JPH0353083A - How to prevent metal contamination of semiconductor devices - Google Patents

Abstract

PURPOSE:To inhibit the deposition of a metal on the surface of a semiconductor element by adding a small amt. of a specified anionic surfactant to liq. chemicals for washing or etching the element. CONSTITUTION:When a semiconductor element is washed or etched with a treating soln. consisting of two or more among hydrofluoric acid, an aq. ammonium fluoride soln., an aq. hydrogen peroxide soln., an aq. ammonia soln., sulfuric acid, hydrochloric acid, nitric acid, alcohol and pure water, one or more kinds of anionic surfactants selected among CxFyCOOH, CxFySO3H, CxHyCOOH and CxHySO3H (x is 4-7 and y is 9-15) each having a normal chain or side chain alkyl group or salts of them are added to the treating soln. by 1-500ppm. This method is effective in washing or etching the semiconductor element by a wet process in the case where the element is more fined or highly integrated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to cleaning or enoching of semiconductor devices. More specifically, it relates to a method for preventing metal contamination of semiconductor devices by adding a certain type of short-molecular-length anionic surfactant to the chemical solution when semiconductor devices are cleaned or etched using a wet method. be. [Prior Art] The semiconductor device manufacturing process consists of many steps from silicon single crystal to the final semiconductor device, and usually before and after each step, wet or dry cleaning is performed to remove silicon device particles, It is also known that metal contamination needs to be removed.

In dry cleaning and etching techniques such as plasma processing, the elements that can be removed from the semiconductor element surface as gaseous halides are Si, AI, Cr, WSMo. ．． Ta,P,
Limited to B, C, As, etc., alkali metals such as Li, NaSK, alkaline earth metals such as Mg, Ca, Sr, Cu,
It is difficult to remove heavy metals such as Ni and Zn.

In order to compensate for these drawbacks of the dry method, wet cleaning,
Etching is used concurrently in semiconductor fabrication processes.

The following combinations are known as typical examples of wet cleaning and etching.

■ RCA method (cleaning) NH40H + HtOz, flF, HCI +
I{zOt, pure water rinsing ■ Aqua regia method (washing) }ICI + HNO, , IIF, HCI + HN
O3, pure water rinsing■ Piranha + HF method (cleaning) HzSO4+ HtOx, HF, pure water rinsing■ Banfered hydrofluoric acid method (etching) NH4F + H
F. Pure water rinsing [Problem to be solved by the invention] As described above, many chemicals are used for cleaning and etching, but as semiconductor devices become smaller and more highly integrated, the degree of contamination from particles and metals becomes even more serious. must be managed at a low level. However, when such a chemical solution is used for the purpose of cleaning or etching, Cu, Hg, Ag, PL. ．． It is also known that elements such as Au are likely to electrochemically deposit on the surface of a silicon element. In addition, Pb, Ni, and F whose electronegativity is close to Si
E, etc. may also be deposited. In particular, this phenomenon is more likely to occur on the metal silicon surface than on the silicon oxide film.

Therefore, among chemical solutions, when it dissolves the oxide film on the surface of metal silicon, such as hydrofluoric acid, other
a Metal impurities are more likely to be deposited during cleaning and etching processes than with mineral acids or rinsing water. In this case, it is difficult to actually prevent contamination even if a chelating agent is added to the chemical solution to trap metal ions.

There is a danger that various metal elements may be mixed in not only from chemicals but also from many factors such as equipment, environment, process gas, processing products, etc., and as semiconductor devices become smaller and more integrated, stricter cleaning requirements are required. degree management is inevitable.

[Means and effects for solving the problem] As a result of intensive research, the present inventors found that in order to solve the problems of the conventional wet cleaning and etching mentioned above, a certain type of surfactant was added as an additive to these methods. It was discovered that when a small amount of this compound was added to a chemical solution, metal deposits on the surface of a semiconductor element were suppressed, and the present invention was completed. That is, the gist of the present invention is to add alkyl The purpose of this invention is to prevent metal contamination of semiconductor devices by adding a small amount of at least one anionic surfactant having 4 to 7 carbon atoms. By the way, a predetermined amount of soluble metal fluoride salts is dissolved in a typical chemical solution used for various cleanings and etchings, and sulfuric acid/hydrogen peroxide, pure water,
A bare silicon wafer that has been cleaned in 1O% hydrofluoric acid is immersed for 1 hour at room temperature. After rinsing with pure water and blow-drying with clean nitrogen gas, the amount of deposited metal ions was measured using an electron beam microanalyzer. Table 1 shows the types of elements that tend to deposit when 100 ppm of various metal ions are added to the original chemical solution.

The amount of ion deposition shown in the table is expressed in the form of peak ratio detected by an electron beam microanalyzer for various metals to silicon (CPS/CPS). This table shows that the amount and state of deposition differ depending on the type of metal ion, and is influenced by ionization tendency and electronegativity. In many cases, adsorption from other drugs whose deposition amount is much smaller than the example in Table 1 cannot be ignored.

Table 2 shows that 7
The graph shows the amount of metal deposited depending on the type of surfactant added at night. The amount of copper ions added is 0. 17mm
ol/L, the amount of surfactant added is 0.67 mm
It is ol/L. As in Table 1, the amount of ion deposition is shown by the detected peak ratio in electron beam microanalyzer measurement.

As can be seen from this table, the effects of surfactants coexisting in a chemical solution vary greatly depending on their type, suggesting that certain types of surfactants may be able to prevent chemical deposition.

However, adding additives in the semiconductor manufacturing process, even though it can prevent metal contamination, is itself a form of system contamination, and the surfactants added are among the types that do not have a negative effect on the process. from,
The selection must be made after thorough examination.

First, stable characteristics are required in the cleaning and etching steps. It must be a chemically stable compound that dissolves transparently in a chemical solution and maintains its molecular structure even after being added and used or stored in the drug solution for a long period of time. For example, there is an ester structure or an ether structure in the molecular structure, which must not be hydrolyzed during use. Furthermore, surfactants that are adsorbed onto the filter during circulation filtration of the chemical solution, which is normally carried out in wet processing systems to remove particles generated within the system, are also disadvantageous. Most commercially available surfactants cannot be used because they are adsorbed. Impurities in chemical solutions used in semiconductor processes must be controlled to a low level as semiconductor devices to be cleaned and etched become smaller and more highly integrated. For example, impurity metal ions must be controlled to a low level of 0. Since 1 to 1 ppb or less is desired, even if only a small amount of surfactant is added, it must be able to be purified to the same level. On the other hand, miniaturization
As integration becomes higher, the processing size unit of the element surface to be cleaned and etched is, for example, (0.1 to 10) x 10
Even if the monomolecular film of the surfactant used is formed on the surface of the element, unless the molecular length of the surfactant that naturally arranges is extremely small, the film will be uneven, resulting in microscopic formation. Uniform cleaning and etching of the area cannot be achieved.

Preferably, it is not a commercially available surfactant with a linear carbon chain of several hundred or more, but a shorter molecule with a carbon number of about 4 to 8, which causes steric arrangement hindrance in the microfabricated part. may occur.

It must also be avoided that the addition of a surfactant affects the processing conditions and device characteristics obtained when no surfactant is added.

The foaming property, which is a general characteristic of surfactants, must be avoided as much as possible because bubbles that adhere to the surface of a semiconductor element will inhibit cleaning and etching, leading to the creation of an uneven surface. To avoid this, it may be possible to add an antifoaming agent, but it is preferable to use a surfactant that has almost no foaming properties. It is also essential that the added surfactant is easily removed and does not remain during the pure water rinse that follows cleaning and etching. If the surfactant remains on the surface, it can be said to be a type of organic contamination, which will adversely affect subsequent steps and the electrical characteristics of the device. Surfactant residue may occur due to excessive addition amount or type.
For example, many cationic surfactants cannot be used because they tend to react with the silanol groups (→SiOH) normally present on the surface of the oxide film on the device. In addition, cationic surfactants cannot be used because they also have the same problem of significantly reducing the etching rate when etching silicon oxide films on devices. Based on these phenomena, the present inventors found that surfactants added to chemical solutions used in cleaning and etching processes can prevent metal contamination of semiconductor devices, have stable characteristics, and have negative effects on processing characteristics of device processing. As a result of searching for various surfactants that do not give C. HVCO○H, CXHv
S O x H , CXFVCOOH, C. F. S.O.
H (wherein, X is an integer of 4 to 7, Y is an integer of 9 to 15)
We have discovered that only anionic surfactants, or their salts, can be adapted to these harsh conditions. On the other hand, apart from the fact that the addition of surfactants helps to prevent metal contamination during cleaning and etching of semiconductor devices, as has been known for some time, surfactants also have an inherent effect on the chemical solution and the solids that come into contact with it. The state of the interface changes. Generally, when a surfactant is added to a chemical solution, it reduces the surface tension of the chemical solution, and also reduces the contact angle at the interface between the element and the chemical solution.
As a result, wetting of the element surface and penetration of the chemical into the microfabricated areas are promoted. In addition, solid particles that are secondary agglomerated in the chemical solution and floating organic oils, which can harm the semiconductor device fabrication process if left as they are, may disperse into small primary particles or adhere to the device surface. solid particles,
The effect of adding a surfactant, such as extracting organic oil, foamy gas, etc. into the chemical solution and stably dispersing it, has great significance in improving the yield of the device processing process. Coincidentally, the surfactant discovered in the present invention also has the best properties that such surfactants are originally required to have, and is thought to be partially compatible with the principles of the present invention. The alkyl group, which is a hydrophobic group of the surfactant in the present invention, is not preferable because, if the number of carbon atoms is 3 or less, the inherent properties of the surfactant such as the surface tension and contact angle of various chemical solutions do not change even when added in large quantities.

When adding the surfactant based on the present invention to a chemical solution for cleaning or enoting, there is no restriction that only one type of surfactant is added;
It is possible to use more than one, and in fact, it may produce a better combined effect. Regarding the amount of surfactant added, 1 to 5001) I) I1
The effect of the present invention can be expected within the range of (all)pll or less, which is an amount that cannot form a monomolecular layer of surfactant on the surface of the semiconductor element that is the object to be treated, and it will not uniformly cover the element surface. Unable to prevent metal contamination. Moreover, if the amount added is 500 ppm or more, the amount greatly exceeds the amount necessary to cover the surface layer of the element, and it is rather inconvenient that it cannot be easily removed by rinsing with pure water after treatment. Although it varies somewhat depending on the type of chemical solution, the type of element, and the cleaning and etching conditions, a concentration range of 10 to 20 Opp- is particularly preferable within the above range. [Effects of the Invention] The method of preventing metal contamination of semiconductor elements according to the present invention is extremely effective when cleaning or etching is performed using a wet method in response to miniaturization and higher integration of semiconductor elements. ．． [Examples 1 to 5 and Comparative Examples 1 to 10) CZ
- After cutting a P-type (100) silicon wafer into 15 x 15 aa squares, it was cleaned according to the following steps ① to ②, and copper fluoride trihydrate soluble in various chemical solutions was converted into copper ions at 0. 1
7 1I1!101/L, and various surfactants were added at 0.1I1!101/L. It was immersed for one hour in a sample solution prepared by adding 67 mmol/L.

■ 98%H. SO4: 3 1%HtOt = 4
: 1. 5 minutes ■ Pure water washing, 5 minutes ■ 50% HF:H. ○=1=5, after rinsing with pure water for 1 minute and blow drying with clean nitrogen gas, the amount of deposited copper ions on the silicon wafer surface was measured using an electron beam microanalyzer. The amount of deposition is determined by the detection peak ratio of steel ions to silicon by an electron beam microanalyzer (Cu-Kα rays/Si-Kα (2)
It is calculated in the form of a line). Table 2 shows those examples and, for comparison, a comparative example using a comparative sample solution prepared in the same manner as in the examples.

(Hereafter, extra white) Table 1 Metal deposition in various chemical solutions

Claims (1)

[Claims] 1. Directly apply to semiconductor device cleaning or etching chemicals consisting of a mixed aqueous solution of two or more of hydrofluoric acid, ammonium fluoride solution, hydrogen peroxide solution, ammonia solution, sulfuric acid, hydrochloric acid, nitric acid, alcohol, and pure water. C_XH_YCOOH, having a chain type or side chain type alkyl group,
C_XH_YSO_3H, C_XF_YCOOH, C_
XF_YSO_3H (wherein, X is an integer from 4 to 7, Y is 9
15. A method for preventing metal contamination of a semiconductor device, characterized by adding 1 to 500 ppm of at least one anionic surfactant which is an integer of 1 to 15) or a salt thereof.