^-1 decreases;
new bands of stretching vibrations of С-Н bonds of 2960-2870 cm ^-1 appear.

c) The spectrum of the film modified with diethylaminopropyltriethoxylane (DEAPTES) directly during the deposition process is characteristic. A comparison with the spectrum of unmodified film (a) shows that
the absorption in the region of 2200-2300 cm ^-1 practically did not change,
the relative intensity of the oscillations in the region of 3300-3700 cm decreased,
new absorption bands appeared in the region of 2960-2870 cm ^-1 , the relative intensity in them is less than in spectrum (b).

 A comparison of spectra (b) and (c) shows that the degree of modification upon annealing in modifier pairs is higher.

 The use or selection in practice of the first or second method of modification is determined by the type of sensitive element of the solid-state sensor.

. Проведено 10 последовательных напусков SO₂ при 0,5 торр. При откачивании SO₂ наблюдается обратимость процесса адсорбции.The effect of SO ₂ adsorption and the reversibility of this process were observed using a high-speed automatic ellipsometer. In fig. Figure 2 shows typical results of measuring the polarization angle ψ upon adsorption of SO ₂ on a modified layer with a thickness of 2075

. Conducted 10 consecutive inlets of SO ₂ at 0.5 torr. When pumping out SO ₂ , the adsorption process is reversible.

Adsorption of SO ₂ changes some of the physical properties of the modified layers, for example, dielectric constant and charge state of the layer.

 The proposed method for producing modified layers differs from the previously known methods in that it is based on the process of deposition of silicon dioxide layers from the gas phase at low temperatures, which can be used in semiconductor technology for the manufacture of miniature solid-state gas sensors.

 This method allows to obtain in a controlled manner and reproducibly modified layers of the desired thickness and a certain degree of modification. There are no restrictions on the thickness of the resulting layers, at least up to 1.5-2 microns.

 The two considered modification options mutually complement each other and make it possible to obtain the ratio of the integrated amino groups to the number of at. Si in the film from 1-0.01.

 The first option to obtain modified layers includes one technological operation. You can get the degree of modification from 0.1 to 0.01.

 The second option consists of two technological operations: the deposition of layers and annealing them in pairs of the modifier. You can get the degree of modification from 1 to 0.1.

 The requirements for the degree of modification are determined by the design and operation principle of the sensor element of the solid-state sensor.

Claims (1)

1 1. A method of obtaining modified layers of silicon dioxide under isothermal conditions in the presence of vapors of organic compounds containing amino groups, characterized in that the simultaneous formation and modification of the layers is carried out at a temperature of 120-200 <198> C, a total pressure of 0.5 1 mm RT. Art. from a gas mixture containing monosilane and oxygen in a concentration ratio of 1 0.4, at a partial pressure of monosilane of 0.3 0.7 mm Hg in the presence of a vapor modifier of organic compounds containing amino groups at a partial pressure of 2 <195> 10 <M ^> - <D> <M ^> 3 <D> 5 <195> 10 <M ^> - <D> <M ^ > 3 <D> mmHg 2. 2. The method according to claim 1, characterized in that diethylaminopropyltriethoxysilane is used as a modifier.2 3. The method of producing modified layers of silicon dioxide under isothermal conditions in the presence of vapors of organic compounds containing amino groups, characterized in that the formation of silicon dioxide layers is carried out by deposition from a gas mixture containing monosilane and oxygen a concentration ratio of 0.6 0.4, at a partial pressure of silane 0.5 0.7 mm Hg. Art. at a temperature of 70 120 <198> C and a total pressure of 0.8 1 mm Hg and the modification is carried out in the presence of a modifier of vapors of organic compounds containing amino groups by annealing at a temperature of 150-200 <198> C.2 4. The method according to p. 3, characterized in that triethanolamine is used as a modifier.

Images