JPH08120447A - Film formation by sputtering - Google Patents

Abstract

PURPOSE: To provide an inexpensive and easy sputtering film forming method capable of forming a film at high precision to a prescribed film thickness even if the temp. of a substrate is changed in the process of sputtering. CONSTITUTION: In a sputtering process in which the temp. of a substrate is changed, previously, the relational formula between the substrate temp. and film forming rate and the relational formula between the substrate temp. and elapsed time are previously registered at a sputtering time setting device, and the past film forming rates are preserved each time every batch is finished. Then, before the start of sputtering the sputtering time setting device calculates the sputtering rate from the same two relational formulae and the past forming rates, this time is set to the sputtering device. Moreover, after the completion of sputtering, the actual film forming rate is registered at the sputtering time setting device from the film thickness actual value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering film forming method capable of forming a film having a predetermined film thickness with high accuracy even if the substrate temperature is changed during sputtering.

[0002]

2. Description of the Related Art Sputtering (sputtering) is a technique widely used in thin film manufacturing processes for semiconductors, magnetic heads and the like because it has relatively good film quality and reproducibility of film thickness in the thin film process. However, this is a process that has many fluctuation factors such as a vacuum environment and that the process is performed while flowing a reactive gas, and it is a technical subject to reduce variations in film thickness and film quality. As a general method, when the parameters such as the degree of vacuum and gas flow rate change, the physical properties of the thin film change, so variable parameters such as input power, degree of vacuum, gas flow rate, and substrate temperature are possible. The desired film quality is obtained by keeping the amount constant. Then, the target film thickness is usually obtained by dividing the target film thickness value by the previous actual film forming rate to calculate the sputtering time.

As a method for keeping the film forming rate constant, a sputtering apparatus for keeping the film forming rate constant by performing plasma density measurement applying an optical system in the vicinity of a target during sputtering is proposed in Japanese Utility Model Publication No. 01-26366. ing. In addition, a sputtering apparatus that controls the film formation rate by using laser light to detect changes in the frequency and period of the thin film is disclosed in Japanese Patent Laid-Open No. 01-278.
Proposed in 013. However, these methods have the problems that they require extensive remodeling of the apparatus, require labor and cost, and are susceptible to noise, and the film formation rate cannot be controlled as accurately as expected.

In a high frequency sputtering apparatus, subtle changes such as reactive power and inflow gas flow rate during sputtering are measured, the film thickness is estimated during the sputtering by multivariate analysis, and the sputtering is terminated when a predetermined film thickness is reached. The method is
It is proposed in Japanese Patent Publication No.-88772. This method has the advantage that it does not require major modification of the equipment, but it controls the film thickness in the process of changing the substrate heating such that the initial layer of the thin film is heated to a constant temperature and the rest is stopped. Is impossible.

Further, there is a method capable of controlling the film thickness with high accuracy even in the process of changing the substrate temperature during film formation.
It is proposed in Japanese Patent No. 63983. This method is 1
By maintaining a constant substrate temperature in the second layer, the physical conditions at the interface between the substrate and the thin film are satisfied, and in the second layer, substrate heating is stopped to shorten the substrate cooling time after film formation and improve productivity. Greatly effective in the process. As a similar publicly known example, there is Japanese Patent Laid-Open No. 02-274875, in which the sputter time is calculated and set in advance without controlling the sputter stop, so that the man-hour and cost for newly forming the control device are reduced. are doing. However, since these two sputtering methods do not predict the change in the film forming rate with respect to the time-dependent change in the film forming rate due to erosion or the like, it is difficult to obtain the film thickness with high accuracy throughout the life cycle of the target. is there.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to predict the change with time of the deposition rate in advance in the process of changing the substrate temperature during sputtering and calculate an appropriate sputtering time. To propose a film forming method.

[0007]

The present invention provides a relational expression between a substrate temperature and a film forming time, and a substrate temperature after the substrate heating is stopped, in a sputtering film forming method in which sputtering conditions other than the substrate temperature are constant. The relational expression of time is registered in the sputtering time setting device, and the past film forming rate is saved each time each batch is completed. Then, before the sputtering is started, the sputtering time setting device calculates the sputtering time from the above-mentioned two relational expressions and the film forming rate stored in the past, and sets this time in the sputtering device. Further, in the sputtering film forming method, after the completion of sputtering, the actual film forming speed is converted from the actual film thickness value into a film having a constant substrate temperature and registered in the sputtering time setting device.

[0008]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is an example of a system configuration for implementing the present invention. In the figure, 1 is a high frequency magnetron sputtering apparatus (sputtering apparatus). Reference numeral 2 denotes a sputtering time setting device composed of a microcomputer, which connects an input / output device 3 having a keyboard and a display and an external storage device 4 such as a hard drive. The sputter device 1 is connected to the sputter time setting device 2, and the sputter time is set in the sputter device 1 by transmitting it through the communication cable 6. The sputtering apparatus 1 also includes a thermocouple output 7 for measuring the substrate temperature and a substrate heater switch 8.
Further, the sputtering device 1 is connected to the substrate temperature control device 5 via the thermocouple output 7 and the substrate heating heater switch 8. The substrate temperature control device 5 is the sputtering device 1
The substrate temperature is taken in through the output 7 of the thermocouple, and the switch 8 of the substrate heating heater is turned on and off to reach the set temperature. The substrate temperature control device 5 is provided with a thermocouple output 9 so that the sputtering time setting device 2 can automatically measure the substrate temperature for a long time.

A procedure for calculating the sputtering time using such an apparatus is shown in the flowchart of FIG. 2, and the following description will be given according to the flowchart. The substrate temperature is fixed at the reference temperature in the first layer, and the substrate temperature is gradually decreased in the second layer by stopping the substrate heating.

1) Derivation of Relational Expression between Substrate Temperature and Film Forming Rate First, within a variable range of substrate temperature, the substrate temperature is set from 5 points to
The film forming rate at each substrate temperature is obtained by selecting 0 points and performing sputtering with the substrate temperature fixed. Then, the film formation rate at each temperature obtained above is applied to an appropriate polynomial using the method of multiple regression analysis to obtain a relational expression between the substrate temperature and the film formation rate. A conceptual diagram of this relational expression is shown in FIG. Here, the vertical axis is the ratio of the film forming rates when the film forming rate at a certain reference temperature is 1, and the horizontal axis is the substrate temperature. Further, the plotted points are obtained from the actual measurement values of the film forming rate obtained by the experiment, and the curve is obtained by converting the relational expression into one in which the film forming rate at a certain reference temperature is 1. The relational expression of the film formation rate obtained from the substrate temperature thus obtained is expressed by g
It is registered as (T) in the external storage device 4 in FIG. (T: substrate temperature)

2) Derivation of Relational Expression between Elapsed Time and Substrate Temperature Next, a relational expression between the elapsed time after the substrate heating is stopped and the substrate temperature is obtained. This relational expression is closely related to the heat capacity and heat conduction inside the sputtering apparatus, but the internal structure of the sputtering apparatus is not simple and cannot be easily obtained by a desktop simulation. The relational expression is obtained by measuring. The output voltage of the substrate temperature measuring thermocouple provided in the sputtering apparatus 1 of FIG. 1 is taken into the sputtering time setting device 2 of FIG. 1 via the substrate temperature control device 5 at regular intervals (for example, 10 seconds). This is repeated until the maximum possible sputtering time. The relational expression between the measured substrate temperature and the elapsed time is obtained using the method of multiple regression analysis. The relational expression of the substrate temperature obtained from the elapsed time obtained in this way is defined as f (t).
Is registered in the external storage device 4 (t: elapsed time). A conceptual diagram of this relational expression is shown in FIG. In this figure, the vertical axis is the substrate temperature, and the horizontal axis is the substrate temperature after the substrate heating is stopped. This means that the substrate temperature is kept at the reference temperature up to the origin of the horizontal axis, and thereafter the substrate heating is stopped and the substrate temperature gradually drops. To reduce the difference in heat capacity between batches,
It is necessary to adjust the number of substrates so that the same heat capacity is obtained each time during sputtering.

3) Measurement / registration of initial value of film formation rate For a certain period of time, the substrate temperature is set to a reference temperature and sputtering is performed to obtain an initial value of film formation rate. This initial value is registered in the external storage device 4 of FIG. 1 as a record of the film forming speed of the past 5 to 10 times. The reason for registering the past 5 to 10 times as the record of the film forming rate is 4). When estimating the film forming rate, the influence of the fluctuation of the film forming rate of one batch is reduced, and the extremely large or small estimation result is obtained. This is because the film velocity is not calculated. After registration, a graph of the relationship between the number of times of sputtering and the film formation rate as shown in FIG. 5 is obtained.

4) Calculation of Sputtering Time Immediately after setting the initial value of the film-forming rate, the current time is estimated using the method of multiple regression analysis from the relationship between the number of times of sputtering and the film-forming rate as shown in FIG. Calculate the film formation rate. Let R be the estimated film formation rate obtained here. In the process of this embodiment, the substrate is fixed at the reference temperature in the first layer and a fixed film thickness (L1) is sputtered, and in the second layer, the substrate heating is stopped and the remaining film thickness (L2 = L−). L1, L: Target value of film thickness, L2: 2
The layer thickness) shall be sputtered. Then, the sputtering time (t1) of the first layer is calculated using the following formula. t1 = L1 / R ... (a) t1: 1st layer (fixed reference temperature) Sputtering time L1: 1st layer film thickness R: Estimated deposition rate and 2 layers The eye sputter time (t2) is obtained by solving the following integral equation. t2: Sputtering time of the second layer (after the heating of the substrate is stopped) g (T): Film forming rate with respect to the substrate temperature (T) f (t): Change of the substrate temperature over time

5) Setting of sputter time and automatic operation The sputter time (t1, t2) obtained in 4) is set in the sputter device via the communication cable of FIG. 1 to perform automatic sputter operation.

6) Measurement / registration of actual film thickness value After the sputtering is completed, the actual film thickness value (L ') is measured,
The result is registered in the sputtering time setting device 2 using the input / output device 3 of FIG.

7) Calculation / Registration of Actual Deposition Rate The following equation (c) can be obtained from the equations (a) and (b). R: R '= L: L' (c) This means that the ratio between the film thickness target value (L) and the film thickness actual value (L ') is , And the ratio of the estimated film forming rate (R) and the actual film forming rate (R ′). The actual film forming rate (R ′) here is converted into the film forming rate for sputtering with the substrate temperature kept constant. By solving this equation, the actual film deposition rate (R ′) at this time is obtained and stored in the external storage device 4 of FIG. This means that the transition graph of the film formation rate as shown in FIG. 6 is updated every time each batch is completed.

8) Next Sputtering When performing the next batch of sputtering, when the target is replaced with a new one, the process is restarted from the initial value measurement / registration of the film forming rate in 3). If not replaced, restart from the calculation of the sputter time in 4).

[0018]

The present invention described above has the following effects. 1) Even if the substrate temperature is changed during sputtering, the target film thickness can be accurately formed without being affected by the erosion of the target. 2) In particular, in a process in which the substrate is kept at a constant temperature for a certain period of time after the start of sputtering and thereafter the substrate heating is stopped, the productivity is greatly improved by shortening the cooling time. 3) Since the sputtering apparatus main body does not need to be extensively modified, productivity can be improved and film thickness accuracy can be improved at low cost.

[Brief description of drawings]

FIG. 1 is a system configuration diagram for implementing the present invention.

FIG. 2 is a flowchart showing a procedure for realizing the present invention.

FIG. 3 is a relationship diagram between substrate temperature and film formation rate

FIG. 4 is a relationship diagram between elapsed time and substrate temperature

FIG. 5 is a diagram showing the relationship between the film forming speed and the number of times of sputtering (immediately after setting the initial value).

FIG. 6 is a relationship diagram between the film forming rate and the number of times of sputtering (second time and thereafter)

[Explanation of symbols]

 1 Sputtering device 2 Sputtering time setting device 3 Input / output device 4 External storage device 5 Substrate temperature control device

Claims (1)

[Claims] 1. In a sputtering film forming method in which manufacturing conditions other than the substrate temperature are constant, a relational expression of the substrate temperature and the film forming rate, a relational expression of the time change of the substrate heating, and the past film forming rate of each batch The change is registered in the sputtering time setting device, the estimated film formation rate is predicted from the change in the past film formation rate, and the estimated film formation rate and the above two relational expressions are used to calculate the sputtering time for the film thickness target value. Is calculated and the determined sputtering time is set in the sputtering apparatus.