PL188424B1 - Composition for chemically removing metal ions and atoms from surfaces - Google Patents

Abstract

The composition for chemical purification of surfaces off adsorbed metal ions and atoms is designed for chemical treatment in production technology where basic and auxiliary materials must meet strict requirements concerning purity, especially in case of chemical treatment of siliceous structures and AIII BV structures in semiconductor technology used before operations of epitaxial growth, oxidation, ion implementation, diffusion, annealing and application of thin metal or dielectric coats. According to the invention, the composition for chemical purification of surfaces off adsorbed metal ions and atoms consists of 0.1 - 20 units of weight of sulphomaleic anhydride, 0.1 - 50 units of weight of disulphomaleic anhydride, which is used in the composition as an activator of change of water molecule in cation hydration sheath during formation of chelate and water. It is most effective if used in the amount of 0.1 - 2 units of weight of the composition to purify siliceous plates before thermal process, and in the amount of 10 - 20units of weight of the composition to purify diffusive pipes.

Description

The subject of the invention is a composition for the chemical cleaning of surfaces from adsorbed metal ions and atoms of semiconductor wafers and devices in which they are produced and used in production, where high demands are placed on the purity of basic and auxiliary materials, in particular, it can be used in the chemical treatment of structures silicon and A ^ffl B ^v in semiconductor technology prior to epitaxial growth, oxidation, ion implementation, diffusion, annealing and thin layers of metal or dielectric.

There are known compositions of preparations for the chemical treatment (etching) of wafers of semiconductor structures, containing organic solvents, inorganic acids and their salts, alkalis, detergents, complex compounds (USSR patents: No. 505272 of 1974, No. 531435 of 1975, No. 682053 of 1978 "No. 1023960 of 1981- No. 1055286 of 1982, No. 1088586 of 1984, No. 1480676 of 1987).

Etching agents based on a mixture of concentrated acids: hydrofluoric, sulfuric, nitric, hydrochloric, acetic, etc. are widely used.

The disadvantage of using the above solutions is that they have major disadvantages:

• as a result of the release of acid vapors, they are distinguished by work instability and the results are unstable, • their instability causes their frequent replacement, • the release of acid vapors causes very quick destruction of the basic technological equipment.

A composition for cleaning the surface of wafer semiconductor structures prior to the application of an epitaxial layer, containing ammonium hydroxide and hydrogen peroxide, is known (US Patent 5127984).

The disadvantage of using the above composition is that the treatment process in a solution of ammonium hydroxide and hydrogen peroxide also does not provide qualitative cleaning of silicon wafers, on which a significant amount of microscopic contamination remains, leading to deterioration of electrophysical parameters of integrated circuits, and in particular an increase in the threshold voltages found MOS transistors in them. The presence of alkaline ammonia in the solution leads to etching the surface of silicon wafers in the cleaning process at a temperature of 75-80 ° C. In addition, the cleansing properties of the solution are lowered by the decomposition of the peroxide

Hydrogen at elevated temperature, thereby increasing the pH of the solution. Increasing the alkaline properties of the solution lowers the oxidizing properties of hydrogen peroxide.

The composition of the solution (PFS-1) for surface treatment (Russian patent 2052868), in particular of semiconductor materials, containing water and sulfomaleic anhydride, in the following ratio (weight percent) is known:

• sulfomaleic anhydride -0.1-70, • water - others.

The disadvantage of using the above composition is that:

• by dissolving ions on the surfaces of semiconductor structures, it does not remove atomic metal particles;

• a small amount of treated tiles per unit volume of the composition is obtained;

• the physical and chemical characteristics of the instruments are comparable to those obtained after treatment in acids.

The composition for the chemical cleaning of surfaces from adsorbed metal ions and atoms of semiconductor wafers and the devices in which they are produced is characterized by the fact that it contains in percent by weight:

- sulfomaleic anhydride from 0.1 to 20,

- disulfomaleic anhydride from 0.1 to 50,

- other water.

Concentrations of 0.1 to 2 parts by weight of the composition are used to clean silicon wafers prior to thermal processing, and concentrations of 10 to 70 percent by weight of the composition are used for cleaning production equipment.

The advantage of the above solution is:

• creating a composition for the chemical cleaning of the surface of semiconductor structures from adsorbed metal ions and atoms;

• increasing the amount of processed wafers of semiconductor structures per unit volume of the composition;

• improving the quality of processed products;

• improvement of the physicochemical characteristics of the obtained structures;

• increasing the number of produced functional devices;

• significant reduction of water consumption in technological processes;

• creation of an ecologically safe industrial process for the production of semiconductor devices.

Examples of performed experiments are presented below in descriptive form.

All experiments aimed at testing the new composition and analytical processing of their results were carried out in the conditions of an operating enterprise, using the traditional technology of the process of chemical treatment of wafer surfaces of semiconductor structures applied before thermal operations.

It is known that peroxide-ammonium and peroxide-acid compositions badly remove alkali metal ions (Na and K), therefore the first experiment had to be carried out with the use of the proposed composition (PFS-2) compared to the known composition (PFS-1). and traditional compositions. Below are the chemical compositions of known compositions:

1. PFS-1 - sulfomaleic anhydride, water

2. CARO - H7SO4 + H20 ₂

3. PORE - NH4OH + H ₂ 02

Example No. 1.

Determination of the level of contamination with alkali metal ions on the surface of silicon wafers after chemical treatment.

The experimental samples were prepared as follows:

1) Crystals from phosphor-doped electronic silicon plates - KEF-4.5:

a) after the cbemic treatment of the traditional compositions, then the treatment in the composition

PORE - at 70 ° C for 10 minutes, followed by treatment with CARO - at 120 ° C for 10 minutes;

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b) after chemical treatment in the known composition PFS-1 with the concentration: 0.1; 2.0 and 6.0 weight percent, with an initial treatment temperature of 70 ° C and a final treatment temperature of 90 ° C, during 20 minutes;

c) after chemical treatment in the proposed PFS-2 composition with the same concentrations and technical parameters as for the PFS-1 composition.

2) Crystals from plates of arsenic-doped epitaxial silicon - KEM:

6.5 KEM • 1.2 300 KEM • 0.003

(a) after traditional chemical treatment, in the same technological conditions as monocrystalline silicon crystals;

b) after chemical treatment in aqueous solutions of the known PFS-1 composition, under the same technological conditions as monocrystalline silicon crystals;

c) after chemical treatment in aqueous solutions of the proposed PFS-2 composition, under the same technological conditions as monocrystalline silicon crystals.

Determination of the level of contamination of the surface of silicon wafers with alkali metal ions (Na and K) was carried out according to the method of secondary ion mass spectrometry (WIMS) on a Perkin-Elmer PH 1-6600 instrument. The measurement results are summarized in Table 1.

The data in Table 1 show that:

1) the quality of surface cleaning from Na and K ions on epitaxial silicon plates is 3 times better after chemical treatment with solutions of the known PFS-1 composition and 30 times better after treatment in the proposed PFS-2 composition compared to washing according to the traditional technology in compositions PORE and CARO;

2) the quality of cleaning the surface of the monocrystalline silicon plates in the known PFS-1 composition is approximately 50 times better compared to washing according to the traditional technology in PORE and CARO compositions and 500 times better in washing in the proposed PFS-2 composition compared to washing according to traditional technology in the PORE and CARO compositions, which may be related to the difference in the structure of epitaxial and monocrystalline silicon.

Example No. 2.

Cleaning of equipment for the production of semiconductors (in particular quartz tubes) from metal ions.

Determination of the electric charge in a thin layer of oxides on the control mounts of silicon wafers shows the effectiveness of removing metal ions from diffusive quartz tubes.

The experiment was performed as follows:

Silicon chips (KEF 1: 5-2.5 Ω / cm ² ) were cut in half and processed in a standard way, then they were oxidized for a short time to a thickness of 2000 A, then the 3 half plates were placed in the pipe before its chemical treatment and were kept in the working process for a period of 30 minutes. The remaining halves of the silicon wafers were placed in the quartz tube after its chemical treatment and were also held in the working process for 30 minutes. One pipe was treated according to the traditional technology - hydrofluoric acid, 3 pipes (one pipe for each solution concentration) were treated with the known PFS-1 composition, and the other 3 pipes were treated with the PFS-2 composition.

The work of the pipes was performed in one process.

The charge (Qss) on the control plates was calculated according to the formula:

Qss = AUFbC0 where:

Co - the maximum capacity of the MOS structure;

AUfij - shift which is a necessary condition for flat zones (comparison of the theoretical and real volt-farad characteristics).

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Assessment of the quality of cleaning the surface of silicon wafers from alkali metals with the proposed PFS-2 composition in comparison to the known PFS-1, PORA and CORO compositions. Table 1.

Aqueous solutions of PFS-2 | 6% solution t = 70-90 ° C + 0.0056 0.0032 1 ₊ ^B N 0.0050 1 0.0047 2% solution t = 70-90 ° C 0.0052 and 0.0030 * C3 WITH 0.0046 0.0042 0.1% - solution t = 70-90 ° C L J 0.045 0.028 L ₊ ^B N i 0.061 0.039 Aqueous solutions of PFS-1 | <5 O ź ον os £ 6 V sD + 0.059 1 0.019 ⁺ σ) Z 0.047 0.053 2% solution t = 70-90 ° C with 1 0.050 0.026 ⁺ cd Z 0.043 0.050 - ¹ 0.1% - solution t = 70-90 ° C k: r- m ABOUT 0.083 * cont WITH 0.52 0.095 and Traditional processing: - PORF first stage (t = 75 ° C) - printing stage WHAT RO (t = 125 ° C) + iZ CM r- about + What with 3.35 0.145 Types of experimental patterns KEF-4.5 silicon plate crystals Crystals from epitaxial silicon plates ń5KFM 1 7_ 300 KFM 0 003 m No col. -and CM

CM cd c3

Z £

oh oh

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HJ cd • I £ 2 ryL · c «3 X)

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Ł-ą 2 ° * u KT ϊ N -ż C »- (-¾ Μ I — I tX« OX \ O λ O ** ^-

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C O ω N _Z c * -> _o ar— • s £ · ε σ ^ ι a | c o o

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U X tn r— 'u u CuX>' S o

The results of the determination of the diffusion charge of the quartz tubes after chemical treatments have been generalized and are presented in Table 2.

Based on the data in Table 2, the following conclusions can be drawn: a) after conventional chemical treatment in hydrofluoric acid, the electric charge of the diffusion quartz tubes does not decrease but increases or does not change;

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b) after chemical treatment in aqueous solutions of the known PFS-1 composition, the electric charge of the diffusion quartz tubes is lower and more stable than after traditional treatment;

c) the results of the experiment show that a 20% aqueous solution of the proposed PFS-2 composition lowers the surface electric charge twice as effectively as the known PFS-1 composition;

d) the optimal concentration of the solution for the chemical treatment of diffusion quartz tubes of the proposed PFS-2 composition is 20%; increasing the concentration of the solution does not lead to a decrease in the surface charge of the quartz tubes, i.e. it does not lead to an increase in the amount of metal ions removed from the surface.

Example No. 3.

Determination of the number of properly made capacitors by examining the physicochemical parameters of the Si-SiO2 and Si'-SiO2-Si structures on silicon, pretreated before oxidation with a solution of the known PFS-1 composition and the proposed PFS-2 composition.

During the experiment, the following parameters of the SiO2-Si partition limit were measured:

• electric charge density on the outer division surface - Q _n , • electric charge density on the inner division surface - Qe, • electric charge density in the area between the outer and inner silicon division surface - Q.Si, • compensation voltage, measured in the dark on the silicon surface - Vkt, • compensation voltage when illuminating the surface with light, measured on the same trajectory as V _K t - Vkc, • potential difference Vkt - Vkc. resulting from the bending of zones on the Si surface in the dark and in the light - φ ₅ , • homogeneity of the SiO2 conductivity - AV ⁺ kt, • voltage to which the surface is charged at the exit - V0, • electrical strength - E +, • threshold voltage - Vn *, • density of surface states - N _ss , • oxide thickness - Dox Parameters Qn, Qe, Qsi, E +, AVkt, 9s, V0, were measured with the IPP006 device (non-contact millivoltmeter, scanning with a Kelvin probe to record the distribution of small ion concentrations on the surface of bodies constants; systematic measurement error ± 2.5 mV), and parameters Vn +, Nss by the (CV) method.

The following operations were performed in the production of Si-SiO2 and Si'-SiO2-Si structures:

1. forming a batch of KEF and KDB tiles;

2. measurement of surface parameters with the use of the IPP006 instrument;

3. forming groups of plates (2 groups);

4. Chemical treatment of the plates with solutions of the known PFS-1 composition and PFS-2 composition;

5. surface oxidation of both groups;

6. measurement of the oxide parameters (IPP006);

7. thermochemical application of polysilicon;

8. ionic doping of polysilicon;

9. photo-engraving of polysilicon surfaces;

10. measurement of parameters of Si'-SiO2-Si capacitors (using IPP006 and C-V methods).

The formation of Si-SiO2 structures ended in operation No. 5, and Si'-SiO2-Si structures in operation No. 9. Figures 1 and 2 show the obtained results in the form of Vkt and Vkc diagrams- Figure 1 shows the Vkt and Vkc diagram of the matrix Si'-SiO2-Si. On the scanning trajectory (plate diameter), 15 Si'-SiO2-Si structures were arranged. Capacitor surfaces are marked as Q). Prior to acid treatment, the silicon surface was treated in a 2% PFS-2 solution.

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Figure 1 shows that the bending of zones φ ₅ is the same both on polysilicon and on "pure" oxide. Charge on the outer surface of SiO? - Q _n is equal to 6.8-10 '% / cm ² , and Qsi = -3.5-10' ⁰ e / cm, which proves a low value of the density of surface states (N _ss ).

Diagram of Si'-SiO2-Si capacitor matrix. Prior to oxidation, the silicon surface was chemically treated in a solution of PFS-1 composition.

Figure 2 shows a diagram of Si'-SiO2-Si structures for comparison, also on KDB10 silicon, the surface of which was treated with a 2% solution of PFS-1 composition. It can be seen that in this case there is no "barrier φ ₅ = 0" on the silicon surface, which proves the lack of impurity ions. 15 Si'-SiO2-Si structures were also placed on the scanning trajectory. The surfaces of the capacitors are marked with jOco (f). It can be seen that the bending of the zones is the same and equal to <p _s = 0 on all structures. The load on the outer surface is equal to

Qsi = -3.5-10 ' ^lo e / cm2, Q _sc = 0.

PFS-2

Picture 2.

Diagram of a matrix of Si'-SiC> 2-Si capacitors. Prior to oxidation, the silicon surface was chemically treated in a solution of PFS-2 composition.

The presence of the bending of zones in Figure 1 shows that there is a barrier on the surface in the oxide, which was created as a result of Frenkel defects. In other words, it is evidence of the lack of impurity ions in the oxide and a low effective value of the density of surface states Nss. All the obtained results are shown in Figure 3.

Figure 3 shows the distribution of the number of properly made Si'-SiO2-Si structure capacitors depending on the type of silicon conductivity and resistance, as well as

188,424 methods of cleaning the surface from oxidation. Figure 3 shows that in the case where the silicon surface was chemically cleaned in PFS-2 solutions before oxidation, all types of capacitors on PCBs have higher electrical strength. The maximum number of properly made Si'-SiO ₂ -Si structure capacitors is achieved with the electric strength equal to 50A / V (70-90). The percentage of properly made Si'-SiO ₂ -Si structure capacitors with a cover surface area of 3x3 mm is 1.5 to 3 times higher in the case when the silicon surface was cleaned with aqueous solutions of PFS-2 composition before oxidation, compared to its cleaning at with solutions of the known PFS-1 composition.

A / V A / VA / VA / V _0/15 30 50 100 15 30 50 100> 15 30 50 100>

1 Γ 11 r ^- -1-1-1- -1 — i — r ~ -1- 1 \ Lb, PFS-2 PFS-2 V 1 \ 1 / B In <p K. / / l ' 1 T? \ 1 '1 \ i i \ and 1 \ 1 izts \ PFS-1 1 As I 1 \ / 1 \ PFS-2 and \ . AND\_ 1 * In 1, \ , PFS-1 \ 1 / \ _! PFS-1 1 1

KEF 0.3 70 KEF 30 KDB-10

Picture nr 3.

Electronic strength distribution of pin-type Si'-SiO ₂ -Si capacitors Before oxidation, the silicon surface was chemically treated in PFS-2 θ Before oxidation, the silicon surface was chemically treated in PFS-1

Table 3 presents an additional summary of the values of the charge states of Si'-SiO ₂ -Si structures, measured with the CV and IPP006 methods.

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Table 3

Parameters of Si'-SiO2-Si structures, measured by the CV method (D _ox , V ", N _ssfb ) and by the KRP method (Q _n , Q _sc , φ ₅ )

Type shallow No plate and structure Type machining chemical D, "- t0 ³ [A] v _n [V] Nssfb -ΙΟ ^'10 [e / cm2] Qn-101 ° [e / cm ² ] Qse-10- '° [e / cm2] φχ [mV] KDB10 2-2-1 PFS-1 1,260 -1.178 3.869 1.8 -4.3 120 2-3-1 PFS-1 1.149 -0.974 3.170 1.8 -5 140 2-4-1 PFS-1 1.612 -0.732 2.627 0.8 -5 150 2-1-1 PFS-1 1.246 -0.023 1.946 -0.8 -3.5 100 1-1 PFS-2 1.864 -3.412 7.849 0.54 -4.2 130 70KEF30 2-1-2 PFS-1 1.235 -4.019 3.697 3.0 1.2 thirty 2-2-2 PFS-1 1.403 -4.318 3.544 3.6 1.6 thirty 2-3-2 PFS-1 1.131 -3.668 3.726 2.0 1.2 thirty 2-4-2 PFS-1 1.042 -4.268 6.369 - - - 2-5-2 PFS-1 1.034 -5.650 8.014 4.8 1.12 thirty 3-2 PFS-2 1.127 -8.196 -5.707 11.777 9.2 0.5 thirty KEF03 2-1-3 PFS-1 1.055 1.952 3.6 0.9 15 2-2-3 PFS-1 1.018 -6.390 3.091 5.8 0.9 15 2-3-3 PFS-1 1.011 -5.406 1.655 3.0 1.0 twenty 2-4-3 PFS-1 1.0 -5.196 2.096 3.0 1.0 25 2-5-3 PFS-2 1.133 -5.845 3.860 2.6 1.1 thirty

Based on the analysis of the obtained results, the following differences in the properties of these structures can be found with various chemical surface treatments in the proposed PFS-2 composition compared with the treatment in the known PFS-1 composition:

• during surface treatment with PFS-1, high surface heterogeneity is observed;

• the same level of space charge area of Si'-SiO2-Si capacitors is observed during chemical surface treatment in PFS-1 and PFS-2 solutions;

• the charge on the plates of Si'-SiO2-Si capacitors is higher when the surface is chemically treated before oxidation in PFS-2 solutions.

Example No. 4.

Cleaning metal surfaces of devices from metal atoms after the process of sputtering silicon wafers with aluminum, nickel, silver and other metals.

The experimental results showed that the optimal concentration of the proposed PFS-2 composition to dissolve the metal applied by sputtering is a 70% aqueous solution. The cleanliness of metal surfaces was assessed visually.

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Claims (1)

Patent claim A composition for the chemical surface cleaning of adsorbed metal ions and atoms of semiconductor wafers and the equipment in which they are produced, consisting of sulfomaleic anhydride and water, characterized in that it consists of a percentage by weight: - sulfomaleic anhydride - 0.1-20, - disulfomaleic anhydride - 0.1-50, - others - water. wherein concentrations of 0.1 to 2 parts by weight are used for cleaning the silicon wafers prior to thermal processing, and concentrations are used for cleaning production equipment from 10 to 70 percent by weight of the composition.