JP3073537B2 - Control method of metal thin film formation condition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to the formation of thin metal films.
In particular, the present invention relates to a method for controlling conditions for forming a thin film necessary for obtaining a predetermined film quality.

[0002]

2. Description of the Related Art As a method for forming a metal thin film, means such as sputtering, heat evaporation, ion plating, and plating are conventionally known. In any method, in order to obtain good film quality, it is important to reduce the amount of impurities taken in during the formation process. The following two typical methods have been employed as methods for obtaining a high-purity metal thin film by reducing the amount of impurities. The first is a method for improving the raw material purity of the thin film. Purity control of raw materials is relatively easy in mass production technology and is generally performed.

A second method is to control the atmosphere in the reaction chamber or the formation chamber at a constant level so as to reduce contamination and to prevent impurities from being taken in during the process of forming a thin film. It is difficult to measure the contamination of impurities during the film forming process in-process in terms of measurement sensitivity, and in many cases, it is often unsuitable especially in a mass production process. For controlling the atmosphere in the reaction chamber or the formation chamber, analysis of residual impurity components in the chamber is used. Another method is to estimate the concentration of impurities taken into the thin film from the characteristic values of the completed thin film, such as hardness, particle diameter, and specific resistance of the thin film, and feed this information back to the formation process to control the indoor atmosphere. Has been adopted.

For example, when an Al thin film is formed by a sputtering method, the residual gas in the sputtering chamber affects the film quality.
Although a mass spectrometer is used to measure the residual gas, several tens of tens of masses are contained in Ar gas used in the sputtering process.
It is practically impossible in a mass production process to continuously measure impurities such as impurities H ₂ O, N ₂ , O _2, and CO mixed in the order of ppm.

For this reason, a method has been adopted in which the physical properties of a film after formation are measured and it is determined from the measured values whether or not the formation conditions are normal. In the mass production process, it is necessary to quickly feed back the information on the correctness to the formation process. The success or failure of the thin film formation conditions depends on the Knoop hardness H of the thin film.
Judgment is made empirically from _K or the specific resistance ρ.

[0006]

However, the above hardness,
Physical properties such as particle diameter and specific resistance are insensitive to, for example, the minute structure of the thin film, that is, the amount of impurities precipitated at the grain boundary, and cannot be an accurate index for controlling the formation conditions.

The present invention has been made in view of the above-mentioned problems, and uses the physical properties of a metal thin film different from those of the prior art as an index to reliably take in minute impurities or accurately detect errors in the substrate temperature during film formation. Monitorable.

[0008]

According to the present invention, there is provided a method for controlling the conditions for forming a metal thin film formed on a substrate, comprising the steps of measuring the temperature-internal stress characteristics of the formed metal thin film. And adjusting the formation conditions in the thin film formation step based on information obtained from the characteristics;
And the information is based on the temperature-internal stress characteristics.
At the starting temperature of migration of the constituent atoms of the thin film when the temperature rises
There is .

In a preferred embodiment, the formation condition is, for example, the amount of impurities in the atmosphere when forming the thin film or the temperature of the substrate. The present invention is particularly suitable for controlling conditions in a process of forming an Al thin film as a conductive layer on a semiconductor substrate such as Si.

[0010]

According to the present invention, the relationship between temperature and internal stress is measured for a plurality of metal thin films having different formation conditions such as the amount of impurities taken in during film formation or the substrate temperature, and these data are accumulated. Based on these data, the temperature of the metal thin film actually formed as a product
The characteristic curve of the internal stress is obtained, and in particular, the concentration of impurities contained in the film, the substrate temperature at the time of film formation, and the like are estimated from the migration start temperature of the atoms constituting the thin film. The temperature-internal stress diagram (loop) drawn by heating and cooling is
Since the characteristics are different between the case where the impurity concentration is different and the case where the substrate temperature during film formation is different, they can be distinguished from each other. The obtained information is fed back to the thin film forming process to control the thin film forming conditions. That is, for example, when the impurity concentration is higher than the standard value, the amount of impurities in the atmosphere is reduced to reduce the impurity concentration, and when the substrate temperature is out of the predetermined value, the correction is made so as to approach the predetermined value.

The metals to which the present invention can be applied include Al,
Al alloy (Al-Si, Al-Si-Cu, etc.), W, M
High melting point metals such as o, Ti, Ta, and Zr, and silicides of high melting point metals are conceivable. Due to the difference in the coefficient of thermal expansion from the substrate, a high stress is usually applied to the refractory metal thin film on the Si substrate at room temperature, but the stress is relaxed by annealing at about 800 ° C. Therefore, by measuring the internal stress from the amount of warpage of the thin film at this time and estimating the impurity concentration or the substrate temperature at the time of film formation, the conditions for forming the thin film can be controlled as described above.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an Al thin film for wiring formed on a silicon semiconductor substrate will be described. [Example 1]

First, a silicon oxide film, for example, a silicon dioxide film having a thickness of 100 nm was formed on the surface of a silicon semiconductor substrate having a (111) orientation. This silicon oxide film is provided to suppress the reaction between Si and Al. The film is formed symmetrically on the front and back surfaces of the silicon semiconductor substrate so as to be in a mechanically balanced state. Next, on the silicon oxide film, a generally used thickness of 1.0
μm Al (containing 1 wt% Si) thin film at a substrate temperature of 150
It formed by the sputtering method at ° C. At the time of thin film formation, a mass spectrometer was attached to the sputtering apparatus, and the amount (concentration) of impurities mixed was measured. This is for obtaining the correlation between the impurity concentration and the temperature-internal stress characteristic.

According to the above-described procedure, Al having different impurity concentrations
Two samples A and B having a thin film were formed. The thin film of sample A has a total impurity content (H
₂ O, N ₂ , O ₂ , CO) is 30 ppm or less, and the thin film of Sample B has a total amount of mixed impurities of about 450 ppm.

After the formation of samples A and B, each sample was taken from room temperature to 45
The temperature was changed to 0 ° C., and the internal stress of the thin film was determined from the amount of warpage of the thin film or the sample at each temperature. FIG. 1 shows the temperature-stress characteristics of the thin films in Samples A and B. In the figure, line A indicates sample A, and line B indicates sample B.

Since the Al thin film has a larger coefficient of thermal expansion than the Si substrate, the substrate is subjected to a tensile stress at room temperature lower than the temperature at the time of forming the thin film. However, as the temperature rises, the tensile stress is first relaxed substantially linearly in the negative direction according to a coefficient depending on the difference between the thermal expansion coefficients of Al and Si. The tensile stress is once negative (ie, compressive stress) and is subsequently affected by the migration of Al atoms in the thin film initiated at a certain temperature, for example, T _A or T _B (FIG. 1). . Therefore, the rate of change of the stress changes rapidly, and the stress approaches zero.

When the temperature is lowered from 450 ° C., the tensile stress initially increases substantially linearly in the plus direction according to a coefficient depending on the difference in the coefficient of thermal expansion between Al and Si. And the temperature at which the tensile stress has increased to some extent,
For example, migration of Al atoms occurs at T _A ′ or T _B ′ (FIG. 1), and the rate of change in stress changes somewhat.

At the time of temperature rise, T _A = 240 for sample A
While the migration of Al atoms starts at a temperature of ° C., the temperature of sample B starts at T _B = 310 ° C. The fact that the migration of B of the sample having a higher impurity concentration starts at a higher temperature indicates that impurities precipitated at the grain boundaries and the like are obstacles to the migration of Al atoms. In sample B, rapid stress relaxation is observed in a higher temperature region. On the other hand, when the temperature is lowered, the temperature of the sample B drops sufficiently before the migration of the Al atoms occurs, so that the rate of change of the stress does not change much.

When the Knoop hardness was measured for the samples A and B, it was determined that the difference in impurity concentration was within this range, and no significant difference was recognized. In contrast, temperature - can keep internal stress characteristics, for example, as shown in a migration start temperature T _A, T _B in FIG. 1, clear difference between the samples A and B appeared.

FIG. 2 shows the above-mentioned atomic migration start temperature and MTTF (Mean Time To Fail, hereinafter MTTF) in a disconnection stress migration (Stress Migration) test.
(Abbreviated as TF).

What is the disconnection stress migration test?
A semiconductor element (for example, S
After sealing the samples A and B) having the Al thin film formed on the i-substrate in an envelope made of a resin layer or the like, maintaining and leaving the temperature at about 140 ° C. to forcibly apply a stress to the wiring layer to disconnect the wire. This is a compulsory test that measures the time to reach. By maintaining the temperature, impurities are self-diffused at the grain boundaries of the wiring layer to form notches, and further, the wiring layer is broken in the direction of stress relaxation.

The MTTF refers to an average time during which an element fails, and the quality of the element is often determined by an experienced person. In the present invention, those having an MTTF value of 2000 hours or more were regarded as good.

The samples A and B and the other samples were subjected to a disconnection stress migration test at a standing temperature of 125 ° C. In this test, Sample A at T _A = 240 ° C. had an MTTF value of 2000 hours or more.
Sample B at _B = 310 ° C. had an extremely poor MTTF value of 450 hours. As shown in FIG. 2, it was found that the migration start temperature should be 270 ° C. or less to compensate for the life of 2000 hours or more. In addition, instead of the migration start temperature at the time of temperature rise, the inflection point temperature T _A ′ at the time of temperature fall,
T _B 'can also be used as an index of the impurity concentration. [Example 2]

Except for the temperature condition of the substrate, two more samples C and D were formed under the same conditions (including the impurity concentration) and procedure as the sample A of Example 1. The temperature conditions of the substrate when forming the thin film were as follows: 150 ° C. for sample A, 300 ° C. for sample C, and 2 ° C. for sample D.
5 ° C.

After the formation of the above samples, these samples were moved from room temperature to 4
The temperature was changed to 50 ° C., and the internal stress of the thin film was determined from the amount of warpage of the thin film or the sample at each temperature. FIG. 3 shows samples A, C and D
3 shows the temperature-stress characteristics of the thin film at the time of Example 1. In the figure, line A indicates sample A, line C indicates sample C, and line D indicates sample D.

The crystal grain size of the formed Al thin film varies depending on the heating temperature of the substrate when the thin film is formed. The particle size is
2 μm for sample A, 3 to 5 μm for sample C, and 3 μm for sample D
0.3 to 0.5 μm. Further, since the Al thin film has a larger thermal expansion coefficient than the Si substrate, the lower the temperature of the substrate at the time of film formation, the smaller the initial tensile stress of the thin film at room temperature.
Due to these factors, the temperature-stress characteristics of the thin film greatly differ depending on the substrate temperature at the time of film formation.

The above differences become apparent in the migration start temperatures T _A , T _C , and T _D when the temperature is raised, as shown in FIG. However, since the sample A, C, and D have low impurity concentrations, once the temperature is increased to 450 ° C. and annealed,
The crystal grain diameters of the thin film are substantially the same, so that the characteristic curve at the time of temperature decrease has substantially the same shape. Therefore, the temperature-internal stress diagram (loop) of the thin film when the substrate temperature during film formation is different has a different characteristic from that when the impurity concentration is different, and can be distinguished from the case where the impurity concentration is different. .

[0028]

According to the present invention, the measurement of the temperature-internal stress characteristics of the thin film makes it possible to reliably monitor the introduction of minute impurities or the error in the substrate temperature during film formation. The measurement of the temperature-internal stress characteristics of the thin film in one sample can be performed in more than ten minutes. By feeding back information obtained from the measurement to the thin film forming process, predetermined forming conditions can be reliably controlled.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between temperature and internal stress in thin films having different impurity concentrations, where the horizontal axis indicates temperature and the vertical axis indicates stress.

FIG. 2 is a graph showing a relationship between an atomic migration start temperature and an MTTF value in a disconnection stress migration test, in which the horizontal axis shows the atomic migration start temperature and the vertical axis shows the MTTF value.

FIG. 3 is a graph showing the relationship between temperature and internal stress in thin films having different substrate temperatures during film formation, wherein the horizontal axis indicates temperature and the vertical axis indicates stress.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoji Aoyama 1 Kosaka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Tamagawa Plant (56) References JP-A-1-316451 (JP, A) JP-A-1-316451 63-105966 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 14/00-14/58 C23C 16/00-16/56

Claims (3)

(57) [Claims] 1. A method for controlling conditions for forming a metal thin film formed on a substrate, comprising: a step of measuring a temperature-internal stress characteristic of the formed metal thin film; and a method based on information obtained from the characteristic. Adjusting the formation conditions in the thin film formation step.
And the above information is the temperature rise in the temperature-internal stress characteristic.
Method that is the migration start temperature of the constituent atoms of the thin film at the time . 2. The method according to claim 1, wherein the forming conditions are different from those in forming the thin film.
The method according to claim 1, wherein the amount is an amount of impurities in the atmosphere . 3. The method according to claim 1, wherein the forming conditions are the same as those described above when forming a thin film.
The method of claim 1, wherein the temperature is the temperature of the substrate .